OSAP User's Guide

Copyright © 2010 American Bureau of Shipping. All rights reserved.

Offshore Structure Assessment Program (OSAP)

Version 2.0

OSAP User’s Guide

March 2010

American Bureau of Shipping 16855 Northchase Drive

Houston, Texas 77060, USA

OSAP User’s Guide

Copyright © 2010 American Bureau of Shipping 1-ii

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OSAP User’s Guide

Copyright © 2010 American Bureau of Shipping 1-iii

CONTENTS Chapter 1: Introduction ................................................................................................................... 1 Chapter 2: Using the OSAP Applications ..................................................................................... 15 Chapter 3: A2ABSCHK.mac - An OSAP Interface Program with ANSYS ............................... 151 Chapter 4: OSAP Technical Basis............................................................................................... 157

OSAP User’s Guide

Copyright © 2010 American Bureau of Shipping i



OSAP User’s Guide

Chapter 1: Introduction

OSAP User’s GuideChapter 1: Introduction

Copyright © 2010 American Bureau of Shipping ii



Copyright © 2010 American Bureau of Shipping iii

CONTENTS 1 Overview .................................................................................................................................... 1 2 Before Getting Started ................................................................................................................ 2

2.1 Install OSAP....................................................................................................................... 2 2.2 Filename Convention ......................................................................................................... 2 2.3 Project Working Directory ................................................................................................. 2

3 OSAP Project.............................................................................................................................. 3 3.1 Create a New Project .......................................................................................................... 3 3.2 Open an Existing Project .................................................................................................... 4

4 User Interface ............................................................................................................................. 5 4.1 Resizable Windows ............................................................................................................ 6

4.1.1 Project Tree Window .............................................................................................. 6 4.1.2 Application Window............................................................................................... 6 4.1.3 Graphics Display Window...................................................................................... 7 4.1.4 Messages Window .................................................................................................. 8 4.1.5 Log Details Window............................................................................................... 8

4.2 Status Bar ........................................................................................................................... 9 4.3 Main Menu Commands ...................................................................................................... 9

4.3.1 Project Menu Commands........................................................................................ 9 4.3.2 Application Menu Commands .............................................................................. 10 4.3.3 Graphics Menu Commands................................................................................... 10 4.3.4 View Menu Commands ........................................................................................ 10 4.3.5 Tools Menu Commands........................................................................................ 12 4.3.6 Help Menu Commands ......................................................................................... 12

4.4 Using Mouse & Keyboard Operations ............................................................................. 13


Copyright © 2010 American Bureau of Shipping iv



Copyright © 2010 American Bureau of Shipping 1

1 Overview ABS Eagle Offshore Structure Assessment Program (OSAP) allows designers of offshore drilling and production platforms such as semisubmersibles, TLPs and spars to check the compliance of their designs more easily with ABS class requirements. The program is a comprehensive and user-friendly engineering tool that can create structural load cases, communicate with leading commercial analysis software and provide intuitive indicators of design adequacy based on ABS class requirements. The program is open and flexible; the software’s architecture can easily interface with other commercial design software. OSAP 2.0 supplies built-in data interfaces to industry-leading structural analysis software, ANSYS and MSC NASTRAN, and hydrodynamic analysis software, AQWA and WAMIT. OSAP 2.0 also provides a well documented neutral file system that allows users to readily customize the data interface linking their preferred design software to the program. ABS Eagle OSAP 2.0 consists of six main functions:

• Load generation • Design wave calculation • Load mapping and balancing • Global strength assessment • Fatigue assessment • Buckling and ultimate strength analysis

Capabilities of OSAP 2.0 include:

• Application of hydrodynamic loads contributed by Morison elements, drag elements, mooring lines and tendons in addition to the panel pressures

• Pressure integration for the splitting force and moment calculation along a user-defined cutting plane on the hydrodynamic model

• Design wave calculation based on either the deterministic approach using regular waves or the stochastic approach using wave spectra

• Robust algorithm to map hydrodynamic loads including pressures, forces and internal tank loads to the structural finite element model

• Interface to ANSYS and MSC NASTRAN to export the load, constraint and mass input data for finite element analysis and retrieving the analysis results

• Automatic panel search function and individual panel editing function facilitating the panel buckling check using global finite element analysis results

• Fatigue assessment based on either the spectral-based approach or the simplified method using assumed long-term stress distributions

• Calculation sheets for the buckling and ultimate strength check for five types of structural members including beam-columns, stiffened panels, corrugated panels, cylindrical shells and tubular joints

• Integrated graphic environment featuring powerful 2-D and 3-D visualization capabilities as well as user-friendly GUIs for navigating between application modules, providing input and administrating program execution

To obtain the technical support on OSAP, please contact [email protected]. All licensing requests should be directed to the ABS local office.



2 Before Getting Started

2.1 Install OSAP For the purposes of this user guide, it is assumed the user has installed the OSAP application. Refer to the OSAP 2.0 Installation and Licensing Guide for details.

2.2 Filename Convention The filenames in the application require the use of underscores instead of spaces. Spaces or special symbols such as / \" ? < > * : | . { } and # are not allowed in the file-directory structure.

2.3 Project Working Directory After creating a new project in OSAP, a project working directory is created under the user specified path. It contains up to six sub-directories, each of which represents an application module. All files generated for the project will be saved in this project directory. The following shows an example of how the project working directory, .\Demo, is organized.

Note that:

• If there has been no content (solution) generated for an application, the subdirectory for that application module will not be created.

• The user should not alter subdirectory names because they are used by OSAP to manage the analysis project.



3 OSAP Project To start OSAP, double-click the OSAP icon on the Windows Desktop, or click the Windows quick launch menu “Start” and then choose:

After the license is verified, the OSAP program main GUI starts up as shown below.

3.1 Create a New Project To create a new project, first go to Project menu > New Project. Enter a new project Name in

the New Project dialog as shown below for example. Click to select a path on the computer where the project working directory is to be created.



After a project is created, the Project Tree window is activated and a project working directory is also created at the user specified path. Once the solution is added to the application module, the relevant subdirectory will be created in the project working directory. Refer to 1/4.3.1 and 1/4.3.2 for further details.

3.2 Open an Existing Project

To open an existing project, go to Project menu > Open Project and click to choose the project file (*.PRJ). Only one project can be opened at a time.

After clicking , the user can use the dropdown list in File name field as shown below to quickly access the previously opened projects.



4 User Interface The OSAP user interface comprises a graphics display area surrounded by menus, toolbars and windows that can be enlarged or hidden.

NOTE: This graphic is in View mode. Input mode messages and status gauge have been superimposed for illustrative purposes.

Current project Log Details window: Step by step record of project activities . Scroll or resize to view . Right-click to copy . Log file resides in the project folder

Shortcut toolbars: Quick access to frequently used functions

Main menu commands & drop-down functions

Status bar

Messages window: Color-coded status of last analysis performed. Blue=Runtime Black=Application Red=Error

Graphics workspace window: Resizable & interactive

Application Window

Manage input data, submit analysis job,

and control the displaying of results tab-based panels.

Project Tree: Use to navigate

amongst application

modules.

Status gauge

OSAP software release version

Active units



4.1 Resizable Windows

Except for the graphic window, all windows can be resized or rearranged. Use in the corner to unlock or close a window. Double-clicking the title line of an unlocked window re-docks the window to its original location. The user can also show or hide a specific window from view by going to View menu > Windows and toggling the window on or off.

4.1.1 Project Tree Window The Project Tree displays the analyses the user has completed and is used to navigate amongst the application modules and solutions.

4.1.2 Application Window Double-click a solution in the Project Tree window to open the Application window with the Input menu activated. If the analysis results are also available, the View Menu will be activated as well. The title line of the Application window shows the type of application module currently being opened. The available contents on the Application window depend on the application module selected: • Load Generation • Load Mapping • Design Wave • Global Strength • Fatigue Assessment, Simplified and Spectral • Buckling Ultimate Strength

Project name

Application modules

Application solution



4.1.3 Graphics Display Window This resizable window cannot de deleted or hidden from view like the other windows. It displays the analysis model and results using a 2D or 3D plot. 3D Hydro Model (Load Generation)

2D Curve Plot (Load Generation)



4.1.4 Messages Window Color-coded status of the latest calculation is displayed in the Messages window as follows:

Blue = Runtime messages Black = OSAP application messages Red = Error messages

4.1.5 Log Details Window All major steps of OSAP project operations are recorded in a project log file (*.log). The log is displayed in a resizable and scrollable Log Details window. Right-click the window to open a dialog from which the user can copy, select all, or clear the contents of the window. The user can also open the log file directly in Microsoft Notepad to view the details.



4.2 Status Bar The status bar shows the current OSAP version, project name, active measurement unit system, and the progress status of the on-going analysis.

4.3 Main Menu Commands The following menus are available.

For quick access, the following commonly used main menu commands can be added to the toolbar (see 4.3.4).

4.3.1 Project Menu Commands The top-level Project menu commands are used for project management.

Project toolbar:

New Project Create a new project

Open Project Open an existing project

Close Project Close the current project (not shown in toolbar)

Create Solution Create a new solution

Import Solution Create a new solution by importing an existing one of the same type

Delete Solution Delete a solution

Save Input Save existing data in input files

Exit Exit the application (not shown in toolbar)

Project Graphics View Tools



4.3.2 Application Menu Commands These commands are used to activate an application module in the project tree as the working application.

As the user selects a menu command which is associated with one of six application modules, it is highlighted in the project tree.

4.3.3 Graphics Menu Commands These commands are for initiating the graphic display of a FE or hydrodynamic model or analysis results.

Graphics toolbar:

Model View Hydro Model or FE Model in the graphic display window

Results View analysis results in the graphic display window

4.3.4 View Menu Commands These commands are for manipulating graphic displays. They do not alter the model or results in any way.

View toolbar:



Option Display a dialog to change the default settings of the graphic display for:

Model (See 2/5.2.3 for further details.)

Results (See 2/5.2.4 for further details.)

Zoom Zoom In (applicable to 3D plot) Zoom Out (applicable to 3D plot)

Box Zoom (applicable to 2D plot)

Fit to Window (applicable to 3D plot)

Pan Move the display without zooming or rotation:

Pan (This is a toggle on/off selection.)

Left

Right

Up

Down

Rotate Toggle on to allow the mouse left button to drag and rotate a 3D plot. Toggle off to disable dynamic rotation

Set View Select angle/orientation at which to view the model: Front Back Top Bottom Left Right ISO I ISO II ISO III

Set Style Set style for the 3D graphic display:

Point Frame Wireframe Hidden Lines Shaded

Smooth Shaded Toolbars Display or hide Project, Graphics, View, and Tools toolbars

Windows Display or hide Project Tree, Application Messages, and Log windows.



4.3.5 Tools Menu Commands These commands are used to apply operational functions to the plot.

Tools toolbar:

Query Query the property of individual entity (Element or Node) on the graphic display

Clip Set clipping plane and reset back to the original full view. Choose either Plane… or Reset Clip.

Group Edit or create Element or Node group (set): Set: Add or Remove a Element or Node group ID: Edit an element/node group using element or node IDs Type: Edit an element group using element types Material: Edit an element group using material types Property: Edit an element group using property types NOTE: This function is available when the model is displayed using

Model.

Edit Panel Edit the program generated panel definition file (*.PNL file). NOTE: This function is available when the buckling check is requested in the Global Strength application.

Save Plot Save the current plot as an image file to the solution folder

Save All Plots Save all generated plots as image files to the solution folder

4.3.6 Help Menu Commands These commands are used to open the software documentation.

User’s Guide Open the OSAP V2.0 User’s Guide (PDF) Data File Online Help Open the OSAP V2.0 Data File Online Help (HTML) Installation and Licensing Open the software installation instruction and license agreement

About Show the software release version



4.4 Using Mouse & Keyboard Operations In addition to the menus and toolbars, OSAP provides an alternative approach to manipulate the 3D graphic display. The table below summarizes the capabilities currently available. When the toolbar or menu options are inactive in certain graphic display modes such as node/element picking mode, mouse and keyboard operations remain functioning.

Mouse and/or Keyboard Operations Function Shift + Mouse right button Rotate Ctrl + Mouse right button Pan Mouse scroll wheel Zoom in/out Shift + mouse scroll wheel Zoom in/out in vertical direction Right & left arrow key Rotate along window’s vertical axis Up & Down arrow keys Rotate along window’s horizontal axis Ctrl + Right/left arrow key Pan towards right/left Shift + right/left arrow key Rotate along one axis Ctrl + Up/Down arrow keys Pan towards up/down





OSAP User’s Guide

Chapter 2: Using the OSAP Applications

OSAP User’s GuideChapter 2: Using the OSAP Applications





1 Tutorial Examples Used in This Chapter.................................................................................. 15 2 Load Generation (LG) Analysis ............................................................................................... 17

2.1 Create/Import/Open an LG Solution ................................................................................ 17 2.2 LG Solution Processing Dynamic Loads ......................................................................... 18

2.2.1 Input and View Window....................................................................................... 18 2.2.2 Analysis Settings................................................................................................... 19 2.2.3 Load Condition Input for Dynamic Loads............................................................ 20

2.2.3.1 Hydrodynamic Loads............................................................................ 20 2.2.3.2 Morison Elements................................................................................. 21 2.2.3.3 Spring Elements.................................................................................... 22

2.2.4 Mass Distribution.................................................................................................. 24 2.2.4.1 Slicing Plane ......................................................................................... 24 2.2.4.2 Mass Properties..................................................................................... 26

2.2.5 Result Files............................................................................................................ 27 2.3 LG Solution Processing Static Loads ............................................................................... 28

2.3.1 Input and View Window....................................................................................... 28 2.3.2 Analysis Settings................................................................................................... 29 2.3.3 Load Condition Input for Static Loads ................................................................. 30

2.3.3.1 Options.................................................................................................. 30 2.3.3.2 Model Definition .................................................................................. 31 2.3.3.3 Current Profile ...................................................................................... 33 2.3.3.4 Wind Loads........................................................................................... 34 2.3.3.5 Mooring Loads ..................................................................................... 35 2.3.3.6 Other Static Loads ................................................................................ 36

2.3.4 Result Files............................................................................................................ 37 3 Design Wave (DW) Analysis ................................................................................................... 38

3.1 Create/Import/Open a DW Solution................................................................................. 38 3.2 DW Solution Using the Deterministic Method ................................................................ 39

3.2.1 Input and View Menu ........................................................................................... 39 3.2.2 Design Wave – RAO Data .................................................................................... 41 3.2.3 Design Wave – Sea States..................................................................................... 43 3.2.4 Export Design Waves ........................................................................................... 44 3.2.5 View Data Files..................................................................................................... 44 3.2.6 View Analysis Results in Graphic Window ......................................................... 44

3.3 DW Solution Using the Stochastic Method...................................................................... 46 3.3.1 Input and View Menu ........................................................................................... 46 3.3.2 Design Wave – RAO Data .................................................................................... 47 3.3.3 Design Wave – Sea States..................................................................................... 47 3.3.4 Export Design Waves ........................................................................................... 49 3.3.5 View Data Files..................................................................................................... 49 3.3.6 View Analysis Results in Graphic Window ......................................................... 49

4 Load Mapping (LM) Analysis.................................................................................................. 51 4.1 Create/Import/Open an Load Mapping Solution .............................................................. 51 4.2 Load Mapping Analysis – STRENGTH Option .............................................................. 53

4.2.1 Specify Job Type (*.TYP File) ............................................................................. 55 4.2.2 Setup FE Model (*.MTF File) .............................................................................. 56 4.2.3 Import Hydro Model and Results.......................................................................... 61 4.2.4 Input Mass/Weight (*.MAS File) ......................................................................... 62 4.2.5 Input Constraints (*.FIX File)............................................................................... 64



4.2.6 Generate Structural Loads..................................................................................... 66 4.2.7 View Load Mapping Results................................................................................. 68

4.3 Load Mapping Analysis – SFATIGUE Option ................................................................ 71 4.3.1 Specify Job Type (*.TYP File) ............................................................................. 73 4.3.2 Setup FE Model (*.MTF File) .............................................................................. 73 4.3.3 Import Hydro Model and Results.......................................................................... 73 4.3.4 Input Mass/Weight (*.MAS File) ......................................................................... 73 4.3.5 Input Constraints (*.FIX File)............................................................................... 74 4.3.6 Generate Structural Loads..................................................................................... 74 4.3.7 View Load Mapping Results................................................................................. 74

4.4 Load Mapping Analysis – For Nastran Solution Translation Only.................................. 75 4.4.1 Specify Job Type (*.TYP File) ............................................................................. 75 4.4.2 Setup Load Cases (*.LCS File)............................................................................. 77 4.4.3 Setup FE Model (*.MTF File) .............................................................................. 78 4.4.4 Translate Nastran Results ..................................................................................... 79

5 Global Strength Analysis.......................................................................................................... 80 5.1 Create/Import/Open a Global Strength Solution .............................................................. 80 5.2 Input and View for Global Strength Analysis .................................................................. 81

5.2.1 Input Global Strength Data ................................................................................... 82 5.2.2 Input Buckling Data .............................................................................................. 84 5.2.3 View FE Mesh ...................................................................................................... 84 5.2.4 Display Results as Contour Plots .......................................................................... 85 5.2.5 Display and Save View Options ........................................................................... 88 5.2.6 Set Clipping Plane................................................................................................. 89 5.2.7 Elements and Nodes Query Mode ........................................................................ 89 5.2.8 Panel Editing Mode............................................................................................... 91

5.2.8.1 Create a Panel ....................................................................................... 92 5.2.8.2 Modify a Panel...................................................................................... 94 5.2.8.3 Delete a Panel ....................................................................................... 96

5.2.9 Result Files............................................................................................................ 97 6 Simplified Fatigue Analysis ................................................................................................... 102

6.1 Create/Import/Open a Simplified Fatigue Analysis Solution......................................... 102 6.2 Input and View for Simplified Fatigue Analysis............................................................ 103

6.2.1 Analysis Settings................................................................................................. 104 6.2.2 Fatigue Loads...................................................................................................... 104 6.2.3 SN Curves ........................................................................................................... 108 6.2.4 Structural Details ................................................................................................ 109 6.2.5 View Model and Results ..................................................................................... 110 6.2.6 Result Files.......................................................................................................... 111

7 Spectral Fatigue Analysis ....................................................................................................... 113 7.1 Create/Import/Open a Spectral Fatigue Analysis Solution............................................. 113 7.2 Input and View for Spectral Fatigue Strength Analysis ................................................. 114

7.2.1 Analysis Settings (*.SFA File)............................................................................ 115 7.2.2 SN Curves (*.SNC File) ..................................................................................... 116 7.2.3 Stress RAOs (*.STF File) ................................................................................... 117 7.2.4 Hotspot Definitions (*.HOT File) ....................................................................... 121 7.2.5 Environmental Data (*.ENV File) ...................................................................... 123 7.2.6 View Model and Results ..................................................................................... 127 7.2.7 Result Files.......................................................................................................... 128

8 Buckling and Ultimate Strength (BUS) Analysis................................................................... 131


Copyright © 2010 American Bureau of Shipping v

8.1 Work with BUS Solutions.............................................................................................. 131 8.1.1 Create a New Solution ........................................................................................ 131 8.1.2 Create a new Solution by Importing an Existing One......................................... 132 8.1.3 Open an Existing Solution .................................................................................. 133 8.1.4 Work with the Calculation Sheet ........................................................................ 133 8.1.5 Display Analysis Results .................................................................................... 134

8.2 Individual Member Buckling Ultimate Strength Check................................................. 136 8.3 Stiffened Panel Buckling Ultimate Strength Check ....................................................... 139 8.4 Corrugated Panel Buckling Ultimate Strength Check.................................................... 142 8.5 Cylindrical Shell Buckling Ultimate Strength Analysis................................................. 145 8.6 Tubular Joints Buckling Ultimate Strength Analysis ..................................................... 148


Copyright © 2010 American Bureau of Shipping vi




1 Tutorial Examples Used in This Chapter An existing OSAP project in the <OSAP_Installation_Path>\Examples\Demo folder is used throughout this chapter to demonstrate the usage of OSAP application modules. The top level project file, Demo.prj, defines the project tree structure. The subdirectory contains examples for each of six OSAP application modules. Some of the input data referred by those examples are located at OSemi_Data and SemiT_Data folder. Note that the name of directory for each application module is created by OSAP and should not be altered by the user.

To open Demo project, go to Project menu > Open Project (or click the icon) and then

click to choose Demo.prj from OSAP_Installation_Path>\Examples\Demo folder.



Click OK. The project is opened and the Project Tree is activated as follows:



2 Load Generation (LG) Analysis

2.1 Create/Import/Open an LG Solution To create a new solution node for the Load Generation application, the user needs to first go to Application menu > Load Generation to activate the Load Generation module in the project

tree. OSAP then allows either creating a new empty solution by clicking or importing an

existing solution by clicking and selecting the Load Generation main input file (*.HLG).

If there is an existing solution under Load Generation, double-click the solution name to open that solution and activate the Application window. Here, the user can use the tab-based panels to edit the input data, administrate the analysis run, and visualize the analysis results.



