The infragravity (IG) period oscillations inside an elongated rectangular harbor excited by bichromatic wave groups are simulated using a fully nonlinear Boussinesq model. Based on an IG wave analysis technique, this study presents a comprehensive investigation on how bound and free IG waves and their relative components change with respect to the amplitudes and wavelengths of incident primary (short) waves under the condition of the lowest four resonant modes. For the given harbor and ranges of wavelength and amplitude of the primary waves studied in this paper, it is shown that the amplitudes of both the bound and free IG waves become more evident when the short wavelengths increase, and the latter are always larger than the former due to resonant amplification. The amplitudes of both the bound and free IG waves change quadratically with the amplitudes of the incident short waves.
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