Numerical simulation of interaction between wind and 2D freak waves

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThis paper presents a newly developed approach for the numerical modelling of wind effects on the generation and dynamics of freak waves. In this approach, the quasi arbitrary Lagrangian-Eulerian finite element method (QALE-FEM) developed by the authors of this paper is combined with a commercial software (StarCD). The former is based on the fully nonlinear potential model, in which the wind-excited pressure is modelled using a modified Jeffreys' model (C. Kharif, et al. J. Fluid Mech. 594:209-247,2008).The latter has a volume of fluid (VOF) solver which can handle violent air-wave interaction problems. The combination can simulate the interaction between freak waves and winds with an improved computational efficiency. The numerical approach is validated by comparing its predictions with experimental data.Satisfactory agreements are achieved. Detailed numerical investigations of the interaction between winds and 2D freak waves are carried out, which not only explore different air flow states but also reveal the wind effects on the change of freak wave profiles. Both breaking and non-breaking freak waves are considered.

Did the Draupner wave occur in a crossing sea?

“…The main features of the QALE-FEM are that the unstructured mesh is moving at every time step using a specially developed spring analogy method for free surface problems and the velocity is calculated by a three-point technique suitable for any mesh structures (Ma 2008;Yan & Ma 2010a). More importantly, the QALE-FEM can model highly nonlinear free surfaces and three-dimensional overturning waves.…”

MLPG_R method for modelling 2D flows of two immiscible fluids

“…This paper mainly concerns multiphase flow in marine engineering, where the dynamic viscosity of fluids, such as water and air, is very small ( ) and plays a less important role as discussed by [20] and [34]. In addition, the results for wind-wave interaction in [35] and for water-air sloshing in [36] demonstrate that the tangential velocity near interface can change from one direction to another in a thin layer, typical shear flow phenomenon. Based on these facts, the tangential velocity is not constrained to be continuous, i.e., 'slip' condition may be applied on the interface like on a rigid boundary.…”

“…Different particle numbers of 25,30,35,40,55 and 80 along the depth of are then tested for the case, corresponding to initial particle distances of 0.04m, 0.033m, 0.029m, 0.025m,0.018m and 0.013m, respectively. The time step is determined by the courant number of 0.018.…”

Improved model for air pressure due to wind on 2D freak waves in finite depth

“…This pressure model is developed by analysing the pressure distribution over freak waves using the QALE-FEM/StarCD approach, which combines the quasi arbitrary LagrangianEulerian finite element method (QALE-FEM) with the commercial software package StarCD and has been proven to be sufficiently accurate for such cases according to our previous publication [8]. In this model for air pressure, the pressure is decomposed into the components related to the local wave profiles and others.…”

“…Considering the strong nonlinearity associated with freak waves, four numerical strategies may be implemented as summarised in [8,9]. Only the second strategy, in which a fully nonlinear potential flow (FNPT) is applied to govern the wave motion coupling with a model expressing the wind-excited pressure, and the fourth one, which combines a FNPT model with a Navier-Stokes solver, have been attempted for the cases with freak waves [8].…”