正装结构非线性应力应变累加规律研究

基于有限位移理论的正装结构非线性分析理论对解决超大跨度、柔性结构的非线性计算有重大意义.文中探讨了正装结构非线性的分析特点,研究了其应变场与应力场的Kirchhoff应力张量与Lagrange应变张量的适用性,提出了正装结构非线性分析中应力场与应交场的累加规律,导出了拖动坐标法的虚功增量方程,以此对杆系结构非线性分析常用的CR法和UL列式进行了精度比较分析.文中研究成果可为正装结构的非线性分析提供理论指导.     

Late-Stage Vortical Structures and Eddy Motions in a Transitional Boundary Layer

A high-order direct numerical simulation of flow transition over a flat-plate at a free stream Mach number 0.5 is carried out. Formation and development of three-dimensional vortical structures, typically shown as λ-vortices, hairpin vortices and ring-like vortices, are observed. Numerical results show that there is a strong downdraft motion of fluid excited by every ring-like vortex in the late-stage of the transition process. At two sides of the vortical structure centerline, the downdraft motions induced by the ring-like vortex and the rotating legs superimpose. This is responsible for the appearance of a high-speed streak associated with the positive spike observed in a previous investigation and the appearance of a high-shear layer in the near wall region.     

THE APPLICATION OF WEINSTEIN-CHIEN′S METHOD——THE UPPER AND LOWER LIMITS OF FUNDAMENTAL FREQUENCY OF RECTANGULAR PLATES WITH EDGES ARE THE MIXTURE OF SIMPLY SUPPORTED PORTIONS AND CLAMPED PORTIONS

In this paper, the method of relaxed boundary conditions is applied to rectangular plates with edges which are a sort of the mixture of simply supported portions and clamped portions, so that the lower limit of fundamental frequency of such plates is evaluated. A kind of polynomial satisfying the displacement boundary conditions is designed, os that it is enabled to evaluate the upper limit of fundamental frequency by Ritzmethod. The practical calculation examples solved by these methods have given satisfactory results. At the end of this paper, it is pointed out that the socalled exact solution of such plates usually evaluated by the force superposition method is essentially a kind of lower limit of solution, if the truncated error of series which occurs in actual calculation is considered.     

基于子集模拟法的风机叶片可靠度分析

风机叶片是风机机组中最重要的组件之一,其可靠性对整个发电系统的健康运行十分关键。传统的蒙特卡罗法可靠度计算效率较低,本文将子集模拟法应用到风机叶片的可靠度计算中,通过合理选取中间失效事件临界值和建议概率密度函数,采用Metropolis算法模拟产生一系列的样本,极大地提高了抽样效率。结果表明,子集模拟法在风机叶片可靠度计算中精度较高,且结构的失效概率越小,相比于传统蒙特卡罗法效率更高,可以极大地减轻计算压力。     

主动格栅紊流场对典型主梁颤振导数影响的研究

为研究紊流积分尺度对桥梁颤振导数的影响,选取了理想平板、流线型箱梁以及高宽比1∶6矩形断面三种气动外形渐变的典型断面,采用主动格栅模拟了二维大积分尺度紊流场,利用强迫振动装置测试了主动格栅紊流场中三种断面节段模型的颤振导数,并与均匀流场试验值进行了对比。试验结果表明,紊流积分尺度对颤振导数的影响随断面钝化逐渐减弱;主动格栅二维紊流对流线型断面颤振导数影响较小,无明显趋势性变化;对钝体矩形断面影响显著,并且随折减风速增加而加剧,其气动阻尼项导数由正向负衰减显著,有利于改善结构颤振性能。     

四边简支部分固定矩形薄板的弯曲

本文对混合边界矩形薄板的弯曲问题,提出一个基于广义变分原理和广义伽辽金法的近似解法;具体计算了几个典型的边界问题。数值结果与文献(1)的实验结果吻合良好。与(1)相较,本文简化了计算方法,且就几个具体算例来看,收敛速度也较快。     

万因斯坦-钱伟长法的应用——简支与固支混合边界矩形板基频上下限

本文将边界条件放松法应用于简支与固支混合边界矩形板,求得此类板的基频下限值。文中还设计了一种能满足位移边界条件的多项式作为振型试函数,从而用里兹法得到相应的上限值。具体算例得到了满意的结果。最后本文指出,通常用力法迭加法得到的此类板的所谓精确解,若考虑实际计算的级数截断误差,本质上是一种下限解。     

轴对称动力扭转的边界单元法BEM与圆形基础的动力响应

1.引言轴对称静扭转的BEM早已建立.建立动力问题的BEM的主要困难是必须先获得相应的基本解;这一工作已由我们在文[3]中完成.这里报道我们在文[3]的基础上建立的BEM及其在动力基础计算中的应用. 2.轴对称动力扭转问题的边界积分方程轴对称问题只须在r-2平面上求解.设求解区域是r-2平面上的A,而C是A的边界;U_(Ψφ),T_(Ψφ)是文[3]中给出的动力扭转的基本解与相应的切向面力,其表达式太长这里从略;X′是r-2面上任意点,Y′是C