2.2 LG Solution Processing Dynamic Loads In this section, solution SemiT under Load Generation application module is used to demonstrate the input and view options for the case when dynamic loads are to be generated.

2.2.1 Input and View Window Use the Input and View menus to view and edit if necessary the solution parameters. After analysis is completed successfully, use the View menu to display graphics and view results.

Files available for view:



Input Description Analysis Settings Open the Settings dialog to specify LG analysis type Load Condition Open the Dynamic Loads dialog for this example to:

• Import an AQWA-LINE, WAMIT, or OSAP input file • Define inertia and drag forces on Morison elements • Define spring element properties and calculate mooring and

tendon induced dynamic forces Mass Distribution Open the Mass Distribution dialog for this example to:

• Add/delete slicing planes • Define slicing planes either by node or by offset • Define reference point coordinates • Define mass properties

The user can also import an existing OSAP mass file (*.HMAS). Run Analysis Run the Load Generation analysis View Result File(s) View results after analysis. Files reside in the solution folder

where they can be viewed/printed outside the OSAP application.

2.2.2 Analysis Settings Select load analysis type and calculate critical response RAOs.

Option Description Apply Dynamic Loads To process dynamic loads Apply Static Loads To process static loads Calculate Critical Response RAOs

To calculate RAOs of critical response parameter and export an result file (*.HCLP) to be used by the Design Wave analysis. Note: This checkbox is active only when the Apply Dynamic Loads option is selected.



2.2.3 Load Condition Input for Dynamic Loads

2.2.3.1 Hydrodynamic Loads

Input the hydrodynamic analysis model and results.

File Type For SemiT, AQWA-LINE (*.lis) option is selected.

Other options are: • WAMIT (*.dfg, *.pot, *.frc, config file) • OSAP (*.hydr, *.mrao, *.prao)

File Name & Path Click to browse for the file in the SemiT_Data folder



2.2.3.2 Morison Elements

NOTE: The SemiT solution does not have Morison elements. Calculate Inertia/Drag Forces on Morison Element

Tick the checkbox to define optional input for calculating inertia/drag forces on Morison element

Inertia & Drag Forces Number of Divisions on Tubular Element

Enter number of divisions (>=1) on the Morison element. The Morison element is equally divided into segments and the Morison force is calculated for each segment. Note: FLOW.DAT (AQWA-FLOW input format) or FIELD.DAT (WAMIT *.FRC format) is generated to provide the coordinates of each Morison element segment for which the wave kinematics need to be calculated. See 1/2.2.5 for more details.

Input of Wave Kinematics Choose: • Non-disturbed Wave • AQWA-FLOW Output of water particle velocity • WAMIT Output for water particle velocity

Input File Click and use Explorer to browse for the appropriate input file for water particle velocity

Representative Sea State for Linearization

Signification Wave Height Enter signification wave height Peak Period (in seconds) Enter wave peak period (in seconds) Peakedness Parameter Enter wave spectral peakedness parameter



2.2.3.3 Spring Elements

NOTE: The SemiT solution does not have spring element properties (mooring lines, tendons, and tether forces). Calculate Dynamic Forces Induced by Mooring, Tendon or Tether

Tick the checkbox to defined optional input of spring element simulating station keeping devices

Spring Element Properties Spring element properties table 1 Auto-generated serial number Struc_X Enter the X coordinate of attachment point on structure Struc_Y Enter the Y coordinate of attachment point on structure Struc_Z Enter the Z coordinate of attachment point on structure Seabed_X Enter the X coordinate of attachment point on seabed. Seabed_Y Enter the Y coordinate of attachment point on seabed

Seabed_Z Enter the Z coordinate of attachment point on seabed Pretension Enter the pretension load Stiffness Enter the spring stiffness constant

Add a row to the table

Delete a row from the table

OSAP reads in all the input data. If there are existing element group data created from previous runs in the



solution folder, the Group Data File Generation dialog is prompted requesting for action.

The elements sets are added to the Project Tree and the mesh data for the solution is plotted.



2.2.4 Mass Distribution Mass distribution data is required only when Calculate Critical Response RAOs option is selected in Load Generation Settings window (see 2/2.2.2). The user can manually enter data in the dialogs, or import the data from an existing OSAP mass definition file (*.HMAS file).

2.2.4.1 Slicing Plane

Slicing Plane Manage slicing plane(s) Slicing Plane ID Slicing plane ID

Add a slicing plane. Note: At least one slicing plane has to be defined

Remove a slicing plane

Slicing Plane Definition Definition of slicing plane. Choose either: • Defined by Nodes (and pick nodes from the graphic) • Offset from Coordinate Plane

Defined by Nodes Node 1 – Node 3 If using three nodes to define a slicing plane, interactively

pick Nodes 1 – 3 from the plot or directly enter the node IDs Offset from Coordinate Plane Coord. Plane Choose ID of coordinate plane: XY, YZ, or XZ. Direction Choose either: +ve along positive axis direction or –ve along

negative axis direction



Offset Enter offset value from the selected coordinate plane. It

can be positive or negative, i.e. offset opposite to the normal direction of coordinate plane.

Reference Point Reference Point Coordinates: X Ref., Y Ref., Z Ref.

Coordinates of reference point for load parameter calculation Browse for an existing OSAP mass definition file (*.HMAS input file).



2.2.4.2 Mass Properties

If earlier the user imported data from an existing *.hmas input file, the fields in this dialog will already be populated.

Mass Properties table 1… Auto-generated serial number

Note: At least one mass point has to be defined. Mass Mass value X Coordinate X coordinate of the location of mass point Y Coordinate Y coordinate of the location of mass point Z Coordinate Z coordinate of the location of mass point Inertia Ixx Inertia Ixx of mass point Inertia Ixy Inertia Ixy of mass point Inertia Ixz Inertia Ixz of mass point Inertia Iyy Inertia Iyy of mass point Inertia Iyz Inertia Iyz of mass point Inertia Izz Inertia Izz of mass point

Add a row to the table.

Delete a row from the table.

Browse for an existing OSAP mass definition file (*.HMAS file)



2.2.5 Result Files

Click to execute the Load Generation analysis. Once the analysis is successfully completed, use the View Result File(s) dropdown list to open the data result files in the viewer. These text files reside in the application folder where they can be viewed/printed outside the OSAP application.

• Main Input for Load Generation Analysis (*.HLG file) • Input of point mass distribution (*.HMAS file) • Input/Output of hydrodynamic analysis model (*.HYDR file) • Output of motion, velocity and acceleration RAOs (*.MRAO file) • Output of panel element pressure RAOs (*.PRAO file) • Output of dynamic force RAOs (*.FRAO file) • Output of RAO amplitudes of critical load parameters (*.HCLP file) • Output of analysis intermediate results for data check (*.out file) • FLOW.DAT – Points for wave kinematics calculation (AQWA-FLOW Format) – only

available when the Morison Inertia/Drag Force calculation is requested in OSAP input and the Morison members are included in the input AQWA model or OSAP *.HYDR file. See 2/2.2.3.2.

• FIELD.DAT – Points for wave kinematics calculation (WAMIT *.FRC Format) – only available when the Morison Inertia/Drag Force calculation is requested in OSAP input and the Morison members are included in the input hydro model (OSAP *.HYDR file). See 2/2.2.3.2.

On each slicing plane defined in *.HMAS file (see 2.2.4), the load parameters, i.e. sectional forces and moments, are calculated with respect to the reference point. The load parameter label is defined as FX_##, FY_##, FZ_##, MX_##, MY_## and MZ_##, where ## stands for the ID number of slicing plane starting from 01, for three force and moment components respectively.



2.3 LG Solution Processing Static Loads In this section, solution OSemi is used to demonstrate the input and view options for the case when static loads are to be generated.

2.3.1 Input and View Window Use the Input and View menus to enter the input data, display the graphics, and view the results after analysis.

Input Decription Analysis Settings Open the Settings dialog to define the type of LG analysis Load Condition Open the Static Loads dialog for this example to:

• Import an AQWA, WAMIT, or OSAP model and result files • Define inertia and drag forces on Morison elements • Define spring element properties and calculate mooring, tendon,

and tether- induced dynamic forces Run Analysis Run the Load Generation analysis. View Result File(s) Select result files from the dropdown list to open them in the viewer.

The files reside in the solution folder where they can be viewed /printed outside the OSAP application.

Files available after analysis:



2.3.2 Analysis Settings

Click to open the Settings dialog.

Option Description Apply Dynamic Loads To process dynamic loads (See 2/2.2.3) Apply Static Loads To process static loads (used in this Section to

demonstrate the program functions)



2.3.3 Load Condition Input for Static Loads

Click to open the Static Loads dialog. The user can populate the dialogs either manually or by importing from an existing OSAP Static Load File (*.STAT).

2.3.3.1 Options

NOTE: This dialog is inactive for the OSemi solution. Static Loads Use AQWA-LIBRIUM Output Tick checkbox to use the output from an existing AQWA-

LIBRIUM result file (*.lis file). If this option is chosen, all other tabs become inactive.

Enter the full path location of a *.lis file or click to browse for the file

Browse for an existing OSAP static load file (*.STAT) and import the data



2.3.3.2 Model Definition



Model File Type File Type Choose WAMIT model and result files as input. Other

options available are • AQWA-LINE (*.lis) – using AQWA-Line results file • OSAP (*.HYDR) – using OSAP hydro model file

File Name Tick checkbox to enter a pathname and filename, or click

to browse the input. In this example, it is WAMIT model file for OSemi.

Equilibrium Position Enter equilibrium positions defined in the coordinates of hydrodynamic analysis model.

Surge Enter the equilibrium position in surge direction Sway Enter the equilibrium position in sway direction Heave Enter the equilibrium position in heave direction Roll (deg) Enter the equilibrium position in roll direction Pitch (deg) Enter the equilibrium position in pitch direction Yaw (deg) Enter the equilibrium position in yaw direction Reference point: X Ref., Y Ref., Z Ref

Enter coordinates of reference points for roll, pitch, yaw and moments defined in the hydrodynamic analysis model

Morison Element Number of Divisions on Tubular Element

Enter number of divisions (>=1) on the Morison element. The Morison element is equally divided into segments and the Morison force is calculated for each segment. Note: FLOW.DAT (AQWA-FLOW input format) or FIELD.DAT (WAMIT *.FRC format) is generated to provide the coordinates of each Morison element segment for which the wave kinematics need to be calculated. See 1/2.2.5 for more details.




2.3.3.3 Current Profile

NOTE: This dialog is inactive for the OSemi solution. Apply Static Current Loads on Morison Elements

Tick checkbox if applying static current loads to Morison elements

Current Profile Current Direction (deg) Enter current direction 1… Auto-generated serial number Profile ID Enter profile ID Depth to Still Water Line Enter depth to still water line Current Speed Enter current speed






2.3.3.4 Wind Loads

NOTE: This dialog is inactive for the OSemi solution. Apply Static Wind Loads Tick checkbox to apply static wind loads by entering data

manually or by importing it from an existing static load file.

Wind Loads table 1… Auto-generated serial number X, Y, and Z coordinates Enter wind force center Fx, Fy, Fz, Mx, Mx, and Mz Enter wind forces relative to the wind force center






2.3.3.5 Mooring Loads

NOTE: This dialog is inactive for the OSemi solution. Apply Static Mooring Loads Tick checkbox to apply static mooring loads by

entering data manually or by importing it from an existing static load file.

Mooring Loads table 1 Auto-generated serial number Mooring Line ID Identifying number of each mooring line Fairlead X, Fairlead Y, Fairlead Z Enter coordinates of fairlead Fx, Fy, Fz Enter mooring forces






2.3.3.6 Other Static Loads

NOTE: This dialog is inactive for the OSemi solution. Apply Other Static Loads Tick checkbox to apply other static loads by entering data

manually or by importing it from an existing static load file. Other Static Loads table 1… Auto-generated serial number X, Y, and Z coordinates Enter the location where static loads apply to Fx, Fy, Fz Enter component static forces Mx, My, Mz Enter component static moments



Open Explorer to import data from an existing OSAP Static Load File (*.STAT) for the solution.

The hydro model is imported, the group data file is generated, and the mesh data is plotted for the solution.



2.3.4 Result Files

Click to run the Load Generation analysis. Once the analysis is completed, use the View Result File(s) dropdown list to open the data files in the viewer. These text files reside in the application folder where they can be viewed/printed outside the OSAP application.

• Main Input for Load Generation Analysis (*.HLG file) • Input for static load case (*.STAT file) • Input/Output of hydrodynamic analysis model (*.HYDR file) • Output of static loads (*.FSTA file) • Output of analysis intermediate results for data check (*.out file)



3 Design Wave (DW) Analysis This section demonstrates the design wave analysis using the deterministic (regular wave) method and the stochastic (irregular wave) method, respectively, in OSAP Design Wave application module.

3.1 Create/Import/Open a DW Solution To create a new solution node for the Design Wave application, the user needs to first go to Application menu > Design Wave to activate the Design Wave module in the project tree.

OSAP then allows either creating a new empty solution by clicking or importing an

existing solution by clicking and selecting the Design Wave (DW) main input file (*.INP).

If there is an existing solution under Design Wave, double click the solution name opens that solution and activates the application window, on which the user can edit the input data, administrate the analysis run, and visualize the analysis results.



3.2 DW Solution Using the Deterministic Method In this section, solution SemiT_RegularWave is used to demonstrate the input and view options for the case when deterministic method is applied to the design wave analysis in OSAP.

3.2.1 Input and View Menu Use the Input menu to view and edit if necessary the input parameters. After the analysis is completed, use the View menu to display graphics and view results files.




Input Description

Open the Design Wave – RAO Data dialog to provide input of hydrodynamic model and analysis results (RAOs) as well as other relevant input

Open the Design Wave – Sea States dialog to provide input of sea state data

Run the design wave analysis

Edit and save design waves to an ascii file (*.DWH) which is to be used in the Load Mapping analysis for STRENGTH option (2/4.2)

View Data File(s) View data files after analysis. Files reside in the solution folder where they can be viewed/printed outside the OSAP application.



3.2.2 Design Wave – RAO Data

Click to provide the input of hydro model and RAOs of motion, velocity, acceleration, and optional critical load parameters.



Design Wave Analysis Option

Calculate design waves for the following optional parameters • Accelerations (ACCs) • Critical load parameters (CLPs) • Critical load parameters (CLPs) & Accelerations (ACCs)

OSAP HCLP File Critical Load Parameter RAOs (*.HCLP)

Click to load the critical load parameter RAO input file created during the Load Generation analysis. Note: This is not required for the Accelerations (ACCs) design wave analysis option.

Location in Hydro Model for Acceleration Calculation

Enter the X, Y, and Z coordinate of the reference point in the hydro model. (Normally it is CoG location)

Acceleration of gravity (g) Enter acceleration of gravity Note: The unit of acceleration of gravity should be consistent with the unit system employed in the hydrodynamic analysis model.

Motion RAOs (*.MRAO) Click to load the motion RAO input file created during the Load Generation analysis.



3.2.3 Design Wave – Sea States

Click to provide the input of sea states.

Number of Sea States Enter the number of sea states to use in the calculation Sea State Type Regular Waves option is selected for this example. See 2/3.3

for the application of the Irregular Waves option

Complete the Wave Data dialog by entering a set of wave height and associated wave period (limit wave curve). The number of rows is determined by the input to Number of Sea States field. Note: Click the right mouse button on a selected area in the table to copy or paste data between OSAP tables and Microsoft Excel spreadsheets.



3.2.4 Export Design Waves

Click to run the design wave analysis. When the calculation is completed, click

to generate a design wave table and save it to a data file (*.DWH file). The initial value entered in DWH file is extracted from the design wave analysis output file (*.DWC file). The user can edit the *.DWH file to generate design waves that will be used in the subsequent Load Mapping analysis. The *.DWH file resides in the solution folder.

3.2.5 View Data Files Upon the successful completion of the analysis, the user can use the View Data File(s) dropdown list in the Input menu to open the data files in the viewer. These text files reside in the application folder where they can be viewed/printed outside the OSAP application.

• Input of RAO amplitudes of critical load parameters (*.HCLP file created in the Load Generation analysis)

• Input of motion, velocity and acceleration at reference point (*.MRAO file created in the Load Generation analysis)

• Output of acceleration RAOs at a user specified location (*.ACC file) • Output of design wave analysis results (*.DWC file). • Output of intermediate analysis results for data check (*.out file)

• Output of design wave height (optional *.DWH file generated by )

3.2.6 View Analysis Results in Graphic Window

After the calculation is successfully completed, click Results to plot the results and use the View menu to change plot parameters. The plot title includes wave type, parameter, and wave heading.



Type • Select WaveLimit*RAOs to plot the results of Limit Wave

Curve multiplied by RAOs of critical response parameter • Select Response RAOs to plot the RAO of selected

parameter Parameter Choose a parameter for which the curve is to be plotted Wave Heading (Deg) Choose a wave direction Show Data Points Tick checkbox to display data points

The 2D curves can be zoomed in to allow the user to read more precise coordinates. Click icon, choose Box Zoom option, and then use then left mouse button to select an area to zoom in. Select Fit to reset the plot back to its original size.



3.3 DW Solution Using the Stochastic Method In this section, solution SemiT_IrregularWave is used to demonstrate the input and view options for the case when stochastic method is applied to the design wave analysis. Double click the SemiT_IrregularWave solution name under Design Wave application module activates the application window, on which the user can edit the input data, administrate the analysis run, and visualize the analysis results.

3.3.1 Input and View Menu Use the Input menu to view and edit if necessary the input parameters. After analysis, use the View menu to display graphics and view results.




Input

Open the Design Wave – RAO Data dialog to provide input of hydrodynamic model and analysis results (RAOs) as well as other relevant input.

Open the Design Wave – Sea States dialog to provide input of sea state data

Run the design wave analysis

Edit and save design waves to an ascii file (*.DWH) which is to be used in the Load Mapping analysis for STRENGTH option (2/4.2)

View Data File(s) View data files after analysis. Files reside in the solution folder where they can be viewed/printed outside the OSAP application.

3.3.2 Design Wave – RAO Data

Click to provide the input of hydro model and RAOs of motion, velocity, acceleration, and optional critical load parameters. Refer to 3.2.2 for details.

3.3.3 Design Wave – Sea States

Click to provide the sea state data.



Number of Sea States Enter the number of sea states to be used in the

calculation. This input determines the number of rows of input in Enter Wave Period – Height – Gamma Values dialog

Sea State Type In the example, Irregular Waves is selected from the dropdown list. See 2/3.2for the Regular Waves option.

Irregular Waves Spectrum Type Choose PM(Gamma=1) or JONSWAP (Gamma>1).

Another option is Ochi-Hubble 6-parameter spectrum. Wave Period Type Choose between zero up-crossing period Tz and peak

period Tp from the dropdown list. Load Factor Enter the load factor. This is the factor to account for the

exceedence probability of the extreme value of critical response parameter.

Limit Wave (for curve plotting only) 100-yr Return Period Wave in the

North Sea Check to select

Steepness of Limit Wave Enter steepness of limit wave Max. Limit Wave Height Enter the maximum limit wave height

Complete the Wave Data dialog with height and gamma values for each wave period. The contents of the table depend on the input to Number of Sea States, Sea State Type, and Spectrum Type. Note: Click the right mouse button on a selected area in the table to copy or paste data between OSAP tables and Microsoft Excel spreadsheets.



3.3.4 Export Design Waves

Click to run the design wave analysis. When the calculation is completed, click

to generate a design wave table and save it to a data file (*.DWH file). The initial value entered in DWH file is extracted from the design wave analysis output file (*.DWC file). The user can edit the *.DWH file to generate design waves that will be used in the subsequent Load Mapping analysis. The *.DWH file resides in the solution folder.

3.3.5 View Data Files Upon the successful completion of the analysis, the user can use the View Data File(s) dropdown list in the Input menu to open the data files in the viewer. These text files reside in the application folder where they can be viewed/printed outside the OSAP application. The results are similar to those obtained from analyzing the regular wave solution. See 3.2.5

3.3.6 View Analysis Results in Graphic Window

After the calculation is successfully completed, click Results to plot the results and use the View menu to change plot parameters. The plot title includes wave type, parameter, and wave heading.



Type • To plot the design wave curves, select Design Wave Height.

• To plot the critical response RAOs, select Response RAOs. Parameter Choose a parameter for which the curve is to be plotted Wave Heading (Deg) Choose a wave direction Show Data Points Tick checkbox to display data points Show Limit Wave Height Tick checkbox to display wave height limit. The 2D curve plot can be zoomed in to show more precisely the coordinates of data point. Click

icon, choose Box Zoom option, and then use the left mouse button to select an area to zoom in. Select Fit to reset the plot back to its original size. See 3.2.6 for example.



4 Load Mapping (LM) Analysis The Load Mapping application module maps hydrostatic or hydrodynamic pressures, forces, and internal tank loads from a hydro model to a structural FE model. The loaded FE model can be used as the input for structural analysis. The format of loaded FE model can be either in NASTRAN or ANSYS format and is determined by the format of input FE model used in the load mapping analysis. It should be noted that OSAP does not provide automatic balancing capability. Instead, the user can use OSAP to apply displacement constraints and/or point masses, i.e. ‘controlled’ inertia relief, to the FE model in order to balance the loaded FE model. The user should resolve all unbalanced forces for each load case before starting running FE analysis.

