Autodesk Algor Simulation CFD_2011

Autodesk Algor Simulation CFD 2011

Seminar Notes

II Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010

Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010 III

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Autodesk Algor Simulation CFD 2011 Seminar Notes

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IV Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010

Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010 V

TABLE OF CONTENTS

Introduction ................................................. 1 Overview .................................................................................................................................... 1

Installing and Running Autodesk Algor Simulation ....................................................... 1 System Requirements ....................................................................................................... 2 Autodesk Algor Simulation Help ....................................................................................... 3 Subscription Center ........................................................................................................... 4 Web Links .......................................................................................................................... 4 Tutorials ............................................................................................................................. 4 Webcasts and Web Courses ............................................................................................ 4 How to Receive Technical Support .................................................................................. 5 Updates.............................................................................................................................. 5

Background of FEA ................................................................................................................... 6 What is Finite Element Analysis? ..................................................................................... 6

Fluid Flow Review ..................................................................................................................... 7 Equations Used in the Solution ......................................................................................... 7 Limitations of CFD ............................................................................................................. 7 Basic FEA Concepts ......................................................................................................... 7 The General Flow of an Analysis ...................................................................................... 9

Chapter 1: Autodesk Algor Simulation CFD Example ......... 11 Chapter Objectives ..................................................................................................................11 Ball Valve Example .................................................................................................................11

Meshing the Model ..........................................................................................................12 Setting up the Model .......................................................................................................13 Analyzing the Model ........................................................................................................16 Reviewing the Results .....................................................................................................17 Creating an Animation .....................................................................................................18 Generating a Report ........................................................................................................19

Chapter 2: Basics of Fluid Flow Analysis .................. 23 Chapter Objectives ..................................................................................................................23 Fluid Flow Elements ................................................................................................................23 Meshing Options .....................................................................................................................24

Fluid Generation ..............................................................................................................24 Tetrahedral and Boundary Layer Meshes ......................................................................26 Example of Internal Fluid Generation and Boundary Layer Meshing ...........................28

Loading Options ......................................................................................................................32 Prescribed Inlet/Outlets ...................................................................................................32 Prescribed Velocity ..........................................................................................................33 Pressure/Traction ............................................................................................................33

Load Curves ............................................................................................................................36 Convergence Controls for the "Mixed GLS" and "Penalty" Formulation Options .........38 Output and Printout Intervals ..........................................................................................38 Convergence Controls for the "Segregated" Formulation Option .................................38

Turbulence ...............................................................................................................................39 Surface Prescribed Turbulence Conditions ....................................................................40 Wall Roughness ..............................................................................................................40 Reviewing the Results .....................................................................................................41

Exercise A: Venturi Model ......................................................................................... 43

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VI Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010

Chapter 3: Results Evaluation and Presentation ............ 45 Chapter Objectives ..................................................................................................................45 Result Types ............................................................................................................................45

Reaction Forces ..............................................................................................................45 Velocity.............................................................................................................................45 Pressure ...........................................................................................................................45 Vorticity ............................................................................................................................45 Vorticity Precision ............................................................................................................46 Flow Rate .........................................................................................................................46 Stress ...............................................................................................................................46

Presentation Options ...............................................................................................................47 3-D Visualization of 2-D Elements ..................................................................................47 Slice Planes .....................................................................................................................47 Particle Paths ...................................................................................................................48 Streamlines ......................................................................................................................50

Exercise B: 3-D Flow around a Building .................................................................. 53

Chapter 4: Additional Loading Options ..................... 55 Chapter Objectives ..................................................................................................................55 Using a Fan Surface ...............................................................................................................55

Fan Swirl Effects ..............................................................................................................56 Example of Fan Surfaces ................................................................................................57

Overview of Rotating Frames of Reference ...........................................................................60 Applying a Rotating Frame of Reference ...............................................................................60 Number of Rotating Frames of Reference .............................................................................61

Example of a Rotating Frame of Reference ...................................................................63 Exercise C: Fan Model ............................................................................................... 65

Chapter 5: Open Channel Flow .............................. 67 Chapter Objectives ..................................................................................................................67 Open Channel Flow Overview ................................................................................................67

Loads Not Available for Open Channel Flow Analysis ..................................................68 Initial Fluid Volume ..................................................................................................................68 Results Unique to Open Channel Flow ..................................................................................70

Volume of Fluid ................................................................................................................70 Open Channel Flow Example .................................................................................................70

Extracting the Model Archive ..........................................................................................70 Defining the Initial Fluid Volume and Inlet/Outlet Surfaces ............................................71 Defining the Material and Analysis Parameters .............................................................72 Performing the Analysis ..................................................................................................72 Animating the Results .....................................................................................................73

Chapter 6: Multiphysics ................................... 75 Chapter Objectives ..................................................................................................................75 Forced Convection (Uncoupled Fluid Flow and Heat Transfer) ............................................75 Natural Convection (Couple Fluid Flow and Thermal) ...........................................................76

Additional Program Installation Requirements ...............................................................77 Fluid Structural Interaction (FSI) .............................................................................................78 Thermal Stress ........................................................................................................................78 Joule Heating ...........................................................................................................................79

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Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010 VII

Result Options .........................................................................................................................79 Pipe Tee Example Uncoupled Fluid/Thermal/Stress ..........................................................79

Fluid Part Creation and Meshing ....................................................................................80 Setting up and Analyzing the Fluid Flow Model .............................................................83 Reviewing the Fluid Flow Results ...................................................................................84 Setting up and Analyzing the Thermal Model ................................................................85 Reviewing the Thermal Results ......................................................................................87 Setting up and Analyzing the Structural Model ..............................................................88 Reviewing the Structural Results ....................................................................................90

Heat Exchanger Example Coupled Fluid/Thermal .............................................................92 Opening and Meshing of the Model................................................................................93 Setting up the Model .......................................................................................................95 Analyzing the Model ........................................................................................................98 Reviewing the Results .....................................................................................................99

Exercise D: Heat Sink Model ................................................................................... 103

Self Study: Formulation Options, Porous Media, and Transient Mass Transfer ...................... 105

Fluid Flow Formulation Options ........................................................................................... 105 Mixed GLS Formulation: .............................................................................................. 106 Segregated Formulation:.............................................................................................. 107 Penalty Formulation: .................................................................................................... 108

Porous Media ....................................................................................................................... 109

Example of Flow through Porous Media ..................................................................... 109 Using Porous Media in a Steady or Unsteady Fluid Flow Analysis ............................ 114 Example of Using Porous Media in a Steady Fluid Flow Analysis ............................. 115

Self Study Exercise: Flow through Porous Media with Gravity ........................... 121 Transient Mass Transfer Overview...................................................................................... 123 Meshing Requirements ........................................................................................................ 123 Defining Species .................................................................................................................. 123 Loading Options ................................................................................................................... 124

Part-Based Loads ......................................................................................................... 124 Surface Based Loads ................................................................................................... 125 Nodal Loads.................................................................................................................. 127

Analysis Parameters ............................................................................................................ 128 Result Types ......................................................................................................................... 128

Species Concentration ................................................................................................. 128 Mass Flux ..................................................................................................................... 128 Mass Rate of Face ....................................................................................................... 128

Table of Contents

VIII Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010

Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010 1

Introduction

Overview

This course will introduce you to performing computational fluid dynamics (CFD) analyses on 3-D models. All of the available load and constraint options for CFD analyses will be covered. You will learn how to evaluate the results of CFD analyses and create presentations of the results, including images, animations, and HTML reports. For information regarding the basics of the user interface, refer to the Autodesk Algor Simulation course and Seminar Notes, which is a prerequisite to this CFD course. The program Help files may also be consulted for basics not covered within the CFD training manual.

