二维T-S波在壁面局部喷吸边界层流中的演化

采用壁面设置局部法向速度模拟喷吸条件,数值计算获得稳定的三维边界层基本流的数值解。在此基础上,研究不稳定的二维扰动T-S波在空间演化过程的非线性问题;探讨边界层壁面局部无量纲喷吸速度0.004,0.000 6对二维T-S波非线性演化的影响及其对增长率的贡献。数值计算结果表明,边界层平均流剖面的改变促进了扰动波的快速增长,增强了流体运动的不稳定性,扩大了中性曲线的不稳定区域范围,不稳定的二维T-S波获得了更大的增长率;不稳定的二维扰动T-S波在非线性演化过程中,由于非线性相互作用不断增强,逐渐诱导激发出三维扰动速度及高次谐波,其三维扰动基本波的流向波数和频率与二维扰动波的流向波数和频率相同;正、负相间流向涡及强剪切层已初步形成。     

自由剪切流中沿流向变化的二次失稳研究

该文以考虑厚度变化的二维相干结构为背景流动作二次失稳研究,分析流向各位置处三维扰动展向空间尺度选择机制。结果表明:用能量法考虑流向变化影响及采用局部平行假设获得二维相干结构为基础流动,进行二次失稳分析的方法,可用于研究快速增长的二次失稳问题。还说明了三维相干结构的出现是二维相干结构对三维基本扰动的二次失稳的结果,这种失稳过程对展向波数有很强的选择性。     

岩体三维主干裂隙网络渗流分析

基于流体力学的基本理论和二维岩体裂隙网络渗流原理，推广得到了三维岩体裂隙网络渗流基本方程。将三维岩体裂隙网络渗流理论及有限元数值方法应用于主干岩体裂隙网络渗流分析中，得到了令人满意的结果。     

粗粒料二维与三维孔隙率的对应关系研究

为了使粗粒料二维数值试验更精确完善,针对数值模型的二维孔隙率与实际三维孔隙率等价性问题,设计能够囊括工程级配范围的一系列级配曲线,分别用二维、三维颗粒流程序模拟极值孔隙率试验,得出二维与三维极值孔隙率。研究结果表明,二维极值孔隙率与三维孔隙率具有较好的线性相关性。     

用MPS方法数值分析孤立波与平板相互作用问题

表面孤立波与海洋结构物的相互作用常伴随有砰击、上浪等现象,是船舶与海洋工程领域需要研究的重要问题之一。该文采用基于无网格半隐式移动粒子MPS法开发的MLParticle-SJTU求解器,对孤立波与平板结构相互作用问题进行数值计算分析研究。模拟了二维孤立波对平板的冲击作用过程,得到的平板受力与实验结果吻合良好,验证了MLParticle-SJTU求解器在处理此类问题上的可行性。通过对孤立波与平板相互作用过程的三维模拟,观察到了有别于二维空间下的波浪在平板上表面演化过程,即呈现U型演化过程,说明对此类问题进行三维数值模拟的必要性。     

悬沙淤积问题的湍流液-固两相流动的数值模拟

本文从湍流两相流动基本理论出发，建立了挟沙水流的湍流液-固两相流动的时均方程组和封闭模型.结合实际工程建立了定常悬沙淤积的二维水深平均的全场模型以及准三维模型.数值预报与潮汐水流物模试验比较表明：二维水深平均的全场模型模拟所得回流区内旋涡外缘的悬沙淤积量大于涡心处的悬沙淤积量，这一数值预报结果与物模试验结果不符，说明二维水深平均全场模型不适宜于预报悬沙淤积；准三维模型模拟所得回流区涡心处的悬沙淤积量大于旋涡外缘处悬沙淤积量而且回流区中的悬沙淤积厚度的数值预报结果与物模试验结果比较接近，这说明准三维模型用来预报回流区的悬沙淤积是可行的.     

悬沙淤积问题的湍流液固两相流动的数值模拟

本文从湍流两相流动基本理论出发，建立了挟沙水流的湍流液固两相流动的时均方程组和封闭模型．结合实际工程建立了定常悬沙淤积的二维水深平均的全场模型以及准三维模型．数值预报与潮汐水流物模试验比较表明：二维水深平均的全场模型模拟所得回流区内旋涡外缘的悬沙淤积量大于涡心处的悬沙淤积量，这一数值预报结果与物模试验结果不符，说明二维水深平均全场模型不适宜于预报悬沙淤积；准三维模型模拟所得回流区涡心处的悬沙淤积量大于旋涡外缘处悬沙淤积量而且回流区中的悬沙淤积厚度的数值预报结果与物模试验结果比较接近，这说明准三维模型用来预报回流区的悬沙淤积是可行的．     

