Efficient two-layer non-hydrostatic wave model with accurate dispersive behaviour

Robert T. McCall,Kees Nederhoff,Ad J.H.M. Reniers,Menno P. de Ridder,Ap R. van Dongeren,Pieter B. Smit

doi:10.1016/j.coastaleng.2020.103808

Abstract

A 2-layer non-hydrostatic model with improved dispersive behaviour is presented. Due to the assumption of a constant non-hydrostatic pressure distribution in the lower layer, the dispersive behaviour is improved without much additional computational time. A comparison with linear wave theory showed that this 2-layer model gives a better result for the dispersion relation and shoaling of waves in intermediate water. This means that the 2-layer model is applicable in shallow and intermediate water depths (up to relative depths kh equals 4), whereas the 1-layer model is only applicable in shallow water depths (kh smaller than 1). Three laboratory experiments, including a fringing reef and a barred beach, were used to validate the presented mode for different hydrodynamic conditions. Based on these results, it can be concluded that the 2-layer model can be applied to accurately simulate the bulk wave height and spectral properties. The low frequency wave height, the setup and in particular the second order statistics contain more scatter, but the model accurately captured the general trend. Furthermore, the model showed good results for complex bathymetries in shallow to intermediate water.

Highlights

Numerical wave models are routinely used to transform offshore waves to nearshore conditions in order to design and evaluate coastal structures, sea defences and port operations (McComb et al, 2009; Cavaleri et al, 2007; Thomas and Dwarakish, 2015)
The wave height decreases with 20%, whereas linear wave theory does not show a decrease of wave energy
First the hydrodynamic behaviour of the barred beach is shown for test 1C, which shows com parable results as the other tests

Summary

Introduction

Numerical wave models are routinely used to transform offshore waves to nearshore conditions in order to design and evaluate coastal structures, sea defences and port operations (McComb et al, 2009; Cavaleri et al, 2007; Thomas and Dwarakish, 2015). This trans formation is efficiently performed by spectral-domain models such as SWAN (Booij et al, 1996), which transform phase-averaged properties of the wavefield, under the assumption of weakly-nonlinear (small wave steepness), homogeneous (small spatial gradients) wave motion. Other shallow-water processes such as wave run-up, reflection, and diffraction are typically not accounted for

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