Experimental investigation on multi-mode resonances in a rectangular harbor

Abstract

Physical experiments were conducted to investigate the oscillations in a rectangular harbor for different modes with the same resonant frequency. Two multimode resonances, that is, case A for modes (0, 2) and (3, 1) and case B for modes (1, 1) and (2, 0) excited by bichromatic waves, were examined. The results showed that the multimode resonance was excited. During the response process when the resonance is initially excited, the subharmonic energy mainly focused on mode (0, 2) for case A and mode (2, 0) for case B. With the continuous input of wave energy, periodic modulations for the infragravity waves in the harbor were observed, implying that the subharmonic energy transfers freely between the two modes in a quasi-steady state. During the damping process, with no waves, the subharmonic energy returns to the mode that occupies the response process. The phenomenon that the subharmonic energy concentrates in the same mode in the response and damping processes is possibly because these modes are more easily excited than the others.