The Stress State of an Elastic Orthotropic Medium with an Ellipsoidal Cavity

The stress-concentration problem for an elastic orthotropic medium containing an ellipsoidal cavity is solved. The stress state in the elastic space is represented as a superposition of the principal state and the perturbed state due to the cavity. The equivalent-inclusion method, the triple Fourier transform in spatial variables, and the Fourier-transformed Green function for an infinite medium are used. Double integrals over a finite domain are evaluated using the Gaussian quadrature formulas. The results for particular cases are compared with those obtained by other authors. The influence of the geometry of the cavity and the elastic properties of the material on stress concentration is studied__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 3, pp. 93–100, March 2005.     

土性参数各向异性随机场的表征与建模方法

土性参数在空间上的相关性具有各向异性,因此对各向异性随机场表征与建模方法的研究具有重要的意义.本文首先通过对相关函数的分析,将各向异性相关的问题归结到相关距离函数的探讨上,给出了一种描述参数各向异性相关的方法;其次分析了 目前常用的两种随机场反演方法在处理各向异性问题所面临的问题,(1)局部平均划分法只适合横观各向同性...     

基于Welch法的协方差随机子空间方法的模态参数识别

对工程结构进行环境激励下的模态参数识别具有重要意义,而随机子空间法作为适合环境激励下模态参数识别的时域方法,由于噪声和复杂激励的原因,会产生虚假模态、真实模态遗漏、系统自动定阶难和计算效率等问题,这些问题阻碍了该方法在实际工程中的广泛应用.本文提出了基于Welch法的随机子空间方法,通过Welch法对振动响应在频域进行去噪、降低环境激励和其他不确定性因素影响的处理,把结构固有模态从噪声和激励频率中突显出来,形成富含更多结构模态的Toeplitz矩阵,然后进行奇异值分解和状态矩阵计算,最后进行特征值分析.为了实现自动定阶,对不同奇异值分量构建的状态矩阵得到的特征参数,进行模糊C均值聚类分析和模态的平均相位偏移分析,剔除虚假模态,实现结构模态参数的自动识别.并把本文所提出方法应用于一座大跨悬索桥的实测加速度响应分析,和一座七十层的高层建筑的加速度响应分析,跟频域分解法、传统随机子空间法和基于相关分析的随机子空间法的计算结果进行了比较,发现基于Welch方法的随机子空间法相比于传统随机子空间法和基于相关分析的随机子空间法,在避免模态遗漏和计算效率方面有显著提高,而相对于频域分解法则在自动识别...     

基于单纯形寻优的响应面可靠性分析方法

结构可靠度计算常采用经典的响应面法拟合隐式功能函数或高维功能函数,而对于强非线性功能函数的实际工程问题,尽管其能够计算出结构可靠度的结果,但此时多项式响应面的拟合精度不够,很容易造成不收敛的现象。为了解决上述问题,将响应面法与单纯形寻优的思路进行结合来探求一种有效的计算方法。本文利用单纯形算法对每次迭代的验算点进行优化;再以优化后的设计验算点为中心进行取样,利用响应面法循环迭代计算;最后,沿着真实响应面逐渐逼近最终的验算点。该方法能够解决高维非线性的隐式极限状态方程可靠度计算收敛性的问题,可以提高计算精度和计算效率,具有一定的工程适用性。     

Direct specturm analysis of the state space for random vibration of MDOF linear damped system

This paper proceeds from the general case of the unsymmetric linearized multi-degrees of freedom (MDOF) systems. By adopting the general complex modal theory of the state space, the response analysis for a system subjected to random excitation of the same source is carried out using as a kind of direct spectrum analysis method in frequency domain. With the input of power spectral density function given, the explicit expression of the power spectral density function matrix of the output response can be obtained. By taking Fourier inverse transform, the integrated expressions of the correlation function matrix and of the spectrum moment matrix are obtained. Comparing with the time domain method, this method enjoys the merit of visualization and avoids the procedure of transformation from the obtained response correlation function to be solved for the output spectrum utilizing Fourier transform. This paper has extended the application range of the traditional frequency domain analysis method. The mean square values and variety of statistical values can be obtained conveniently. This method and the time domain method are different in approach but equally satisfactory in their results. The project is supported by National Natural Science Foundation of China and National Education Commission Science Foundation of China     

