An Inter-Model Comparison for Wave Interactions with Sea Dikes on Shallow Foreshores

Vincent Gruwez,Corrado Altomare,Peter Troch,Lorenzo Cappietti,Andreas Kortenhaus,Tomohiro Suzuki,Maximilian Streicher

doi:10.3390/jmse8120985

Abstract

Three open source wave models are applied in 2DV to reproduce a large-scale wave flume experiment of bichromatic wave transformations over a steep-sloped dike with a mildly-sloped and very shallow foreshore: (i) the Reynolds-averaged Navier–Stokes equations solver interFoam of OpenFOAM® (OF), (ii) the weakly compressible smoothed particle hydrodynamics model DualSPHysics (DSPH) and (iii) the non-hydrostatic nonlinear shallow water equations model SWASH. An inter-model comparison is performed to determine the (standalone) applicability of the three models for this specific case, which requires the simulation of many processes simultaneously, including wave transformations over the foreshore and wave-structure interactions with the dike, promenade and vertical wall. A qualitative comparison is done based on the time series of the measured quantities along the wave flume, and snapshots of bore interactions on the promenade and impacts on the vertical wall. In addition, model performance and pattern statistics are employed to quantify the model differences. The results show that overall, OF provides the highest model skill, but has the highest computational cost. DSPH is shown to have a reduced model performance, but still comparable to OF and for a lower computational cost. Even though SWASH is a much more simplified model than both OF and DSPH, it is shown to provide very similar results: SWASH exhibits an equal capability to estimate the maximum quasi-static horizontal impact force with the highest computational efficiency, but does have an important model performance decrease compared to OF and DSPH for the force impulse.

Highlights

Urban areas situated along low elevation coastal zones need to be protected against wave overtopping and flooding during storm conditions
The inter-model comparison of those three numerical models to the experiment (EXP) demonstrated that they are all capable of modelling the dominant wave transformation and the wave–structure interaction processes involved leading up to the impacts on the vertical wall, albeit with a varying degree of accuracy
These statistics were plotted over the wave flume to provide spatial insight into the model performance, and the pattern statistics were plotted in a skill diagram, which visualised both the model performance and pattern statistics in a summarised way

Summary

Introduction

Urban areas situated along low elevation coastal zones need to be protected against wave overtopping and flooding during storm conditions. In the design of these structures, such wave loading needs to be considered This is a challenging task, because along the cross section of a hybrid beach–dike coastal defence system, storm waves are forced to undergo many transformation processes before they reach the structures on the dike. These hydrodynamic processes include shoaling, wave dissipation by breaking (turbulent bore formation) and bottom friction, energy transfer from the sea/swell or short waves (hereafter SW) to their super- and subharmonics (or long waves: hereafter LW) by nonlinear wave–wave interactions, reflection, wave run-up and overtopping on the dike, bore impact on a wall or building, and reflection back towards the sea interacting with incoming bores on the promenade

Objectives

Methods

Results

Discussion

Conclusion