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SIMPACK
Getting Started
SIMPACK Release 8.6
24th September 2003/SIMDOC v8.607
COPYRIGHT 2003 c©
GETS:0.0 -2
Contents
1 Introduction to SIMPACK 1.1 -7
1.1 The Software What are you intending to do? . . . . . . . 1.1 -7
1.2 Modes of Analysis . . . . . . . . . . . . . . . . . . . . . . 1.3 -8
1.3 Program Structure . . . . . . . . . . . . . . . . . . . . . 1.3 -8
1.4 Pre-processing (Model Set-up) . . . . . . . . . . . . . . . 1.4 -9
2 Introduction to the SIMPACK Getting Started Guide2.2 -11
2.1 The Software . . . . . . . . . . . . . . . . . . . . . . . . 2.2 -11
2.2 From Concept to Simulation . . . . . . . . . . . . . . . . 2.2 -12
2.3 What the User Will Learn . . . . . . . . . . . . . . . . . 2.3 -15
2.4 Some Useful Hints When Working with SIMPACK . . . 2.0 -16
3 Starting a SIMPACK session 3.3 -17
3.1 How to Start a SIMPACK Session . . . . . . . . . . . . . 3.3 -17
Windows NT users . . . . . . . . . . . . . . . . . . . . . 3.3 -17
UNIX Users . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 -17
3.2 Exiting SIMPACK . . . . . . . . . . . . . . . . . . . . . 3.3 -17
3.3 The SIMPACK GUI . . . . . . . . . . . . . . . . . . . . 3.3 -18
4 File and Model Management 4.1 -21
4.1 Creating a New Model . . . . . . . . . . . . . . . . . . . 4.1 -21
4.2 Copying a Model . . . . . . . . . . . . . . . . . . . . . . 4.3 -23
4.3 Removing a Model . . . . . . . . . . . . . . . . . . . . . 4.3 -23
4.4 Opening a Model . . . . . . . . . . . . . . . . . . . . . . 4.6 -25
4.5 Starting the Pre-Processor . . . . . . . . . . . . . . . . . 4.6 -25
4.6 Exiting the Pre- or Post-Processor . . . . . . . . . . . . . 4.0 -26
4.7 Getting Help . . . . . . . . . . . . . . . . . . . . . . . . 4.0 -26
5 Pendulum Model 5.1 -27
5.1 Setting up the Model . . . . . . . . . . . . . . . . . . . . 5.1 -27
5.2 Data for the Mechanical System Pendulum . . . . . . . . 5.4 -29
5.3 Opening the Model . . . . . . . . . . . . . . . . . . . . . 5.4 -29
5.4 Starting the Pre-Processor . . . . . . . . . . . . . . . . . 5.4 -29
GETS:0.0 -4 CONTENTS
5.5 Modifying the Reference Frame . . . . . . . . . . . . . . 5.5 -32
5.6 Discarding Changes . . . . . . . . . . . . . . . . . . . . . 5.6 -33
5.7 Modifying the Rigid Body . . . . . . . . . . . . . . . . . 5.7 -35
5.8 Modifying the Joint . . . . . . . . . . . . . . . . . . . . . 5.8 -39
5.9 Defining the g-Vector . . . . . . . . . . . . . . . . . . . . 5.11 -45
5.10 Modifying the Sensors . . . . . . . . . . . . . . . . . . . 5.11 -45
5.11 Saving the Model to Disk . . . . . . . . . . . . . . . . . 5.12 -46
5.12 Creating the 3D Geometry . . . . . . . . . . . . . . . . . 5.12 -47
5.13 Graphical Representation of Body - Prism - Primitive . . 5.14 -52
5.14 Manipulating the View . . . . . . . . . . . . . . . . . . . 5.14 -52
5.15 On/Off Line Integration . . . . . . . . . . . . . . . . . . 5.15 -55
On Line Integration . . . . . . . . . . . . . . . . . . . . . 5.15 -56
Off Line Integration . . . . . . . . . . . . . . . . . . . . . 5.15 -57
Performing the Time Integration . . . . . . . . . . . . . 5.16 -60
5.16 Calculating Measurements . . . . . . . . . . . . . . . . . 5.16 -60
5.17 Animating the Results of the Integration . . . . . . . . . 5.17 -61
6 The Double–Pendulum 6.1 -63
6.1 About the Model ‘Double–Pendulum’ . . . . . . . . . . . 6.1 -63
6.2 Extending the Pendulum Model to a Double Pendulum . 6.3 -65
6.3 Adding a Marker to a Body . . . . . . . . . . . . . . . . 6.3 -65
6.4 Creating a New Body and Adding a Marker . . . . . . . 6.4 -67
6.5 Modifying a Joint . . . . . . . . . . . . . . . . . . . . . . 6.5 -70
7 Creating and Importing a Substructure to a Model7.1 -73
7.1 Creating a Substructure . . . . . . . . . . . . . . . . . . 7.1 -73
8 Adding a Force Element to the Double Pendulum Model8.1 -77
8.1 Adding the Force Element . . . . . . . . . . . . . . . . . 8.1 -77
8.2 Plots of the Results . . . . . . . . . . . . . . . . . . . . . 8.2 -81
2D State Plots of the Joint States and Velocities . . . . . 8.2 -81
General 2D plots . . . . . . . . . . . . . . . . . . . . . . 8.2 -81
8.3 Static Equilibrium . . . . . . . . . . . . . . . . . . . . . 8.3 -84
8.4 Calculation of the Nominal Force Parameters . . . . . . . 8.4 -85
8.5 Eigen Behaviour . . . . . . . . . . . . . . . . . . . . . . . 8.5 -88
Animation of the Mode Shapes . . . . . . . . . . . . . . 8.5 -88
9 Addition of a Force Element to be Used as a Bump Stop9.0 -91
CONTENTS GETS:0.0 -5
10 A Slider Crank Mechanism 10.3 -93
10.1 About the Slider Crank Mechanism . . . . . . . . . . . . 10.3 -93
10.2 Extending the Double Pendulum Force Model to a Slider Crank10.3 -93
10.3 Defining a Constraint (Closed Loop) . . . . . . . . . . . 10.3 -93
10.4 Dependent and Independent Joints . . . . . . . . . . . . 10.4 -95
10.5 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 -98
10.6 On-line Kinematics . . . . . . . . . . . . . . . . . . . . . 10.6 -99
Defining a Slider Bar . . . . . . . . . . . . . . . . . . . . 10.6 -99
Interactive Kinematics . . . . . . . . . . . . . . . . . . . 10.7 -101
10.7 Inverse Kinematics . . . . . . . . . . . . . . . . . . . . . 10.7 -102
Configuration of the Inverse Kinematics Solver . . . . . . 10.7 -104
Performing Inverse Kinematics . . . . . . . . . . . . . . . 10.0 -105
11 How to Move On 11.0 -107
GETS:0.0 -6 CONTENTS
GETS:1. Introduction to SIMPACK
SIMPACK: (SImulation of Multi-body systems PACKage)
GETS:1.1 The Software: What are you intending todo?
The SIMPACK software package is a tool to assist engineers to model,simulate, analyse and design all types of mechanical system, such asvehicles, robots, machines and mechanisms. It is able to analyse vibra-tional behaviour, calculate forces and accelerations as well as describeand predict the motion of multi-body systems.
The basic concept of SIMPACK is to create the equations of motion formechanical and mechatronic systems and then from these equations,apply various different mathematical procedures to produce a solution(e.g. time integration). The SIMPACK model is built up using the SIM-PACK modelling elements. SIMPACK will then automatically generatethe system equations from this model.
The equations of motion can be generated both symbolically and nu-merically (where the numeric form is the usual form). The symboliccode allows the user to export the SIMPACK model as standard FOR-TRAN or C code which can be run independently, for example in realtime, in a ‘hardware in the loop’ environment.
The software has a comprehensive range of modelling and calculationfeatures, together with a user interface well adapted to an engineer’sneeds. Due to its comprehensive modelling abilities, it has been suc-cessfully applied within industry, university and research institutions.The following is a list of many of the fields to which SIMPACK has beenapplied.
• Automotive vehicles• Tracked vehicles• Robotics• Machine tools• Printing machines• Packaging machines• Ground dynamics of aeroplanes
GETS:1.3 -8 Program Structure
• Dynamics of spacecraft• Electrical machine design• Biomechanics
GETS:1.2 Modes of Analysis
A wide range of analysis features are available to analyse and designdynamic systems:
• Static Analysis• Kinematic Analysis• Non-linear Dynamic Analysis• Linear System Analysis
• Symbolic Code Generation• Eigenvalue Analysis
GETS:1.3 Program Structure
Figure GETS:1.3.1 shows the main functional modules and interfacesto external software tools.
Figure GETS:1.3.1: SIMPACK Program Structure
The window oriented interface of SIMPACK serves four main purposes:
• The user interface includes a dialogue driven model set-up win-dow, which includes list boxes for the MBS-library elements, pa-rameters etc. This interactive module generates all the data nec-
Pre-processing (Model Set-up) GETS:1.4 -9
essary for a complete physical and graphical description of theMBS. It also generates all the necessary data for SIMPACK toperform the numerical evaluation methods.
• It prevents the user from creating inconsistent models. Logicaldata checks of the input deck are made by SIMPACK as well ascalculations performed on-line for closed loop systems to ensurethat the model is viable.
• It provides help on all menu items. Thus the necessary ‘manualresearch work’ is reduced to a minimum.
• It gives the engineer complete control of the model creation andsimulation processes.
GETS:1.4 Pre-processing (Model Set-up)
In SIMPACK, the pre-processor Model Setup window is a graphical 3Dwindow. At each step of the modelling process the user has a directgraphical impression of the system. The model data is stored in theMBS database which is used as the basic input for a SIMPACK analysis.It is possible to access this data which is user readable and represents aclear description and documentation of the MBS. This data is in ASCIIformat and so is therefore available to users of all platforms.
Extensive libraries of coupling elements such as joints and force ele-ments, as well as excitation functions, help the engineer build theirmodel. Common SIMPACKmodels include suspension or other complexjoint kinematics, force models for hydraulics, various tyre type models,aerodynamics models, etc. Subsystem modelling techniques enable theuser to establish complicated non-standard kinematical and/or forcesystems. User written subroutines extend the modelling options. Inorder to represent flexible bodies, several pre-processors can be used tosupply the SIMPACK computation modules with flexible body data.
SIMPACK is an open system which possesses various links to externalstandard software products. For arbitrary flexible geometry, a file inter-face to FEM programs is available. This gives access to mass, stiffnessand damping matrices as well as to the associated second order terms.In addition, loads computed by SIMPACK can be transferred to theFEM code. For the purpose of incorporating physical and graphicalCAD data, SIMPACK can be linked by an interface to CAD packages,thus increasing the model set-up capabilities enormously. This link en-ables data consistency between MBS and CAD data at each step ofthe modelling process. It is also possible to perform SIMPACK on-linecalculations from the CAD package and to have the results presentedin the CAD environment. In general this feature is not guaranteed byusing file interfaces alone.
