具有随机拉索刚度的预应力钢桁架随机内力摄动分析

本文在建立拉索式预应力钢桁架基本计算理论的基础上，考虑到拉索刚度的随机性，推导了拉索式平面预应力钢桁架随机内力摄动分析的一般公式及敏度分析式，并给出了算例。为进一步进行预应力钢桁架可靠性分析奠定了基础。     

随机边界弹性约束预应力钢桁架随机内力摄动分析

为了更合理地模拟实际边界条件，本文在钢桁架各支承处引入一组弹性约束，并以边界性约束刚度的随机性，在建立拉索式预应力钢桁架基本计算基本理论的基础上，推导了拉索式预应力钢桁架随机内力摄动分析一一般公式，并给出了算例。     

随机拉索刚度预应力空间钢桁架随机内力摄动分析

基于已建立的拉索式平面预应力钢桁架基本理论 ,考虑到拉索刚度的随机性 ,得到了拉索式空间预应力钢桁架随机内力摄动分析的一般公式及敏度分析式 ,给出了空间预应力钢桁架随机内力统计特性计算表达式。为进一步进行空间预应力钢桁架可靠性分析奠定了一定的理论基础。最后针对工程中常见的三角形立体钢桁架 ,给出了算例     

随机边界弹性约束空间预应力钢桁架随机内力摄动分析

本文在文献[2]-[4]的基础上,进一步建立了具有任意弹性约束的拉索式空间预应力钢桁架计算模型,其中所有弹性约束均由一组弹簧模拟,在此基础上考虑到边界弹性约束刚度的随机性,进一步建立了拉索式预应力空间钢桁架随机内力摄动分析的计算公式,并针对三角形立体钢桁架进行了分析,为预应力立体钢桁架的可靠性研究奠定了一定的理论基础。     

予应力钢桁架刚度反演分析的摄动迭代法

基于文（１）所建立的拉索式予应力钢桁架基本计算,根据矩阵摄动原理进一步给出了以竖向为位移为约束反演确定任意布索张拉予应力钢桁架单元刚度和的索刚度的摄动迭代公式。算例表明,该方法具有较高的精度,可满足工程设计需要。     

求解无斜腹杆桁架的一种新近似法

无斜腹杆桁架越来越多地应用于各类公共建筑,作为一种小型而具有高次超静定结构,它缺乏方法简单且结果合理的计算手段．利用结构力学原理和对称性导出了上述钢桁架内力的近似计算方法．通过精度分析和实例计算证明其结果合理,算法简单,便于应用．     

超静定桁架变形协调方程 的新方法

在三角形桁架变形协调的基础上，提出了建立超静定桁架的变形协调方程的新方法，此法简便易行，更利于数值计算。     

基于FOSM法的预应力钢桁架系统可靠性分析

基于一次二阶矩法(FOSM)建立了索张拉预应力钢桁架任意单元失效模式可靠性指标的计算模型,并分别根据点估计法和窄界限法得到了整体结构失效概率的计算公式,随机内力统计特性-均值和标准差则根据随机摄动理论确定.该计算模型中的基本随机参数包括任意折线索单元和桁架单元的截面面积 (或综合刚度) 、张拉钢索的预拉力、外荷载及弹性约束刚度等.利用本文计算模型编写的计算程序对工程中普遍采用的结构形式进行了可靠性分析,并对影响结果的有关参数进行了讨论,为索张拉预应力钢结构整体可靠性设计奠定了一定的基础.分析表明,窄限法得到的整体可靠性指标与点估计法(PNET)所确定的基本一致, 这是因为本文计算模型中各失效模式间的相关系数较小之故.此外,随机变量的相关性对预应力钢结构不同阶段可靠性指标有不同的影响,其中加载阶段影响更大.     

波形钢腹板PC组合箱梁纯扭作用下抗扭承载力计算模型

以扭转理论和固定角软化桁架模型为基础,推导了纯扭作用下波形钢腹板PC组合箱梁的抗扭承载力计算模型.该模型针对组合箱梁极限状态时,波形钢腹板处于屈服和未屈服状态两种情况,分别建立了剪应交连续与剪力流连续方程,模型同时考虑了不同位置预应力筋对抗扭承载力的不同作用.通过四根试验梁抗扭承载力理论计算结果与试验数据的对比分析,结果表明本文提出的计算模型不仅能够有效的计算抗扭承载力,还能计算出混凝土开裂后的扭矩-扭率曲线.     

空间静不定桁架的变形协调条件及求解

根据桁架受载后各杆件的伸长量、各杆件夹角的变化之间的几何关系，以各杆的伸长量和夹角的微小变化为未知量，建立了空间静不定桁架的变形协调条件，并结合实例给出了求解空间静不定桁架的一种计算方法．     

Estimates for Some Functionals for Open Sets

We solve new extremal problems of nonoverlapping domains with free poles on rays. Similar results are obtained for open sets. __________ Translated from Neliniini Kolyvannya, Vol. 8, No. 2, pp. 147–153, April–June, 2005.     

Dimensions of attractors for discretizations for Navier-Stokes equations

In this paper, we discretize the 2-D incompressible Navier-Stokes equations with the periodic boundary condition by the finite difference method. We prove that with a shift for discretization, the global solutions exist. After proving some discrete Sobolev inequalities in the sense of finite differences, we prove the existence of the global attractors of the discretized system, and we estimate the upper bounds for the Hausdorff and the fractal dimensions of the attractors. These bounds are indepent of the mesh sizes and are considerably close to those of the continuous version.     