Software Installation, Services, and Support

Installing and Running Autodesk Algor Simulation

The simulation software is distributed on DVDs with the exception of software for the Linux platform, which is distributed on CDs. In addition, the software may be downloaded from the Autodesk website. When you place the software DVD into a DVD-ROM drive, a launch dialog having four options will appear. If you want to set up the software on a client workstation, whether you will be using a license locked to a single computer or a network license, press the "Install Products" button. If using a network license, you must already have the license server software installed to a computer on the network. If you wish to create pre-configured deployments for installing the product on multiple client workstations, choose the "Create Deployments" command. If you want to set up the computer as a license server to control the number of concurrent users through a network, or, if you wish to install optional reporting tools, press the "Install Tools and Utilities" command. Finally, a fourth command on the launch screen, "Read the Documentation," leads to a screen from which you can access a ReadMe file and other installation and licensing guides. During the product installation process, you will need to specify your name, the name of your organization. You will also need to enter the product serial number and the product key. Otherwise, you will be limited to a 30-day trial period. To customize the installation location on your computer, the components to be installed, and/or to specify a network license server, you will have to press the "Configuration" button that appears on one of the screens during the installation process. Then, follow the prompts, provide the required information, and click the "Configuration Complete" button to continue the installation process. Any time after the installation, you will be able to start the software by using the available shortcut found in the "Start" menu folder, "All Programs: Autodesk: Autodesk Algor Simulation." The version number is included in the start menu folder name and shortcut. The name of the shortcut will depend upon which package has been purchased ("Simulation," "Simulation MES," "Simulation CFD," or "Simulation Professional"). In the dialog that appears when the program is launched, you will be able to open an existing model or begin a new model. The simulation software will be used to create, analyze, and review the results of an analysis within a single user interface, regardless of the analysis type.

Introduction

2 Autodesk Algor Simulation CFD 2011 Seminar Notes 3/15/2010

System Requirements

We recommend the following system specifications for a Microsoft Windows platform running Autodesk Algor Simulation. These specifications will allow you to achieve the best performance for large models and advanced analysis types.

32-Bit 64-Bit *

Dual Intel 64 or AMD 64 Processor, 3 GHz or higher

2 GB RAM or higher (3 GB for MES and CFD applications)

30 GB of free disk space or higher

256 MB or higher OpenGL accelerated graphics card

DVD-ROM drive

Dual Intel 64 or AMD 64 Processor, 3 GHz or higher

8 GB RAM or higher

100 GB of free disk space or higher

512 MB or higher OpenGL accelerated graphics card

DVD-ROM drive

Supported Operating Systems:

Microsoft Windows 7 (32-bit and 64-bit editions) Microsoft Vista (32-bit and 64-bit editions) Microsoft Windows Server 2003 and Windows Server 2008 Microsoft Windows XP (32-bit and 64-bit editions) Linux **

Other Requirements (All Platforms):

Mouse or pointing device Sound card and speakers *** Internet connection *** Web browser with Adobe Flash Player 10 (or higher) plug-in ***

* We recommend usage of a 64-bit version of the operating system to run large models of any analysis type and for Mechanical Event Simulation, CFD, and Multiphysics analyses. While a 32-bit machine can be configured for larger system memory sizes, architectural issues of the operating system limit the benefit of the additional memory.

** Linux may be used as a platform for running the solution phase of the analysis only. It

may be used for a distributed processing (or clustering) platform. However, pre- and post-processing is done in the graphical user interface, which must be installed and run on a Microsoft Windows platform.

*** These requirements are due to the use of multimedia in our product line and the

availability of distance learning webcasts, software demos, and related media. Minimum system requirements and additional recommendations for Linux platforms may be found on the Autodesk website. Navigate to the Autodesk Algor Simulation web page from the "Products" list on the Autodesk homepage (www.autodesk.com). Next, click on the "Features" link near the top of the product page. Then, click on the "System Requirements" link near the top of the Features page.

Introduction


Autodesk Algor Simulation Help

Autodesk Algor Simulation Help, often referred to as the Help files or Users Guide, contains the following information: Documentation for all of the model creation options within the user interface Documentation for all of the Autodesk Algor Simulation analysis types Documentation for all of the result options available within the user interface Step-by-step examples that illustrate many modeling and analysis options How to Access the Help Files

From the user interface, access the HELP pull-down menu and select the "Contents" command. The Autodesk Algor Simulation Help title page of will appear.

You can navigate through the user's guide via the table of contents to the left or by using the "Search" or "Index" tabs.

Features of the Help Files

Autodesk Algor Simulation Help is a set of compiled help files that are installed with the software but are also accessible from the Autodesk website.

Hyperlinks and a table of contents make it easy to move quickly from topic to topic. The Help window contains a standard Internet browser toolbar, so you can move forward

and backward and print with ease.

Figure I.1: Autodesk Algor Simulation Users Guide

Introduction


Search the Help Files using Keywords

All of the pages in the Help files can be searched based on keywords. The keywords are entered at the top of the "Search" tab on the left side of the Users

Guide screen. Topics that match the search criteria are listed below. Keywords are used to search the Help files. You may use single or multiple keywords. Boolean operators (AND, OR, NEAR, and NOT) are available to enhance the search utility.

Also, phrases may be enclosed in quotes to search only for a specific series of words.

Subscription Center

Along with your Autodesk Algor Simulation software purchase, you have the option of purchasing various levels of Subscription Center access and support. The Subscription Center is accessible via the "key" icon near the right end of the program title bar and also via the "Help: Web Links" menu. Through the Subscription Center, you can download software updates, service packs, and add-on applications. You can access training media, such as topical webcasts. Finally, you can also submit technical support requests via the Subscription Center.

Web Links

Within the HELP pull-down menu of the Autodesk Algor Simulation user interface, there is a "Web Links" pull-out menu. The following content can be accessed via the web links within this menu: Autodesk Algor Simulation product page Subscription Center Services and Support information Discussion Group Training course information Autodesk Labs where you may obtain free tools and explore developing technologies Manufacturing Community

Tutorials

Tutorials are available that demonstrate many of the capabilities of the Autodesk Algor Simulation software. Each analysis is presented through step-by-step instructions with illustrations to assist the user. The tutorials are accessed from the "Help: Tutorials" command and the associated model files are in the "\Tutorials\models" subdirectory within the program installation folder. The tutorials will appear next to the user interface. You will be able to follow the steps using the software without switching between the two windows.

Webcasts and Web Courses

Webcasts focus on the capabilities and features of the software, on new functionality, on accuracy verification examples, and on interoperability with various CAD solid modeling packages. These streaming media presentations are available for on-demand viewing from the Subscription Center via your web browser. Similarly, web courses are also available for on-demand viewing. Web courses are typically longer in duration than webcasts and focus on more in-depth training regarding the effective usage of your simulation software. The topics cover a wide variety of application scenarios.

