Dynamic stiffness problem show no results

[simulation_engineer_2022]

Hi everyone!

I'm trying to get dynamic stiffness for cylindrical part with blind hole and could not get any result (all requested data have zero values).

The scenario is the following:
Clamp from one side, Reference Point with coupling from the other side (fix U1,U2,U3,UR1,UR2, free UR3)
Applied rotation to Reference Point 0.01 radians at the 1st step.
Unit Torque to Reference Point at the 3rd step.

Steps sequence:
1) Static Step - structure loading with applied rotation.
2) Frequency Step - extracting first 100 natural frequencies for loaded structure.
3) Steady-State Dynamics Modal Step - getting structure response for unit torque in all requested natural frequencies range.

All requested displacements and rotations for reference point show zero values for whole frequencies range.

Generally speaking it is quite close to real problem I'm trying to solve now, but for this thread I've made test example which is described above. Just for clarity - I get zero-value results both in real problem and in the test one. Does anyone know how to deal with it? Maybe this solution has physical meaning, but from my perspective I should get reaction due to applied torque. Input file is attached as well as explanatory screenshots. Thanks in advance!

 

[FEA way]

It will work if you apply the prescribed rotation in preload step with equivalent torque. That rotation BC is propagated as fixed.

 

[simulation_engineer_2022]

FEA way, thank you!

But what if in my real problem torque loading leads to non-convergence? Is there any other options? I know that prescribed translation/rotation gives better convergence that equivalent force/torque, so I used this approach.

 

[FEA way]

You can use *Boundary, op=new to reset the boundary conditions in the second step and redefine only those that are necessary (without the one applied to DOF 6 of the reference point).