Application of Energy Methods in Mechanical Shock to Study Base Excited Nonlinear System Response

Abstract

The paper describes a structural dynamic analysis of a notional ground combat vehicle instrumentation display rack. The rack was subjected to hypothetical base accelerations typical for vehicle mobility loads, but not actual data. The rack concept was used as a surrogate to study the accuracy of an approach using an acceleration time-history synthesized to be compatible with a prescribed shock response spectrum (SRS). The SRS was determined from an original (given) acceleration-time history. Both the original and the synthesized time histories were applied to a simple lumped mass six degree-of-freedom (6DOF) model of the display rack. The rack was modeled with both linear and nonlinear shock mounts. Comparisons of displacements were made using the original and synthesized time histories at five different system frequencies. At certain system frequencies there was good agreement, poor agreement at other frequencies. Evolving energy methods in mechanical shock were used to explore the root cause of the frequency based variability in the system response. Input energy spectra were generated for each time history and compared to the maximum energies from the 6 DOF model at each system frequency.