Introduction


For a list of available webcasts and web courses, follow the "Training" link from the home page of the Subscription Center. Choose the "Autodesk Algor Simulation" product in the "Browse the Catalog" list. This leads to the Autodesk Algor Simulation e-Learning page, in which the available webcasts and web courses are listed according to topic.

How to Receive Technical Support

Technical support is reachable through several contact methods. The means you can use may depend upon the level of support that was purchased. For example, customers with "Silver" support must obtain their technical support from the reseller that sold them the software. "Gold" subscription customers may obtain support directly from Autodesk. Five ways to contact Technical Support:

Reseller: Obtain phone, fax, and/or e-mail information from your reseller. Subscription Center: Access the Subscription Center from the link provided in the program

interface. Click the Tech Support link on the left side of the page and then click on the "Request Support" link.

Autodesk Phone: (412) 967-2700 [or in USA/Canada: (800) 482-5467] Autodesk Fax: (412) 967-2781 Autodesk E-mail: [email protected]

When contacting Technical Support:

Have your contract number ready before contacting Technical Support. Know the current version number of your software. Have specific questions ready. Remember, Technical Support personnel cannot perform, comment on, or make

judgments regarding the validity of engineering work.

Updates

The software is updated with new functionality on a continual basis. The following three types of releases are provided: 1. A major version: Indicated by the four-digit year of the software release (based upon

the Autodesk fiscal year, not the calendar year)

2. A "subscription" version: Customers with a current maintenance subscription are eligible for additional releases that may be made available between major product version releases. These are designated by the addition of the word "Subscription" after the major version number.

3. A service pack: Incorporates minor improvements to a major or subscription release and is indicated by the letters "SP" and a service pack number after the major or subscription version number.

Introduction


How to Determine the Software Version

Access the HELP pull-down menu in the user interface and select the "About" command. This dialog will display the version that you are using. In addition, the program title bar and the splash screen that appears at each program launch will indicate the major version number of the software. However, as with the start menu group name and program shortcut, it will not indicate the subscription and service pack variants.

How to Obtain an Update

Update notifications are provided via the "Communication Center" within the user interface. The Communication Center icon is located at the right end of the program window title bar. Whenever new information is available, the state of the Communication Center icon changes. The Communication Center provides up-to-date product support information, software patches, subscription announcements, articles, and other product information through a connection to the Internet. Users may specify how frequently the Live Update information will be polledon-demand, daily, weekly, or monthly. When a program update notification is received, the user will be given the option of downloading and installing it.

Background of FEA

What is Finite Element Analysis?

Finite element analysis (FEA) is a computerized method for predicting how a real-world object will react to forces, heat, vibration, etc. in terms of whether it will break, wear out or function according to design. It is called "analysis", but in the product design cycle it is used to predict what will happen when the product is used. The finite element method works by breaking a real object down into a large number (1,000s or 100,000s) of elements (imagine little cubes). The behavior of each element, which is regular in shape, is readily predicted by established mathematical equations. The computer then combines the individual behaviors to predict the behavior of the actual object. The "finite" in finite element analysis comes from the idea that there are a finite number of elements in the model. Alternately, engineers have employed integral and differential calculus, which breaks objects down into an infinite number of elements. However, for complex geometry or physical events, derivation of the mathematical expressions can be very difficult, if not impossible. The finite element method is employed to predict the behavior of objects with respect to virtually all physical phenomena: Mechanical stress (stress analysis) Mechanical vibration Heat transfer - conduction, convection, radiation, and resultant temperatures Fluid flow - both liquid and gaseous fluids Electrostatic or MEMS (Micro Electro Mechanical Systems)

Introduction


Fluid Flow Review

Equations Used in the Solution

For fluid flow analyses, the incompressible Navier-Stokes equations are the momentum equations subject to the incompressibility constraint. Certain body forces are considered, including gravity, buoyancy, porous media resistance, centrifugal, and Coriolis forces. The equations are:

f+=

+ vpvv

t

v 2 (1)

0v = (2)

where:

v = velocity p = pressure = density = viscosity f = other body forces

Equations (1) and (2) represent the velocity-pressure formulation. This method is applicable to both 2-D and 3-D analyses. For a 2-D analysis, there are three unknowns, two velocity components and the pressure. These values can be directly calculated. For a 3-D analysis, there is an additional unknown velocity component. For more information on the fluid flow background and how these equations are solved, refer to the program Help files.

Limitations of CFD

Autodesk Algor Simulation CFD's capabilities will allow you to analyze incompressible viscous flows. Theoretically, incompressible flow has a Mach number of 0. However, flows with Mach numbers of less than 0.3 can be considered to be incompressible. In general, the following parameters should be followed for CFD models: Separate fluid domains (no mixture of different fluids) Viscous fluids (non-zero friction) Incompressible material (constant density) Isothermal (material properties are independent of temperature)

Basic FEA Concepts

Nodes and Elements

A node is a coordinate location in space where the degrees of freedom (DOFs) are defined. The DOFs of a node represent the possible reactions of this point due to the loading of the model. The DOFs also represent which loads are transferred from one element to the next. In a fluid flow analysis, velocity and pressure results are given at the nodes.

Introduction


An element is a mathematical relation that defines how the DOFs of one node relate to the next. Elements can be 2-D areas or 3-D volumes. Degrees of Freedom

The degrees of freedom at a node characterize the response and represent the relative possible reaction of a node.

The type of element being used will characterize which DOFs a node will require.

A node on a 3-D fluid flow element would have the DOFs shown in Figure I.2. V represents velocity, which has three global components (Vx, Vy, and Vz). In addition, each node has a pressure degree of freedom (P).

Figure I.2: Degrees of Freedom of a Node

Element Connectivity

Elements can only communicate to one another via common nodes. In the left half of Figure I.3, velocities will not be transferred between the elements. Elements must have common nodes to transfer loads from one to the next, such as in the right half of Figure I.3.

Figure I.3: Communication through Common Nodes

NOTE: The "Smart Bonding" feature that is discussed in the Autodesk Algor Simulation

Seminar Notes and course is not applicable to fluid flow analyses. The meshes must be matched where adjacent parts meet for flow to take place. Therefore, to ensure compatibility between different phases of a multiphysics analysis involving fluid flow, smart bonding should be disabled for all design scenarios. Smart bonding is enabled or disabled via the "Contact" tab of the "Analysis Parameters" dialog and, depending upon your software version, may be on or off by default. For version 2010, it will be off by default for newly created models. The setting for existing models will retain its prior state.

No Communication Between the Elements

Communication Between the Elements

Introduction


Types of Elements

The actual DOFs calculated are dependent on the type of element being used.

The general element types are: 2-D Planar Elements: The mesh represents a cross-section of a fluid part. Each element

must consist of 3 or 4 lines enclosing an area and lying in the YZ plane. A thickness may be specified in the Element Definition screen and this value is used only for 3-D visualization purposes within the results environment. Flow rate results are output on a per unit thickness basis.