SIMPACK may also be linked as a fully non-linear tool into non-linearoptimisation and control tools such as MATLAB, SIMULINK, etc. Thisallows the use of SIMPACK and its parameter variation capability to beused in an optimisation loop for the efficient design of dynamic sys-
GETS:1.0 -10 Pre-processing (Model Set-up)
tems. Due to its ability to numerically linearise the system equations,SIMPACK can also be used as a simulation tool within linear controldesign tools. A further link is provided to external post-processingtools in addition to the extensive internal post-processing capabilitiesof SIMPACK.
The 2D and 3D visualisation tools enable the user to view simulationresults in many different forms. These include tables, plots and real-time animation of the graphical models created by SIMPACK.
Figure GETS:1.4.2: Trademarks
GETS:2. Introduction to theSIMPACK Getting Started Guide
The purpose of this guide is to introduce the user to SIMPACK and itsfeatures. After completing this guide the user will have learnt manyof the features of SIMPACK and will be able to start modelling andsimulating their own mechanical systems.
It is estimated that it will take the user approximately 10 hours tocomplete the Getting Started guide. It is possible however, to savethe model at any stage and then return at a later date. No previousexperience of multi-body systems software or any understanding of thetheory upon which the software is based is required of the user.
The user is taken through the guide step-by-step, but is encouraged,at certain points, to undertake some tasks unaided and therefore applywhat has been previously learnt. New features are introduced at everystage ensuring the user becomes familiar with many of the features ofSIMPACK by the end of the Getting Started guide. The guide contains,within the text, snapshots of SIMPACK dialogue boxes to ensure theuser is entering the data correctly.
GETS:2.1 SIMPACK: The Software
SIMPACK is a multi-body simulation package which allows the user tosimulate and model complex mechanical systems. The software alsoallows the inclusion of electrical, hydraulic and pneumatic elements.The purpose of the software is to improve the design process involvingmulti-body systems. The user is likely to see reduced lead times, asimpler design process and at the end, a better product.
The more common requirements of the user from SIMPACK include anyfrom the following:
• Optimisation of design parameters• Calculation of dynamically interacting forces within critical com-ponents
• Effect of varying design parameters• Determining major design parameters affecting dynamic be-haviour
• Analysing weak points of the mechanical design
GETS:2.2 -12 From Concept to Simulation
GETS:2.2 From Concept to Simulation
From the initial concept stage to the point where SIMPACK has pre-sented the results, there are six steps. The first three steps are per-formed outside SIMPACK. They are as follows:
1. Problem definition
2. Development of a mechanical model
3. Provision of the physical parameters for the model
The first three steps may appear obvious, but should be com-pleted before entering SIMPACK
Steps 4 to 6 are performed within SIMPACK
4. Pre-processing: Input the data set, obtained from steps 1-3, withthe help of the SIMPACK user interface
5. Problem Solution: Generation and solution of the motion govern-ing differential equations
6. Post-processing: Presentation of the results
By following these steps, will ensure that you make the best possibleuse of SIMPACK’s features and solver capabilities.
These steps will now be explained in a little more detail:
Step 1. Problem Definition
Figure GETS:2.2.1: Truck and Trailer as an Example of a PhysicalSystem
Step 2. Development of a Mechanical Model
• The mechanical structure is divided into bodies and joints, theinterconnecting structures
• Constraints are then defined, which contsrains the mobility of theelements by removing degrees of freedom
• Forces in-between the ground and the bodies are defined
From Concept to Simulation GETS:2.2 -13
α 7β 9
β 8z 7
z 1
γ1
z 2
β 2
α2
β 1β
γ1
α 1
x 1
z 3
α 3
β 4
β 5
Figure GETS:2.2.2: Mechanical Model
Step 3. Provision of the Model Parameters
• The physical parameters for the model such as the mass, momentsof inertia and centre of mass for the various different bodies aredefined
• The geometry of the structure and how it fits together are defined;i.e. the distances in-between coupling points
• The parameters for the coupling elements are defined, such as theforce element values and constraints
Figure GETS:2.2.3: Typical Model Parameters
Step 4. Pre-Processing
This section is where the model data is entered into SIMPACK. Thisdata includes:
• The physical model; i.e. bodies and joints• All the input functions for the model including the constraints,forces and excitation functions
• The associated 3D geometrical data for the graphical representa-tion of the bodies
GETS:2.2 -14 From Concept to Simulation
• The numerical calculation settings• The settings for the output quantities• The settings for the optimisation and parameter variation
Step 5. SIMPACK Calculations
• The differential equations are generated from the data entered inthe previous step and then solved within SIMPACK
Step 6. Post-processing: Presentation of Results
SIMPACK can present the results in any of the following forms:
• User determined plots such as load indices or limiting values• 2D line plots
• SIMPACK contains various different mathematical algorithms i.e.Fast Fourier Transforms which can be used to process the resultsof SIMPACK’s calculations
• 3D animation of the model i.e. mode shape animation
• Export to Microsoft Excel and MATLAB
What the User Will Learn GETS:2.3 -15
GETS:2.3 What the User Will Learn
This section will explain what the user will be doing in the SIMPACKGetting Started Guide. The guide takes the user through buildingup a relatively simplistic model, which begins as a pendulum and isdeveloped into a slider-crank mechanism. Along the way the user isintroduced to SIMPACK’s extensive modelling features. The featureswhich the user will meet are detailed as follows:
• They will be introduced to the pre-processor and the main buildcommands, which include New, Modify and Remove. The userwill learn how to create the basic physical model using referenceframes, bodies, markers and joints. As well as the pull-downmenus, the user will learn how to access features using the toolbarshortcut buttons.
After developing the model the user will learn how to solve itin SIMPACK (both off- and on-line integration methods will betaught). Following this, the user will be shown how to access anduse the features within the post-processor
• They will be taught how to assign sensors to the structure whichallow the user to see the response, from within the post-processor,of different, predetermined parts of the structure (i.e. positions,velocities or forces at exact locations on the model can be anal-ysed)
• After entering the physical data, the user will be taught how toassign primitives to the bodies, joints etc. and therefore create aphysical 3D geometry
• The user will also be taught how to create the interaction in-between the physical parts using force elements and constraints
• A number of features will not be introduced to the user in theGetting Started guide. These include a number of the toolbarfunctions. However help topics are available when the user wishesto use any of these functions
GETS:2.0 -16 Some Useful Hints When Working with SIMPACK
GETS:2.4 Some Useful Hints When Working withSIMPACK
• Work through the model set-up one step at a time• Be aware that SIMPACK can only provide the solution of themodel data, which is an approximation of a real physical system
• Always plan your model before you start working with SIMPACK
• Draw sketches of your model and refer back to them when workingin a SIMPACK session
• Be patient, you are not the first to make mistakes
GETS:3. Starting a SIMPACK session
The main features you will learn at this stage are as follows:
• How to start a SIMPACK session
• Basic file management• Ending a SIMPACK session
GETS:3.1 How to Start a SIMPACK Session
Windows NT users:
• Either click on the SIMPACK desktop item
Figure GETS:3.1.1: SIMPACK Desktop Item
• Or from the taskbar menu select Programs, followed by ‘SIMPACKv.8.6 folder’ and then finally click on the SIMPACK v.8.6 icon
UNIX Users:
• Open a terminal window• Type sim
The SIMPACK user interface window appears GETS:3.1.2:
Figure GETS:3.1.2: SIMPACK User Interface
GETS:3.2 Exiting SIMPACK
From the menu bar on the user interface select Exit from File on thepull-down menu: File �
Exit
GETS:3.3 -18 The SIMPACK GUI
GETS:3.3 The SIMPACK GUI
This window is the main operating interface between the user and SIM-PACK. This window contains a menu bar, along with a shortcut toolbar.The different menu items and toolbar buttons will be explained as youwork through this guide.
However here is a quick overview of the different menubar functions.
File
This menu provides the basic file and model management op-tions and is where the user can exit from SIMPACK.
PreProcess
This menu option allows the user access to the pre-processor inthe 3D Model Setup window. There are various other pre-processingoptions available including the generation of symbolic code.
Calculation
Under this menu is where you can control what is happeningwith the SIMPACK solver. You can start and stop the time integrationmodule, inverse kinematics module etc.
ParVariation
This feature of SIMPACK is particularly useful. If the effect ofvarying a different parameter is required, SIMPACK is able to dothis automatically i.e. the user does not have to vary the parameterdirectly, but can instruct SIMPACK to see the effect that varying aparameter has (the mass of a body for example) on the motion ofthe system. This parameter variation is available in a number of thedifferent SIMPACK solver modules.
Optimisation
The basic idea is similar to parameter variation. The parame-ters to be optimised are modified in such a way that selected criteria,(e.g. the RMS-value of an acceleration) are minimised. SIMPACKemploys a sophisticated algorithm to evaluate the resulting perfor-mance. This provides the ‘best’ (pareto-optimal) parameter within ashort iteration period. The optimisation process is not limited to onecalculation method nor even to one simulation model. The optimisedparameter may result from the consideration of several optimisationcriteria, for example for a railway vehicle problem, parameters such asride comfort, track quality and safety could all be considered.
PostProcess
The SIMPACK GUI GETS:3.0 -19
This menu gives you access to the main post-processing func-tions.
Help
This provides access to the main SIMPACK documentation, in-cluding help topics on the SIMPACK keywords, plus general SIMPACKinformation as well as details of the current SIMPACK release.
GETS:3.0 -20 The SIMPACK GUI
GETS:4. File and ModelManagement
Figure GETS:4.0.1: On-Line View of a SIMPACK Session
In this section you will learn how to open, copy, create and removemodels.
GETS:4.1 Creating a New Model
From the user interface either click on the Open Model toolbar but-ton GETS:4.1.2 or click on Open Model from File �
Open Model
GETS:4.1.3.
GETS:4.1 -22 Creating a New Model
Figure GETS:4.1.2: Open Model From the Toolbar
Figure GETS:4.1.3: Open Model from the Pull-Down Menu
The open model dialogue box then appears, figure GETS:4.1.4:
Figure GETS:4.1.4: The Open Model Dialogue Box
You must now select which directory you would like to save the modelin. On the left hand side of the Open Model dialogue box you will seea directory list box. Either double click on a directory or double clickon .. to look in a parent directory. Once you are in the directory you
would like to save your model in, then click on✞
✝
�
✆New and enter the
model name✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁pendulum in the list box that appears. You must
then hit✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁Return . The model name will be displayed at the top
of the SIMPACK user interface window.
