Focused wave group propagation over fringing reef and its impact on the vertical wall mounted on a reef flat: Experiment and RANS modeling

This paper presents flume experiments and numerical simulations of focused wave group propagation over an idealized fringing reef profile and its impact on the vertical wall mounted on reef flat. The large transient wave group is produced over the steep fore-reef slope by focusing JONSWAP wave trains. The numerical simulations are performed using the compressible two-phase OpenFOAM model. Wavelet and FFT analysis of the surface elevation time histories clearly show wave focusing process and the generation of higher harmonics due to the nonlinear wave-wave interactions. For the high peak frequency cases, the low frequency wave motion increases gradually after wave breaking, but the peak frequency motion still dominates energy spectrum partially due to wave defocusing and reformation of broken waves. However, the magnitude of low frequency wave motion is higher than those around peak frequency and high harmonics for the lower peak frequency cases. It is found that the contribution of low frequency wave motion to the total force exerted on the wall is comparable to or higher than peak frequency wave motion. The effect of geometry characters of fringing reef and focusing position on the maximum horizontal force on the vertical wall is investigated utilizing the validated OpenFOAM model.