NUMERICAL SIMULATION OF NONLINEAR WAVE FLOW AROUND COCHLEA CHANNELED STERN SHIPS

A nonlinear method based on Gadd's model [1] [2] is developed to simulate the wave flow around cochlea-channeled stern ships. The subsurface division method is capable of dividing the complicated hull into panels and defining the computer simulated 3-D graphs. Good results are obtained and depicted by computer graphs.     

NUMERICAL STUDY OF SOLITARY WAVE FISSION OVER AN UNDERWATER STEP

Solitary wave fission over an underwater step is numerically investigated. The numerical model is based on the enhanced Boussinesq equations, which appropriately represent both the nonlinearity and dispersivity of surface water waves. The finite difference method defined on the staggered grid in space with an implicit scheme for time stepping is employed for the numerical solution of the governing equations. It is demonstrated that Boussinesq type equations, though they are vertically integrated, can describe the details of the solitary wave fission process with very good accuracy. Numerical results of the reflected and transmitting wave heights, the number of solitons emitted from the transmitting wave and their amplitudes all agree very well with the analytical solution derived from KdV equation by virtue of a linear long wave approximation in the vicinity of the underwater step.     

NUMERICAL SIMULATION OF SOLITARY WAVE RUN-UP AND OVER-TOPPING USING BOUSSINESQ-TYPE MODEL

In this article,the use of a high-order Boussinesq-type model and sets of laboratory experiments in a large scale flume of breaking solitary waves climbing up slopes with two inclinations are presented to study the shoreline behavior of breaking and non-breaking solitary waves on plane slopes.The scale effect on run-up height is briefly discussed.The model simulation capability is well validated against the available laboratory data and present experiments.Then,serial numerical tests are conducted to study the shoreline motion correlated with the effects of beach slope and wave nonlinearity for breaking and non-breaking waves.The empirical formula proposed by Hsiao et al.for predicting the maximum run-up height of a breaking solitary wave on plane slopes with a wide range of slope inclinations is confirmed to be cautious.Furthermore,solitary waves impacting and overtopping an impermeable sloping seawall at various water depths are investigated.Laboratory data of run-up height,shoreline motion,free surface elevation and overtopping discharge are presented.Comparisons of run-up,run-down,shoreline trajectory and wave overtopping discharge are made.A fairly good agreement is seen between numerical results and experimental data.It elucidates that the present depth-integrated model can be used as an efficient tool for predicting a wide spectrum of coastal problems.     

NUMERICAL SIMULATIONS OF WATER WAVE DYNAMICS BASED ON SPH METHODS

A numerical model was established for simulating water wave dynamic problems by adopting the Smoothed Particle Hydrodynamics (SPH) methods of iterative solution of Poisson's equation for pressure field, and meanwhile the sub-grid turbulence model was applied in the simulation so as to more accurately describe the turbulence characteristics at the time of wave breaking. In this article, simulation of the problem of the dam collapsing verifies the compoting accuracy of this method, and its results can be identical with the results of VOF method and the experimental results by comparison. Numerical simulations of the course of solitary wave and cnoidal wave run-up breaking on beaches were conducted, and the results are basically consistent with experimental results. This indicates that the SPH method is effective for the numerical simulation of the complex problems of water wave dynamics.     

NUMERICAL SIMULATIONS OF HIGHLY NONLINEAR STEADY AND UNSTEADY FREE SURFACE FLOWS

A numerical simulation model based on an open source Computational Fluid Dynamics (CFD) package-Open Field Operation and Manipulation (OpenFOAM) has been developed to study highly nonlinear steady and unsteady free surface flows. A two-fluid formulation is used in this model and the free surface is captured using the classical Volume Of Fluid (VOF) method. The incompressible Euler/Navier-Stokes equations are solved using a finite volume method on unstructured polyhedral cells. Both steady and unsteady free surface flows are simulated, which include: (1) a submerged NACA0012 2-D hydrofoil moving at a constant speed, (2) the Wigley hull moving at a constant speed, (3) numerical wave tank, (4) green water overtopping a fixed 2-D deck, (5) green water impact on a fixed 3-D body without or with a vertical wall on the deck. The numerical results obtained have been compared with the experimental measurements and other CFD results, and the agreements are satisfactory. The present numerical model can thus be used to simulate highly nonlinear steady and unsteady free surface flows.     

