渗流方程自适应非均匀网格Dagan粗化算法

在粗网格内先统计渗透率在粗网格中的概率分布，利用Dagan渗透率粗化积分方程通过渗透率概率分布计算粗化网格的等效渗透率，并由等效渗透率计算了粗化网格的压强分布，计算压强时还将渗透率自适应网格技术应用于三维渗流方程的网格粗化算法中，在渗透率或孔隙度变化异常区域自动采用精细网格，用直接解法求解渗透率或孔隙度变化异常区域的压强分布。整个求解区采用不均匀网格粗化，在流体流速高的区域采用精细网格。利用本文方法计算了三维渗流方程的压强分布，结果表明这种算法的解在渗透率或孔隙度异常区的压强分布规律非常逼近精细网格的解，在其他区域压强分布规律非常逼近粗化算法的解，计算速度比采用精细网格提高了约100倍。     

单窄条控制件对横向振荡柱体尾流 2P模式 旋涡脱落的改变

横向强迫振荡柱体尾流控制是柱体涡激振动控制的基础,在海洋、土木等工程中具有重要意义. 横向强迫振荡柱体尾流中存在一种锁频旋涡脱落模式,即在一个振荡周期内柱体上、下侧各脱落旋转方向相反的一对涡,称为2P模式. 本文将相对宽度b/D=0.32的窄条控制件置于横向强迫振荡柱体下游,对振幅比A/D=1.25, 无量纲振频f_e D/V_∞=0.22,雷诺数Re=1 200的2P模式旋涡脱落进行干扰,并通过改变控制件位置,研究旋涡的变化规律. 采用二维大涡模拟和实验验证方法进行研究,在控制件位置范围0.8≤X/D≤3.2, 0.4≤Y/D≤3.2内,得到了2P, 2S, P+S和另外6种新发现的旋涡脱落模式,并对各模式旋涡的形成过程作了详细描述. 在控制件位置平面上给出了各旋涡模式的存在区域,画出了旋涡脱落强度的等值线图,并发现在一个相当大的区域内,旋涡脱落强 度可减小一半以上,尾流变窄. 发现柱体大幅振荡引起的横向剪切流在旋涡生成中起关键作用. 探讨了控制件对横向剪切流的影响,分析了控制件在每种旋涡模式形成中的作用机制.      

NON-SYMMETRICAL LARGE DEFORMATION OF A SHALLOW THIN SPHERICAL SHELL

ＮＯＮ－ＳＹＭＭＥＴＲＩＣＡＬＬＡＲＧＥＤＥＦＯＲＭＡＴＩＯＮＯＦＡＳＨＡＬＬＯＷＴＨＩＮＳＰＨＥＲＩＣＡＬＳＨＥＬＬＷａｎｇＸｉｎｚｈｉ（王新志）ＲｅｎＤｏｎｇｙｕｎ（任冬云）ＷａｎｇＬｉｎｘｉａｎｇ（王林祥）ＹｅｈＫａｉｙｕａｎ（叶开沅）（Ｇａｎ...     

THE CALCULATION OF EIGENVALUES FOR THE STATIONARY PERTURBATION OF COUETTE－POlSEUILLEFLOW

ＴＨＥＣＡＬＣＵＬＡＴＩＯＮＯＦＥＩＧＥＮＶＡＬＵＥＳＦＯＲＴＨＥＳＴＡＴＩＯＮＡＲＹＰＥＲＴＵＲＢＡＴＩＯＮＯＦＣＯＵＥＴＴＥ－ＰＯｌＳＥＵＩＬＬＥＦＬＯＷＳｏｎｇＪｉｎｂａｏ（宋金宝）ＣｈｅｎＪｉａｎｎｉｎｇ（陈建宁）（ＲｅｃｅｉｖｅｄＤｅｃ．３...     

