SIMPACK
Getting Started
SIMPACK Release 8.624th September 2003/SIMDOC v8.607
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 T he 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 T he 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
5Pendulum 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 T ime 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 Model 7.1 -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
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
GETS:1.
Introduction to SIMPACK
SIMPACK: (SImulation of Multi-body systems PACKage)GETS:1.1
The Software: What are you intending to
do?
The SIMPACK software package is a tool to assist engineers to model, simulate, analyse and design all types of mechanical system, such as vehicles, robots, machines and mechanisms. It is able to analyse vibra-tional behaviour, calculate forces and accelerations as well as describe and predict the motion of multi-body systems.
The basic concept ofSIMPACK is to create the equations of motion for mechanical and mechatronic systems and then from these equations, apply various different mathematical procedures to produce a solution (e.g. time integration). TheSIMPACK model is built up using the SIM-PACK modelling elements. SIMSIM-PACK will then automatically generate the 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 symbolic code allows the user to export the SIMPACK model as standard FOR-TRAN or C code which can be run independently, for example in real time, in a ‘hardware in the loop’ environment.
The software has a comprehensive range of modelling and calculation features, together with a user interface well adapted to an engineer’s needs. 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 whichSIMPACK has been applied. • Automotive vehicles • Tracked vehicles • Robotics • Machine tools • Printing machines • Packaging machines
GETS:1.3 -8 Program Structure
• Dynamics of spacecraft • Electrical machine design • Biomechanics
GETS:1.2Modes of Analysis
A wide range of analysis features are available to analyse and design dynamic 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 interfaces to 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 the MBS. It also generates all the necessary data for SIMPACK to perform the numerical evaluation methods.
• It prevents the user from creating inconsistent models. Logical data checks of the input deck are made by SIMPACK as well as calculations performed on-line for closed loop systems to ensure that the model is viable.
• It provides help on all menu items. Thus the necessary ‘manual research work’ is reduced to a minimum.
• It gives the engineer complete control of the model creation and simulation processes.
GETS:1.4
Pre-processing (Model Set-up)
In SIMPACK, the pre-processor Model Setup window is a graphical 3D window. At each step of the modelling process the user has a direct graphical impression of the system. The model data is stored in the MBS database which is used as the basic input for aSIMPACK analysis. It is possible to access this data which is user readable and represents a clear description and documentation of the MBS. This data is in ASCII format 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 their model. CommonSIMPACK models include suspension or other complex joint kinematics, force models for hydraulics, various tyre type models, aerodynamics models, etc. Subsystem modelling techniques enable the user to establish complicated non-standard kinematical and/or force systems. User written subroutines extend the modelling options. In order to represent flexible bodies, several pre-processors can be used to supply the SIMPACK computation modules with flexible body data. SIMPACK is an open system which possesses various links to external standard software products. For arbitrary flexible geometry, a file inter-face to FEM programs is available. This gives access to mass, stiffness and damping matrices as well as to the associated second order terms. In addition, loads computed by SIMPACK can be transferred to the FEM code. For the purpose of incorporating physical and graphical CAD 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 of the modelling process. It is also possible to perform SIMPACK on-line calculations from the CAD package and to have the results presented in the CAD environment. In general this feature is not guaranteed by using file interfaces alone.
SIMPACK may also be linked as a fully non-linear tool into non-linear optimisation and control tools such as MATLAB, SIMULINK, etc. This allows the use ofSIMPACK and its parameter variation capability to be used 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 control design tools. A further link is provided to external post-processing tools in addition to the extensive internal post-processing capabilities of SIMPACK.
The 2D and 3D visualisation tools enable the user to view simulation results in many different forms. These include tables, plots and real-time animation of the graphical models created by SIMPACK.
GETS:2.
Introduction to the
SIMPACK Getting Started Guide
The purpose of this guide is to introduce the user to SIMPACK and its features. After completing this guide the user will have learnt many of the features of SIMPACK and will be able to start modelling and simulating their own mechanical systems.
