A Semi-Infinite Numerical Wave Tank Using Discrete Particle Simulations

With an increasing number of offshore structures for marine renewable energy, various experimental and numerical approaches have been performed to investigate the interaction of waves and structures to ensure the safety of the offshore structures. However, it has been very expensive to carry out real-scale large experiments and simulations. In this study, numerical waves with various relative depths and a wide range of wave steepness are precisely simulated by minimizing the wave reflection with a mass-weighted damping zone located at the end of a numerical wave tank (NWT). To achieve computational efficiency, optimal variables including initial spacing of smoothed particles, calculation time step, and damping coefficients are studied, and the numerical results are verified by comparison with both experimental data and analytical formula, in terms of wave height, particle velocities, and wave height-to-stroke ratio. Those results show good agreement for all wave steepness smaller than 0.067. By applying the proposed methodology, it is allowed to use a numerical wave tank of which the length is smaller than that of the wave tank used for experiments. The developed numerical technique can be used for the safety analysis of offshore structures through the simulation of fluid-structure interaction.

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Investigation of Focusing Wave Properties in a Numerical Wave Tank with a Fully Nonlinear Potential Flow Model

Journal of Marine Science and Engineering ◽

10.3390/jmse7100375 ◽

2019 ◽

Vol 7 (10) ◽

pp. 375 ◽

Cited By ~ 2

Author(s):

Weizhi Wang ◽

Arun Kamath ◽

Csaba Pakozdi ◽

Hans Bihs

Keyword(s):

Wave Height ◽

Potential Flow ◽

Wave Steepness ◽

Numerical Wave Tank ◽

Wave Groups ◽

Wave Tank ◽

Fully Nonlinear ◽

Nonlinear Potential ◽

Numerical Wave ◽

Focused Wave

Nonlinear wave interactions and superpositions among the different wave components and wave groups in a random sea sometimes produce rogue waves with extremely large wave heights that appear unexpectedly. A good understanding of the generation and evolution of such extreme wave events is of great importance for the analysis of wave forces on marine structures. A fully nonlinear potential flow (FNPF) model is proposed in the presented paper to investigate the different factors that influence the wave focusing location, focusing time and focusing wave height in a numerical wave tank. Those factors include wave steepness, spectrum bandwidth, wave generation method, focused wave spectrum, and wave spreading functions. The proposed model solves the Laplace equation together with the boundary conditions on a σ -coordinate grid using high-order discretisation schemes on a fully parallel computational framework. The model is validated against the focused wave experiments and thereafter used to obtain insights into the effects of the different factors. It is found that the wave steepness contributes to changing the location and time of focus significantly. Spectrum bandwidth and directional spreading affect the focusing wave height and profile, for example, a wider bandwidth and a wider directional spread lead to a lower focusing wave height. A Neumann boundary condition represents the nonlinearity of the wave groups better than a relaxation method for wave generation.

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Development of 3-D Numerical Wave Tank and Applications on Comb-Type Breakwater

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 6 ◽

10.1115/omae2010-20337 ◽

2010 ◽

Author(s):

Zhuo Fang ◽

Liang Cheng ◽

Ningchuan Zhang

Keyword(s):

Offshore Structures ◽

Wave Generation ◽

Irregular Waves ◽

Secondary Wave ◽

Wave Forces ◽

Numerical Wave Tank ◽

Wave Reflections ◽

Wave Tank ◽

Numerical Wave ◽

Source Wave

In this study, a 3-D numerical wave tank is developed, based on a commercial computational fluid dynamics (CFD) package (FLUENT) to predict wave forces on coastal and offshore structures. A source wave-generation method is introduced to FLUENT through user-defined functions to generate incident waves. Spongy layers are used on both upstream and downstream sides of the wave tank to reduce the effects of wave reflections and secondary wave reflections. Various wave trains, such as linear monochromatic waves, second order Stokes waves and irregular waves were generated by using different source functions. It is demonstrated through numerical examples that the source wave-generation method can accurately generate not only small amplitude waves but also nonlinear waves. The present numerical wave tank is validated against standing waves in front of a vertical breakwater. Interactions between waves and a comb-type breakwater are simulated using the present model. The numerical results are compared with physical experimental results. It is found that the present numerical wave tank simulated the wave and breakwater interactions well.

