Introduction to SimCreator and Multi-Body Dynamics

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Introduction to SimCreator and Multi-Body Dynamics

• April 25, 2005

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What is SimCreator?

• GUI Based System Modeling Package
• Similar to Simulink, SystemBuild, EASY5
• Specialized for Realtime System Modeling Driving
  Simulation, Flight Simulation, Games, Embedded
  Control
• Modeling Constructs also Support Complex Off-Line
  Simulation

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Typical SimCreator Session
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SimCreator Capabilities

• Support for Single and Double Precision Models
• Easy Editing of User Coded Components
• Component Connectors Include a Description and
  Units
• Vector Connections
• Variable Width Components
• Enhanced Metafile Based Icons
• HTML Based Help Files
• Sub Models

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SimCreator Capabilities

• Easy Access to and Setting of Initial Conditions
• State Values Can be Overridden Inside User Code
• Automatic C Code Generation
• Multiprocessing with Multirate Integration
• Generated C Code Uses Datafile Based Constants
  and Initial Conditions
• Multiple Inputs and Outputs for User Coded
  Components
• External Code Hooks to Inputs, Outputs, and
  Initial Conditions

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SimCreator Capabilities

• Highly Efficient Realtime Code
• Mixed Continuous and Algebraic Inputs to Same
  User Code Block
• Multiple Connections Can Be Made Between
  Components with a Single Mouse Click
• Generates Embedded Code
• Parallel and Distributed Build and Execution
  Environment
• Highly Efficient Execution Interpretor

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Standard Library
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Math Library
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Altia Interface for GUIs
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GUI Plotting Dialog
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Driving Simulator
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Distributed Simulator
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Multi-Body Dynamics

• SimCreators multi-body dynamics component
  library is based on Composite Rigid Body Methods
  (CRBM) (recursive method)
• CRBM method is used for open kinematic chains
• For closed kinematic chains, constraint equations
  with corresponding Lagrange multipliers are
  introduced and are used to augment the mass
  matrix

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Recursive Multi-Body Approach
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Mass Matrix

• To maintain real-time must select the appropriate
  joints to minimum the number of equations in the
  mass matrix

Joint Type of Equations
Revolute 1
Prismatic 1
Cylindrical 2
Universal 2
Screw 1
Spherical 3
Cut Spherical 3
Distance Constraint 1
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Double Pendulum Example
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Double Pendulum Results

• Z in SimCreator isY in DADS

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4 Bar Example
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4 Bar Results
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MTVR Model (Working with John Weller and Steve
Schultz)
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MTVR Corner Module
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Lateral Displacement vs Roll Angle(DADS vs.
SimCreator)
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Realtime Performance

• The MTVR had the following complexity
• 66 equations in the augmented mass matrix
• 36 equivalent joints
• 25 equivalent bodies
• 115 states
• Full powertrain
• 2nd order Runge-Kutta method at 500 Hz.
• Using a computer with a 1.7 GHz Pentium M
• MTVR model took 22 seconds to perform a 60 second
  simulation.

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Powertrain

• Vehicle subsystems are also broken down into
  reusable modules
• Lowest level components are C code

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MTVR Powertrain
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SimCreator Conversion (Phase I SBIR)

• DADS is a Cartesian multi-body modeling approach.
  Several steps are required to translate a
  Cartesian model into a recursive (CRBM) model,
  needed for real-time simulation in SimCreator.
  These steps include
• Determine weighting factors for each joint
• Determine the best joints to cut
• Determine the optimal base body
• Build a recursive spanning tree
• Minimize mass matrix size
• Minimize tree length

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Advantage Of GUI

• Structured Framework to Build C Code Components
• Causality
• Unified Integration Algorithm
• Built in Data Management and Plotting
• Greater Insight Into the Model
• Hierarchical Viewing
• Model and Component Reuse