Automatic Generation of Real-Time Simulation Code for Vehicle Dynamics using Linear Graph Theory and Symbolic Computing

System Design Engineering

Morency, Kevin

University of Waterloo

关键词: System Design Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/3002/1/morencythesis.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

In recent years, hardware-in-the-loop (HIL) simulation has assumed a prominent rolein the vehicle development process. A physical part, which may be a prototype at any stage of development, is tested, while the rest of the vehicle is represented by a mathematical model. Vehicle models used with hardware-in-the-loop must be capable of simulating an event in less time than it takes the event to occur in reality. Fast simulation necessitatesa model that is represented by very efficient simulation code. This thesis presentsa procedure for automatically generating this simulation code, given a description of thevehicle as input.For this work, a symbolic formulation procedure based on linear graph theory andthe principle of orthogonality is used to generate governing equations for vehicle systems;this procedure forms the basis of the DynaFlexPro software package. In order to generatesimulation code for vehicle dynamics studies, the DynaFlexPro component model templatewas extended to include rules for calculating intermediate variables and rules forcalling external functions. These changes enabled the development of a tire componentmodel, known as DynaFlexPro/Tire, that adds critically important (and computationallyefficient) blocks to the overall vehicle simulation code. The combination of DynaFlexProand DynaFlexPro/Tire allows analysts to construct a model for any vehicle topology andgives analysts great freedom to define how tire forces and moments will be calculated.Simulation code describing the vehicle model is automatically generated using symboliccomputing techniques. The accuracy of the approach was validated by comparing resultsfor DynaFlexPro vehicle models to results for equivalent models developed in awell-established tool for vehicle dynamics simulation (MSC.ADAMS).Two different vehicle models were constructed using DynaFlexPro and DynaFlex-Pro/Tire: a generic 4-wheeled vehicle with independent suspension and an articulatedforestry skidder. Both models had an open-loop topology. When appropriate modelingvariables were selected, each model was described by a minimal set of ordinary differentialequations (ODEs) and the simulation code generated by DynaFlexPro was capableof being used for hardware-in-the-loop applications; the braking and handling behaviorof the example models was simulated faster than real-time on a desktop PC with a 3.2GHz Pentium 4 processor and 1 GB of RAM. For the same vehicle models, a differentchoice of modeling variables resulted in a mixed set of differential and algebraic equations(DAEs); in that case, HIL-capable simulation code could not be consistently generated.The approach works well for vehicle models described by ODEs, but more research isneeded into the treatment of DAEs for real-time simulation of vehicle dynamics.