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Steep Wave Effects on Wave Induced Vertical Bending Moment Using a 3D Numerical Wave Tank

Volume 1: Offshore Technology ◽

10.1115/omae2017-61161 ◽

2017 ◽

Author(s):

Shivaji Ganesan Thirunaavukarasu ◽

Debabrata Sen ◽

Yogendra Parihar

Keyword(s):

Comparative Study ◽

Incident Wave ◽

Bending Moment ◽

Wave Steepness ◽

Numerical Wave Tank ◽

Wave Tank ◽

Strip Theory ◽

Numerical Wave ◽

Wave Induced ◽

Vertical Bending Moment

This paper presents a detail comparative study on wave induced vertical bending moment (VBM) between linear and approximate nonlinear calculations using a 3D numerical wave tank (NWT) method. The developed numerical approach is in time domain where the ambient incident waves can be defined by any suitable wave theory. Certain justifying approximations employed in the solution of the interaction hydrodynamics (diffraction and radiation) enabling the NWT to generate stable long duration time histories of all parameters of interest. This is an extension of our earlier works towards the development of a practical NWT based solution for wave-structure interactions [1]. After a brief outline of the implemented numerical details, a comprehensive validation and verification of vertical shear force (VSF) and bending moment RAOs computed using the linearized version of the NWT against the usual linear results of strip theory and 3D panel codes are presented. Next we undertake the comparative study between the fully linear and approximate nonlinear versions of the present code for different incident wave steepness. In the approximate nonlinear formulation, the ambient incident wave is defined by the full nonlinear numerical wave model based on Fourier approximation method which can generate very steep steady periodic nonlinear waves up to the near wave breaking limit. The nonlinearities associated with the incident Froude Krylov and hydrostatic restoring forces/moments are exact up to the instantaneous wetted surface at the displaced location, but the hydrodynamic diffraction and radiation effects are linearized around the mean wetted surface. The standard S175 container hull is considered for the comparative studies because of its geometric nonlinearities. Numerical simulations are performed for four different wave lengths with increasing wave steepness. It is observed that the computed wave induced VBM amidships from the approximate nonlinear results can be almost 30% higher compared to the results from a purely linear solution, which can be a critical issue from the safety point. Significant higher harmonics are also observed in the approximate nonlinear results which at some times may be responsible for exciting the undesirable whipping/springing responses.

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Simulation of Wave Slamming on Open-Piled Structures Based on FLUENT

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.256-259.1960 ◽

2012 ◽

Vol 256-259 ◽

pp. 1960-1964

Author(s):

Feng Jin

Keyword(s):

Experimental Data ◽

Wave Height ◽

Impact Pressure ◽

Two Dimensional ◽

Numerical Wave Tank ◽

Regular Wave ◽

Wave Impact ◽

Wave Tank ◽

Wave Slamming ◽

Numerical Wave

In order to study the specialties of wave slamming on open-piled structures, a two-dimensional regular wave tank was established based on commercial CFD software FLUENT. Three typical cases of regular wave slamming on the open-piled structures were reproduced by using the numerical wave tank and compared with the experimental data available. Good agreements were obtained between the numerical and experimental results and the average of peak impact pressure was chosen as the characteristic impact pressure. Then regular wave impact pressure on the open-piled structures under various wave height, period and over height were simulated. The influences of the three parameters on the distribution of impact pressure were analyzed.

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Generation of Offshore Environments in the Numerical Wave Tank to Model Metocean Conditions Interaction with Offshore Structure Near the Free Surface

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/945/1/012018 ◽

2021 ◽

Vol 945 (1) ◽

pp. 012018

Author(s):

Mushtaq Ahmed ◽

Zafarullah Nizamani ◽

Akihiko Nakayama ◽

Montasir Osman

Keyword(s):

Free Surface ◽

Offshore Structures ◽

Operating Conditions ◽

Wave Crest ◽

Extreme Conditions ◽

Numerical Wave Tank ◽

Offshore Structure ◽

Wave Tank ◽

Numerical Wave ◽

Operating Wave

Abstract Offshore structures play a vital role in the economy of offshore oil-producing countries, where mostly fixed jacket type structures are used to produce oil and gas installed in shallow water. In an offshore environment where structures are installed, there exist met ocean forces such as wind, waves, and currents. These met ocean conditions when interacting with offshore structures near the free surface, generate loads. The estimation of such loads is very much important for the proper design of these structures. The primary aim of this study is to investigate the interaction of waves with a jacket platform by generating offshore environments in the numerical wave tank (NWT). To achieve this goal, ANSYS Fluent is used for the flow analysis by using continuity and Navier Stokes equation. Results are verified and validated with the analytical work. Wave crests under operating condition generate a force of 1.3 MN which is the lowest in magnitude as compared to wave crest which produces 4.5 MN force under extreme conditions. Unlike operating wave crest, the operating wave trough generates a higher force of 1 MN than extreme conditions which account for 1.5 MN forces. Forces produced by the extreme offshore environment are 30% higher than those generated under operating conditions. It is concluded from the results that a positive force is exerted onto the structure during the water entry phase while a negative force is observed when the water leaves the structure.

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Numerical Wave Tank Including a Fixed Vertical Cylinder Subjected to Waves, Towards the Investigation of Floating Offshore Wind Turbine Hydrodynamics

Volume 6A: Ocean Engineering ◽

10.1115/omae2020-18797 ◽

2020 ◽

Author(s):

Constance Clément ◽

Pauline Bozonnet ◽

Guillaume Vinay ◽

Adria Borras Nadal ◽

Philippe Pagnier ◽

...

