Journal of Offshore Mechanics and Arctic Engineering, 2011
Roll-on/roll-off vessels appear to be sensitive to rapid capsizing due to an abrupt ingress of wa... more Roll-on/roll-off vessels appear to be sensitive to rapid capsizing due to an abrupt ingress of water caused by maritime accidents. As a result of the damage creation, the flooded ship can experience intermediate stages, which might be more devastating than the final condition, as the sudden loading could significantly alter the ship stability characteristics. Far from a probabilistic analysis, the paper under study presents the state-of-the-art in regards to flooding physics by treating some relevant important topics. It sheds light on the transient and progressive flooding stages, focuses on relevant factors, and suggests combinations between factors that strongly affect the flooding before the steady state is reached. Furthermore, the authors comment on some points, which remain difficult to take into consideration either numerically or experimentally, and propose, where found necessary, recommendations for a more reliable assessment of the flooding process. This review shows that...
Liu and Yue [1] developed a numerical scheme for propagating waves over a variable bathymetry wit... more Liu and Yue [1] developed a numerical scheme for propagating waves over a variable bathymetry with a High-Order Spectral (HOS) Method. The development of this nonlinear model is detailed and validated on three different test cases. They intend to demonstrate that such a model may be applied to small bottom variations as considered in [1] but also on cases where the bottom variation may be important. In this concern, the very well documented test case of a 2D underwater bar is studied in details. Comparisons are provided with both experimental and numerical results.
The capability of wave generation and absorption in a viscous flow solver becomes important for a... more The capability of wave generation and absorption in a viscous flow solver becomes important for achieving realistic simulations in naval and offshore fields. This study presents an efficient generation of nonlinear wave fields in the viscous flow solver by using a nonlinear potential solver called higher-order spectral method (HOS). The advantages of using a fully nonlinear potential solver for the generation of irregular waves are discussed. In particular, it is shown that the proposed method allows the CFD simulation to start at the time and over the space of interest, retrieved from the potential flow solution. The viscous flow solver is based on the open source library OpenFOAM. The potential solvers used to generate waves are the open source solvers HOS-Ocean and HOS-NWT (Numerical Wave Tank). Several simulation parameters in the CFD solver are investigated in the present study. A HOS wrapper program is newly developed to regenerate wave fields in the viscous flow solver. The w...
for 33rd IWWWFB, Brest, France, 2018 Preliminary study on coupling of viscous and potential flow ... more for 33rd IWWWFB, Brest, France, 2018 Preliminary study on coupling of viscous and potential flow using domain decomposition and relaxation zones Choi Y.M.1, Malenica Š.2, Bouscasse B.1, Seng S.2, Monroy C.2, Gentaz L.1, and Ferrant P.1 1Ecole Centrale de Nantes, Nantes, France CNRS UMR 6598 2Bureau Veritas, Paris, France Introduction The use of RANS based CFD methods has increased recently in naval and offshore engineering to overcome the limits of classical potential flow methods. The problem of seakeeping with forward speed causes many difficulties even for the linear potential flow methodolgy based on boundary integral equation (BIE) and enormous efforts are demanded when the wave steepness becomes higher, especially when wave breaking occurs. The computing resources becomes more powerful nowadays, and it encourages usage of CFD for naval applications, though it is still demanding. There are still many difficulties for practical application of CFD methods. Generation of meshes is...
