The Base Excitation node is used to represent an acceleration that is applied at all constraints. The main use case is for modal-based analyses, in which case it is not possible to directly prescribe nonzero displacements at constrained degrees of freedom. It is, however, possible to use Base Excitation in any type of dynamic analysis.

The Global coordinate system is selected by default. The Coordinate system list contains all applicable coordinate systems in the component. The coordinate system must have orthonormal coordinate axes, and be defined in the spatial frame. Select a coordinate system in which the base acceleration vector is represented. Only systems with space-independent axis directions are consistent with the assumptions of the base excitation.

Enter the Base acceleration, ab.

For postprocessing purposes, the feature also computes the absolute velocity and displacement vectors by integrating the base acceleration ab. These variables are available with the names <phys>.v_abs and <phys>.u_abs (for example, solid.u_absX for the X-component of the absolute displacement vector). For further details, see Frame Acceleration Forces in the Structural Mechanics Theory chapter