Linkoping Electronic Articles in Computer and Information Science Vol nr Tools for Design Interactive Simulation and Visualization for Dynamic Analysis of Mechanical Mo dels Vadim Engelson Linkoping University Electronic Press Linkoping Sweden httpwwwepliuseeacis PublishedonDecember by Linkoping University Electronic Press Linkoping Sweden Linkoping Electronic Articles in Computer and Information Science ISSN Series editor Erik Sandewal l c Vadim Engelson Typeset by the author using FrameMaker Recommended citation Author Title Linkoping Electronic Articles in Computer and Information Science Vol nr httpwwwepliuseeacis December This URL wil l also contain a link to the authors home page The publishers wil l keep this article online on the Internet or its possible replacement network in the future for a periodofyears from the date of publication barring exceptional circumstances as describedseparately The online availability of the article implies apermanent permission for anyone to read 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its WWW home p age httpwwwepliuse or by conventional mail to the address statedabove Abstract The complexity of mechanical and multidomain simulation mo d els is rapidly increasing Therefore new metho ds and standards are needed for mo del design A new language Mo delica has b een prop osed by an international design committee as a stan dard ob jectoriented equationbased language suitable for de scription of the dynamics of systems containing mechanical elec trical chemical and other typ es of comp onents However it is complicated to describ e system mo dels in textual form whereas CAD systems are convenient to ols for this purp ose Therefore we have designed an environment that supp orts the translation from CAD mo dels to standard Mo delica representation This tation is then used for simulation and visualization As represen sembly information is extracted from CAD mo dels from which a Mo delica mo del is generated By solving equations expressed in Mo delica the system is simulated We have designed several interactive D visualization to ols whichdisplay exp ected and ac tual mo del b ehavior as well as additional graphical elements for the purp ose of engineering visualization We applied this envi ronment for rob ot movement and helicopter ight simulation Supported by WITAS The Wal lenberg Laboratory for Information Technology and Autonomous Systems and by the European Commission via the REALSIM project Authors aliation Vadim Engelson Department of Computer and Information Science Linkoping University Linkoping Sweden 1 Contents 1 Background 2 1.1 Visualization Requirements Induced by Simulation Goals. 3 1.2 External Factors Important for Simulation Software and its Life Cycle . ................... 5 1.3 Structure of the report . ................... 6 2 Overview of Approaches to Dynamic Simulation of Mechanical Models 7 2.1 Multibody Simulation Tools . 8 2.1.1 ADAMS . ................. 8 2.1.2 Working Model 3D . 13 2.1.3 Integrated Environments for Computer-Based Ani- mation (3D Studio Max) . ........ 14 2.2 Equation-Based Simulation Tools . 16 2.2.1 SIMULINK/Systembuild . 16 2.2.2 Mechanical Packages for General Purpose Com- puter Algebra Systems . 17 3 Using the Modelica Language for Dynamic Analysis 18 3.1 Modelica . ........................ 18 3.2 Basic Features of the Modelica Language . 20 3.2.1 Implementation of Model Simulation . 22 3.3 Introduction to Modelica Syntax . 22 3.3.1 Introduction to the library of Electrical Components 22 3.3.2 Example . ................. 23 3.3.3 Using connectors . 24 3.4 Introduction to the Modelica Multibody System Library . 26 3.5 Using the MBS library . 29 3.5.1 Kinematic outline . ....... 29 3.5.2 Example: Kinematic Outline of Double Pendulum 32 3.5.3 Adding masses. 32 3.5.4 Adding Masses to the Double Pendulum Example. 32 3.5.5 Adding Geometrical Shapes . 34 3.5.6 Adding Shapes for Double Pendulum . 35 3.5.7 Interface to Non-Mechanical Parts of the Model . 36 3.6 Advantages of Using MBS for Dynamic Analysis . 37 3.6.1 Interpretation and Compilation in Mechanical Sim- ulation . ................. 37 3.6.2 Multidomain Simulation . 38 3.7 Difficulties of using the MBS library . 38 4 CAD Tools 38 4.1 CAD Tools and Dynamic Analysis . 39 4.2 Comparison of Various CAD tools . 40 4.2.1 SolidWorks . 40 4.2.2 Working Model 3D . 40 2 4.2.3 3D Studio Max . 41 4.2.4 Mechanical Desktop . 41 4.2.5 Pro/ENGINEER Tool Family . 43 5 Mechanical Model Design in SolidWorks and Model Transla- tion 45 5.1 Design of SolidWorks Parts and Assemblies . 45 5.2 Mating Example ....................... 45 5.3 Classification of mates . 