Volume-of-Fluid Model Comflow Simulations of Wave Impacts on a Dike

Abstract

ComFLOW is a 3D Volume-of-Fluid (VOF) model to solve the incompressible Navier-Stokes equations including free surface, or to solve the Navier-Stokes equations for two-phase flow problems (two-phase flow: both an incompressible viscous fluid (e.g., water) and a compressible viscous fluid (e.g., air) are present). The problem statement of the present study reads: ‘Is ComFLOW capable of accurate prediction of wave impacts on (impermeable) coastal structures such as dikes? And, if so, what are the preferred model settings and associated computing times?’. In this paper, ComFLOW is validated for this purpose by comparison against pressure data as measured in the Delta flume by pressure sensors at dikes. We have selected three different experiments, with typical dike geometries (slope 1:3.5, with and without berm) at which more than 20 pressure sensors were installed. The results can be summarized as follows. The pressure measurements are reproduced well in the simulations. A grid with about 170 grid cells per wave length in the horizontal, and between 4 and 6 grid cells per wave height in the vertical, proves to be sufficiently fine. At such a grid resolution and with about 450 by 35 grid cells in the computational domain, a typical CPU time is 35 minutes for simulations with a model time of 10 wave periods. For the present application, it is preferable to use the one-phase flow model rather than the two-phase flow model, since the former gives better results in the lower located pressure sensors and consumes less CPU time.

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

“…For example, volume-of-fluid methods (VOF) based on the Reynolds-averaged Navier-Stokes equations (RANS) have been widely employed during the last decades. Using RANS models, processes such as wave transformation [8,19,20], wave overtopping [7,21,22], and wave impact on coastal structures [3,[23][24][25][26] have been modelled and validated, but never before at the same time (to the knowledge of the authors). They are computationally very expensive to apply, but have shown their value particularly for wave-structure interaction phenomena involving complex geometries.…”

Force and water jet impact reduction on adjacent structures by means of free surface breakwaters

“…The solver has been validated to properly model violent free-surface flows such as wave interaction with breakwaters [28], sloshing [3,27], wave run-up [17,29], green water impacts [2]. This makes it suitable for estimating breakwater induced wave energy dissipation by wave breaking, wave run up and overtopping, return flow and the disturbance of the wave orbital path.…”

“…The most energetic waves of sea state 2 are longer so have even more cells per wave length. For calculating the pressures on impermeable coastal structures it is recommended to use about 170 grid cells per wave length and between 4 and 6 grid cells per wave height, see [29].…”

Multi-fidelity Kriging extrapolation together with CFD for the design of the cross-section of a falling lifeboat

“…Examples of extreme FSI are found when waves impact with structures [2,29,42,44,45]. Note that when waves are concerned, simulations benefit from Generating Absorbing Boundary Conditions [5,6], both in terms of accuracy and of computing time.…”