In this work, the roll damping behavior of the offshore heavy lift DP3 installation vessel Orion from the DEME group is studied. Boundary element codes using potential flow theory require a roll damping coefficient to account for viscous effects. In this study, the roll damping coefficient is calculated using the Computational Fluid Dynamics (CFD) toolbox STAR-CCM+. Firstly, the CFD model setup is validated by performing roll decay tests and comparing the results with experimental scale model tests in a towing tank. Secondly, the roll damping is assessed by the Harmonic Excited Roll Motion (HERM) technique for various excitation frequencies and for different forward speeds. These high-fidelity full-scale simulations result in better estimations of roll damping coefficients for various conditions. This enhances the accuracy of efficient Boundary Element Methods (BEM) codes for wave-current-structure interactions simulations.

In this work, the roll damping behavior of the offshore heavy lift DP3 installation vessel Orion from the DEME group is studied. Boundary element codes using potential flow theory require a roll damping coefficient to account for viscous effects. In this work, the roll damping coefficient is calculated using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The two-phase Navier-Stokes fluid solver is coupled with a motion solver using a partitioned fluid-structure interaction algorithm. The roll damping is assessed by the Harmonic Excited Roll Motion (HERM) technique. An oscillating external moment is applied on the hull and the roll motion is tracked. Various amplitudes and frequencies of the external moment and different forward speeds, are numerically simulated. These high-fidelity full-scale simulations result in better estimations of roll damping coefficients for various conditions in order to enhance the accuracy of efficient boundary element codes for wave-current-structure interactions simulations.

In this work, the offshore heavy lift DP2 jack-up vessel Innovation from the DEME group is studied using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The two-phase Navier-Stokes fluid solver is coupled with a motion solver using a partitioned fluid structure interaction algorithm. Firstly, two dimensional numerical simulations of a cross-section of the hull are performed using two different mesh motion techniques: a mesh morphing method and an overset mesh method. Subsequently, the addition of a bilge keel pair on the hull is studied numerically by performing a two dimensional roll decay simulation. Finally, a three dimensional simulation is performed for a roll decay test and validated by using experimental data measured in the MARIN seakeeping and manoeuvring basin. As a first result, the coupled CFD motion solver proofs to be a promising toolbox for the study of fluid-structure interaction problems of realistic marine structures such as an offshore installation vessel.

This paper presents a study on the coupling between a fluid solver and a motion solver to perform fluid–structure interaction (FSI) simulations of floating bodies such as point absorber wave energy converters heaving under wave loading. The two-phase fluid solver with dynamic mesh handling, interDyMFoam, is a part of the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The incompressible Navier–Stokes (NS) equations are solved together with a conservation equation for the Volume of Fluid (VoF). The motion solver is computing the kinematic body motion induced by the fluid flow. A coupling algorithm is needed between the fluid solver and the motion solver to obtain a converged solution between the hydrodynamic flow field around and the kinematic motion of the body during each time step in the transient simulation. For body geometries with a significant added mass effect, simple coupling algorithms show slow convergence or even instabilities. In this paper, we identify the mechanism for the numerical instability and we derive an accelerated coupling algorithm (based on a Jacobian) to enhance the convergence speed between the fluid and motion solver. Secondly, we illustrate the coupling algorithm by presenting a free decay test of a heaving wave energy converter. Thirdly and most challenging, a water impact test of a free falling wedge with a significant added mass effect is successfully simulated. For both test cases, the numerical results obtained by using the accelerated coupling algorithm are in a very good agreement with the experimental measurements.

In this paper we use the Computational Fluid Dynamics (CFD) toolbox OpenFOAM to perform numerical simulations of multiple floating point absorber wave energy converters (WECs) arranged in a geometrical array configuration inside a numerical wave tank (NWT). The two-phase Navier-Stokes fluid solver is coupled with a motion solver to simulate the hydrodynamic flow field around the WECs and the wave-induced rigid body heave motion of each WEC within the array. In this study, the numerical simulations of a single WEC unit are extended to multiple WECs and the complexity of modelling individual floating objects close to each other in an array layout is tackled. The NWT is validated for fluid-structure interaction (FSI) simulations by using experimental measurements for an array of two, five and up to nine heaving WECs subjected to regular waves. The validation is achieved by using mathematical models to include frictional forces observed during the experimental tests. For all the simulations presented, a good agreement is found between the numerical and the experimental results for the WECs’ heave motions, the surge forces on the WECs and the perturbed wave field around the WECs. As a result, our coupled CFD–motion solver proves to be a suitable and accurate toolbox for the study of fluid-structure interaction problems of WEC arrays.