2-D Axisymmetric Elements: The mesh represents a cross-section of an axisymmetric part. Each element must consist of 3 or 4 lines enclosing an area and lying in the YZ plane. All geometry must be in the Y-positive half of the plane but may extend to the Z-axis (Y=0). The Z-axis is the cross-sections axis of revolution for all 2-D axisymmetric models. Fluid flow rate results are output on a per-radian of revolution basis. In other words, to get the flow rate for the full object being represented by the cross-section, multiply the result by 2 (since there are 2 radians in 360).

3-D (Solid) Elements: Must be 4, 5, 6 or 8 nodes enclosing a volume. DOFs for element types: 2-D Planar and Axisymmetric: Velocity in the Y and Z directions and pressure at each

node.

3-D: Velocity in the X, Y and Z directions and pressure at each node.

The General Flow of an Analysis

Create a Mesh

Start Autodesk Algor Simulation Open your model in the FEA Editor environment Select the analysis type Create your mesh Define the FEA Data

Assign the loads and constraints Define the material Define the analysis parameters and load curves

Run the Analysis

Review and Present Results

Review the desired result types Save images and animations Create presentations and HTML reports

Introduction



Autodesk Algor Simulation CFD Example Chapter Objectives

Overview of creating a 3-D fluid flow model. Overview of adding velocities and boundary conditions to a model. Overview of defining material properties. Overview of performing an analysis. Overview of reviewing results. Overview of generating a report.

Ball Valve Example

This example is an introduction to the CFD software. The example will give step-by-step instructions for creating a mesh and analyzing a three-dimensional (3-D) model of water flowing through a partially opened ball valve. There are three sections: Setting up the model Open the model in the FEA Editor environment and create the

mesh on the model. Then add the necessary loads and constraints and define the model parameters. Visually check the model for errors with the Results environment.

Analyzing the model Analyze the model using the fluid flow processor.

Reviewing the results View the velocity results graphically using the Results environment. Use the model, Ball Valve.ach, located in the "Chapter 1 Example Model\Input File" folder of the class directory or Solutions CD. We will create a simple model of the water flowing through a ball valve (see Figure 1.1). Water will enter the model at a velocity of 0.5 in/s in the Z direction and exit from the opposite end of the model, where an inlet/outlet condition will be specified. We will ramp up the velocity in 1 second using 10 steps and will continue running at the same velocity for another 9 seconds using 10 more steps.

Figure 1.1: Ball Valve Model

Chapter

1

Chapter 1: Example Using Autodesk Algor Simulation


Meshing the Model

The FEA Editor environment is used to create a mesh for all solid models. You can open CAD models originating from any of the various CAD solid modelers that are supported, including the formats of thirteen proprietary CAD products. You can also open models of any of four supported universal CAD formats (ACIS, IGES, STEP, and STL).

"Start: All Programs: Autodesk: Autodesk Algor Simulation: Autodesk Algor Simulation"

Press the Windows "Start" button and access the "All Programs" pull-out menu. Select the "Autodesk" folder and then the "Autodesk Algor Simulation" pull-out menu. Choose the "Autodesk Algor Simulation" command.

"Open" Click on the "Open" icon at the left side of the dialog.

"Algor Simulation Archive (*.ach)"

Select the "Algor Simulation Archive (*.ach)" option in the Autodesk Algor Files section of the "Files of type:" drop-down box.

"Ball Valve.ach" Select the file "Ball Valve.ach" in the "Chapter 1 Example Model\Input File" directory. "Open" Press the "Open" button.

"OK" Select the location where you want the model to be extracted and press the "OK" button. The model will appear in the FEA Editor environment. We will use a boundary layer mesh that produces a greater concentration of nodes near the surface of the fluid, where velocity gradients are the steepest. For the inlet and outlet surfaces, boundary layers are not desirable. We will exclude these two surfaces from receiving boundary layers.

"Mesh: Model Mesh Settings"

Access the MESH pull-down menu and select the "Model Mesh Settings" command.

"Options" Press the "Options" button in the "Model Mesh Settings" dialog.

"Absolute mesh size" Select the "Absolute mesh size" option in the "Type" drop-down box. 0.2 Type "0.2" in the "Size" field. "Solid" Select the "Solid" icon on the left edge of the "Model Mesh Settings" dialog.

"Tetrahedra and wedges (boundary layer)" Select the "Tetrahedra and wedges (boundary layer)" radio button.

"OK" Press the "OK" button.


"View: Orientation: Top View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Top View" command.

"Selection: Shape: Point"

Access the SELECTION pull-down menu and select the "Shape" pull-out menu. Select the "Point" command. This will allow you to select objects by clicking directly on them.

"Selection: Select: Surfaces"

Access the SELECTION pull-down menu and choose the "Select" pull-out menu. Select the "Surfaces" command. This will allow you to select surfaces.



Mouse Click on the circular surface facing the screen.

Mouse Right-click in the display area.

"CAD Mesh Options: Exclude from Boundary Layer" Select the "CAD Mesh Options" pull-out menu and select the "Exclude from Boundary Layer" command.

"View: Orientation: Bottom View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Bottom View" command.



"CAD Mesh Options: Exclude from Boundary Layer" Select the "CAD Mesh Options" pull-out menu and select the "Exclude from Boundary Layer" command.

"Mesh: Generate Mesh" Access the MESH pull-down menu and select the "Generate Mesh" command.

"No" Press the "No" button when asked if you want to review the meshing results.

"View: Rotate"

Access the VIEW pull-down menu and select the "Rotate" option. Inspect the mesh on the model, rotating it by pressing the left mouse button and dragging the cursor around the screen. This mesh appears to be acceptable.

Press the key to cancel the view rotate mode.

"View: Orientation: Isometric View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Isometric View" command.

Setting up the Model

The ball valve model will appear as shown in Figure 1.2. If you zoom in on the inlet and outlet surfaces, which were excluded from receiving boundary layers, you will clearly see the boundary layers applied to the adjacent cylindrical surfaces.

Figure 1.2: Ball Valve Model in FEA Editor Environment



The FEA Editor environment is used to specify all of the element and analysis parameters for your model and to apply the loads and constraints. You will notice a red X on certain headings in the tree view. This signifies that this data has not yet been specified. You will need to eliminate all of the red Xs before analyzing the model. Since you have created a solid mesh, the "Element Type" heading in the tree view is already set to "3-D" and the default "Element Definition" parameters have been accepted.

Adding Constraints

We must assume that the velocity of the fluid at the wall of the pipe is zero. By default, before the analysis begins, the program will automatically apply zero-velocity constraints to all outer surfaces that do not have a load applied or have not been defined as prescribed inlet/outlets. Therefore we will assign a prescribed velocity at the inlet and apply a prescribed inlet/outlet at the outlet. The remaining surfaces will be held to zero-velocity.



Mouse Click on the surface at the end of the model facing the screen.


"Add: Surface Prescribed Velocity"

Select the "Add" pull-out menu and select the "Surface Prescribed Velocity" command. The dialog shown in Figure 1.3 will appear.

Figure 1.3: Surface Prescribed Velocity Dialog

Mouse Activate the "Z Magnitude" checkbox.

0.5 Type "0.5" in the "Z Magnitude" field.




"View: Orientation: Top View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Top View" command.

Mouse Click on the surface at the end of the model facing the screen.


"Add: Surface Prescribed Inlet/Outlet"

Select the "Add" pull-out menu and select the "Surface Prescribed Inlet/Outlet" command. A green "I" will appear on each node in that surface.