4.1 Create/Import/Open an Load Mapping Solution To create a new solution node for the Load Mapping application, the user needs to first go to Application menu > Load Mapping to activate the Load Mapping module in the project tree.

O


existing solution by clicking and selecting the project folder that contain the existing input and output files.



If there is an existing solution under Load Mapping model in the project tree, double click the solution name opens that solution and activates the application window. If all result files are available, the application window will be set to the View module for graphic display. The user can use the Input menu to view and edit the input data. After running through all steps within

, use the View menu to display graphics and open the results files using

.



4.2 Load Mapping Analysis – STRENGTH Option In this section, solution Osemi_GS is used to demonstrate the input and view options for the case when STRENGTH option is selected to generate loaded FE model for Global Strength analysis and Simplified Fatigue analysis.

Input Specify Job Type Specify type of job (2/4.2.1) Setup FE Model Open the Load Mapping: Setup FE Model dialog4.2.2 Hydro Model & Results Open the Load Mapping: Import Hydro Model & Results

dialog (2/4.2.3) Mass/Weight (.MAS) Open the Load Mapping: Mass Input dialog (2/4.2.4)

Constraints (.FIX) Open the Load Mapping: Input Constraints dialog (2/4.2.5) Run Analysis Generate Structural Loads Open the Load Mapping: Generate Structural Loads dialog

(2/4.2.6) Translate Nastran Results After the user solves the loaded NASTRAN FE model, this

button is used to Translate NASTRAN results to OSAP neutral format mesh and stress files.

View Data File(s) View input data files and output data files. The files reside in the solution folder where they can be viewed/printed outside the OSAP application.

Input Files available for View

Output Files available for View



Data files available for direct access via are summarized as follows: Input Data File HYDR, MRAO, PRAO, FRAO, FSTA

Hydro model and load input generated by Load Generation analysis (see 2)

DWH Design wave data input generated by Design Wave analysis (see 3)

TYP Load mapping job type (see 4.2.1) MTF Model translation file (see 4.2.2) MAS Mass input (see 4.2.4) FIX Constraint definition (see 4.2.5) Output Data File LCS Load case definition file (see 4.2.7) RPT Output of mass and model check report BBS Summary of unbalanced force of loaded FE model BBA Report of balance loads of loaded FE model Data files of the loaded FE model are located in the solution folder. For NASTRAN format B<solution_name>.NAS NASTRAN FE model L<solution_name>_GS_D00.DAT NASTRAN input file for the model subject to static

loads (not available if the FSTA file is not specified in the load mapping analysis)

L<solution_name>_GS_D00.PARAM NASTRAN analysis settings file L<solution_name>_GS.DAT NASTRAN input file for the model subject to the

hydrodynamic loads associated with the design waves specified in the *.DWH file. Each design wave corresponds to a load case pair representing real and imaginary load components.

L<solution_name>_GS.PARAM NASTRAN analysis settings file For ANSYS format B<solution_name>.ANS ANSYS FE model L<solution_name>_GS_D00.DAT ANSYS load input file for static loads (not available if

the FSTA file is not specified in the load mapping analysis)

L<solution_name>_GS.DAT ANSYS load input file for the load cases associated with design waves defined in the *.DWH file. Each design wave corresponds to a load case pair representing real and imaginary load components.



4.2.1 Specify Job Type (*.TYP File) Analysis control file *.TYP is generated through the following window.

Model Type Model type (Only Global Option is available) Model Name Model name which is set to be the same as the

solution name Directory Path location of the solution folder which is defined

when creating or importing a project. Analysis Type Choose STRENGTH option for this example.

Options available STATIC – for generating loaded FE model for

global strength analysis STRENGTH – for generating loaded FE model

for global strength and simplified fatigue analysis

SFATIGUE – for generating loaded FE model using for spectral fatigue analysis (see 2/4.3)

Note: The FSTA file must be specified if the STATIC option is selected. See 2/4.2.3

For NASTRAN Solution Translation Only Check if this is only to translate NASTRAN results into OSAP neutral format mesh and stress files. When this option is selected, Analysis Type option is irrelevant. (see 2/4.4)



4.2.2 Setup FE Model (*.MTF File) This input is to specify the FE model and/or hydro model information and convert the FE model file into OSAP interim files.

Click to open the Load Mapping: Setup FE Model dialog.

Open the Load Mapping: Information for Project Source Model dialog to generate the MTF file and use it to define the FE model.

Translate the FE model into OSAP interim data file for load mapping analysis and graphic display

Click in the Load Mapping: Setup FE Model dialog to open the Load Mapping: Information for Project Source Model dialog for generating a new or editing an existing MTF file. Enter the required data in the individual tabs to define platform data, structural model details, tank descriptions, and hydrodynamic model details.



Platform Data

Analysis Type Auto-populated with Global. Parent Model Name Auto-populated with name of solution. User Favorite Unit Unit System (Length, Force, Mass) Select the unit system to be used for input data and

output results.



Structural Model

Model Type Select FE model type: NASTRAN or ANSYS. This input

also determines the format of loaded FE model generated by OSAP Load Mapping analysis

Input File Enter the FE model input file

Browse for the source model FEM filename to be converted

Orientation of Model Axes +X, +Y, +Z

Select the input model coordinate orientations from the dropdown lists

Model Units of Length, Force, Mass

Select the length, force, and mass units used in the input FE model

Reference Point: X Reference, Y Reference, Z Reference

Enter the location of reference points of input FE model in the coordinates system that will be used to generate the output loaded FE model. A reference point is a fixed point in space that will become the coordinate origin of the translated FEM. It must be located at the intersection of the vessel's centerline and bottom plate at a user-selected longitudinal location.



Tank Description

Add User Defined Tanks Tick the checkbox if using user-defined tanks. By default,

Load Mapping application automatic searches for the matching components between FE model and hydro model.

Tank ID number

Add tank(s) to the tank list

Delete a tank from the tank list

Tank Name Enter the user defined tank name Tank Input Tank Type Select a type of tank from the dropdown list. The user can

specifically define the tank through the following options: SHELL – Vessel external shell BLLST – Ballast tank CARGO – Cargo tank TUBE – Tube plate elements DISC – Disc plate elements STUB – Stub plate elements Note: SHELL Tank must be defined as the first tank and only one entry of SHELL Tank is allowed

Tank Input File Type Choose type of file, either NASTRAN or ANSYS. Input File Choose a NASTRAN file or ANSYS file.

Browse for the tank input file Density of tank contents Enter the density of the tank contents Added pressure head Enter tank pressure head



Hydro Model

Orientation of Hydro Model Axes +X, +Y, +Z

Set the hydro model coordinate orientation.

Hydro Model Units of Length, Force, Mass

Select the unit system used in the input hydro model and hydro analysis results

Hydro Reference Point: X Reference, Y Reference, Z Reference

Enter the location of reference points of input hydro model in the coordinates system that will be used to generate the output loaded FE model. Note: The hydro model and FE model should have the same origin after the model transferred.

Once the input to create .MTF file is ready, click to translate the model. When the translation process is completed, a graphic display of the FE model is plotted.



4.2.3 Import Hydro Model and Results This input window is to specify the hydro model, hydro static/dynamic loads data and design wave input locations, and copy the related files to the solution folder.

Click to use the Load Mapping: Import Hydro Model & Results dialog to load input files. The hydro model and results can be obtained from the Load Generation and Design Wave solution.

Required Hydro Model and Result Input File Name for OSAP .HYDR,

.MRAO, and .PRAO Files Load hydro model and results *.HYDR, *.MRAO, and *.PRAO input files obtained by Load Generation analysis.

Required Design Wave Input OSAP .DWH File Enter the design wave input file generated by

Design Wave analysis. This input is required for STRENGTH analysis type as specified in 4.2.1

Optional Hydro Result Input File Name for OSAP .FRAO

and/or .FSTA Files • Specify the hydrodynamic forces RAOs

(*.FRAO file - optional for the STRENGTH or SFATIGUE option, not required for the STATIC option)

• Specify the hydrostatic forces *.FSTA input files (required for the STATIC option, optional for the STRENGTH, not required for the SFATIGUE option)

Use Explorer to select an input file from the solution folder.



4.2.4 Input Mass/Weight (*.MAS File) This data input window is to define the mass distribution of the loaded FE model. It also allows to define additional point mass to be applied to the FE model and specify the mass property check plane at a given location.

Click to open the Load Mapping: Mass Input dialog for generating or editing the *.MAS file.



Mass Distribution Mass Calculation Options Choose:

Define New Mass Density – Change the FE model mass density value. No Distributed Mass

– Ignore the FE model mass. Use Mass Density in FE Model

– Use input FE model mass density value. Density Enter density when the user selected the Define New Mass

Density option. The units are correlated to the input to the *.MTF file.

Include Mass Elements in FE Model

Check to include mass elements in FE model

Point Mass Input Node ID Node ID Mass (tf) Mass OffsetX X offset of the center of gravity of the mass from the node OffsetY Y offset of the center of gravity of the mass from the node OffsetZ Z offset of the center of gravity of the mass from the node I11, I21, I22, I31, I32, I33 Mass moment of Inertia

Note: 1. Mass moments of inertia are calculated with respect to the mass point location. 2. Mass = ∫ρdV, I11=∫ρ(x32+x22)dV, I22=∫ρ(x12+x32) dV, I33=∫ρ(x12 + x22) dV, I21=∫ρx1x2 dV, I31=∫ρx1x3 dV, I32=∫ρx2x3 dV.

Toggle on to pick the node ID for point mass. Choose either: Sequential Cells (continuous picking fills the node ID into cells sequentially) or Current Cells (single picking fills in the currently activated cell only)

Add a row to point mass table.

Delete a row from point mass table.

Mass Check Location Mass Check Location Plane Direction Plane Direction: Select Longitudinal, Vertical, and

Transverse. Plane Location Plane Location defined by the offset from the selected

coordinate plane in Plane Direction.

Add a row to Mass Check Location table.

Delete a row from Mass Check Location table.

Toggle on to pick the node on screen. Choose either: Sequential Cells or Current Cells. The coordinate of the node along with Plane Direction is entered into Plane Location cell.

Choose either Point Mass Input or Mass Check Location to hide/show a portion of the input window.



4.2.5 Input Constraints (*.FIX File) This input window is to

• Define the model constraints and boundary conditions for the FE model. • Constrain the rigid body motion of the model by setting specific nodes as fixed points or

setting certain nodes as slaves to master nodes. • Constrain Finite Element model nodes (termed Slave Nodes) by tying them with their

parent nodes (termed Master Nodes) with regard to translational and/or rotational displacements.

Click to open the Load Mapping: Input Constraints dialog for generating a new or editing an existing *.FIX file. Constrained Nodes



1… Auto-generated serial number. Node (ID) Enter the ID of each node to be constrained in current

FEM. Boundary Conditions Select symmetry consideration. Translation: All, Longitudinal, Vertical, Transverse

Check the appropriate box(es) to indicate node with translational restraints along any one, two, or all XYZ coordinate axes.

Rotation: All, Longitudinal, Vertical, Transverse

Check the appropriate box(es) to indicate node with rotational restraints along any one, two, or all XYZ coordinate axes

Insert row in table.


Toggle on to pick the node ID for point mass. Choose either: Sequential Cells (continuous picking will fill the Node ID into cells sequentially) or Current Cells. (single picking fills in the currently activated cell only).

Slave-Master Nodes Define the slave-master nodes for NASTRAN format FE model.



User Override Slave-Master Constraints

1… Auto-generated serial number Slave Node Enter a slave node ID Master Node Enter a master node ID Translation: All, Longitudinal, Vertical, Transverse

Check the appropriate box(es) to indicate node with translational restraints along any one, two, or all XYZ coordinate axes.

Rotation: All, Longitudinal, Vertical, Transverse

Check the appropriate box(es) to indicate node with rotational restraints along any one, two, or all XYZ coordinate axes

Factor Enter the proportionality factor of slave to master. The sum of all factors for any one DOF at one slave node should be 1.0.

Insert row in table


Choose either: Sequential Cells (continuous picking fills the Node ID into cells sequentially) or Current Cells (single picking fills in the currently activated cell only). Toggle on to pick up the node ID for point mass.

Program Determined Slave-Master Constraints

Choose either No Automation or Apply Constraints (by default).

4.2.6 Generate Structural Loads Using the input model data and hydro results, the Load Mapping application module transfers the hydro forces and pressures to the FE model, generates the tank pressures and inertial forces for the FE model, and finally exports loaded FE model(s) that can be solved by either NASTRAN or ANSYS.

Click to open the Load Mapping: Generate Structural Loads dialog.



The user can click sequentially on each button to execute the operation in step-by-step mode, which gives the user more exposure to the interim analysis results and resolve the issue raised during the analysis before going into the next step. The load mapping analysis could be a time

consuming process. Alternative, the user can also click to let OSAP automatically run through all the analysis.

After creating the loaded NASTRAN model, the user can click to define the NASTRAN executable location and start the FE analysis. Upon the completion of the FE analysis, OSAP transfers the NASTRAN solutions into the OSAP neutral format mesh and stress files, which are saved to the load mapping solution directory. When the loaded FE model is in ANSYS format, the user need to run the FE analysis within ANSYS environment and then use the data interface program A2ABSCHK.mac, which is a ANSYS script language program developed by ABS, to generate the OSAP neutral format mesh and stress files. Chapter 3 provides more details about A2ABSCHK.mac program



4.2.7 View Load Mapping Results

Click Results to open the graphic window for visualizing the load mapping results. Load Mapping Results Descriptions Tank Boundaries FE mesh of tank boundary for the user defined tanks Tank Pressure Tank pressure distribution for the user defined tanks Hydro Pressures • Hydrostatic (Load Case 1) pressure on hydro panel model

• Real and imaginary components of hydrodynamic pressure on hydro panel model.

NOTE: Hydrostatic pressure is available only when optional FSTA file is provided in the input (see 4.2.3)

Hydro Forces (optional) • Hydrostatic (Load Case No.1) force on hydro panel model • Real and imaginary components of hydrodynamic force on

hydro panel model. NOTE: 1. Hydrostatic force is available only when optional .FSTA file is

provided in the LM input and the file contains the definition of hydrostatic forces generated in Load Generation analysis. (see 4.2.3 and 2.3)

2. Hydrodynamic force is available only when optional FRAO file is provided in the LM input (see 4.2.3). FRAO file is generated in Load Generation analysis (see 2.2)

Hydro Inertia Loads Inertia forces distribution on FE nodes Tank Hydro Loads Tank pressure on the FE mesh defining tank boundary Loaded FE Model Load (nodal force and moment or element pressure) distribution on

FE mesh Sample graphic displays are illustrated below.



Real component of hydrodynamic pressure distribution on the hydro panel model

Nodal forces on the loaded FE model mapped from the hydrodynamic pressures and inertia forces



Click to open the Select Load Cases dialog. Select the static (Load Case 1) as well as real and imaginary dynamic load cases. The load case referred in the visualization of load mapping results is defined in *.LCS file which can be opened through . In the case that the STRENGTH option is selected for the load mapping analysis (see 4.2), the active load cases are determined by the *DWH file (design wave data input) and only available for those direction and period combinations for which the design waves are defined. In the *.LCS file, the active load cases associated with STRENGTH option are those LS_IDs with KYB=1. The last column of LABEL in *.LCS file shows the direction and period of the correlated design waves defined in the *.DWH file.



4.3 Load Mapping Analysis – SFATIGUE Option In this section, solution Osemi_FA is used to demonstrate the input and view options for the case when SFATIGUE option is selected to generate loaded FE model for Spectral Fatigue analysis.

Input Specify Job Type Specify type of job (2/4.2.1) Setup FE Model Open the Load Mapping: Setup FE Model dialog4.2.2 Hydro Model & Results Open the Load Mapping: Import Hydro Model & Results

dialog (2/4.2.3) Mass/Weight (.MAS) Open the Load Mapping: Mass Input dialog (2/4.2.4)

Constraints (.FIX) Open the Load Mapping: Input Constraints dialog (2/4.2.5) Run Analysis Generate Structural Loads Open the Load Mapping: Generate Structural Loads dialog

(2/4.2.6) Translate Nastran Results After the user solves the loaded NASTRAN FE model, this

button is used to Translate NASTRAN results to OSAP neutral format mesh and stress files.

View Data File(s) View input data files and output data files. The files reside in the solution folder where they can be viewed/printed outside the OSAP application.


Output Files available for View



Data files available for direct access via are summarized as follows. Note the, in comparison to the input files required for the STRENGTH option, DWH file and FSTA file is not required in generating the load FE model for the subsequent spectral fatigue analysis. Input Data File HYDR, MRAO, PRAO, FRAO Hydro model and load input generated by Load

Generation analysis (see 2) TYP Load mapping job type (see 4.2.1) MTF Model translation file (see 4.2.2) MAS Mass input (see 4.2.4) FIX Constraint definition (see 4.2.5) Output Data File LCS Load case definition file (see 4.2.7) RPT Output of mass and model check report BBS Report of unbalanced force of loaded FE model BBA Report of balance loads of loaded FE model Data files of the loaded FE model are located in the solution folder. For NASTRAN format B<solution_name>.NAS FE model L<solution_name>_D01.DAT … L<solution_name>_D##.DAT

NASTRAN input file for the loaded FE model. Each file contains two times number of periods/frequencies load cases. Each period/frequency corresponds to a pair of real and imaginary load cases organized sequentially in the file. There are number of directions input files being generated by the load mapping analysis. ‘##’ in the file name stands for the number of directions.

L<solution_name>_D00.PARAM … L<solution_name>_D##.PARAM

NASTRAN analysis settings

For ANSYS format B<solution_name>.ANS FE model L<solution_name>_D01.DAT … L<solution_name>_D##.DAT

ANSYS load input file for the loaded FE model. Each file contains two times number of periods/frequencies load cases. Each period/frequency corresponds to a pair of real and imaginary load cases organized sequentially in the load file. There are number of directions input files being generated by the load mapping analysis. ‘##’ in the file name stands for the number of directions.



4.3.1 Specify Job Type (*.TYP File) Analysis control file *.TYP is generated through the following window.

4.3.2 Setup FE Model (*.MTF File) Refer to 4.2.2 for details.

4.3.3 Import Hydro Model and Results Refer to 4.2.3 for details with the only difference being that the DWH file and optional FSTA file are not required for the SFATIGUE option.

4.3.4 Input Mass/Weight (*.MAS File) Refer to 4.2.4 for details.



4.3.5 Input Constraints (*.FIX File) Refer to 4.2.5 for details.

4.3.6 Generate Structural Loads Refer to 4.2.6 for details.

4.3.7 View Load Mapping Results Refer to 4.2.7 for details. Note that the load case associated with SFATIGUE option is active (KFTG=1) for each direction and period combination as shown in the following *.LCS file. Therefore, analysis results are available for display for all cells, i.e. load cases, in the Select Load Case window.



4.4 Load Mapping Analysis – For Nastran Solution Translation Only In this section, solution Osemi_NAS is used to demonstrate the capability of generating the OSAP neutral format MESH and STRS files by importing the MSC NASTRAN analysis model and results (OP2 file). NASTRAN models may be created and solved outside of OSAP. In this regard, the For Nastran solution translation only option serve as a data interface program that converts the NASTRAN model and results to the OSAP neutral format input files required in the OSAP strength code check applications. It is recommended that the load case ID in the NASTRAN model, as shown in the example below, should not be larger than 5000. This is mainly because a large load case ID may reduce the performance of Setup Load Case input window (see 4.4.2).

4.4.1 Specify Job Type (*.TYP File)

Analysis control file *.TYP is generated through the following window. When the option For Nastran solution translation only is selected, Analysis Type cell becomes inactive and Input menu is also updated accordingly.



Input Specify Job Type Specify type of job Setup Load Cases Open the Load Mapping: Setup Load Cases dialog to

specify selected load cases for which the FEA results need to be extracted for MSC NASTRAN database (OP2 file)

Setup FE Model Open the Load Mapping: Setup FE Model dialog to define the FE model being translated

Translate Nastran Results Translate NASTRAN results to OSAP neutral format mesh (MESH) and stress (STRS) files.

Data files available for direct access via are summarized as follows. Input Data File TYP Load mapping job type (see 4.2.1) MTF Model translation file (see 4.2.2) LCS Load case definition file (see 4.2.7) Data files of the loaded FE model are located in the solution folder. OSAP neutral format files <solution_name>.mesh FE model <solution_name>.strs FEA result file that are required input for the

strength, plate buckling, and fatigue check




4.4.2 Setup Load Cases (*.LCS File) The user can select those load cases whose FEA results need to be extracted from NASTRAN result database (OP2 or PCH file) and export to OSAP neutral format STRS file.

Define Load Cases

The largest load case ID number specified in the NASTRAN model or whose associated FEA results need to be extracted for result database (OP2 or PCH file)

This button is activated when Maximum Load Case Number input is changed. Click it to update the array of load case check boxes.