Numerical study of the axially symmetric motion of an incompressible viscous fluid in an annulus between two concentric rotating spheres

The research reported herein involved the study of the transient motion of a system consisting of an incompressible Newtonian fluid in an annulus between two concentric, rotating, rigid spheres. The primary purpose of the research was to study the use of a numerical method for analysing the transient motion that results from the interaction between the fluid in the annulus and the spheres which are started suddenly by the action of prescribed torques. The problems considered in this research included cases where: (a) one or both spheres rotate with prescribed constant angular velocities and (b) one sphere rotates due to the action of an applied constant or impulsive t?orque. In this research the coupled solid and fluid equations were solved numerically by employing the finite difference technique. With the approach adopted in this research, only the derivatives with respect to spatial variables were approximated with the use of the finite difference formulae. The steady state problem was also solved as a separate problem (for verification purposes), and the results were compared with those obtained from the solution of the transient problem. Newton's algorithm was employed to solve the algebraic equations which resulted from the steady state problem, and the Adams fourth-order predictor–corrector method was employed to solve the ordinary differential equations for the transient problem. Results were obtained for the streamfunction, circumferential function, angular velocity of the spheres and viscous torques acting on the spheres as a function of time for various values of the system dimensionless parameters.     

Efficient retrieval of the thermo‐acoustic flame transfer function from a linearized CFD simulation of a turbulent flame

The stability of thermo‐acoustic pressure oscillations in a lean premixed methane‐fired generic gas turbine combustor is investigated. A key element in predicting the acoustically unstable operating conditions of the combustor is the flame transfer function. This function represents the dynamic relationship between a fluctuation in the combustor inlet conditions and the flame's acoustic response. A transient numerical experiment involving spectral analysis in computational fluid dynamics (CFD) is usually conducted to predict the flame transfer function. An important drawback of this spectral method application to numerical simulations is the required computational effort. A much faster and more accurate method to calculate the transfer function is derived in this paper by using a most important basic assumption: the fluctuations must be small enough for the system to behave linear. This alternative method, which is called the linear coefficient method, uses a linear representation of the unsteady equations describing the CFD problem. This linearization is applied around a steady‐state solution of the problem, where it can consequently describe the dynamics of the system. Finally, the flame transfer function can be calculated from this linear representation. The advantage of this approach is that one only needs a steady‐state solution and linearization of the unsteady equations for calculating a dynamic transfer function, i.e. no time‐consuming transient simulations are necessary anymore. Nevertheless, as a consequence of the large number of degrees of freedom in a CFD problem, an extra order reduction step needs to be performed prior to calculating the transfer function from the linear representation. Still, the linear coefficient method shows a significant gain in both speed and accuracy when calculating the transfer function from the linear representation as compared to a spectral analysis‐based calculation. Hence, this method gives a major improvement to the application of the flame transfer function as a thermo‐acoustic design tool. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of transient response of saturated porous elastic soil under cyclic loading using element-free Galerkin method

A two-dimensional numerical procedure is presented to analyse the transient response of saturated porous elastic soil layer under cyclic loading. The procedure is based on the element-free Galerkin method and incorporated into the periodic conditions (temporal and spatial periodicity). Its shape function is constructed by moving least-square approximants, essential boundary conditions are implemented through Lagrange multipliers and the periodic conditions are implemented through a revised variational formulation. Time domain is discretized through the Crank–Nicolson scheme. Analytical solutions are developed to assess the effectiveness and accuracy of the current procedure in one and two dimensions. For only temporal periodic problems, a one-dimensional transient problem of finite thickness soil layer is analysed for sinusoidal surface loading. For both temporal and spatial periodic problems, a typical two-dimensional wave-induced transient problem with the seabed of finite thickness is analysed. Finally, a moving boundary problem is analysed. It is found that the current procedure is simple, efficient and accurate in predicting the response of soil layer under cyclic loading.     