La dynamique d’un tube flexible rempli d’eau est determinee a l’aide des equations de Navier-Stok... more La dynamique d’un tube flexible rempli d’eau est determinee a l’aide des equations de Navier-Stokes integrees radialement et couplees a une equation de paroi en materiau hyper-elastique. L’equation de la dynamique non-lineaire est decomposee sur une base modale qui permet de prendre en compte les effets hydrodynamiques exterieurs. Les resultats obtenus sont compares a des mesures obtenues lors d’essais en bassins
Global navigation satellite systems (GNSSs) and modern motion-sensor packages allow the measureme... more Global navigation satellite systems (GNSSs) and modern motion-sensor packages allow the measurement of ocean surface waves with low-cost drifters. Drifting along or across current gradients provides unique measurements of wave-current interactions. In this study, we investigate the response of several combinations of GNSS receiver, motionsensor package and hull design in order to define a prototype "surface kinematics buoy" (SKIB) that is particularly optimized for measuring wave-current interactions, including relatively short wave components that are important for air-sea interactions and remote-sensing applications. The comparison with existing Datawell Directional Waverider and Surface Wave Instrument Float with Tracking (SWIFT) buoys, as well as stereo-video imagery, demonstrates the performance of SKIB. The use of low-cost accelerometers and a spherical ribbed and skirted hull design provides acceptable heave spectra E(f) from 0.09 to 1 Hz with an acceleration noise level (2πf) 4 E(f) close to 0.023 m 2 s −3. Velocity estimates from GNSS receivers yield a mean direction and directional spread. Using a low-power acquisition board allows autonomous deployments over several months with data transmitted by satellite. The capability to measure currentinduced wave variations is illustrated with data acquired in a macro-tidal coastal environment.
The present paper is concerned with the numerical simulation of magneto-hydrodynamic (MHD) proble... more The present paper is concerned with the numerical simulation of magneto-hydrodynamic (MHD) problems with industrial tools. MHD has received attention some thirty to twenty years ago as a possible alternative in propulsion applications; MHD propelled ships have even been designed to that purpose. However such propulsion systems have been proved of low efficiency and fundamental researches in the area have progressively received much less attention over the past decades. Numerical simulation of MHD problem could however provide interesting solutions in the field of turbulent flow control. The development of recent efficient numerical techniques for multi-physic applications provide promising tool for the engineer for that purpose. In the present paper, some elementary test cases in laminar flow with magnetic forcing terms are analyzed; equations of the coupled problem are exposed and analytical solutions are derived in each case, highlighting the relevant non-dimensional number which drives the physics of the problem. Several analytical calculations are then proposed and discussed. The present work will serve as basis for validation of numerical tools (based on the finite element method) for academic as well as industrial application purposes.
This paper describes the development of an innovative wind generation system for physical model t... more This paper describes the development of an innovative wind generation system for physical model test of offshore floating structures (e.g. floating offshore wind turbines). A CFD modeling is also carried out to verify the wind field in the wave basin. The experimental setup is associated with the Ocean Engineering Wave Tank of Ecole Centrale de Nantes in order to reproduce offshore winds with respect to their mean speed vertical gradient, including dynamic aspects (frequency spectrum, gusts) above directional water waves. Developed within a collaborative framework between Centre Scientifique et Technique du Bâtiment (C.S.T.B) and E.C.N, the wind generation system is based on several centrifuge fans located behind the wavemaker. Flexible air ducts are carrying the airflow to the vicinity of floating models. The experimental facilities engaged are unique in the field of academic research in France.
Water entry of a solid through a free surface is of interest in ship hydrodynamics applications, ... more Water entry of a solid through a free surface is of interest in ship hydrodynamics applications, namely to study ships behavior in slamming cases for instance. The present study deals with the introduction of an enhancement of SPH method, and aiming at an accurate numerical prediction of the free motion of a body in a free surface flow. The validation case exposed here is the water entry of a massive wedge, and comparisons with experimental data are provided.
In most of cases, free surface impacts may be correctly described without taking care of air effe... more In most of cases, free surface impacts may be correctly described without taking care of air effects. But depending on the shape and dimensions of the solid involved in the impact, these effects may have some non negligible influences on the impact features at the entry beginning, as it would be observed in the occurrence of air-cushioning. In this paper, through a two-dimensional numerical simulation of a body in free motion within a multi-phase flow using Smoothed Particles Hydrodynamics (SPH) method, these influences are taken into account and discussed. The application presented here deals with fluids having a high density difference, implying a need for some special care on the SPH formulation to adopt. Successive effects of air and water on the body are included, and numerical results are validated through some comparisons with experimental data, showing good agreements.