Check the appropriate box(es) to indicate that the FEA results for that (those) load case(s) need to be extracted from NASTRAN result database and export to OSAP neutral format FEA results file (STRS file). NOTE: • For those load cases not defined in NASTRAN model

but selected by the user in this dialog, no FEA result will be extracted and exported to OSAP STRS file.

• In the specified example referred in this section, the largest load ID defined in the NASTRAN model is 107. There are four load cases, i.e. 20, 21, 106, and 107 defined in the model and corresponding FEA results are stored in OSemi_NAS.op2 file. Only the selection from these load cases generates OSAP STRS file.

Click to select all load cases shown in Select Load Case to be Translated dialog

Click to unselect all load cases shown in Select Load Case to be Translated dialog.

Optional Solution If no input is provide, the program will search the solution folder for <solution_name>.OP2 or <solution_name>.PCH.

Choose a NASTRAN result database to be copied to <solution_name>.OP2 or <solution_name>.PCH in the current solution folder



4.4.3 Setup FE Model (*.MTF File) Refer to 4.2.2 for details. The MTF file is defined with only Platform Data and Structural Model tabs active. The other input to MTF file is not relevant in this case.

Click Input Project Source Model Info (MTF) button to open the input dialog as shown below. Refer to 2/4.2.2 for the description of the input parameters on the dialogs.



Once the input to create MTF file is ready, clicking button starts the model translation process. A graphic display of the FE model is plotted upon the completion of the translation.

4.4.4 Translate Nastran Results

Clicking on the Input menu as shown in 2/4.4.1 transfers the NASTRAN solutions into the OSAP neutral format mesh and stress files in the current load mapping solution directory. Those files are to be used as input in the global strength or fatigue analysis in OSAP.



5 Global Strength Analysis OSAP Global Strength Analysis requires an OSAP neutral format FE mesh file (*.MESH) and result file (*.STRS) as input. These OSAP neutral format files can be created using the data interface with MSC NASTRAN, as described in 4.2.6 and 4.4, or ANSYS as shown in Chapter 3. The Global Strength analysis generates strength code check results for yielding check and plate buckling check.

5.1 Create/Import/Open a Global Strength Solution To create a new solution node for the Global Strength application, the user needs to first go to Application menu > Global Strength to activate the Global Strength module in the project tree.


existing solution by clicking and selecting the project folder that contain the existing input (*.INP file) and output files.

If there is an existing solution under Global Strength application module in the project tree, double click the solution name to open that solution and activate the application window. If all result files are available, the application window will be set to the View module for graphic display. The user can use the Input menu to view and edit input data. After completing the global strength analysis, the user can



• Open the results files through .

• Click Model icon to display the FE mesh

• Click Results icon to open the View menu and plot the results in the graphic window

5.2 Input and View for Global Strength Analysis This section uses the SemiT solution to demonstrate global strength analysis in OSAP. Once an existing input file has been imported or opened, the user can either accept the data as is, or use the Input menu to modify the data before analysis. The View menu lets the user display graphics and view results after the analysis.

Input

Open the Global Strength Data dialog

Open the Buckling Input File dialog

Run the global strength code check. Note: Computing time depends on the size of the FE model, the number of load cases, and whether panel search is requested.

View Result File(s) Select each result file from the dropdown list to open it in the graphic window. The files reside in the solution folder where they can be viewed /printed outside the OSAP application. See 5.2.9 for further details. Note: The changes made to the input are not effective on

the results until is clicked to re-run the analysis. The user needs to ensure that the graphic display is not using the results from previous analysis runs.

Result files available for view



5.2.1 Input Global Strength Data

Click to open the Global Strength Data dialog.

Unit Conversion Factors (mm, MPa): Units, Length, Stress

Enter the unit system used in the input data If a pre-defined unit system is chosen, the Length and Stress fields are populated automatically. If the 99-User Specified option is chosen, the user needs to enter the input in the Length and Stress fields.

Input FE Model File Click to select an OSAP neutral format FE model file (*.MESH) to be used in the analysis. NOTE: For the demonstration purpose, SemiT.mesh is selected for the SemiT solution.

Number of Element Stress Files

Enter the number of finite element result input files (*.STRS) to be used in the analysis.



Click to browse for the *.STRS files for the SemiT solution.

Note: Use the first button to import multiple element stress input files at once.

Number of Load Cases Enter the number of load cases to be analyzed

In the Load Cases Input dialog, for each load case, specify Analysis Type (whether yielding check, buckling check, or both); define the load combination by selecting the labels for static and dynamic load cases from the respective drop-down list; and define the applicable safety factors Note: Static Load label can not be None.

OSAP reads in all the input data. If there is an existing element group data file created from previous runs in the solution folder, the Group Data File Generation dialog is prompted requesting for action.



5.2.2 Input Buckling Data When the panel buckling check is requested in the load case definition, see 2/5.2.1,

button becomes active. Click it to open the Buckling Input File dialog.

Generate Panel File Generate a panel definition file (*.PNL file) automatically by

OSAP and save it to the solution folder Select Panel File To save computing time, use an existing panel definition file. In

the Panel File Name field, click to browse for the panel definition file (*.PNL). NOTE: Because the panel definition file is determined by the FE model, as long as the FE model remains unchanged, it remains valid and can be re-used.

5.2.3 View FE Mesh

To display the FE mesh of whole structural model in the graphic window, click Model icon and select FE Model. The following plot shows the SemiT mesh with both Plate and Beam elements turned on.

To change the setting of labeling and style options, click icon to open the View Options

window. More view options are available via toolbar (see Chapter 1).



To display an element set/group, double-click an element set name listed under Mesh Element Sets in the Project Tree.

To display a node set, double-click an node set name listed under Mesh Node Sets in the Project Tree.

5.2.4 Display Results as Contour Plots

Click Results and use the View menu to select output type, load cases, and parameters for the graphic display.



Output Type Select type of analysis results from the dropdown list

Yielding Check or Buckling Check. Load Case Select a load case to display its contour plot. The availability of load

cases is determined by the number of load cases specified in the Global Strength Data dialog and the types of analysis specified in the Load Cases Input dialog. See 5.2.1. ALLC stands for the maximum envelope of unity check results among all user defined load cases

Parameter Determined by the selected Output Type. See the table below for details.

Legend - UnityCheck Results categories in color-coded format (Only for Unity Check results) The plot below shows an example of contour plot.



Output Type Parameter

Yielding Check[1]

UnityChk yielding unity check results S_EQV element equivalent stress used for yielding check S_Phase stress phase angle that results in S_EQV S++_S static stress components S++_R real part of dynamic stress components S++_I imaginary part of dynamic stress components

Buckling Check[2]

Unity_B_Avg unit check for panel buckling state limit under average in-plane panel stresses Unity_U_Avg unit check for panel ultimate strength state limit under average in-plane panel stresses Unity_L_Avg unit check for panel ultimate strength state limit under average panel lateral pressure and in-plane panel stresses Unity_B_Max maximum unit check result for panel buckling state limit under in-plane stresses calculated using panel element stresses Unity_U_Max maximum unit check result for panel ultimate strength state limit under in-plane stresses calculated using panel element stresses Unity_L_Max maximum unit check result for panel ultimate strength state limit under lateral pressure and in-plane stresses calculated using panel element stresses S**_B_Avg average panel stress components used for buckling check S**_U_Avg average panel stress components used for ultimate strength check S**_P_Avg average panel stress components used for lateral pressure check Pres_Avg average panel lateral pressure S**_B_max panel element stress components leading to the maximum unity check for buckling state limit S**_U_max panel stress components leading to the maximum unity check for ultimate strength state limit under in-plane stresses S**_P_max panel stress components leading to the maximum unity check for ultimate strength state limit under lateral pressure and in-plane stresses Pres_max panel lateral pressure leading to the maximum unity check for ultimate strength state limit under lateral pressure and in-plane stresses

Notes: 1. ‘++’ = ‘xx’, ‘yy’, ‘zz’, ‘xy’, ‘yz’, or ‘xz’ representing the stress component defined in the

FE model coordinate system. 2. ‘**’ = ‘xx’, ‘yy’, or ‘xy’ representing the stress component defined in the panel local

coordinate system.



5.2.5 Display and Save View Options

Click to change the settings for displaying contour plots in the graphic window.

Edit the contour plot title

Edit the contour plot legend title and the settings of contour levels Default: 10 levels of color shades automatically adjusted to accommodate the maximum and minimum value of each contour plot Custom: user specified contour level fixed for all plot once selected.

Set the display filter using element types

Set the type of contour plot

Preview Preview the effect of current View Option setting OK Save the current setting and apply to the plot Cancel Discard any change and return to the previous plot



More view options are available via toolbar icons (see Chapter 1).

Click Save Plot to save the current plot as a bitmap file (*.bmp) in the solution folder, or

click Save All Plots to save the plots for every output type and load case plotted in the session.

5.2.6 Set Clipping Plane To apply clipping planes, use Clipping Plane in the toolbar. Select Reset Clip to remove the clipping plane.

5.2.7 Elements and Nodes Query Mode

To query an element, enlarge the plot with Zoom if necessary, click Query and select Element for the query. Use the mouse pointer to interactively pick an element in the plot. The properties of the selected element are displayed in the Query Element Data dialog. To exit

element query mode, click Query and un-select Element



To query a node, enlarge the plot with Zoom if necessary, click Query and select Node for the query. Use the mouse pointer to pick a node in the plot. The Node ID, X, Y, and Z

axes are displayed in the Query Node Data dialog. To exit node query mode, click Query and un-select Node



5.2.8 Panel Editing Mode The panel search and individual panel editing functions facilitate the panel buckling check using

global FE analysis results. Click Edit Panel icon to activate the panel editing mode and the Panel menu. The structural panels, i.e. the flat plates bounded by adjacent stiffeners, girders, or bulkheads as defined in *.PNL file, are superimposed on FE mesh and plotted using patch colors. The user can use the mouse pointer to interactively pick panels, elements, or nodes and create, modify, or delete panels.

The following criteria are applied when a new panel is created or an existing panel is modified.

• The panel must be quadrilateral. • All the panel vertices must be on the same plane (within the specified warping tolerance)

and in the sequence following the right hand rule. • The minimum distance and the angle between the panel element and the panel plane must

be within the specified tolerance limits. • One of the panel vertices must connect the longest and the shortest panel edge. • A warning message will be issued if the panel edge enclosed area is different from the

total area of the elements on the panel. • A warning message will be issued if the ratio between the longest and shorted panel

edges exceeds 10.



5.2.8.1 Create a Panel

Choose the Create radio button to add a panel to the graphic.

Create Create a panel using those plate elements that are currently not

associated with any panel. These elements are termed as Unidentified Elements and highlighted in gray in the graphic display.

Interactively pick unidentified elements on a panel and list them in the elements table

Deselect elements from the panel and remove them from the table

Deselect all elements from the graphic and clear the table

Only display the selected elements to be used to construct a panel. Interactively pick nodes on the graphic. They are listed in the corner node table.



In the table, select individual corner nodes and click

or to unselect them in the graphic and remove them from the Corner Nodes table. NOTE: The criteria specified in 5.2.8 need to be observed.

Tolerance Specify the warping tolerance Angle Enter the allowed warping angle (in degrees) between adjacent

elements within a panel and between the panel and each element on the panel

Distance Ratio Enter the allowed ratio of the distance between an element node and panel plane to the shortest panel edge

Submit the request to create a new panel. A status window is displayed to report the validity of the newly created panel.

Clear all fields

Unidentified Elements Color code for those plate elements that are currently not associated with any panel



5.2.8.2 Modify a Panel

Use the Modify radio button to modify a panel on the graphic by removing the elements from the panel or adding the Un-identified Elements to the panel.

Modify Modify an existing panel definition on the graphic display

Interactively pick a panel in the graphic

Panel ID Automatically populated with the user picked panel

List IDs of the element on the selected panel in a table. The user can • Add more element IDs of Un-identified Elements to the

list using mouse picking • Select the IDs of the elements in the list that need to be

removed from the panel. Click Remove to remove the selected element. Click Remove All to remove all elements from the list and therefore deselect the panel.



Only display the selected elements to be used to construct a panel. Interactively pick nodes on the graphic. They are listed in the corner node table.

In the table, select individual corner nodes and click

or to unselect them in the graphic and remove them from the Corner Nodes table. NOTE: The criteria specified in 5.2.8 need to be observed.

Tolerance Specify the warping tolerance Angle Enter the allowed warping angle (in degrees) between

adjacent elements within a panel and between the panel and each element on the panel

Distance Ratio Enter the allowed ratio of the distance between an element node and panel plane to the shortest panel edge

Submit the request to modify the selected panel. A status window is displayed to report the validity of the modified panel.

Deselect panel and clear all fields



5.2.8.3 Delete a Panel

Use the Delete radio button to delete a panel on the graphic.

Delete Interactively delete a panel on the graphic.

Pick a panel on the graphic window use the mouse pointer

Panel ID Automatically populated with the panel ID of user picked panel

Request to delete the selected panel. The plate elements of the deleted panel become Un-identified Elements and are plotted in gray.

Deselect panel and clear all fields



5.2.9 Result Files The following result files are generated and saved to the solution folder upon the completion of global strength analysis Click the View Result File(s) dropdown list to open the files. <solution_name>.PNL Panel definition file

<solution_name>_yield.ALLC The maximum envelope of yielding unity check results among all user defined load cases

<solution_name>_yield.LC## Yielding check results

<solution_name>_buckle.ALLC The maximum envelope of buckling unity check results among all user defined load cases

<solution_name>_buckle.LC## Panel buckling and ultimate strength check results Notes: 1. ‘##’stands for the load case id number. Panel Definition File



OSAP Yielding Unity Check: Maximum Envelope Results



OSAP Yielding Unity Check Results for Each Code Check Case



OSAP Panel Buckling Unity Check: Maximum Envelope Results



OSAP Panel Buckling Unity Check Results for Each Code Check Case



6 Simplified Fatigue Analysis

6.1 Create/Import/Open a Simplified Fatigue Analysis Solution To create a new solution node for the Fatigue Assessment application, the user needs to first go to Application menu > Fatigue Assessment > Simplified Fatigue Analysis to activate the Fatigue Assessment module in the project tree.


existing solution by clicking and selecting the project folder that contain the existing input (*.INP file) and output files.

If there is an existing Simplified Fatigue Analysis solution under Fatigue Assessment, double click the solution name to open that solution and activate the application window. If all result files are available, the application window will be set to the View module for graphic display. The user can use the Input menu to view and edit the input data. After completing the Simplified Fatigue Analysis, the user can

• Open the results files via .





6.2 Input and View for Simplified Fatigue Analysis This section uses the SemiT_SimpFA solution to demonstrate simplified fatigue analysis in OSAP. Once an existing input file has been imported or opened, the user can either accept the data as is, or use the Input menu to modify the data before analysis. The View menu lets the user display graphics and view results after the analysis.

Input

Open the Fatigue Analysis: Settings dialog to specify units of measure and conversion factors.

Open the Fatigue Analysis: Fatigue Loads dialog to import an FE model input file, element stress files, and load cases.

Open the Fatigue Analysis: SN Curves dialog to either use built-in SN curves or define SN curves.

Open the Fatigue Analysis: Structural Details dialog to define the structural details to be analyzed.

Run the simplified fatigue analysis

View Result File(s) View results after analysis. The files reside in the solution folder where they can be viewed/printed outside the OSAP application. See 2/6.2.5 for more details. Note: The changes made to the input are not effective on the results

until is clicked to re-run the analysis. The user needs to ensure that the graphic display is not using the results from previous analysis runs.

Files available after analysis



6.2.1 Analysis Settings

Click to open the Fatigue Analysis: Settings dialog.

Unit System (Length, Force, Mass) Choose units of input data from the dropdown list. Unit Conversion Factors (mm, MPa) For pre-defined unit system, the two input fields are

populated automatically. If the 99-User Specified option is selected, the user needs to enter the input in Length and Stress fields.

6.2.2 Fatigue Loads

Click to open the Fatigue Analysis: Fatigue Loads dialog. There are two options available to enter the fatigue load data.

• Use Direct Input option does not need OSAP neutral format mesh and stress files. The user can enter the stress components directly into a table.

• User FEA Results requires an OSAP neutral format FE mesh file (*.MESH) and result file (*.STRS) as input. These OSAP neutral format files can be created using the data interface with MSC NASTRAN, as described in 4.2.6 and 4.4, or ANSYS as shown in Chapter 3.



Fatigue Loads Choose Use Direct Input Dynamic Stress Amplitude 1… Serial number of load case Dynamic Real Load Stress components for dynamic real load Dynamic Imaginary Load Stress components for dynamic imaginary load





Fatigue Loads Choose Use FEA Results Input FE Model File Click to select an OSAP neutral format FE model file

(*.MESH) to be used in the analysis. NOTE: For the demonstration purpose, SemiT.mesh is selected for the SemiT solution.

Number of Element Stress Files

Enter the number of finite element result input files (*.STRS) to be used in the analysis.



Click to browse for the *.STRS files for the SemiT solution.

NOTE: Use the first button to import multiple element stress input files at once.

Load Case NOTE: Click the right mouse button on the selected area in the

table to copy or paste 1… Serial number of load case Dynamic Real Load Label of dynamic real load case Dynamic Imaginary Load Label of dynamic imaginary load case



OSAP reads in all the input data. If there is an existing element group data file created from previous runs in the solution folder, the Group Data File Generation dialog is prompted requesting for action.



6.2.3 SN Curves

Click to open the Fatigue Analysis: SN Curves dialog. For the definition of built-in SN curve, refer to ABS Guide for Fatigue Assessment of Offshore Structures (2003).

SN curves Choose either:

Use OSAP Built-in SN Curves Specify Additional SN Curves

NOTE: Click the right mouse button on the selected are to copy or paste SN Curve Definition Use table to define additional SN curves. 1… Auto-generated serial number Name Name of user-specified SN curve (maximum 6 characters) Length Unit Choose units: mm or in. Stress Unit Choose units of stress: MPa or ksi. A ‘A’(N=A/Sm) parameter of SN curve slope 1 (>0) m ‘m’(N=A/Sm) parameter of SN curve slope 1 (>0) C ‘C’(N=C/Sr) parameter of SN curve slope 2 (>=0; =0: for one slope) r ‘r’(N=C/Sr) parameter of SN curve slope 2 (>=0; =0: for one slope) THK0 Branch thickness (>0; =0 for no adjustment) THK1 Reference thickness (>0 if THK0>0; =0 otherwise) THKExp Exponent used to adjust thickness (>0 if THK0>0; =0 otherwise) Endurance Limit Endurance limit of SN curve





6.2.4 Structural Details

Click to open the Fatigue Analysis: Structural Details dialog.

1… Auto-generated serial ID number ElemGroup Element group (set) name defining a structure joint. Choose from existing

element set or All for the whole model. The element group can be generated or modified as shown in 2/6.2.5.

JointType Structural detail type associated with the SN curves. Select a type of joint: • Non Tubular Joint • Tubular Joint • Cast Steel Components • User Defined (available when the user defined SN curve is specified.)

SN_env Environmental condition associated with the SN curves. Choose from • In Air • Sea Water w/ cp • Sea Water w/o cp (not applicable to Cast Steel Components). NOTE: This input is not relevant for the User Defined joint type.

SN_screen SN curve used for fatigue code check: • JointType = Non Tubular Joint: B, C, D, E, F, F2, G, or W • JointType = Tubular Joint: T, X, or X' • JointType = Cast Steel Components: CS • JointType = User Defined: One of the names of user defined SN curve

SCF Stress concentration factor FDF Fatigue design factor DesignLife Fatigue design life in years Ncycle_DL Stress/wave cycles in the design fatigue life Ncycle_DW Stress/wave cycles in the return period of design wave WeibullShape Shape parameter of Weibull distribution of stress range





6.2.5 View Model and Results

Click to execute the assessment. When the calculation is finished, the Project Tree displays the existing element and node sets. The element set can be created, modified, or deleted

using the options provided through toolbar menu (see Chapter 1).

Click to display the FE mesh. Click to display the analysis results and use the View menu to change structural details, load cases, and parameters. View options described in 5.2.3 through 5.2.7 can be applied.

Analysis Type Parameter

Simplified Fatigue Check

UnitChk-# fatigue unity check against the selected SN curve ‘#’ (See 6.2.4 ) PrStrsRange element principal stress range used for fatigue check Life-# fatigue life calculated using SN curve ‘#’ (See 6.2.4)



6.2.6 Result Files The following result files are generated and saved to the solution folder upon the completion of simplified fatigue analysis. Click the View Result File(s) dropdown list to open files in the viewer. Files reside in the solution folder where they can be viewed/printed outside the OSAP application.

<Solution_Name>_fatigue.ALLC The maximum envelope of fatigue unity check results among all user defined load cases

<Solution_Name>_fatigue.LC## Fatigue check result for each code check case Notes: 1. ‘##’stands for the load case id number. OSAP Simplified Fatigue Analysis Results: Maximum Envelope



OSAP Simplified Fatigue Analysis Results: Individual Load Case



7 Spectral Fatigue Analysis

7.1 Create/Import/Open a Spectral Fatigue Analysis Solution To create a new solution node for the Fatigue Assessment application, the user needs to first go to Application menu > Fatigue Assessment > Spectral Fatigue Analysis to activate the Fatigue Assessment module in the project tree.


existing solution by clicking and selecting the project folder that contain the existing input (*.SFA file) and output files.

If there is an existing Spectral Fatigue Analysis solution under Fatigue Assessment, double click the solution name to open that solution and activate the application window. If all result files are available, the application window will be set to the View module for graphic display. The user can use the Input menu to view and edit the input data. After completing the Spectral Fatigue Analysis, the user can

• Open the results files via .





7.2 Input and View for Spectral Fatigue Strength Analysis This section uses the SemiT_SpecFA solution to demonstrate spectral fatigue analysis in OSAP. Once an existing input file has been imported or opened, the user can either accept the data as is, or use the Input menu to modify the data before analysis. The View menu lets the user display graphics and view results after the analysis.

Input

Open the Fatigue Analysis: Settings dialog to specify units of input data and conversion factors

Open the Fatigue Analysis: SN Curves dialog to either use built-in SN curves, or specify user defined SN curves

Open the Fatigue Analysis: Stress RAOs dialog to define the direction of stress RAOs, periods or frequency, and FEA model and results

Open the Fatigue Analysis: Hotspot Definitions dialog to define hotspot stress and geometrical properties

Open the Fatigue Analysis: Environmental Data dialog to define vessel orientation and sea states

Execute the assessment

View Result File(s) View results after analysis. The files reside in the solution folder where they can be viewed/printed outside the OSAP application.




7.2.1 Analysis Settings (*.SFA File)

Click to open the Fatigue Analysis: Settings dialog.

Unit System (Length, Force, Mass) Choose units of input data from the dropdown list. Unit Conversion Factors (mm, MPa) For pre-defined unit system, the two input fields are

populated automatically. If the 99-User Specified option is selected, the user needs to enter the input in Length and Stress fields.



7.2.2 SN Curves (*.SNC File)

Click to open the Fatigue Analysis: SN Curves dialog. For the definition of built-in SN curve, refer to ABS Guide for Fatigue Assessment of Offshore Structures (2003).

SN curves Choose either:

• Use OSAP Built-in SN Curves • Specify Additional SN Curves

Note: Click the right mouse button on the selected are to copy or paste SN Curve Definition Use table to define additional SN curves. 1… Auto-generated serial number Name Name of user-specified SN curve (maximum 6 characters) Length Unit Choose units of measurement: mm or in. Stress Unit Choose units of stress: MPa or ksi. A ‘A’(N=A/Sm) parameter of SN curve slope 1 (>0) m ‘m’(N=A/Sm) parameter of SN curve slope 1 (>0) C ‘C’(N=C/Sr) parameter of SN curve slope 2 (>=0; =0: for one slope) r ‘r’(N=C/Sr) parameter of SN curve slope 2 (>=0; =0: for one slope) THK0 Branch thickness (>0; =0 for no adjustment) THK1 Reference thickness (>0 if THK0>0; =0 otherwise) THKExp Exponent used to adjust thickness (>0 if THK0>0; =0 otherwise) Endurance Limit Endurance limit of SN curve





7.2.3 Stress RAOs (*.STF File)

Click to open the Fatigue Analysis: Stress RAOs dialog. Directions

Directions (deg) Enter directions used to define stress transfer functions

Note: • The input value must be sorted in an ascending or descending order. • The direction must be between -360deg and 360 deg.





Periods/Frequencies

Period/frequency table Choose between Period(s) and Angular Frequency (rad/s)

used to define stress transfer functions 1… Auto-generated serial number Periods/Frequencies Enter the value of selected parameter

NOTE: The input value must be sorted in an ascending or descending order.





FEA Model & Results

Number of FE Models Enter the number of FE models being used Input Format Choose input file format, either Concise or Extended

Open the Fatigue Analysis: FEA Model & Result Files dialog For the Concise option:

The program will search the user specified file folder for <FE Model Name>.MESH and <FE Model Name>_D##.STRS files, where ‘##’ is the two digits direction ID ranging from ‘01’ to ‘total number of direction’. Each STRS file contains pairs of real and imaginary stress components for all periods/frequencies and is sorted in the same order as periods/frequencies.



For the Extended option

The user needs to specify a MESH file and the associated STRS files of real or imaginary stress components, respectively, for each direction. Each STRS file contains either real or imaginary stress components associated with all periods/frequencies.



7.2.4 Hotspot Definitions (*.HOT File)

Click in the Spectral Fatigue Analysis Input dialog to open the Fatigue Analysis: Hotspot Properties dialog.

Hotspot Properties 1… Auto-generated serial ID number Name User-specified hotspot name (maximum 6 characters) JointType Structural detail type associated with the SN curves. Select a type of

joint: • Non Tubular Joint • Tubular Joint • Cast Steel Components • User Defined (available when the user defined SN curve is

specified.) SN_env Environmental condition associated with the SN curves.

Choose from: • In Air • Sea Water w/ cp • Sea Water w/o cp (not applicable to Cast Steel Components). NOTE: This input is not relevant for the User Defined joint type.

SN_screen SN curve used for fatigue code check: • JointType = Non Tubular Joint: B, C, D, E, F, F2, G, or W • JointType = Tubular Joint: T, X, or X' • JointType = Cast Steel Components: CS • JointType = User Defined: One of user defined SN curves



SCF Stress concentration factor FDF Fatigue design factor DesignLife Fatigue design life in years ElemSurf Element surface on which the weld line is located. StrsType Type of stress used in the fatigue analysis. Choose from

• Principal - Element maximum principal stress • Component - Element component stress normal to weld line

Hotspot Geometry 1… Auto-generated serial ID number Elem. No. 1 ID of No.1 element containing the weld toe (>0) Elem. No. 2 ID of No.2 element adjacent to No.1 element (>=0)

NOTE: Elem No.2-4 are defined for calculating hotspot stress using extrapolation. Enter 0 when the stress extrapolation is not required.

Elem. No. 3 ID of No.3 element adjacent to No.2 element (>=0) Elem. No. 4 ID of No.4 element adjacent to No.3 element (>=0) Weld Node 1 Node ID defining the element edge aligning with weld toe in element

No.1. Enter 0 when StrsType = Component Weld Node 2 Node ID defining the element edge aligning with weld toe in element

No.1. Enter 0 when StrsType = Component Weld Toe Distance between the weld toe and the edge defined by Weld Nodes 1

and 2. Enter 0 when StrsType = Component

Only show the Hotspot Geometry table in the dialog.

Toggle on to pick the element ID on graphic display. Choose either: Sequential Cells (continuous picking fills the element ID into cells sequentially) or Current Cells (single picking fills in the currently activated cell only)

Toggle on to pick the node ID on graphic display. Choose either: Sequential Cells (continuous picking fills the node ID into cells sequentially) or Current Cells (fills in the currently activated cell only)





7.2.5 Environmental Data (*.ENV File)

Click in the Spectral Fatigue Analysis Input dialog to open the Fatigue Analysis: Environmental Data dialog. Wave Spectral Type

Vessel Orientation Vessel Heading w.r.t. Wave Ref

Direction (deg) Angle (in degree) between platform +X (surge) axis and the reference axis used to measure wave directions

Sea States Choose from P-M/JONSWAP Spectrum Ochi-Hubble Spectrum

Options Apply to P-M/JONSWAP Spectrum only OmniDirectional Sea States Check if using omnidirectional sea states. Number of Wave Scatter diagrams Enter number of wave scatter diagrams.



Wave Scatter Diagram for the P-M/JONSWAP Spectrum Option

Wave Scatter Diagram # Choose wave scatter diagram ID number Name Enter name of wave scatter diagram. Type of Wave Period Choose type of wave period, either Tp or Tz. Scaling Factor for Hs Enter scaling factor for the Hs in scatter diagram Spectral Shapes Vary With Choose either Hs or Tp/Tz. The input determines how peakedness

(Gamma) parameter is defined.

Open the Input Occurrence of Sea States dialog to define wave probability or number of occurrence table. Click the right mouse button on a selected area to copy and paste. Check fields show the status of the cell, row, column, and table at which the mouse is pointing.



Wave Directionality for the P-M/JONSWAP Spectrum Option

Wave directionality table 1… Auto-generated serial number. Wave Direction Wave direction Spreading COS^n Exponent of cosine spreading function Rainflow Correction Rainflow correction Scatter Diagram Name of scatter diagram Occurrence Probability Occurrence probability



Check Total Probability Display the sum of occurrence probability



Wave Scatter Diagram for the Ochi-Hubble Spectrum Option

Wave Scatter Diagram Scaling Factor for Hs Scaling factor for the Hs in scatter diagram 1… Auto-generated serial number. Wave Direction Wave direction Spreading COS^n Exponent of cosine spreading function Rainflow Correction Rainflow correction Hs_1, Tp_1, Shape_1,

Hs_2, Tp_2, Shape_2 Six parameters of Ochi-Hubble spectrum

Occurrence Probability Occurrence probability



Check Total Probability Display the sum of occurrence probability



7.2.6 View Model and Results

Click to execute the assessment. When the calculation is finished, the Project Tree displays the existing element and node sets. The element set can be created, modified, or deleted

using the options provided through toolbar menu (see Chapter 1).

Click to display the FE mesh. Click to display the analysis results and use the View menu to change parameters for graphic display. View options described in 5.2.3 through 5.2.7 can be applied to the contour plot.



7.2.7 Result Files The following result files are generated and saved to the solution folder upon the completion of spectral fatigue analysis. Click the View Result File(s) dropdown list to open the files in the viewer. Files reside in the solution folder where they can be viewed/printed outside the OSAP application. <Solution_Name>_HOT.out Hotspot properties and stress transfer function <Solution_Name>_LIFE.out Spectral fatigue analysis results



OSAP Spectral Fatigue Analysis Results: Hotspot Properties



OSAP Spectral Fatigue Analysis Results: Fatigue Life and Weibull Fitting



8 Buckling and Ultimate Strength (BUS) Analysis This section presents the OSAP buckling and ultimate strength analysis for the following structural components: beam columns, corrugated panels, cylindrical shells, stiffened panels, and tubular joints.

8.1 Work with BUS Solutions To create a new solution node, the user needs to first go to Application menu > Buckling Ultimate Strength to activate the application module in the project tree.

8.1.1 Create a New Solution

Click to create a new empty solution and specify the type of structural component by choosing from Select Type option list. A calculation sheet window is opened for the selected structural member type. All the input, output and analysis operations are located on the same calculation sheet.



After the analysis is completed, the button becomes active while the Select Type

option is disabled for the current solution. Click to open the calculation sheet where the user can edit the input and re-run the analysis.

8.1.2 Create a new Solution by Importing an Existing One In addition to creating a new empty solution, OSAP also allows creating a new project by

importing an existing solution by clicking and selecting the project folder that contain the existing input file.

OSAP checks the imported data to determine which type of structural component is to be

analyzed. Click to open the calculation sheet where the user can edit the input and re-run the analysis.



8.1.3 Open an Existing Solution If there is an existing solution under Buckling Ultimate Strength application module in the project tree, double click the solution name to open that solution and activate the application

window. Click to open the calculation sheet where the user can edit the input and re-run the analysis.

8.1.4 Work with the Calculation Sheet



If the user changes stiffener ID, click this button to update the link to the Stiffener Library

Clear fields of all tables

Run the buckling and ultimate strength analysis

Save the analysis input data in the solution folder

Close the dialog



Pointing the mouse pointer on top of a parameter in the table title line brings up the dynamic help information that includes the description of the parameter and section number in the ABS Guide for Buckling and Ultimate Strength Assessment for Offshore Structures where the parameter is defined.

The input data can be copied or pasted between different columns or between the calculation sheet and Excel spreadsheet. Click the right mouse button to open copy/paste menu.

8.1.5 Display Analysis Results There are three options to display and report in Buckling Ultimate Strength module. The unity check results are available in the Results section on the calculation sheet.

After completing the analysis, the user can open the result file (*.BUS file) which contains the unity check results as well as intermediate analysis results. A companion HTML format analysis

report can also be generated by clicking . Both BUS and HTML files are saved in the current solution folder.





8.2 Individual Member Buckling Ultimate Strength Check Double click Beam_Column solution in Demo Buckling Ultimate Strength to open the

solution. Click to open the BUS – Individual Members calculation sheet.

Choose units system from the dropdown list. For pre-defined unit system, the input fields for unit conversion factors are populated automatically. If the 99-User Specified option is selected, the user needs to enter the input in Length, Stress and Force fields.



The table below lists the help info for each input and output parameter on the calculation sheet. The reference is made to the ABS Guide for Buckling and Ultimate Strength Assessment for Offshore Structures (2008). OSAP Symbols Help Info Reference

INPUT Name name of structural member

η allowable utilization factor (1/11& 2/1.9) Type cross-section type (1, 2, 3, 4, 5, 6 or 7) (2/Table1) l total length (2/Fig.1) l_local length of tubular member between ring stiffeners (2/9.5) E Young's modulus ν Poisson's ratio (2/9.7)

σ0 specified minimum yield stress (2/1.9) Pr proportional linear elastic limit (2/1.9) ky effective length factor about y axis (2/5. 3 & 2/3.3) ky effective length factor about z axis (2/5.3 & 2/3.3) Cmy moment reduction factor about y axis (2/5.3) Cmz moment reduction factor about y axis (2/5.3) d (D) diameter(tubular member) or web depth (2/Table1)

tw (t) shell(tubular member) or web thickness (2/Table1) b flange width (2/Table1) tf flange thickness (2/Table1) b2 flange offset for Welded Box (2/Table1) P axial force (positive for compression) (2/1.3) My bending moment about major (y) axis (2/3.5) Mz bending moment about minor (z) axis (2/3.5)

q external pressure for tubular members (2/1.3) OUTPUT

Compact? Compact? (2/1.7 & 2/Table1) GlobalBuck unity check of overall buckling (2/3, 2/5 & 2/7) LocalBuck unity check of local buckling (2/9)



Click to execute the analysis. The Results section is populated after the calculation is completed. Red flag will be raised for the BUS code check that fails for a specific failure mode (i.e. unity check is larger than 1.0).





8.3 Stiffened Panel Buckling Ultimate Strength Check Double click Stiffend_Panel solution in Demo Buckling Ultimate Strength to open the

solution. Click to open the BUS – Plates and Stiffened Panels calculation sheet.




The table below lists the help info for each input and output parameter on the calculation sheet. The reference is made to the ABS Guide for Buckling and Ultimate Strength Assessment for Offshore Structures (2008). OSAP Symbol Definition Reference


η allowable utilization factor (1/11 & 3/1.7) l (l_stf) length of plate long edge (stiffener span) (3/Fig.1 & 3/Fig.5) s length of plate short edge (stiffener spacing) (3/Fig.1 & 3/Fig.5) t plat thickness (3/3.1.1) E Young's modulus ν Poisson's ratio (2/9.7)

σ0 specified minimum yield stress (2/1.9) Pr proportional linear elastic limit (2/1.9) σxmax maximum compressive stress in x (3/Fig.5) σxmin minimum compressive stress in x (3/Fig.5) σymax maximum compressive stress in y (3/Fig.5) σymin minimum compressive stress in y (3/Fig.5) τ shear stress (3/Fig.5)

q pressure on plate (3/Fig.5) SID stiffener ID defined in the library lstf_r stiffener span reduction (3/Fig.7) σa_stf Compressive stress along stiffener (3/5.1) q_stf lateral pressure on stiffener (3/5.1) GID girder ID defined in the library nBracket number of tripping brackets (3/7)

l_grd girder span (3/7 & 3/5) lgrd_r girder span reduction (3/Fig.7) σa_grd compressive stress along girder (3/7 & 3/5) σymax_grd average stress normal to girder (3/7 & 3/5) q_grd lateral pressure on girder (3/7 & 3/5.1) Cm bending adjustment factor (3/5.1)

OUTPUT

PltBuck Plate buckling check (3/3.1) PltUlt Plate ultimate strength check (3/3.3) PltUlp Plate ultimate strength check (lateral pres.) (3/3.5)



SBeam Stiffener beam-column buckling check (3/5.1) STorsn Stiffener flexural torsional buckling check (3/5.3) SWebLoc Stiffener web local buckling check (3/5.5) SFlgLoc Stiffener flange local buckling check (3/5.5)

GBeam Girder beam-column buckling check (3/7 & 3/5.1) GTorsn Girder flexural torsional buckling check (3/7 & 3/5.3) GWebLoc Girder web local buckling check (3/7 & 3/5.5) GFlgLoc Girder flange local buckling check (3/7 & 3/5.5) SWebPro Stiffener web proportion check (3/9.9) SFlgPro Stiffener flange proportion check (3/9.7) SStiff Stiffener stiffness check (3/9.1)

GWebPro Girder web proportion check (3/9.9) GFlgPro Girder flange proportion check (3/9.7) GStiff Girder stiffness check (3/9.5)






8.4 Corrugated Panel Buckling Ultimate Strength Check Double click Corrugated_Panel solution in Demo Buckling Ultimate Strength to open the

solution. Click to open the BUS – Corrugate Panel calculation sheet.






η allowable utilization factor (1/11 & 3/1.7) L length of the panel (3/Fig.3) B width of the panel (3/Fig.3) a top flange width (3/Fig.4) b bottom flange width (3/Fig.4) c web width (3/Fig.4)

t plate thickness (3/Fig.4) φ angle of corrugation (3/Fig.4) Cm bending moment coefficient (3/11.3) Type corrugation type (=1:asymmetric, =2:symmetric) E Young's modulus ν Poisson's ratio (2/9.7) σ0 specified minimum yield stress (2/1.9)

Pr proportional linear elastic limit (2/1.9) σxmax maximum compression stress in x (3/Fig.5) σxmin minimum compression stress in x (3/Fig.5) σymax maximum compression stress in y (3/Fig.5) σymin minimum compression stress in y (3/Fig.5) Τ shear stress (3/Fig.5) qu plate pressure upper portion (3/11.3)

qL plate pressure lower Portion (3/11.3) σx average compression stress in x (3/11.5) σy average compression stress in y (3/11.5) Τ_global average shear stress (3/11.5)

OUTPUT FlgBuck Web local buckling check (3/11.1) WebBuck Flange local buckling check (3/11.1)

UnitBuck Beam-column buckling check for unit corrugation (3/11.3) GlobalBuck Overall buckling check (3/11.5)








8.5 Cylindrical Shell Buckling Ultimate Strength Analysis Double click Cylindrical_Shell solution in Demo Buckling Ultimate Strength to open the

solution. Click to open the BUS – Cylindrical Shells calculation sheet.




The table below lists the help info for each input or output parameter on the calculation sheet. The reference is made to the ABS Guide for Buckling and Ultimate Strength Assessment for Offshore Structures. OSAP Symbol Definition Reference

INPUT Name name of structural member η allowable utilization factor (1/11 & 4/1.7) L total length (4/Fig.1) s length between ring stiffeners (4/Fig.1) r mean radius (4/Fig.1)

t shell thickness (4/3.3) RinID ring ID stiffener in library (=0 no ring) StrID stringer ID stiffener in library (=0 no stringer) Ns number of stringer stiffeners (4/5.5 & 4/7.5) k effective length factor (Ch4_11) (4/11) E Young's modulus ν Poisson's ratio (2/9.7)

σ0 specified minimum yield stress (2/1.9) Pr proportional linear elastic limit (2/1.9) P axial force (positive for compression) (4/13.1) M bending moment (4/13.1) q external pressure (4/13.2)

OUTPUT PresType type of pressure(1=radial, 2=hydrostatic) (4/13.3)

BayBuck Bay buckling check (4/3.1 or 4/7.1) PnlBuck Curved panel buckling check (4/5.1) TrsnBuck Flexural-torsional buckling check (4/9.1) BeamBuck Beam column buckling check (4/11) RStiff Ring stiffener stiffness check (4/15.1) RWebPro Ring stiffener web proportion check (4/15.5) RFlgPro Ring stiffener flange proportion check (4/15.7)

SStiff Stringer stiffener stiffness check (4/15.3) SWebPro Stringer stiffener web proportion check (4/15.5) SFlgPro Stringer stiffener flange proportion check (4/15.7)








8.6 Tubular Joints Buckling Ultimate Strength Analysis Double click Tubular Joints solution in Demo Buckling Ultimate Strength to open the

solution. Click to open the BUS – Tubular Joints calculation sheet.






