Physics Programs

ID #1073

I have a multi-vehicle simulation. One of the vehicles is stopped for a period and then begins moving again. While it is stopped, the lateral acceleration output is a constant -0.4g throughout this period. (more)

QUESTION:  I have a multi-vehicle simulation. One of the vehicles is stopped for a period and then begins moving again. While it is stopped, the lateral acceleration output is a constant -0.4g throughout this period. Despite this, the vehicle has no v velocity during this period. Could you help me shed some light on this?

The issue is a classic example of the need for non-zero termination velocities: When you set them to 0, the equations of motion continue to be executed (because in discrete timestep numerical integration, velocity will NEVER be exactly zero). So the simulation is continuing to calculate tire forces, which happen to have a slip angle, which says there’s a lateral force, which says there’s a lateral acceleration.

To solve the problem, set the Termination Linear and Angular velocities to an acceptably small value, say 0.1. This will have ~nil effect on your analysis and makes the equations of motion happy.

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Last update: 2012-06-11 19:36
Author: edccorp
Revision: 1.0

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