共查询到20条相似文献，搜索用时 781 毫秒
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Hamid Teymouri Mohammad Rahimian Ronald Y. S. Pak 《Marine Georesources & Geotechnology》2020,38(8):923-938
AbstractThe equations of wave motion are considered in this article for three-layered medium which consists of liquid and porous layers with finite depth and solid half-space such as ocean bed. By virtue of scalar potential functions for each layer, complicated differential equations of layers are reduced to ordinary differential equations. An analytical method is applied to determine the Green’s functions of media based on an arbitrary shaped time-harmonic excitation at the interface of liquid and porous layers. A Mathcad code is provided to compute the complex integrals. Displacement and stress fields of three layers are discussed. Comparing with special cases, existing answers represent the validity of the proposed method. Numerical results are carried out for circular patch, ring and point loads, and the effects of various parameters on the behavior of the system are plotted. Finally, the achieved results were under discussion. 相似文献
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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
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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
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How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain.Based on the Bessel function,an Ordinary Differential Equation(ODE)was derived for time-domain Green function and its gradients in this paper.A new efficient calculation method based on solving ODE is proposed.It has been demonstrated by the numerical calculation that this method can improve the precision of the time-domain Green function.Numerical research indicates that it is efficient to solve the hydrodynamic problems. 相似文献
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Experimental research on the marine hydrodynamic action on the consolidation process of the sediments in the Yellow River Estuary 总被引：1，自引：0，他引：1
Based on the in-situ measurements,the impact of the marine hydrodynamics,such as wave and tide,in the rapidly deposited sediments consolidation process was studied.In the tide flat of Diaokou delta-lobe,one test pit was excavated.The seabed soils were dug and dehydrated,and then the powder of the soil was mixed with seawater to be fluid sediments.And an iron plate covered part of the test pit to cut off the effect of the marine hydrodynamics.By field-testing methods,like static cone penetration test (SPT) and vane shear test (VST),the variation of strength is measured as a function of time,and the marine hydrodynamics impact on the consolidation process of the sediments in the Yellow River estuary was studied.It is shown that the self-consolidated sediments’ strength linearly increases with the depth.In the consolidation process,in the initial,marine hydrodynamics play a decisive role,about 1.5 times as much as self-consolidated in raising the strength of the sea-bed soils,and with the extension of the depth the role of the hydrodynamics is reduced.In the continuation of the consolidation process,the trend of the surface sediments increased-strength gradually slows down under the water dynamics,while the sediments below are in opposite ways.As a result,the rapidly deposited silt presents a nonuniform consolidation state,and the crust gradually forms.The results have been referenced in studying the role of the hydrodynamics in the soil consolidation process. 相似文献
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复杂海洋环境中,顶张力立管顶部平台受到不同分量叠加的波浪作用,导致其轴向张力与多个频率相关,系统产生多频参激与涡激的联合振动,其动力学行为变得更为复杂,尤其是分岔和混沌等非线性振动特性有待进一步分析。首先,基于欧拉—伯努利梁理论,引入范德波尔尾流振子,建立和推导受多频参激—涡激联合作用下立管的动力学模型及其运动微分方程;接着,利用伽辽金法得到离散后的常微分方程组,采用多尺度法得到系统共振响应的调谐方程;最后,通过数值算例探究系统在多源和多频载荷联合作用下的共振响应。结果表明：对于多频参数激励,其中一个参数激励幅值在立管振动中起主导作用,而另一个会引起分岔的位置、数量和性质发生改变;随质量—阻尼参数增大,系统共振响应幅值整体先增大后减小,各分岔点出现的位置整体先向泄涡频率较大处移动,随后向泄涡频率较小处移动;质量—阻尼参数的变化还可能诱使系统发生倍周期分岔和混沌现象,危害结构安全。此外,采用直接数值积分求解微分方程组,验证近似分析结果,两者吻合较好。 相似文献
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An integrated hydrodynamics and control model to simulate tethered underwater robot system is proposed. The governing equation of the umbilical cable is based on a finite difference method, the hydrodynamic behaviors of the underwater robot are described by the six-degrees-of-freedom equations of motion for submarine simulations, and a controller based on the fuzzy sliding mode control (FSMC) algorithm is also incorporated. Fluid motion around the main body of moving robot with running control ducted propellers is governed by the Navier–Stokes equations and these nonlinear differential equations are solved numerically via computational fluid dynamics (CFD) technique. The hydrodynamics and control behaviors of the tethered underwater robot under certain designated trajectory and attitude control manipulation are then investigated based on the established hydrodynamics and control model. The results indicate that satisfactory control effect can be achieved and hydrodynamic behavior under the control operation can be observed with the model; much kinematic and dynamic information about tethered underwater robot system can be forecasted, including translational and angular motions of the robot, hydrodynamic loading on the robot, manipulation actions produced by the control propellers, the kinematic and dynamic behaviors of the umbilical cable. Since these hydrodynamic effects are fed into the proposed coupled model, the mutual hydrodynamic influences of different portions of the robot system as well as the hydrological factors of the undersea environment for the robot operation are incorporated in the model. 相似文献
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水下拖曳升沉补偿系统水动力数学模型研究 总被引：4，自引：2，他引：2
