Qualification Criteria for the Verification of Numerical Waves – Part 1: Potential-Based Numerical Wave Tank (PNWT)

2021 ◽  
Author(s):  
Sébastien Fouques ◽  
Eloïse Croonenborghs ◽  
Arjen Koop ◽  
Ho-Joon Lim ◽  
Jang Kim ◽  
...  
Keyword(s):  
Numerical Models ◽  
Laws Of Nature ◽  
Offshore Structures ◽  
Wave Loads ◽  
Wave Impact ◽  
Wave Tank ◽  
Numerical Studies ◽  
Experimental Facilities ◽  
Numerical Wave

Abstract There is an increasing trend towards using numerical wave simulations for the design of offshore structures, especially for the stochastic prediction of nonlinear wave loads like those related to air-gap and wave impact. Unlike experimental facilities, where the complex nonlinear physics of wave propagation is simply enforced by the laws of nature, numerical wave tanks (NWTs) rely on assumptions and simplifications to solve the propagation equations in a reasonable amount of time. It is therefore important to verify the quality of the waves generated by NWTs in terms of realistic physical properties. As part of the effort to develop reliable numerical wave modeling practices in the framework of the “Reproducible Offshore CFD JIP”, qualification criteria are formulated for the wave solutions generated from either potential-flow based or CFD-based codes. The criteria have been developed based on experiences from physical wave tank tests and theoretical/numerical studies. They are being evaluated using results from several numerical models and available benchmark data. This paper presents the proposed qualification criteria and on-going evaluation efforts by comparing results from different codes.

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

2017 ◽  
Vol 139 (3) ◽  
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.

Qualification Criteria and the Verification of Numerical Waves: Part 2: CFD-Based Numerical Wave Tank

2021 ◽  
Author(s):  
Benjamin Bouscasse ◽  
Andrea Califano ◽  
Young Myung Choi ◽  
Xu Haihua ◽  
Jang Whan Kim ◽  
...  
Keyword(s):  
Wave Spectrum ◽  
Vertical Direction ◽  
Offshore Structures ◽  
Irregular Waves ◽  
Numerical Wave Tank ◽  
Regular Waves ◽  
Wave Impact ◽  
Wave Tank ◽  
Modeling Practices ◽  
Numerical Wave

Abstract There is increasing interest in numerical wave simulations as a tool to design offshore structures, especially for the prediction of stochastic nonlinear wave loads like those related to air-gap and wave impact. Though the simulations cannot replace all experiments, they are now competitive on some topics such as the computations of wind and current coefficients. To proceed further it is necessary to improve the procedure to account for another complex environmental factor, wave motion. This paper addresses an industrial collaboration to develop modeling practices and qualification criteria of CFD-based numerical wave tank for offshore applications. As a part of the effort to develop reliable numerical wave modeling practices in the framework of the “Reproducible Offshore CFD JIP”, qualification criteria are formulated for the wave solutions generated from either potential-flow based codes in Part 1 of this work. Part 2 presents first a set of solutions for forcing the qualified waves obtained with the potential codes in the CFD domain. Those solutions follow a set of coupling protocols previously proposed in the JIP framework. Two potential codes and two CFD solvers are combined, so that four possible methods of generating waves and modalities are described. Two different potential models are considered, one using the higher order spectral method for numerical wave tank (HOS-NWT), and another using the finite-element method in the horizontal direction and a modal expansion after a sigma transform in the vertical direction (solver is called TPNWT). Both are equipped with a breaking model to generate extreme sea states. The two CFD solvers tested are Simcenter STAR-CCM+ and OpenFOAM. Simulation setups are proposed for both software. Simulation results from eight academic or industrial partners are presented for two sets of 2D test cases in deep water, one with regular waves and one with irregular waves, both with one very steep condition (ratio of wave height over wavelength of 10% for regular waves and 1000 year return period for Gulf of Mexico for irregular waves). The irregular waves are simulated for 10 sets of 3 hours to apply a stochastic approach to verify the quality of the waves generated in the numerical domain. Attention is given to the wave spectrum and the ensemble probability of the crest distribution, both obtained from the wave elevation at the center of the domain.

scholarly journals Efficient Wave Modeling Using Nonhydrostatic Pressure Distribution and Free Surface Tracking on Fixed Grids

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Hans Bihs ◽  
Arun Kamath ◽  
Ankit Aggarwal ◽  
Csaba Pakozdi
Keyword(s):  
Stokes Equations ◽  
Wave Model ◽  
Offshore Structures ◽  
3D Simulation ◽  
Wave Forces ◽  
Wave Loads ◽  
Two Phase ◽  
New Approach ◽  
2D Simulation ◽  
Numerical Wave

