The wind effect on the efficiency of a coastal defense structure is studied in this paper. It is normally assumed that the strength of the wind impact is characterized by the impulse parameter. If it is lower than a certain value, the wind is expected to have a dominant effect on the wave overtopping rate. In contrast to the regular observation, this study reports a new regime of wave overshoot when a low value of the impulse parameter does not lead to increased importance of wind. It is argued that the new regime appears due to the triplet instability previously studied by others. The variation of the standing wave height and the overshooting jet between the sequential cycles results in independence of the overtopping rates of the wind speed.

Wind effects on wave overtopping over a fully impermeable vertical sea wall were studied numerically using the open-source computational fluid dynamics library OpenFoam. A pressure gradient correction term was incorporated in the momentum equations. In recent studies, it was found that, in the absence of wind, an increase in wave steepness results in a reduction of wave overtopping. This is related to the instability of the standing wave formed at the front of a vertical structure. Such instability was noticed in the range of steepness 0.285-0.443 from previous physical experiments for a regular wave interacting with a vertical structure. The existence of this regime was confirmed in the current study. It was also found that the stability of the standing wave determines the shape and volume of the overshooting jet, which has a strong effect on wave overtopping. When the wind is relatively weak (e.g. a wind speed of 10 m/s) it is unable to alter the overshooting jet very much, meaning a weak wind effect on wave overtopping. When the wind is strong (e.g. a wind speed of 30 m/s) it completely deforms the overshooting jet resulting in overtopping discharge almost three times that without wind.

This study contributes to the Collaborative Computational Project in Wave–Structure Interaction blind test series 2 by numerically investigating the dynamic response of two simplified point absorber wave energy converters (WECs – a hemispherical-bottom cylinder and a cylinder with moon-pool) under the action of focused waves of varying steepness. The open source toolbox OpenFOAM along with its new overset grid functionality is applied and evaluated for the complex flow problem involving both large free surface deformations and large-amplitude motions of floating objects. The quality of the numerically generated focused wave groups is first examined and validated against the experimental data. The effects of both wave steepness and the moon-pool on the dynamic responses and mooring loads of the simplified WECs are then analysed.

Multiphase flow impact problems are frequently encountered in natural events and industrial applications. Violent water waves may cause severe damage to ships, offshore platforms and coastal defences. Traditionally the influence of trapped air pockets on plunging waves was ignored due to the small density of air compared to water. The problem becomes even more complicated when air bubbles are present in the water. In hydrodynamics, ordinary (non-breaking) water waves are usually considered as separated-phase flows, in which the free-surface separates the gas- and liquid-components completely. Computations of water-air shock tube problems are known to be challenging for numerical methods, particularly around the material interface where spurious nonphysical oscillations may occur. Some researchers have claimed that cavitation occurs in hydrodynamic slamming events as the pressure descends dramatically after the shock load. The air bubbles rise from the bottom of the ocean basin to the water surface and break up.

Wind effects on wave overtopping over fully impermeable vertical sea defence is studied in a shallow water flume based on a physical model for the Livermeade defence system. The investigation is mainly focused on impulse type wave interaction with the sea defence, when the overshooting jet is high during overtopping. We are able to identify distinct types of overtopping flows where moderate wind speed is not found to be affecting uniformly in all cases. We try to find explanation of this behaviours by studying the standing waves at the defence and complementary CFD simulations.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/byRz_N9zoXk

We introduce a fluid-structure interaction (FSI) framework for the resolution of two-phase fluid flow problems and isothermal non-linear elastic bodies. The discretisation of both the fluid and solid governing equations relies exclusively on the finite volume method. A strong coupling partitioned approach is implemented to ensure the two-way coupling of information between the fluid and solid regions defined in the simulation. Moreover, this FSI framework is integrated on top of a multi-region coupling procedure developed in companion papers [Mart́ınez-Ferrer et al. (2016, 2018)], which has been successfully applied in numerical wave tanks (NWTs), and shown to work transparently with standard domain decomposition techniques used in parallel simulations. Therefore, this retained approach results in a high performance computing strategy to carry out accurate and efficient FSI simulations of wave impacts against structures characteristic of ocean and coastal engineering problems. We conduct a series of test cases to verify the implementation of this FSI framework and its parallel performance for an increasing number of CPU cores. These benchmarks include the dynamic and static responses of cantilever and clamped beams under various loads, a lid-driven flow in an elastic cavity, the water entry of an elastic wedge and, finally, a water dam impact on an elastic plate. The results obtained in this work agree well with analytical solutions, laboratory measurements as well as other numerical simulations reported in the literature.

Quantitative assessments of wind effects on wave overtopping are carried out using CFD simulations with the open source solver OpenFOAM. The desired wind speeds are achieved efficiently by introducing artificial pressure gradient terms for desired zones inside the computational domain. A new run-time post processing utility has been developed to track the overtopping water over a sea defence. Numerical results are validated using (1) a past experimental study with simple sloped defence and (2) new experiments that were conducted at HR Wallingford with a more realistic structure. Several additional calculations with both small and large water depths reveal that with a high wind speed the overtopping volume can be increased by 30% compared to that without wind. The 2D code is then extended to wave overtopping at a semi-circular beach in the plane as a hypothetical 3D sea defence in order to investigate the 3D effect of wind speeds.