应用响应面方法结合空间映射方法的可靠性评价

应用响应面结合空间映射方法,在第1次迭代拟合极限状态函数,其它迭代 应用映射技术在第1迭代响应面基础上映射调整得到新的极限状态函数,并进行可靠性分析. 这样就改变了序列响应面方法评价可靠性时需要反复对模型进行试验设计、分析并拟合极限状 态函数的执行过程,从而大大降低了模型分析的计算量.     

Static Equilibrium of an Elastic Orthotropic Medium with an Elliptic Crack under Bending

The static-equilibrium problem for an elastic orthotropic space with an elliptic crack is solved. The stress state of the space is represented as a superposition of the principal and perturbed states. To solve the problem, Willis' approach is used. It is based on the Fourier transform in spatial variables, the Fourier-transformed Green function for anisotropic material, and Cauchy's residue theorem. The contour integrals appearing during solution are evaluated using Gaussian quadratures. The results for particular cases are compared with those obtained by other authors. The influence of anisotropy on the stress intensity factors is studied __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 8, pp. 72–81, August 2005.     

Stress State of an Elastic Orthotropic Medium with an Elliptic Crack Under Tension and Shear

The static-equilibrium problem for an elastic orthotropic space with an elliptical crack is solved. The stress state of the space is represented as a superposition of the principal and perturbed states. To solve the problem, Willis’s approach is used. It is based on the Fourier transform in spatial variables, the Fourier-transformed Green function for anisotropic material, and Cauchy’s residue theorem. The contour integrals appearing during solution are evaluated using Gaussian quadratures. The results for particular cases are compared with those obtained by other authors. The influence of anisotropy on the stress intensity factors is studied__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 4, pp. 20–29, April 2005.     

Randomness effects in crashworthiness analysis

—Crashworthiness studies involve computational analyses of complex structures. If the randomncss of the structural properties is neglected, however, the results of the analysis turn out not to be in agreement with the ones of laboratory tests. The paper systematizes a probabilistic approach to this problem which uses a response surface approximation in terms of spatial averages of the design variables. It includes the randomness of variables, vectors, and fields; it is shown to be efficient and accurate. The method requires an accurate design of the experiments to be carried out in order to identify the response surface parameters. The correlation between response variables is also analysed. A numerical example is presented. The derived results are validated by simulation.     

基于Kriging模型的结构可靠性分析

在结构极限状态方程(LSF)未知的情况下,通常采用响应面法(RSM)模拟结构的极限状态方程,逐步修正求解。由于响应面法对于极限状态方程的多项式假定,使其在计算精度上存在一定的缺陷。本文通过随机选取的部分结构响应,采用K rig ing模型模拟未知状态的结构响应,然后附以最优化的方法求解可靠性指标。该方法突破了极限状态方程的形式对于可靠性计算的制约,避免数学表达式的不同对于可靠性计算的影响。通过数值算例,可以看到本文的方法具有较高的精度和稳定性。     

Stress State of a Transversely Isotropic Medium with an Arbitrarily Oriented Spheroidal Inclusion

The stress-concentration problem for an elastic transversely isotropic medium containing an arbitrarily oriented spheroidal inclusion (inhomogeneity) is solved. The stress state in the elastic space is represented as the superposition of the principal state and the perturbed state due to the inhomogeneity. The problem is solved using the equivalent-inclusion method, the triple Fourier transform in space variables, and the Fourier-transformed Green function for an infinite anisotropic medium. Double integrals over a finite domain are evaluated using the Gaussian quadrature formulas. In special cases, the results are compared with those obtained by other authors. The influence of the geometry and orientation of the inclusion and the elastic properties of the medium and inclusion on the stress concentration is studied__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 33–40, February 2005.     