When a new model is created, SIMPACK automatically creates a defaultmodel with the following parameters:
Copying a Model GETS:4.3 -23
• Inertia reference frame ‘$B Isys’ with a marker ‘$M Isys’placed at the origin of the inertia reference frame
• One body ‘$B Body1’ with a marker ‘$M Body1’ placedon the body fixed reference frame
• One joint ‘$J Body1’, which connects the inertia frameand the body with zero degrees of freedom
• One sensor ‘$S Body1’ between the two markers• A default gravity vector• A default 3D–geometry for the inertia frame and thebody
GETS:4.2 Copying a Model
Open the Open Model dialogue box and select the ‘pendulum’ modelyou have just created, click with the right hand mouse button in thissection (Models section) of the Open Model window and select ‘CopyModel’. Click again with right hand mouse button and select ‘PasteModel’. You will then be asked to whether you want to overwrite theexisting model, select ‘No’ and in the ‘New Model’ window that thenappears enter the new name for the copied model.
Models can also be copied across directories. The model should becopied in exactly the same way. Then switch to the directory in whichyou would like to copy your model and click on ‘Paste Model’. Themodel data will be copied to this directory and will have the name ofthe original model.
You should now create the model ‘deleteme’ which is a copy of the‘pendulum model’ and will be located in the same directory as the’pendulum’ model.
GETS:4.3 Removing a Model
Open the Open Model dialogue box and select the model ‘deleteme’which you have just created. Click on
✞
✝
�
✆Remove . The following dia-
logue box will appear on the screen, figure GETS:4.3.5.
GETS:4.3 -24 Removing a Model
Figure GETS:4.3.5: Remove Model Window
Opening a Model GETS:4.6 -25
There are 5 options that appear. Three of the options are for workingonly with the selected model and the other two options are for workingwith the entire active directory.
The options for the current model are:
• To remove the current model with all the results• To remove all the results from the current model; this removes allthe output files of the selected model
• To remove measurement results only from the current model; thisremoves all the measurement results from the current model, butkeeps all the simulation results
The final option keeps only the basic results files and model files. Thisis useful as the results files from the simulation are kept, which mayhave taken a significant amount of computer time to produce. The mea-surement files are removed, which often take up a significant amount ofdisk space, but can be restored very quickly. Calculating measurementswill be explained later in the guide.
The options for the entire directory are as follows:
• To remove all the results from all the models in the current di-rectory
• To remove all the measurement results from all the models in thecurrent directory
Select ’remove current model with all results’ and click on✞
✝
�
✆OK . Con-
firm that you want to remove this model and when you return to theOpen Model dialogue box click on
✞
✝
�
✆Close .
GETS:4.4 Opening a Model
Open the Open Model window once more. Find the directory whichcontains the pendulum model, which you have just created. Doubleclick on the pendulum model or select the model and then click on✞
✝
�
✆OK .
SIMPACK only allows you to work on one model at a time. You will beunable to load up a new model in SIMPACK if the pre- or post-processoris running with another model. To begin working on a new model youmust close the pre- or post-processor.
GETS:4.5 Starting the Pre-Processor
The pre-processor can be opened either from the pull-down menuPreProcess �
Model Setupor from Model Setup / 3D-animation
on the shortcut toolbar.
GETS:4.0 -26 Getting Help
GETS:4.6 Exiting the Pre- or Post-Processor
Either select from File �Exit
in the 3D Model Setup window or
click on the Exit toolbar button. You will then be prompted to see ifyou wish to save your model or not.
GETS:4.7 Getting Help
SIMPACK provides the user with many help options. Help is most easilyaccessible via the on-line help HTML pages, which are accessed throughHelp �
Documentationon the pull-down menu in the SIMPACK
user interface.
If the user clicks on help from within the menu bar in other windowsthen they are presented with two options from within the pull-downmenu.
1. ‘Help on context,’ can be selected where a short help text is avail-able for many fields within the SIMPACK windows
2. ‘Help on window,’ brings up a HTML document in a browserwindow, which provides help on functions within that window
GETS:5. Pendulum Model
GETS:5.1 Setting up the Model
In this lesson you will learn how to create and develop a model. Youwill learn how to:
• Create and work with reference frames, bodies, joints and markersand learn how to add sensors
• Create the 3D graphical representation of the physical parts
• Add force elements, including global forces as well as adding con-straints
• Use the more advanced model and file management features ofSIMPACK
• Use SIMPACK to integrate the differential equations generatedfrom the model data. Subsequently you will learn how to calculatemeasurements and animate the model from the simulation results
• Manipulate the view of the model in the Model Setup windowYou will build a relatively simplistic model of a pendulum which willbe developed into a slider-crank mechanism by the end of the GettingStarted guide. Figure GETS:5.1.1 shows the pendulum which you willcreate in the first section of the Getting Started guide.
GETS:5.1 -28 Setting up the Model
Figure GETS:5.1.1: Pendulum Model
Data for the Mechanical System Pendulum GETS:5.4 -29
GETS:5.2 Data for the Mechanical System Pendulum
• Body pendulum:mass = 4.0 [ kg ]centre of gravity (x,y,z) = ( 0, 0, -0.25 ) [ m ]
inertia tensor I =
10.0 0.0 0.00.0 10.0 0.00.0 0.0 1.0
[ kgm2]
• Joint:joint mobility = rotation about x-axis —initial joint state = 0.707 [ rad ]initial angular velocity = 0.0 [ rad/s ]
• Gravity:acceleration due to gravity along z-axis,g = 9.81 [ m/s2 ]
Geometric data for the pendulum:
• Prism, representing the pendulum:
co-ordinates of the prism —
y z−0.1 0.00.0 −0.10.1 0.00.0 0.7
[ m ]
thickness = 0.05 [ m ]
• Cylinder, representing the rotational axis:length = 0.5 [ m ]diameter = 0.05 [ m ]
GETS:5.3 Opening the Model
Start a SIMPACK session and open the pendulum model which youcreated previously.
GETS:5.4 Starting the Pre-Processor
The pre-processor is where all the work is done in SIMPACK before youask SIMPACK to solve the equations. This step is Step 4 in the 6 stepsrequired to go from the concept stage to the simulation stage.
The pre-processor can be opened either from the pull-down menuPreProcess �
Model Setupor from Model Setup / 3D-animation
on the shortcut toolbar.
Two windows will appear on the screen. Figure GETS:5.4.2 is theSIMPACK 3D Model Setup window. In this window there is a 3D axisand this is where the model that you build will be shown. Along thetop and side of the window you will find the shortcut toolbars as wellas a menubar.
GETS:5.4 -30 Starting the Pre-Processor
Figure GETS:5.4.2: SIMPACK 3D Model Setup Window
Starting the Pre-Processor GETS:5.4 -31
The other window that appears is the SIMPACK Echo Area window, fig-ure GETS:5.4.3. This window displays the working status of SIMPACKas well as any error or calculation messages:
Figure GETS:5.4.3: SIMPACK Echo Area
GETS:5.5 -32 Modifying the Reference Frame
GETS:5.5 Modifying the Reference Frame
At least one reference frame is required to describe the motion of aphysical system. Reference frames are co-ordinate frames with a strictlydefined (completely rheonomically driven) motion relative to the iner-tia frame which means therefore, that reference frames do not havedynamics of their own. It is possible to represent the axes using 3Dgeometry. The reference frame is normally of the type inertially fixed.
Either click on the ’Reference Frames toolbar button’ or from the pull-down menu select Elements �
Reference Frames
The following dialogue box, figure GETS:5.5.4 will appear:
Figure GETS:5.5.4: SIMPACK MBS Reference Frames
Discarding Changes GETS:5.6 -33
This dialogue box contains all the defined reference frames in the MBSmodel. There should only be one reference frame present which is thereference frame $B Isys. From this dialogue box you should now eitherdouble click on the reference frame $B Isys or select it and then click on✞
✝
�
✆modify . The following dialogue box, figure GETS:5.5.5 will appear:
Figure GETS:5.5.5: Reference Frames Dialogue Box
From this dialogue box you can edit the reference frame data. You candefine various different parameters for the reference frame as well asdefine its guiding motion.
Try selecting✞
✝
�
✆Type . This starts the window Reference System List.
From this window you can select the type of reference frame you require.Click on
✞
✝
�
✆Cancel to return back to the Define Reference System dia-
logue box. You can also try selecting✞
✝
�
✆Markers or
✞
✝
�
✆3D Geometry .
Clicking on✞
✝
�
✆Show the Reference Frame will highlight the refer-
ence frame in the 3D Model Setup window. Click on✞
✝
�
✆OK to close
the Define Reference System window. You will learn how to create andmodify markers later in this guide.
GETS:5.6 Discarding Changes
Before going any further with developing the model, it is necessary toexplain how to discard any unwanted modifications.
SIMPACK does not have an undo facility. If you as the user wish toremove a number of changes to the model you have just made, then itis necessary to reload the model from the last save.
GETS:5.6 -34 Discarding Changes
The model can be reloaded either from File and then Reload on the pull-down menu File �
Reloador by clicking on ’Reload’ in the toolbar.
This Reload function is found in the 3D Model Setup window as shownin figures GETS:5.6.6 and figure GETS:5.6.7.
Figure GETS:5.6.6: Reload MBS
Figure GETS:5.6.7: Reload MBS Toolbar
Modifying the Rigid Body GETS:5.7 -35
Reloading the database from the last save means all the changes youhave made since the last save will be removed. If however, you wouldonly like to remove one or two changes then it is more advisable tomodify the model (such as a joint or marker). Modifying varying dif-ferent aspects of the model will be explained at various different stagesthroughout this guide.
GETS:5.7 Modifying the Rigid Body
Whenever a new body is created, SIMPACK automatically assigns ita body fixed marker. This marker serves as a reference frame for thebody, therefore its position and orientation cannot be changed.
The following items are defined with respect to this body fixed referencesystem:
• Position of the centre of gravity relative to the body fixed refer-ence frame
• Built-in position and orientation of markers on the bodySelect either ’Bodies’ on the toolbar or from the pull-down menu in the3D Model Setup window Elements �
Bodies
The Bodies list box, figure GETS:5.7.8 will appear on the screen, con-taining the default body $B Body1 in the list box.
GETS:5.7 -36 Modifying the Rigid Body
Figure GETS:5.7.8: Bodies List Box
Modifying the Rigid Body GETS:5.7 -37
Double click on $B Body1 or select it with the mouse and then clickon
✞
✝
�
✆Modify . The MBS Define Body dialogue box appears, within this
window you can select whether the data used for the body is inputlocally (i.e. by you in the pre-processor) or from a database. You canalso select whether the body is rigid or elastic. For this model you willenter the data by hand, i.e. not from the database and you will definethe body as rigid.
Within this dialogue box you can enter the physical attributes of thebody. These include the mass, centre of mass and the inertia-tensor.
The inertia-tensor can be set relative to either the centre of mass, thebody fixed reference system or to a marker. Normally it is set relativeto the centre of mass, which is the case for the pendulum model here.
