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1.
臧跃龙  张琦 《力学季刊》1994,15(1):61-66
本文给出了气垫船在静水中航行时稳态船波势问题的边界元数值分析方法,根据本文的数值计算方法,可以得到气垫船行时所兴起的波浪形状以及气垫附近流场情况,由此可计算气垫所受到的兴波阻力,本文的方法适用于任意已知气压分布情况。  相似文献   

2.
应用直接边界元法在时域中求解稳定航速运动的三维自由面兴波问题.基于格林定理,在所有边界面上划分网格,对边界积分方程进行数值离散,采用线性自由面边界条件,随时间步进更新自由面势.由于物体空间位置移动辐射条件不需要单独表述,迭代过程中自由面计算域保持不变.以割划水面NACA0024为例,计算模拟了自由面兴波稳定波形;提出了求解矩阵方程组奇异性的处理方法和解决割划问题的动网格技术.本文计算结果和有限体积法及有关试验结果对比表明,该方法是可靠的.  相似文献   

3.
变深度浅水域中非定常船波   总被引:1,自引:0,他引:1  
陈波  吴建康 《力学学报》2003,35(1):64-68
以Green—Naghdi(G—N)方程为基础,采用波动方程/有限元法计算船舶经过变深度浅水域时非定常波浪特性.把运动船舶对水面的扰动作为移动压强直接加在Green-Naghdi方程里,以描述运动船体和水面的相互作用.以Series60 CB=0.6船为算例,给出自由面坡高,波浪阻力在船舶经过一个水下凸包时变化规律,并与浅水方程的结果进行了比较.计算结果表明,当船舶经过凸包时,波浪阻力先增加,后减少,并逐渐趋于正常.同时发现,当船速小于临界速度时(Fr=√gh<1.0),G—N方程给出的船后尾波比浅水方程的结果明显,波浪阻力也比浅水方程的结果有所提高,频率散射必须考虑.当船速大于临界速度时(Fr=√gh>1.0),G—N方程的计算结果与浅水方程差别不大,频率散射的影响可以忽略.  相似文献   

4.
本文第一部分对于直接法弹性力学边界积分方程的基本理论作了论述,全文采用内积公式以加权余量形式来建立边界积分方程.论述范围包括位势问题、弹性静力学问题和克希霍夫型平板理论的边界积分方程—边界元法.文中同时写出相应的变分格式.并讨论了非光滑边界的处理.本文第二部分简介对若干具体问题用特定的基本解进行的有关数值计算.文中介绍的研究组所获初步结果包括:迴转体的扭转、轴对称问题和弯曲问题,以及平板弯曲问题的边界积分方程—边界元法应用的具体结果.计算结果表明对于改进和扩充工程实用应力集中数据及平板计算(包括自由边界及角点问题)将是有益的.  相似文献   

5.
基于转化域方程为边界积分方程的极限定理及一个新颖的基本解分解技术, 建立间 接变量规则化边界积分方程, 它有效地避免了奇异积分的直接计算. 与已有方法比, 该方法不将问题变换为各向同性的问题去处理, 因而无需反演运算, 也有别 于Galerkin方法, 无需计算重积分. 可计算任意边界位势梯度, 而不仅限于法向通 量. 针对椭圆边界的边值问题, 提交一种精确单元来描述边界几何. 数值算例表 明, 所提算法稳定且效率高, 所得数值结果与精确解吻合较好.  相似文献   

6.
复杂载荷三维裂纹分析双重边界元法   总被引:11,自引:1,他引:10  
陆山  黄其青 《力学学报》2002,34(5):715-725
提出可用于高温、高转速状态下的热动力机械三维含裂构件热弹性分析方法——双重边界元法.首先建立了考虑温度及离心载荷的双重边界积分方程组,并对边界积分方程组的选取及适用范围进行了讨论。然后提出角非快调元模型离散技术。接着提出超奇异积分方程分析去除奇异性方法及数值积分技术.数值算例表明计算结果与有关权函数解十分吻合,说明了用双重边界元法计算复杂载荷条件下三维应力强度因子的有效性.还讨论了有关热应力强度因子权函数解的适用范围.  相似文献   

7.
陈波  吴建康 《应用力学学报》2005,22(2):159-163,i001
以Green-Naghdi(GN)方程为基础,采用波动方程和运动网格的有限元法研究多船在浅水域中集体航行时的波浪干涉特性。把运动船舶对水面的扰动作为移动压强直接加在GN方程里,以描述运动船体和水面的相互作用。GN方程合理地考虑非线性和频率散射对浅水船波的影响。以Series60 CB=0.6船体为算例,给出两船并行、前后跟随、三船品字形编队航行时的波浪干涉图形,波浪阻力及侧向力的数值分析结果。计算结果表明:1)当两船并行时,两船承受侧向吸引力,同时波浪阻力稍有增加。2)当两船前后跟随时,两船的波浪阻力都减小。3)当三船品字形航行时,前船的阻力减小,后船的阻力增加,同时后面两船的吸力减小。  相似文献   