建立变缆长的水下拖曳升沉补偿系统水动力学偏微分方程组和边界条件.拖缆动力学模型基于Ablow and Schechter模型,拖体采用水下运载体六自由度方程模拟,运用有限差分法离散偏微分方程组和牛顿迭代法计算变缆长情况下拖体深度与拖缆各点张力的动态取值.数值计算结果表明采用收放拖缆的升沉补偿方法能够有效削弱母船升沉运动对拖体深度和拖缆张力的影响. 相似文献
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Seung-Keon Lee 《Ocean Engineering》2000,27(1)
The traditional governing equations for sway–yaw maneuvering motion are a set of ordinary differential equations with constant coefficients. But, as is well known, integro–differential equations with impulse response functions are more strict governing equations that can handle the frequency dependence of hydrodynamic forces.In this paper, the two types of equation are compared and used to calculate the 10°–10° zig-zag maneuver in waves. Differences between the solutions are discussed. 相似文献
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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
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A Unified Variational Principle of Fluid Mechanics and Application on Solitary Subdomain or Point 总被引：1，自引：0，他引：1
-According to basic equations of fluid mechanics, this paper presents a unified variational principle of fluid mechanics (UVPFM) by using the optimization method of weighted residuals (OMWR). The advantages are as follows, the establishment of the functional and the variational principle is easy, it can change various problems of fluid mechanics derived by basic equations into a unified optimization problem, and the solution is the optimum one in some sense. According to the OMWR for the solitary subdomain, this paper uses UVPFM onto any solitary subdomain and gives the solution of the hydrodynamics equation which is suitable only for that solitary subdomain. According to the OMWR for solitary point, this paper uses UVPFM to any solitary point and gives the solution of the hydrodynamics equation (point solution) which is suitable only for that solitary point. As the solution for the solitary subdomain or solitary point is developed independently, the compatibility with other subdomain or other points, do 相似文献
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主动式声纳列阵拖曳系统姿态数值计算 总被引：2，自引：1，他引：2
主动式声纳列阵拖曳系统是用于探测潜艇的新型声纳系统，为了准确探测潜艇的位置，必须首先预报声纳列阵的瓷态，本文通过对其三维力学模型的分析，得到该系统的运动微分方程，其中缆索的力学方程是基于Ablow和Milinazzo的模型，而对于拖体则运用六自由度空间运动方程模拟，结合边界条件，用有限差分法求解，通过对拖船的不同运动状态如匀速，变速和回转的计算，证明本文的方法对于预报声纳列阵的姿态是有效的。 相似文献
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Hydrodynamic characters on a horizontal, thin, rigid plate located beneath the free surface are numerically investigated. Assuming a linear, time-harmonic potential flow and utilizing Green identity, the governing Laplace equation can be simplified into Fredholm integral equation ofthe second kind. Supposing linear-order discontinuous elements along intersecting vertical boundaries, and by use of the boundary element method, numerical solution about source strength distribution on the plate can be changed into a series of algebraic equations. The 3D Green function is introduced to set up the integral equations, and the GMRES solver is performed for solving the large dense linear system of equations. The added-mass, damping force and exciting force are evaluated directly from the equations. It is found that the added-mass coefficient becomes negative for a range of frequencies when the plate is sufficiently close to the free surface. 相似文献
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张荣培 《中国海洋大学学报(自然科学版)》2012,(Z1):208-212
积分因子(IF)方法是近年来提出的求解刚性常微分方程组的一种有效的数值方法。本文应用改进的紧致隐积分因子(cIIF)方法求解二维反应扩散方程。在空间离散上采用二阶中心差分方法。数值模拟得到各种斑图结构与所引文献结果相当一致。 相似文献
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海流发电机(MCT)是开发海洋可再生能源的重要装置。在预测海流发电机水动力性能方面,修正叶素动量理论(M-BEMT)方法被验证是一种简单有效的方法。为了进一步提高M-BEMT方法的适用性和准确性,基于M-BEMT方法开发M-BEMT2.0方法包括时均法(TA-BEMT2.0)和瞬态积分法(TI-BEMT2.0),新方法考虑了来流的轴向非均匀性和周向非均匀性。首先使用文献的试验结果验证均匀来流时新方法的适用性。然后使用计算流体力学(CFD)计算结果验证非均匀来流时新方法的适用性。最后结合新方法和CFD方法深入研究两个串列排布海流发电机(MCTA)的水动力性能。基于M-BEMT2.0研究发现,均匀来流时计算结果与试验结果基本吻合,非均匀来流时新方法的计算结果优于M-BEMT的计算结果。对于MCTA,当第一个MCT的叶尖速度比越大,第二个MCT功率比和推力比恢复到90%的距离越短。 相似文献
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Numerical analyses for the Bragg resonant reflection of carrier waves associated long waves due to sinusoidally varying seabeds are performed by using a set of coupled ordinary differential equations derived from the Boussinesq equations. The Boussinesq equations are firstly approximated with the Fourier decomposition. The coupled governing equations are then derived and used to simulate evolution of both short and long wave components. It is also found that wave groups are generated by two carrier waves with slightly different frequencies. The wave energy of the initial wave components is transferred to other harmonic components during propagation over a long distance. Evolution and reflection of both short and long waves were largely affected by nonlinearity. 相似文献
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Pipeline spans may occur due to natural seabed irregularities or local scour of bed sediment. The pure in-line (IL) vortex-induced vibrations (VIV) analysis of the free spans is an important subject for design of pipeline in uneven seabed. The main objective of this paper is to analyze the characteristics of pure IL VIV of a free spanning pipeline under general boundary conditions. An IL wake oscillator model which can describe the coupling of pipeline structure and fluctuating drag is introduced and employed. The coupled partial differential equations of structure and wake are transformed into a set of ordinary differential equations using two-mode Galerkin method. Some case studies are presented and thoroughly discussed in order to investigate the effects of internal fluid, axial force and boundary conditions on the pure IL VIV. 相似文献