Mode-based Frequency Response Function and Steady State Dynamics in LS-DYNA

Two new features used for frequency domain structural analysis --- frequency response function (FRF) and steady state dynamics (SSD), have been implemented in LS-DYNA, based on mode superposition techniques. As a characteristic of a structure, FRF is the transfer function which represents structural response resulting from applied unit harmonic excitations. The harmonic excitations can be given in the form of nodal force, base acceleration or pressure. The FRF feature provides user the opportunity to acquire a spectrum of structural response (displacement, velocity and acceleration) for the applied unit excitation. As a direct extension of FRF, SSD calculates the steady state dynamic response of a system subjected to a given spectrum of harmonic excitations. Both FRF and SSD give results in complex variable form, enabling user to obtain not only amplitude of response, but also phase angle. A benchmark example of a rectangular plate is included to demonstrate the effectiveness of both features. Some discussions regarding the effect of damping and individual mode contributions are also included.