渗流力学问题中的数值反演解

介绍了一种拉普拉斯变换数值反演的新方法——Ｃｒｕｍｐ方法以及它在渗流力学问题中的应用。在数值解例中，将Ｃｒｕｍｐ方法和精确解及Ｓｔｅｈｆｅｓｔ方法进行了比较，Ｃｒｕｍｐ方法的解与精确解吻合良好，较之Ｓｔｅｈｆｅｔ方法有很大改进。在油气井现代试井分析中，用Ｃｒｕｍｐ方法绘制的典型曲线更精确     

不可压缩Navier-Stokes方程的差分格式研究

本文对二维不可压缩Nayier-Stokes方程构造了一类精确解,并在精确的初始条件和边界条件之下,用七种常用的差分格式进行了数值求解。以所构造的精确解为基准,对这七种格式进行了稳定性分析和误差分析,比较了它们的优劣,得到了一些对N-S方程的差分方法求解也许会具有一定普遍指导意义的结论。     

简化Navier-Stokes方程组(SNSE)的几个精确解

对不可压二维驻点流、三维驻点流和旋转圆盘附近的流动等三种流动情况,本文给出简化Navier-Stokes方程组(SNSE)及其精确解。表明:文献[1]理论的SNSE的精确解,在三种流动情况下均与完全Navier-Stokes方程组(NSE)的精确解完全一致;文献[3]SNSE的精确解的速度解与完全NSE精确解的速度解一致,但压力解在三种流动情况下均与完全NSE精确解的压力解不同。文献[3]SNSE精确解给出的压力分布相对与完全NSE精确解给出的压力分布的最大相对误差为100％。     

结构可靠性分析的自适应子集模拟方法

结构可靠性分析需要精确高效的失效概率计算方法。为解决高维非线性可靠性分析问题中的失效概率计算问题,本文提出了两种以失效概率估计精度为停机控制参数的自适应子集模拟方法。理论分析和数值算例表明:(1) 两种自适应子集模拟方法能根据失效概率的估计精度要求自适应调整样本量;(2) 考虑样本量优化的自适应子集模拟方法能进一步减少总样本量,提高计算效率。本文所提方法为研究者对结构进行精确高效的可靠性分析提供了一条可行途径。     

求超静定结构精确影响线方程的简捷方法

本文提供了一种确定超静定结构精确影响线方程的方法,而且用的数学手段非常简单,无论是在结构力学教学中还是在有关的工程实际中都是一种值得提倡的方法.     

二维边界元奇异积分和多域缩聚法分析

基于基本解的一种新的表达式，对二维边界元分析中奇异积分的精确求解进行了讨论，从几何方面对基本解的奇异性进行了分析，给出了超参非连续元离散位势和弹性力学问题边界积分方程时奇异积分计算的精确式，从而为判断各种近似方法的优劣和间接方法的精度提供了依据，也为精确地分析了大规模问题提供了一条有效的途径。     

爆轰加载下柱壳断裂时刻微小差异测量方法

对于断裂时刻差异较小的对比实验,提出一种判读方法:同时采用高速摄影和干涉测速,利用高速摄影判读壳体断裂时刻应变,利用干涉测速获取壳体位移及应变曲线,两者结合得出较为精确的壳体断裂时刻差异。利用该方法得出45钢柱壳在JO-9159和JOB-9003两种炸药加载下断裂时间相差0.45 μs,钨合金柱壳在两种炸药加载下的断裂时间相差0.39 μs。同时该方法可以推广应用于单发壳体膨胀断裂实验中,更精确测定壳体的断裂时刻。     

与结构动特性协同的自适应Newmark方法

提出了一种与结构动特性协同的自适应Newmark方法,其参数可基于数值弥散和数值耗散最小化的条件用解析方法求得.对线性单自由度动力学系统,该方法的相位误差精确为零并且谱半径为1.对线性多自由度系统和非线性系统,该方法在所有二阶积分解法中最精确.数值结果验证了新提出格式的高精度和结论.      

三维常数势边界元中的精确积分

对三维问题边界元方法中应用最广泛的常数边界元的积分提出一种精确积分方法。借助于一个假想的闭合曲面,将特定的势场应用于边界积分方程,发现对于三维问题,常数势项的积分可以化作球面三角型的面积计算,而导数项的积分则可在平面域用极坐标进行。本文方法结果精确,公式简单,同一计算公式可以用来计算非奇异、几乎奇异和奇异积分,统一了积分算法。     

用辅助变量法研究落体问题

给出一种在考虑地球自转情况下求解自由落体运动方程的精确解的较简便方法，指出赤道处的自由落体的运动轨迹为一条严格的摆线．     

水库地区的水岩作用及其地质环境影响

本文综述了水库地区水环境系统的变化及水岩作用类型和机制, 在此基础上讨论了水库区地质环境的变化和环境灾害的发生, 提出以水环境变化和水岩作用为中心的水库地质环境评价和灾害预测的研究方向。     

A Least-Squares Mixed Scheme for the Simulation of Two-Phase Flow in Porous Media on Unstructured Grids

A least-squares mixed formulation is developed for simulation of two-phase flow in porous media. Such problems arise in petroleum applications and ground-water flow. An adaptive strategy based on the element residual as an error indicator is developed in conjunction with unstructured remeshing and tested for the two-phase flow of oil and water. An element-by-element conjugate-gradient scheme (EBE-CG) is compared to a band solution algorithm.     

