Force oscillation on geometric bodies in MBD process

Raheem Sterling_22160

Hi, 

For example, I applied a force in y direction increased from 0kN-100kN in linear on the geometry within 0-1s, but from the total force in analysist tree, the total force in y direction oscillation as below, I don't know which aspects can mitigate this oscillation.

The force was applied with PID, but I only set Kp due to the force increased in linear, and the resititution coefficient between geometry and particles was 0.0001.

Thanks

Stephen Cole

Hi Raheem,

Was this a custom code using the coupling interface?  You could add a damping to the code.

 

However with restitution I think 0.1 should be the lowest value, or if you do go lower you may need to have very low time-steps.  You can go lower than 0.1 and theoretically there is no lower limit however it is quite difficult to resolve the forces at a restitution of 0 or close to 0 so for stability I try to keep the minimum to around 0.1 and look at other damping factors.  What you may find is that at 0.0001 the simulation is unstable and actually increasing this gives more damping if the case is more stable.

Regards

Stephen

Raheem Sterling_22160

Stephen Cole_21117 said:

Hi Raheem,

Was this a custom code using the coupling interface?  You could add a damping to the code.

 

However with restitution I think 0.1 should be the lowest value, or if you do go lower you may need to have very low time-steps.  You can go lower than 0.1 and theoretically there is no lower limit however it is quite difficult to resolve the forces at a restitution of 0 or close to 0 so for stability I try to keep the minimum to around 0.1 and look at other damping factors.  What you may find is that at 0.0001 the simulation is unstable and actually increasing this gives more damping if the case is more stable.

Regards

Stephen

Hi Stephen,

Yes, I've tried to added a damping force to my simple test model as below. The applied force was F, and damping force was set as (-damp_coeff)*F. But it seems a little change in the total force as below. The target force is 233kN. Maybe it will be better to relate velocity.

Regards!

Raheem