1.4.12 Double cantilever subjected to multiple base motions

Product: ABAQUS/Standard  

Enforced motion is often the primary source of excitation in vibration problems. Examples include vehicle suspensions responding to road irregularities and civil structures subjected to seismic ground motions. In these problems the forcing functions are given by the time history of motions at the supports of the structure.

For modal-based analyses using the *MODAL DYNAMIC and the *STEADY STATE DYNAMICS procedures, the support motions are simulated by prescribed excitations, called base motions. Base motions are applied by constraining groups of degrees of freedom into one or more “bases” by using the BASE NAME parameter on the *BOUNDARY option in the *FREQUENCY step. Multiple bases are required if base motions cannot be described by a single set of rigid body motions.

Degrees of freedom that are constrained without being assigned to a named base make up the primary base. This is the only base if the motion can be described by a single set of rigid body motions. Constrained degrees of freedom that are associated with named boundary conditions make up the secondary base or bases. ABAQUS uses the modal participation method for primary base motions and the “large mass” method for secondary base motions (see Base motions in modal-based procedures, Section 2.5.9 of the ABAQUS Theory Manual).

Problem description

Results and discussion

Input files

Figures

Figure 1.4.12–1 Double cantilever beam.

Figure 1.4.12–2 Base acceleration record.

Figure 1.4.12–3 Total transverse displacement response of beam midspan to base excitations with and without the 0.25 second time shift.

Figure 1.4.12–4 Total transverse displacement responses of beam midspan to base motions without time shift.

Figure 1.4.12–5 Total transverse displacement responses of beam midspan to base motions with the 0.25 second time shift.