You should now enter the following data for the body:
Edit $B Body1:
mass =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁4
Centre of mass z =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁-0.25
Ixx =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁10
Iyy =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁10
Izz =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁1
Inertia-tensor relative to centre of mass
Figure GETS:5.7.9 shows how the MBS Define Body dialogue boxshould look:
GETS:5.7 -38 Modifying the Rigid Body
Figure GETS:5.7.9: MBS Define Body
Modifying the Joint GETS:5.8 -39
Click on✞
✝
�
✆OK
GETS:5.8 Modifying the Joint
Joints are zero mass connections between two bodies. Every body musthave a joint and this joint must either be attached to another body orto a (kinematically driven) reference frame. Joints can have from 0 to6 degrees of freedom. To modify the joint:
• Select Joints from either, the pull-down menu under Elements orfrom the toolbar
• In the next dialogue box select $J Body1 and as you did with$B Body1 click on
✞
✝
�
✆Modify or double click on it
The dialogue box MBS Define Joint, figure GETS:5.8.10 will appear.
Figure GETS:5.8.10: MBS Define Joint
At the top of the dialogue box the name of the joint is shown. Themarkers to which it is attached as well as the type of joint are alsoshown. When defining the markers associated with a joint, it is nec-essary to follow the tree structure which starts from the inertia frame
GETS:5.8 -40 Modifying the Joint
and moves outwards. Therefore the ‘from marker i’ should be nearerthe reference frame than the ‘to marker j’. SIMPACK takes this intoaccount when it offers you the markers.
Click on✞
✝
�
✆From Marker i and the dialogue box, figure GETS:5.8.11
appears:
Figure GETS:5.8.11: MBS Marker List
Modifying the Joint GETS:5.8 -41
• Select marker $M Isys and then click on OK. This marker is thedefault marker set by SIMPACK on the reference frame
• Select $M Body1 as marker j. This is the default marker set bySIMPACK on Body1
• It is then necessary to select a joint type. Click on✞
✝
�
✆Joint Type .
The window GETS:5.8.12 appears with a list of the different typesof joint, e.g. Rheonomic Joints. The individual joints can befound under the relevant joint type. Open the folder ‘General:Free Motion’ and from the list that appears select joint ‘RevoluteJoint al’. This is a 1 degree of freedom joint, which allows onlyrotation about the x axis (angle Alpha). Figure GETS:5.8.12shows what you should select:
Figure GETS:5.8.12: Joint List
GETS:5.8 -42 Modifying the Joint
• Press✞
✝
�
✆OK to close the subwindow and you will return to the
MBS Define Joint Dialogue box. Click on the first line of theinitial state box as shown in figure GETS:5.8.13:
Figure GETS:5.8.13: MBS Define Joint
Modifying the Joint GETS:5.8 -43
In the following input window you can enter the initial state of the jointin terms of both position and velocity.
Enter the following modifications into the input panel.
Position =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.707
Velocity =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.0
The input panel should look as follows, figure GETS:5.8.14:
Figure GETS:5.8.14: Input Panel
GETS:5.8 -44 Modifying the Joint
Click on✞
✝
�
✆OK and the MBS Define Joint dialogue box should look as
follows, figure GETS:5.8.15:
Figure GETS:5.8.15: Completed MBS Define Joint Dialogue Box
Defining the g-Vector GETS:5.11 -45
Click on✞
✝
�
✆OK again, to close the MBS Define Joint window
GETS:5.9 Defining the g-Vector
This is the section where you can set the g-vector. If you would like toundertake an analysis without the g-vector present you must explicitlytell SIMPACK, otherwise it is defined automatically and is negativealong the z-axis.
To modify the g-vector you must select ’Gravity’ from within Globals inthe pull-down menu Globals �
Gravityfrom the 3D Model Setup
window. Figure GETS:5.9.16 shows the g-vector dialogue box:
Figure GETS:5.9.16: Define g-Vector
For this analysis stay with the default value which is negative along thez axis.
GETS:5.10 Modifying the Sensors
Sensors are a very important part of SIMPACK. They yield the relativekinematic quantities between two markers. SIMPACK automaticallyassigns one sensor to each body that is created. However sensors canbe defined between any two markers on the MBS. They are used whenthe relative translation, rotation, velocity or acceleration between twomarkers is of interest.
The measurements taken by the sensor are from marker ‘i’ to marker‘j’ and are denoted in co-ordinates of ‘i’. The measurements are takenoff-line after the time integration.
• Select ’Sensors’ from either the pull-down menu under Elementsor from within the shortcut toolbar
• In theMBS Sensors window that appears is the sensor $S Body1,either double click on it or select it and click on
✞
✝
�
✆Modify
The dialogue box, figure GETS:5.10.17 will appear:
Again marker ‘i’ should be closer to the inertia frame, so select $M Isysfor this marker. For marker ‘j’ select $M Body1. Keep the other de-faults within the window and click on
✞
✝
�
✆OK .
GETS:5.12 -46 Saving the Model to Disk
Figure GETS:5.10.17: Define Sensors Dialogue Box
GETS:5.11 Saving the Model to Disk
As mentioned previously there is no undo facility in SIMPACK, so itis therefore necessary to reload the MBS data from the last save toremove unwanted changes to the model.
This means that it is advisable to make a habit of saving the data reg-ularly to prevent losing too much work if the model has to be reloaded.
To reload the model data from the previous save either click onthe ’Reload MBS-Model’ toolbar button or from the pull-down menuFile �
Reload
A useful function of SIMPACK is to be able to save the model under adifferent name. This can be done using the ’Save As’ option which isalso found under ’File’ and on the toolbar. This creates a copy of themodel and doesn’t change the session name.
When SIMPACK writes the model data to disk, it does so in two differ-ent files. The file FILENAME.sys contains the information about theMBS definition, whilst the file FILENAME.ani contains the informa-tion concerning the shape, colour and view definitions.
What is important to note is that when SIMPACK executes a commandsuch as time integration it reads the model data from these files. Itis therefore vital, immediately before asking SIMPACK to perform atask with the model data, that you save the model data and thereforeupdate these files.
You can save the model data either from the pull-down menu File �
Saveor by clicking on the ’Save’ toolbar button. The save function
is found in the Model Setup window.
Creating the 3D Geometry GETS:5.12 -47
GETS:5.12 Creating the 3D Geometry
The 3D geometry of bodies and reference frames consists of one or moreensembles. Every ensemble consists of one of more graphic primitivessuch as co-ordinate frames, cuboids, cylinders, prisms, etc. These primi-tives are grouped together to form a 3D ensemble. Even complex shapesproduced by CAD packages can be attached to an ensemble. Road andrailway track primitives will usually be attached to the inertia frame.The ensembles are guided by the position vector and orientation matrixof one single sensor.
When SIMPACK creates a new body it will automatically assign a de-fault sensor ensemble and primitive to the body. The default ensembleis assigned to the default sensor. In most cases you will keep this en-semble attached to this default sensor. The default graphic primitivesare a co-ordinate frame and a cuboid primitive.
Select $B Isys for modifying. If you need help refer back to GETS:5.5on modifying the reference frame.
Select✞
✝
�
✆3D-Geometry
The SIMPACK 3D Geometry window appears. This window shows theensembles and primitives that are associated with this reference frame.Under ’Primitives of Selected Ensembles’ click on
✞
✝
�
✆New as shown in
figure GETS:5.12.18:
GETS:5.12 -48 Creating the 3D Geometry
Figure GETS:5.12.18: 3D Geometry
Creating the 3D Geometry GETS:5.12 -49
In the input box that then appears you should enter the name $P axleand then click on
✞
✝
�
✆OK .
The SIMPACK Primitive Definition window appears and in this windowclick on
✞
✝
�
✆Type to change the primitive type, figure GETS:5.12.19.
Figure GETS:5.12.19: Primitive Definition Window
GETS:5.12 -50 Creating the 3D Geometry
Figure GETS:5.12.20 shows the available primitives. In this windowselect primitive type ‘Cylinder’ and click on
✞
✝
�
✆OK .
Figure GETS:5.12.20: Primitive Types List Box
You will return back to the Primitive Definition window and in thiswindow you must enter the following parameters.
Enter: diameter =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.05
length =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.2
number of planes =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁8
smooth =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁1
Edit the built-in vector matrix
Revolve primitive 90o on z–axis (gamma =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁+90 )
The dialogue box should look as follows, figure GETS:5.12.21:
Creating the 3D Geometry GETS:5.12 -51
Figure GETS:5.12.21: Completed Primitive Definition Window
GETS:5.14 -52 Manipulating the View
Click on✞
✝
�
✆OK and then again in the 3D Geometry box and then click
on✞
✝
�
✆OK in the Define Reference System dialogue box.
GETS:5.13 Graphical Representation of Body - Prism -Primitive
In the next section you will develop the body as you did with thereference frame. You will change the body from a cuboid to a prism tolook like the hand of a clock.
The steps are similar to those that you went through for applying the3D geometry to the reference frame.
• Access the body $B Body1 and click on✞
✝
�
✆3D Geometry . The
3D Geometry window appearsWithin this window you will find the default ensemble $E Body1and the default primitives of this ensemble. There is the primitive$P Body1, a co-ordinate axis representing the body referenceframe and a cuboid $P Body1 cuboid.
• Select the cuboid and click on✞
✝
�
✆Rename
• Change the name to $P Hand• Click on
✞
✝
�
✆Modify to change the primitive parameters of the hand
• Change the Primitive type to ‘Prism by Coordinates’
• Back in the Primitive Definition window change the prism thick-ness to 0.05 and the No. of shape points to 4
• In the shape/line list box enter the four shape points as follows:
Enter in 1. line: x = -0.1 y = 0.02. line: x = 0.0 y = -0.13. line: x = 0.1 y = 0.04. line: x = 0.0 y = 0.7
• Edit the built-in vector and rotation matrix
Rotate primitive −90o on y–axis (beta =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁-90 )
Rotate primitive 90o on z–axis (gamma =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁+90 )
Figure GETS:5.13.22 shows how the primitive dialogue boxshould look:
• Click on✞
✝
�
✆OK and
✞
✝
�
✆OK again to get back to MBS Define Body
and then✞
✝
�
✆OK to close this window
• Save the model
GETS:5.14 Manipulating the View
It is possible to manipulate the view in the 3D Model Setup window.You can alter the angle it is viewed from, zoom in or out, or move the
Manipulating the View GETS:5.14 -53
Figure GETS:5.13.22: Completed Body-Primitive Definition Window
model within or around the screen axes or within the Reference systemaxes.
You will learn, in this section, how to move the model within the 3DModel Setup window. However, before changing the view you shouldsave the model. You therefore only need reload the model data to getback to the original view settings.