"View: Orientation: Isometric View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Isometric View" command.

Assigning the Material Properties

Once the model has been constructed and the loads and constraints have been applied, use the FEA Editor environment to specify material properties. Mouse Right-click on the "Material" heading for Part 1.

"Modify Material" Select the "Modify Material" command. The "Element Material Selection" dialog will appear.

"Water" Highlight the "Water" item from the list of available materials as shown in Figure 1.4.

Figure 1.4: Element Material Selection Dialog

"OK" Press the "OK" button to accept the information entered in the "Element Material Selection" dialog for Part 1.



Assigning the Analysis Parameters

The prescribed velocities will follow a load curve throughout the analysis. This load curve must be defined in the "Analysis Parameters" dialog. Three indices will be required for the load curvethe zero-velocity initial condition, the end of the velocity ramp-up interval (at 1 second), and the end of the steady inlet velocity interval (at 10 seconds). Mouse Right-click on the "Analysis Type" heading in the tree view.

"Modify Analysis Parameters" Select the "Modify Analysis Parameters" command.

0 Type "0" in the first row of the "Multiplier" column in the "Time-Stepping Settings" table. "Add Row" Press the "Add Row" button.

10 Type "10" in the second row of the "Steps" column. "Add Row" Press the "Add Row" button.

10 10 Type "10" in the third row of the "Time" column, press twice and type "10" in the third row of the "Steps" column.

The "Time-Stepping Settings" table should appear as shown in Figure 1.5

Figure 1.5: Prescribed Velocity Load Curve

"OK" Press the "OK" button. The model is now ready to review in the Results environment.

"Analysis: Check Model"

Access the ANALYSIS pull-down menu and select the "Check Model" command to review elements, geometry and loads in the Results environment before running the analysis.

"Tools: FEA Editor"

Once you approve the model, access the TOOLS pull-down menu and select the "FEA Editor" command to move back to the FEA Editor environment to run the analysis.

Analyzing the Model

"Analysis: Perform Analysis"

Access the ANALYSIS pull-down menu and select the "Perform Analysis" command to run the analysis. This opens the model in the Results environment. The results will automatically update as calculations are completed.

Mouse Click the "Toggle Load and Constraint Display" toolbar icon to hide the load and constraint symbols.

The preceding step may be done while the solution is running. In addition, you may minimize the Unsteady Fluid Flow analysis window to better see the model, if desired. The displayed time step will automatically be incremented as each step converges during the solution phase.



When the analysis has been completed, the analysis window will close and the associated task bar button will go away.

Reviewing the Results

Adding a Slice Plane

A slice plane will allow us to view the velocity profile on the interior of the model. Remember that the velocity for all of the outside boundaries, where no prescribed velocity, pressure, or inlet/outlet condition was defined, will be zero (dark blue color).

"View: Orientation: Left View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Left View" command.

Mouse Right-click on the "Slice Planes" heading under the "Presentations" heading in the tree view.

"Add Slice Plane: 3) YZ" Select the "Add Slice Plane" pull-out menu and select the "3) YZ" command.

Mouse Right-click on the "YZ Slice Plane" heading in the tree view. "Hide" Select the "Hide" command.

"Results Options: Load Case:" "Previous" or "Next"

Access the RESULTS OPTIONS pull-down menu and select the "Load Case" pull-out menu. Use the "Previous" or "Next" commands to toggle through the velocity results throughout the analysis.

Adding Stream Lines

Streamlines can be added to show the path that the fluid takes through the ball valve. The colors along the length of the streamlines will reflect the change in velocity as the fluid moves along its path through the ball valve.

"Selection: Shape: Rectangle" Access the SELECTION pull-down menu and select the "Shape" pull-out menu. Select the "Rectangle" command.

"Select: Select: Nodes" Access the SELECTION pull-down menu and choose the "Select" pull-out menu. Select the "Nodes" command.

Mouse Draw a rectangle enclosing the bottom edge of the model.


"Add Streamlines" Select the "Add Streamlines" command.

Mouse Drag the "Streamlines" dialog out of the way if it is obstructing the view of the results legend or model. The model should now appear as shown in Figure 1.6.



Figure 1.6: Model with Streamlines

Creating an Animation

Before creating an animation, we will fix the legend display range so that it is the same for all frames. We have twenty time steps available, so we'll use a frame rate of 5 fps, yielding a four second animation.

Mouse Click on the "X" icon in the upper right corner of the "Streamlines" dialog to close it.

"Display Options: Plot Settings" Access the DISPLAY OPTIONS pull-down menu and select the "Plot Settings" command.

"Range Settings" Select the "Range Settings" tab.

Mouse Deselect the "Automatically calculate value range" checkbox.

1 Enter "1" in the "High" field under the "Current Range" heading. "OK" Click on the "OK" button.

"Animation: Save As AVI" Access the ANIMATION pull-down menu and select the "Save As AVI" command.

5 Enter "5" in the "Playback Frames per Second (FPS)" field. "640x480" Using the drop-down box in the "Preset" field under the "Target Resolution" heading, select "640x480."



"1" Enter "1" in the "Start Step" field. This will exclude the time step zero frame, which has no streamlines.

"Save" Press the "Save" button to save the animation to an AVI file format.

"No" Press the "No" button when asked if you want to view the animation.

Generating a Report

In this section, you will automatically create an HTML report using the Report Configuration Utility. We will include a user-specified animation within the report.

"Tools: Report" Access the TOOLS pull-down menu and select the "Report" command to change to the Report environment.

Mouse Right-click on the "HTML Report" heading in the tree view.

"Configure report" Select the "Configure report" command. This will open the dialog shown in Figure 1.7.

Figure 1.7: Report Configuration Utility

NOTE: When selecting portions of the report to modify, click on the item name and not on the checkbox. Clicking on the checkbox will toggle the inclusion state of the item (that is, whether it is to be included or excluded from the HTML report).

Mouse Activate the "Logo" checkbox. The default Autodesk logo will be used. Note that you can browse to a logo of your own choice. Five popular image formats are supported.

Mouse Select the "Project Name" heading.

Ball Valve Click and drag the mouse to select the text "Design Analysis" and type "Ball Valve" to replace it.



Analysis of Water Flowing through a Ball Valve

Click and drag the mouse to select the text "Project Name Here" and replace this text by typing "Analysis of Water Flowing through a Ball Valve".

Mouse Select the "Title and Author" heading. Your Name Type your name into the "Author" field. Your Department Type your department name into the "Department" field. Mouse Select the "Reviewer" heading.

Person who checked model Type the name of the person who checked the model into the "Reviewer" field.

Department of person who checked the model Enter the name of the department of the person who checked the model into the "Department" field.

Passed all FEA tests Type "Passed all FEA tests" into the "Comments" field.

Mouse Deselect the "Executive Summary" item by clicking on the associated checkbox. This item will be excluded from the report.

NOTES: Text can be added as desired within the "Executive Summary" section using the built-in

word processor features. A variety of font and paragraph styles are included, such as bullet or numbered lists, tables, tabs, and various text justification settings.