This paper presents a numerical wave tank based on the overset mesh approach. Overset mesh is favourable to the moving mesh method owing to its ability to represent complex geometries whilst maintaining a good quality mesh, especially for large amplitude body motions. The numerical wave tank is developed by integrating a generic overset mesh functionality with an efficient wave generation library in OpenFOAM®. A series of benchmark test cases, including 2D regular waves interacting with a floating cylinder and box-shaped body with superstructures, 2D water entry of a rigid wedge and a ship hull section as well as the heave decay of a point absorber wave energy converter and the lifeboat motion in regular waves, are carried out to evaluate the capabilities of the developed numerical wave tank. The computed solutions agree well with the experimental data and other reference results reported in the literature, which demonstrates the capability of the numerical wave tank for modelling flow around structures with complex geometries under various wave conditions. The parallel efficiency of the solver, effects of the overlapping area on the solution accuracy and comparisons with the results from a dynamic mesh are also discussed.

Results from Blind Test Series 1, part of the Collaborative ComputationalProject in Wave Structure Interaction (CCP-WSI), are presented. Partici-pants, with a range of numerical methods, simulate blindly the interactionbetween a fixed structure and focused waves ranging in steepness and di-rection. Numerical results are compared against corresponding physicaldata. The predictive capability of each method is assessed based on pres-sure and run-up measurements. In general, all methods perform well inthe cases considered, however, there is notable variation in the results(even between similar methods). Recommendations are made for appro-priate considerations and analysis in future comparative studies.

We introduce a fluid-structure interaction (FSI) framework for the resolution of two-phase fluid flow problems and isothermal non-linear elastic bodies. The discretisation of both the fluid and solid governing equations relies exclusively on the finite volume method. A strong coupling partitioned approach is implemented to ensure the two-way coupling of information between the fluid and solid regions defined in the simulation. Moreover, this FSI framework is integrated on top of a multi-region coupling procedure developed in companion papers [Martinez-Ferrer et al. (2016, 2018)], which has been successfully applied in numerical wave tanks (NWTs), and shown to work transparently with standard domain decomposition techniques used in parallel simulations. Therefore, this retained approach results in a high performance computing strategy to carry out accurate and efficient FSI simulations of wave impacts against structures characteristic of ocean and coastal engineering problems. We conduct a series of test cases to verify the implementation of this FSI framework and its parallel performance for an increasing number of CPU cores. These benchmarks include the dynamic and static responses of cantilever and clamped beams under various loads, a lid-driven flow in an elastic cavity, the water entry of an elastic wedge and, finally, a water dam impact on an elastic plate. The results obtained in this work agree well with analytical solutions, laboratory measurements as well as other numerical simulations reported in the literature. Crown Copyright (C) 2018 Published by Elsevier Ltd. All rights reserved.

This paper extends a recently proposed multi-region based numerical wave tank (Martinez-Ferrer et al. [11) to solve water entry problems in naval engineering. The original static linking strategy is developed to enable the dynamic coupling of several moving regions. This permits the method to deal with large amplitude motions for structures slamming into water waves. A background grid and one or more component meshes are firstly generated to overlay the whole computational domain and the sub-domains surrounding the structures, respectively. During computation, the background mesh is fixed while the small grids move freely or as prescribed without deformation and regeneration. This effectively circumvents the large and often excessive error-prone dynamic deformation of a single-block mesh as well as the complex and time-consuming mesh regeneration. Test cases of dam breaking with and without obstacles are first conducted to verify the developed code by comparing the numerical solution against experimental data. Then the new code is used to solve prescribed and free-fall water entry problems. The obtained results agree well with experimental measurements and other computational results reported in the literature. (C) 2018 Elsevier Ltd. All rights reserved.

Copyright © 2018 by the International Society of Offshore and Polar Engineers (ISOPE) In the present paper, the open source toolbox OpenFOAM was applied for analysis of the hydrodynamic force and motion of a floating lifeboat in regular waves. The Reynolds averaged Navier-Stokes (RANS) equations were solved and the free surface tracking was achieved by using the volume of fluid method. An overset mesh method was applied for the moving boundary of the lifeboat, in which a body-fitted mesh was generated around the lifeboat using the utility snappyHexMesh and a hexahedral background mesh was produced by the utility blockMesh. The field values were interpolated in the overlapping area between these two layers of meshes. The hydrodynamic forces and the motion of the lifeboat were calculated under the condition that the lifeboat was off-centered in the wave flume to mimic the effects of a larger mother ship. Due to the unsymmetrical condition, full six-degree of freedom (DOF) motion needs to be taken into account. The predicted hydrodynamic force and surface elevation for the fixed lifeboat, and the six DOF motion of the lifeboat were compared to the experimental data. Satisfactory agreement was achieved except the roll moment and motion, for which large discrepancies were observed.