NUMERICAL SIMULATIONS OF NONLINEAR WAVES OVERTOPPING AN OBSTRUCTION

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NUMERICAL STUDY OF MULTIDIRECTIONAL FOCUSING WAVE RUN-UP ON A VERTICAL SURFACE-PIERCING CYLINDER

In this article,a numerical model based on improved Boussinesq equations and the Finite Element Method(FEM)with unstructured triangular elements is proposed and verified by experimental results for the focusing wave group interaction with a vertical surface-piercing cylinder.The multidirectional focusing waves with different directional spreading parameters and their interaction with a vertical surface-piercing cylinder are numerically simulated.The directional spreading parameter influences the wave form,that is,a wider directional spreading would induce a narrower wave form in space.The wave run-up on the cylinder increases with the increase of the wave directional spreading parameter,but when the parameter is greater than 30-40,the wave run-up changes only slightly and the influence of the directional spreading can be neglected.A larger diameter cylinder may have a larger wave run-up at the front face.But at the back side,it is other way round.     

NUMERICAL SIMULATION OF TRAVELING WAVE CONVECTION IN A WEAKLY NONLINEAR REGIME

1.　INTRODUCTIONExperimentsontravelingwave(TW)convectionofabinaryfluidmixtureinfinitegeometrieshavefoundthatthesystemundergoesatransitionofalinearinstability[1][2]　attheonsetofconvectiontoaweaklynonlinearbranch[3～10]　　　inverycloseonsetofconvectionforacertainparameters.AlongthisweaklynonlinearbranchtherichdynamicshasbeenobservedinexperimentsforaseparationratiowithorderofΨ～-10-2.Spatiallyandtemporallymodulatedtravelingwaves(MTW)statefortheconvectionofabinaryfluidmixtureinalongandnar…     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF WAVE SLAMMING ON AN OPEN STRUCTURE

The three-dimensional numerical simulation of wave slamming on an open structure in the splash zone is carried out based upon the Volume Of Fluid (VOF) method.A wave basin is established by solving the...     

THE EFFECT OF WAVE GROUPINESS ON A MOORED SHIP STUDIED BY NUMERICAL SIMULATIONS

Waves with the same wave parameters, such as significant wave height and period, but with different wave groupiness factors are simulated, to study the motion behavior of a moored ship under the action of waves with different Groupiness Factors of Height (GFH) and Group Length Factors (GLF). The numerical results show that both the sway and heave motions increase with an increase in GFH. In contrast, the influence of GLF on the motions of a moored ship is weak.     

STUDY OF NONLINEAR LONG WAVE APPOXIMATION IN UNIFORM CHANNELS VIA HAMILTONIAN STRUCTURE

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NUMERICAL SIMULATIONS OF CAVITATING FLOWS

BRIEFINTRODUCTIONOFTHEPAPER :　Thisthesismainlyresearchesonthehydrodynamiccharacteristicsandmechanismfor 3Dcavitatingflowsaroundaxisymmetricbodies ,aswellasthe2Dcavitatingflowsaroundhydrofoils .Anewcavi tatingflowmodel,whichinvolvesviscousandmul ti phaseeffects,isestablishedintwo phaseflowcategory .Accordingtothelocalizedvariationofdensitywithinpredominantlyincompressiblewatermediumandthecharacteristicsofsoundspeedinwater vapormixture ,arelationbetweendensityandpressureisassumed ,in…     

NUMERICAL SIMULATION OF WAVE RESISTANCE OF TRIMARANS BY NONLINEAR WAVE MAKING THEORY WITH SINKING AND TRIM BEING TAKEN INTO ACCOUNT

Up to now, there are no satisfactory numerical methods for simulating wave resistance of trimarans, mainly due to the difficulty related with the strong nonlinear features of the piece hull wave making and their interference. This article proposes a numerical method for quick and effective calculation of wave resistance of trimarans to be used in engineering applications. Based on Wyatt’s work, the nonlinear free surface boundary condition, the time domain concept, and the full nonlinear wave making theory, using the Rankine source Green function, the 3-D surface panel method is expanded to solve the trimaran wave making problems, with high order nonlinear factors being taken into account, such as the influence of the sinking and trim, transom, and ship wave immersed hull surface. And the software is successfully developed to implement the method, which is validated. Several trimaran models, including a practical trimaran with a sonar dome and the transom, are used as numerical calculation samples, their wave making resistance is calculated both by the present method and some other methods such as linear (Dawson) methods. Moreover, sample model resistance tests were carried out to provide data for comparison, validation and analysis. Through the validation by model experiments, it is concluded that present method can well predict the wave making resistance, sinking and trim, and the accuracy of wave making resistance calculation is significantly improved by taking the trim and sinking into account, especially at high speeds.     

NUMERICAL SIMULATION OF EXTREME WAVE GENERATION USING VOF METHOD

Numerical simulations of extreme wave generation are carried out by using the Volume Of Fluid (VOF) method. Extreme waves are generated based on wave focusing in a 2-D numerical model. To validate the capability of the VOF-based model described in this article, the propagation of regular waves is computed and compared with the theoretical results. By adjusting the phases of wave components, extreme waves are formed at given time and given position in the computation. The numerical results are compared with theoretical solutions and experimental data. It is concluded that the present model based on the VOF technique can provide acceptably accurate numerical results to serve practical purposes.     