η allowable utilization factor (1/11 & 5/1.9) Type =1: K shape; =2: T/Y shape; =3: X shape (5/1.7) D chord outer diameter (5/Fig.1) T chord thickness (5/Fig.1) d brace outer diameter (5/Fig.1) t brace thickness (5/Fig.1)

θ brace angle (5/Fig.1) G brace gap (5/Fig.1) σ0c specified minimum yield stress for chord (5/3.1) σ0B specified minimum yield stress for brace (5/3.1) Can =0: without can; =1: with can (5/3.3) Lc can effective length (5/3.3) Tc can thickness (5/3.3)

Grout =0: without grout; =1: with grout (5/5.5) Tp inner tube thickness (5/5.5) Tg grout filling thickness (5/5.5) PB axial force for brace (5/1.3 & 5/Fig.1) MIPB in-plane bending moment for brace (5/1.3 & 5/Fig.1) MOPB out-of-plane bending moment for brace (5/1.3 & 5/Fig.1) PC axial force for chord (5/1.3 & 5/Fig.1)

MIPC in-plane bending moment for chord (5/1.3 & 5/Fig.1) MOPC out-of-plane bending moment for chord (5/1.3 & 5/Fig.1)

OUTPUT JointUlt Tubular joint buckling check (5/3.5)







OSAP User’s Guide

Chapter 3: A2ABSCHK.mac – An OSAP Interface to ANSYS

OSAP User’s GuideChapter 3: A2ABSCHK.mac





CONTENTS

1 Introduction ............................................................................................................................ 151 2 Usage Syntax of A2ABSCHK.mac ........................................................................................ 151

2.1 Working with ANSYS Classic Interface........................................................................ 153 2.2 Working with ANSYS Workbench ................................................................................ 155





Copyright 2010 American Bureau of Shipping 151

1 Introduction A2ABSCHK.mac is a data interface with ANSYS. It is developed using the ANSYS APDL script language and has been tested using ANSYS Release 9, 10 and 11 classic interfaces (Design Modeler) and Release 11 Workbench. The program is used to create the OSAP neutral format FE model and result input files by extracting the mesh data of a user selected portion of FE model and the associated FE solutions from the ANSYS database. OSAP Data File Online Help provides more details on OSAP neutral file formats. The execution time of A2ABSCHK.mac in the ANSYS classic interface or Workbench depends on the size of FE model and the number of analysis load steps, as well as the performance of the computer hardware. The program has been optimized to enhance its efficiency by using the ANSYS APDL intrinsic functions to the maximum extend. Nevertheless, A2ABSCHK.mac is inherently a script language based program which tends to be slower than those written in compilable language such as Fortran or C++. To obtain a general sense of execution time, the user may try this interface program using the example SemiT provided in the OSAP Examples folder. The interface program A2ABSCHK.mac can be found in the OSAP installation folder. The program is in ASCII format so that the user can easily customize it to fit his/her specific needs. This represents one of the advantages of using ANSYS APDL scripts to develop the interface program. Another important advantage is to minimize the compatibility conflicts between the data interface program and the various versions of ANSYS products. The user can look up the ANSYS help manual for instructions on developing and executing user defined macros. Alternatively, the current release of OSAP provides an option to import MSC NASTRAN model and analysis results. Refer to 2/4.4 for details.

2 Usage Syntax of A2ABSCHK.mac By default, no input parameter (argument) is required when using the interface program with the ANSYS classic interface. However, the user can use a number of optional input parameters to fine-tune the implementation of A2ABSCHK.mac. The usage syntax of A2ABSCHK.mac is summarized in the following table.



Usage Syntax of ANSYS Macro

A2ABSCHK, ['filename'], [FlagMesh], [MatYield], [MatProR], [NLS], [LS1], [LS2], ..., [LSNLS] Optional Argument Value Description

0 / blank (Default) use ANSYS job name as output file name arg1: ‘filename’ a quoted string

(up to 32 characters) user specified output file name (for *.MESH and *.STRS files)

0 / blank (Default) extract FE mesh from the ANSYS database arg2: FlagMesh

-1 do not extract FE mesh from the ANSYS database (no *.MESH file output)

0 / blank (Default) use the pop-up window accepting material yield strength and proportional limit ratio

arg3: MatYield > 0

suppress the pop-up window and use arg3 & arg4 for all materials (used for the FE model with more than 20 material types or for using with ANSYS Workbench)

0 / blank (Default) default value (0.6) of material proportional limit ratio arg4: MatProR

> 0 user specified material proportional limit ratio

0 / blank (Default) extract FE solutions at the end of each available load steps

-1 do no extract FE solutions (no *.strs file output) arg5: NLS

> 0 and < max. number of load steps

extract FE solutions at the end of each load steps specified starting from arg6

If arg5 > 0, arg6 arg(5+arg5): LS1 LSNLS

> 0 selected load step id number where FE solutions need to be extracted

Output Files filename.mesh (when arg2 = 0/blank) OSAP neutral format file for FE node, element, and material definitions (See OSAP Data File Online Help) filename.strs (when arg5 >= 0/blank) OSAP neutral format file for FEA results at the end of each selected load step (See OSAP Data File Online Help) Notes: A2ABSCHK.mac is verified using ANSYS Release 9.0 to 11.0 classic interface and Release 11 Workbench. A2ABSCHK.mac recognizes the following ANSYS element types: SHELL 41, 43, 63, 91, 93, 99, 181, 281 LINK 8, 180 BEAM 4, 44, 188, 189 PIPE 16, 20, 59



2.1 Working with ANSYS Classic Interface The following figures illustrate running A2ABSCHK.mac in ANSYS classic interface (Design Modeler). Since no argument follows the macro command, all the arguments are taken as “blank” and the default values and operations are applied. A process status window is generated to monitor the execution of A2ABSCHK.mac in the ANSYS classic interface.



Two pop-up windows request the input of material yield strength and proportional limit ratio. The windows appear at the last step during the execution of A2ABSCHK.mac in ANSYS classic interface. It should be noted that A2ABSCHK.mac can only accept the input for up to 20 material types defined in FE model. For more than 20 material types, the following alternative approaches may be used:

• Edit the last data block of the filename.mesh file to enter additional definitions beyond 20. See OSAP Data File Online Help for the details of file format.

• Use positive input of “arg3: MatYield” to suppress the pop-up windows and assign the input value to all material types. The user may need to edit the filename.mesh file, if there exist more than one material yield strength or proportional limit ratio.

• By setting “arg2: FlagMesh” to –1, the output of filename.mesh file is not requested, and therefore the pop-up windows for material data input as shown above will not appear.



2.2 Working with ANSYS Workbench The data interface program, A2ABSCHK.mac, is an ANSYS macro program and can be readily plugged into the workflow tree in the ANSYS Workbench as a user defined command. The screenshot below shows an example of using A2ABSCHK.mac in Workbench. Since ANSYS Workbench (Release 11) does not support pop-up windows, the interactive input of material yield strength and ratio of proportional limit, as shown in 3/2.1, is not functioning. There are three alternative approaches to address this issue:

• Use ANSYS classic interface (Design Modeler) as described in 3/2.1. • Use positive input of “arg3: MatYield” to suppress the pop-up windows and assign the

input value to all material types. The user may need to edit the filename.mesh file, if there exist more than one material yield strength or proportional limit ratio. See OSAP Data File Online Help for the details of file format.

• By setting “arg2: FlagMesh” to -1, the output of the filename.mesh file is not requested, and therefore the pop-up windows for material data input as shown above will not appear.





OSAP User’s Guide

Chapter 4: Technical Basis

OSAP User’s GuideChapter 4: Technical Basis





CONTENTS

1 Introduction ............................................................................................................................ 157 2 OSAP Unit System................................................................................................................. 158 3 Load Generation (LG) Module............................................................................................... 159

3.1 Coordinate System ......................................................................................................... 159 3.2 Hydrodynamic Model..................................................................................................... 161

3.2.1 Panel.................................................................................................................... 161 3.2.2 TUBE .................................................................................................................. 161 3.2.3 STUB .................................................................................................................. 163 3.2.4 DISC ................................................................................................................... 164 3.2.5 PBOY.................................................................................................................. 165

3.3 Mooring/tendon model ................................................................................................... 166 3.3.1 Static Case........................................................................................................... 166 3.3.2 Dynamic Case ..................................................................................................... 166

3.4 Linearization of the Morison Force................................................................................ 166 3.5 Sectional Force/Moment Calculation ............................................................................. 167 3.6 I/O Structures of LG Application Module...................................................................... 169 3.7 Restrictions of the program ............................................................................................ 170

4 Design Wave Analysis (DW) Module.................................................................................... 172 4.1 Design Wave Analysis Method...................................................................................... 172 4.2 I/O Structures of DW Application Module .................................................................... 175

5 Load Mapping (LM) Module ................................................................................................. 176 5.1 Introduction .................................................................................................................... 176 5.2 Load Mapping Procedures.............................................................................................. 177 5.3 Load Cases Definition .................................................................................................... 177 5.4 Mesh Mapping................................................................................................................ 178 5.5 Load Mapping ................................................................................................................ 179

5.5.1 Hydro Pressure Mapping to FE Model ............................................................... 179 5.5.2 Hydro Force Mapping to FE Model.................................................................... 179 5.5.3 Inertial Loads ...................................................................................................... 180 5.5.4 Internal Tank Pressure ........................................................................................ 181

5.6 Load Balancing............................................................................................................... 182 5.7 Constraints in Finite Element Model.............................................................................. 183

6 Global Strength (GS) Analysis Module.................................................................................. 184 6.1 Introduction .................................................................................................................... 184 6.2 Yielding Strength Check ................................................................................................ 185 6.3 Panel Buckling & Ultimate Strength Check................................................................... 185 6.4 I/O Structures of GS Application Module...................................................................... 187

7 Fatigue Assessment (FA) Module .......................................................................................... 188 7.1 Introduction .................................................................................................................... 188 7.2 Simplified Fatigue Analysis Module.............................................................................. 188 7.3 I/O Structures of Simplified Fatigue Analysis Module .................................................. 190 7.4 Spectral Fatigue Analysis ............................................................................................... 191 7.5 I/O Structures of Spectral Fatigue Analysis Module...................................................... 193

8 Buckling & Ultimate Strength (BUS) Code Check Module .................................................. 194 8.1 Introduction .................................................................................................................... 194 8.2 Individual Tubular and Rolled Shape Members............................................................. 194 8.3 Plates & Stiffened Panels ............................................................................................... 195 8.4 Corrugated Panels........................................................................................................... 195



8.5 Cylindrical Shells ........................................................................................................... 195 8.6 Tubular Joints ................................................................................................................. 195

9 References .............................................................................................................................. 196



1 Introduction This chapter is intended to provide a summary of the technical basis of OSAP Version 2.0. The main subjects covered by this chapter include

• Methodologies and ABS Rules and Guides implemented in the six application modules o Load Generation (LG) o Design Wave Analysis (DW) o Load Mapping (LM) o Global Strength Analysis (GS) o Fatigue Assessment (FA) o Buckling and Ultimate Strength Analysis (BUS)

• Program I/O structures

The following flowchart illustrates schematically how OSAP can fit into a typical structural assessment process for a floating offshore structure.

3D Hydrodynamic Analysis Model

Geometry and Mesh Generator

Hydrodynamic Analysis Program

FEA Solver

Global Structural FE Model (Coarse Mesh for Yielding and Panel Buckling Check)

Global Structural FE Model (Locally Refined Mesh for

Fatigue Check)

Structural Responses (Stress, Strain and

Displacement)

OSAP 2.0 User Selected Third-party Applications

Need Local FEA

Local FE Model with Refined Mesh

Y

N

End

Yielding, Buckling & Fatigue Code Check

Global FE Model, Loads, and Constraints Input

Load Mapping & Balancing

Load Cases for Strength

& Fatigue

Design Wave Calculation

Load Generation

Critical Responses RAOs

Motion RAOs Pressure RAOs Fluid Velocity



2 OSAP Unit System OSAP adopts a default unit system for the internal calculations in the Global Strength (GS), Fatigue Assessment (FA), and Buckling & Ultimate Strength (BUS) application modules. The default units are: • Length: mm (unit of area is mm2; unit of moment of inertia is mm4) • Stress: MPa (also applies to pressure, modulus, etc) • Force: N (unit of bending moment is N*mm) This default unit system is connected to the user preferred unit system through the unit conversion factors, as shown in the following relation. User_Unit = Unit_Conversion_Factor * OSAP_Unit For OSAP users, the default unit system should only be used to determine the unit conversion factors. Once unit conversion factors are defined, all other input data and output of GS, FA, and BUS code check results are based on the user’s unit system. In the Load Mapping (LM) application module, more specific requirements and options are implemented. The user needs to provide input to correlate the unit system of input FE model, and the unit system of input hydro model. The user may also choose to convert the unit system of input FE model to another unit system in the resultant loaded FE model ready to be solved. Note that the default unit system is not implemented in the Load Generation (LG) and Design Wave (DW) application modules. In all cases, it is the user’s responsibility to ensure the self-consistency of unit system in the input data.



3 Load Generation (LG) Module

3.1 Coordinate System Global Coordinate System The coordinate system has its origin on the mean water surface with Z axis pointing upwards, X and Y on the mean water surface. The mean water surface is at Z=0. The following parameters are given in the global coordinate system:

• The vertical center of gravity (VCG) with relative to the still water line • The static roll-pitch-yaw motions • Current speed direction and profile with relative to the still water line. (Current profile

must be defined by at least two points, and current can only have one uniform direction) • Wave heading and origin • Static wind loads, mooring/tendon loads, and other static loads (in the *.STAT file)

Coordinate System

Directions for wave, wind, and current are specified by giving the direction in which wave (wind and current) is progressing (toward). Positive direction is defined as counter-clockwise from the Global X-axis.

Definition of Directions of Wave, Wind, & Current in the Global Coordinate System



Body Coordinate System The body coordinate system is fixed on the body. The origin of the body coordinate system can be any point fixed on the body. The following nodes/points/loads are given in this system:

• Nodes for panels and Morison elements • Load action points • Mooring/tendon attachment points (both ends) • Center of gravity • Center of buoyancy • Reference point for motion • Definition of distributed mass points • Definition of slicing plane locations • Dynamic loads in the *.FRAO file • Static loads in the *.FSTA file

Definition of Phase Definition of phases is based on ITTC’1975 standard.



3.2 Hydrodynamic Model The hydrodynamic model supported by OSAP consists of the following five types of element:

• Panel element • TUBE element • STUB element • DISC element • PBOY element

3.2.1 Panel The panel normal direction is defined by the right-hand rule and must point towards water [6]. Total pressure applied on the panel element consists of three components:

• Hydrostatic pressure • Hydrodynamic pressure • Hydrostatically variant pressure

Force and moments in body coordinate system are calculated by integrating the total pressures over the body surfaces. The static force and moments are calculated by integrating the static pressure. The dynamic forces and moments are calculated by integrating the dynamic pressure. NOTE: The hydrostatically variant pressure is considered as dynamic pressure in calculating the dynamic forces and moments.

3.2.2 TUBE TUBE is used to define circular Morison elements [7]. Forces applied on the Morison elements include hydrostatic forces and dynamic forces:

• Buoyancy forces (static) • Drag forces • Froude-Krylov forces (F-K forces) • Diffraction forces • Added-mass forces • Hydrostatic variation

TUBE is defined by two end points with given diameter and hydrodynamic coefficients. TUBE can be closed or open.



TUBE

The submergence of a TUBE member is determined by two end points at the centerline. If one end point is above the water surface and the other end point is below the water surface, the TUBE is considered as partially submerged (surface-piercing). If both end points are above the water surface, the TUBE is considered as totally above the water. If both end points are below water surface, the TUBE is considered as fully submerged. Special considerations are needed for a surface-piercing TUBE in force calculations.

Determination of Submergence of TUBE

The forces are integrated along the TUBE by the two (2)-point Gaussian Quadrature. Forces are first computed at two (2) points, and then linearly distributed over the length.

Partially submerged

Totally above water

Fully submerged



3.2.3 STUB

STUB is used to define Morison elements with non-circular cross section [7]. Forces applied on the Morison elements include hydrostatic forces and dynamic forces:

• Buoyancy forces (static) • Drag forces • Froude-Krylov forces (F-K forces) • Diffraction forces • Added-mass forces • Hydrostatic variation

STUB

STUB is defined by three points with given diameters and hydrodynamic coefficients. The first two points are to define the two end points. The axial direction is defined as local X-axis. The perpendicular from the third point to the local X-axis is the local Z-axis. The local Y-axis forms a right-handed set.

Definition of the local Y-axis and Z-axis of STUB Element

Y

Z

DY

DZ



The submergence of a STUB member is determined by two end points at the centerline. If one end point is above the water surface and the other end point is below the water surface, the STUB is considered as partially submerged (surface-piercing). If both end points are above the water surface, the STUB is considered as totally above the water. If both end points are below water surface, the STUB is considered as fully submerged. Special considerations are needed for a surface-piercing STUB in force calculations.

Determination of Submergence of STUB

The forces are integrated along the STUB by the two (2)-point Gaussian Quadrature. Forces are computed at two (2) points, then linearly distributed over the length.

3.2.4 DISC A DISC element has no thickness and no mass, but has drag coefficient and added-mass coefficient in its normal direction [7]. Therefore, a DISC does not have Froude-Krylov and hydrostatic force. A DISC element has only the following forces:

• Drag forces • Diffraction forces • Added-mass forces

A DISC element is defined by two points with given diameter and hydrodynamic coefficients. One point is at the DISC center. The other point is to define the DISC normal direction. The second point can be on either side of the DISC.

Partially submerged

Totally above water

Fully submerged



DISC

The submergence of a DISC member is determined by the center point only. If the center point is above the water surface, the DISC is considered as totally above the water. If the center point is below the water surface, the DISC is considered as fully submerged.

Determination of Submergence of DISC

The forces are assumed evenly distributed over the DISC surface and always in the normal direction. Velocity and accelerations are only calculated at the center of the DISC.

3.2.5 PBOY PBOY represents point buoyancy which is a constant force in the Global Z-axis [7]. Total buoyancy force consists of:

• Static buoyancy force • Hydrostatic variation (dynamic)

Totally above water

Fully submerged



3.3 Mooring/tendon model

3.3.1 Static Case Mooring loads can be defined in the *.STAT files. Please note that all loads in the *.STAT file are given in the global coordinate system. Instead of defining the static loads in the *.STAT file, the program can also read the *.lis file after a AQWA-LIBIUM run [7]. The program reads the following loads as mooring loads (Fx, Fy, Fz) acting at the attachment point to the body:

• LINE (Deck 14) • NLIN (Deck 14) • WNCH (Deck 14) • FORC (Deck 14) • LNDW (Deck 14) • THRS (Deck 10)

Note that thruster forces (THRS) are given in body coordinate system in AQWA-LIBRIUM. The program will convert all the loads to the global coordinate system and write the loads to the *.STAT file. Refer to AQWA-LIBRIUM manual [7] for details about “LINE”, “NLIN”, “WNCH”, “FORC”, “LNDW” and “THRS”.

3.3.2 Dynamic Case In the dynamic analysis, the mooring/tendon is modeled as massless linear springs, with one end attached at the body, the other end attached to the seabed. The stiffness matrix can be derived assuming the surface platform moves through small displacements relative to the spring length involved. Further details are referred to [10].

3.4 Linearization of the Morison Force To account for the drag loads in a frequency domain approach, the drag term of the Morison equation can be written in a generic linear form [11]:

uCDLF dLIN ρ21

=r

A common approach is to calculate the linearized drag term dC from equating the energy dissipation from the linear and nonlinear drag contribution (equivalent linearization), or by minimizing the error between the linear and nonlinear force (stochastic linearization).



Assuming a zero current velocity, the stochastic linearization of force due to a random oscillation in irregular waves, leads to,

))(8(21

sfudLIN uuCDLF rrr−= σ

πρ

where uσ : standard deviation of the relative velocity

fur : fluid velocity

sur : body velocity

3.5 Sectional Force/Moment Calculation The sectional forces are calculated on a slicing plane for the partial body on the same side of the plane normal.