Copyright © 2018 by the International Society of Offshore and Polar Engineers (ISOPE) The present paper summarizes the results for numerical simulation of a fixed FPSO-shaped body in uni-directional phase-focused wave groups, which is prepared as a short report for the CCP-WSI Blind Test Workshop on Focused Wave Impact on a Fixed FPSO at the 28th International Ocean and Polar Engineering Conference (ISOPE 2018). The numerical simulations were carried out using the open source toolbox OpenFOAM. An overset mesh method was applied, where two layers of mesh were generated, namely the background mesh and the overlapping body-fitted mesh. The incident focused wave groups were first validated against the experimental data at several positions. With the propagation of the waves, it was found that the waves generated by the numerical model were slightly dissipated due to numerical diffusion. Therefore, smaller wave crest was predicted from the numerical model. Then the simulations were conducted for the same wave conditions with the FPSO structure in place. The surface elevation and the pressure at several locations based on the validation criteria are reported.

We introduce a dynamic-boundary numerical wave generation procedure developed for wave structure interaction (WSI) simulations typical of ocean and coastal engineering problems. This implementation relies on a dynamic mesh which deforms in order to replicate the motion of the wave-maker, and it is integrated in wsiFoam: a multi-region coupling strategy applied to two-phase Navier-Stokes solvers developed in our previous work [Martinez Ferrer et al. A multi-region coupling scheme for compressible and incompressible flow solvers for two-phase flow in a numerical wave tank. Computer Si. Fluids 125 (2016) 116-1291. The combination of the dynamic boundary method with a multi-region mesh counteracts the increase in computational cost, which is intrinsic to simulations featuring dynamic domains. This approach results in a high performance computing wave generation strategy that can be utilised in a numerical wave tank to carry out accurate and efficient simulations of wave generation, propagation and interaction with fixed structures and floating bodies. We conduct a series of benchmarks to verify the implementation of this wave generation method and the capabilities of the solver wsiFoam to deal with wave structure interaction problems. These benchmarks include regular and focused waves, wave interaction with a floating body and the modelling of a wave energy converter, using different wave-maker geometries: piston, flap and plunger. The results gathered in this work agree well with experimental data measured in the laboratory and other numerical simulations.

© 2017 by the International Society of Offshore and Polar Engineers (ISOPE). This paper presents the development of a multi-region computational fluid-structure dynamics (CFSD) method which is integrated in our virtual wave structure interaction solver wsiFoam, based on the open-source OpenFOAM library, in order to account for the hydro-elastic effects produced by violent wave impacts against deformable bodies. This strategy relies entirely on the finite volume method (FVM) and does not require any third-party solvers, which renders it suitable for efficient parallel computing. We validate this novel approach against previous experimental and numerical results corresponding to a dam break of water impacting on a highly deformable plate as well as a flexible wedge entering water at a constant speed. In general, our preliminary results agree qualitatively well with previous data whilst the performance of parallel implementation evidences the potential of this method to be used in future high performing computing (HPC) applications.

Coastal vegetation can reduce long wave run-up on beaches and inland propagation distances and thus mitigate these hazards. This paper investigates periodic long wave run-up on coastal rigid vegetation sloping beaches via a numerical study. Rigid vegetation is approximated as rigid sticks, and the numerical model is based on an implementation of Morison's formulation [21] for rigid structures induced inertia and drag stresses in the nonlinear shallow water equations. The numerical model is solved via a finite volume method on a Cartesian cut cell mesh. The accuracy of the numerical model is validated by comparison with experimental results. The model is then applied to simulate various hypothetical cases of long periodic wave run-up on a sloping vegetated beach with different plant diameters and densities, and incident long waves with different periods. The sensitivity of long wave run-up to plant diameter, stem density and wave period is investigated by comparison of the numerical results for different vegetation characteristics and different wave periods. The numerical results show that rigid vegetation can effectively reduce long wave run-up and that wave run-up is decreased with increase of plant diameter and stem density. Moreover, the attenuation of long periodic wave run-up due to vegetation is sensitive to the variation of the incident wave period, and the attenuation of wave run-up is not increased or decreased monotonically with incident wave period.

This paper presents the numerical investigations of an oscillating wave surge converter (OWSC) operating in extreme sea states leading to slamming.We use the open-source computational fluid dynamics (CFD) library OpenFOAM to carry out the two-dimensional numerical simulations.A preliminary study is done to verify the convergence of our results, while scalability tests confirm the high-performance computing capabilities of OpenFOAM and the possibility of extending this study to large three-dimensional configurations.The OWSC device is simulated with both incompressible and compressible solvers, and the results are compared against previous numerical and experimental results.It is shown that an incompressible solver can capture the dynamics and general behavior of the flap device.Nevertheless, the compressibility effects can be reproduced only with the aid of a compressible solver, which takes into account the density changes in the air and water phases.Those effects produce high-frequency, small oscillations on the seaward side of the flap but do not contribute to further increasing the peak pressure values characteristic of slamming.

Fundamental principles of computational fluid dynamic (CFD) modelling are presented together with a brief review of CFD applied to wave energy converters. Results are presented for a range of models including incompressible and compressible two-phase flows. Limitations of CFD modelling are discussed together with future developments in CFD.