THE WAVE-MAKING CHARACTERISTICS OF A MOVING BODY IN A TWO-LAYER FLUID

The Wave-making characteristics of a moving body in a two-layer fluid with free surface is investigated numerically and experimentally. The numerical analysis is based on the modified layered boundary integral equation system. The wave characteristics on the free surface and interface generated by a moving sphere and an ellipsoid is numerically simulated in both finite depth and infinite depth of lower layer model. The numerical results of the sphere are compared with the analytical results for a dipole with the same velocity in a two-layer fluid of finite depth. The dependence of the wave systems and structures on the characteristic quantities is discussed. Three kinds of measurement techniques are used in model experiments on the internal waves generated by a sphere advancing in a two-layer fluid. The effects of the varying velocity and stratification on the wavelength, wave amplitudes and the maximum half angles of internal waves are analyzed qualitatively.     

WAVES GENERATED BY A SUBMERGED BODY MOVING IN STRATIFIED FLUIDS AND VERTICAL STRUCTURES OF INTERNAL WAVES

This dissertation deals with the internal waves generated by a submerged moving body in stratified fluids by combining theoretical and experimental methods. Our purpose is to provide some scientific evidences for non-acoustic detection of underwater moving bodies based on the principles of dynamics of the internal waves. An approach to velocity potentials obtained by superposing Green‘s functions of sources and sinks was proposed for Kelvin waves at the free surface or interface in a two-layer fluid. The effects of interacting surface and internal wave modes induced by a dipole on the surface divergence field were investigated. A new theoretical model formulating the interaction of a two dimensional submerged moving body with the conjugate flow in a three-layer fluid was established. An exact solution satisfying the two dimensional Benjamin Ono equation was obtained and the vertically propagating properties of the weakly nonlinear long waves were studied hy means of the ray theory and WKB method. The above theoretical results are qualitatively consistent with those obtained in the experiments conducted by the author.     

THE RADIATION AND DIFFRACTION OF WATER WAVES BY A BOTTOM-MOUNTED CIRCULAR CYLINDER IN A TWO-LAYER FLUID

An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as well as the wave excitation forces of the circular cylinder were obtained by an eigenfunction expansion method. The hydrodynamic forces on the bottom-mounted circular cylinder in a two-layer fluid include not only the added mass and damping coefficients, but also the wave forces of the surface and internal-wave modes. This is different from the case of a homogenous fluid. Some examples were given, showing that density stratification can have a relative large effect on these hydrodynamic forces over a wide range of frequencies.     

FREE-SURFACE WAVES AND FAR WAKES GENERATED BY A FLOATING BODY IN A VISCOUS FLUID

1 .　INTRODUCTIONThewavemotionduetoamovingdisturbancehasbeenoflong standinginterest .Butthecorre spondingwakestructuredidnotreceivemuchat tentionuntilthesyntheticapertureradarcollectedanumberofimagesofV likewakepatternsgener atedbyships (Milgram 1988;Brownetal.1989) .Thewakestructuresarethoughttobeclassifiedin tothreecategories :theKelvinwavewakes ,thetrubulentwakesandtheinternalwavewakes(Griffin 1988;Lydenetal.1988;GuandPhillips1994 ) .TheKelvinwakesarethefar fieldwavepatternsgenerate…     

UNSTEADY FREE-SURFACE WAVES GENERATED BY BODIES IN A VISCOUS FLUID

BRIEFINTRODUCTIONOFTHEPAPER :　Inthefirstpartofthisthesis ,thefundamentalsolutionsforthesingularStokesandOseenflowsinanun boundedfluidarederivedinauniversalformwhichinvolvestheHamiltonian ,Hessian ,andLaplacianoperators ,andelementaryfunctions .Inthesecondpart,theinteractionofunsteadylow Reynolds numberflowswithafreesurfaceisinvestigatedanalytically .Thedisturbedflows ,generatedbysubmergedbodiesmovingverticallydownwardsawayfromthesurfaceofthefluid ,aregovernedbytheunsteadyStokeseq…     

SURFACE AND INTERFACIAL GRAVITY WAVES INDUCED BY AN IMPULSIVE DISTURBANCE IN A TWO-LAYER INVISCID FLUID

The transient gravity waves due to an impulsive source in a two-layer fluid system are investigated analytically.The fluid is assumed to be inviscid and incompressible.The density of each of the two layers is constant.Five different boundary conditions are considered.The depth of each of the two layers is infinite or finite.The upper fluid of finite depth is covered by a rigid lid or a free surface.Based on the assumption of small-amplitude waves,a linear system is established.The integral solutions for the free-surface and interfacial waves are obtained by means of the Fourier-Laplace transform.The corresponding asymptotic representations are derived for large time with a fixed distance-to-time ratio by the Stokes and Scorer methods of stationary phase.The analytical solutions show that there are two different modes,namely the free-surface and interfacial wave modes.The wave profiles observed depend on the relation between the distance-to-time ratio and the maximal group velocities and on the limiting values of the second derivatives of the frequencies as well.     

AN INTEGRAL EQUATION DESCRIBING RIDING WAVES IN SHALLOW WATER OF FINITE DEPTH

1 .　INTRODUCTIONSmall scalewavessuperposedonlarge scalewavesarecalled“ridingwaves” .Small scalewavesonoceansurfacehasaroused greatinterestwiththegreatimprovementofprecisionofmeasuringinstrumentsusedinthefieldofremotesensing .Thisstudyaimsatunderstandingthemotionofthelarge scalewavesandtheenergyexchangebetweenairandseathroughsomeinformationofsmall scalewaves .Henyeyetal .[2 ] derivedthemotione quationtothefirstorderofridingwavesbyusingacanonicalHamiltonianformulationandassumingsmallwave…     

FISSION LAWS OF INITIALLY INTERFACE SOLITARY WAVES IN TWOLAYER OCEAN

A 2 D KdV equation of two-layer stratified ocean with 2-D topography is recapitulated in the present paper. Based on a reduced version of this 2-D KdV equation, the fission laws of the initially internal solitary waves are studied by means of numerical calculation. From the numerical results, it is shown that the initially interface solitary waves can fission on the continental slope like the initially surface solitary waves and the fission process is a significant generating mechanism of internal interface soliton packet on the continental shelf.     

WAVE-BODY INTERACTIONS FOR A SURFACE-PIERCING BODY IN WATER OF FINITE DEPTH

Nonlinear wave-body interactions for a stationary surface-piercing body in water of finite depth with flat and sloping bottoms are simulated in a two-dimensional numerical wave tank,which is constructed mainly based on the spatially averaged Navier-Stokes equations with the model for simulating the turbulence.The equations are discretized based on the finite volume method and the scheme of the pressure implicit splitting of operators is employed to solve the Navier-Stokes equations.By using the force time h...     

3-D NUMERICAL SIMULATION OF CONVOY-GENERATED WAVES IN A RESTRICTED WATERWAY

We consider waves generated by the passing of convoys in a restricted waterway. The magnitude of these waves depends mainly on the geometrical and kinematical parameters of the convoy, such as the speed and the hull geometry. The objective of this study is to predict the relationship between these geometrical and kinematical parameters and the amplitude of ship-generated waves as well as the water plane drawdown. Numerical simulations are conducted by solving the 3-D Navier-Stokes equations along with the standard k model for turbulent processes. The results are compared first with the empirical model and second with experimental measurements performed by the French company Compagnie National du Rh ne (CNR).     

PROBABILITY DISTRIBUTION OF IN-LINE WAVE FORCES ON A PILE IN IRREGULAR WAVES

The probability distribution of in-line wave forces on a pile can bemathematically summed up to that of a theory and the assumption of wave period being constantare used and the above probability distribution is simplified to that of a single dimentsionfunction.The probability density functions of the peak values of total wave forces on a wholevertical pile in irregular waves are derived from that of wave height which is the Rayleighdistribution(deep water wave)or the Kerohovski distribution(shallow water waves)on the baseof the Morison Equation.The identification with experimental data shows that suchsimplification is successful.These distributions are compared with Weibull distribution andRayleigh distribution and the result shows that the shallow water distribution of wave forcesobtained here is the best one and can be used in practice.     

SIMULATION OF EDDIES AFFECTED BY TOPOGRAPHY IN A BAROTROPICAL QUASI-GEOSTROPHIC FLUID

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｓｏ ｓｃａｌｅｅｄｄｉｅｓａｒｅａｃｏｍｍｏｎｄｙｎａｍｉｃｐｈｅ ｎｏｍｅｎｏｎｉｎｔｈｅｏｃｅａｎ ,ｗｈｉｃｈａｌｓｏｐｌａｙａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｍｅｔｅｏｒｏｌｏｇｙ .Ｉｎｔｈｅｍｏｖｅｍｅｎｔｏｆａｔｍｏ ｓｐｈｅｒｅ ,ｔｈｅａｐｐｅａｒａｎｃｅｏｆｂａｒｒａｇｅｈｉｇｈ ｐｒｅｓｓｕｒｅａｎｄｉｎｔｅｒｃｅｐｔｉｖｅｌｏｗ ｐｒｅｓｓｕｒｅｃａｎｐｒｏｄｕｃｅｌａｒｇｅ ｓｃａｌｅｅｄ ｄｉｅｓ;ｌｉｋｅｗｉｓｅ ,ｉｎｔｈｅｍｏｖｅｍｅｎｔｏｆ…     

INVESTIGATION OF BUOYANT TRAJECTORY OF THERMAL WAKE BEHIND A SLENDER STREAMLINED HEATED BODY OF REVOLUTION IN STRATIFIED FLUID

In this paper, the buoyant trajectories of laminar far thermal wakes behind slenderstreamlined heated bodies of revolution in stable stratified fluid have been investigated in theoryand experiment. It has been found that the buoyant trajectories of thermal wakes in stratifiedfluid are different from that in homogeneous fluid. The buoyant trajectories of thermal wakes instratified fluid are wavy. The factors influencing the buoyant trajectories of axisymmetric lami-nar thermal wakes in stratified fluid are Richardson number, Nusselt number and number.The validity of theoretical analysis has been proved by the results of measurements and visualiza-tions. The buoyant trajectories of thermal wakes after underwater bodies can be estimated by re-sults herein presented.     

NUMERICAL SIMULATIONS OF WAVE-INDUCED SHIP MOTIONS IN TIME DOMAIN BY A RANKINE PANEL METHOD

A time domain prediction of wave-induced ship motions by a Rankine panel method is investigated. Linear boundary conditions on free surface and mean wetted body surface are adopted, while the numerical damping method is used for the radiation conditions. The motions of two ships in regular head waves are computed by the present method. The related numerical results are compared with the experiment data and those from linear strip theory. The comparison shows satisfactory agreements for pitch and heave transfer functions.     

用三维弹塑性有限元确定水电站坝内埋管强度安全度

在总体弹性分析和局部薄弱区域正常工况弹塑性有限元分析的基础上，对大坝引水管道穿坝管段结构进行超载工况下的三维弹塑性有限元分析研究，分析考虑了钢管钢筋混凝土的联合承载，确定了引水管道穿坝管段的强度安全度。     

FINITE ELEMENT ANALYSIS OF A VERTICAL RECTANGULAR PLATE COUPLED WITH AN UNBOUNDED FLUID DOMAIN ON ONE SIDE USING A TRUNCATED FAR BOUNDARY

The dynamic pressure distribution on a rectangular plate attached to a rigid wall and supporting an infinitely large extent of fluid subjected to a harmonic ground excitation is evaluated in the time domain. Governing equations for the fluid domain are set considering the compressibility of the fluid with negligibly small change in density and a linearized free surface. A far boundary condition for the three-dimensional fluid domain is developed so that the far boundary is truncated at a closer proximity to the structure. The coupled problem is solved independently for the structure and the fluid domain by transferring the acceleration of the plate to the fluid and pressure of the fluid to the plate in sequence. Helmholtz equation for the three-dimensional fluid domain and Mindlin's theory for the two-dimensional plate are used for the solution of the interacting domains. Finite element technique is adopted for the solution of this problem with pressure as nodal variable for the fluid domain and displacement for the plate. The time dependent equations are solved in each of the interacting domain using Newmark-b method. The effectiveness of the technique is demonstrated and the influences of surface wave, exciting frequency and flexibility of the plate on dynamic pressure are investigated.