Experiments on crack identification in cantilever beams

In this paper we present an experimental investigation of the identification of crack location and size. By providing the first three natural frequencies through vibration measurements, curves of crack equivalent stiffness versus crack location are plotted, and the intersection of the three curves predicts the crack location and size. In the experiments, the cracked specimens were made using a wire-cut electrical discharge machine, and the cantilever beams were excited next to the free end by means of an impulse force hammer. In order to obtain the accurate natural frequencies from the transient signal measured, the method of zoom fast Fourier transform is adopted to improve frequency resolution. From experimental results, it is observed that the identification errors of crack location and size are less than 2% and 4%, respectively. The effectiveness of crack identification through vibration measurements is verified.     

DYNAMIC ANALYSIS OF A LOADED SHOULDER-POLE DURING WALKING

建立了扁担挑物的动力学模型和动力学方程,并进行了数值求解。扁担挑物时存在三种频率,即重物类似于单摆的振动频率、挑运者的步行频率和扁担-重物系统铅垂方向的振动频率。计算结果表明,为了获得较好的挑担体验,三种频率应该相互协调。当人挑担行走的频率为扁担-重物系统铅垂方向振动频率的70%,$\sim$,80%时,肩部铅垂附加动反力为重物重力的30%左右且与肩部铅垂运动同相,当重物类似于单摆的振动频率为人步行频率的25%,$\sim$,30%时,重物的摆角和肩部受到的水平附加动反力均较小,从而有利于人挑担行走。     

应用相位移法的二维光栅测量

本文介绍了二种二维位移测量的光栅方法。测试系统采用CCD摄象系统记录正交光栅图象,通过调整摄象机变焦镜头的放大倍数来控制采样的空间频率。采样后用数字信号处理的方法,通过软件手段实现水平向和垂直向光栅信号的分离,然后运用了相位移技术及载波—相位移技术得到二维位移。所开发的测试系统除具有高精度、高灵敏度的特点外,还具有较高的空间分辨率。     

对胡海昌的小参数法的补充

专著提出了计算特征向量摄动的一种非模态展开法，本文对这一方法中参数μ或者矩阵μ如何选取的问题进行了研究，分析了μ的数学本质，并指出对于重特征值问题，μ只要是一个适当选定的标量常数既可，无需是个矩阵。     

Complex dynamics in double-diffusive convection

The dynamics of a small Prandtl number binary mixture in a laterally heated cavity is studied numerically. By combining temporal integration, steady state solving and linear stability analysis of the full PDE equations, we have been able to locate and characterize a codimension-three degenerate Takens–Bogdanov point whose unfolding describes the dynamics of the system for a certain range of Rayleigh numbers and separation ratios near S=-1. PACS 44.25.+f, 47.20.Bp, 05.45.-a     

传递矩阵－多项式法的改进及其应用

本文提出一种计算转子－滑动轴承－挤压油膜阻尼器转子系统的阻尼固有频率及稳定性的方法，即将传递矩奉多项式法改进后，应用于这类具有分叉结点的系统，直接得到系统的特征多项式，然后用Ｂａｉｒｓｔｏｗ－Ｎｅｗｔｏｎ僻因子法求出全部特征根。本方法具有占内存少、计算速度快、数值稳定等特点，文中对一转子模型进行了计算，其结果与实测基本相符。     

中心集中力作用下圆薄板的固有频率—载荷特征关系

本文讨论了中心集中静载作用下圆薄板在非线性弯曲静平衡构形附近的微幅自由振动,其静平衡问题采用问题的精确解在此基础上,用伽辽金法获得了其最低固有频率——载荷特征关系.所得结果可供这类谐振弹性元件设计中参考.     

正交正放类网架结构固有频率及屈曲分析的样条Galerkin法

本文根据考虑剪切变形的具有３个广义位移的平板弯曲理论，把正交正放类平板网架假设为由三层不同性质材料组成的各向正交异性夹层板。文中以双５次Ｂ样条函数中的一组基底作为试函数，用加权残值法中的离散型Ｇａｌｅｒｋｉｎ法，导出了这类网架的频率方程和屈曲方程。数值算例表明，这种方法是方便而精确的。     

A GEOMETRIC THEORY IN INVESTIGATION ON MODE LOCALIZATION AND FREQUENCY LOCI VEERING PHENOMENA

According to the mapping theory in complex plane,the geometric features of eigen fre-quency loci of systems undergoing free vibrations are investigated.It is concluded that the phenomenaof curve coalescence and veering can be described in a unified manner from the singularities of map-ping from the complex parameter plane onto the complex frequency plane.The formation of a branchpoint in the parameter space is the foundation of explaining localization and veering phenornena.Bythe use of condensation to reduce the dimension of a system,the scope of application of the geometrictheory is widely expanded.The theory is applied to examples to verify the validity of the proposed ap-proach.The present work is an improvement and extension of recent work by M.S.Traintafyllou etal.,     

Conjugate natural convection from an array of discrete heat sources: part 2 — a numerical parametric study

Coupled conduction and natural convection transport within a discretely heated cavity have been investigated numerically. One vertical wall of the cavity is composed of discrete, isoflux heat sources mounted in a substrate of finite thermal conductivity. The opposite vertical wall and the horizontal walls are assumed to be isothermal and adiabatic, respectively. The governing steady-state partial differential equations for the fluid and solid region are solved simultaneously using a control volume formulation, coupled with an additive correction multigrid procedure that increases the convergence rate of the solution. The fluid Prandtl number and heater/fluid thermal conductivity ratio are fixed at 25 and 2350, respectively, corresponding to a dielectric fluid (FC-77) and heaters manufactured from silicon. With increasing modified Rayleigh number (10⁴ < Ra_Lz^* < 109), the cavity flow becomes more boundary layer-like along the vertical walls, and multiple fluid cells develop in the central region. Thermal spreading in the substrate increases with decreasing modified Rayleigh number and with increasing values of the substrate/fluid thermal conductivity ratio (10⁻¹ <- R_s ≤ 10³). For large R_s, the discrete heat sources lose their thermal identity, and the streamlines and isotherms resemble those associated with a differentially heated cavity. Thermal spreading in the substrate also has a significant effect on circulation in the cavity and on maximum surface temperatures.