Keyword(s):

Turbulence Model ◽

Wave Generation ◽

Hydrodynamic Forces ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Numerical Wave Tank ◽

Time Step ◽

Cfd Simulations ◽

Wave Tank ◽

Numerical Wave

Abstract Specific engineering tools are used to design Floating Offshore Wind Turbines (FOWT). These so-called aero-hydro-servo-elastic solvers simulate the coupled behaviour of the turbine subjected to wind with the floater motion due to waves, including elasticity of the whole structure. The implemented hydrodynamic forces rely on a strong Oil&Gas background and include potential flow theory and empirical laws, such as Morison forces. The undergoing study aims at re-evaluating the validity range of such theories, when applied to FOWT. To do so, CFD simulations will be run to model wave propagation and interaction with a FOWT floater. Hydrodynamic forces will be extracted from the CFD simulations and compared to current hydrodynamic theories. A fixed cylinder in regular second order deep water waves (steepness of 0.9) is simulated and results are validated against experiments [1]. This basic first case implemented with Open-FOAM using waves2Foam library allows to master regular wave generation and interaction with a rather simple structure, running multiple simulations. Convergence (mesh refinement, time step) and parameterization (numerical schemes, turbulence models) studies are carried out to ensure controlled wave generation. An accurate Numerical Wave Tank (NWT) is finally obtained. However, the resolution of air/water interface with Volume Of Fluid (VOF) MULES method seems to be responsible for extreme air velocities on crests resulting in wave damping. This phenomena is solved by decreasing time step. Hydrodynamic forces on the cylinder match experiments with an error below 3%. As the flow is turbulent (Re = 105), a turbulence model is included in the simulation giving results rather close to the ones obtained without turbulence model.

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Comparison of Numerical Methods for Wave Generation by VOF-Based Numerical Wave Tank

Volume 6: Ocean Engineering ◽

10.1115/omae2011-49777 ◽

2011 ◽

Cited By ~ 1

Author(s):

Bingjie Guo ◽

Sverre Steen

Keyword(s):

Grid Size ◽

Navier Stokes ◽

Numerical Wave Tank ◽

Mass Source ◽

Time Step ◽

Wave Tank ◽

Inlet Velocity ◽

Numerical Wave ◽

2D And 3D ◽

Selection Of

Based on the Reyonlds Averaged Navier-Stokes (RANS) equation for incompressible, viscous fluid, a VOF-based numerical wave tank which could accurately generate and absorb waves is investigated. Three different wave-making functions, namely ‘Inlet-velocity boundary condition (IBC)’, ‘Momentum source (MOS)’, ‘Mass source (MAS)’ are investigated, and the advantage of each method is analyzed to guide an optimal selection of these functions. Moreover, the effects of viscous model, grid size, time step, and discretization method on the accuracy of the wave simulation are discussed. The interaction between the wave and current is also studied. In order to verify the applicability of these methods, the numerical results in both 2D and 3D tanks are compared with analytical solutions.

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Benchmarking of a Computational Fluid Dynamics-Based Numerical Wave Tank for Studying Wave Load Effects on Fixed and Floating Offshore Structures

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4035475 ◽

2017 ◽

Vol 139 (3) ◽

Cited By ~ 2

Author(s):

Ali Nematbakhsh ◽

Zhen Gao ◽

Torgeir Moan

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Offshore Structures ◽

Numerical Results ◽

Wave Loads ◽

Numerical Wave Tank ◽

Wave Load ◽

Wave Tank ◽

Load Effects ◽

Numerical Wave

A computational fluid dynamics (CFD) based numerical wave tank (NWT) is developed and verified to study wave load effects on fixed and free floating offshore structures. The model is based on solving Navier–Stokes equations on a structured grid, level set method for tracking the free surface, and an immersed boundary method for studying wave–structure interaction. This paper deals with establishing and verifying a CFD-based NWT. Various concerns that arise during this establishment are discussed, namely effects of wave reflection which might affect the structure response, damping of waves in downstream, and three-dimensional (3D) effects of the waves. A method is described and verified to predict the time when incoming waves from wave generator are affected by reflecting waves from the structure which can help in better designing the dimensions of NWT. The model is then used to study sway, heave, and roll responses of a floating barge which is nonuniform in density and limited in sway direction by a spring and damper. Also, it is used to study wave loads on a fixed, large diameter, surface piercing circular cylinder. The numerical results are compared with the experimental and other numerical results, and in general very good agreement is observed in all range of studied wave frequencies. It is shown that for the studied fixed cylinder, the Morison equation leads to promising results for wavelength to diameter ratio larger than 2π (kD < 1), while for shorter wavelengths results in considerable over prediction of wave loads, due to simplification of wave diffraction effects.

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