方柱绕流CFX三维数值模拟

该文利用计算流体力学软件CFX,对恒定来流条件下黏性不可压缩流体的圆柱和方柱绕流进行了数值模拟。采用有限体积法和SIMPLE计算方法,求解不可压缩Navier-Stokes方程。首先开展雷诺数(Re)等于100和300时的圆柱和方柱绕流问题的二维数值模拟,分析比较了网格大小和时间步长对模拟结果的影响,并比较了不同柱体情况下的流体流动的差异性。进而对Re=100、300时方柱绕流问题进行了三维数值模拟,重点分析了各截面上阻力和升力系数、Strouhal数以及涡量特性与二维结果的差异。发现Re=300时,周向压力、速度场和涡量场与Re=100时相比存在明显的三维特性,并且由于二维流动结构发展成三维流动结构时需要消耗能量,导致三维的阻力升力系数计算结果均小于二维计算结果。研究表明,该文的数值结果与文献结果吻合良好。     

二维三维渗流计算在工程中的联合应用

建立二维或三维模型进行渗流计算是目前用来研究岩土工程中渗流问题常见的两种方法。以某工程围堰作为研究对象,分别采用上述两种方法对土石围堰的渗漏进行了计算分析。通过对围堰渗流量、渗流流速、渗透坡降、浸润面等表征渗漏的特征值进行对比,结果发现,二者存在一定的相合性和互补性,指出只有将二维模型和三维模型的计算结果结合起来,才能更好地反映工程实际。     

带自由液面 Navier-Stokes 流动问题的ALE 分步有限元方法

将任意的拉格朗日 欧拉 (ArbitraryLagrange Euler,简称ALE)描述引入到Navier Stokes方程中 ,以速度和压力为基本变量 ,在时间域上采用分步求解格式 ,利用Galerkin加权余量法推导了分步格式的ALE有限元数值离散方程。并对带有自由液面的Navier Stokes流动问题的定解条件进行了分析讨论。最后利用所得到的ALE分步有限元方法对二维及三维不可压粘性液体大幅晃动问题进行了算例数值模拟 ,数值计算结果验证了本文方法及计算机仿真软件的正确性与可靠性     

3-D NONLINEAR SUPERCAVITATING FLOW IN A GRAVITY FIELD

In this paper,perturbation method and Fourier-cosine-expansion method are used to solve a 3-D nonlinear problem of a supercavitating flow in an inclined field of gravity at large Froude numbers.By expanding the velocity potential into a power series of a small parameter,the original 3-D nonlinear problem is reduced to a number of 2-D ones. The solutions of the first three orders are derived in detail and expressed in terms of the complete elliptic integrals of the first and second kinds.Then the boundary integral equation method is applied to get the numerical solutions for each order.Computational results are provided for supercavitating flows past cones under various flow conditions.     

ASYMPTOTIC ANALYSIS OF DOWNSTREAM EIGENVALUES FOR STATIONARY PERTURBATION OF COUETTE-POISEUILLE FLOW

1 .　INTRODUCTIONIncompressibleviscousflowinachannelhasbeenthesubjectofvariouscomputationalstudies.Avarietyofchannelgeometrycanbeconsidered .ButmostoftheproblemsofthistypeassumethePoiseuilleflowfardownastrainghtchannelorpipeaseithertheentryflowortheexitfloworboth .Theeigenvalue problemthat governstherateofdecayforastationaryperturbationofthePoiseuilleflowinastraightchannelhasbeeninves tigatedbyWilson (196 9)andothers (e .g .,Bram leyandDennis 1982 ;BramleyandDennis 1984 ;Ache 1989) .Re…     

The mechanical energy equation for total flow in open channels

The mechanical energy equation is a fundamental equation of a 1-D mathematical model in Hydraulics and Engineering Fluid Mechanics. This equation for the total flow used to be deduced by extending the Bernoulli＇s equation for the ideal fluid in the streamline to a stream tube, and then revised by considering the viscous effect and integrated on the cross section. This derivation is not rigorous and the effect of turbulence is not considered. In this paper, the energy equation for the total flow is derived by using the Navier-Stokes equations in Fluid Mechanics, the results are as follows：（1） A new energy equation for steady channel flows of incompressible homogeneous liquid is obtained, which includes the variation of the turbulent kinetic energy along the channel, the formula for the mechanical energy loss of the total flow can be determined directly in the deduction process.（2） The theoretical solution of the velocity field for laminar flows in a rectangular open channel is obtained and the mechanical energy loss in the energy equation is calculated. The variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are obtained.（3） The turbulent flow in a rectangular open channel is simulated using 3-D Reynolds averaged equations closed by the Reynolds stress model（RSM）, and the variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are discussed.     