The following sections are automatically generated and cannot be modified. The analyst may

only include or exclude these items or alter their order of appearance within the report:

Summary Analysis Parameters Parts Element Material Loads Constraints Probes Rotating Frames (applicable to fluid flow analysis) Initial Fluid Volume (applicable to open-channel analysis) Watermark Results Presentations Processor Log Files Group Code Checking Single Load Case Code Checking Detailed Code Checking All Load Cases

"Tree: Add AVI File" Access the TREE pull-down menu and select the "Add AVI File" command. This will allow you to include an animation file within the report.

"Ball Valve.avi" Navigate to the model folder and select Ball Valve.avi as the file to attach to the report. "Open" Press the "Open" button.



- Fluid Velocity Streamlines Append " Fluid Velocity Streamlines" to the end of the default "Header Text:".

"Generate Report" Press the "Generate Report" button. This will automatically bring up the report, which will appear as shown in Figure 1.8 below.

Figure 1.8: Completed Report

NOTE: The default title image is the model as it currently appears within the FEA Editor

environment. A different image may be substituted for this one and/or the image may be resized using the report configuration utility. To resize the image, click and drag the handles that appear around the image border while it is selected or right-click on the image and choose the "Format Image" command.

Mouse Scroll through and review the full report. The animation should appear at the bottom of the report and be looping continuously.

A completed archive of this model, including results, Ball Valve.ach, is located in the "Chapter 1 Example Model\Results Archive" folder of the class directory or Solutions CD.


Basics of Fluid Flow Analysis Chapter Objectives

Learn the types of 3-D elements available for fluid flow analysis. Learn how to create models of the fluid geometry starting from models of the solid geometry. Learn how to generate a boundary layer mesh. Learn how to use prescribed velocities. Learn how to use pressure/tractions. Learn how to use prescribed inlet/outlets. Learn how to create load curves.

Fluid Flow Elements

Fluid flow analysis supports 2-D and 3-D elements. 2-D elements can either be 3 or 4 sided planar elements and must be drawn in the YZ plane. 2-D elements can be used to model planar or axisymmetric flows. Each node on a 2-D element has two DOFs. These are the velocity in the Y and Z direction. No velocity is allowed in the X direction. An additional pressure DOF exists for each element at the centroid. Just like in static stress, there are four possible geometrical configurations that can be used to create 3-D fluid flow elements. These are displayed in Table 2.1

Table 2.1: 3-D Element Geometry Configurations

8-noded Brick

6-noded Wedge

5-noded Pyramid

4-noded Tetrahedral

Chapter

2

Chapter 2: Basics of Fluid Flow Analysis


Each node on a 3-D element has four DOFs. These are the velocity components in the X, Y, and Z directions and the pressure. There are four viscosity models available for both 2-D and 3-D elements. The Newtonian model is the most commonly used viscosity model and is the default option. This model assumes a constant viscosity. The other viscosity models will be discussed in a later chapter. 2-D and 3-D elements behave almost identically, the only major difference being the support of velocity in the X direction for 3-D elements. The main difference is that there are more solution options available for 3-D elements. These options will be discussed later in this manual.

Meshing Options

All of the methods taught in the Autodesk Algor Simulation course and the Advanced Modeling Supplement can be used to create meshes for 2-D and 3-D fluid flow models. This includes starting from CAD solid models and constructing the mesh by hand within the FEA Editor environment. The user interface has a couple of features for CAD solid models that are beneficial primarily for fluid flow analyses.

Fluid Generation

In order to perform a fluid flow analysis, a model representing the fluid must be created. When performing an analysis of the fluid flow inside or around an object, many times only a model of the object is provided. Autodesk Algor Simulation provides the capability to easily generate a model of the fluid from the solid part or assembly geometry. This can be done using the "Fluid Generation" pull-out menu in the MESH pull-down menu. Generally, this operation can only be used on models that were opened using the "Surface Knitting" operation. Occasionally, fluid part generation will work for single-part CAD models, even though surface knitting was not performed when the model was imported into Autodesk Algor Simulation. However, it is best to ensure the fluid generation capability by always choosing to perform surface knitting when a fluid part will be derived from the CAD geometry. For a new/clean installation of the software, the surface knitting option is turned off by default. There are two ways to change the setting

1. Access the TOOLS pull-down menu and select the "Options" command.

2. Go to the "CAD Import" tab of the Options screen and click on the "Global CAD Import Options" button.

3. To the right of the "Knit surfaces on import:" heading there are three radio buttons. Select either the "Yes" or the "Ask each time" button, depending upon the preferred behavior.

If you choose the "Yes" option, surface knitting will be performed whenever a CAD solid model is opened in Autodesk Algor Simulation. If the "Ask each time" option is chosen, a dialog will appear asking if you want to perform a surface knitting operation whenever a CAD solid model file is opened. In order to ensure the fluid generation functionality, press the "Yes" button when prompted with this question.

NOTE: The exercises in this training manual assume that the program is configured with default options (including the no surface knitting option). When performing an exercise in which fluid generation will be performed, we will enable surface knitting. At the conclusion of the exercise, we will restore the default setting ("Knit surfaces on import:" = "No"). This will



keep the specified keystrokes, meshing behavior, and results consistent with the remaining exercises and their results archives. Surface knitting adds feature lines where parts intersect and therefore may have an effect on the surface mesh. Thus, when comparing a knit model to a non-knit model, there may be a slight difference in the results. There are two types of fluid generation that can be performedexternal and internal. External

If you want to model the flow of a fluid around a part, select the "External" command in the "Mesh: Fluid Generation" pull-out menu. The "Generate Fluid Exterior" dialog shown in Figure 2.1 will appear. The values in the data entry fields will vary depending on the model geometry.

Figure 2.1: Generate Fluid Exterior Dialog

In addition to the appearance of the dialog, a transparent rectangular prism will be displayed over the model. This represents the 3-D part that will be created to model the fluid. You can control the size and location of the prism by entering values in the "Center (Point A)" and "Edge Lengths" sections. By default the prism will be centered at the centroid of the volume and will extend a small distance past the model in all three global directions. Changing the parameters will change the location and size of the prism. When you press the "OK" button a new part will be created in the model. This part will be the rectangular prism minus the volume of the model. When performing the fluid flow analysis, you will want to deactivate the part(s) representing the original CAD geometry. Note that, if there are openings in the exterior of the solid part, the fluid region will also fill the interior of the solid part, as would occur if you actually submerged the part or assembly in fluid. Conversely, if there are not openings in the solid part (that is, if any interior cavities are completely contained and isolated from the exterior), then the resulting fluid region will be solely external.



Internal

If you want to model the flow of a fluid inside a part, select the "Internal" command in the "Mesh: Fluid Generation" pull-out menu. The "Generate Fluid Interior" dialog shown in Figure 2.2 will appear.

Figure 2.2: Generate Fluid Interior Dialog

There are two input parameters which you must specify. First, click on a single surface on the interior of the model, around the cavity that you want to fill with fluid. Any one surface that will be in contact with the fluid is sufficient. You do not need to select them all. Once the surface is selected in the display area, press the "Select" button in the "Interior surface" field. The part and surface information will appear in the adjacent field. Next, select a surface on the exterior of the model that will define the end of the fluid part. Each individual opening in the CAD part or assembly must be surrounded by a single surface, which may be used to defined a termination face for the fluid region. Once the surface is selected, press the "Add" button in the "Bounding Surfaces" section. The part and surface information will appear in the adjacent list. Repeat this process until every boundary of the fluid region has been defined. Multiple bounding surfaces can also be added in a single operation. If the interior cavity or cavities are completely contained within the part or assembly (that is, if there are no openings to the exterior region), then you will not have to specify any bounding surfaces in order to generate the internal fluid part. Press the "OK" button to generate a new part representing the fluid.

