The Rotating Frame and
Linearly Accelerated Frame nodes have a domain selection. They can be applied selectively, and also depend on the coordinates. When applied to a set of selected domains, such loads are applied also to lower dimensional objects, for example, a point mass or an added mass on an edge.
When a structure is subjected to an acceleration which is applied to all its support points, then it often more convenient to replace the support acceleration by an acceleration force, using a Base Excitation node. In particular, this is necessary when using modal based dynamic analyses, in which nonzero prescribed displacements cannot be used. Changing to a frame acceleration load does not affect the distribution of forces and stresses. It will however imply that displacements, velocities, and accelerations are measured relative to the supports, and not relative to a room fixed coordinate system. The
Base Excitation node does however also define absolute acceleration variables, which are what would be measured by an accelerometer.