It is estimated that it will take the user approximately 10 hours to complete the Getting Started guide. It is possible however, to save the model at any stage and then return at a later date. No previous experience of multi-body systems software or any understanding of the theory 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 apply what has been previously learnt. New features are introduced at every stage ensuring the user becomes familiar with many of the features of SIMPACK by the end of the Getting Started guide. The guide contains, within the text, snapshots of SIMPACK dialogue boxes to ensure the user is entering the data correctly.
GETS:2.1
SIMPACK: The Software
SIMPACK is a multi-body simulation package which allows the user to simulate and model complex mechanical systems. The software also allows the inclusion of electrical, hydraulic and pneumatic elements. The purpose of the software is to improve the design process involving multi-body systems. The user is likely to see reduced lead times, a simpler design process and at the end, a better product.
The more common requirements of the user fromSIMPACK include any from 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
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, with the 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 possible use 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 Physical System
Step 2. Development of a Mechanical Model
• The mechanical structure is divided into bodies and joints, the interconnecting structures
• Constraints are then defined, which contsrains the mobility of the elements by removing degrees of freedom
From Concept to Simulation GETS:2.2 -13 α7 β9 β8 z7 z1 γ1 z2 β2 α2 β1 β γ1 α1 x1 z3 α3 β4 β5
Figure GETS:2.2.2: Mechanical Model
Step 3. Provision of the Model Parameters
• The physical parameters for the model such as the mass, moments of inertia and centre of mass for the various different bodies are defined
• 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 the force 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. T his data 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 in the 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 results of 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 SIMPACK Getting Started Guide. The guide takes the user through building up a relatively simplistic model, which begins as a pendulum and is developed into a slider-crank mechanism. Along the way the user is introduced to SIMPACK’s extensive modelling features. The features which the user will meet are detailed as follows:
• They will be introduced to the pre-processor and the main build commands, which include New, Modify and Remove. The user will learn how to create the basic physical model using reference frames, bodies, markers and joints. As well as the pull-down menus, the user will learn how to access features using the toolbar shortcut buttons.
After developing the model the user will learn how to solve it in SIMPACK (both off- and on-line integration methods will be taught). Following this, the user will be shown how to access and use the features within the post-processor
• They will be taught how to assign sensors to the structure which allow 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 to assign primitives to the bodies, joints etc. and therefore create a physical 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 the
Getting Started guide. These include a number of the toolbar functions. However help topics are available when the user wishes to use any of these functions
GETS:2.0 -16 Some Useful Hints When Working with SIMPACK
GETS:2.4
Some Useful Hints When Working with
SIMPACK
• Work through the model set-up one step at a time
• Be aware that SIMPACK can only provide the solution of the model 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 working
in a SIMPACK session
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 ‘SIMPACK v.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:3.2Exiting SIMPACK
From the menu bar on the user interface select Exit from File on the pull-down menu: File
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 you work 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 in the 3D Model Setup window. There are various other pre-processing options available including the generation of symbolic code.
Calculation
Under this menu is where you can control what is happening with the SIMPACK solver. You can start and stop the time integration module, inverse kinematics module etc.
ParVariation
This feature of SIMPACK is particularly useful. If the effect of varying a different parameter is required, SIMPACK is able to do this automatically i.e. the user does not have to vary the parameter directly, but can instruct SIMPACK to see the effect that varying a parameter has (the mass of a body for example) on the motion of the system. This parameter variation is available in a number of the different 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. SIMPACK employs a sophisticated algorithm to evaluate the resulting perfor-mance. This provides the ‘best’ (pareto-optimal) parameter within a short iteration period. The optimisation process is not limited to one calculation method nor even to one simulation model. The optimised parameter may result from the consideration of several optimisation criteria, for example for a railway vehicle problem, parameters such as ride comfort, track quality and safety could all be considered.
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 SIMPACK information as well as details of the current SIMPACK release.
GETS:4.
File and Model
Management
Figure GETS:4.0.1: On-Line View of a SIMPACK Session In this section you will learn how to open, copy, create and remove models.
