Polytech. Univ., Rte. 110, Farmingdale, NY 11735
Two complementary descriptions can be employed to characterize the transient wave response of a fluid-loaded structure. In the oscillatory description, the wave phenomena are synthesized by global resonances that take the form of damped sinusoidal responses. In the progressing description, the wave phenomena can be organized in terms of wave fronts that travel from the source to the scatterer, and then interact with the scatterer to generate new wave fronts that travel to the sensor. Regarding the computational efficiency, the progressing description is effective to represent the early time arrivals because of time causality, but the oscillatory description is convenient to describe the late arrivals where the medium has fully responded to the excitation. With respect to data acquisition and interpretation, both arrival times of wave fronts and resonant frequencies of oscillatory waves are good physical observables. Therefore, a hybrid combination of these two representations are desirable for applications such as detection and classification. Here, the concept is demonstrated by a systematic formulation and numerical examples. Time-frequency analysis is also employed to interpret the simulation results. [Work supported by ONR and NRL.] [sup a)]On sabbatical leave and is visiting Naval Res. Lab., Washington, DC.