The application of a fully nonlinear boundary element method to the simulation of wave-body-curre... more The application of a fully nonlinear boundary element method to the simulation of wave-body-current interactions in the time domain is presented. Stream function theory is used to model the incoming flow composed of nonlinear regular waves combined with a uniform current. A time-dependent boundary value problem for the nonlinear diffraction flow is formulated and solved using a boundary element method based on triangular isoparametric elements. A 4th-order Runge-Kutta method is applied for the time marching. New and original results on the nonlinear influence of wave steepness and current velocity on the wave runup about a bottom-mounted vertical cylinder are presented and discussed. Results include time series as well as harmonic components of the runup.
This work presents a numerical method able to take into account wind wave coupling and energy dis... more This work presents a numerical method able to take into account wind wave coupling and energy dissipation related to wave breaking in a deterministic sea state model. We carry out such simulations with an HOS model developed at LMF-ECN since 2002 and based on the work of West et al. (1987) and Dommermuth & Yue(1987). This model performs direct numerical simulations of the fully nonlinear primitive equations by mean of a spectral method in term of decomposition on a basis of eigenfunctions. A parametric coupling for wind forcing is achieved under Miles(1957)'s formulation, and an associated parameterization following Hasselmann(1974)'s theory enables to account for dissipation. The formulation and set parameters referred as BAJ [Bidlot et al.(05)], widely used in phase averaged spectral model solving the balance equation of energy spectra, are implemented and analyzed.
Atmosphérique (LHEEA) b. Centre Scientifique et Technique du Bâtiment (CSTB) Résumé : Ce travail ... more Atmosphérique (LHEEA) b. Centre Scientifique et Technique du Bâtiment (CSTB) Résumé : Ce travail porte sur l'étude expérimentale du comportement dynamique d'uneéolienne offshore flottante sous l'action conjuguée de la houle et du vent. Pour cela, un nouveau moyen d'essai permettant la génération de vent aété développé sur le bassin de génie océanique de l'École Centrale de Nantes. Dans un second temps, un modèle réduit d'éolienne flottante aété dimensionnéà l'échelle du 1/50 e suivant une méthodologie adaptéeà ce type d'essai. Cette maquette a ensuiteétéétudiée en bassin afin de caractériser son comportement sous l'action de la houle et du vent.
This paper presents recent offshore applications of the SWENSE (Spectral Wave Explicit Navier-Sto... more This paper presents recent offshore applications of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach which is an original solution scheme for the time simulation of wave-body interactions using a combined potential / RANSE approach and a decomposition of the nonlinear flow in incident and diffracted parts. The viscous free surface flow around an TLP is computed in cases of regular and irregular waves. The incoming regular wave field is given by an algorithm based on stream function theory (Rienecker & Fenton, 1981) while the incoming irregular wave field is computed by a Higher Order Spectral (HOS) model (Bonnefoy et al, 2004). This latter model is validated against the previous one for a case of regular waves. Concerning results on the TLP structure, time histories of free surface elevations and pressure loads are compared to results from a time domain nonlinear potential flow solver (Ferrant, 1996; Ferrant et al, 2003b). Results obtained with the SWENSE method show an overall good agreement with second order potential flow results. Essential non linear effects associated with the interaction with the free surface are captured, while noticeable viscous effects are also observed, in the form of vortices shed by pontoons corners. More in-depth comparisons with experimental or numerical data have to be undertaken but these preliminary results are a good indication of the capacity of the SWENSE scheme for simulating wave-body interactions in the offshore context.
This paper presents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations... more This paper presents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach, a method for simulating fully nonlinear wave-body interactions including viscous effects. Potential flow theory is used to compute the incident waves while viscous effects are taken into account by using a Reynolds Averaged Navier-Stokes Equations (RANSE) solver to obtain the diffracted field in the full domain. Arbitrary incident wave systems can be described, including regular, irregular waves, multidirectional waves and focused wave events. The model may be fixed or moving with arbitrary speed and 6 degrees of freedom motion. This paper is devoted to the validation of the SWENSE method in irregular head waves, in the case of an extensively long 2 DoF simulation. Results of the present approach compare favorably with experimental data.
