L. Gentaz

A Potential/RANSE Approach for Regular Water Wave Diffraction about 2-d Structures

Abstract A new formulation is proposed for the simulation of viscous flows around structures in waves. It consists in modifying the Reynolds-averaged Navier-Stokes equations: velocity, pressure or free-surface elevation fields are split into incident and diffracted fields to compute the diffracted flow only. The incident flow may be explicitly given by a stream function theory for non-linear regular waves, or by a spectral method for irregular waves. This method avoids classical problems (large CPU time, poor quality of generated wave) of numerical generation of waves in a viscous flow solver. The 2D flow around an immersed square in regular waves demonstrates the effectiveness of the method.

Numerical simulation of a 3D viscous flow around a vertical cylinder in non-linear waves using an explicit incident wave model

The numerical simulation of 3D wave-body interaction problems in viscous fluid still leads to numerical difficulties, mainly due to large grid and CPU time requirements, especially for wave generation and propagation aspects. The correct treatment of open boundary conditions also remains problematic in direct approaches The method proposed here allows to avoid these problems by solving a modified problem for the diffracted flow only, the incident wave field being explicitly described by potential flow models. A set of results, both on 2D and 3D geometries is presented and commented, showing the capacity of the proposed scheme to solve problems of practical interest in ocean or offshore engineering in an efficient and accurate manner.Copyright

Fully Nonlinear Potential/RANSE Simulation of Wave Interaction With Ships and Marine Structures

This paper documents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach, a method for simulating fully nonlinear wave-body interactions including viscous effects. The methods efficiently combines a fully nonlinear potential flow description of undisturbed wave systems with a modified set of RANS with free surface equations accounting for the interaction with a ship or marine structure. Arbitrary incident wave systems may be described, including regular, irregular waves, multidirectional waves, focused wave events, etc. The model may be fixed or moving with arbitrary speed and 6 degrees of freedom motion. The extension of the SWENSE method to 6 DOF simulations in irregular waves as well as to manoeuvring simulations in waves are discussed in this paper. Different illlustative simulations are presented and discussed. Results of the present approach compare favorably with available reference results.Copyright

Simulation of Wave-Body Interaction Using a Single-Phase Level Set Function in the SWENSE Method

The purpose of this paper is to present combination of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations – [1]) method — an original method to treat fully nonlinear wave-body interactions — and a free surface RANSE (Reynolds Averaged Navier-Stokes Equations) solver using a single-phase Level Set method to capture the interface. The idea is to be able to simulate wave-body interactions under viscous flow theory with strong deformations of the interface (wave breaking in the vicinity of the body, green water on ship decks…), while keeping the advantages of the SWENSE scheme.The SWENSE approach is based on a physical decomposition by combining incident waves described by a nonlinear spectral scheme based on potential flow theory and an adapted Navier-Stokes solver where only the diffracted part of the flow is solved, incident flow parameters seen as forcing terms.In the single-phase Level Set method [2, 3], the air phase is neglected. Thus, only the liquid phase is solved considering a fluid with uniform properties. The location of the free surface is determined by a Level Set function initialised as the signed distance. The accuracy of simulation depends essentially on the pressure scheme used to impose free surface dynamic boundary condition.Comparisons of numerical results with experimental and numerical data for US navy combatant DTMB 5415 in calm water and in head waves are presented.Copyright