Nonlinear Interactions of Waves on Shallow Water
This paper presents the results of theoretical and experimental investigations of second-order nonlinear interactions between standing surface waves on shallow water. The nonlinearity is introduced by the nonlinear terms in the Navier–Stokes equation and in the boundary conditions. The wave amplitudes are kept small enough for amplitude dispersion to be negligible, and the surface is treated as a resonantly driven, damped, harmonic oscillator. A pure first-order mode is excited by applying time periodic electrical stresses onto the free fluid surface, and this mode self-interacts to drive resonantly a second-order mode. The amplitudes are ultimately limited by dissipative processes in the fluid. These processes are taken into account in the theory, and the experimental results justify the assumptions made. Wave amplitudes could be monitored to a spatial resolution of 5 × 10−4 cm by an optical technique.