ABSTRACT Because of the continuous advances in computational fluid dynamics, the use of numerical simulation to assist ship and marine structure hydrodynamic performance prediction has become common. This paper presents a numerical study of the generation and propagation of long- crested wave. ITTC double-parameter wave spectrum is chosen for the study, and the wave spectrum is spilt based on equal-frequency method. The self-developed MPI based in-house code is used for the study. The computations are carried out by a PC cluster. In this study, the finite difference method is used to discretize the partial differential equations, and the conservative level set method is used to capture the free surface. The behavior of the free surface elevation along the basin and over time has been evaluated by time domain waveform comparison with theoretical solutions, frequency domain and statistical analysis. The results obtained for the free surface elevation for numerical wave tank indicated that the numerical model could correctly capture the wave profile. The results in this study show the in-house code is reliable and could be used to simulate the complex 3D wave and flow fields. INTRODUCTION At present, there are two kinds of irregular waves studied. One is the long-crested wave, which can be understood as the combination of different regular waves with the same direction. Therefore, in recent years, the simulation of wave environment is mostly aimed at regular wave, and the simulation of long-crested wave is not much. Therefore, it is necessary to conduct more simulation research on long-crested wave. Numerical wave tank is a very effective method to study wave in recent years. Since the calculation of the numerical wave tank is carried out by computer, the numerical wave tank can save a lot of cost compared with the traditional physics wave tank, and it is also easier to monitor and observe the features of wave. In recent years, many researchers have devoted themselves to the development and construction of numerical wave tank. In this paper, based on self-developed MPI code, the simulation of long-crested wave is carried out by numerical wave tank, so as to have more understanding of irregular waves, and evaluate the reliability of the numerical wave tank developed.

ABSTRACT: Numerical simulations were performed for the evaluation of wave and current loads on fixed cylindrical platform model for ocean wind turbine using ANSYS-CFX package. The numerical wave tank was actualized by specifying velocity at the inlet and applying momentum loss as wave damper at the end of the wave tank. Volume-Of-Fluid (VOF) scheme was adopted to capture the air-water interface. Accuracy validation of numerical wave tank with truncated vertical circular cylinder had been accomplished by comparing the CFD results with Morison's formula and the experimental data. The parametric study has been carried out by varying the wave length and amplitude alternatively. As a meaningful engineering application, in the present study, three kinds of conditions have considered, i.e. the cases with current, waves and the combination of current and progressive wave, respectively, passing through a cylindrical platform model. It was found that CFD results show reasonable agreement with experimental data and Morison's formula when only progressive wave is considered, however, when current is included, CFD gives smaller load than Morison's formula. INTRODUCTION Wind turbine foundations installed at offshore sites are subject to ocean waves and current directly. Recently the structural integrity of Ocean Wind Turbine (OWT) foundation draws much attention as renewable wind energy market grows. As the main component to the wind turbine system, cylindrical foundation has been widely used. Flow around circular cylinders has been a research topic in fluid mechanics for decades because of its complex physical phenomena, such as separation and vortex shedding, deformation of incoming wave. For a planar oscillatory flow around a circular cylinder, there are many experimental and numerical studies, providing the basic knowledge to further understand complex flow environments, such as the combination of oscillatory flow by incoming wave and current-induced vortex shedding.

ABSTRACT: This study aims the investigation of depth effects in the motion response of floating structures. To this end, a Rankine panel method adopting higher-order B-spline basis function is applied in time domain. The topology of sea bottom is assumed to be either constant or varied. Taking the advantage of the Rankine panel method, any bottom topology near floating structures can be considered by distributing the solution panels on the bottom surface. The numerical analysis includes the radiation, diffraction problems and floating motion responses for typical hull forms, e. g. LNG carrier and barge. The result is compared with other numerical solution for validation purpose. The motion RAOs are observed for different water depth and varying bottom topology. INTRODUCTION Recently moving inland facilities into coastal area is seriously considered. In coastal area, water waves and floating-body motion have different property by restricted water depth. Therefore considering bottom effect is important to predict the motion responses of such coastal platforms. The motion responses of floating bodies in constant depth have been considered as one of classical problems in marine hydrodynamics, and several methods have been introduced. For instant, strip method has been utilized by Tuck (1970), Tasis et al. (1978), Andersen (1979), Perunovic and Jensen (2003). This method is still used nowadays for practical purpose, however it has limitation as a two-dimensional theory. To complement such limitation, Kim (1999) introduced a new unified theory for the finite-depth effect, showing much improved accuracy. Nowadays, three dimensional panel method programs such as WAMIT (Lee, 1995), which contains solution procedure for constant depth, are available. For an offshore structure, Teigen (2005) has showed motion responses of floating barge over constant and sloped bottom. Ship motion over sloping bottom has been considered by Buchner (2006), Ferreira and Newman (2008) and Hauteclocque et al. (2009).

