NOTES: Integration Time Step, Vehicle Shape, etc

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MSI
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Joined: Thu Jun 18, 2009 12:37 pm

NOTES: Integration Time Step, Vehicle Shape, etc

Post by MSI »

Recently heard some folks in a forum discussing integration step size and suggesting using increments sized larger than 0.001 seconds?
NOOOOOO!
You should ALWAYS use 0.001 sec integration time increments!
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On higher speed impacts you can even try 0.0001 second increment!
  • We've investigated time step back in the 80s and if interested please get the book Computer Methods for Mathematical Computations which is a classic textbook on numerical methods for scientists and engineers.
    • See Chapter 2: Floating Point Computation which includes examples of round off errors and sensitivity of certain problems.
      • We did.
      • We concluded 0.001 second integration time increment should be used.
  • Original and clone SMAC documents recommend the use of 0.01 for the DTCOLT separation time increment, 0.05 for the DTTRAJ trajectory time increment, 0.001 for the DTCOLL collision time increment.
    • These suggested times were for mainframe applications from 1974
    • The only reason the option to change the integration time step was added back in the 70s was because that was back in the mainframe computer days where you paid for CPU time so reducing the amount of resources and time a simulation ran saved money
  • On modern computers simulation runs are FAST so ALWAYS USE 0.001 second
  • A problem with larger time-increments is the fact that they may reduce the accuracy of the predicted results.
Today on a PC, NO POINT!

also in looking over our older post:
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I see we mention:
  • "In the SMAC program, each vehicle is represented by a rectangular box with the length and width dimensions of the simulated vehicle. "
It works fine since how much force does it take to get rid of a corner?
However we want to use the periphery of the 3D Models as the vehicle shape so in the process of making those modifications.
We hope and expect to add that option in the very new future

The following is a comparisons of rectangle and the actual vehicle shapes...using the polygon shape will simply insure no forces until structures interact
rectangle.jpg
rectangle.jpg (63.61 KiB) Viewed 104 times
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