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 -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 model in. On the left hand side of the Open Model dialogue box you will see a directory list box. Either double click on a directory or double click on .. 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 default model 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’ placed
on the body fixed reference frame
• One joint ‘$J Body1’, which connects the inertia frame and the body with zero degrees of freedom
• One sensor ‘$S Body1’ between the two markers • A default gravity vector
• A default 3D–geometry for the inertia frame and the body
GETS:4.2Copying a Model
Open the Open Model dialogue box and select the ‘pendulum’ model you have just created, click with the right hand mouse button in this section (Models section) of the Open Model window and select ‘Copy Model’. Click again with right hand mouse button and select ‘Paste Model’. You will then be asked to whether you want to overwrite the existing model, select ‘No’ and in the ‘New Model’ window that then appears enter the new name for the copied model.
Models can also be copied across directories. The model should be copied in exactly the same way. Then switch to the directory in which you would like to copy your model and click on ‘Paste Model’. The model data will be copied to this directory and will have the name of the 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-✆
GETS:4.3 -24 Removing a Model
Opening a Model GETS:4.6 -25
There are 5 options that appear. Three of the options are for working only with the selected model and the other two options are for working with 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 all the output files of the selected model
• To remove measurement results only from the current model; this removes all the measurement results from the current model, but keeps all the simulation results
The final option keeps only the basic results files and model files. This is useful as the results files from the simulation are kept, which may have taken a significant amount of computer time to produce. The mea-surement files are removed, which often take up a significant amount of disk space, but can be restored very quickly. Calculating measurements will 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 the current 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 the Open Model dialogue box click on ✞
✝
✆
Close .
GETS:4.4
Opening a Model
Open the Open Model window once more. Find the directory which contains the pendulum model, which you have just created. Double click 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 be unable to load up a new model inSIMPACK if the pre- or post-processor is running with another model. To begin working on a new model you must close the pre- or post-processor.
GETS:4.5
Starting the Pre-Processor
The pre-processor can be opened either from the pull-down menu
PreProcess
Model Setup
or 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 if you wish to save your model or not.
GETS:4.7
Getting Help
SIMPACK provides the user with many help options. Help is most easily accessible via the on-line help HTML pages, which are accessed through
Help
Documentation
on the pull-down menu in the SIMPACK user interface.
If the user clicks on help from within the menu bar in other windows then they are presented with two options from within the pull-down menu.
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 browser window, 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. You will learn how to:
• Create and work with reference frames, bodies, joints and markers and 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 of SIMPACK
• Use SIMPACK to integrate the differential equations generated from the model data. Subsequently you will learn how to calculate measurements and animate the model from the simulation results • Manipulate the view of the model in the Model Setup window You will build a relatively simplistic model of a pendulum which will be developed into a slider-crank mechanism by the end of the Getting Started guide. Figure GETS:5.1.1 shows the pendulum which you will create in the first section of the Getting Started guide.
GETS:5.1 -28 Setting up the Model
Data for the Mechanical System Pendulum GETS:5.4 -29
GETS:5.2Data 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 = 100.0.0 10.0 0.00.0 0.0 0.0 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 0.0 0.0 −0.1 0.1 0.0 0.0 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 you created previously.
GETS:5.4
Starting the Pre-Processor
The pre-processor is where all the work is done inSIMPACK before you ask SIMPACK to solve the equations. This step is Step 4 in the 6 steps required to go from the concept stage to the simulation stage.
The pre-processor can be opened either from the pull-down menu
PreProcess
Model Setup
or from Model Setup / 3D-animation on the shortcut toolbar.
Two windows will appear on the screen. Figure GETS:5.4.2 is the SIMPACK 3D Model Setup window. In this window there is a 3D axis and this is where the model that you build will be shown. Along the top and side of the window you will find the shortcut toolbars as well as a menubar.
