How should collision problems be confronted?
Collision detection and response can be responsible for making a simulation run extremely slowly. If your simulation runs properly and without warnings, but takes a great deal of time to compute, see What can cause a simulation to be computed extremely slowly?. If your simulation yields warning messages and collisions seem to be the culprit, read on.
WM3D uses a complex algorithm to effectively compute collisions. Occasionally however, two bodies will collide in such a way that the response is extremely difficult for the algorithm to compute. This document presents a good approach to diagnosing such collision associated problems.
The italics writing below is intended to be a step by step explanation of how to accomplish what is described. For example, Edit - Select All means go to the Edit menu and select Select All.
1. Turn off all collisions to confirm that collisions are responsible for the model's problem.
- Edit - Select All. Object - Penetrate All.
If the model's problem persists there is more to the problem than collision anomalies. See How should warning messages be interpreted when eliminating problems in a model?
2. Redefine collisions one-by-one to ensure that only those bodies that you wish to collide are set to do so.
- Highlight bodies two at a time (see What methods can be used to select objects in WM3D?) and select Object - Collide.
Run the simulation after each collision definition until the warning reappears.
3. Reduce the Animation Step (try by a factor of 10, then 100, then 1000) in the Simulation Accuracy dialog.
- World - Accuracy - Animation Step: modify the animation step.
Run the simulation to see if the problem has been solved.
4. Set the Coefficients of Restitution and Coefficients of Friction to 0 for all of the colliding bodies.
- Available under the Material tab of the Properties window.
WM3D may respond to contact anomalies by issuing either of the two following warning messages:
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Working Model 2D, visualNastran 3D Motion, 4D, SimWiseData ultimo aggiornamento: 2 settembre 2011
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