Journal of Offshore Mechanics and Arctic Engineering, 2011
Roll-on/roll-off vessels appear to be sensitive to rapid capsizing due to an abrupt ingress of wa... more Roll-on/roll-off vessels appear to be sensitive to rapid capsizing due to an abrupt ingress of water caused by maritime accidents. As a result of the damage creation, the flooded ship can experience intermediate stages, which might be more devastating than the final condition, as the sudden loading could significantly alter the ship stability characteristics. Far from a probabilistic analysis, the paper under study presents the state-of-the-art in regards to flooding physics by treating some relevant important topics. It sheds light on the transient and progressive flooding stages, focuses on relevant factors, and suggests combinations between factors that strongly affect the flooding before the steady state is reached. Furthermore, the authors comment on some points, which remain difficult to take into consideration either numerically or experimentally, and propose, where found necessary, recommendations for a more reliable assessment of the flooding process. This review shows that...
Liu and Yue [1] developed a numerical scheme for propagating waves over a variable bathymetry wit... more Liu and Yue [1] developed a numerical scheme for propagating waves over a variable bathymetry with a High-Order Spectral (HOS) Method. The development of this nonlinear model is detailed and validated on three different test cases. They intend to demonstrate that such a model may be applied to small bottom variations as considered in [1] but also on cases where the bottom variation may be important. In this concern, the very well documented test case of a 2D underwater bar is studied in details. Comparisons are provided with both experimental and numerical results.
The capability of wave generation and absorption in a viscous flow solver becomes important for a... more The capability of wave generation and absorption in a viscous flow solver becomes important for achieving realistic simulations in naval and offshore fields. This study presents an efficient generation of nonlinear wave fields in the viscous flow solver by using a nonlinear potential solver called higher-order spectral method (HOS). The advantages of using a fully nonlinear potential solver for the generation of irregular waves are discussed. In particular, it is shown that the proposed method allows the CFD simulation to start at the time and over the space of interest, retrieved from the potential flow solution. The viscous flow solver is based on the open source library OpenFOAM. The potential solvers used to generate waves are the open source solvers HOS-Ocean and HOS-NWT (Numerical Wave Tank). Several simulation parameters in the CFD solver are investigated in the present study. A HOS wrapper program is newly developed to regenerate wave fields in the viscous flow solver. The w...
for 33rd IWWWFB, Brest, France, 2018 Preliminary study on coupling of viscous and potential flow ... more for 33rd IWWWFB, Brest, France, 2018 Preliminary study on coupling of viscous and potential flow using domain decomposition and relaxation zones Choi Y.M.1, Malenica Š.2, Bouscasse B.1, Seng S.2, Monroy C.2, Gentaz L.1, and Ferrant P.1 1Ecole Centrale de Nantes, Nantes, France CNRS UMR 6598 2Bureau Veritas, Paris, France Introduction The use of RANS based CFD methods has increased recently in naval and offshore engineering to overcome the limits of classical potential flow methods. The problem of seakeeping with forward speed causes many difficulties even for the linear potential flow methodolgy based on boundary integral equation (BIE) and enormous efforts are demanded when the wave steepness becomes higher, especially when wave breaking occurs. The computing resources becomes more powerful nowadays, and it encourages usage of CFD for naval applications, though it is still demanding. There are still many difficulties for practical application of CFD methods. Generation of meshes is...
