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…     

WAVES GENERATED BY A 3D MOVING BODY IN A TWO-LAYER FLUID OF FINITE DEPTH

This paper is concerned with the waves generated by a 3-D body advancing beneath the free surface with constant speed in a two-layer fluid of finite depth. By applying Green‘s theorem, a layered integral equation system based on the Rankine source for the perturbed velocity potential generated by the moving body was derived with the potential flow theory. A four node isoparametric element method was used to treat with the solution of the layered integral equation system. The surface and interface waves generated by a moving ball were calculated numerically. The results were compared with the analytical results for a moving source with constant velocity.     

UNSTEADY WAVES DUE TO AN IMPULSIVE OSEENLET BENEATH THE CAPILLARY SURFACE OF A VISCOUS FLUID

The two-dimensional free-surface waves due to a point force steadily moving beneath the capillary surface of an incompressible viscous fluid of infinite depth were analytically investigated. The unsteady Oseen equations were taken as the governing equations for the viscous flows. The kinematic and dynamic conditions including the combined effects of surface tension and viscosity were linearized for small-amplitude waves on the free-surface. The point force is modeled as an impulsive Oseenlet. The complex dispersion relation for the capillary-gravity waves shows that the wave patterns are characterized by the Weber number and the Reynolds number. The asymptotic expansions for the wave profiles were explicitly derived by means of Lighthill’s theorem for the Fourier transform of a function with a finite number of singularities. Furthermore, it is found that the unsteady wave system consists of four families, that is, the steady-state gravity wave, the steady-state capillary wave, the transient gravity wave, and the transient capillary wave. The effect of viscosity on the capillary-gravity was analytically expressed.     

UNSTEADY INTERFACIAL WAVES DUE TO SINGULARITIES IN TWO SEMI-INFINITE INVISCID FLUIDS

1.INTRODUCTION ThelinearCauchy Poissonproblems,which areconcernedwiththegenerationandpropagation offree surfacewavesduetoaninitialelevationor apointpressureactingonthefreesurfaceofanin compressibleinviscidfluid,havebeeninvestigated bymanyresearchersinviewofitstheoreticalinterestandpracticalimportance[15].Thetransient developmentoftwo dimensionalgravitywavesdue toanoscillatingsurfacepressurewasconsideredby Miles[6]whoproposedawell posedinitialvalue problemtocorrectStoker'sformulation[2].A…     

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.     

EVOLUTION EQUATIONS FOR NONLINEAR WAVES IN A THREELAYER FLUID MODEL

ＥＶＯＬＵＴＩＯＮＥＱＵＡＴＩＯＮＳＦＯＲＮＯＮＬＩＮＥＡＲＷＡＶＥＳＩＮＡＴＨＲＥＥＬＡＹＥＲＦＬＵＩＤＭＯＤＥＬ￥ＺｈｕＹｏｎｇ（ＳｈａｎｇｈａｉＩｎｓｔｉｔｕｔｅｏｆＡｐｐｌｉｅｄＭａｔｈｅｍａｔｉｃｓａｎｄＭｅｃｈａｎｉｃｓ，Ｓｈａｎｇｈａｉ...     

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.     

A NOTE ON THE COMPLEX DISPERSION RELATION FOR STEADY VISCOUS SHIP WAVES

Based on the double Fourier integral representation for steady viscous ship waves, which involves a generic amplitude function and a complex dispersion relation, the phase function for three dimensional ship waves in the far field was asymptotically derived by means of the Lighthill twostage scheme combining the Cauchy residue theorem and the method of steepest descents, and the effect of viscosity on wavelengths was numerically investigated with the Newton iteration method. It is found that the transverse and diverging waves are elongated due to the presence of viscosity and the latter is more heavily affected and that the phase differences between the viscous transverse and diverging waves are larger than those of the corresponding inviscid waves.     

AN ASYMPTOTIC SOLUTION OF VELOCITY FIELD IN SHIP WAVES

1. INTRODUCTION It is well known that behind the ships, V-shaped steady-state ship waves are created while ships move on the water. The classical Kelvin ship wave pattern, which is obtained when a ship is taken as a point impulse moving at a constant velo…     

SECOND ORDER TRANSIENT WAVES AROUND A VERTICAL CYLINDER IN A TANK

ＳＥＣＯＮＤＯＲＤＥＲＴＲＡＮＳＩＥＮＴＷＡＶＥＳＡＲＯＵＮＤＡＶＥＲＴＩＣＡＬＣＹＬＩＮＤＥＲＩＮＡＴＡＮＫ￥Ｑ．Ｗ．Ｍａ，Ｇ．Ｘ．Ｗｕ（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃａｌＥｎｇｉｎｅｅｒｉｎｇＵｎｉｖｅｒｓｉｔｙＣｏｌｌｅｇｅＬｏｎｄｏ...     

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.     

FINITE ELEMENT ANALYSIS OF THE FLOW INDUCED BY ROTATING BLADES IN AN INCOMPRESSIBLE VISCOUS FLUID

Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.     

A STUDY OF VELOCITY FIELD IN SHIP WAVES

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＷｈｅｎａｓｈｉｐｉｓｉｎｍｏｔｉｏｎｏｎｔｈｅｏｃｅａｎ ,ａＶ ｓｈａｐｅｄｓｈｉｐｗａｖｅａｐｐｅａｒｓｂｅｈｉｎｄｔｈｅｓｈｉｐ .ＷｉｔｈＳｙｓ ｔｈｅｔｉｃＡｐｅｒｔｕｒｅＲａｄａｒ (ＳＡＲ ) ,ｔｈｅｓｈｉｐｗａｖｅｃａｎｂｅｄｉｓｃｏｖｅｒｅｄ.ＩｎＲｅｆ.[1]ｉｔｗａｓａｌｒｅａｄｙｒｅｐｏｒｔｅｄｔｈａｔ ,ｗｉｔｈｔｈｅｔｅｃｈｎｏｌｏｇｙｏｆＳＡＲ ,ｔｈｅｙｏｂｔａｉｎｅｄｔｈｅｉｎｆｏｒ ｍａｔｉｏｎａｂｏｕｔｏｆｔｈｅｍｏｔｉｏｎｏｆｓｈｉｐｓｉｎｔｈ…     

NUMERICAL SIMULATION OF TRANSIENT FLOW AROUND A SHIP IN UNSTEADY BERTHING MOTION

Ship berthing is a specific maneuver operation. The flow around a berthing ship and the forces acting on the hull are quite different from those for a ship in normal navigation. By solving the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations, the transient flow field around a ship undergoing unsteady lateral motion is simulated and the varying lateral hydrodynamic force acting on the hull is evaluated in this article. The numerical results obtained with different turbulence models are analyzed and compared with experimental results and other numerical results published in literature, and a turbulence model more suitable for simulation of the viscous flow around a ship undergoing unsteady berthing is determined.     

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…     

A STUDY ON TRANSIENT FLUID FLOW OF HORIZONTAL WELLS IN DUAL-PERMEABILITY MEDIA

To adopt horizontal wells in dual media reservoirs,a good understanding of the related fluid flows is necessary.Most of the recent studies focus on dual porosity media instead of dual permeability media.In this article,through both integral transformation and sink-source superposition,a new Laplace-domain solution is obtained for the slightly-compressible fluid flow in the 3-D dual-permeability media in which the horizontal well is operating in a constant rate of production.Major asymptotic characteristics of diagnosis curves of dimensionless downhole pressure are analyzed by the limited analysis.Effects of parameters of dual-permeability media including mobility ratio κ,storativity ratio ω and inter-porosity flow parameter κ on the downhole pressure are studied by using the Laplace numerical inversion.The new solution obtained in this article includes and improves the previous results and then can be used as a basis for either pressure transient analysis or formation behavior evaluation for the typical reservoir with horizontal wells.     

EFFECT OF A MOVING BOUNDARY ON THE FLUID TRANSIENT FLOW IN LOW PERMEABILITY RESERVOIRS

In a low permeability reservoir, the existence of a moving boundary is considered in the study of the transient porous flow with threshold pressure gradient. The transmission of the moving boundary directly indicates the size of the drainage area as well as the apparent influences on the pressure behavior. The nonlinear transient flow mathematical model in which the threshold pressure gradient and the moving boundary are incorporated is solved by advanced mathematical methods. This paper presents some new analytical solutions describing the pressure distribution at a constant rate and the production decline in a constant pressure production with the boundary propagation. It is shown that the greater the threshold pressure gradient, the slower the transmission of the moving boundary, the larger the pressure loss will be, and there is no radial flow in the middle and later phases of the wellface pressure for a well at a constant rate. We have the the maximum moving boundary at a specific drawdown pressure for a low permeability reservoir. The greater the threshold pressure gradient, the smaller the maximum moving boundary distance, the quicker the production decline for a well in a constant pressure production will be. The type curve charts for the modern well test analysis and the rate transient analysis with a moving boundary are obtained and the field test and the production data are interpreted as examples to illustrate how to use our new results.