Identification of evolving interfacial waves by spatial harmonic analysis

This paper is concerned with an analysis of image processing data to identify interfacial waves at the interface between two fluid layers in a laboratory flume. The interfacial waves are excited through a non-linear resonant interaction with a surface wave traveling in a wave flume filled with a two-layer fluid. A spatial harmonic analysis is proposed to extract information about the nonlinear evolution of the constituent waves from the interface oscillation data. The analysis is capable of handling different stages of the resonance in the wave flume and gives accurate and consistent results on time variations of the wave amplitudes. Contrary to a temporal harmonic analysis, the proposed method does not require prescription of a functional form for the amplitude variations. The experimental measurements are compared to the theoretical predictions and available methods. The proposed method provides an efficient solution for detecting these waves and capturing their behaviors.