Towards Robust Input Synthesis for Multi-Axis Vibration Testing

Defining multi-axis vibration test input specifications based on arbitrary known structural responses is addressed in this article. The nominal excitations can include any combination of local forces, distributed loads and enforced support motion. Measured responses or reference data derived from correlated finite element method (FEM) models can be employed. Expressions for the optimal excitations to be applied to a desired set of degrees of freedom (DOFs) are given for the cases of harmonic and random vibration analysis. Solution optimality is defined in a bounded-variable least-squares (BVLS) sense, allowing the practical constraints of test facilities to be accounted for. The proposed method is validated with a spacecraft mass dummy, by means of both simulation and physical tests. Responses due to rotation-dominant 6-DOF base random vibration are computed in FEM, reduced to an equivalent 3-DOF translational excitation using the BVLS method and finally executed on a triaxial shaker. The recorded correlation between numerical results and test measurements is conferred.