THE ASYMPTOTIC SOLVING EQUATIONS OF THICK RING SHELL AND ITS SOLUTION UNDER MOMENT M＿O

ＴＨＥＡＳＹＭＰＴＯＴＩＣＳＯＬＶＩＮＧＥＱＵＡＴＩＯＮＳＯＦＴＨＩＣＫＲＩＮＧＳＨＥＬＬＡＮＤＩＴＳＳＯＬＵＴＩＯＮＵＮＤＥＲＭＯＭＥＮＴＭ＿ＯＺｈａｏＸｉｎｇ－ｈｕａ（赵兴华）（ＳｈａｎｇｈａｉＵｎｉｒｅｒｓｉｔｙ；ＳｈａｎｇｈａｉＩｎｓｔｉｔｕ...     

THE PROBLEMS OF THE NONLINEAR UNSYMMETRICAL BENDING FOR CYLINDRICALLY ORTHOTROPIC CIRCULAR PLATE（II）

ＴＨＥＰＲＯＢＬＥＭＳＯＦＴＨＥＮＯＮＬＩＮＥＡＲＵＮＳＹＭＭＥＴＲＩＣＡＬ．ＢＥＮＤＩＮＧＦＯＲＣＹＬＩＮＤＲＩＣＡＬＬＹＯＲＴＨＯＴＲＯＰＩＣＣＩＲＣＵＬＡＲＰＬＡＴＥ（ＩＩ）ＨｕａｎｇＪｉａｙｉｎ（黄家寅）;ＱｉｎＳｈｅｎｇｌｉ（秦圣立）;Ｘｉ...     

数值模拟在钱塘江涌潮分析中的应用──Ⅰ.数值计算方法

利用数值模拟的方法对钱塘江涌潮从杭州湾口开始形成、发展直至消失的全过程进行了深入全面的描写．从杭州湾口到钱塘江出口,采用二维圣维南浅水波方程描述水波的运动,而在钱塘江河内采用一维圣维南浅水波方程描写涌潮的发展过程．详细描述用于一维和二维圣维南方程计算钱塘江涌潮的数值计算方法,首次把无结构网格上的NND格式应用于求解二维圣维南方程,并给出了详细的推导过程．对上下游水边界分别采用无反射边界条件和特征线方法,而对于动边界问题本文也给出了相应的处理方法．     

The onset of three‐dimensionality in an oscillating flow past a fixed circular cylinder

A computational study of the sinusoidally oscillating flow past a fixed circular cylinder has been performed to examine the viscous transition from 2D to 3D in the wake of the cylinder, i.e., the Honji instability. The primitive variables form of the Navier–Stokes equations was used with the discretization in the form of a combined finite‐difference/spectral‐method. Numerical results were obtained at a frequency parameter value of 196 and for a range of Keulegan–Carpenter (KC) numbers from 1 to 4. The calculations agreed quite well with experimental results. At KC=1, the wake is 2D; spanwise structures begin to appear at KC=2; separation has occurred by KC=3.2; and the vortex structures have become chaotic by KC=4. Calculated values of the force coefficients also agree extremely well with the experimental values. Copyright © 1999 John Wiley & Sons, Ltd.     

A curvature‐free multiphase flow solver via surface stress‐based formulation

In this note, we show the link between the classical continuous surface stress and continuous surface force approaches together with special finite element method techniques toward a fully implicit level set method. Based on a modified surface stress formulation, neither normals nor curvature has to be explicitly calculated. The method is space‐dimension independent. Prototypical numerical tests of benchmarking character for a rising 2D bubble are provided for validating the accuracy of this new approach. We show additionally that the explicit redistancing can be avoided using a nonlinear PDE so that a fully implicit and even monolithic formulation of the corresponding multiphase problem gets feasible.     