For the estimation of wave loads on offshore structures, relevant extreme wave events need to be identified. In order to achieve this, long-term wave simulations of relatively large scales need to be performed. Computational fluid dynamics (CFD) based numerical wave tanks with an interface capturing two-phase flow approach typically require too large computational resources. In this paper, a three-dimensional (3D) nonhydrostatic wave model is presented, which solves the Navier–Stokes equations and employs an interface tracking method based on the continuity of the horizontal velocities along the vertical water column. With this approach, relatively fewer cells are needed in the vicinity of the air–water interface compared to CFD-based numerical wave tanks. The numerical model solves the governing equations on a rectilinear grid, which allows for the employment of high-order finite differences. The capabilities of the new wave model are presented by comparing the wave propagation in the tank with the CFD approach in a two-dimensional (2D) simulation. Further, a 3D simulation is carried out to determine the wave forces on a vertical cylinder. The calculated wave forces using the new approach are compared to those obtained using the CFD approach and experimental data. It is seen that the new approach provides a similar accuracy to that from the CFD approach while providing a large reduction in the time taken for the simulation. The gain is calculated to be about 4.5 for the 2D simulation and about 7.1 for the 3D simulation.

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

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.

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

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.

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

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.

scholarly journals A Semi-Infinite Numerical Wave Tank Using Discrete Particle Simulations

2020 ◽  
Vol 8 (3) ◽  
pp. 159 ◽  
Author(s):  
Sangmin Lee ◽  
Jung-Wuk Hong
Keyword(s):  
Wave Height ◽  
Numerical Technique ◽  
Analytical Formula ◽  
Offshore Structures ◽  
Wave Steepness ◽  
Numerical Wave Tank ◽  
Time Step ◽  
Wave Tank ◽  
Wide Range ◽  
Numerical Wave

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.

Response Behaviour of Perforated Cylinders in Regular Waves

2011 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
S. Parameswara Pandian
Keyword(s):  
Outer Cylinder ◽  
Wave Structure ◽  
Offshore Structures ◽  
Experimental Investigations ◽  
Coastal Protection ◽  
Wave Loads ◽  
Wave Impact ◽  
Protection Measures ◽  
Cylindrical Structures ◽  
Perforated Cylinder

In order to reduce the direct wave impact, coastal and offshore structures are often constructed with one or more perforated layers. Several permeable breakwaters and docks have been deployed in coastal protection measures to reduce direct impact due to encountered wave loads and to reduce wave reflection in front of these structures as well; compared with the traditional ones, such structural forms are found to be more economical. Such structures result in lesser surface fluctuation in harbours due to the low reflection, which is vital for loading and unloading of ships. Deploying permeable breakwaters posses other advantages namely: i) increasing water circulation; ii) retaining water quality and iii) enhances coastal protection. Emerged and submerged perforated cylindrical structures reduce wave-structure interactions and scouring problems considerably, but their use on floating structures is scarce in the literature. This study is focused on detailed experimental investigations carried out on impermeable inner cylinder encompassed by a larger outer cylinder with perforatios along its length. By varying the porosity and perforatio diameter, their influence on the hydrodynamic response of the cylindrical member is highlighted through the current study. The conclusions on the comparison of forces in the cylinder with and without perforated cylinder coverage are presented.

scholarly journals Estimation of Wave Loads Acting on Stationary Floating Body Using Viscous Numerical Wave Tank Technique

2013 ◽  
Vol 27 (3) ◽  
pp. 43-52
Author(s):  
Kyung-Mi Kim ◽  
Jae-Kyung Heo ◽  
Se-Min Jeong ◽  
Jong-Chun Park ◽  
Wu-Joan Kim ◽  
...  
Keyword(s):  
Floating Body ◽  
Wave Loads ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Numerical Wave

scholarly journals Development of Combined Load Spectra for Offshore Structures Subjected to Wind, Wave, and Ice Loading

2021 ◽  
Author(s):  
Moritz Braun ◽  
Alfons Dörner ◽  
Kane Falco ter Veer ◽  
Tom Willems ◽  
Marc Seidel ◽  
...  
Keyword(s):  
Wind Wave ◽  
Fatigue Testing ◽  
Numerical Models ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Combined Load ◽  
Load Spectra

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered, but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider effects of ice loading and its stochastic nature on fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.

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