Nonlinear Interactions of Two Incident Internal Waves

We present experiments and analysis of the nonlinear interactions of two incident internal gravity wave beams of comparable amplitude. By using a wave maker consisting of a flexible boundary to a tank, driven by an array of independent actuators, incident beams of large amplitude several wavelengths in width are generated. Additional wave beams, produced via triadic interactions, are observed emanating from where incident beams of moderate amplitude cross. We decompose the fields, both temporally and spatially, in order to identify the transfer of energy between the modes. A perturbation approach is used to predict the the frequencies of the generated waves, which is in close agreement with observations. Finally, in the related con guration where the two incident frequencies are the same, wave breaking with the emission of other internal waves is observed when a large amplitude wave refects off an interface.