46 5.4 Translation of mates into joints . 47 5.4.1 Multibody Systems with a Kinematic Loop . 48 5.5 User Interface for Configuration of Joints . 49 5.6 Mechanism Example – Crank model . 49 5.7 Mechanism Example – a Swing Model . 52 6 Structure of the Integrated Environment 57 7 Requirements for Visualization of Mechanical Models 60 7.1 Design Requirements . ................... 60 7.2 Usage Requirements . 61 8 MVIS - Modelica Interactive Visualization Tool 63 8.1 Offline and online Visualization Interfaces from Modelica . 64 8.1.1 Data Structures Used in Visualization . 64 8.1.2 Force and Torque Equations for Visualization Classes 67 8.1.3 Standard and New Classes for Visualization . 68 8.2 Rendering Properties and Design Aspects . 68 8.3 MODIC, Modelica Interactive Control Interface . 72 8.3.1 Interface for Output Values . 72 8.3.2 Interface for Input Values . 74 8.4 Synchronization Problem in the Interface for Input Values . 74 9 Modelica Visualization on the Internet 79 9.1 VRML-Based Simulation Visualization . ....... 80 9.2 Cult3D Approach . 83 9.3 Using 3DStudioMax . ................... 85 10 Conclusions 86 11 Acknowledgments 86 1 Background The use of computer simulation in industry is rapidly increasing. Simula- tion is typically used to optimize product properties and to reduce product development cost and time to market. Whereas in the past it was considered sufficient to simulate subsystems separately, the current trend is to simulate 3 increasingly complex physical systems composed of subsystems from mul- tiple domains such as mechanical, electric, hydraulic, thermodynamic, and control system components. In this chapter we concentrate on simulation of mechanical models, in particular, systems of multiple rigid bodies, as well as simulations where such models are major components in the simulated system. This means that flexible bodies, fluid and gas mechanics, molecular physics and some other simulation and visualization areas are outside the scope of this work. We define a simulation for our models as a particular execution of the software that given initial conditions and other input uses physical laws in order to reproduce the behavior of idealized physical models during some time span. 1.1 Visualization Requirements Induced by Simulation Goals. When discussing design, simulation and visualization issues it is useful to be goal oriented, since different goals can be set up. The goals can be either application- or tool-driven. The purpose of an application can for example be to optimize product properties and to reduce product development cost and time. This means that the simulation should be able to predict behavior of the system, or an- alyze what happened with some system in case of an unexpected behavior. The purpose of simulation tools is to provide adequate technology nec- essary for applications. In particular, tools should be tested for capabilities and performance requirements – whether these can handle complex models and demanding simulations. Of course, products will not become better and cheaper if they are just simulated. Attention should be paid to quality of simulation and availabil- ity of results. If there are too many inadequate assumptions and simplifi- cations, the simulation will be cheap, and may be fast, inaccurate and use- less. If the assumptions are adequate, all relevant details are taken into ac- count and everything possible is measured with highest degree of accuracy, simulation requires very complicated mathematical analysis, complex pro- gramming models, and is able to produce numerically correct results. Such simulations may require extremely high computational power and proceed very slowly; often it is very hard to predict the time needed for computa- tion. It might happen that these simulations are useless anyway - if the goal of simulation has been set incorrectly, or if results cannot be visualized in a comprehensible way. The efforts of simulation software designers are focusing on finding a golden middle way between the two mentioned extremes, finding the trade- off between the computing resources and computation accuracy. Several categories of general simulation goals are established; these goals can be described in a mathematical notation. Requirements for visu- alization of simulation results are depending on the goals of the simulation. F Assume that x is some input data for a simulation function , that produces x simulation results F . The simulation results for mechanical system are 4 movement trajectories (position, rotation, velocity, acceleration) of bodies as well as force, torque, pressure and other dynamically changing values.