GETS:5.4 -30 Starting the Pre-Processor
Starting the Pre-Processor GETS:5.4 -31
The other window that appears is theSIMPACK Echo Area window, fig-ure GETS:5.4.3. This window displays the working status of SIMPACK as well as any error or calculation messages:
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 a physical system. Reference frames are co-ordinate frames with a strictly defined (completely rheonomically driven) motion relative to the iner-tia frame which means therefore, that reference frames do not have dynamics of their own. It is possible to represent the axes using 3D geometry. 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:
Discarding Changes GETS:5.6 -33
This dialogue box contains all the defined reference frames in the MBS model. There should only be one reference frame present which is the reference frame $B Isys. From this dialogue box you should now either double 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 can define various different parameters for the reference frame as well as define 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 and modify markers later in this guide.
GETS:5.6
Discarding Changes
Before going any further with developing the model, it is necessary to explain how to discard any unwanted modifications.
SIMPACK does not have an undo facility. If you as the user wish to remove a number of changes to the model you have just made, then it is 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
Reload
or by clicking on ’Reload’ in the toolbar. This Reload function is found in the 3D Model Setup window as shown in figures GETS:5.6.6 and figure GETS:5.6.7.
Figure GETS:5.6.6: Reload MBS
Modifying the Rigid Body GETS:5.7 -35
Reloading the database from the last save means all the changes you have made since the last save will be removed. If however, you would only like to remove one or two changes then it is more advisable to modify the model (such as a joint or marker). Modifying varying dif-ferent aspects of the model will be explained at various different stages throughout this guide.
GETS:5.7
Modifying the Rigid Body
Whenever a new body is created, SIMPACK automatically assigns it a body fixed marker. This marker serves as a reference frame for the body, therefore its position and orientation cannot be changed.
The following items are defined with respect to this body fixed reference system:
• Position of the centre of gravity relative to the body fixed refer-ence frame
• Built-in position and orientation of markers on the body
Select either ’Bodies’ on the toolbar or from the pull-down menu in the 3D 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
Modifying the Rigid Body GETS:5.7 -37
Double click on $B Body1 or select it with the mouse and then click on✞
✝
✆
Modify . T he MBS Define Body dialogue box appears, within this
window you can select whether the data used for the body is input locally (i.e. by you in the pre-processor) or from a database. You can also select whether the body is rigid or elastic. For this model you will enter the data by hand, i.e. not from the database and you will define the body as rigid.
Within this dialogue box you can enter the physical attributes of the body. These include the mass, centre of mass and the inertia-tensor. The inertia-tensor can be set relative to either the centre of mass, the body fixed reference system or to a marker. Normally it is set relative to 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 box should look:
GETS:5.7 -38 Modifying the Rigid 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 must have a joint and this joint must either be attached to another body or to a (kinematically driven) reference frame. Joints can have from 0 to 6 degrees of freedom. To modify the joint:
• Select Joints from either, the pull-down menu under Elements or from 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. The markers to which it is attached as well as the type of joint are also shown. 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 nearer the reference frame than the ‘to marker j’. SIMPACK takes this into account when it offers you the markers.
Click on ✞
✝
✆
From Marker i and the dialogue box, figure GETS:5.8.11
appears:
Modifying the Joint GETS:5.8 -41
• Select marker $M Isys and then click on OK. This marker is the default marker set by SIMPACK on the reference frame
• Select $M Body1 as marker j. This is the default marker set by SIMPACK 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 types of joint, e.g. Rheonomic Joints. The individual joints can be found under the relevant joint type. Open the folder ‘General: Free Motion’ and from the list that appears select joint ‘Revolute Joint al’. This is a 1 degree of freedom joint, which allows only rotation about the x axis (angle Alpha). Figure GETS:5.8.12 shows what you should select:
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 the initial state box as shown in figure GETS:5.8.13:
Modifying the Joint GETS:5.8 -43
In the following input window you can enter the initial state of the joint in 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:
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:
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 to undertake an analysis without the g-vector present you must explicitly tell SIMPACK, otherwise it is defined automatically and is negative along the z-axis.
To modify the g-vector you must select ’Gravity’ from within Globals in the pull-down menu Globals
Gravity
from 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 the z axis.
