It is generally accepted that nonlinear wave-wave interactions play an important role in harbor resonance. Nevertheless it is not clear how waves take part in those interactions. The aim of this paper is to investigate those processes for a rectangular harbor at transient phases. Long-period oscillations excited by bichromatic waves are simulated by the Boussinesq model. The simulations start from calm conditions for the purpose of studying the response process. The internal wavemaker stops working after the oscillations have reached a quasi-steady state, and it is used to simulate the damp process. In order to analyze temporary features of wave-wave interactions in different states, the wavelet-based bispectrum is employed. The influence of the short wave frequencies on long-period oscillations is investigated, and reasons are tried to be given from nonlinear triad interactions between different wave components and the interaction of short waves and the bay entrance. Finally, the response time and the damp time are estimated by a simple method.
harbor resonance, infragravity waves, wavelet-based bispectrum, wave-wave interactionsCitation: Dong G H, Wang G, Ma X Z, et al. Numerical study of transient nonlinear harbor resonance.When ocean waves of certain periods come into a harbor opening, they are often trapped and amplified. The phenomenon of such external energy trapped in a semi-enclosed domain and exciting large oscillations is called harbor resonance. Harbor oscillations are excited by the resonance that results from the agreement of frequencies of incident waves and the natural frequencies of the harbor. These large-amplitude oscillations could break mooring lines, damage fenders, cause hazards in berthing and loading, navigation through the entrance, etc. For many harbors, the most important natural modes have rather long periods, ranging from several minutes to an hour. Tsunamis and moves or fluctuations of atmospheric pressure have been shown to drive these oscillations [1,2]. The primary energy source for the occurrence of long-period waves in the coastal region is the nonlinear interactions of short-period waves. Low-frequency waves are generated following the propagation of these short waves. Mei and Agnon [3] and Wu and Liu [4] used different algebraic methods to show that long-period oscillations can be excited by the incident group of short waves. Not only the bound long waves can be amplified inside the harbor, but also the free long waves will be released when short wave groups propagate through the entrance. Such free long waves can further resonate the natural modes of the harbor basin. These conclusions were supported by De Girolamo [5] in the laboratory.During the last decade, Boussinesq-type equations with improved dispersion characteristics and nonlinear properties have traditionally been solved, and applied to model wave propagation from nearly deep water to the shoreline [6−9]. In order to flexibly fit the complex geometries of harbors and increase the computational accuracy, Woo and Liu...