Development of two-dimensional numerical wave tank based on lattice Boltzmann method

A 2-D numerical wave tank(NWT)is developed using the lattice Boltzmann method(LBM)and a multi-relaxation-time(MRT)collision model coupled with an algebraic volume of fluid(VOF)scheme for free surface tracking.An external force based on the momentum source function is used to generate the waves,and a zone of porous media is used to absorb the waves.Numerical simulations of the progressive and standing waves show that the NWT can generate stable wave trains in agreement with the analytical solutions and eliminate the re-reflection waves.The NWT is used to simulate two problems encountered in practice,namely:the wave transformation over a submerged breakwater and the wave runup on a sea dike.The numerical predictions are in good agreement with the measured data.

Research on Numerical Wave Tank Based on the Improved Moving-Particle Semi-Implicit Method with Large Eddy Simulation

Moving-particle semi-implicit(MPS) method is a new mesh-free numerical method based on Lagrangian particle. In this paper, MPS method is applied to the study on numerical wave tank. For the purpose of simulating numerical wave, we combine the MPS method with large eddy simulation(LES) which can simulate the turbulence in the flow. The intense pressure fluctuation is a significant shortcoming in MPS method. So, we improve the original MPS method by using a new pressure Poisson equation to ease the pressure fluctuation. Divergencefree condition representing fluid incompressible is used to calculate pressure smoothly. Then, area-time average technique is used to deal with the calculation. With these improvements, the modified MPS-LES method is applied to the simulation of numerical wave. As a contrast, we also use the original MPS-LES method to simulate the wave in a numerical wave tank. The result shows that the new method is better than the original MPS-LES method.

A third-order KdV solution for internal solitary waves and its application in the numerical wave tank

A third-order KdV solution to the internal solitary wave is derived by a new method based on the weakly nonlinear assumptions in a rigid-lid two-layer system.The solution corrects an error by Mirie and Su(1984).A two-dimensional numerical wave tank has been established with the help of the open source CFD library OpenFOAM and the third-party software waves2Foam.Various analytical solutions,including the first-order to third-order KdV solutions,the eKdV solution and the MCC solution,have been used to initialise the flow fields in the CFD simulations of internal solitary waves.Two groups including 11 numerical cases have been carried out.In the same group,the initial wave amplitudes are the same but the implemented analytical solutions are different.The simulated wave profiles at different moments have been presented.The relative errors in terms of the wave amplitude between the last time step and the initial input have been analysed quantitatively.It is found that the third-order KdV solution results in the most stable internal solitary wave in the numerical wave tank for both small-amplitude and finite-amplitude cases.The finding is significant for the further simulations involving internal solitary waves.

A simple method of depressing numerical dissipation effects during wave simulation within the Euler model

Numerical wave tanks are widely-acknowledged tools in studying waves and wave-structure interactions. They can generate waves under realistic scales and offers more information on the fluid field. However, most numerical wave tanks suffer from issues known as the numerical dissipation and numerical dispersion. The former causes wave energy to be slowly dissipated and the latter shifts wave frequencies during wave propagation. This paper proposes a simple method of depressing numerical dissipation effects on the basis of solving Euler equations using the finite difference method(FDM). The wave propagation solutions are solved analytically taking into account the influence of the damping terms. The main idea of the method is to append a source term to the momentum equation, whose strength is determined by how strong the numerical damping effect is. The method is verified by successfully depressing numerical effects during the simulation of regular linear waves, Stokes waves and irregular waves. By applying the method, wave energy is able to be close to its initial value after long distance of travel.

Comparative Experimental and Numerical Study of Wave Loads on A Monopile Structure Using Different Turbulence Models

This study numerically and experimentally investigates the effects of wave loads on a monopile-type offshore wind turbine placed on a 1:25 slope at different water depths as well as the effect of choosing different turbulence models on the efficiency of the numerical model.The numerical model adopts a two-phase flow by solving Unsteady Reynolds-Averaged Navier−Stokes(URANS)equations using the Volume Of Fluid(VOF)method and three differentk-ωturbulence models.Typical environmental conditions from the East China Sea are studied.The wave run-up and the wave loads applied on the monopile are investigated and compared with relevant experimental data as well as with mathematical predictions based on relevant theories.The numerical model is well validated against the experimental data at model scale.The use of different turbulence models results in different predictions on the wave height but less differences on the wave period.The baseline k-ωturbulence model and Shear-Stress Transport(SST)k-ωturbulence model exhibit better performance on the prediction of hydrodynamic load,at a model-scale water depth of 0.42 m,while the laminar model provides better results for large water depths.The SST turbulence model performs better in predicting wave run-up for water depth 0.42 m,while the laminar model and standard k-ωmodel perform better at water depth 0.52 m and 0.62 m,respectively.