Convexity conditions for strain-dependent energy functions for membranes

The forms that the convexity, polyconvexity, and rank-one convexity inequalities take when the strain energy is required to be a function of the strain G are studied. It is shown in particular that W(G) must be an increasing function of G, in the sense that W(G)W(G) if G – G is non-negative definite. Relatively simple sufficient conditions in terms of G alone are given. Necessary and sufficient conditions in terms of G alone are found to be rather complex.     

A new algorithm for workspace analysis for robot manipulators

Summary A new algorithm to determine the workspace of a robot manipulator is presented in this paper. The method is based on the concept of dividing the robot structure into a regional structure and an orientational structure and is much more efficient than many methods currently available. Another advantage is that the method is expedient to plot the contours of the workspace of a robot manipulator on an arbitrarily defined plane or determine the extreme points along a general direction. The problem of determining subspaces of different joint configurations is also addressed and a method to compute them is proposed. Since for an ordinary industrial robot the regional structure is usually solvable to the first three joint variables, the method proposed is efficient computationally. The applicability of the method is demonstrated by some numeric examples.

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Sommario Nel lavoro viene presentato un nuovo algoritmo per determinare il campo di lavoro di un manipolatore robotico. Il metodo utilizza il concetto di dividere la struttura del manipolatore ad una struttura regionale ed una struttura orientamentale ed è molto più efficace di molti metodi esistenti. Un altro vantaggio del metodo è che esso è conveniente per disegnare i contorni del campo di lavoro su un piano specificato arbitrariamente oppure per determinare i punti estremi lungo una direzione generale. Nel lavoro è studiato anche il problema di determinare i sottospazi di configurazioni diverse dei giunti e viene presentato un metodo per calcolarli. Siccome per un robot industriale la struttura regionale è normalmente risolubile per le prime tre variabili dei giunti, il metodo presentato è molto efficace computazionalmente. L'applicabilità del metodo è dimostrata da qualche esempio numerico.

     

Discrete-layer models for multilayered shells accounting for interlayer continuity

Based on adiscrete-layer approach, in a recent series of papers, the first author has developed the equations governing the elastodynamic behaviour of moderately thick multilayered anisotropic plates by making use of a displacement field which allows a non-linear variation of the in-plane displacements through the laminate thickness and fulfilsa priori the static and geometric continuity conditions at the interfaces between two adjacent layers. Based on this approach, in the present paper we derive the equations of motion and variationally consistent boundary conditions of moderately multilayered anisotropic shells. To show the accuracy and reliability of the proposed approach, closed-form solutions are given and compared with results from three-dimensional elasticity and other approximate bi-dimensional models with and without continuous interlayer stresses. Based on this numerical investigation, the proposed approach appears to work very well.

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Sommario Facendo uso di un approccio del tipodiscrete-layer, in una recente serie di lavori, il primo autore ha rieavato le equazioni del moto indefinite e le condizioni al contorno per piastre anisotrope multistrato, moderatamente spesse. L'approccio si basa sull'assunzione di una legge di variazione degli spostamenti secondo il piano tangente alla superficie media, ottenuta sovrapponendo una legge cubica ad una legge continua lineare a tratti; in tal modo risultano soddisfatte le condizioni di continuitá degli spostamenti e delle tensioni tangenziali all'interfaccia tra due strati. Nel presente lavoro, tale approccio viene esteso al caso di gusci multistrato anisotropi, moderatamente spessi. La validitá dell'approccio proposto viene suffragata mediante confronti numerici con risultati, reperiti in letteratura, ottenuti utilizzando o la teoria dell'elasticitá tridimensionale o altri modelli bidimensionali piú o meno sofisticati.

     

离散元数值模拟中查找邻居元关系的改进算法

离散元方法是近年发展起来的有前途的新概念数值模拟方法,然而查找邻居元关系耗费大量机时和内存。本文引入一种改进算法-“区域法”,并对其原理、算法、运行时间和空间进行了分析。和原算法中的“窗口法”的比较结果表明,新算法在运行时间和空间方面均明显优于原算法。     

A method for deriving hydrodynamic equations for complicated systems

A general algorithm is proposed for constructing a uniformly valid asymptotic solution of the kinetic equations under conditions when the number of slowly varying macroscopic variables is greater than the number of integral invariants of the collision operator. The case of a chemically reacting gas mixture is considered, and a method for constructing the asymptotic solution for this case is described. The hydrodynamic equations for reacting and relaxing gas mixtures are described in general form and it is noted that consistent allowance for the disequilibrium of the reaction and relaxation processes leads to the appearance in the hydrodynamic equations of a number of additional terms, which describe the dependence of the rates of these processes on the spatial derivatives of the hydrodynamic variables.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 96–105, May–June, 1981.     

A new approach for failure criterion for sheet metals

The interpretation of sheet forming simulations relies on failure criteria to define the limits of metal deformation. The common requirements for these criteria across a broad range of application areas have not yet been satisfied or fully identified, and a single criterion to satisfy all needs has not been developed. Areas where existing criteria appear to be lacking are in the comprehension of the effects of non-proportional loading, general non-planar and triaxial stress loading, and process and material mechanisms that differentiate between necking and fracture. This study was mainly motivated to provide an efficient method for the analysis of necking and fracture limits for sheet metals. In this paper, a model for the necking limit is combined with a model for the fracture limit in the principal stress space by employing a stress-based forming limit curve (FLC) and the maximum shear stress (MSS) criterion. A new metal failure criterion for in-plane isotropic metals is described, based on and validated by a set of critical experiments. This criterion also takes into consideration of the stress distribution through the thickness of the sheet metal to identify the mode of failure, including localized necking prior to fracture, surface cracking, and through-thickness fracture, with or without a preceding neck. The fracture model is also applied to the openability of a food can for AA 5182. The predicted results show very good agreement with the experimentally observed data.