有自由面渗流分析的流形单元法

提出了用于渗流分析的流形单元法。该方法用物理覆盖来确定材料的分区与自由面，通过迭代求出自由面边界，计算区域逐步逼近实际渗流区域，适用于稳定和非稳定渗流计算。算例表明，该方法用于有自由面的渗流分析是简单有效的。     

基于改进弃单元法的渗流自由面计算

为了将计算渗流自由面的弃单元法应用于ANSYS软件中,对其进行了改进,即根据每次迭代计算结果,将节点全部位于自由面以上的单元均删掉,从而使得总体传导矩阵的阶数不断降低,计算效率得到提高。在计算复合单元等效渗透系数时,对复合单元进行二次细分,以减小单元尺寸对计算结果的影响。计算收敛后,对复合单元上的节点插值求出零压头点坐标,再对零压头点进行曲线拟合或曲面拟合即得自由面。基于该方法,利用ANSYS的APDL语言编制了渗流自由面分析程序,并进行了实例分析。结果表明,提出的改进方法结构简单、精度较高。     

渗流自由面计算的边界元法

用边界元法求解渗流自由面需预先设定自由面的初始位置.先对自由面初始位置进行优化,以便得到合理的计算网格,再按常规方法迭代求解.计算结果表明,与有限元法相比计算精度较高,具有更好的收敛性与更高的计算效率.     

采用边界元法确定渗流自由面的一种改进方法

渗流自由面的确定是无压渗流分析中非常重要的问题。相对有限元法而言 ,采用边界元法确定渗流自由面具有明显的优势。本文基于传统的确定渗流自由面的迭代边界元法 ,提出了改进的采用边界元法确定渗流自由面的迭代方法 ,并运用算例说明了改进方法的精度和有效性     

渗流作用下边坡稳定有限元分析

基于二维无压稳定渗流基本原理,采用改进的单元渗透系数矩阵调整法模拟边坡渗流场,计算了土体单元的渗透力;以渗透力代替单元周边的孔隙水压力,采用有限元强度折减法分析渗流作用下边坡的稳定性.算例分析表明,采用有限元强度折减法进行渗流作用下边坡稳定性分析是可行的.     

基于渗透张量的裂隙渗流有限元计算中反常水头现象初探

针对利用等效连续导水介质模型研究岩体裂隙渗流问题时,有限元计算部分结果出现的水头反常现象,经多因素分析,认为渗透张量与渗流区域边界形状之间存在着相互协调的条件,当这种条件被超越时,就会使计算结果出现水头反常现象。     

基于变分不等式法的渗流有限元分析及程序设计

针对变分不等式法的渗流分析特点特别适用于边界强非线性渗流问题的数值模拟,采用统一建模语言(UML)分析了面向对象渗流有限元各类的关系,利用面向对象程序设计的封装、继承、多态三大机制,在UML类图的指导下对基于变分不等式法的渗流有限元分析进行了程序设计与开发.并通过两个算例验证了该程序的有效性和正确性.     

层状裂隙岩体有自由面的渗流分析

针对互层状裂隙岩体中的渗流问题,总结了互层状裂隙岩体中的层面裂隙和构造裂隙发育规律,提出了一种互层状岩体中裂隙网络生成方法并基于双重介质饱和一非饱和渗流模型分析了软岩中存在和不存在切层裂隙两种情况下自由面渗流问题,讨论了层面裂隙、层问裂隙和切层裂隙隙宽对自由面的影响.结果表明,在互层状裂隙岩体有自由面渗流中可能出现多层自由面的现象,取决于层间、切层及层面裂隙隙宽的组合.     

低渗透油藏非达西渗流定向井产能计算及影响因素分析

为了评价定向井非达西渗流模型产能,基于常规直井达西模型产能公式和井斜负表皮系数,建立定向井达西模型产能公式,通过引入拟启动压力梯度模型、非线性渗流模型对定向井达西模型产能公式进行修正,得到适用于低渗透油藏的定向井拟启动压力梯度模型、非线性渗流模型产能公式。对比三种定向井渗流模型产能大小以及与A油藏实际定向井产能之间的误差,并研究井斜角、应力敏感因子对三种定向井渗流模型产能的影响。分析结果认为:在相同生产压差下,达西模型产能最大,非线性渗流模型次之,拟启动压力梯度模型最小;与实际产能相比,达西模型产能误差最大,拟启动压力梯度模型次之,非线性渗流模型最小,采用非线性渗流模型的产能公式计算低渗透油藏定向井产能较为精确;随着井斜角增加,三种渗流模型产能增加,在井斜角小于30°时,三种渗流模型产能均变化平缓,井斜角大于30°时,产能均变化增大;应力敏感系数增加,三种渗流模型产能减小,产能下降趋势变缓。     