8.
研究二维弹性力学问题边界积分方程,通过分部积分变换消除了常规导数边界积分方程中的超奇异积分,获得仅含强奇异积分的应力自然边界积分方程.对于近边界应力的计算,进一步运用正则化算法解析计算其中的几乎强奇异积分.较常规边界元法相比,应力自然边界积分方程可以求解离边界更加接近的内点应力值.算例证明了文中方法的可应用性和有效性.  相似文献   

9.
本文提出了一个用边界积分方程——边界元法解克希霍夫平板弯曲问题的协调方案.这个方案在边界上的协调程度与一般有限元法的协调板单元方案相当. 文中给出了边界积分方程的建立方法及有关公式,叙述了数值解的有关过程,对几种角度的悬臂三角板进行了计算.计算结果表明:此方案具有较高的精度,在达到同样精度的前提下可以降低计算成本,所以它对于改进与补充平板计算的数值方法是有益的.  相似文献   

10.
导数场边界积分方程通常难以应用,因为存在着超奇异主值积分的计算障碍。弹性理论中有几类不同的位移导数边界积分方程,本文采用算子δij和∈ij(排列张量)作用于这些导数边界积分方程,做一系列变换,原有的超奇异积分被正则化为强奇异积分获解。从而建立了这些位移导数边界积分方程之间的转换关系,它们均可以归结为自然边界积分方程。自然边界积分方程仅存在容易计算的Cauchy主值积分。自然边界积分方程分析可直接获得边界应力和位移导数。  相似文献   

11.
《Wave Motion》2014,51(2):193-205
A free surface Green function method is employed in numerical simulations of hydrodynamic performance of a submerged spheroid in a fluid of infinite depth. The free surface Green function consists of the Rankine source potential and a singular wave integral. The singularity of the wave integral is removed with the use of the Havelock regular wave integral. The finite boundary element method is applied in the discretisation of the fluid motion problem so that the panel integral of the Rankine source potential is evaluated by the Hess–Smith formula and the panel integral of the regular wave integral is evaluated in a straightforward way due to the regularity nature. Present method’s results are in good agreement with earlier numerical results.  相似文献   

12.
采用常数边界元对船舶与流体界面进行离散,求解船舶兴波势及船舶兴波阻力。这种方法可避免在船舶与流体自由面交线上安置节点,因而避免了这些节点建立补充方程。因为满足自由面条件的Havelock源函数的源点和场点不能同时在自由面上,使得自由面上的节点无法用Havelock源函数的建立方程。如对自由面交线上的节点建立补充方程,则要对线性自由面条件中包含的未知势函数的二阶导数用差分形式表达,引入较大误差。  相似文献   

13.
A regular wave integral method is developed in the discretisation of a linear hydrodynamic problem on radiation and diffraction of surface waves by a floating or submerged body. The velocity potential of the problem is expressed as a solution of a body boundary integral equation involving the pulsating free surface Green function or pulsating free surface sources distributed on the body surface. With the use of a discretisation on the regular wave integral rather than discretisations on the singular wave integral of the Green function as in earlier investigations, the singular wave integral is approximated as an expansion of regular (or nonirregular) wave potentials. Influence coefficients between pulsating free surface source points are computed by the approximate expansion together with Hess–Smith panel integral formulas. Thus the velocity potential solution is evaluated by a boundary element algorithm. The numerical results produced from the proposed method agree well with semi-analytic solution results.  相似文献   

14.
A fully nonlinear irregular wave tank has been developed using a three‐dimensional higher‐order boundary element method (HOBEM) in the time domain. The Laplace equation is solved at each time step by an integral equation method. Based on image theory, a new Green function is applied in the whole fluid domain so that only the incident surface and free surface are discretized for the integral equation. The fully nonlinear free surface boundary conditions are integrated with time to update the wave profile and boundary values on it by a semi‐mixed Eulerian–Lagrangian time marching scheme. The incident waves are generated by feeding analytic forms on the input boundary and a ramp function is introduced at the start of simulation to avoid the initial transient disturbance. The outgoing waves are sufficiently dissipated by using a spatially varying artificial damping on the free surface before they reach the downstream boundary. Numerous numerical simulations of linear and nonlinear waves are performed and the simulated results are compared with the theoretical input waves. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