A Slicing Plane Cutting through the Body

Part 2 Part 1 nr



External forces applied on ‘Part 1’and the internal forces applied on the cutting plane follow Newton’s Second Law:

η&&r

rr

rr

M=⎥⎦

⎤⎢⎣

⎡

++

ExternalInternal

ExternalInternal

MMFF

where

⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−−−−−−−−

−−−−−−−−−

=

333231

232221

131211

0)()()(0)()()(0

0)()(00)(0)(00)()(000

IIIxxmyymIIIxxmzzmIIIyymzzm

xxmyymmxxmzzmmyymzzmm

refgrefg

refgrefg

refgrefg

refgrefg

refgrefg

refgrefg

M

⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

=

3

2

1

3

2

1

αααξξξ

η

&&

&&

&&

&&

&&

&&

&&r - 6-DOF body acceleration at reference point ),,( refrefref zyx

m - mass of Part 1

),,( ggg zyx - center of gravity of Part 1

),,( refrefref zyx - reference point of sectional moments calculation

ijI - moment of inertia of Part 1 with relative to ),,( refrefref zyx The external forces (expressed in body coordinate system) include all the forces applied on the Panel model, TUBE elements, STUB elements, DISC elements, PBOY elements, and mooring /tendon loads. The external forces should also include the following gravity forces (g-effects):

jgmigmkgmFg

rrrrr12)( ααα −=×=

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡−

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

−−−−−−−−−

=×−=00)()(

)(0)()()(0

)( 1

2

gmgm

xxyyxxzz

yyzzFrrM

refgrefg

refgrefg

refgrefg

grefgg αα

rrrr



3.6 I/O Structures of LG Application Module

AQWA-LINE AQWA-LIBRIUM

WAMIT

Other Hydrodynamic Analysis Programs

*.cfg *.gdf *.pot *.frc FRC.4 (Motion RAO) FRC.5p (Pressure RAO)

*.lis (use PRPR option, If from restart use PRDL/PRCE option)

User to prepare OSAP Neutral files: Hydro_Model:*.HYDR Hydro_MRAO: *.MRAO Hydro_PRAO: *.PRAO

OSAP Load Generation

Sectional Loads (for Design Wave)

*.HCLP

Distributed Loads (for Load Mapping)

*.FRAO,*.FSTA

Steering file *.HLG

OSAP Neutral Files (for

WAMIT/AQWA) *.HYDR, *.MRAO,

Damping Matrix Stiffness Matrix

*.out

Points for Wave Kinematics Calculation



• Main Input for Load Generation Analysis (*.HLG file) • Input of point mass distribution (*.HMAS file) • Input/Output of hydrodynamic analysis model (*.HYDR file) • Output of motion, velocity, and acceleration RAOs (*.MRAO file) • Output of panel element pressure RAOs (*.PRAO file) • Output of dynamic force RAOs (*.FRAO file) • Output of static loads (*.FSTA file) – Only available for the static load case • Output of RAO amplitudes of critical load parameters (*.HCLP file) • Output of analysis intermediate results for data check (*.out) • FLOW.DAT – Points for Wave Kinematics Calculation (AQWA-FLOW format) – only

available for the dynamic load cases when the Morison Inertia/Drag Force calculation is requested in the OSAP input and the Morison members are included in the input AQWA model or OSAP *.HYDR file. See 2/2.2.3.2.

• FIELD.DAT – Points for Wave Kinematics Calculation (WAMIT *.FRC format) – only available for the dynamic load cases when the Morison Inertia/Drag Force calculation is requested in OSAP input and the Morison members are included in the input hydro model (OSAP *.HYDR file) See 2/2.2.3.2.

3.7 Restrictions of the program The OSAP Load Generation module works under the following conditions: WAMIT Run Options

• Only one (1) body should be defined in the system. Under some circumstance, the program may still run, but the results may not be correct (for example, forces may not be balanced).

• All six (6)-degree freedom should be set as free mode motions. The program will not work if any degree of freedom set as “fixed.”

• In WAMIT, the motion RAOs can be calculated based on the wave forces using the Haskind relationship. In order to get a better force balance, it is recommended to calculate the motion RAOs based on the wave forces using pressure integration.

• The program will skip the infinite and zero periods. • The program cannot handle generalized modes. • The program cannot handle TRIMMED waterlines. • The program can only handle explicitly defined lower-order panels (quadrilateral or

triangular elements). • The program cannot handle a high-order mesh model. • The program cannot handle MultiSurf geometry files. • The program cannot handle bodies with thin submerged elements. • The program cannot handle a hydro-dynamic model with internal tanks.



AQWA-LINE Run Options

• The program is only tested when there is only one (1) body (structure) modeled in the system.

• If use “REST 1 5,” the program will not read DECK 8 – 18 related information in the *.lis file. Consequently, scale effects, changes of hydrodynamic coefficients, etc., may not be correctly accounted for.

• The “PRPR” option must be used to output pressure in the *.lis file. The program will read the pressure. The program also determines if the hydrodynamic model has symmetrical plans using the related output in the *.lis file. (The “PRCE” option is optional.)

AQWA-Librium Run Options

• Use the ‘PRCE” option if the model has symmetry planes. • CURR card applies to both “CUFX/CUFY/CURZ” and Morison Elements. • CPRF card ONLY applies to Morison Elements. • Current loads on Morison Elements are “MORISON DRAG.” • “CURRENT DRAG” is considered as other static loads. • All loads expect for “Gravity,” “Hydrostatic,” “Morison Drag,” “Wind,” “Thruster,” and

“Mooring Loads” are treated as “other loads.”



4 Design Wave Analysis (DW) Module

4.1 Design Wave Analysis Method The methodology of design wave calculation in OSAP is based on the ABS Rules for Building and Classing Mobile Offshore Drilling Units (ABS MODU Rules) (2008) [1], Part 3, Chapter 2, Appendix 2. The design wave calculation can be performed using the deterministic (regular wave analysis) or stochastic (spectral analysis) approach, depending on the availability of wave information. The two flowcharts in this section summarize the major steps used to carry out the design wave calculation using the two methods. For each load case, the response analysis determines the critical wave periods and headings that produce the maximum wave induced loads. It further permits the establishment of a regular wave, which replicates the maximum wave induced load as determined from the response analysis. The equivalent wave, denoted the “Design Wave,” can then be used for the design of the global structural strength.

Establishing Design Waves Using the Deterministic Method

Select the design wave with the wave height and period

associated with the maximum response load

Calculate the RAOs of critical response parameters and determine

the critical period TC, and the corresponding maximum RAO

amplitude (RAOC)

Determine "wave height limit" (H) for a range of wave period based on (1) the

Owner selected design wave environment for MODUs, or (2) the site specific environmental conditions for FPIs

Calculate the response load by multiplying RAOs with H

at each wave period



Establishing Design Waves Using the Stochastic Method

When using the stochastic method (“Irregular Wave”) option in OSAP, the user must be aware of the following:

• The design wave calculation is based on the most probable extreme response obtained from the spectral analysis within three-hour storm duration.

• There is a note placed at the beginning of the *.DWC file stating “Each program-selected design wave is based on the peak RAO amplitude of corresponding response parameter. Users must verify the results using Design-Wave-Height curves plotted via Graphics->Results in OSAP.” This note is to prompt the user to appropriately consider the following two potential issues: a. Response RAOs may have spurious peak amplitudes at the high frequency regime so

that OSAP-DWC may select the design waves based on those peaks. In addition to checking with the design wave curves, the user may also need to look at the plots of response RAO amplitudes.

b. The process of selecting design waves should involve the user’s engineering judgment. This is especially important when attempting to maximize the associated

Calculate the RAOs of critical response parameters and determine the critical period TC, which is the period for the maximum RAO amplitude (RAOC)

Derive wave energy spectrum for each irregular sea state with (HS, TZ) based on

(1) the Owner selected design wave environment for MODUs, or (2) the site

specific environmental conditions for FPIs

Calculate response spectrum using response RAOs and wave spectrum for each sea state

Predict the maximum response for each irregular sea state

Select the maximum response among all the irregular sea states

Calculate design regular wave amplitude associated RAOC at the

critical wave period TC



response parameters along with a specific response parameter whose RAOs are used to determine the design wave.

• The input of Limit Wave on Design Wave – Sea States window, as shown in the

following screenshot, is only used to draw a “Wave Limit” curve in the “Design Wave Height” curve plot. It is meant to provide a convenient tool to visualize the physically meaningful wave height limit at a given wave period. It is not used in the calculation of design waves, but assists the user in selecting the design waves.



4.2 I/O Structures of DW Application Module

• Design Wave analysis main input file (*.INP file) • Input of RAO amplitudes of critical load parameters (*.HCLP file created in the Load

Generation analysis) • Input of motion, velocity and acceleration at reference point (*.MRAO file created in the

Load Generation analysis) • Output of acceleration RAOs at a user specified location (optional *.ACC file) • Output of design wave analysis results (*.DWC file). • Output of intermediated analysis results for data check (*.OUT file) • Output of design wave height (optional *.DWH file generated by the OSAP application)

<solution_name>.inp

OSAP Design Wave

*.HYDR *.MRAO *.HCLP (optional)

Design Wave Analysis Results <solution_name>.dwc

Design Wave Height for Load Mapping Input <solution_name>.DWH

Intermediate Results for Data Checking <solution_name>.out

Acceleration RAOs at a User Specified Location <solution_name>.ACC



5 Load Mapping (LM) Module

5.1 Introduction The Load Mapping (LM) module is designed to transfer, or map, the hydrostatic and hydrodynamic loads calculated using hydrodynamic analysis model to the structural loads applied to the finite element structural analysis model. Through the Load Generation application module, the LM module interfaces with the hydrodynamic analysis program AQWA and WAMIT to get the input of hydro model and analysis results. In a more general case, by using OSAP’s neutral format file system, the LM module can work with any other hydrodynamic analysis program. The loaded finite element model generated by the LM module can be directly solved by ANSYS or NASTRAN. The modeling process in hydrodynamic analysis and structural analysis are inherently different. The OSAP LM module currently supports the hydrodynamic model composed of panel, TUBE, STUB, DISC, PBOY, and mass elements (see 4/3.2). Hydrostatic and hydrodynamic pressures are calculated at the panel centroids, while the forces are calculated on TUBE, STUB, DISC, PBOY elements as well as mooring line or tendon connections. On the other hand, a typical offshore structural global FE model whose geometry, configuration, and stiffness approximate the actual offshore platform structure, consists of four types of elements:

• For stiffeners: o Truss element (rod element) with axial stiffness only and a constant cross-

sectional area along the length of the element. o Beam element with axial, torsional, and bi-directional shear and bending stiffness

with constant properties along the length of the element. • For plates:

o Membrane plate element (i.e., plane-stress element) with bi-axial and in-plane shear stiffness and constant thickness.

o Bending plate element with in-plane stiffness as the membrane element, plus out-of-plane bending stiffness and constant thickness.

These four types of structural finite elements are currently supported by the LM module as well as the strength code check modules in OSAP. In practice, the following table lists the possible element mapping correlation between the hydrodynamic model and the structural finite element model.

FE Model Hydrodynamic Model Plate/Shell Rod Beam Node

PANEL TUBE STUB DISC PBOY

Mooring/Tendon Attachment Point



5.2 Load Mapping Procedures

The LM module serves as a post-processor to the Load Generation & Design Wave analysis and a pre-processor to the structural FEA analysis using either ANSYS or NASTRAN and the subsequent code check analysis in OSAP. It consists of four main procedures as shown below.

Schematic Layout of the Load Mapping Procedure

5.3 Load Cases Definition

In the case that the load mapping is carried out to generate the loaded FE model for Spectral Fatigue Analysis, i.e. the SFATIGUE option in the job type definition, the LM module generates a pair of real and imaginary FE structural load cases for any one combination of period and direction of hydrodynamic load RAOs. Total number of FE load cases = 2 × Number of periods × Number of wave directions In the case that the load mapping is carried out to generate the loaded FE model for the Global Strength of Simplified Fatigue Analysis, i.e. the STRENGTH option in the job type definition, the active load cases are determined by the *DWH file (design wave data input) and only available for those direction and period combinations for which the design waves are defined. If the hydrostatic load input is provided, the LM module also generates a static load case, which is defined as the first load case with zero wave direction ID number and zero period ID number. Total number of FE load cases = 2 × Number of design waves + Static load case (optional).

OSAP Load Generation and Design

Wave Analysis

Mesh Mapping

Translate FE model

Hydro model

FE model, Tank model

Load Mapping FE Mass Constraints

Motion RAOs Force RAOs Pressure RAOs Wave Designs Static pressures, forces

FEA Load Interface FEA Solver

MSC/NASTRAN or ANSYS



5.4 Mesh Mapping There are two options offered in the LM application module to map the hydro mesh model to the FE model. User defined tank method The user provides the mapped FE models for each of the hydro model components. There are six types of components (or tanks): SHELL, BLLST, CARGO, TUBE, DISC and STUB. The user can specify any or all of these. SHELL tank includes all of the external plate/shell elements in FE model that are associated with the panel elements on hydro model’s external surface. BLLST is the ballast tank component in the FE model. CARGO is the cargo hold tank in the FE model. BLLST and CARGO tanks are used to calculate the internal tank pressures in the FE analysis. TUBE, DISC and STUB tanks are the FE element groups which map to the hydro model’s TUBE, DISC and STUB elements respectively. If a TUBE, DISC, or STUB tank is defined, there must be a related TUBE, DISC or STUB element in hydro model. For a SHELL tank, the LM module searches all FE elements within the SHELL tank elements for each panel in the hydro model. For other tanks, if the LM module finds any hydro model element falling into the tank dimension and satisfying the matching criteria, the input tank elements are automatically mapped to the matched hydro model element without further action. The following are the criteria for mapping the tank elements to the hydro model elements. For hydro TUBE elements:

• TUBE element geometrical dimensions should be within the boundary of FE tank elements.

• TUBE normal (the longitudinal direction) should be perpendicular to the FE tank element normal (within 5°).

• There are at least more than half of total FE tank elements selected for this TUBE element.

• If more than one tanks find for a hydro TUBE element, select the one with the minimum distance between the TUBE center and the tank center

For hydro DISC elements:

• Hydro DISC element geometrical dimensions should be within the boundary of FE tank elements.

• Hydro DISC element normal should be parallel to the tank element normal (within 5°). • There are at least more than half of total FE tank elements selected for a DISC element. • If more than one tank find for a hydro DISC element, select the one with the minimum

distance between the DISC center and the tank center. For hydro STUB elements;

• Hydro STUB element geometrical dimensions should be within the boundary of FE tank elements.

• Hydro STUB element normal (the longitudinal direction) should be perpendicular to the tank element normal (within 5°).

• There are at least more than half of total FE tank elements selected for a STUB element.



• If more than one tank find for a STUB element, select the one with the minimum distance between the STUB center and the tank center.

For hydro PANEL elements, only FE plate elements are included. Within the boundary of FE tank elements:

• Find all plate elements meeting within the panel dimension, • Using the selected elements, find the elements whose normal is closely parallel to the

panel normal (within 45°). • Check the element connectivity within the rest plate elements. • Check the nodes of the selected plate elements if they are located in the panel. • Check if the panel is located inside a plate element. • Save all the left plate elements as mapped elements for the panel.

Automatic tank search method If the user can not provide the mapped FE models for the hydro model, the LM application module can be configured to perform the automatic mapping between given hydro and FE mesh. However, due to the complex nature of structural geometry and the inevitable discrepancy between hydro model and FE model, it is strongly recommended that the user verify the mapped FE model elements for each of the hydro model components (tanks) before proceeding to the next step of the load mapping procedure.

5.5 Load Mapping

5.5.1 Hydro Pressure Mapping to FE Model Hydro pressures are only applied on the diffraction panel elements in the hydrodynamic analysis. When the hydro model mesh mapping is completed and verified, the hydro mesh to FE model mapping information can be used to transfer the hydro pressures to the FE model. The detailed pressure mapping procedures are performed as follows:

• In the hydro mesh mapping, one panel may have one or many FE plate elements mapped. To smooth the pressures on the FE plate elements, the nodal pressures in the FE model are first calculated using the mapped hydro pressures.

• FE plate element pressures are then calculated using the nodal pressures. • Using the FE plate element pressures, the pressure induced nodal forces are calculated

using the element area weighted average for each node of the plate elements.

5.5.2 Hydro Force Mapping to FE Model The Load Generation module calculates the Morison element forces for TUBE, STUB and DISC elements, point buoyancy static forces, and mooring/tendon forces. These hydrostatic and hydrodynamic forces must be mapped to the FE model. For hydro TUBE/STUB elements:



• At each sample point, extract the FE mapped elements into a set of element group. If any FE element is above the waterline, it is removed from the group because the Morison forces on TUBE/STUB elements are only counting to the waterline.

• For the rod/beam elements in the extracted element group, assign the nodal forces to the rod/beam nodes by the linear interpolation method, using the sample point coordinates.

• For the plate elements in the extracted element group, the Morison forces at the sample points on TUBE/STUB elements are first averaged by the total element area in the extracted element group. The individual nodal forces are then calculated by multiplying the weighted element area for each node of a plate element.

For hydro DISC elements:

• From the hydro mesh mapping, extract the FE mapped elements within the circular area around the DISC center into an element group. Any FE element above the waterline is removed from the group because the Morison forces on DISC element are only counting up to the waterline.

• In the extracted element group, the Morison forces on DISC elements are first averaged by the total element area in the extracted element group. The individual nodal forces are then calculated by multiplying the weighted element area for each node of a plate element.

For PBOY elements, the point buoyancy forces are first averaged by the total FE mapped elements at this PBOY element. The nodal forces are then calculated by multiplying the weighted element area for each node of a plate element. For mooring/tendon loads, the LM module identifies the plate elements whose center location is in the vicinity of the mooring/tendon attachment location provided by the Load Generation analysis results. If any element found, the mooring loads are first averaged by the extracted element area. Then the element nodal forces are calculated by multiplying the weighted element area for each node of the plate element.

5.5.3 Inertial Loads

The inertial loads in the FE structural analysis are calculated from the motion RAOs. To account for the inertial loads acting on a structure, the acceleration and steel mass distributions in the FE model must be calculated. The LM module maps the inertial loads to each node in the FE model. The structural mass calculation at each node shows as follows. For rod/beam and triangle plate elements, the nodal mass is evenly distributed to the element nodes. For quadrilateral elements, the following distribution method is used.



If A is the total area of the quadrilateral element, A123 is the triangle area of node 1, 2 and 3, A124 is the triangle area of node 1, 2 and 4, A134 is the triangle area of node 1, 3, and 4, and A234 is the triangle area of node 2,3 and 4, the nodal masses in node 1, 2,3 and 4 are

Massnode 1 = (A+A123)/6 Massnode 2 = (A+A124) /6 Massnode 3 = (A+A134)/6 Massnode 4 = (A+A234)/6

For mass elements, add the mass to the node. Accelerations calculation at each node gives as follows:

)()( 00 kgrraarrrrrrr

−×+−×+= αα where ar = Acceleration at a node

0ar = Translational acceleration at a node about the reference point rr = Node coordinate vector in model’s coordinate system

0rr

= Reference point position vector in model’s coordinate system αr

= Rotational acceleration about the reference point g = Acceleration of gravity

kr

= Vertical direction unit vector × = Vector product The motion induced inertial load at a node is computed by:

amF rr−=

where m is the nodal mass calculated from section1). Or Section 1?

5.5.4 Internal Tank Pressure The internal tank pressure is the motion-related load components that consist of the “quasi-static” component arising from the rigid body motion of the structure, and an “inertial” component. The quasi-static component results from gravity for instantaneous roll and pitch rotation. The inertial component is due to the acceleration of the fluid caused by the platform’s motion in six degrees of freedom. These motion components can be obtained from the motion analysis performed in the Load Generation module.

1 2

3 4



The inertial component is due to the instantaneous accelerations (longitudinal, lateral, and vertical) at the tank boundary points, calculated in conjunction with the load effect component RAOs. The total instantaneous internal tank pressure for each of the tank boundary points is calculated by combining the inertial and quasi-static components as follows: 2/1222

0 ))()()(( zzyyxxt agagaghPP −+−+−+= ρ where P = Total internal tank pressure at a tank boundary point P0 = Value of the pressure relief valve setting Ρ = Density of the fluid cargo or ballast ht = Total pressure head defined by the height of the projected fluid column in the direction to

the total instantaneous acceleration vector ax, ay, az = Longitudinal, vertical and lateral motion wave-induced acceleration relative to the

vessel’s axis system at a tank boundary point gx, gy, gz = Longitudinal, vertical and lateral instantaneous gravitational acceleration relative to

the vessel’s axis system at a tank boundary point

The instantaneous acceleration at a tank boundary point can be calculated following 4/5.5.3 For static internal tank pressure, the above equation reduces to:

ghPP tρ+= 0 Note that the above derivation of the internal tank pressure is only for filled, pressurized tanks, due to an overflow head or vapor pressure. Partially fill tanks are not supported in the current release of OSAP.

Internal Tank Pressure on a Filled Tank

5.6 Load Balancing The loaded structural model should be close to equilibrium when all the loads (static and dynamic) are applied. The unbalanced forces in the model’s global coordinate system for each load case must be identified and resolved. In the current release of OSAP, automatic load balancing process is not implemented. If the loads obtained from the hydrodynamic analysis are balanced, the loaded FE model should also be



reasonably close to the balanced status, provided the FE model does not make significant changes to mass distribution and geometrical configuration compared to the hydro model. The output files with extension .BBS and .BBA provide detailed load balancing check results for each load case.

5.7 Constraints in Finite Element Model Since forces, pressures, and moments on the loaded structural FE model are unlikely to reach a precise balance, the finite element model needs some supports in order to remove rigid body motions. These supports should be arranged in a way to minimizing the effects on global structural responses. The following are the recommended boundary supports applied by using rod/truss elements (NASTRAN) or link elements (ANSYS) in both the vertical and horizontal directions. These supports should have one end connected to the model and the other end totally fixed. The cross sectional area of the supporting elements may be calculated as follows:

LlA

LlA

A ss 77.0)1

1( =+

=ν

where A = Cross-sectional area of the supporting rod element v = Poisson’s ratio of the material As = Shearing area of the entire cross sectional area of the member (such as the cross-sectional

area of the considered side shell or longitudinal bulkhead) L = Cargo hold length (i.e., one half span of the beam) l = Length of the supporting rod element The resulting cross-sectional area, A, is the total equivalent area for the supporting rod elements connected to the same structural member (i.e shell or longitudinal frame). The area for the supporting rod is equal to A divided by the number of rods.