GETS:5.10
Modifying the Sensors
Sensors are a very important part ofSIMPACK. They yield the relative kinematic quantities between two markers. SIMPACK automatically assigns one sensor to each body that is created. However sensors can be defined between any two markers on the MBS. They are used when the relative translation, rotation, velocity or acceleration between two markers 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 taken off-line after the time integration.
• Select ’Sensors’ from either the pull-down menu under Elements or from within the shortcut toolbar
• In the MBS 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 Isys for this marker. For marker ‘j’ select $M Body1. Keep the other de-faults within the window and click on ✞
✝ ✆
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 it is therefore necessary to reload the MBS data from the last save to remove 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 on the ’Reload MBS-Model’ toolbar button or from the pull-down menu
File
Reload
A useful function of SIMPACK is to be able to save the model under a different name. This can be done using the ’Save As’ option which is also found under ’File’ and on the toolbar. This creates a copy of the model 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 the MBS definition, whilst the file FILENAME.ani contains the informa-tion concerning the shape, colour and view definiinforma-tions.
What is important to note is that whenSIMPACK executes a command such as time integration it reads the model data from these files. It is therefore vital, immediately before asking SIMPACK to perform a task with the model data, that you save the model data and therefore update these files.
You can save the model data either from the pull-down menu File
Save
or 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:5.12Creating the 3D Geometry
The 3D geometry of bodies and reference frames consists of one or more ensembles. Every ensemble consists of one of more graphic primitives such as co-ordinate frames, cuboids, cylinders, prisms, etc. These primi-tives are grouped together to form a 3D ensemble. Even complex shapes produced by CAD packages can be attached to an ensemble. Road and railway track primitives will usually be attached to the inertia frame. The ensembles are guided by the position vector and orientation matrix of one single sensor.
When SIMPACK creates a new body it will automatically assign a de-fault sensor ensemble and primitive to the body. The dede-fault ensemble is assigned to the default sensor. In most cases you will keep this en-semble attached to this default sensor. The default graphic primitives are a co-ordinate frame and a cuboid primitive.
Select $B Isys for modifying. If you need help refer back to GETS:5.5 on modifying the reference frame.
Select ✞
✝
✆
3D-Geometry
The SIMPACK 3D Geometry window appears. This window shows the ensembles and primitives that are associated with this reference frame. Under ’Primitives of Selected Ensembles’ click on ✞
✝ ✆
New as shown in
GETS:5.12 -48 Creating the 3D Geometry
Creating the 3D Geometry GETS:5.12 -49
In the input box that then appears you should enter the name $P axle and then click on ✞
✝ ✆
OK .
TheSIMPACK Primitive Definition window appears and in this window click on ✞
✝
✆
Type to change the primitive type, figure GETS:5.12.19.
GETS:5.12 -50 Creating the 3D Geometry
Figure GETS:5.12.20 shows the available primitives. In this window select 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 this window 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
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 the reference frame. You will change the body from a cuboid to a prism to look like the hand of a clock.
The steps are similar to those that you went through for applying the 3D geometry to the reference frame.
• Access the body $B Body1 and click on ✞✝3D Geometry . T he✆
3D Geometry window appears
Within this window you will find the default ensemble $E Body1 and the default primitives of this ensemble. There is the primitive $P Body1, a co-ordinate axis representing the body reference frame 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 = 0.0
2. line: x = 0.0 y = -0.1 3. line: x = 0.1 y = 0.0 4. 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 box should 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 system axes.
You will learn, in this section, how to move the model within the 3D Model Setup window. However, before changing the view you should save the model. You therefore only need reload the model data to get back to the original view settings.
• Select View Setup from View on the pull-down menu in the 3D Model Setup window. The following dialogue box will appear, figure GETS:5.14.23
GETS:5.14 -54 Manipulating the View
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 to determine the translational movement of the model within the screen. When the screen co-ordinates are selected the bottom left hand corner of the 3D Model Setup window becomes the origin. Try also rotating the model around the screen using the slider bars.
One very useful feature in SIMPACK allows you to operate with 4 user defined views. You will find these at the top of the View Setup dialogue box. You can toggle between four views or just the one view. You can also toggle between the four different views.