In this work, the performance of a buoyancy-modified turbulence model is shown for simulating wave breaking in a numerical wave flume. Reynolds-Averaged Navier-Stokes (BANS) modelling is performed by applying both a k-omega and a k-omega SST turbulence model using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. In previous work of the authors (Devolder et al., 2017), the observed significant decrease in wave height over the length of the numerical wave flume based on RANS turbulence modelling for the case of propagating waves has been avoided by developing a buoyancy-modified k-omega SST model in which (i) the density is explicitly included in the turbulence transport equations and (ii) a buoyancy term is added to the turbulent kinetic energy (TKE) equation. In this paper, two buoyancy-modified turbulence models are applied for the case of wave breaking simulations: k-omega and k-omega SST. Numerical results of wave breaking under regular waves are validated with experimental data measured in a wave flume by Ting and Kirby (1994). The numerical results show a good agreement with the experimental measurements for the surface elevations, undertow profiles of the horizontal velocity and turbulent kinetic energy profiles. Moreover, the underlying motivations for the concept of a buoyancy-modified turbulence model are demonstrated by the numerical results and confirmed by the experimental observations. Firstly, the buoyancy term forces the solution of the flow field near the free water surface to a laminar solution in case of wave propagation. Secondly in the surf zone where waves break, the buoyancy term goes to zero and a fully turbulent solution of the flow field is calculated. Finally and most importantly, the buoyancy-modified turbulence models significantly reduce the common overestimation of TKE in the flow field.

The surf zone dynamics are governed by important processes such as turbulence generation , nearshore sediment transport , wave run-up and wave overtopping at a coastal structure. During field observations , it is very challenging to measure and quantify wave breaking turbulence . Complementary to experimental laboratory studies in a more controlled environment , numerical simulations are highly suitable to understand and quantify surf zone processes more accurately. In this study, wave propagation and wave breaking over a fixed barred beach profile is investigated using a two­ phase Navier-Stokes flow solver. We show that accurate predictions of the turbulent two-phase flow field require special attention regarding turbulence modelling. The numerical wave flume is implemented in the open­ source OpenFOAM library. The computed results (surface elevations , velocity profiles and turbulence levels) are compared against experimental measurements in a wave flume (van der A et al., 2017) .

The objective of the present work is to investigate wave run-up around a monopile subjected to regular waves inside a numerical wave flume using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM®. Reynolds-Averaged Navier-Stokes (RANS) turbulence modelling is performed by applying the k-ω SST model. Boundary conditions for wave generation and absorption are adopted from the IHFOAM toolbox. Simulations of propagating water waves show sometimes excessive wave damping (i.e. a significant decrease in wave height over the length of the numerical wave flume) based on RANS turbulence modelling. This anomaly is prevented by implementing a buoyancy term in the turbulent kinetic energy equation. The additional term suppresses the turbulence level at the interface between water and air. The proposed buoyancy-modified k-ω SST turbulence model results in an overall stable wave propagation model without significant wave damping over the length of the flume. Firstly, the necessity of a buoyancy-modified k-ω SST turbulence model is demonstrated for the case of propagating water waves in an empty wave flume. Secondly, numerical results of wave run-up around a monopile under regular waves using the buoyancy-modified k-ω SST turbulence model are validated by using experimental data measured in a wave flume by De Vos et al. (2007). Furthermore, time-dependent high spatial resolutions of the numerically obtained wave run-up around the monopile are presented. These results are in line with the experimental data and available analytical formulations.

This paper uses the CFD toolbox OpenFOAM to perform numerical simulations of a single Floating Point Absorber (FPA) Wave Energy Converter (WEC) unit inside a numerical wave flume. The Navier-Stokes fluid solver is coupled with a motion solver to simulate wave-induced rigid body motions restricted to the heave direction only. Laboratory experiments are undertaken to validate the numerical model for a free decay test and specific regular wave trains. A general methodology is reported for modelling a WEC inside a numerical wave flume taking small deviations in geometry and friction into account. Several CFD simulations are presented with varying time step and grid resolution. The obtained heave motion of the WEC during a free decay test shows a good agreement with the experimental data. In addition, the radiated wave field due to the WEC's motion is captured very accurately by the CFD solver. Even more accurate results are obtained by implementing a linear damper to take the friction in the experimental model in consideration. Subsequently, a WEC is subjected to two specific regular wave trains and both its heave motion and the perturbed wave field are in very good agreement compared to the experimental data. OpenFOAM proofs a suitable and accurate CFD toolbox to study wave-structure interaction of a floating body.

The classic approach of studying the wave interaction with coastal structures is performing physical model testing on a scaled model of the structure in a wave flume in the laboratory. During the last decade, numerical modelling has become a powerful and efficient research tool in the field of coastal engineering. In this paper the numerical model VOFbreak, based on the Navier-Stokes equations and the Volume-Of-Fluid (VOF) technique for treating free surfaces, is presented which is capable of simulating the wave propagation and interaction with a variety of coastal structures. Two practical test cases illustrate features, advantages and limitations of the numerical model. In the first test case, wave propagation into a porous rubble mound breakwater and attenuation of the induced pore pressures is investigated. The second test case presents simulations of wave run-up and overtopping at an impermeable sea dike.

During the last years, the complexity of coastal and offshore structures has grown significantly. One example is the evolution of foundation types for offshore wind turbines from basic monopiles towards complex jacket structures and very recently up to innovative floating wind turbines. This increasing complexity results in a great interest for numerical tools in addition to analytical verification methods and traditional small-scale experimental modelling. Numerical modelling is nowadays very popular for R&D activities due to the availability of extremely powerful computational resources. Since a few years, the coastal and offshore community shows interest in numerical wave tanks (NWTs) to answer specific design questions for a structure installed offshore or nearshore.