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MODELING METHODOLOGIES

Active Modeling: A Method for Creating and Simulating Variable-Complexity Models

[+] Author and Article Information
D. Geoff Rideout

Faculty of Engineering and Applied Science, Memorial University, St. John’s, NL, A1B 3X5, Canadag.rideout@mun.ca

Kazi T. Haq

Faculty of Engineering and Applied Science, Memorial University, St. John’s, NL, A1B 3X5, Canadab26kth@mun.ca

J. Dyn. Sys., Meas., Control 132(6), 061201 (Oct 28, 2010) (12 pages) doi:10.1115/1.4002472 History: Received September 29, 2008; Revised December 10, 2009; Published October 28, 2010; Online October 28, 2010

Effective and efficient simulation-based design is facilitated by models of appropriate complexity. A single model will not have the most appropriate level of complexity throughout all phases of a simulation maneuver if inputs or parameters vary. Ideally, a model for which complexity can be varied as necessary will achieve the best possible trade-off between accuracy and computational efficiency. A method is presented for switching system model elements on and off as their importance changes, and predicting the response of the resulting variable-complexity model. A modified transformer element removes the dynamic output of a model element to the rest of the system when the moving average of its absolute power falls below a user-defined threshold. When the element is “off,” the input from the system to the element is still passed through the transformer so that an estimate of element power and importance can continue to be calculated and the element switched back “on” if necessary. The bond graph formalism is used to facilitate implementation. Switch configurations are defined for both causally weak and causally strong energy storage and dissipative elements. The method is applicable to linear or nonlinear systems that can be modeled with lumped parameter elements. The approach is demonstrated for quarter- and half-car vehicle models subject to a road profile of varying frequency. The appropriate model complexity at all stages is determined and implemented continuously without prior knowledge of input or parameter changes.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Bond graph element interaction with system

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Figure 2

Nonpower conserving transformer to partially disconnect element

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Figure 3

MAP sensor to calculate MAPI for C element

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Figure 4

Switching via MAPI sensor output to MTF

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Figure 5

Switching of a causally strong I element

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Figure 6

Large and small inactive I elements

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Figure 7

Supplementing external element switches with internal bond switches

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Figure 8

Quarter car schematic

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Figure 9

Quarter car bond graph with causally weak sprung mass

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Figure 10

U values indicating switch time and status of elements

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Figure 11

Comparison of switched and nonswitched model outputs

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Figure 12

Quarter car bond graph with causally strong sprung mass

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Figure 13

U values indicating switch status of elements

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Figure 14

Comparison of switched and nonswitched model outputs

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Figure 15

Quarter car with switched sprung mass

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Figure 16

Physical interpretation of Table 4 scenarios

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Figure 17

Energy comparison of inactive elements when on and off

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Figure 18

Half-car schematic

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Figure 19

Switched half-car bond graph

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Figure 20

Element switch values for half-car

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Figure 21

Full and variable-complexity model outputs

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Figure 22

Simple nonlinear hydraulic damper

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