As well as the View Setup window you can also control the view by holding down the control key and one of the mouse keys. By scrolling with the mouse and trying each of the mouse keys in turn you can see the effect each has on the view.
It is also possible to manipulate the view from on the toolbars. There is a refit function, as well as a zoom in and zoom out function.
Once you have finished experimenting with the different views, reload the MBS model data from the previous save and you will return to the SIMPACK standard view.
GETS:5.15
On/Off Line Integration
Before you will learn how to perform the time integration, here is just a 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 package in that, it only generates one equation of motion for each degree of freedom which is defined by the user.
Later in the guide you will create a double pendulum model (with 2 DOFs), which you will then use to produce a slider crank mechanism (with 1 DOF). SIMPACK will generate two differential equations for the double pendulum model, but only one however for the slider crank model. The slider crank model has the same number of joints, but has a constraint added. This reduces the degrees of freedom from two to one. With the constraint added, the motion of the second body is dependent, via an algebraic equation on the motion of the first body and the restriction applied by the constraint. SIMPACK will therefore only create one equation of motion for the slider crank model.
The next stage after setting up the model is for SIMPACK to form the motion 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 model whilst 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 end time. 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:
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 then click on ✷ Go . The pendulum starts to oscillate about the x axis, which can be seen in the 3D window. The time integration can 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 is off-line. Off-line integration is normally used for large complex models with a large number of degrees of freedom. The CPU time required to integrate the equations may be high, which makes it unfeasible to animate the model whilst performing the time integration.
Before starting an off-line integration, SIMPACK must be told what to perform in the integration. SIMPACK must be told the initial start time for the integration as well as the end time. These values must be posi-tive as SIMPACK does not allow you to integrate backwards. SIMPACK also requires the number of communication points. These communi-cation points determine how many times SIMPACK writes data to the results’ files in the integration process. For example, an integration time of 10 seconds with 100 communication points would mean that results are available for every tenth of a second.
• From the pull-down menu in the SIMPACK user interface select
Calculation
Time Integration Configure
The Time Integration window will appear and in this window enter the following parameters:
Initial Time = ✞ ✝ ✆ ✄✂ ✁✄✂ ✁✄✂ ✁0.0 End Time = ✞✝✄✂ ✁✄✂ ✁✄✂ ✁5.0✆ Number of Communication Points = ✞
✝
✆ ✄✂ ✁✄✂ ✁✄✂ ✁101
GETS:5.15 -58 On/Off Line Integration
On/Off Line Integration GETS:5.15 -59
• The integration method SODASRT will be automatically selected as the SIMPACK default integration method. SODASRTis SIM-PACK’s standard integration integrator which is optimised for a wide range of mechanical systems. You will find that this method is appropriate for almost all cases, however for some certain cases there are other more appropriate solvers available to the user. For example for complicated non-linearities other solver methods are available. The wide range of SIMPACK solvers means that virtually 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:
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 defaults in 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 the model. As mentioned previously whenSIMPACK performs a calculation it reads the data from the model files. These files are not updated until the model is saved. To ensureSIMPACK is reading the correct data you must save your model before starting the time integration.
SIMPACK is now ready for you to begin the integration process. From the SIMPACK user interface select either from the pull-down menu
Calculation
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 of SIMPACK 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 of the 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 possible to stop the time integration. This is done from the pull-down menu
Calculation
Time Integration Stop
GETS:5.16
Calculating Measurements
It is necessary to calculate measurements to animate the results of the integration process.
The movements of the ensembles are determined by the output data from the sensors. These measurements are the first measurements taken when the perform measurements module is executed. The next mea-surements taken are those associated with the kinematics, the applied forces, the internal force law variables and the constraint forces. All the results are saved in the subdirectory ‘/output’ of the current directory. To start the perform measurements module, click on the pull-down
Animating the Results ofthe 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 integration results. In the Model Setup window either select Time History from Animation on the pull-down menu or click on the Animation of Time Histories toolbar button. The following window then appears, figure GETS:5.17.27:
GETS:5.0 -62 Animating the Results ofthe Integration
At the top of the window you will see it says ‘frame number’. There should be the same number of frame numbers as communication points that you entered in the Configure Time Integration window. Therefore there should be 101 frame numbers available.
