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Simmechanics (1G): Low intertia slows down simulation

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I am trying to simulate a multi-body system that consists of small bodies, connected by springs and dampers. The intertia of a single part is about 1e-9 kg*m^2, which seems to cause problems for the solver. My observation is that the lower I set the intertia, the slower is the simulation. I could simply set the inertia to a very high value to reach a decent simulation speed, but this would be at the cost of a realistic simulation.
Does anybody have an idea how to solve this problem? According to the Simmechanics 1G manual, even bodies with zero intertia are possible, but this doesn't seem to work in my case- the simulation gets even slower then.

Answers (1)

Steve Miller
Steve Miller on 25 Jun 2021
Hi there,
When you have incredibly small inertias, tiny forces lead to gigantic accelerations. This can make a number of variable change very rapidly, and the solver has to take very tiny steps to make sure it captures the dynamics. I am not sure what your application is, but 1e-9 kg*m^2 is roughly one grain of sand.
In the current release, you can scale your variables so that the error tolerances the solver is trying to adhere to can be applied consistently, which will speed up your simulation.

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