Tetrahedral and Boundary Layer Meshes

For most analysis types, the "Bricks and tetrahedral" solid mesh type is ideal and is the default. This mesh creates high quality elements at the exterior of the model and lower quality elements at the interior. However, since the interior mesh is important for a fluid flow analysis, the "All tetrahedra" solid mesh type is selected by default for all models that are initially defined as fluid flow analyses. This can also be specified manually by pressing the "Options" button on the "Model Mesh Settings" dialog. Select the "Solid" icon on the left side of the dialog and then select the "All tetrahedra" radio button in the "General" tab. The all tetrahedra mesh type will create all 4-noded elements. This will result in higher quality and more uniform elements throughout the model than the "Bricks and tetrahedral" mesh option would.



An additional solid mesh type, which can be used for fluid flow models, is the boundary layer mesh. This is specified by selecting the "Tetrahedra and wedges (boundary layer)" radio button. The boundary layer mesh type will create thin boundary layers of wedges at all of the exterior surfaces of the model. Tetrahedral elements will be created for the remaining interior of the model. This will allow you to capture the results more accurately around the walls of the model, where velocity gradients are steepest. In addition, this mesh type ensures the generation of interior nodes in small and/or narrow fluid passages, which might otherwise be spanned by a single tetrahedra. This would make flow impossible due to the absence of interior nodes (since the exterior nodes will be constrained to zero-velocity). When either of these mesh types are selected, the "Tetrahedra" tab will become available. This tab is shown in Figure 2.3.

Figure 2.3: Tetrahedra Tab

The "Tetrahedral meshing options" section will allow you to control the quality of the tetrahedral elements. The "Target edge length based on" drop-down box will determine how the value in the "Target edge length" field is used to control the size of the tetrahedral elements as follows:

If the "Fraction of mesh size" option is selected, the value in the "Target edge length" field will be multiplied by the surface mesh size to determine the size of the tetrahedral elements.

If the "Absolute mesh dimension" option is selected, the value in the "Target edge length" field will be used for the size of the tetrahedral elements.

You can control the relative size of adjacent tetrahedral elements in areas where the mesh transitions from large element to small elements using the "Transition rate" field. The value in this field will be the ratio of the average edge lengths of adjacent elements. This value must be greater than 1. A large value will result in a lower quality mesh. The value in the "Quality" field will be used as an upper limit for the aspect ratio of the elements.



The "Boundary layer options" section can be used to control the wedge element boundary layers. This section will only be available if the boundary layer mesh type is selected. The "Extrusion distance based on" drop-down box will determine how the value in the "Total extrusion distance" field is used to control the combined length of all of the boundary layers as follows:

If the "Fraction of mesh size" option is selected, the value in the "Total extrusion distance" field will be multiplied by the surface mesh size. The resulting value will be the total thickness of the boundary layers.

If the "Absolute length dimension" option is selected, the value in the "Total extrusion distance" field will be the total thickness of the boundary layers.

If the "Percentage average local size" option is selected, the value in the "Total extrusion distance" field will be used as a percentage of the surface mesh size in the area of the boundary layer.

You can specify how many boundary layers will be created in the "Layers" field. The "Growth rate" field is used to specify the ratio of the mesh sizes between adjacent layers. This value must be greater than one. The outermost layer of wedges will be the thinnest and the subsequent layers will each increase in thickness. It is strongly recommended that you exclude all inlet and outlet surfaces from the boundary layer mesh to avoid poor mesh quality at the fluid inlets and outlets. The basic guideline is to use boundary layers only where a real wall exists. To exclude surfaces, first select the ones to be excluded, right-click in the display area, and choose the "CAD Mesh Options: Exclude From Boundary Layer" command.

Example of Internal Fluid Generation and Boundary Layer Meshing

To illustrate the internal fluid generation functionality, we will use the model, Internal Fluid.step, located in the "Chapter 2 Example Model\Input Files" folder of the class directory or Solutions CD. This is a model of a T-intersection of two pipes, with one of the ends capped. We want to analyze the flow inside the pipes. We will derive the fluid part automatically within the simulation software. To ensure the fluid generation capability, surface knitting will be performed when importing the CAD model. As stated previously, the default behavior for a new software installations is to NOT perform surface knitting. We will change this option during the file opening process for this exercise and then restore the default settings after importing the CAD solid model.

"Start: All Programs: Autodesk: Autodesk Algor Simulation: Autodesk Algor Simulation"

Press the Windows "Start" button and access the "All Programs" pull-out menu. Select the "Autodesk" folder and then the "Autodesk Algor Simulation" pull-out menu. Choose the "Autodesk Algor Simulation" command.

"Open" Click on the "Open" icon at the left side of the dialog.

"STEP (*.stp, *.ste, *.step)" Select the "STEP (*.stp, *.ste, *.step)" option in the CAD Files section of the "Files of type:" drop-down box.

"Options" Click on the "Options" button in the lower left corner of the "Open" dialog box.

"Global" Select the "Global" tab of the "CAD Import: STEP files Properties" dialog box.

"Yes" Activate the "Yes" radio button. Surface knitting will be performed for this model and for importing of all future CAD models, unless the option is changed once again.




"Internal Fluid.step" Select the file "Internal Fluid.step" in the "Chapter 2 Example Model \Input Files" directory. "Open" Press the "Open" button.

"Use STEP file units" "OK"

Choose the option to "Use STEP file units" if it is not already selected and click the "OK" button. The original STEP file length unit is inches.

"Fluid Flow: Steady Fluid Flow"

A "Choose Analysis Type" dialog will appear. Press the arrow button next to the analysis type field and select the "Fluid Flow" pull-out menu. Select the "Steady Fluid Flow" command.

"OK" Press the "OK" button. The model should appear in the FEA Editor environment, as shown in Figure 2.4.

Figure 2.4: Model in the FEA Editor Environment

"Tools: Options: CAD Import" Access the TOOLS pull-down menu and select the "Options" command. Click on the "CAD Import" tab.

"Global CAD Import Options" Press the "Global CAD Import Options" button.

"No" Activate the "No" radio button to the right of the "Knit surfaces on import:" heading. This will restore the default CAD import behavior for future models.

"OK" Press "OK" to exit the Global CAD Import Options dialog.

"OK" Press "OK" to exit the Options dialog.



"Mesh: Fluid Generation: Internal"

Access the MESH pull-down menu and select the "Fluid Generation" pull-out menu. Select the "Internal" command.

"Selection: Shape: Point" Access the SELECTION pull-down menu and select the "Shape" pull-out menu. Select the "Point" command.

"Selection: Select: Surfaces" Access the SELECTION pull-down menu and choose the "Select" pull-out menu. Select the "Surfaces" command.

Mouse Click on a surface on the inside of the pipe.

"Select" Press the "Select" button in the "Interior surface" section of the "Generate Fluid Interior" dialog.