北京市海子水库南副坝渗流及稳定性分析

基于工程地质勘察资料和水文资料,结合工程实况引入等效渗流系数的概念,选取典型断面,对海子水库南副坝及坝基的渗流进行了有限元模拟计算,分析了正常蓄水位、设计洪水位、校核洪水位时渗流作用下的下游坝坡的稳定性,并对混凝土防渗墙深度对渗透量和稳定安全系数的影响进行了分析,得到海子水库南副坝可以加深防渗墙至55 m,渗透量减少35%左右,并且防渗墙的加深对坝坡的稳定性还有一定的加强作用。     

Thermal optimization of tapered pin fin exposed to nonuniform surface heat transfer coefficient

In the present work, thermal analysis and design optimization of tapered pin fin subjected to variable surface heat transfer coefficient have been numerically carried out. It is well known that heat is transferred through the fin by conduction along its length and dissipated from the fin surface via natural convection to the ambient. The thermal analysis and the optimum dimension were carried out using finite element (FE) modeling software ANSYS-17.2. The thermal performance of the tapered pin fin has been studied over a wide range of physical dimensions. In addition, the effect of base to tip surface heat transfer coefficient ratio (ε) on the fin performance is evaluated. It was found that the effect of variable heat transfer coefficient has a significant impact on the fin efficiency. The rate of increase of fin efficiency was lower in the low as well as in high range of ε, meanwhile, it was steeper in the intermediate range of ε. It was also observed that the optimal values of the heat dissipation were higher for lower values of ε at the same conditions.     

Sensitivity analysis in thermoelastic problems using the complex finite element method

This article presents the complex finite element method (ZFEM) for the sensitivity analysis of thermoelastic systems. ZFEM, based on the complex Taylor series approach, performs finite element procedures using complex variables such that the response variables (temperature, stress) and their sensitivities with respect to an input parameter of interest (shape, mechanical and thermal properties, loading) are obtained simultaneously. ZFEM offers significant advantages over alternative sensitivity analyses that require direct derivations of the sensitivity formulae, multiple runs, and/or remeshing. To verify the numerical implementation, a hollow cylinder with convective boundary conditions on the inside and outside surface was considered. First-order derivatives of the stress fields were compared with exact solutions to demonstrate the accuracy of ZFEM sensitivities. The results indicate that the ZFEM-based derivatives are of high accuracy, thereby showing its applicability in the design and analysis of thermoelastic problems.     

刘家峡大坝坝基渗压系数变化及影响因素分析

详细分析坝基渗压系数变化 ,渗压系数与库水位关系。幕前观测孔 U7- 1 渗压系数接近常量 ,与库水位线性相关具有同步性。分析了坝基渗压分布与坝前泥沙淤积铺盖防渗性、帷幕灌浆、渗水断层裂隙分布关系     

Probability strength design of steam turbine blade and sensitivity analysis with respect to random parameters based on response surface method

Many stochastic parameters have an effect on the reliability of a steam turbine blade during practical operation. To improve the reliability of blade design, it is necessary to take these stochastic parameters into account. An equal cross-section blade is investigated and a finite element model is built parametrically. Geometrical parameters, material parameters and load parameters of the blade are considered as input random variables while the maximum deflection and maximum equivalent stress are output random variables. Analysis file of the blade is compiled by deterministic finite element method and applied to be loop file to create sample points. A quadratic polynomial with cross terms is chosen to regress these samples by step-forward regression method and employed as a surrogate of numerical solver to drastically reduce the number of solvers call. Then, Monte Carlo method is used to obtain the statistical characteristics and cumulative distribution function of the maximum deflection and maximum equivalent stress of the blade. Probability sensitivity analysis, which combines the slope of the gradient and the width of the scatter range of the random input variables, is applied to evaluate how much the output parameters are influenced by the random input parameters. The scatter plots of structural responses with respect to the random input variables are illustrated to analyze how to change the input random variables to improve the reliability of the blade. The results show that combination of the finite element method, the response surface method and Monte Carlo method is an ideal way for the reliability analysis and probability strength design of the blade. __________ Translated from Proceedings of the CSEE, 2007, 27(20): 12–17 [译自: 中国电机工程学报]     

Group Theory Analysis of Free Convective Boundary—Layer Behavior at a Stretching Surface

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压力钢管外压稳定性分析的传统解析法存在问题初探

由于水电站压力钢管失稳破坏的非线性,所以传统的基于圆拱理论的外压稳定分析法存在着许多缺陷与不足,本文尝试将其指出,并提出利用柱壳有限条单元的半解析法来解决压力管道的外压稳定性问题。