• Select View Setup from View on the pull-down menu in the 3DModel Setup window. The following dialogue box will appear,figure GETS:5.14.23
GETS:5.14 -54 Manipulating the View
Figure GETS:5.14.23: View Set-Up Window
On/Off Line Integration GETS:5.15 -55
• Click on ✷ Standard Views . A list of standard views appears.Click on each different view
• Try clicking on ✷ Zoom/Translate/Rotate
You can see the effect the slider bars have on the view. You can tog-gle between screen co-ordinates and reference system co-ordinates todetermine the translational movement of the model within the screen.When the screen co-ordinates are selected the bottom left hand cornerof the 3D Model Setup window becomes the origin. Try also rotatingthe model around the screen using the slider bars.
One very useful feature in SIMPACK allows you to operate with 4 userdefined views. You will find these at the top of the View Setup dialoguebox. You can toggle between four views or just the one view. You canalso toggle between the four different views.
As well as the View Setup window you can also control the view byholding down the control key and one of the mouse keys. By scrollingwith the mouse and trying each of the mouse keys in turn you can seethe effect each has on the view.
It is also possible to manipulate the view from on the toolbars. Thereis a refit function, as well as a zoom in and zoom out function.
Once you have finished experimenting with the different views, reloadthe MBS model data from the previous save and you will return to theSIMPACK standard view.
GETS:5.15 On/Off Line Integration
Before you will learn how to perform the time integration, here is justa short note on how SIMPACK’s solver algorithm operates.
SIMPACK uses a particularly efficient algorithm to generate the equa-tions of motion. It is unlike any other multi-body simulation packagein that, it only generates one equation of motion for each degree offreedom which is defined by the user.
Later in the guide you will create a double pendulum model (with 2DOFs), which you will then use to produce a slider crank mechanism(with 1 DOF). SIMPACK will generate two differential equations forthe double pendulum model, but only one however for the slider crankmodel. The slider crank model has the same number of joints, buthas a constraint added. This reduces the degrees of freedom from twoto one. With the constraint added, the motion of the second body isdependent, via an algebraic equation on the motion of the first bodyand the restriction applied by the constraint. SIMPACK will thereforeonly create one equation of motion for the slider crank model.
The next stage after setting up the model is for SIMPACK to form themotion governing differential equations and then solve them.
The integration of the differential equations can be done either off-or on-line. On-line integration is when SIMPACK animates the modelwhilst performing the integration process. Off-line integration is when
GETS:5.15 -56 On/Off Line Integration
SIMPACK is told for how long to integrate for, using a start and endtime. The animation of the model is performed later by SIMPACK.
On Line Integration
• To begin integrating on-line select Time Integration from Calcula-tions in the pull-down menu within the 3D Model Setup window.The following window will appear , figure GETS:5.15.24:
Figure GETS:5.15.24: On-Line Time Integration Window
On/Off Line Integration GETS:5.15 -57
• To save the moving data to animate later, switch the Protocol,at the top of the window, from ✷ No to ✷ Yes
• To start integrating the equations and animating the model thenclick on ✷ Go . The pendulum starts to oscillate about the xaxis, which can be seen in the 3D window. The time integrationcan be followed in the SIMPACK echo area
• To stop the integration click on ✷ Stop
• When finished click on✞
✝
�
✆OK
Off Line Integration
Normally however, the integration that is performed by SIMPACK isoff-line. Off-line integration is normally used for large complex modelswith a large number of degrees of freedom. The CPU time requiredto integrate the equations may be high, which makes it unfeasible toanimate the model whilst performing the time integration.
Before starting an off-line integration, SIMPACK must be told what toperform in the integration. SIMPACK must be told the initial start timefor the integration as well as the end time. These values must be posi-tive as SIMPACK does not allow you to integrate backwards. SIMPACKalso requires the number of communication points. These communi-cation points determine how many times SIMPACK writes data to theresults’ files in the integration process. For example, an integrationtime of 10 seconds with 100 communication points would mean thatresults are available for every tenth of a second.
• From the pull-down menu in the SIMPACK user interface selectCalculation �
Time Integration �Configure
The Time Integration window will appear and in this windowenter the following parameters:
Initial Time =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.0
End Time =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁5.0
Number of Communication Points =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁101
The dialogue box should look as follows, figure GETS:5.15.25:
GETS:5.15 -58 On/Off Line Integration
Figure GETS:5.15.25: Off-Line Time Integration Window
On/Off Line Integration GETS:5.15 -59
• The integration method SODASRT will be automatically selectedas the SIMPACK default integration method. SODASRT is SIM-PACK’s standard integration integrator which is optimised for awide range of mechanical systems. You will find that this methodis appropriate for almost all cases, however for some certain casesthere are other more appropriate solvers available to the user.For example for complicated non-linearities other solver methodsare available. The wide range of SIMPACK solvers means thatvirtually any system can be integrated
Click on the✞
✝
�
✆Settings... button to see how the solver settings
can be changed.
The SODASRT window appears, figure GETS:5.15.26:
Figure GETS:5.15.26: SODASRT Window
GETS:5.16 -60 Calculating Measurements
• In this window it is possible to configure how the solver will inte-grate the equations. However at this stage, stay with the defaultsin the window. Click on
✞
✝
�
✆OK or
✞
✝
�
✆Cancel
• You will be back in the time integration window. Click on✞
✝
�
✆Save
and then✞
✝
�
✆Exit
Performing the Time Integration
Before performing the time integration it is necessary for you to save themodel. As mentioned previously when SIMPACK performs a calculationit reads the data from the model files. These files are not updated untilthe model is saved. To ensure SIMPACK is reading the correct data youmust save your model before starting the time integration.
SIMPACK is now ready for you to begin the integration process. Fromthe SIMPACK user interface select either from the pull-down menuCalculation �
Time Integration �Perform Time Integration
or click on the Perform
Time Integration Only toolbar button.
The integration process then starts. You can trace the progress ofSIMPACK in the Echo Area window.
The results from the integration process are written to 5 different files.These files contain information about the state of the model at each ofthe communication points as well as documentation about the integra-tion process.
The results are stored in the subdirectory ‘/output’ of the current di-rectory. The files have the following extensions:*.cmo *.czu *.ide *.intinfo *.ist *.izu
If the time integration process is taking too long then it is possibleto stop the time integration. This is done from the pull-down menuCalculation �
Time Integration �Stop
GETS:5.16 Calculating Measurements
It is necessary to calculate measurements to animate the results of theintegration process.
The movements of the ensembles are determined by the output datafrom the sensors. These measurements are the first measurements takenwhen the perform measurements module is executed. The next mea-surements taken are those associated with the kinematics, the appliedforces, the internal force law variables and the constraint forces. All theresults are saved in the subdirectory ‘/output’ of the current directory.
To start the perform measurements module, click on the pull-down
Animating the Results of the Integration GETS:5.17 -61
menu Calculation �Perform Measurements �
Full
or click on the Perform Measurements
toolbar button.
GETS:5.17 Animating the Results of the Integration
The animations that can be performed include:
• Time integration• Inverse kinematics• Mode shapes• Externally calculated moving data
The animation you will perform is the animation of the time integrationresults. In the Model Setup window either select Time History fromAnimation on the pull-down menu or click on the Animation of TimeHistories toolbar button. The following window then appears, figureGETS:5.17.27:
Figure GETS:5.17.27: Animation Control Window
GETS:5.0 -62 Animating the Results of the Integration
At the top of the window you will see it says ‘frame number’. Thereshould be the same number of frame numbers as communication pointsthat you entered in the Configure Time Integration window. Thereforethere should be 101 frame numbers available.
Directly underneath these frame numbers you will see the buttons whichyou use to control which frame number is displayed in the 3D ModelSetup window. Experiment with these pushbuttons to see the effectthey have on the animation. Once finished click on
✞
✝
�
✆OK .
GETS:6. The Double–Pendulum
GETS:6.1 About the Model ‘Double–Pendulum’
Figure GETS:6.1.1: Model Double–Pendulum
GETS:6.1 -64 About the Model ‘Double–Pendulum’
Data for the mechanical system ‘double–pendulum’:
Bodies:
• Body–1:mass = 4.0 [ kg ]centre of gravity (x,y,z) = ( 0, 0, -0.25 ) [ m ]
inertia tensor I =
10.0 0.0 0.00.0 10.0 0.00.0 0.0 1.0
[ kgm2]
Additional marker on body–1:built–in–vector with re-spect to body fixed Ref-Sys
= (0.0, 0.0,−0.7) [ m ]
• Body–2:mass = 2.5 [ kg ]centre of gravity (x,y,z) = ( 0, 0, -0.5 ) [ m ]
inertia tensor I =
15.0 0.0 0.00.0 15.0 0.00.0 0.0 1.0
[ kgm2]
Joints:
• Joint connecting body-1 and the inertia frame:joint mobility = rotation about x-axisinitial joint state = 0.707 [ rad ]initial angular velocity = 0.0 [ rad/s ]
• Joint connecting body-2 and body-1:joint mobility = rotation about x-axisinitial joint state = -0.2 [ rad ]initial angular velocity = 1.0 [ rad/s ]
Gravity:
• acceleration due to gravity along z–axis, g = 9.81 [ m/s2 ].
Extending the Pendulum Model to a Double Pendulum GETS:6.3 -65
Data for the graphic representation of the ‘double–pendulum’:
• Geometric parameters of body–1:Body–1 is graphically represented by a prism.
definition points =
y z−0.1 0.00.0 0.10.1 0.00.0 −0.7
[ m ]
thickness = 0.05 [ m ]
• Geometric parameters of body–2:
Body-2 is graphically represented by a cuboid.
Co-ordinates of thecuboid diagonal vec-tor:
=
x y z−0.025 −0.025 0.00.025 0.025 −1.0
[ m ]
GETS:6.2 Extending the Pendulum Model to a DoublePendulum
The first body of the double pendulum, which you have just created,looks like the hand of a clock. This has one degree of freedom, whichis a rotation about the x axis. This axis is represented by a smallcylinder. The second body of the double pendulum looks like a rodand is connected to the first body by a revolute joint which allowsrotation about the x axis only.
• Make sure the Model Setup window has been closed (i.e. the 3DModel set-up window)
• Create a new model which is identical to the pendulum model andname this model double pendulum. If you need help on copyingthe model refer back to GETS:4.2
• Finally open the pre-processor.
GETS:6.3 Adding a Marker to a Body
On all bodies, (including the kinematically driven reference system)markers can be defined. These markers are used as:
• Linking points for joints• Linking points for force elements• Reference points for sensors• Select $B Body1 in the MBS Define Body window and then clickon Markers
• From the Marker List window that then appears click on✞
✝
�
✆New
GETS:6.3 -66 Adding a Marker to a Body
and name this new marker $M Body1 1Figure GETS:6.3.2 shows how the window should look:
Figure GETS:6.3.2: Marker List for the Body
• Double click on the new marker and the MBS Define Markerwindow appears. This window allows you to edit the built invector and orientation matrix that describe the marker’s position.These co-ordinates are given relative to the body fixed referenceframe
The orientation matrix determines a constant orientation of the markerrelative to the body fixed reference frame. There are four possibleoptions to determine the orientation:
• E-Matrix (Identity matrix)• Cardan angles• 3x3 orientation matrix• 3 points (PQR-vectors)
For this model you will stay with the default, the E-Matrix.
