Directional Infragravity Waves Induced by Bichromatic and Bidirectional Waves: Theoretical Approach and Experimental Affirmation

Abstract

This work presents a theoretical discussion and experimental results about the directional bound waves generated by second-order nonlinear interaction between two noncollinear wave trains. Research focus is set on presence, characteristics, and effects of the angle difference between the primary wave trains on the generation of super- and subharmonic bound wave components as well as propagation direction, orbital velocity, and the resulting radiation stress field. An analytical model is derived, and computations thereof conducted for different conditions of wave height, period, and depth. Laboratory tests, systematically conducted in a wave basin, confirm computational results from analytical formulation and indicate that (i) the magnitude of all second-order properties (setup and setdown of the mean water level, orbital velocities) are strongly dependent on the individual combination of periods and directions of the primary wave trains, (ii) the direction of the bound wave differs from those of the primary waves, and (iii) the radiation stress components show a spatial and temporal oscillatory pattern outside the surf zone.