Waves in elastic material

Sea ice covers about 7% of the Earth's surface and 12% of the world's oceans. The presence of global warming and an increase in human activities in the polar region has resulted in significant interest in the behaviour of waves and ice interaction. In this study, the experimental investigation of waves-ice interaction is presented in the form of propagating waves in elastic materials. This investigation aims to study wave propagation, and energy transition as waves enter from open water to a water region covered with an elastic sheet. As the waves propagate in the elastic material, the waves immediately attenuate, suggesting a loss in energy. This loss in energy cannot be explained in the classical sense (breaking etc.) as the elastic sheet's existence prevents the breaking in waves of large amplitudes. The underlying mechanism as waves adapt to the elastic region is crucial for understanding the possibility of build-up in wave energy within the elastic sheet.

 

For the experiments, a JONSWAP spectrum was used to generate wave fields. Ultrasonic probes were used to measure the surface elevation of the elastic layer and the open water free surface, and these two were compared. The attenuation rates are investigated as a function of distance. The spatio-temporal properties of the wave fields are investigated using 2D FFT to obtain the wavenumber-frequency spectrum. We find significant second-order nonlinear effects as the waves propagate with an elastic cover. Especially the occurrence of second-order difference interactions, sometimes called the group line, was found to be conspicuous in some of the wave fields.