Numerical solution of Cauchy problems in linear elasticity in axisymmetric situations

An iterative method for solving axisymmetric Cauchy problems in linear elasticity is presented. This kind of problem consists in recovering missing displacements and forces data on one part of a domain boundary from the knowledge of overspecified displacements and forces data on another part of this boundary. Numerical simulations using the finite element method highlight the algorithm’s efficiency, accuracy and robustness to noisy data as well as its ability to deblur noisy data. An application of the inverse technique to the identification of a friction coefficient is also presented.     

斜井单螺杆抽油泵柱和扶正器间距的最优设计

在对斜井中单螺杆抽油杆柱进行受力分析的基础上建立了适合于斜、直井的一般力学模型 ,在四个约束条件下同时考虑可靠性最大和扶正器数目最少两个优化目标 ,对斜、直井中单螺杆泵系统的杆柱的杆径和扶正器合理间距进行优化设计。四个约束条件分别为 :1 .组合变形的最大剪应力强度 ;2 .疲劳强度 ;3.最大挠度 ;4 .井眼曲线的尺寸。根据分层优化的方法 ,分解为两个层次优化 ,第一个层次给定杆径以杆长为设计变量 ,扶正器数目最小为目标 ;第二个层次以杆径为设计变量 ,可靠性最大为目标 ;借助动态规划的思想 ,由井深最大的设计井段向上逐段求解。并编制了优化设计程序 ,在文中给出了优化设计的计算实例     

Rectangular Tubular Steel Columns Loaded Biaxially

An inelastic analysis of rectangular tubular steel columns subjected to a constant axial load and a gradually increasing biaxial end moment is presented. Analytical thrust-moment-curvature relationships are given for the cross section with bilinear material stress-strain characteristics. An iterative procedure based on column deflection curves is used to predict moment-deflection curves up to collapse, and numerical examples are given for square and rectangular tubular steel columns. The interaction of biaxial moments, as well as the effect of strain-hardening, is explained for the non-proportional loading considered. The technique can be modified for beam-columns with other types of end moments.     

Prediction of the steady surface thermal plume in crossflow

This paper presents a two-dimensional numerical procedure which employs finite-difference techniques to solve the partial-differential equations governing the steady flow and heat transfer of a surface thermal plume above a crossflowing ambient fluid in the near field. An earlier model developed for predicting thermal plumes in stagnant surroundings is extended by the inclusion of curvature terms in the momentum equations. An integral equation is also solved to determine the trajectory of the thermal plume. Comparisons of present model calculations with two sets of experimental data show that the centre-line trajectories as well as the velocity and temperature decays are well predicted.     

A review of microstructure in concentrated suspensions and its implications for rheology and bulk flow

An overview of present understanding of microstructure in flowing suspensions is provided. An emphasis is placed on how the microstructure leads to observable bulk flow phenomena unique to mixtures. The bridge between the particle and bulk scales is provided by the mixture rheology; one focus of the review is on work that addresses the connection between microstructure and rheology. The non-Newtonian rheology of suspensions includes the well-known rate dependences of shear thinning and thickening, which have influence on bulk processing of suspensions. Shear-induced normal stresses are also measured in concentrated suspensions and include normal stress differences, and the isotropic particle pressure. Normal stresses have been associated with shear-induced migration, and thus have influence on the ultimate spatial distribution of solids, as well as the flow rate during processing; a second focus is on these uniquely two-phase behaviors and how they can be described in terms of the bulk rheology. An important bulk fluid mechanical consequence of normal stresses is their role in driving secondary flows.     

Axisymmetric flow through a permeable near-sphere

An analytical approach is described for the axisymmetric flow through a permeable near-sphere with a modification to boundary conditions in order to account permeability. The Stokes equation was solved by a regular perturbation technique up to the second order correction in epsilon representing the deviation from the radius of nondeformed sphere. The drag and the flow rate were calculated and the results were evaluated from the point of geometry and the permeability of the surface. An attempt also was made to apply the theory to the filter feeding problem. The filter appendages of small ecologically important aquatic organisms were modeled as axisymmetric permeable bodies, therefore a rough model for this problem was considered here as an oblate spheroid or near-sphere.     

Temperature Variations of Forced Convection in Porous Media for Heating and Cooling Processes: Internal Heating Effect of Viscous Dissipation

An analytical study on fully developed forced convection in a homogeneous porous medium is reported. Incorporating the internal heating effect of viscous dissipation, closed form solutions of the temperature distributions in the transverse direction are obtained and analyzed for both heating and cooling processes. Variations of Nusselt number as a function of Darcy number and Brinkman number and the existence of singularity in Nusselt number are also discussed. An erratum to this article can be found at     

Analysis of data on the relation between eddies and streaky structures in turbulent flows using the placebo method

An artificially synthesized velocity field with known properties is used as a test data set in analyzing and interpreting the turbulent flow velocity fields. The objective nature of this approach is utilized for studying the relation between streaky and eddy structures. An analysis shows that this relation may be less significant than is customarily supposed.