• However change the built-in position to z=-0.7.Figure GETS:6.3.3 shows how the dialogue box should look:
If you click on✞
✝
�
✆Update 3D Scene you will see that a set of axes
appears at the bottom of the pendulum, where the marker has beenadded. This marker will be used as an attachment point to the secondbody. You will attach a joint to this marker which in turn will be
Creating a New Body and Adding a Marker GETS:6.4 -67
Figure GETS:6.3.3: MBS Define Marker
attached to a marker on the second body. Return back to the MBSBodies window.
GETS:6.4 Creating a New Body and Adding a Marker
In the MBS Bodies window click on✞
✝
�
✆New . Enter the name Body2
and click on✞
✝
�
✆OK .
Names of bodies begin with $B SIMPACK will automatically add thisfor you.
When this new body is created SIMPACK automatically assigns defaultsettings for the mass and inertia tensor. SIMPACK also automaticallyassigns:
• A marker to the body
• A default 3D geometry including two primitives to represent thebody graphically (a co-ordinate axis and default cuboid)
• A zero degree of freedom joint which connects this body to theinertia frame
• A sensor between the inertia frame and the body fixed frame
The MBS Define Body window should have appeared. Enter in thefollowing values for the model:
GETS:6.4 -68 Creating a New Body and Adding a Marker
mass = 2.5Centre of mass z = −0.5Ixx = 15Iyy = 15Izz = 1
I-Tensor relative to the centre of mass
Figure GETS:6.4.4 shows how the completed dialogue box should look:
Figure GETS:6.4.4: Definition of the Second Body
• Edit the 3D geometry by clicking on✞
✝
�
✆3D Geometry
• Select $P Body2 cuboid in the Primitives List box• Click on
✞
✝
�
✆Rename and change the name to Rod
• Click on✞
✝
�
✆Modify to modify this element. The default primitive
type is a cuboid, which you will keep
• Enter the following lengths:
Creating a New Body and Adding a Marker GETS:6.4 -69
Enter x =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.05
y =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.05
z =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁1.0
These lengths are entered by clicking on each of the input lines ‘lengthin x’ ‘length in y’ and ‘length in z’ in the parameter box.
If you look in the Model Setup window you will see that the rod’s centreis at the origin of the inertia frame. To move the rod, enter in the ‘buildin vector box’ the following data:
Shift the cuboid on the z–axis: z =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁-0.5
The Primitive Definition window should look as follows, figureGETS:6.4.5:
Figure GETS:6.4.5: Definition of the Primitive for the Second Body
GETS:6.5 -70 Modifying a Joint
• Select✞
✝
�
✆Back To Body Definition to close this window
• You now need to add a marker to this body. Click on✞
✝
�
✆Markers
and then select✞
✝
�
✆New
• Enter the name as Body2 1• Click on
✞
✝
�
✆Modify and then change the Built-In Position:
Shift the cuboid on the z–axis: z =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁-1.0
• Click on✞
✝
�
✆OK
A marker should appear at the bottom end of the rod. You should nowreturn to the MBS bodies window.
GETS:6.5 Modifying a Joint
As mentioned previously when a body is created it is assigned a jointwith zero degrees of freedom. This joint is also attached to the inertiaframe. The joint on body2 has to be modified so that it is connectedto both body 1 and body 2. The joint to be used is a revolute jointabout the x-axis.
• Select Joints from either the pull-down menu under Elements orclick on the toolbar button
• Double click on the joint $J Body2. The Define Joint windowappears
• Select✞
✝
�
✆From Marker i . The Marker List box should appear
• Select $M Body1 1 and click on✞
✝
�
✆OK
• Select✞
✝
�
✆To marker j and then select $M Body2 and click on
✞
✝
�
✆OK
• Select✞
✝
�
✆Joint Type and in the Joint List window select ‘Revolute
Joint al’ and click on✞
✝
�
✆OK
• Enter the initial joint state and velocity as follows:Position = -0.2Velocity = 1.0
If the dialogue box looks the same as figure GETS:6.5.6 click on✞
✝
�
✆OK
Modifying a Joint GETS:6.5 -71
Figure GETS:6.5.6: Definition of the Joint $J body2
GETS:6.0 -72 Modifying a Joint
You should now save your model and as described in section GETS:5.15begin the time integration and model animation. If you can, try per-forming the time integration without referring back.
GETS:7. Creating and Importing aSubstructure to a Model
In this section you will build a substructure and then import this sub-structure into your main model. You will add a third part to thestructure which will be another pendulum body. This will be attachedto the lower end of the second body.
The SIMPACK substructures modelling element facilitates the inclusionof MBS substructures into other models. When building complex mod-els, such as a car with a detailed representation of the suspension sys-tem, it may be that some parts of the mechanical structure are identicalto other structures or are a mirror image of other structures. SIMPACKallows substructures to be defined, which can be used to reduce themodelling effort required for systems with identical mechanical struc-tures. Any mechanical system model that has been built in SIMPACKcan be defined as a substructure. Substructures can be used more thanonce within the same model and they can also be used in any othermodel.
Example
In order to build a model of a car, the suspension system only needs tobe defined for one side of the vehicle as a substructure. The suspensionsystem on the other side of the vehicle is created simply by reflectingthe substructure which has already been defined.
GETS:7.1 Creating a Substructure
The substructure will be completely separate to the main model. Ifchanges are made to the substructure then it is not necessary to updatethe substructure in the main model as this is done automatically bySIMPACK. This is a particularly useful feature when the substructureis used by a number of models.
Ensure that the pre-processor is running with the double pendulummodel. You should also save the model.
You will use the body $B Body2 as the basis of the substructure. Youwill remove $B Body1 and then save the model as a different name.This model will now be used as the substructure.
First of all it is necessary to change the ‘From marker’ of joint $J Body2.This marker is currently attached to a marker on body $B Body1. SIM-PACK will not allow you to remove $B Body1 until the joint is connectedto another structure. When the body is removed all the markers, jointsetc. will also be removed.
GETS:7.1 -74 Creating a Substructure
• In the Joints dialogue box select $J Body2. For the ‘From markeri’ you should select the inertia frame $M Isys
You will see that $B Body2 moves and is now attached to theinertia frame.
• You should now remove $B Body1. This is done by going into theBodies window. You should select this body and click on button✞
✝
�
✆Remove . The Remove MBS Element window appears which
shows all the elements which will be removed. Click on✞
✝
�
✆OK to
confirm that you want to remove all these elements
What you are left with is the substructure that you will importinto the main model.
• In the 3D Model Setup window you should click on the SaveAs toolbar button. Name the MBS configuration as pendu-lum substructure
• You should now click on the Reload MBS toolbar button in the3D Model Setup window. This reloads the previously saved modeldouble pendulum
You have now created the substructure under the filename pendu-lum substructure, which can be imported into the double pendulummodel.
• You should either click on the Substructures toolbar button orclick on Substructures from within Elements. The Substructureswindow will appear.
• In this window click on✞
✝
�
✆New and the SIMPACK Substructure
window will appear.
It is from within this window where you select which file will beloaded.
• Click on✞
✝
�
✆File . The MBS Element Info List window appears.
This window displays all the files within the current directory.Any of which could be used as a substructure
• Select the substructure you have just created, pendu-lum substructure and in Name in the MBS, enter Body3. Thenames of all substructures begin with $S SIMPACK will auto-matically assign this for you. The window should look as follows,figure GETS:7.1.1:
Creating a Substructure GETS:7.1 -75
Figure GETS:7.1.1: Substructure Dialogue Box
• Finally click on✞
✝
�
✆Load substructure . The substructure which
you have just created will appear and is attached to the origin ofthe inertia reference frame. It is necessary to attach the end ofthe substructure to the body $B Body2
• Open the MBS Elements Joints window. You will now see thejoint $J S body3 J body2. Double click on this joint and changethe ‘From Marker i’ to $M body2 1, which is a marker at thebottom of $B Body2
The 3D Model Setup window should look as follows, figureGETS:7.1.2:
Figure GETS:7.1.2: On-Line View of the Structure
GETS:7.0 -76 Creating a Substructure
• It is now possible to perform the time integration
• For the next stage of the Getting Started the substructure is notrequired and should be removed. This can be done by clicking on✞
✝
�
✆Remove in the Substructures window with $S body3 selected
For more information on substructures see section: HWTU:2.6 in thehow to use section of the documentation or section SIMREF:4.12 inSIMPACK fundamentals.
GETS:8. Adding a Force Element tothe Double Pendulum Model
In this chapter you will attach a spring between a marker at the end ofthe body named hand and a marker on the inertia frame.
GETS:8.1 Adding the Force Element
Data for the mechanical system ‘double pendulum force’:
The force element is a spring–damper combination placed between thehead of the hand and a marker on the ‘inertia frame’.Coupling points of the spring:
• head of the hand: (marker $M Body1 1)• new marker on the inertia frame:built–in vector =
(0 1.7 0.0
)
Data for the spring:• length of the unloaded spring: lo = 0.5 m• stiffness of the spring: c = 50 N/m• damping coefficient of the spring: d = 5 Ns/m
You will use the double pendulum model as the basis for the new model;double pendulum force.
Copy the double pendulum model to double pendulum force and openthe new model. Start the pre-processor by clicking on the Model Setuptoolbar button
You will define a spring-damper between a new marker on the inertiaframe (marker $M I1 on inertia frame $B Isys) and the head of thehand ($M Body1 1 on body $B Hand).
• First you must create the coupling point $M I1. Modify the in-ertia frame $B Isys and create the new marker $M I1
• Set the built-in position to y=1.7. If you are having problemsrefer back to GETS:6.3 under adding a marker to a body
• Select Force Elements from under Elements in the pull-downmenu Elements �
Force Elementsor from the toolbar and
create a new force element and call it Force1
• Select✞
✝
�
✆From Marker k in the MBS Force Element box and
pick marker $M I1 as the first coupling point
GETS:8.1 -78 Adding the Force Element
• Select✞
✝
�
✆To Marker l as the second coupling point and pick
marker $M Body1 1
• Click on✞
✝
�
✆Force Type . The Force Type List window opens,
which contains a list of the different force types. The differentforce types are located in folders, i.e. for a tyre force element,then opening the folder ‘Tyres’ will display the available tyre forceelements see fig GETS:8.1.1.