用DSPI方法和栅线投影法测量任意曲表面的三维变形

本文采用数字散斑干涉法和栅线投影法同时测量了任意曲表面的三维位移和三维形貌，并运用数字图像处理技术分析了曲表面的三维应变场，用实验方法获得了曲表面的主应变和主方向。     

非线性双曲型守恒律的高精度MmB差分格式

构造了一维非线性双曲型守恒律方程的一个高精度、高分辨率的广义G odunov型差分格式。其构造思想是:首先将计算区间划分为若干个互不相交的小区间,再根据精度要求等分小区间,通过各细小区间上的单元平均状态变量,重构各等分小区间交界面上的状态变量,并加以校正;其次,利用近似R iem ann解算子求解细小区间交界面上的数值通量,并结合高阶R unge-K u tta TVD方法进行时间离散,得到了高精度的全离散方法。证明了该格式的Mm B特性。然后,将格式推广到一、二维双曲型守恒方程组情形。最后给出了一、二维Eu ler方程组的几个典型的数值算例,验证了格式的高效性。     

三维溃坝流的光滑粒子动力学方法模拟

采用光滑粒子动力学SPH(Smoothed Particle Hydrodynamics)方法对三维溃坝流问题进行了数值模拟。为了逼真地模拟出坝内水体与壁面间相互作用而产生的水花飞溅、融合以及近壁面流动等现象,加入了混合长度形式的湍流模型。为了有效地防止粒子穿透固壁,提出了一种新型的适合三维数值模拟的固壁边界处理方法。应用SPH方法对三维溃坝流进行了数值模拟,并分别考虑了未添加障碍物和添加圆柱障碍物两种情形。计算结果表明,改进SPH方法能够精细地捕捉溃坝流在不同时刻的自由液面,并获得稳定而精确的数值结果。     

正交异性扁壳的等价关系式和不变量

提出各向同性扁壳比拟法,分析满足条件D_3=D_(12)=(D_1D_2)~(1/2)的正交异性扁壳大挠度弯曲和超屈曲问题,导出了正交异性扁壳与各向同性扁壳之间,两种不同正交异性扁壳之间坐标变量、扁壳厚度和曲率半径、荷载、挠度、转角、弯矩、扭矩、中面应力的等价关系式,还证明了等价正交异性扁壳的几个等价不变量。     

Hypo-Elasticity Model Based upon the Logarithmic Stress Rate

Recently these authors have proved [46, 47] that a smooth spin tensor Ω^log can be found such that the stretching tensor D can be exactly written as an objective corotational rate of the Eulerian logarithmic strain measure ln V defined by this spin tensor, and furthermore that in all strain tensor measures only ln V enjoys this favourable property. This spin tensor is called the logarithmic spin and the objective corotational rate of an Eulerian tensor defined by it is called the logarithmic tensor-rate. In this paper, we propose and investigate a hypo-elasticity model based upon the objective corotational rate of the Kirchhoff stress defined by the spin Ω^log, i.e. the logarithmic stress rate. By virtue of the proposed model, we show that the simplest relationship between hypo-elasticity and elasticity can be established, and accordingly that Bernstein's integrability theorem relating hypo-elasticity to elasticity can be substantially simplified. In particular, we show that the simplest form of the proposed model, i.e. the hypo-elasticity model of grade zero, turns out to be integrable to deliver a linear isotropic relation between the Kirchhoff stress and the Eulerian logarithmic strain ln V, and moreover that this simplest model predicts the phenomenon of the known hypo-elastic yield at simple shear deformation. This revised version was published online in August 2006 with corrections to the Cover Date.     

General Analytic Solutions and Complementary Variational Principles for Large Deformation Nonsmooth Mechanics

