ASA 125th Meeting Ottawa 1993 May

5aUW11. Free and forced vibrations in a floating ice sheet: Modeling and comparison with data.

T. C. Yang

Naval Res. Lab., Washington, DC 20375

T. Yates

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.