Prescribed Acceleration
The Prescribed Acceleration node adds a boundary or domain condition where the acceleration is prescribed in one or more directions. This condition is applicable for time- dependent and frequency domain studies. It is possible to prescribe an acceleration in one direction, leaving the structure free in the other directions. The Prescribed Acceleration node is a constraint and overrides any other constraint on the same selection.
To prescribe accelerations on the top or bottom surfaces of the shell, use Prescribed Acceleration, Interface.
Shell Properties
The selection in this section only acts as a filter for the boundary selection.The condition is applied all through the thickness of the shell.
If the same layer is selected in two Prescribed Acceleration nodes being active on the same boundary, the second definition will override the previous.
All other settings for the Prescribed Acceleration node are described in the documentation for Prescribed Acceleration in the Solid Mechanics interface.
Location in User Interface
Context Menus
Ribbon
Physics tab with  Layered Shell selected: