Validation of RANS Modelling for Wave Interactions with Sea Dikes on Shallow Foreshores Using a Large-Scale Experimental Dataset

Abstract

In this paper, a Reynolds-averaged Navier–Stokes (RANS) equations solver, interFoam of OpenFOAM®, is validated for wave interactions with a dike, including a promenade and vertical wall, on a shallow foreshore. Such a coastal defence system is comprised of both an impermeable dike and a beach in front of it, forming the shallow foreshore depth at the dike toe. This case necessitates the simulation of several processes simultaneously: wave propagation, wave breaking over the beach slope, and wave interactions with the sea dike, consisting of wave overtopping, bore interactions on the promenade, and bore impacts on the dike-mounted vertical wall at the end of the promenade (storm wall or building). The validation is done using rare large-scale experimental data. Model performance and pattern statistics are employed to quantify the ability of the numerical model to reproduce the experimental data. In the evaluation method, a repeated test is used to estimate the experimental uncertainty. The solver interFoam is shown to generally have a very good model performance rating. A detailed analysis of the complex processes preceding the impacts on the vertical wall proves that a correct reproduction of the horizontal impact force and pressures is highly dependent on the accuracy of reproducing the bore interactions.

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

“…The test included mostly plunging breakers on the 1:10 transition slope and spilling breakers on the 1:35 foreshore slope in front of the dike. All other relevant details of the tests and the processing of the experimental data used in this paper for the inter-model comparison are provided by Gruwez et al [3]. For further information on the experimental model setup, the reader is referred to the work in [4].…”

“…Hydraulic parameters for the WALOWA bichromatic wave test (EXP) and its repetition (REXP): h o is the offshore water depth, h t the water depth at the dike toe, H m0,o the incident offshore significant wave height, R c the dike crest freeboard, f i the SW component frequency, a i the SW component amplitude and δ (=a 2 /a 1 ) the modulation factor. Reproduced from the work in [3], with permission from the authors, 2020. The OpenFOAM ® model and model setup as described by Gruwez et al [3] is used.…”

“…Reproduced from the work in [3], with permission from the authors, 2020. The OpenFOAM ® model and model setup as described by Gruwez et al [3] is used. To summarise, and citing the work in [3], the solver interFoam of OpenFOAM ® v6 [42] is applied, "where the advection and sharpness of the water-air interface are handled by the algebraic volume of fluid (VOF) method [43] based on the multidimensional universal limiter with explicit solution (MULES)" [44][45][46].…”

“…We chose to investigate the performance of each model as standalone for the present work in order to provide a detailed overview of model capabilities and limitations applied to wave-structure interaction phenomena in very shallow water conditions. The RANS model is the same one as presented by Gruwez et al [3], which was validated with large-scale experiments of overtopped wave impacts on coastal dikes with a very shallow foreshore from the WALOWA project [4]. In this paper, the same experiment and RANS model are used as a basis for the inter-model comparison with the (until now untested for this case) DualSPHysics and SWASH models.…”

“…However, numerical modelling has become a possibility as well by applying computational fluid dynamics (CFD) techniques. In particular, Gruwez et al [3] have already shown that numerical modelling with a Reynolds-averaged Navier-Stokes (RANS) model (i.e., interFoam of OpenFOAM ® ) can provide very similar results to large-scale experiments of overtopped wave impacts on coastal dikes with a very shallow foreshore (i.e., from the WAve LOads on WAlls (WALOWA) project [4]). Yet, such Eulerian numerical methods require often expensive mesh generation and need to implement conservative multi-phase schemes to capture the nonlinearities and rapidly changing geometries.…”