The Acceleration Node ()feature adds an acceleration node to the system. This node is used in order to prescribe the acceleration of one or more ports of a component.

Enter a component Name for the acceleration node. The default name (for the first instance) is acc1.

Set the Node name for the acceleration node.

Specify the value of Acceleration, ap1.

Also select Displacement in stationary study — Free or Constrained.

Physics tab with  Lumped Mechanical System selected: