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1.
Fast and accurate computation of the free-surface Green function is of key importance for the numerical solution of linear and second-order wave-structure interaction problems in three dimensions. Integral and series expressions for the Green function are derived for which the limiting values for zero and infinite frequency are consistent with the zero and infinite frequency Green function defined in terms of infinite series of Rankine image sources. The integral expressions presented here have the advantage that they are slowly varying with the non-dimensional wave frequency, making them more efficient to approximate compared with previous expressions. 相似文献
2.
New Derivation of Ordinary Differential Equations for Transient Free-Surface Green Functions 总被引：3，自引：0，他引：3
DUAN Wenyang DAI Yishan 《中国海洋工程》2001,(4):499-508
Based on the Laplace transform, a direct derivation of the ordinary differential equations for the three-dimensional transient free-surface Green function in marine hydrodynamics is presented. The results for the 3D Green function and all its spatial derivatives are a set of fourth-order ordinary differential equations, which are identical with that of Clement (1998). All of these results may be used to accelerate numerical computation for the time-domain boundary element method in marine hydrodynamics. 相似文献
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4.
1 .IntroductionRecentlygreatinteresthasbeenshowninthedevelopmentofverylargefloatingstructuressuchasMegaFloatofJapan (Isobe ,1 999)andMOBofUSA (Remmers ,1 999) .Owingtotheirextremelargesizeandgreatflexibility ,thecouplingbetweenthestructuraldeformationandfluidmotionissignifi cant.Thisisatypicalproblemofhydroelasticity .Efficientandaccurateestimationofthehydroelasticresponseofverylargefloatingstructuresinwavesisveryimportantfordesign .Manymethodshavebeenproposedinliteratureforthepredictiono… 相似文献
5.
使用三维源汇分布法Ⅲ计算有限水深中零航速浮体所受到的波浪力，对两种不同形式的格林函数中所共同存在的奇点问题分别进行了处理。公式推导表明，使用级数形式的格林函数可以使计算更加快捷。最后，对不同尺度的圆柱体进行了验算，在对计算结果与解析解进行了比较之后，工程计算也证明选择格林函数级数计算公式是更令人满意的方案。 相似文献
6.
Clément (2013) derived a second order ordinary differential equation (ODE) satisfied by the free-surface Green function in the frequency domain. Since then, similar ODEs for the gradient of the Green function have been developed. Unfortunately, all these ODEs degenerate at zero frequency. Therefore, it is not possible to initialize the numerical solution of these ODEs from this zero frequency. Alternative methods based on the shifting of the initial condition to frequencies strictly greater than zero have then been developed.The present paper describes an alternative approach to address this issue. It involves a new function which is the solution of a modified ODE which can be solved from the zero frequency.Finally, comparisons with evaluations of the Green function using the classical direct integration method are provided. They show that the new ODE can provide accurate estimates of the Green function. 相似文献
7.
On the evaluation of time-domain Green function 总被引：1，自引：0，他引：1
An analytical method has been developed to evaluate the wave part of the time-domain Green function and its derivatives. Based on Taylor series expansion, the Green function is obtained by solving a fourth-order ordinary differential equation. The method accelerates the convergence of the summation of an infinite series in the numerical computation. The accuracy of this method was demonstrated by its comparison with other method and its application to solve the radiation problem of a floating hemisphere using a panel-free method. The computed hydrodynamic coefficients agree well with the analytical solutions. 相似文献
8.
WANG Yanying ZHU Renchuan MIAO Jie
Professor School of Naval Architecture Marine Engineering Dalian University of Technology 《中国海洋工程》1999,(1)
—Analytical and numerical investigation is made of the source potential for floating structurewith forward speed in waves.A particular form is selected for numerical applications,where the double in-tegral of the Green function is transformed into the single one and the oscillation characteristics forintegrands in the specific computation domain are treated numerically.A comparison of calculated exam-p1es with published data is given and it shows that the numerical simulation is satisfactory and the accura-cy is adequate to engineering application. 相似文献
9.
The derivation of Green function in a two-layer fluid model has been treated in different ways.In a two-layer fluid with the upper layer having a free surface,there exist two modes of waves propagating due to the free surface and the interface.This paper is concerned with the derivation of Green functions in the three dimensional case of a stationary source oscillating.The source point is located either in the upper or lower part of a two-layer fluid of finite depth.The derivation is carried out by the method of singularities.This method has an advantage in that it involves representing the potential as a sum of singularities or multipoles placed within any structures being present.Furthermore,experience shows that the systems of equations resulted from using a singularity method possess excellent convergence characteristics and only a few equations are needed to obtain accurate numerical results.Validation is done by showing that the derived two-layer Green function can be reduced to that of a single layer of finite depth or that the upper Green function coincides with that of the lower,for each case.The effect of the density on the internal waves is demonstrated.Also,it is shown how the surface and internal wave amplitudes are compared for both the wave modes.The fluid in this case is considered to be inviscid and incompressible and the flow is irrotational. 相似文献
10.
A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Eulerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The boundary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropriate wave theory. At the downstream boundary, an artificial damping zone is used to prevent wave reflection back into the computational domain. Using the image Green function in the whole fluid domain, the integrations on the two lateral walls and bottom are excluded. The simulation results on extreme wave elevations in finite and infinite water-depths are compared with experimental results and second-order analytical solutions respectively. The wave kinematics is also discussed in the present study. 相似文献
11.
Rocío Muñoz-Mansilla Joaquín Aranda José Manuel Díaz J de la Cruz 《Ocean Engineering》2009,36(12-13):1025-1038
Parametric models of heave, pitch and roll dynamics of a high-speed craft have been estimated for different wave incidence angles in the frequency domain. Several issues that make the identification problem interesting are the following: type of parameterization, starting values, non-quadratic functions, excitation signals and short data record. The method employed guarantees a fine linear approximation of the nonlinear dynamics of a fast ship for the ultimate goal of stabilization control to reduce motion sickness associated with heave, pitch and roll accelerations. In addition, the approach achieves high-quality starting values and avoids non-quadratic terms in the cost function, which results in less computational load and significantly more accurate models when compared with a previous method employed for the same problem. 相似文献
12.
This paper proposes a new approximation to energy dissipation in time domain simulation of sloshing waves by use of a linear potential theory.The boundary value problem is solved by the NURBS(non-uniform rational B-spline) higher-order panel method,in which a time-domain Green function is employed.The energy dissipation is modeled by changing the boundary condition on solid boundaries.Model experiments are carried out in a partially filled rectangular tank with forced horizontal motion.Sloshing-induced internal pressures and horizontal force obtained numerically and experimentally are compared with each other.It is observed that the present energy dissipation approximation can help produce a fair agreement between experimental forces and those of numerical simulations. 相似文献
13.
This note presents a numerical method for calculating the far field part of the Green's function for a source in steady translation below the surface of fluid of finite depth. The principal steps of the numerical scheme are outlined, with emphasis on those aspects which are needed for a computer implementation of the scheme. Numerical results are given to show the behavior of the function in various parts of the computation domain, the computer requirements of the method, and its expected accuracy. 相似文献
14.
A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Eulerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The boundary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropr... 相似文献
15.
SHI Fengyan DING Pingxing KONG Yazhen
Associate Professor State Key Laboratory of Estuarine Coastal Research East China Normal University Shanghai P. R. China.
Professor State Key Laboratory of Estuarine Coastal Research East China Normal University Shanghai P. R. China.
Senior Engineer State Key Laboratory of Estuarine Coastal Research East China Normal University Shanghai P. R. China. 《中国海洋工程》1999,(2)
Fine grids with small spacing in boundary-fitted coordinates are normally used to treat thecomputation of fluid dynamics for estuarine areas and tidal flats.However,the adoption of Cartesian com-ponents of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a diffculty insolving implicitly the transformed momentum equations,and also complicate the wet-dry point judgementused for flood areas.To solve this problem,equations in terms of generalized contravariant velocityvectors in curvilinear coordinates are derived in the present study,by virtue of which,anAlternative-Direction-Implicit numerical scheme in non-orthogonal grids would then be easily obtained,and wet-dry point judgement would as well be largely simplified.A comparison is made between the explic-it scheme and implicit scheme,showing that the present model is accurate and numerically stable for com-putations of fluid dynamics for estuarine areas and tidal flats. 相似文献
16.
TENG Bin BAI Wei XIANG Yang
Professor the State Key Laboratory of Coastal Offshore Engineering Dalian University of Technology Dalian P. R. China
Doctor the State Key Laboratory of Coastal Offshore Engineering Dalian University of Technology Dalian P. R. China
Senior Engineer China Classification Society Beijing P. R. China 《中国海洋工程》1999,(3)
17.
A numerical model of the modified time-independent mild-slope equation for linear waves over a rapidly changing finite porous bed is presented. In this solution the reflection and phase coefficient shift are solved implicitly. Boundaries are assumed to be open, partially reflecting, or fully absorbing through the second-order parabolic approximation. Discretisation of the governing equation and boundary conditions is by means of a second-order accurate central difference scheme. The resulting sparse-banded matrix is solved using an inexpensive banded solver with Gaussian elimination. The model has been validated and the numerical predictions are in excellent agreement with analytical solutions. 相似文献
18.
A WDM method on a generalized curvilinear grid for calculation of storm surge flooding 总被引：1，自引：0，他引：1
In this paper, the wet-dry grid point method (WDM) with generalized curvilinear computation grids is introduced with the aim of presenting a kind of effective numerical model for real-time forecasting of storm surge flooding. To realize this general WDM method, generalized 2-D shallow sea dynamic equations in curvilinear co-ordinates are derived, and the contravariant components of the velocity vector are employed for easily realizing boundary conditions and making the wet-dry point judgement criterion more reasonable. As the generalized equations are not limited to a specific co-ordinate transformation, a self-adaptive grid generation method, which optimizes simultaneously grid smoothness, orthogonality and variation in cell volumes, is then proposed to meet the needs of WDM with varying spacing grids. The paper also provides a numerically stable difference scheme and this scheme is proved accurate by the verification calculation of observed storm surge. 相似文献
19.
Graham J.M. Copeland 《Coastal Engineering》1985,9(2):125-149
The “mild-slope” equation which describes wave propagation in shoaling water is normally expressed in an elliptic form. The resulting computational effort involved in the solution of the boundary value problem renders the method suitable only for small sea areas. The parabolic approximation to this equation considerably reduces the computation involved but must omit the reflected wave. Hence this method is not suited to the modelling of harbour systems or areas near to sea walls where reflections are considerable. This paper expresses the “mild-slope” equation in the form of a pair of first-order equations, which constitute a hyperbolic system, without the loss of the reflected wave. A finite-difference numerical scheme is described for the efficient solution of the equations which includes boundaries of arbitrary reflecting power. 相似文献
20.
A panel-free method (PFM), based on the desingularized Green’s formulae proposed by Landweber and Macagno, has been developed to solve the radiation problem of a floating body in the time domain. The velocity potential due to a non-impulsive velocity is obtained by solving the boundary integral equation in terms of source strength distribution. The singularity in the Rankine source term of the time-dependent Green function is removed. The geometry of a body surface is mathematically represented by NURBS surfaces. The integral equation can be globally discretized over the body surface by Gaussian quadratures. No assumption is needed for certain degree of approximation of distributed source strength on the body surface. The accuracy of PFM was demonstrated by its application to a classical problem of uniform flow past a sphere. The response function of a hemisphere at zero speed was then computed by PFM. The computed response function, added-mass and damping coefficients are compared with other published results. 相似文献