On the Application of OpenFOAM® in Gravity Water Wave Generation and Wave-Structure Interaction

Abstract

This article presents an investigation on the best practice for modeling of water wave generation and wave-structure interaction using a widely spread two-phase flow solver with a specific interface compression technique in OpenFOAM® (OpenFOAM Foundation Ltd., London, United Kingdom). A series of numerical experiments were conducted to examine the effects of the employed schemes, mesh resolution, time step resolution, and compression coefficient. Both surface elevation and velocity profile were considered as the criteria for assessment of the quality of the generated waves. The numerical experiments showed that by using a blending scheme between the Crank-Nicolson and Euler scheme, relatively high quality waves were produced, where the spurious current at the interface region was effectively reduced. Meanwhile, it was also recommended to apply a compression coefficient Cα = 1, the Courant number limit Co = .1, and a mesh resolution of 18 cells per wave height. This set of parameters was used to validate the numerical model for two sets of cases for wave forces on half-immersed horizontal cylinders. The results in general agreed well with the experimental data, although the inline forces were slightly but consistently overestimated. 1. Introduction In the past few decades, because of the increase in the computing ability and resources, computational fluid dynamic (CFD) approach has been gaining popularity in the naval hydrodynamic communities. Considering that a large portion of naval hydrodynamic problems are concerned with the free-surface flows, e.g., ocean waves and its interaction with structures, a free-surface model is needed to couple with the Navier-Stokes solver. Eventually, as a result of direct application of the first principles, the solver can model both inertia and viscous dominant flows. Even local wave breaking and violent flows can be properly resolved. Different methods have been proposed to track the interface of free-surface flows. This includes height function method and line segment method, which are the simplest techniques to represent and configure a free surface. However, they have deficiencies when two surfaces intersect or when a surface folds over on itself, which are overcome by the marker and cell method proposed in Harlow and Welch (1965). In their method, massless particles are used to track the free surface in a Lagrangian manner. Alternatively, the level-set (LS) method or volume of fluid (VOF) method can be used to implicitly capture the surface in an Eulerian way. The LS method was introduced in Osher (1988) where the interface is defined as the one on which a level-set function is equal to zero. This LS function is continuous across the interface. Therefore, it is not significantly influenced by the numerical diffusion. However, the originally proposed LS method suffers from mass conservation problems, which has been resolved in, e.g., Olsson and Kreiss (2005) and Olsson et al. (2007).