移动简谐荷载作用下桥梁响应的高效计算

在计算移动荷载过桥问题中广泛使用的Newmark方法必须在每一时间步内限制荷载的大小和作用位置都不能改变。精细积分法虽然允许荷载的大小在每一时间步长内发生变化,但是仍假定其作用位置是不变的,未能采取措施以描述荷载沿着桥面的连续移动性。本文提出三种精细积分格式,在每一时间步内不但允许移动荷载的大小按简谐规律连续变化,而且模拟了简谐荷载在空间域的连续移动。通过与Newmark方法和简单问题的解析解进行数值比较,表明用本文提出的方法可以用较粗的结构单元和较大的时间步长而获得很高的计算精度。在精度相同的前提下,计算效率比Newmark方法可提高1~2个数量级。     

Scenario Reduction Algorithms in Stochastic Programming

We consider convex stochastic programs with an (approximate) initial probability distribution P having finite support supp P, i.e., finitely many scenarios. The behaviour of such stochastic programs is stable with respect to perturbations of P measured in terms of a Fortet-Mourier probability metric. The problem of optimal scenario reduction consists in determining a probability measure that is supported by a subset of supp P of prescribed cardinality and is closest to P in terms of such a probability metric. Two new versions of forward and backward type algorithms are presented for computing such optimally reduced probability measures approximately. Compared to earlier versions, the computational performance (accuracy, running time) of the new algorithms has been improved considerably. Numerical experience is reported for different instances of scenario trees with computable optimal lower bounds. The test examples also include a ternary scenario tree representing the weekly electrical load process in a power management model.     

基于BP网络的混凝土耗能器骨架曲线拟合

结合5种混凝土延性柱耗能器在低周期反复荷载作用下的试验数据研究,利用神经网络的工作原理,通过建立神经网络的输入层、隐含层、输出层,确定输入单元、输出单元和隐含层节点数,从而建立了BP神经网络的模型,并根据已有的部分试验数据数据.对网络进行训练,对各种混凝土延性柱耗能器骨架曲线进行了预测拟合,实现混凝土延性柱耗能器骨架曲线的数字化,使其成为具有分析和判断的拟合曲线功能,完整的描绘混凝土延性柱耗能器的骨架曲线,为后续混凝土延性柱耗能器性能研究的仿真模拟提供了可靠的数据模型.结果表明,这种方法是可行的.     

考虑车辆随机停放的停车楼减震设计与可靠度分析

在停车楼的设计中通常将车辆荷载以活荷载的方式均匀分布到结构上,实际上受车辆随机停放的影响,停车楼结构整体质量中心偏移,一旦结构遭遇罕遇地震时,车辆的随机停放可能造成停车楼结构发生扭转破坏.本文在传统减震设计方法的基础上考虑车辆活荷载的随机性,并从可靠度的角度验算减震结构在大震作用下的倒塌概率.结果表明,相同的减震设计布...     

Constrained moving least‐squares immersed boundary method for fluid‐structure interaction analysis

A numerical method is presented for the analysis of interactions of inviscid and compressible flows with arbitrarily shaped stationary or moving rigid solids. The fluid equations are solved on a fixed rectangular Cartesian grid by using a higher‐order finite difference method based on the fifth‐order WENO scheme. A constrained moving least‐squares sharp interface method is proposed to enforce the Neumann‐type boundary conditions on the fluid‐solid interface by using a penalty term, while the Dirichlet boundary conditions are directly enforced. The solution of the fluid flow and the solid motion equations is advanced in time by staggerly using, respectively, the third‐order Runge‐Kutta and the implicit Newmark integration schemes. The stability and the robustness of the proposed method have been demonstrated by analyzing 5 challenging problems. For these problems, the numerical results have been found to agree well with their analytical and numerical solutions available in the literature. Effects of the support domain size and values assigned to the penalty parameter on the stability and the accuracy of the present method are also discussed.     

Finding the buckling load of non-uniform columns using the iteration perturbation method

The aim of this study is to calculate the critical load of variable inertia columns. The example studied in this paper can be used as a paradigm for other non-uniform columns. The wavelength of equivalent vibratory system is used to calculate the critical load of the trigonometrically varied inertia column. In doing so, the equilibrium equation of the column is theoretically studied using the perturbation method. Accuracy of the calculated results is evaluated by comparing the solution with numerical results. Effect of improving the initial guess on the solution accuracy is investigated. Effects of varying parameters of the trigonometrically varied inertia and the uniformly tapered columns on their stability behavior are studied. Finally, using the so-called “perfectibility” parameter, two design goals, i.e., being lightweight and being strong, are studied for the discussed columns.     

Diffusive-Dispersive Traveling Waves and Kinetic Relations: Part I: Nonconvex Hyperbolic Conservation Laws

Motivated by the theory of phase transition dynamics, we consider one-dimensional, nonlinear hyperbolic conservation laws with nonconvex flux-function containing vanishing nonlinear diffusive-dispersive terms. Searching for traveling wave solutions, we establish general results of existence, uniqueness, monotonicity, and asymptotic behavior. In particular, we investigate the properties of the traveling waves in the limits of dominant diffusion, dominant dispersion, and asymptotically small or large shock strength. As the diffusion and dispersion parameters tend to 0, the traveling waves converge to shock wave solutions of the conservation law, which either satisfy the classical Oleinik entropy criterion or are nonclassical undercompressive shocks violating it.     

W/Cu梯度功能材料的高热负荷性能研究

用等离子体喷涂和热压方法制作了W/Cu梯度功能材料(FGM)样品,用大功率ND∶YAG激光对其进行了高热负载模拟实验.结果表明,在100～400MW@m-2的瞬时(脉冲宽度为4ms)热负载下,经过200～700次热循环,未发现有W-Cu复合体开裂.在123MW@m-2的功率密度下作用700次,发现钨表面有再结晶现象及严重的晶界腐蚀和裂纹,再结晶的平均晶粒尺寸约为5～10μm,垂直于表面呈柱状结构,再结晶层厚度约20～30μm.由于激光的淬冷效应,晶粒生长的趋势并不明显.在398MW@m-2功率密度下出现了明显的腐蚀坑,坑内呈疏松的蜂窝结构,坑的边缘出现了明显沉积区,能谱分析表明沉积区集聚了大量的金属杂质.等离子体喷涂试样比热压试样更易产生晶界的断裂的裂纹.在相同的热负荷条件下,W/Cu FGM的重量损失低于石墨材料的重量损失.     

Optimum load scheduling of nuclear-hydro-thermal power systems

This paper considers the problem of short-term optimal operation of nuclear-hydro-thermal electric power systems. The solution is obtained by use of a functional analytic optimization technique that employs the minimum norm formulation.A power system with an arbitrary number of generating stations is considered. The limited flexibility exhibited by the thermal nuclear reactors, when operating in a load-following mode, is accounted for by means of a model of the xenon concentration in their cores. The nonlinear effects induced by trapezoidal water reservoirs and the time delay of the water flow between upstream and downstream hydroplants is taken into consideration as well.A two-level iterative scheme of the feasible type is proposed for implementing the optimal solution.This work was supported in part by the National Research Council of Canada, Grant No. A-4146.     

Dynamic stability of a curved rail under a moving load

The stability of a curved rail under a constant moving load has been investigated using a linear theory; critical speeds of the moving load, and the dynamic rail deflections and rotation were calculated. The effect of the foundation was included through distributed linear springs. It was assumed that the moving load remains in constant contact with the rail and travels along a fixed path on the rail head.