Directly underneath these frame numbers you will see the buttons which you use to control which frame number is displayed in the 3D Model Setup window. Experiment with these pushbuttons to see the effect they have on the animation. Once finished click on ✞
✝ ✆
GETS:6.
The Double–Pendulum
GETS:6.1
About the 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 = 100.0.0 10.0 0.00.0 0.0 0.0 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 = 150.0.0 15.0 0.00.0 0.0 0.0 0.0 1.0 [ kgm2] Joints:
• Joint connecting body-1 and the inertia frame: joint mobility = rotation about x-axis
initial joint state = 0.707 [ rad ] initial angular velocity = 0.0 [ rad/s ] • Joint connecting body-2 and body-1:
joint mobility = rotation about x-axis
initial joint state = -0.2 [ rad ] initial angular velocity = 1.0 [ rad/s ] Gravity:
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 0.0 0.0 0.1 0.1 0.0 0.0 −0.7 [ m ] thickness = 0.05 [ m ]
• Geometric parameters of body–2:
Body-2 is graphically represented by a cuboid.
Co-ordinates of the cuboid diagonal vec-tor: = −0.025 −0.025x y 0.0z 0.025 0.025 −1.0 [ m ]
GETS:6.2Extending the Pendulum Model to a Double
Pendulum
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, which is a rotation about the x axis. This axis is represented by a small cylinder. The second body of the double pendulum looks like a rod and is connected to the first body by a revolute joint which allows rotation about the x axis only.
• Make sure the Model Setup window has been closed (i.e. the 3D Model set-up window)
• Create a new model which is identical to the pendulum model and name this model double pendulum. If you need help on copying the 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 click on Markers
GETS:6.3 -66 Adding a Marker to a Body
and name this new marker $M Body1 1
Figure 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 Marker window appears. This window allows you to edit the built in vector and orientation matrix that describe the marker’s position. These co-ordinates are given relative to the body fixed reference frame
The orientation matrix determines a constant orientation of the marker relative to the body fixed reference frame. There are four possible options 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 been added. This marker will be used as an attachment point to the second body. 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 MBS Bodies 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 this for you.
When this new body is created SIMPACK automatically assigns default settings for the mass and inertia tensor. SIMPACK also automatically assigns:
• A marker to the body
• A default 3D geometry including two primitives to represent the body graphically (a co-ordinate axis and default cuboid)
• A zero degree of freedom joint which connects this body to the inertia frame
• A sensor between the inertia frame and the body fixed frame The MBS Define Body window should have appeared. Enter in the following values for the model:
GETS:6.4 -68 Creating a New Body and Adding a Marker mass = 2.5 Centre of mass z = −0.5 Ixx = 15 Iyy = 15 Izz = 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 ‘length in 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 centre is at the origin of the inertia frame. To move the rod, enter in the ‘build in vector box’ the following data:
Shift the cuboid on the z–axis: z = ✞✝✄✂ ✁✄✂ ✁✄✂ ✁-0.5✆
The Primitive Definition window should look as follows, figure GETS:6.4.5:
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 now return to the MBS bodies window.
GETS:6.5
Modifying a Joint
As mentioned previously when a body is created it is assigned a joint with zero degrees of freedom. This joint is also attached to the inertia frame. The joint on body2 has to be modified so that it is connected to both body 1 and body 2. The joint to be used is a revolute joint about the x-axis.
• Select Joints from either the pull-down menu under Elements or click on the toolbar button
• Double click on the joint $J Body2. The Define Joint window appears
• 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 = -0.2
Velocity = 1.0
If the dialogue box looks the same as figure GETS:6.5.6 click on ✞
✝ ✆
Modifying a Joint GETS:6.5 -71
GETS:6.0 -72 Modifying a Joint
You should now save your model and as described in section GETS:5.15 begin the time integration and model animation. If you can, try per-forming the time integration without referring back.
