Internal wave excitation by a vertically oscillating elliptical cylinder

Laboratory experiments are performed to measure the amplitude of internal waves generated by an elliptical cylinder oscillating vertically with different frequencies and amplitudes in a uniformly stratified fluid. The experimental results are compared with the theoretical predictions of Hurley and Keady (1997). Though in qualitatively good agreement with experiments, the theory underestimates the amplitude of low-frequency waves and overestimates the amplitude of high-frequency waves. The measured beam width is underestimated by theory, which neglects the dynamics of viscous boundary layers surrounding the cylinder. When the cylinder oscillates at a frequency less than half the buoyancy frequency, experiments reveal that two sets of waves beams are generated. The secondary set of waves have double the frequency of the primary waves and are excited due to nonlinear processes.