Numerical investigation of a swirling flow under the optimal perturbation

The nonlinear evolution of 3-D instability of a viscous swirling flow, namely, the Oseen vortex, is addressed by direct numerical simulation with a Reynolds number equal to 5000. The global optimal perturbation is considered as the initial perturbation. In axisymmetric cases, three flow regimes are found: (1) the linear growth; (2) the decay of perturbation energy; (3) secondary energy growth. The linear energy growth, which is characterized by the amplification of radial perturbations, is arrested by the interaction between the vortex ring and the Oseen vortex core. The development of the vortex structure is also investigated for non-symmetric flows.

     

NEARLY VERTICAL WATER ENTRY OF A DISK-CYLINDER

A 3-D nonlinear,unsteady free surface problem of nearly vertical water entryof a disk-cylinder is investigated in this paper.By using a modified perturbation method and theFourier cosine expansion method,the original 3-D nonlinear problem is reduced to a few of 2-Dones and then solved with the boundary integral equation method(BIEM).Numerical results areprovided for the time dependent water surface and cavity surface as well as the pressuredistribution on the bodv during its water entry.     

地表河网-地下水流系统耦合模拟Ⅰ：模型

本文通过采用联立求解地表河流一维明渠非恒定渐变流与地下水拟三维非稳定流运动方程的技术路线，提出了地表河网与地下水流耦合模拟算法。该算法中地表河网流动分别由质量和动量守恒定律而建立的连续性方程和运动方程所组成；地下水流采用多层“拟三维”非稳定流模型，通过彼此间的水力联系，建立了地表河网-地下水流耦合模拟评价模型，该模型可用于地表水与地下水转化关系较为密切地区的水资源综合评价预测中。     

WAVE-CURRENT INTERACTIONS WITH THREE-DIMENSIONAL FLOATING BODIES

A Time-domain Higher-Order Boundary Element Method (THOBEM) is developed for simulating wave-current interactions with 3-D floating bodies. Through a Taylor series expansion and a perturbation procedure, the model is formulated to the first-order in the wave steepness and in the current velocity, respectively. The boundary value problem is decomposed into a steady double-body flow problem and an unsteady wave problem. Higher-order boundary integral equation methods are then used to solve the proposed problems with a fourth-order Runge-Kutta method for the time marching. An artificial damping layer is adopted to dissipate the scattering waves. Different from the other time-domain numerical models, which are often focused on the wave-current interaction with restrained bodies, the present model deals with a floating hemisphere. The numerical results of wave forces, wave run-up and body response are all in a close agreement with those obtained by frequency-domain methods. The proposed numerical model is further applied to investigate wave-current interactions with a floating body of complicated geometry. In this work, the regular and focused wave combined with current interacting with a truss-spar platform is investigated.     

水沙河口衔接数学模型的研究及其应用

在河口水流、泥沙数值计算时提出一、二维衔接的数学模型.根据一、二维水流连续方程、运动方程、悬沙扩散方程、两相流底沙运动方程、床面演变方程,对一维河道采用河网三级联解法、迎风差分格式,对二维海区采用有限元加权集中质量法、三角差分格式,建立水沙河口衔接数学模型.将此模型应用于天津泰达永定新河河口工程的研究上,经实测水沙资料验证,计算值与实测值基本吻合.为河口改造时引起的河道与海区的水流及泥沙稳定性问题提供了可行的研究方法.     

VISCOUS FLOW BEHAVIOR IN A CURVED ANNULAR DUCT

ＶＩＳＣＯＵＳＦＬＯＷＢＥＨＡＶＩＯＲＩＮＡＣＵＲＶＥＤＡＮＮＵＬＡＲＤＵＣＴ￥ＺｈａｎｇＢｅｎ－ｚｈａｏ（Ｄｅｐｔ．ｏｆＭｅｃｈａｎｉｃｓ，ＺｈｅｊｉａｎｇＵｎｉｖｅｒｓｉｔｙ，Ｈａｎｇｚｈｏｕ３１００２７，Ｐ．Ｒ．Ｃｈｉｎａ）ＦａｎＤａｂ－ｎｉｎ...     

再论异重流和均质流动的一些相似关系

在对上层静止下层流动的异重流和均质明渠流之间相似关系研究的基础上,本文将这一成果推广,给出了上层流动下层静止的异重流和均质明渠流之间的一些相似关系,并将结果应用于二维重叠式排取水口的水深计算,结果与前人的实验一致。考虑到实际的重叠式排取水口都是三维的,所以本文利用前人的实验结果,进一步给出了三维重叠式排取水口高度及水深的计算方法,所得结果揭示了排水口温差水跃的形成机理和形成条件。