Comparison of a spectral wave model with a fully nonlinear potential flow wave model

This study evaluates the performance of the MIKE 21 Spectral Wave (SW) model by comparing the evolution of the spectrum with the fully nonlinear potential flow model OceanWave3D. We test only the shoaling, nonlinear wave–wave interaction and whitecapping terms by considering a two-dimensional shoaling problem on a mild slope bottom without wind, or bottom friction effects and before reaching the breaking zone at the beach. A JONSWAP spectrum is introduced at the deep-water boundary and allowed to propagate freely up to a relatively shallow shelf. The peak wave is in relative water depth 𝑘ℎ = 4 at the deep water boundary where 𝑘 = 2𝜋∕𝜆 is the wave number, 𝜆 the wavelength and ℎ the water depth. For the peak relative water depth greater than about 𝑘ℎ = 0.8, the spectrum agrees well with the fully nonlinear results, but below this value significant differences appear. In particular, the long-wave difference frequency effects are mostly absent,
indicating a need for improvement in the SW triad interaction model.