SOLUTION OF A KIND OF LINEAR INTERNAL WAVE EQUATION

1.INTRODUCTIONIn density stratified ocean,vertical displaments can cause internal waves.Take the effectdensity compactness of seawater into account,toscillation frequency isN=(-ρg0ddρz0-Cg22)1/2(whereNis one of the most i mportant environmparameters of ocean dynamics which is callBrunt-Vaisala frequency,gthe gravity acceletion,Cthe traveling speed of sound in seawatBothgandCcan be deemed as constants.Soscholars neglectedg2/C2in expression(1).Itbeen proved that in the seawater200m bel…     

DEFORMATION AND BREAKINC OF NONLINEAR WAVE IN WATER OF GRADUALLY VARYING DEPTH

Based upon the perturbation method,this paper used the method of conformalmapping to solve the deformation and breaking of nonlinear waves in water of gradually varyingdepth.The wave characteristics,such as wave deformation,velocity field,breaker type andbreaker height are discussed by the third order approximation.Results obtained are comparedwith experimental data.     

NUMERICAL SIMULATIONS OF 2D PERIODIC UNSTEADY CAVITATING FLOWS

1. INTRODUCTION Cavitation is a natural phenomenon especially existing in liquids. A cavitating flow generally involves a large number of vapor structures such as bubbles or vortices which are convecting downstream. When they reach high pressure zones, th…     

NUMERICAL STUDY OF EFFECT OF WAVE AROUND SINGLE BREAK-WATER WITH THE SWAN MODEL

A new version of the Stimulating Wave Nearshore(SWAN)model(version 40.51)was used to stimulate the evolution of directional irregular wave near a single breakwater and the Wen spectrum was adopted as an input spectrum.The wave diffraction effect of irregular wave,which is the main improvement compared with the previous SWAN versions,was tested with the experimental data of single breakwater collected in the State Key Laboratory of Coastal and Offshore Engineering(SLCOE)at Dalian University of Technology(DUT)and the stimulated results of Wu Yan and JONSWAP spectrum as input data,respectively.By comparing the results in four cases,it is seen that the results stimulated by the SWAN model with the JONSWAP or Wen spectra are better than those with Wu's spectrum,and the results simulated with the Wen spectrum is little larger than those with the JONSWAP spectrum and more closely approximated to the measured data compared to the results with the JONSWAP spectrum.It is then concluded that the new SWAN model with the Wen spectrum can be well used to stimulate wave diffraction around a single breakwater.     

NUMERICAL SIMULATION OF IRREGULAR WAVE-SIMULATING IRREGULAR WAVE TRAIN

In real sea states, damage incidents on offshore floating structures are not due to the whole time series of wave elevation characterized as statistical one but due to few extreme waves or wave groups in irregular wave train. So, using CFD tools to precisely simulate predetermined irregular wave train will lay sound basis for understanding the local characteristic of the flow field and impact loads on offshore floating structures when damage incidents occur. In this article, the generation of single extreme wave is investigated in a numerical wave tank. First, experimental irregular wave train is decomposed into certain number of small-amplitude waves. The Fourier series expansion is performed to determine the amplitude and initial phase angle of each wave component. A hydrodynamic transfer function is used to calculate the amplitude of wave-maker motion associated with each wave component. Then superposition is carried out on all of the wave-maker motion components to get the final wave-maker motion. With the wave-maker motion as input, simulation of the single extreme irregular wave train is modeled successfully. Then the method is applied to simulating a much more complicated irregular wave train. Once again main features of the complicated irregular wave train are reproduced compared with experiment carried out in the new deepwater experimental basin at Shanghai Jiao Tong University. In the simulation, dynamic mesh method is enabled to model the piston-type wave-maker, the Volume Of Fluid (VOF) method is employed to capture the free surface and a dissipation zone is introduced to deal with wave reflection.     

NUMERICAL SIMULATON OF IMPROVED BOUSSINESQ EQUATIONS BY A FINITE ELEMENT METHOD

1 .　INTRODUCTIONAswavespropagatetowardshore ,acombina tionofshoaling ,reflection ,refractionanddiffrac tioneffectsmodifythewaveform .Numericalmod elbasedonthetwo dimensionalBoussinesqequa tionshavebeenshowntobecapableofsimulatingthewavepropagationinthecoastalregionsaccu rately .ThestandardBoussinesqequationsderivedbyPeregrine[2 ] includethelowestordereffectsofnon linearityandfrequencydispersion .Becausetheerrorinthelineardispersionrelationincreaseswiththeincreaseofwaterdepth ,thestandar…