This paper presents a nonlinear dual transformation method and general complementary energy principle for solving large deformation theory of elastoplasticity governed by nonsmooth constitutive laws. It is shown that by using this method and principle, the nonconvex and nonsmooth total potential energy is dual to a smooth complementary energy functional, and fully nonlinear equilibrium equations in finite deformation problems can be converted into certain tensor equations. The algebraic relation between the first and the second Piola–Kirchhoff stresses are revealed. A closed form solution for general three-dimensional large deformation boundary value problems is obtained. The properties of this general solution are clarified by a triality extremum principle. This triality theory reveals an important phenomenon in nonconvex variational problems. Applications are illustrated by nonlinear, nonsmooth equilibrium problems in Hencky's plasticity, 3D cylindrical structures and post buckling analysis of elastoplastic bar with jumping and hardening effects. The idea and methods presented in this paper can be used and generalized to solve many nonlinear boundary value problems in finite deformation theory.Sommario. Il lavoro presenta un metodo di trasformazione duale nonlineare ed un principio generale di energia complementare per la soluzione di problemi di teoria elastoplastica in grandi deformazioni governati da leggi costitutive con discontinuità. Si mostra come, usando il metodo ed il principio proposti, l' energia potenziale totale discontinua e nonconvessa duale di un funzionale energia complementare continuo, e le equazioni di equilibrio nonlineare in problemi di deformazione finita, possano essere convertite in equazioni tensoriali. Vengono mostrate le relazioni algebriche fra il primo ed il secondo tensore delle tensioni di Piola–Kirchhoff. Si ottiene una soluzione in forma chiusa per problemi al contorno generali tridimensionali in grandi deformazioni. Le proprietà di tale soluzione generale vengono chiarite per mezzo di un principio estremale di trialità. La eoria della trialità evidenzia un fenomeno importante in problemi variazionali nonconvessi. Vengono presentate applicazioni a problemi di equilibrio nonlineare con discontinuità in situazioni di plasticità alla Hencky, strutture cilindriche in 3D, e nell'analisi postcritica di una barra elastoplastica con effetti hardening e di jumping. L'idea ed i metodi presentati in questo lavoro possono essere usati e generalizzati per risolvere molti problemi al contorno nonlineari nella teoria delle deformazioni finite.     

Prediction of phonon properties of 1D polyatomic systems using concurrent atomistic–continuum simulation

In this work, we present the simulation results of phonon properties, including phonon dispersion relations, group velocities, phonon relaxation time and mode-specific thermal conductivity, of low-dimensional crystals using the newly developed concurrent atomistic–continuum (CAC) method. With significantly less number of degrees of freedoms than all-atom molecular dynamics, the CAC method predicts the phonon properties of one-dimensional (1D) polyatomic crystals at finite temperatures with the full anharmonicity of the atomic interactions being incorporated. Complete phonon branches of polyatomic crystals are obtained by CAC through the phonon spectral energy density analysis. It is shown that CAC allows medium to long-wavelength phonon transport from atomic to coarsely meshed finite element region without the need of special numerical treatment. The frequency-dependent phonon group velocities are explicitly measured in the simulation. Sub-THz phonon lifetimes in 100 -mm-long polyatomic chains containing 400 million of atoms are predicted. Analysis of the phonon mode-specific thermal conductivity shows that the medium to long-wavelength acoustic phonons are contributing to the majority of the heat transport in 1D crystal, suggesting that the long-wavelength phonons effectively act as thermal carriers in 1D system. This work provides a possible explanation for the anomalous heat transport observed in low-dimensional materials.     

高速弹丸撞靶的侵彻参数的统计分析

弹丸与靶高速碰撞下的侵彻参数是一个随机量,本文对侵彻参数(坑深度p、坑表面孔径d)进行统计分析,给出变量p、d的变差系数,这样,当变差系数C(?)已知时,可对极小样本量m=2、3、4的情况进行统计分析。     

Analysis of Laminated Rubber Bearings with a Numerical Reduction Model Method

In this paper, we present a reduction method for modeling slender laminated elastomeric structures, which is developed in the context of nearly incompressible hyperelasticity. This method, based on a finite element formulation, consists in projecting the unknown fields onto a polynomial basis in order to reduce the dimension of the problem and the model size. Two types of finite elements are used, one for plane-strain and the other for 3D structures. Comparisons with classical finite element models on single layers show the reliability of the present method. The method proposed successfully predicts the global and local behavior and since it reduces both the model size and the computing time. It can be used to model slender bearing consisting of several layers.