Mouse

Click and drag in the display area using the middle mouse button to rotate the model until both open ends of pipe are visible. You may also rotate the mouse wheel to zoom in or out, if desired.

Mouse Click on one of the bounding surfaces as shown in Figure 2.5.

Figure 2.5: Location of the Bounding Surfaces

Mouse Holding down the key, click on the other bounding surface as shown in Figure 2.5.

"Add" Press the "Add" button in the "Bounding Surfaces" section of the "Generate Fluid Interior" dialog.

"OK" Press the "OK" button. A new part will be created representing the fluid inside the pipes. Mouse Right-click on the heading for Part 1 in the tree view.

"Deactivate" Select the "Deactivate" command to exclude it from the analysis. Only the newly created fluid part will now appear, as shown in Figure 2.6.



Figure 2.6: Internal Fluid Part

"Mesh: Model Mesh Settings"

Access the MESH pull-down menu and select the "Model Mesh Settings" command.

"Options" Press the "Options" button.

"Absolute mesh size" Select the "Absolute mesh size" option in the "Type" drop-down box. 0.2 Type "0.2" in the "Size" field.

"Solid" Select the "Solid" icon on the left side of the dialog.

"Tetrahedra and wedges (boundary layer)" Select the "Tetrahedra and wedges (boundary layer)" radio button.



"View: Orientation: Right View"

Access the VIEW pull-down menu and select the "Orientation" pull-out menu. Select the "Right View" command.

Mouse Click on the small circular surface facing the screen.


"CAD Mesh Options: Exclude From Boundary Layer" Select the "CAD Mesh Options" pull-out menu and select the "Exclude From Boundary Layer" command.





"CAD Mesh Options: Exclude From Boundary Layer" Select the "CAD Mesh Options" pull-out menu and select the "Exclude From Boundary Layer" command.

"Mesh: Generate Mesh" Access the MESH pull-down menu and select the "Generate Mesh" command.



"No" Press the "No" button when asked to view the mesh results.

Mouse

Click and drag in the display area using the middle mouse button to rotate the model and inspect the mesh. The meshed model should appear as shown in Figure 2.7.

Figure 2.7: Meshed Internal Fluid Part

We will complete the setup and analysis of this model later in this chapter.

Loading Options

For most fluid flow analyses, the flow is caused by a known pressure or velocity at some area of the model. Therefore prescribed velocities and pressures are the most common fluid flow loads. In addition to these loads, prescribed inlet/outlets allow the user to specify for which exterior surfaces of the model the velocities and pressures are unknown.

Prescribed Inlet/Outlets

A prescribed inlet/outlet can be applied to any node or surface of a model. A prescribed inlet/outlet specifies an area of the model where the velocity and pressure of the flow is not known. A zero-traction state will be applied where a prescribed inlet/outlet exists. This will results in a near zero pressure. If the "Use Automatic Constraints" checkbox in the "Options" tab of the "Analysis Parameters" dialog is activated, the program will automatically add zero velocity boundary conditions to all nodes on exterior surfaces that do not have a prescribed velocity or pressure/traction load applied and are not specified as a prescribed inlet/outlet. These are commonly called wall constraints. This checkbox is activated by default and is recommended because it eliminated the need for the user to manually apply the zero-velocity constraints to every surface of the model. This option is always active while using the "Segregated" solver. A prescribed inlet/outlet can be specified by selecting the desired node or surface and right-clicking in the display area. Select the "Add: Nodal Prescribed Inlet/Outlet" or "Add: Surface Prescribed Inlet/Outlet" command. A red "I" symbol will appear on each selected node for nodal-based inlet/outlets. For surface-based inlet/outlets, a green "I" symbol will appear at every node along the selected surface(s).



Prescribed Velocity

Prescribed velocities can be applied to any node, edge or surface of a model. Prescribed velocities applied to edges or surfaces will apply the velocity conditions to every node on the edge or surface. A prescribed velocity can be applied to a model by selecting the desired node, edge, or surface and right-clicking in the display area. Select the "Add: Nodal Prescribed Velocity", "Add: Edge Prescribed Velocity" or "Add Surface Prescribed Velocity" command. For a selected surface, the dialog shown in Figure 2.8 will appear.

Figure 2.8: Prescribed Velocity Dialog

For each direction in which you want to constrain the velocity, activate the checkbox. If a checkbox is not activated, the velocity in that direction will have no constraint. For example, if you want fluid to flow into a model at 1 in/s in the X direction, activate all three checkboxes. Type "1" in the "X Magnitude" field and leave the other values at 0. If the "Y Magnitude" and "Z Magnitude" checkboxes are not activated, the fluid will be able to flow at a non-zero magnitude in those directions. Generally, it is suggested that you use fully-constrained velocity components except for when you intentionally wish to model symmetrical boundary conditions (that is, boundaries where only the normal velocity is zero). For symmetrical models, leave the velocity in the directions parallel to the symmetry plane undefined and set the velocity normal to the symmetry plane to zero.

Pressure/Traction

Pressures or tractions can be applied to any surface of a model. A pressure is always applied normal to the face of the element. A traction is a uniform load applied along a specified direction. A pressure or traction can be applied to a model by selecting the desired surface and right-clicking in the display area. Select the "Add Surface Pressure/Traction" command. The dialog shown in Figure 2.9 will appear.



Figure 2.9: Surface Pressure/Traction Dialog

If you are applying a traction load (that is, a pressure that acts in a specific direction rather than normal to the selected surfaces), select the "Traction" radio button. Specify the magnitude of the traction in each of the three global directions in the "X Magnitude", "Y Magnitude" and "Z Magnitude" fields. Note that the Traction option is not supported for the Segregated formulation. Select the "Pressure" radio button if you are applying a uniform pressure (that is, one that has the same magnitude over the entire surface and that acts normal to the selected surfaces). Specify the magnitude of the pressure in the "Magnitude" field. The value in the "Magnitude" field will be treated differently depending upon which one of the five radio buttons immediately below the "Magnitude" field is selected. If the "Static pressure" radio button is selected, the value in the "Magnitude" field will be the static pressure component only. If the "Modified pressure for outlet backflow" radio button is selected, the value in the "Magnitude" field will be the static pressure. However, additional calculations will be performed to prevent a backflow through the surface. A backflow condition is when there is inward flow at a portion of an outlet surface or outward flow at a portion of an inlet surface. If the "Total pressure" radio button is selected, the value in the "Magnitude" field will be the total pressure. This can be used to represent a flow that is open to the ambient environment. This can also be used whenever the stagnation pressure is known but the static pressure is unknown and the flow rate and/or velocity is also unknown.

The Vent boundary conditions simulate pressure boundaries with a specified loss coefficient. If the "Vent Inlet" or "Vent Outlet" radio button is selected, the value in the "Magnitude" field will be the total pressure. The Loss Coefficient of the vent must be



specified in the provided data field. Please refer to the program Help files for more information regarding the definition and calculation of the loss coefficient. Note that only the Static pressure option is supported for the Mixed GLS and Penalty formulation options. The other four options will not be available for these formulations. In addition you can specify a loss coefficient. The loss coefficient, KL, will be used to calculate the loss at the vent, p using the fol

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Autodesk Algor Simulation CFD_2011