Base Excitation
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.
When a structure is subjected to a base excitation, displacements, velocities, and accelerations are measured relative to a space-fixed coordinate system.
Coordinate System Selection
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.
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
A degree of freedom should either be constrained or free in the direction where the base excitation acts. Having a constraint acting in a local direction that is not either aligned or orthogonal to the excitation may produce unexpected results.
As other global physics features, Base Excitation is global only within the interface, where it has been added. In case of several coupled structural interfaces in the model, you will need to add such feature under each of the involved interfaces. It will also have no effect on nonstructural interfaces involved in a multiphysics coupling such as, for example, fluid–structure interaction.
Location in User Interface
Context Menus
Solid Mechanics > Base Excitation
Shell > Base Excitation
Layered Shell > Base Excitation
Plate > Base Excitation
Membrane > Base Excitation
Beam > Base Excitation
Pipe Mechanics > Base Excitation
Truss > Base Excitation
Wire > Base Excitation
Multibody Dynamics > Base Excitation
Ribbon
Physics tab with a structural mechanics interface selected:
Global > Base Excitation