6 Global Strength (GS) Analysis Module

6.1 Introduction The OSAP-GS application module uses the FE results to perform the structural strength code check, which includes yielding strength check and plate buckling & ultimate strength check. The table below summarizes the references to the relevant ABS Rules and Guides specifying the strength criteria. OSAP-GS Module Reference to ABS Rules & Guides

Yielding Strength Check

• ABS Rules for Building and Classing Mobile Offshore Drilling Units (2008), Part 3, Chapter 2, Section 1: Structural Analysis

• ABS Guide for Building and Classing Floating Production Installations (2009), Chapter 4: Floating Installations: Ship, Column-Stabilized and Other Types

Panel Buckling & Ultimate Strength Check

• ABS Guide for the Buckling and Ultimate Strength Assessment of Offshore Structures (2008), Section 3/3: Plat Panels



Load Case Input in OSAP GS Module



6.2 Yielding Strength Check The safety factor (SF) for yielding strength check is determined by the type of loading case selected in the “Load Case Input” window (see 4/6.1 for example). For Mobile Offshore Drilling Units (MODUs) [1]:

• SF = 1.43: : Static loadings in calm water • SF = 1.11 : Combined static loadings and dynamic loadings induced by relevant

environmental conditions Different safety factors may be applied for a floating production installation under various design conditions as specified in the references given in 4/6.1. For plate structures, the von Mises equivalent stress is not to exceed the allowable stress, which is equal to the specified minimum yield point reduced by an appropriate safety factor as listed above. The code check results are expressed in the format of unity check, which is defined as the ratio of the von Mises equivalent stress to the allowable stress. A plate structure (FE element) fails the yielding check when its unity check result exceeds 1. For static loads, the equivalent (von-Mises) stress is calculated using the static component stresses ( xxσ , yyσ , xyσ ) at each element to calculate. For a combined static and dynamic loading case, the GS module calculates the wave induced dynamic component stresses ( xxσ , yyσ , xyσ )d using the real and imaginary component stresses for every 1º over a complete stress cycle (i.e. θ =1º ~360º):

)sin()()cos()()(

)sin()()cos()()()sin()()cos()()(

θσθσσ

θσθσσθσθσσ

×+×=

×+×=×+×=

ixyrxydxy

iyyryydyy

ixxrxxdxx

The maximum von Mises equivalent stress is obtained by combining the static and the wave induced dynamic component stresses over a complete stress cycle at each element. In both cases, the stresses on mid-plane of plate/shell elements are used in the calculation for yielding check.

6.3 Panel Buckling & Ultimate Strength Check The GS module uses the global FE model and analysis results to carry out the buckling and ultimate strength code check for the flat panel (Panel), i.e. the plate bounded by adjacent stiffeners, girders, or bulkheads. The safety factor (SF) for Panel buckling & ultimate strength code check is determined by the type of loading selected in the “Load Case Input” window. For MODUs,



• SF = 1.67 : Static loadings in calm water • SF = 1.25 : Combined static loadings and dynamic loadings induced by relevant

environmental conditions Different safety factors may be applied for a floating production installation under various design conditions as specified in the references given in 4/6.1. The GS module checks for three limit states (failure modes) in accordance with ABS Guide for the Buckling and Ultimate Strength Assessment of Offshore Structures (2008) [5] , Section 3/3: Plate Panels. The limit states are:

• Buckling strength • Ultimate strength under combined in-plane stresses • Ultimate strength subjected to uniform lateral pressure

The code check results are expressed in the format of unity check. A Panel fails when the unity check result exceeds 1. When calculating the unity checks for a Panel, the GS module takes all plate elements in the Panel into consideration. The stresses used in the unity check are determined in the following manners:

• Element area weighted average of element stresses (component-wise) within a Panel • Element stresses that leads to the maximum unit check results within a Panel

A Panel is considered satisfactory with the buckling and ultimate strength code check when the unity check using the weighted average of element stresses does not exceed 1. The maximum unity check result based on the individual element stresses in a Panel provides an indication of the upper bound of unity check. For a combined static and dynamic loading case, the GS module calculates the maximum unity check using the panel stresses obtained among every one degree of interval in a full stress cycle. The element stress on mid-plane of plate/shell elements are used to calculate the panel stresses. Since very often the element sizes in the FE model are different from the Panel sizes, the GS module provides a panel searching function that can easily find the Panel and associate the elements with the identified Panel. To ensure the effectiveness of this panel searching function, the user should follow the guidance given below when building the global finite element model. Plate element size should not exceed the Panel size. For stiffened panels, the element size should not exceed one stiffener spacing. The GS module can use one of the following to automatically detect the panel boundary:

• Line elements (i.e. stiffeners should be modeled as beam or truss elements) • Two adjoining plate elements whose faces meet at an angle larger than 30 degrees • Free edges

The output of panel searching is a text-format panel definition file (*.PNL file) which contains the panel geometric boundary, the association between FE elements and panels, and a list of plate elements that are not associated with any panel. This panel definition file is solely determined by the FE model. As long as the FE model remains unchanged, the panel definition file can be re-used in the other GS solution for the code check analysis. The GS module allows importing the existing panel definition file.



6.4 I/O Structures of GS Application Module

• Global Strength Analysis main input file (*.INP file) • Input of FE model and results (*.MESH and *.STRS files) • Input of panel definition file (optional *.PNL file) • Output of the panel definition file (*.PNL file) • Output of the maximum envelope of yielding unity check results among all user defined

load cases (*_yield.ALLC file) • Output of the yielding check results for each load case (*_yield.LC## file, ## standing for

load case ID starting from 01) • Output of the maximum envelope of buckling unity check results among all user defined

load cases (*_buckle.ALLC file) • Output of the panel buckling and ultimate strength check results for each load case

(*_buckle.LC## file, ## standing for load case ID starting from 01)

<solution_name>.inp

OSAP Global Strength

*.MESH file *.STRS file(s) *.PNL (optional)

Design Wave Analysis Results <solution_name>.PNL

Yielding Strength Check Results <solution_name>_yield.ALLC <solution_name>_yield.LC##

Plate Buckling & Ultimate Strength Check Results <solution_name>_buckle.ALLC <solution_name>_buckle.LC##



7 Fatigue Assessment (FA) Module

7.1 Introduction The OSAP-FA application module is developed to facilitate the fatigue assessment according to the ABS Guide for the Fatigue Assessment of Offshore Structures (2003) [3] (ABS Offshore Fatigue Guide). Tow options, i.e. Simplified Fatigue Analysis and Spectral Fatigue Analysis, are provided. OSAP-FA Module Reference to ABS Rules & Guides

Simplified Fatigue Analysis & Spectral Fatigue Analysis

• ABS Guide for the Fatigue Assessment of Offshore Structures (2003), Section 3: S-N Curves; Section 5: The Simplified Fatigue Assessment Method; Section 6: Spectral-based Fatigue Assessment Method

• ABS Commentary on the Guide for the Fatigue Assessment of Offshore Structures (2004)



7.2 Simplified Fatigue Analysis Module The Simplified Fatigue Analysis module implements the simplified fatigue assessment method described in the ABS Offshore Fatigue Guide [3], Section 5. The two-parameter Weibull distribution is assumed to model the long-term distribution of fatigue stress range. It is also assumed that the Palmgren–Miner’s linear fatigue damage accumulative rule is valid. S-N Curves The user can choose either the “Use Built-in S-N Curves” option, which refers to the S-N curves specified in the ABS Offshore Fatigue Guide, Section 3, or the “Specify Additional S-N Curves” option to define other S-N curves to be used in the fatigue analysis. The ABS S-N curves are defined with adjustments for thickness and corrosive environments. Three types of structural details are covered including tubular Joints, Non-tubular (Plate-Type) Joints, and Cast Steel Components. Fatigue Design Factor The user is required to define “Fatigue Design Factor” (safety factor) in the “Load Case Input” window. Different safety factors may be applied under various circumstances as specified in the ABS Rules and Guides (4/7.1). For Mobile Offshore Drilling Units (MODUs), Fatigue Design Factor is normally taken as 1, while the design fatigue life is 20 years or the design life of the MODU, whichever is larger. For Floating Production Installations (FPIs), the selection of Fatigue Design Factor is dependent upon the inspectability, repairability, redundancy, and the ability to



predict failure damage, as well as the consequence of failure of the structure. The minimum requirement is specified in Part 5B of the ABS Guide for Building and Classing Floating Production Installations (2009)[2] and summarized as follows:

Inspectable and Repairable Importance

Yes No

Non-critical 3 5

Critical 5 10

Extreme Long-Term Stress Range The extreme long-term stress range is defined as the maximum principal stress range on top or bottom surfaces of plate/shell elements. The maximum principal stress range is determined using the stress components at every one degree of interval in a full stress cycle (see 4/6.2). The dynamic real and imaginary stress components used in this calculation can be the stresses associated with the design waves. A stress adjustment factor may be applied to accounting for the difference between the fatigue design life and the return period of design waves. Stress Concentration Factor (SCF) Stress concentration factor (SCF) may be applied to adjust the calculated stress range for assessing the fatigue. The selected SCF depends on the S-N curve as well as the consideration of stress concentration due to weld profiles and gross geometric changes. If using OSAP built-in S-N curves, the guidance on calculating SCF is provided in Section 2/3 and 2/5 of the ABS Offshore Fatigue Guide. For the user specified S-N curves, SCF is dependent on how S-N curve is developed and what type of stress (nominal or hotspot stress) is used in the fatigue analysis. For general guidance, refer to the ABS Offshore Fatigue Guide. Fatigue Damage For one Segment S-N Curve

⎟⎟⎠

⎞⎜⎜⎝

⎛+Γ= 1

γδ mA

NDm

T

For two Segment S-N Curve

⎟⎟⎠

⎞⎜⎜⎝

⎛+Γ+⎟⎟

⎠

⎞⎜⎜⎝

⎛+Γ= zr

CNzm

AND

rT

mT ,1,1 0 γ

δγ

δγ

δ ⎟⎟⎠

⎞⎜⎜⎝

⎛= QS

z ;

where D = Accumulated fatigue damages γ = Shape parameter of stress range Weibull distribution NT = Number of stress cycles in design life SR = Extreme long-term stress range in design life A, m, C, r, SQ = Parameters defining S-N Curves δ = SR/(LnNT)1/ γ = Scale parameter of stress Weibull distribution Γ, Γ0 = Gamma functions



Weibull Shape Parameter of Stress Range Distribution The long-term distribution of fatigue stress range is assumed to follow the two parameter Weibull distribution. The user must provide the input of Weibull shape parameter (γ) of stress range distribution. The Weibull parameter incorporates the characteristics of the wave environment and the details of the structural responses (location/load components). Normally it can be determined by measured data, numerical analyses, or experience from previous fatigue analyses. OSAP Spectral Fatigue Analysis may be used to calibrate the selection of Weibull parameter. Fatigue Life Code Check For each combination of “Joint Type” and “S-N Curve Environment” specified by the user, the OSAP Simplified Fatigue Analysis module provides output of the fatigue lives calculated for all available S-N curves. The user must also specify an S-N curve for the fatigue code check. The fatigue code check results are expressed in the format of unity check, which is defined as the ratio of the calculated fatigue life to the design life times the fatigue design factor. A structure detail fails the fatigue code check when its unity check result exceeds 1.

7.3 I/O Structures of Simplified Fatigue Analysis Module

• Simplified Fatigue Analysis main input file (*.INP file). • Input of FE model and results (*.MESH and *.STRS files if using FE results to perform

fatigue analysis). • Output of the maximum envelope of fatigue life unity check results among all user

defined load cases (*_fatigue.ALLC file). • Output of the fatigue check results for each load case (*_fatigue.LC## file, ## standing

for the load case ID starting from 01 for using the FE, i.e. *.MESH, and *.STRS files as input). ## is set to 00 when using the stress table input option.

<solution_name>.inp

OSAP Simplified Fatigue Analysis

*.MESH file (optional) *.STRS file(s) (optional)

Simplified Fatigue Analysis Results <solution_name>_fatigue.ALLC <solution_name>_fatigue.LC## where ##=00 for the stress table input ##=01, 02, … for using FE results input



7.4 Spectral Fatigue Analysis Spectral Fatigue Analysis module implements the spectral-based fatigue assessment method outlined in the ABS Offshore Fatigue Guide [3], Section 6. The main assumptions of spectral fatigue analysis are summarized as follows:

• Linearity – Scaling and superposition of stress range are valid. • Insignificant dynamic effect – Quasi-static finite element analysis is valid. • Short-term stress processes are assumed to be stationary Gaussian and narrow band. The

short-term stress range follows the Rayleigh distribution. • The linear damage accumulation rule (Palmgren-Miner) applies.

Refer to 4/7.3 for the definition of S-N Curves, Fatigue Design Factor, and Stress Concentration Factors. Fatigue Life Code Check Fatigue damage is calculated using the closed form expression for narrow band stress process. A rainflow correction factor, which is an index of the wide band spectrum, is applied to the narrow band equation for damage to form a damage expression for wide band stress. For each combination of “Joint Type” and “S-N Curve Environment” specified by the user, OSAP Spectral Fatigue Analysis provides output of the fatigue lives calculated for all available S-N curves. The user must also specify an S-N curve for the fatigue code check. The fatigue code check results are expressed in the format of unity check, which is defined as the ratio of the calculated fatigue life to the design life times the fatigue design factor. A structure detail fails the fatigue code check when its unity check result exceeds 1. Stress Range OSAP provides options of using either hotspot stress range or nominal stress range in spectral fatigue analysis. Hotspot stress can be obtained in OSAP by either extrapolating the reference stresses, or applying the SCF to the nominal stresses. The following illustrates the definition of hotspot stress (Shot) and reference stresses (SA and SB) used in the stress extrapolation.

t

Stress

A B

Weld Toe

ShotSBSA

1/2t

3/2t lw



A 4-point element stress interpolation is adopted to calculate the reference stresses at 3t/2 (SA) and t/2 (SB) in OSAP. The detailed formulations of stress extrapolation can be found in the ABS Offshore Fatigue Guide, Section 6.

X

(B) (A)

X1

P1 P2 P3 P4

t/2

3t/2

t

X2X3

X4 Environmental Conditions Three wave spectra are available for defining the wave scatter diagram in OSAP:

• Pierson-Moskowitz (P-M) spectrum • JONSWAP spectrum • Ochi-Hubble 6-parameter bi-modal spectrum

For the P-M spectrum and JONSWAP spectrum, OSAP allows specifying multiple directional scatter diagrams and the wave rosette. The cosine wave spreading function may also be applied to account for the confused short-crested sea state. In the current release of OSAP, it is assumed that the wave and swell are co-linear. Weibull Parameter Fitting OSAP calculates the Weibull shape parameter of long-term stress range using the equal-damage criterion. More specifically, the Weibull shape parameter is obtained by matching the fatigue damage calculated by the simplified fatigue analysis with that obtained by the spectral fatigue analysis. The extreme long-term stress range employed in the simplified fatigue analysis is derived from the wave scatter diagram.



7.5 I/O Structures of Spectral Fatigue Analysis Module

• Spectral Fatigue Analysis main input file (*.SFA file) • Input of S-N curve definitions (*.SNC fie) • Input of stress transfer functions for each element (*.STF file) • Input of hotspot geometry and properties (*.HOT file) • Input of environmental conditions (*.ENV file) • Output of hotspot properties and stress transfer functions (*_HOT.out file) • Output of spectral fatigue life analysis results and Weibull parameters (*_LIFE.out file)

Steering Data Input <solution_name>.SFA

OSAP Spectral Fatigue Analysis

S-N Curve Input <solution_name>.SNC

Hotspot Properties and Stress Transfer Function <solution_name>_HOT.out

Hotspot Definition <solution_name>.HOT

Environmental Condition <solution_name>.ENV

Stress Transfer Function <solution_name>.STF

Spectral Fatigue Analysis Results and Weill Parameters <solution_name>_LIFE.out

*.MESH file(s) *.STRS files



8 Buckling & Ultimate Strength (BUS) Code Check Module

8.1 Introduction Cmpared to the automated plate buckling and ultimate strength assessment in the OSAP-GS module, the OSAP-BUS module provides a more interactive and comprehensive buckling and ultimate strength code check for individual structural components in accordance with the ABS Guide for the Buckling and Ultimate Strength Assessment of Offshore Structures (ABS Offshore Buckling Guide) (2008) [5]. There are five different types of structural components covered by OSAP-BUS:

• Individual tubular and rolled shape members • Plates & stiffened panels • Corrugated panels • Cylindrical shells • Tubular joints

The safety factor (SF), or the reciprocal of utilization factor, for buckling & ultimate strength code check is determined by the user’s input. Normally, the following utilization factors should be used for MODUs:

• SF = 1.67 : Static loadings in calm water • SF = 1.25 : Combined static loadings and dynamic loadings induced by relevant

environmental conditions Different safety factors may be applied for a floating production installation under various design conditions as specified in the ABS Guide for Building and Classing Floating Production Installations(2009)[2]. The code check results are expressed in the format of unity check. A structural component fails when the unity check result exceeds 1. Those results marked with “N/A” indicate either the corresponding failure modes do not exist, or other failure modes occur earlier in the failure hierarchy. When preparing the input of forces and stresses for the BUS code check, the user must obey the following convention of signs:

• Positive : Compressive forces or stresses • Negative : Tensile forces or stresses

8.2 Individual Tubular and Rolled Shape Members The buckling and ultimate strength code check is implemented for the beam-column members with seven different cross sectional shapes. Refer to the ABS Offshore Buckling Guide [5], Section 2 for details. A complete list of input and output parameters in OSAP as well as their reference to the Guide is provided in 2/8.2. Two potential failure modes are considered in OSAP-BUS. They are:

• Overall buckling or yielding • Local buckling



8.3 Plates & Stiffened Panels The buckling and ultimate strength code check is implemented for the flat plates and stiffened panels. Refer to the ABS Offshore Buckling Guide [5], Section 3 for details. A complete list of input and output parameters in OSAP as well as their reference to the Guide is provided in 2/8.3. For a stiffened panel, there are three levels of potential failure mode considered in OSAP-BUS:

• Plate between stiffeners level (local buckling, ultimate strength under in-plane stresses, and ultimate strength under lateral pressure)

• Stiffened panel level (stiffener beam-column buckling, flexural-torsional buckling of stiffeners, and local buckling of stiffener web and faceplate)

• Grillage assembly level (insufficient stiffness or proportion of supporting members including stiffeners and girders)

If the plate between stiffeners fails the ultimate strength limit state under in-plane stresses or lateral pressure, OSAP-BUS skips the checks at the stiffened panel level and grillage assembly level and assigns “N/A” to the results.

8.4 Corrugated Panels The buckling and ultimate strength code check is implemented for the corrugated panels. Refer to the ABS Offshore Buckling Guide [5], Section 3/11 for details. A complete list of input and output parameters in OSAP as well as their reference to the Guide is provided in 2/8.4. Two potential failure modes are considered in OSAP-BUS. They are:

• Corrugated panels (local plate buckling and unit corrugation beam column buckling) • Overall buckling of entire corrugate panels

8.5 Cylindrical Shells The buckling and ultimate strength code check is implemented for the un-stiffened and stiffened cylindrical shells. Refer to the ABS Offshore Buckling Guide [5], Section 4 for details. A complete list of input and output parameters in OSAP as well as their reference to the Guide is provided in 2/8.5. There are five potential failure modes considered in OSAP-BUS. They are:

• Local shell plate buckling for ring and stringer stiffened cylindrical shells • Local stringer stiffener flexural-torsional (tripping) buckling • Bay (inter-ring) buckling • Overall buckling (insufficient stiffness or proportion of supporting members) • Beam-column buckling

8.6 Tubular Joints The ultimate strength code check is implemented for the various types of tubular joints. Refer to the ABS Offshore Buckling Guide [5], Section 5 for details. A complete list of input and output parameters in OSAP as well as their reference to the Guide is provided in 2/8.6.



9 References

1. ABS (2008). Rules for Building and Classing Mobile Offshore Drilling Units 2. ABS (2008). Guide for Building and Classing Floating Production Installations 3. ABS (2003). Guide for the Fatigue Assessment of Offshore Structures 4. ABS (2004). Commentary on the Guide for the Fatigue Assessment of Offshore Structures 5. ABS (2008). Guide for the Buckling and Ultimate Strength Assessment of Offshore Structures 6. WAMIT Inc., WAMIT User & Theory Manuals, Version 6.4. 7. ANSYS Inc. (2008). AQWA Manuals, Version 5.7D. 8. Faltinsen, O.M. (1990). Sea Loads on Ships and Offshore Structures. Cambridge University

Press, Cambridge, UK. 9. Newman, J.N. (1977). Marine Hydrodynamics. The MIT Press, Cambridge, MA. 10. Patel, M.H. and Lynch, E. J. (1983). Coupled Dynamic of Tensioned Buoyant Platforms and

Mooring Tethers. Engineering Structure. 5: 299-308. 11. Riaan van’t Veer (2008). Application of Linearized Morison Load in Pipe Lay Stringer

Design, OMAE 2008-57247.

Documents

OSAP User's Guide