Erik Kostson
Ansys Employee

That is much clearer now.

See the reference and help manual for accelerations in a transient analysis (acceleration is a global load and is applied to the entire model).

So in general, you need to model and capture the physics of this part as it is in its physical environment, hence apply the closest boundary conditions and loads that represent the real physical situation.

E.g., one could use a force (which will cause movement of the outer part) scoped to the outer part (say an outer face) and see how much is transmitted to the inner part, just as one can do when looking at transmission and vibration isolators.

All the best