Figure GETS:8.1.1: Force Element Folders
Select the force Spring-Damper parallel PtP, which is located inthe ‘Spring-Damper’ folder. and click on
✞
✝
�
✆OK
• Enter the following spring parameters:length of the unloaded spring: l 0 =
✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.5
stiffness of the spring: c =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁50
damping coefficient of the spring d =✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁5
Figure GETS:8.1.2 shows how the MBS Force Element box should look:
Adding the Force Element GETS:8.1 -79
Figure GETS:8.1.2: MBS Force Element
GETS:8.1 -80 Adding the Force Element
Click on✞
✝
�
✆OK and save your model
You can now integrate the model and then animate it. The doublependulum force model should now oscillate about a new equilibriumposition.
Plots of the Results GETS:8.2 -81
GETS:8.2 Plots of the Results
In SIMPACK there are two different ways of creating plots of the resultsof an integration. The quicker way is via the 2D state plot. The otherway to produce plots is via the 2D general plot module. The 2D stateplot module can be run immediately after the time integration, but canplot only the joint states. The 2D general plot uses the results fromthe sensors. Once the measurements have been performed it is possibleto see the dynamic relationship between any two sensors on the body.
2D State Plots of the Joint States and Velocities
The 2D state plots can be accessed through either the pull-down menuon the user interface or by clicking on the state plot toolbar button.
• Open the PostProcessing: 2D Plots of State window
• Select in this window zg(1):$J Body1 . This will display the
position in time of the joint $J Body1. This can be seen in thefigure below, figure GETS:8.2.3:
Figure GETS:8.2.3: 2D Plot of States
• Try clicking on some of the other plots that are available. zgp
is velocity whereas zg is position. The various different plots
are brought up in the window as you click on them
General 2D plots
If you would like customised plots of the time integration results thenit is necessary to use 2D general plots. To use this module it is neces-sary to calculate the measurements, after the time integration has beenperformed.
• Click on the Perform Measurements toolbar button or from the
GETS:8.2 -82 Plots of the Results
Pull-down menu click on Calculation �Perform measurements �
Full
• Select General Plots from either the toolbar or from the pull-downmenu under PostProcess
• The SIMPACK 2D window appears, in which you can configurethe plotting window. This window contains a sub-window withthe General Plot, plotting area. You can have up to 50 differentpages containing up to 12 different active plots
• In the figure position matrix click inside the top left hand frame• Ensure that curve 1 is selected• Select axis x and click on
✞
✝
�
✆Modify . Select time as the variable
• Select axis y and again click on✞
✝
�
✆Modify . Select State-
Vector X and in the window ‘Select MBS Element’ choosejoint.st.pos(1):$J Body1 and click on
✞
✝
�
✆OK A plot should
appear showing the variation of joint state $J Body1 with time
• As mentioned it is possible to add a further curve to this plot.Select curve 2 and as you have just done select time as the xaxis and then select joint $J Body2 as the variable for the y axis.SIMPACK will display both these curves on the same set of axes
• You can also add a further plot to this window, but on separateaxes. In the figure matrix click on the square in the matrix shown,figure GETS:8.2.4:
Figure GETS:8.2.4: Where to Click
Plots of the Results GETS:8.2 -83
• Select time as the x axis• Select axis y and click on
✞
✝
�
✆Modify
• Select Applied Force• The ‘Select MBS Element’ window appears and in this windowyou will see $F Force1 and select the co-ordinate y as shown infigure GETS:8.2.5
Figure GETS:8.2.5: Select Force Window
There should now be two plots in the window. One showing thetime history of the joint states, the other shows the time history ofthe applied force. The view of the window should look as follows,figure GETS:8.2.6.
GETS:8.3 -84 Static Equilibrium
Figure GETS:8.2.6: 2D General Plot Window
Try adding more curves to this plot page and in different plotpages.
• Once finished select Exit from File on the pull-down menu. Itwill then ask you if you wish to save the 2D configuration beforeclosing. If you would like to have the same plot windows nexttime you open the general plots window in this file, then click on✞
✝
�
✆Yes , otherwise click on
✞
✝
�
✆No
GETS:8.3 Static Equilibrium
SIMPACK is able to calculate the static equilibrium of the multi-bodysystem. A system is said to be in static equilibrium when the sum ofall the accelerations is zero. The velocities may not necessarily be zerowhen the system is in static equilibrium. For example, a car travellingalong a flat road at constant velocity is said to be in static equilibrium.
There are various different iteration methods available for solving thenon-linear set of equations. The default setting is Newton’s method.
• Set the velocities of the joints to zero and then save the model• Under Calculation on the pull-down menu in the SIMPACK userinterface select Static Equilibrium (there is also a static equilib-rium toolbar button). The Static Equilibrium window appears,figure GETS:8.3.7:
Calculation of the Nominal Force Parameters GETS:8.4 -85
Figure GETS:8.3.7: Static Equilibrium Window
• Keep all these settings and then click on✞
✝
�
✆Perform
The SIMPACK Static Equilibrium Results window appears withboth joint states when the system is in static equilibrium. Clickon
✞
✝
�
✆OK
• Click on Save and when the SIMPACK Save window appears keepthe default saves. It is necessary to save the states if you wishto display the static equilibrium of the model. You will return tothe Static Equilibrium window where you should click on
✞
✝
�
✆Exit
• In the Model Setup window either click on the toolbar buttonReload MBS-model or from the File pull-down menu click onReload. The static equilibrium position of the model will now bedisplayed in the Model Setup window
GETS:8.4 Calculation of the Nominal ForceParameters
The nominal force parameters module determines the parameters forthe force elements so that the system is in equilibrium at a given po-
GETS:8.4 -86 Calculation of the Nominal Force Parameters
sition. This can be seen as the complementary function to the staticequilibrium module.
Both these modules work out when the system is in static equilibrium.The difference is:
• Static equilibrium calculates the position in which the model isin equilibrium with a defined set of physical constraints
• Nominal force parameters calculates the necessary physical pa-rameters, so that the system is in equilibrium at a given position
First of all you must set the joint states
• Set joint state $J Body1=1.0• Set joint state $J Body2=-1.0• Set velocity of both joints to zero• Click on Calculation from the pull-down menu in the user in-terface and then on Nominal Force Parameters or click on theNominal Force Parameters toolbar button. The Nominal Forcewindow appears, figure GETS:8.4.8. Stay with the Default valuesfor the solution method
Calculation of the Nominal Force Parameters GETS:8.4 -87
Figure GETS:8.4.8: Nominal Forces Window
• You must now select which of the force parameters will be deter-mined by SIMPACK in the nominal force calculations. Click on✞
✝
�
✆Selection of Force Parameters . The Nominal Force Param-
eter List window appears
• Click on✞
✝
�
✆New to define a new force element to be added to the
nominal force parameter list. The Nominal Force Element Listwindow appears
• Select the only force available $F Force1. The Select NominalForce Parameters window appears
For this analysis you will calculate the force required from thespring for the system to be statically determined.
• In this window select Stiffness and click on✞
✝
�
✆OK and you will
then return to the Nominal Force Parameters List window. Thisshould now look as follows, figure GETS:8.4.9:
• Click on✞
✝
�
✆OK and you will now be back to the Nominal Forces
window
GETS:8.5 -88 Eigen Behaviour
Figure GETS:8.4.9: Nominal Forces Parameter List
• Click on✞
✝
�
✆Perform and SIMPACK will display the spring force
required for the system to be in static equilibrium
• Click on✞
✝
�
✆OK and you will then return to the Nominal Forces
window. Click on✞
✝
�
✆Save to save the results for comparison with
the eigenvalue solution. Keep the default save settings and thenclick on
✞
✝
�
✆Exit
GETS:8.5 Eigen Behaviour
The SIMPACK Eigenvalue module linearises the non-linear equations ofmotion and calculates the eigenvalues and eigenvectors.
The state about which the linear equations can be calculated include:
• Nominal state x 1, used as the initial state for the time integration• Linearisation state x 1, used as the initial state for the time inte-gration
• End state, x end of integration run 1• End state, x end of integration run 2• An arbitrary state x i calculated by time integration from t=t 0to t=t end in i=1 to ntout steps
• Either select Eigenvalues from the pull-down menu or click on theEigenvalues toolbar button. The Eigen Values window appearsfigure GETS:8.5.10
• Choose initial state as the state for linearisation and then clickon
✞
✝
�
✆Perform . The eigenvalues are displayed in this window
• Click on✞
✝
�
✆Exit to close this window
Animation of the Mode Shapes
It is possible for SIMPACK to display the mode shapes in the 3D ModelSetup window.
Eigen Behaviour GETS:8.0 -89
Figure GETS:8.5.10: Eigen Values Window
• Click on animation from the pull-down menu in the 3D windowand then select Mode Shapes. The SIMPACK animation controlwindow appears
• Select one of the two natural frequencies displayed in the list boxand then click on the play button as shown. SIMPACK begins theanimation of the selected mode
• Click on the stop button and then select the other mode whichcan be animated in the same way
GETS:8.0 -90 Eigen Behaviour
GETS:9. Addition of a Force Elementto be Used as a Bump Stop
In this section a force element will be placed in between the inertiaframe and the bottom of the second body ($B body2). The modeldouble pendulum will be used as the basis for this exercise.
This force element is a single sided contact element. The behaviour ofthis element will therefore be non-linear over time. When integratingover time these sudden changes can often cause problems for integrationmodules. If the step size is too large then the integrator may not ‘see’ adiscontinuity which is present and may carry on the integration processas if it didn’t exist.
The solver in SIMPACK is particularly adept when coming across dis-continuities. The following exercise will demonstrate SIMPACK’s capa-bilities in this area of Multi body system dynamics.
• Exit the pre- and post-processor and then copy the dou-ble pendulum model. Name this copied model dou-ble pendulum bumpstop. You should then open this model
• Open the MBS Force Elements window and create a new forceelement. Call this new force element bump
• Select the Force element type ”Unilateral Spring-Damper Cmp”,which is found under the tree item: ”Contact.”
• Select $M Isys as the ‘From Marker k’
• Select $M body2 1 as the ‘To Marker l’
• In the line ‘Contact for y greater than 0’ you should enter in thevalue -1 000 000
• Finally click on✞
✝
�
✆OK to close the MBS Force Element window
It is now necessary to perform the time integration to see the effectthat this bump stop has on how the pendulum behaves. To see whathappens within the SIMPACK solver it is best to use the Off-line timeintegration module.