Numerical Analysis on Motion of Multi-column Tension-Leg-Type Floating Wind Turbine Basement

The offshore wind energy presents a good solution for the green energy demand.The floating offshore wind turbine(FOWT)is one of the most potential choices of the basement construction for offshore wind turbines in deep water.Hydrodynamic performance of multi-column tension-leg-type floating wind turbine is investigated numerically,particularly at its motion responses.Based on the Navier-Stokes equations and the volume of fluid method,a numerical wave tank(NWT)is established to simulate the floating structure system.The analytical relaxation method is adopted to generate regular waves.Dynamic mesh method is used to calculate the motion of the floating body.Hydrostatic decay of motion and hydrodynamic forces in the regular wave are provided.The computation results agree with the experimental data available.Numerical results show that the wave force on the lower pontoon of the system is the greatest while that on the center column is the smallest.Detailed information about the changes of the wave forces on different elements of the floating system is discussed.

全非线性波的高阶谱方法

Efficient generation of an accurate numerical wave is an essential part of the Numerical Wave Basin that simulates the interaction of floating structures with extreme waves.computational fluid dynamics(CFD)is used to model the complex free-surface flow around the floating structure.To minimize CFD domain that requires intensive computing resources,fully developed nonlinear waves are simulated in a large domain that covers far field by more efficient potential flow model and then coupled with the CFD solution nearfield.Several numerical models have been proposed for the potential flow model.the higher-level spectral(HLS)method presented in this paper is the extended version of HLS model for deep water recently been derived by combining efficiency and robustness of the two existing numerical models–Higher-Order Spectral method and Irrotational Green-Naghdi model(Kim et al.2022).The HLS model is extended for the application of finite-depth of water considering interaction with background current.The verification of the HLS model for finite depth is made by checking the qualification criteria of the generated random waves for a wind-farm application in the Dong-Hae Sea of Korea.A selected wave event that represents P90 crest height is coupled to a CFD-based numerical wave tank for the future air-gap analysis of a floating wind turbine.

Prediction of regular wave loads on a fixed offshore oscillating water column-wave energy converter using CFD

In this paper,hydrodynamic wave loads on an offshore stationary-floating oscillating water column(OWC)are investigated via a 2D and 3D computational fluid dynamics(CFD)modeling based on the RANS equations and the VOF surface capturing scheme.The CFD model is validated against previous experiments for nonlinear regular wave interactions with a surface-piercing stationary barge.Following the validation stage,the numerical model is modified to consider the pneumatic damping effect,and an extensive campaign of numerical tests is carried out to study the wave-OWC interactions for different wave periods,wave heights and pneumatic damping factors.It is found that the horizontal wave force is usually larger than the vertical one.Also,there a direct relationship between the pneumatic and hydrodynamic vertical forces with a maximum vertical force almost at the device natural frequency,whereas the pneumatic damping has a little effect on the horizontal force.Additionally,simulating the turbine damping with an orifice plate induces higher vertical loads than utilizing a slot opening.Furthermore,3D modeling significantly escalates and declines the predicted hydrodynamic vertical and horizontal wave loads,respectively.

Coupling potential and viscous flow models with domain decomposition for wave propagations

Either potential flow or viscous flow based model may be flawed for numerical wave simulations.The two-way coupling of potential and viscous flow models with the domain decomposition utilizing respective strengths has been a trending research topic.In contrast to existing literatures in which closed source potential models were used,the widely used open source OceanWave3D,OpenFOAM-v2012 are used in the present research.An innovative overlapping two-way coupling strategy is developed utilizing the ghost points in OceanWave3D.To guarantee computational stability,a relaxation zone used both for outlet damping and data transfer is built over the overlapping region in OceanWave3D.The free surface elevation in the relaxation zone is directly probed in OpenFOAM while the velocity potential is indirectly built upon its temporal variation which is calculated by the free surface boundary condition using the probed velocity.Strong coupling is achieved based on the fourth-order Runge-Kutta(RK)algorithm.Both two-and three-dimensional tests including linear,nonlinear,irregular,and multi-directional irregular waves,are conducted.The effectiveness of the coupling procedure in bidirectional data transfer is fully demonstrated,and the model is validated to be accurate and efficient,thus providing a competitive alternative for ocean wave simulations.