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Efficient Simulation Model for Hybrid Bond Graphs

Efficient Simulation Model for Hybrid Bond Graphs. Christopher Beers ISIS, Vanderbilt University. Introduction. Simulation of hybrid systems must combine two models of computation Hybrid Bond Graphs (HBGs) combine Continuous bond graph (BG) models with Switching junctions controlled by FSM

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Efficient Simulation Model for Hybrid Bond Graphs

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  1. Efficient Simulation Model for Hybrid Bond Graphs Christopher Beers ISIS, Vanderbilt University

  2. Introduction • Simulation of hybrid systems must combine two models of computation • Hybrid Bond Graphs (HBGs) combine • Continuous bond graph (BG) models with • Switching junctions controlled by FSM to provide a topological framework that supports run-time model reconfiguration • However, no computational model associated with HBGs Question: How does one systematically derive simulation models from HBGs? • Approach: Use causal structure implied by BG to derive block diagram models for simulation (SCAP algorithm) "Efficient Simulation Model for Hybrid Bond Graphs," C. Beers

  3. HBG Overview • BG to Block Diagram Computational Model • Constituent element blocks + algebraic relations at junctions • Determining Bond (DB) • One per junction, derived from causality at junction • Determines algebraic relations • HBG Complexities • Junction switches (on and off) may cause causality changes at runtime, thus block diagram may change • Only changes in DBs will change algebraic relations at junction • These changes can propagate "Efficient Simulation Model for Hybrid Bond Graphs," C. Beers

  4. Approaches • Pre-generate block diagrams for all modes • 2n possible configurations • Generate block diagrams from scratch after every mode change • Can be computationally expensive at switches • Smarter approach: derive new block diagram incrementally from old • Start with block diagram in initial mode • Look for changes in DBs • Update block diagram at changes Junction 1a off, junction 1b on: Off DB DB DB Junction 1a on, junction 1b off: No change in DB "Efficient Simulation Model for Hybrid Bond Graphs," C. Beers

  5. Efficient Simulation Model • Causality update triggered by change in discrete state • Start at junctions which switch • If they cause changes in adjacent junction DBs then • update DB’s algebraic constraints • Continue till no DB change or all junctions visited • For efficiency, junctions implemented as S-functions; use global variables(cf. Ptolemy’s director function) "Efficient Simulation Model for Hybrid Bond Graphs," C. Beers

  6. Questions? "Efficient Simulation Model for Hybrid Bond Graphs," C. Beers

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