ABSTRACT: Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor, which comprises the circular ramp and reservoir. It collects the overtopped waves and converting water pressure head into electric power through the hydro-turbines installed in the vertical duct, which is fixed in the sea bed. The performance of OWEC can be represented by the operating water heads of the device, which depends on the amount of the wave water overtopping into the reservoir. In the present paper, the reservoir with the duct connecting to the sea water are studied in the 3D numerical wave tank, which has been developed based on the computational fluid dynamics software Fluent 6.3. Both the overtopping motion and the discharges of the reservoir are investigated together, and several shape parameters and incident wave conditions are varied to demonstrate their effects on the performance of OWEC. INTRODUCTION The generation of electric power utilizing clean and renewable ocean resources is one of the most important alternative energy technologies for overcoming shortages in energy resources caused by excessive use of fossil fuels. Among various ocean resources, wave energy is the most abundantly available and applicable in most coastal and offshore areas. Due to the advantages of simple converting technique and producing cost over other types of ocean energy, the wave energy conversion system is feasible to be established for the commercial power production. Plenty of wave energy absorption devices have been invented, and several of them have been utilized in the electricity generation. Recently, the Oscillating Water Column (OWC) type has been widely employed in the application for the wave energy conversion. The disadvantage of this device is the low wave energy converting efficiency. Overtopping Wave Energy Convertor (OWEC) has the sloping walls and reservoirs to lift waves to the levels above the average surrounding ocean.

ABSTRACT: Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor for collecting the overtopping waves and converting the water pressure head into electric power through the hydro turbines installed in the vertical duct which is fixed in the sea bed. The numerical wave tank based on the commercial computational fluid dynamics code Fluent is established for the corresponding analysis. The Reynolds Averaged Navier-Stokes and two-phase VOF model are utilized to generate the 2D numerical linear propagating waves, which has been validated by the overtopping experiment results. Several incident wave conditions and shape parameters of the overtopping device are calculated. The straight line type and parabolic type of the sloping arm are compared in the optimal designing investigation of the overtopping characteristics and discharge for OWEC device. The numerical results demonstrate that the parabolic sloping arm is available for wave running up and the overtopping discharge increasing. INTRODUCTION Among various ocean renewable resources, wave energy is most abundantly available and applicable in most coastal and offshore areas. Due to the advantages of simple converting techniques and producing cost over other types of ocean energy, the wave energy conversion system is feasible to be established for the commercial power production. Plenty of wave energy absorption devices and plants have been invented, and several of them have been utilized in the electricity generation. Recently, the oscillating water column type has been widely employed in the application for the wave energy conversion. The disadvantage of this type is the low wave energy converting efficiency. Overtopping Wave Energy Convertor (OWEC) has the sloping walls and reservoirs to lift water waves to the levels above the average surrounding ocean. The released reservoir water is used to drive hydro turbines or other converting devices.

ABSTRACT: To study the nonlinear wave interaction with large submerged, rectangular breakwaters, the writers developed a fully nonlinear numerical wave tank, which is based on the mixed Eulerian-Lagrangian (MEL) formulation. The desingularized boundary element method (DBIEM) is adopted here to circumvent the singular integration in the boundary element methods (BEM) that are based on Green's function formulations. After code verification, our nonlinear numerical wave tank is used to study the nonlinear wave scattering by a submerged rectangular step. In comparison with our experiments, we found that higher harmonic wave components generated by nonlinear wave processes in shallower water over the step are well predicted by our DBIEM numerical wave tank. The reflection coefficients and the transmission coefficients of the second harmonic waves are also modeled satisfactorily. The transmission coefficients of the first harmonic waves predicted by the DBIEM demonstrated improvement over those by linear theory. INTRODUCTION Submerged breakwaters are frequently used to provide economic measure in shoreline erosion control. The purpose of a submerged breakwater is not to create completely calm water behind the breakwater, but to reduce the wave intensity behind the breakwater to an acceptable level. Early research on this subject focused on the linear interactions between waves and submerged objects. Following Newman (1965), who first studied the scattering of long waves by submerged obstacles, Mei and Black (1969) investigated the wave scattering by two-dimensional obstacles in waters of finite depth. Recent reviews of linear wave scattering by impermeable submerged steps can be found in Dingemans (2000) or Mei et al. (2005). Ocean waves nearshore are most likely nonlinear in nature and the interactions between waves and the submerged structures are strongly or at least weakly nonlinear as well. It is not always possible to obtain analytical solutions for fully nonlinear problems.

ABSTRACT: A time-domain higher-order boundary element method (HOBEM) is used to simulate the linear and fully nonlinear waves in a threedimensional numerical wave tank (NWT). In order to eliminate reflective waves at the incident boundary and output boundaries, damping layer combined with a nonreflective wave generator, which is composed a series of vertically aligned point source in the computational domain, is applied. The governing equation is solved at each time step by using Rankine sources distributed on all the boundaries. Based on the image theory, a new Green function is applied in the whole fluid domain so that the two lateral surfaces and bottom are excluded. Numerous numerical experiments, on linear and fully nonlinear wave propagation in a wave tank with and without fully reflective wall, demonstrate that the present approach is effective in generating an arbitrary wave profile without reflection not only at the open boundaries but also at the wave generator. It is furthermore shown that scattered waves can pass through the area of generation without significant reflection and the process of generation is not affected by the scatted waves. INTRODUCTION With the increasing use of numerical techniques and computers during the past two decades, it is possible that the numerical wave tanks are used to investigate wave interaction with structures and the considerable efforts have been devoted to developing increasingly accurate and efficient numerical wave tank to investigate various fully nonlinear water wave problems at sea. Such numerical results have been shown to model the wave propagation and overturning in deep water (Dommermuch et al ., 1988), wave shoaling up to breaking over slopes (Grilli et al ., 1994), wave loads on objects (Zhang et al., 1996; Boo and Kim, 1997; Kashiwagi, 1996) and floating body motions (Isaacson,1982; Kashiwagi, 1998) etc.