• Open the SIMPACK Time Integration window from the SIMPACKuser interface window. Calculation �
Time Integration �Configure
• The SODASRT integration should already be selected, if not se-lect it from the pop-down menu ‘Integration Method’. Click onthe button
✞
✝
�
✆Settings... The ‘Time Integration - SODASRT’ win-
dow will appear. You have the choice under Root Functions,
GETS:9.0 -92 GETS:9. ADDITION OF A FORCE ELEMENT TO BE USED AS A BUMP STOP
whether SIMPACK will Ignore or Locate State Events. You shouldselect ‘Locate State Events’. By selecting Roots enabled, SIM-PACK will detect when a root is found and change the integrationstep size accordingly. This ensures these discontinuities withinthe integration process are picked up by the solver
• Click on✞
✝
�
✆OK to return to the Time Integration window. You
should set the End time as 25 and the number of communicationpoints as 1000
• Exit this window and start the SIMPACK time integration module.In the SIMPACK Echo Area TimeInt window you can follow theprocess of the SIMPACK solver. As you have told SIMPACK todetect the roots, you will see that as the solver progresses, thateach time the SIMPACK solver detects a root it will display thisin the Echo Area
• You should now animate the model and see the effect this bumpstop has on the motion of the double pendulum system
GETS:10. A Slider Crank Mechanism
GETS:10.1 About the Slider Crank Mechanism
Figure GETS:10.1.1: Slider Crank Model
In this final section of Getting Started you will learn how to developthe double pendulum force model into a slider crank mechanism. Youwill restrict the motion of the marker at the end of the second body soit is free to move only in the y direction.
GETS:10.2 Extending the Double Pendulum ForceModel to a Slider Crank
• Exit the pre- and post-processor and then copy the dou-ble pendulum force model. Name this copied model slider crank.
• Enter the pre-processor so the 3D Model Setup window appears
• You should now modify the joint states so they are as follows:Joint $J Body1 state=-0.2 and velocity=0.2 Joint $J Body2state=0.4 and velocity=0.0 Reset force parameter to c=50N/m
GETS:10.3 Defining a Constraint (Closed Loop)
A ‘Constraint’ is used in SIMPACK to create kinematically closed sys-tems. The constraint restricts the relative motion between two markers.
GETS:10.3 -94 Defining a Constraint (Closed Loop)
SIMPACK distinguishes between ordinary joints and constraints as do-ing so allows SIMPACK to create the minimum number of equationsrequired to define the system.
This constraint will be defined between two markers.
• Click on Constraints from within the Elements pull-down menuor click on the Constraints toolbar button
• Create a new constraint with the name $L Loop (The procedureis the same as for creating a new body). Double click on this con-straint and the Define Constraints window appears. SIMPACK au-tomatically defines this constraint from the inertia frame marker‘i’ to the inertia frame marker ‘j’. All the rotational and transla-tional constraints are, by default, set to zero
• Select marker $M I1 as Marker i
• Select marker $M Body2 1 as Marker j
• Click on✞
✝
�
✆Constraint Type . The Constraint List window ap-
pears
• Select the User Defined Constraint and click on✞
✝
�
✆OK you
will now return to the Define Constraints window
• Click on the input line Lock Transl. in z of M K and in
the SIMPACK Flags window that then appears select ‘locked.’The Define Constraints window should look as follows, figureGETS:10.3.2:
Dependent and Independent Joints GETS:10.4 -95
Figure GETS:10.3.2: Define Constraints Dialogue Box
GETS:10.4 Dependent and Independent Joints
In systems with closed loops, due to the kinematic tree structure, thereare more joint state variables than are required to define the position ofthe system. For a system to function there must be the same numberof dependent variables as loop closing conditions. SIMPACK’s defaultsetting for joints is dependent.
For this example, with two joints and one constraint, it is not possiblefor the user to define joint states for both joints as it is likely thatthe constraint would no longer apply. The position of the dependentjoint will be determined by both the constraint and the other jointstate. What this means in SIMPACK is that dependent joint states aredetermined by both a combination of the independent joint states andthe restrictions imposed by the constraints.
• In the Define Constraints window click on✞
✝
�
✆Assemble System
If there are the same number of loop closing conditions to depen-dent joint states then SIMPACK will calculate the initial positionand then display it in the 3D window, otherwise SIMPACK will
GETS:10.4 -96 Dependent and Independent Joints
start the Check State Dependence window. Your model currentlyhas two dependent joints, that means the Check State Depen-dence window will open. At the top of this window SIMPACKstates what the problem with the model is
• In this window select joint state joint.st.pos(1):$J Body1
• In the window that then appears select Independent State. TheCheck State Dependence window should look as follows, figureGETS:10.4.3:
Figure GETS:10.4.3: Check State Dependence Dialogue Box
• Click on✞
✝
�
✆OK . You will then be back at the Define Constraints
window
• Click on✞
✝
�
✆Assemble System . SIMPACK will now calculate the
new initial position The model should look as follows, figureGETS:10.4.4:
Dependent and Independent Joints GETS:10.4 -97
Figure GETS:10.4.4: View of the Constraint
• Click on✞
✝
�
✆OK
GETS:10.5 -98 Exercises
GETS:10.5 Exercises
• Save your model• Perform time integration, static equilibrium, eigenvalues, etc
• Try varying the initial state and velocity of $J Body1 in MBS De-fine Joint and calculate the new initial positions. It is interestingto see how the slider crank responds to different initial states andvelocities
• You can also try changing joint1 to dependent and $J Body2 toindependent and then editing the state and velocity of joint2. It ispossible to edit whether the joints are independent or dependentin the MBS Define Joint dialogue box. If you click on the inputline Initial State then in the window that then appears you havethe choice whether the joint is dependent or independent
On-line Kinematics GETS:10.6 -99
GETS:10.6 On-line Kinematics
You will use the slider crank model you have developed. You will learnhow to manipulate the joint states on-line and display their position inthe Model Setup window. You will do this by controlling the state of$J Body1 with the use of an interactive slider bar.
• Copy the slider crank model to slider crank online kinematicsand open this model in the pre-processor
• Ensure that joint $J Body1 is as follows:State =-0.2 and velocity=0.2
• Check, within the Joints Modelling Element, that joint $J Body2is dependent and joint $J Body1 is independent
Defining a Slider Bar
Slider bars are used in on-line kinematics to control the motion of themodel. The slider bars are used in the Kinematics window.
• Click on Kinematics from the pull-down menu Calculations inthe 3D Model Setup window. The Kinematics window will ap-pear. Click on
✞
✝
�
✆Define Interactions as shown below, figure
GETS:10.6.5:
GETS:10.6 -100 On-line Kinematics
Figure GETS:10.6.5: Define Interactions
The SIMPACK 3D MBS interactions window appears
• Click on the pop-text item Interaction 1 and you will see that upto 6 different on-line interactions can be defined. Each of thesecorresponds to an interaction in the Kinematics window. SelectInteraction 1
• Click on the pop-text window Parameter Type and in the pop textwindow that appears select Joint Position State. The SIMPACKMBS Element window appears with the two joints. As you aregoing to control the state of joint $J Body1 then select this joint
• Enter the following information:Parameter Id:
✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁1
Initial Value:✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁-0.2
On-line Kinematics GETS:10.7 -101
Increment:✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁0.15
3D–description text:✞
✝
�
✆
✄✂�✁✄✂�✁✄✂�✁joint state body1
The window should look as follows, figure GETS:10.6.6:
Figure GETS:10.6.6: MBS Interactions
• Click on✞
✝
�
✆Apply and then
✞
✝
�
✆OK and then click on
✞
✝
�
✆OK in the
Kinematics window
• Save your model
Interactive Kinematics
• Open the Kinematics window again from the Calculations pull-down menu in the 3D Model Setup window. You will see that thefirst slider bar is named as joint state body1. You can now usethis slider bar to control the model
• Click on the slider with the mouse and you will then be able tomove the slider bar using the mouse, which in turn will controlthe state of joint $J Body1 as shown in figure GETS:10.6.7:
• Once finished click on✞
✝
�
✆OK
GETS:10.7 -102 Inverse Kinematics
Figure GETS:10.6.7: Interactive Kinematics
GETS:10.7 Inverse Kinematics
In this section you will learn inverse kinematics. This module calculatesthe forces and accelerations occurring when a model moves through apredetermined motion. A constant velocity or velocity profile could beused to describe the motion of a joint.
In this section you will modify the joint of Body1 so it is a constantvelocity joint.
The model must be completely statically determined (0 degree of free-dom) if you wish to perform on-line kinematics. SIMPACK has jointswhich have a completely determined motion and therefore 0 degrees offreedom. You will use one of these joints in this example. They arenormally referred to as rheonomically driven joints.
Inverse Kinematics GETS:10.7 -103
• Copy the slider crank model to slider crank inv kin• Change joint $J Body1 to a constant angular velocity joint, figureGETS:10.7.8
Figure GETS:10.7.8: Selection of the Rheonomically Driven Joint
• Change the other parameters for the joint so they are as follows:Model Data of the modified joint $J Body1:
Type : Joint with constant velocityAxis : Rotational motion about x–axisinitial state of the joint : -0.2 [rad]constant angular velocity : 0.5 [rad/s]
The MBS Define Joint window should look as follows, figureGETS:10.7.9:
GETS:10.7 -104 Inverse Kinematics
Figure GETS:10.7.9: Joint Definition
• Click on✞
✝
�
✆OK
Configuration of the Inverse Kinematics Solver
Before starting the inverse kinematics module you must configure thesolver, as you did for the off-line integration module.
• In the SIMPACK user interface, from Calculations on thepull-down menu select Inverse Kinematics and then ConfigureCalculations �
Inverse Kinematics �Configure
The Inverse Kinematics window
appears. Enter the following data:
Initial Time = 0.0End Time = 100Number of Output Points = 200Initial and end time define when the inverse kinematics startsand stops. The number of output points refers to how manytimes SIMPACK saves the results within the simulation.
• Select First Positions then Velocities The window should
Inverse Kinematics GETS:10.0 -105
look as follows, figure GETS:10.7.10:
Figure GETS:10.7.10: Inverse Kinematics Window
• Click on✞
✝
�
✆Save and then on
✞
✝
�
✆Exit
• Save your model
Performing Inverse Kinematics
You are now ready to start the inverse kinematics module.
• From the SIMPACK user interface select Calculations from thepull-down menu and then Inverse Kinematics and then Perform.SIMPACK starts the calculation. The progress of the solver isshown in the SIMPACK Echo Area
If the calculation is taking too long you can stop the solver moduleby clicking on stop under Calculation and then Inverse Kinematicsfrom the pull-down menu.
• It is now possible to animate the results. You must first performmeasurements from the SIMPACK user interface. You should an-imate the time history and then open the General Plots windowwhere you can plot the joint positions, accelerations as well as theforces applied
• It is also possible to integrate the model on-line from within Cal-culations in the Model Setup window
GETS:10.0 -106 Inverse Kinematics
GETS:11. How to Move On
You have now completed the getting started guide and you should nowhave a good understanding of how to use SIMPACK to build your ownMBS model. You can now go on and build your own models in the SIM-PACK pre-processor. Once you have defined your model in SIMPACK,you should be able to solve it and then manipulate the results withinthe post-processor.
For a brief description of the available SIMPACK handbooks see thesection ‘What to find where.’
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