La dynamique d’un tube flexible rempli d’eau est determinee a l’aide des equations de Navier-Stok... more La dynamique d’un tube flexible rempli d’eau est determinee a l’aide des equations de Navier-Stokes integrees radialement et couplees a une equation de paroi en materiau hyper-elastique. L’equation de la dynamique non-lineaire est decomposee sur une base modale qui permet de prendre en compte les effets hydrodynamiques exterieurs. Les resultats obtenus sont compares a des mesures obtenues lors d’essais en bassins
Global navigation satellite systems (GNSSs) and modern motion-sensor packages allow the measureme... more Global navigation satellite systems (GNSSs) and modern motion-sensor packages allow the measurement of ocean surface waves with low-cost drifters. Drifting along or across current gradients provides unique measurements of wave-current interactions. In this study, we investigate the response of several combinations of GNSS receiver, motionsensor package and hull design in order to define a prototype "surface kinematics buoy" (SKIB) that is particularly optimized for measuring wave-current interactions, including relatively short wave components that are important for air-sea interactions and remote-sensing applications. The comparison with existing Datawell Directional Waverider and Surface Wave Instrument Float with Tracking (SWIFT) buoys, as well as stereo-video imagery, demonstrates the performance of SKIB. The use of low-cost accelerometers and a spherical ribbed and skirted hull design provides acceptable heave spectra E(f) from 0.09 to 1 Hz with an acceleration noise level (2πf) 4 E(f) close to 0.023 m 2 s −3. Velocity estimates from GNSS receivers yield a mean direction and directional spread. Using a low-power acquisition board allows autonomous deployments over several months with data transmitted by satellite. The capability to measure currentinduced wave variations is illustrated with data acquired in a macro-tidal coastal environment.
The present paper is concerned with the numerical simulation of magneto-hydrodynamic (MHD) proble... more The present paper is concerned with the numerical simulation of magneto-hydrodynamic (MHD) problems with industrial tools. MHD has received attention some thirty to twenty years ago as a possible alternative in propulsion applications; MHD propelled ships have even been designed to that purpose. However such propulsion systems have been proved of low efficiency and fundamental researches in the area have progressively received much less attention over the past decades. Numerical simulation of MHD problem could however provide interesting solutions in the field of turbulent flow control. The development of recent efficient numerical techniques for multi-physic applications provide promising tool for the engineer for that purpose. In the present paper, some elementary test cases in laminar flow with magnetic forcing terms are analyzed; equations of the coupled problem are exposed and analytical solutions are derived in each case, highlighting the relevant non-dimensional number which drives the physics of the problem. Several analytical calculations are then proposed and discussed. The present work will serve as basis for validation of numerical tools (based on the finite element method) for academic as well as industrial application purposes.
This paper describes the development of an innovative wind generation system for physical model t... more This paper describes the development of an innovative wind generation system for physical model test of offshore floating structures (e.g. floating offshore wind turbines). A CFD modeling is also carried out to verify the wind field in the wave basin. The experimental setup is associated with the Ocean Engineering Wave Tank of Ecole Centrale de Nantes in order to reproduce offshore winds with respect to their mean speed vertical gradient, including dynamic aspects (frequency spectrum, gusts) above directional water waves. Developed within a collaborative framework between Centre Scientifique et Technique du Bâtiment (C.S.T.B) and E.C.N, the wind generation system is based on several centrifuge fans located behind the wavemaker. Flexible air ducts are carrying the airflow to the vicinity of floating models. The experimental facilities engaged are unique in the field of academic research in France.
Water entry of a solid through a free surface is of interest in ship hydrodynamics applications, ... more Water entry of a solid through a free surface is of interest in ship hydrodynamics applications, namely to study ships behavior in slamming cases for instance. The present study deals with the introduction of an enhancement of SPH method, and aiming at an accurate numerical prediction of the free motion of a body in a free surface flow. The validation case exposed here is the water entry of a massive wedge, and comparisons with experimental data are provided.
In most of cases, free surface impacts may be correctly described without taking care of air effe... more In most of cases, free surface impacts may be correctly described without taking care of air effects. But depending on the shape and dimensions of the solid involved in the impact, these effects may have some non negligible influences on the impact features at the entry beginning, as it would be observed in the occurrence of air-cushioning. In this paper, through a two-dimensional numerical simulation of a body in free motion within a multi-phase flow using Smoothed Particles Hydrodynamics (SPH) method, these influences are taken into account and discussed. The application presented here deals with fluids having a high density difference, implying a need for some special care on the SPH formulation to adopt. Successive effects of air and water on the body are included, and numerical results are validated through some comparisons with experimental data, showing good agreements.
