T. C. Yang
Naval Res. Lab., Washington, DC 20375
Vector Res. Co., Rockville, MD 20852
Time domain waveforms excited by an impulse, point force are modeled using fluid-loaded thin plate theory and compared with measured data collected on ice-implanted geophones. In the frequency domain, the solution, expressed as an integral over wave number, can be expressed in terms of poles (free waves) and branch cuts (forced waves). The time domain solution is obtained by taking a Fourier transform of the frequency response of the plate, weighted by the (measured) source spectrum. The modeled time domain waveform compared favorably with the received time series data. A simple direct time domain solution for the forced wave in a thin plate in air also approximates the data well. It is shown that the forced wave solution produces the ``abnormal'' dispersion relation observed in recent geophone data. The free-wave solutions, which have been extensively studied before, also agree with the geophone data.