15.
The idea of quasi-Green's function method is clarified by considering a free vibration problem of the simply-supported trapezoidal shallow spherical shell. A quasi- Green's function is established by using the fundamental solution and boundary equation of the problem. This function satisfies the homogeneous boundary condition of the prob- lem. The mode shape differential equations of the free vibration problem of a simply- supported trapezoidal shallow spherical shell are reduced to two simultaneous Fredholm integral equations of the second kind by the Green formula. There are multiple choices for the normalized boundary equation. Based on a chosen normalized boundary equa- tion, a new normalized boundary equation can be established such that the irregularity of the kernel of integral equations is overcome. Finally, natural frequency is obtained by the condition that there exists a nontrivial solution to the numerically discrete algebraic equations derived from the integral equations. Numerical results show high accuracy of the quasi-Green's function method.  相似文献   

16.
To model mathematically the problem of a rigid body moving below the free surface, a control surface surrounding the body is introduced. The linear free surface condition of the steady waves created by the moving body is satisfied. To describe the fluid flow outside this surface a potential integral equation is constructed using the Kelvin wave Green function whereas inside the surface, a source integral equation is developed adopting a simple Green function. Source strengths are determined by matching the two integral equations through continuity conditions applied to velocity potential and its normal derivatives along the control surface. After solving for the induced fluid velocity on the body surface and the control surface, an integral equation is derived involving a mixed distribution of sources and dipoles using a simple Green function and one component of the fluid velocity. The normal derivatives of the fluid velocity on the body surface, namely the m‐terms, are then solved by this matching integral equation method (MIEM). Numerical results are presented for two elliptical sections moving at a prescribed Froude number and submerged depth and a sensitivity analysis undertaken to assess the influence of these parameters. Furthermore, comparisons are performed to analyse the impact of different assumptions adopted in the derivation of the m‐terms. It is found that the present method is easy to use in a panel method with satisfactory numerical precision. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

17.
The idea of quasi-Green’s function method is clarified by considering a free vibration problem of the simply-supported trapezoidal shallow spherical shell. A quasi-Green’s function is established by using the fundamental solution and boundary equation of the problem. This function satisfies the homogeneous boundary condition of the prob-lem. The mode shape differential equations of the free vibration problem of a simply-supported trapezoidal shallow spherical shell are reduced to two simultaneous Fredholm integral equations of the second kind by the Green formula. There are multiple choices for the normalized boundary equation. Based on a chosen normalized boundary equa-tion, a new normalized boundary equation can be established such that the irregularity of the kernel of integral equations is overcome. Finally, natural frequency is obtained by the condition that there exists a nontrivial solution to the numerically discrete algebraic equations derived from the integral equations. Numerical results show high accuracy of the quasi-Green’s function method.  相似文献   

18.
Piero Bassanini 《Meccanica》1996,31(4):433-440
The prototype problem of the linearized irrotational gravity-capillarity water waves due to a Havelock doublet in a uniform planar stream is solved via a layer ansatz and a boundary integral formulation. As an effect of surface tension, two distinct flow regimes arise, separated by a critical speed where a resonance occurs. The transcirtical flow is described by including the viscous vorticity diffusion at the free boundary.
Sommario Si risolve, nell' ambito di una formulazione integrale al contorno, il problema linearizzato delle onde di gravità irrotazionali generate da un dipolo di Havelock in presenza di tensione superficiale. Si hanno due distinti regimi di flusso separati da una velocità critica. Il regime transcritico, in cui si ha un fenomeno di risonanza, viene descritto tenendo conto della presenza di uno strato limite viscoso sulla frontiera libera.
  相似文献   

19.
An iterative boundary element method, which was originally developed for both two‐ and three‐dimensional cavitating hydrofoils moving steadily under a free surface, is modified and extended to predict the wave pattern and wave resistance of surface piercing bodies, such as ship hulls and vertical struts. The iterative nonlinear method, which is based on the Green theorem, allows the separation of the surface piercing body problem and the free‐surface problem. The free‐surface problem is also separated into two parts; namely, left and right (with respect to x axis) free‐surface problems. Those all (three) problems are solved separately, with the effects of one on the other being accounted for in an iterative manner. The wetted surface of the body (ship hull or strut, including cavity surface if exists) and the left and right parts with respect to x axis of free surface are modelled with constant strength dipole and constant strength source panels. In order to prevent upstream waves, the source strengths from some distance in front of the body to the end of the truncated upstream boundary are enforced to be zero. No radiation condition is enforced for downstream and transverse boundaries. A transverse wave cut technique is used for the calculation of wave resistance. The method is first applied to a point source and a three‐dimensional submerged cavitating hydrofoil to validate the method and a Wigley hull and a vertical strut to compare the results with those of experiments. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

20.
A sound pulse is scattered by a sphere leading to an initial–boundary value problem for the wave equation. A method for solving this problem is developed using integral representations involving Legendre polynomials in a similarity variable and Volterra integral equations. The method is compared and contrasted with the classical method, which uses Laplace transforms in time combined with separation of variables in spherical polar coordinates.  相似文献   

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