The application of a fully nonlinear boundary element method to the simulation of wave-body-curre... more The application of a fully nonlinear boundary element method to the simulation of wave-body-current interactions in the time domain is presented. Stream function theory is used to model the incoming flow composed of nonlinear regular waves combined with a uniform current. A time-dependent boundary value problem for the nonlinear diffraction flow is formulated and solved using a boundary element method based on triangular isoparametric elements. A 4th-order Runge-Kutta method is applied for the time marching. New and original results on the nonlinear influence of wave steepness and current velocity on the wave runup about a bottom-mounted vertical cylinder are presented and discussed. Results include time series as well as harmonic components of the runup.
This work presents a numerical method able to take into account wind wave coupling and energy dis... more This work presents a numerical method able to take into account wind wave coupling and energy dissipation related to wave breaking in a deterministic sea state model. We carry out such simulations with an HOS model developed at LMF-ECN since 2002 and based on the work of West et al. (1987) and Dommermuth & Yue(1987). This model performs direct numerical simulations of the fully nonlinear primitive equations by mean of a spectral method in term of decomposition on a basis of eigenfunctions. A parametric coupling for wind forcing is achieved under Miles(1957)'s formulation, and an associated parameterization following Hasselmann(1974)'s theory enables to account for dissipation. The formulation and set parameters referred as BAJ [Bidlot et al.(05)], widely used in phase averaged spectral model solving the balance equation of energy spectra, are implemented and analyzed.
Atmosphérique (LHEEA) b. Centre Scientifique et Technique du Bâtiment (CSTB) Résumé : Ce travail ... more Atmosphérique (LHEEA) b. Centre Scientifique et Technique du Bâtiment (CSTB) Résumé : Ce travail porte sur l'étude expérimentale du comportement dynamique d'uneéolienne offshore flottante sous l'action conjuguée de la houle et du vent. Pour cela, un nouveau moyen d'essai permettant la génération de vent aété développé sur le bassin de génie océanique de l'École Centrale de Nantes. Dans un second temps, un modèle réduit d'éolienne flottante aété dimensionnéà l'échelle du 1/50 e suivant une méthodologie adaptéeà ce type d'essai. Cette maquette a ensuiteétéétudiée en bassin afin de caractériser son comportement sous l'action de la houle et du vent.
This paper presents recent offshore applications of the SWENSE (Spectral Wave Explicit Navier-Sto... more This paper presents recent offshore applications of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach which is an original solution scheme for the time simulation of wave-body interactions using a combined potential / RANSE approach and a decomposition of the nonlinear flow in incident and diffracted parts. The viscous free surface flow around an TLP is computed in cases of regular and irregular waves. The incoming regular wave field is given by an algorithm based on stream function theory (Rienecker & Fenton, 1981) while the incoming irregular wave field is computed by a Higher Order Spectral (HOS) model (Bonnefoy et al, 2004). This latter model is validated against the previous one for a case of regular waves. Concerning results on the TLP structure, time histories of free surface elevations and pressure loads are compared to results from a time domain nonlinear potential flow solver (Ferrant, 1996; Ferrant et al, 2003b). Results obtained with the SWENSE method show an overall good agreement with second order potential flow results. Essential non linear effects associated with the interaction with the free surface are captured, while noticeable viscous effects are also observed, in the form of vortices shed by pontoons corners. More in-depth comparisons with experimental or numerical data have to be undertaken but these preliminary results are a good indication of the capacity of the SWENSE scheme for simulating wave-body interactions in the offshore context.
This paper presents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations... more This paper presents recent advances of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach, a method for simulating fully nonlinear wave-body interactions including viscous effects. Potential flow theory is used to compute the incident waves while viscous effects are taken into account by using a Reynolds Averaged Navier-Stokes Equations (RANSE) solver to obtain the diffracted field in the full domain. Arbitrary incident wave systems can be described, including regular, irregular waves, multidirectional waves and focused wave events. The model may be fixed or moving with arbitrary speed and 6 degrees of freedom motion. This paper is devoted to the validation of the SWENSE method in irregular head waves, in the case of an extensively long 2 DoF simulation. Results of the present approach compare favorably with experimental data.
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