Query to apply Bushing or Complant for Fixed Joint in MotionView/MotionSolve

Sun9bro

Query to apply Bushing or Complant for Fixed Joint in MotionView/MotionSolve

I want to input a damping ratio for a fixed joint or bushing in motionsolve. However, there is no space for inputting a damping ratio, and I need to input a damping coefficient. I would like to know the approach used to calculate the damping coefficient in multibody dynamics software, or how to input the damping ratio. (Also, when inputting structural damping for a tower, etc., only the damping ratio can be input.) To calculate the damping coefficient, I need to know the mass and natural frequency, but I don't know which mass and natural frequency should be input for the joint-applied complant or bushing. (Is it the first mode in each direction of the entire system? The second mode? Or the mode between two connected elements? Is the mass the mass of the entire system?)

Praful

Hello @Sun9bro

Through your description it is not clear exactly what kind of system you are trying to model in multi-body. However, generally, you can consider the bushing as a spring-damper system connected between 2 masses. The damping coefficient that is required is related to the damping characteristic of the bushing by itself and may not necessarily relate to the structural damping of the bodies that is connected to.

In the event you want to consider a "damping ratio", you may want to consider the stiffness of the bushing and the amount of mass/inertia of bodies that actually translate/rotate in a particular direction of the bushing to get a "natural frequency" and critical damping coefficient and then obtain the damping coefficient. Of course this is approximate and quite a simplification and does not consider other effects such as cross coupling and frequency dependency.

regards

Praful