An unconditionally stable calculation scheme for the dynamic response of structures by the method of spline collocation

In this paper, by the method of collocation, using the cubic β-spline function as the trial function in the time domain and putting zero residuals of the differential equation of motion of the structure at two points of time, the authors obtain an unconditionally stable calculation scheme for the dynamic response of the structure. When a parameter σ in the scheme is within the interval 0.15<σ <0.5 the scheme is absolutely stable. It is shown that the accuracy of the scheme, as may be measured by AD (the decay of the amplitudes), PE (the elongation of periods) and the algorithmic damping ratio, is better than that of traditional methods—the Wilson-σ's method, the Newmark's method and the Houbolt's method. A numerical example is given in which a certain dynamic response problem is solved by the method of this paper and results are compared with that of the traditional methods and the analytic method showing that the accuracy of the method by this paper is superior to the other ones. The computational scheme for the dynamic response of structures by this paper may be regarded as an effective, convenient and accurate method for dynamic response of structures.     

一种求算结构可靠度指标的新方法

为解决结构功能函数在结构设计点附近非线性程度较高时,一次可靠度计算方法(如JC法)不收敛的问题,提出一种新的可靠度计算方法.该算法根据结构可靠指标的几何意义,先将迭代点靠近极限状态面,再通过在极限状态面上搜索下一迭代点,逐渐减小极限状态面上的点到标准正态空间中坐标原点的距离,从而达到收敛的目的.与其他方法相比,该方法不...     

A shape optimisation method of a body located in adiabatic flows

The purpose of this study is to derive an optimal shape of a body located in adiabatic flow. In this study, we use the equation of motion, the equation of continuity and the pressure–density relation derived from the Poisson’s law as the governing equation. The formulation is based on an optimal control theory in which a performance function of fluid force is taken into consideration. The performance function should be minimised satisfying the governing equations. This problem can be solved without constraints by using the adjoint equation with adjoint variables corresponding to the state equation. The performance function is defined by the drag and lift forces acting on the body. The weighted gradient method is applied as a minimisation technique, the Galerkin finite element method is used as a spatial discretisation and the implicit scheme is used as a temporal discretisation to solve the state equations. The mixed interpolation, the bubble function for velocity and the linear function for density, is employed as the interpolation. The optimal shape is obtained for a body in adiabatic flows.     

The Evolution of States in a Spatial Population Model

The evolution of states in a spatial population model is studied. The model describes an infinite system of point entities in \(\mathbb {R}^d\) which reproduce themselves at distant points (disperse) and die with rate that includes a competition term. The system’s states are probability measures on the space of configurations, and their evolution is obtained from a hierarchical chain of differential equations for the corresponding correlation functions derived from the Fokker–Planck equation for the states. Under natural conditions imposed on the model parameters it is proved that the correlation functions evolve in a scale of Banach spaces in such a way that at each moment of time the correlation function corresponds to a unique sub-Poissonian state. Some further properties of the evolution of states constructed in this way are described.     

Quaternion Regularization of the Equations of the Perturbed Spatial Restricted Three-Body Problem: I

We develop a quaternion method for regularizing the differential equations of the perturbed spatial restricted three-body problem by using the Kustaanheimo–Stiefel variables, which is methodologically closely related to the quaternion method for regularizing the differential equations of perturbed spatial two-body problem, which was proposed by the author of the present paper.A survey of papers related to the regularization of the differential equations of the two- and threebody problems is given. The original Newtonian equations of perturbed spatial restricted three-body problem are considered, and the problem of their regularization is posed; the energy relations and the differential equations describing the variations in the energies of the system in the perturbed spatial restricted three-body problem are given, as well as the first integrals of the differential equations of the unperturbed spatial restricted circular three-body problem (Jacobi integrals); the equations of perturbed spatial restricted three-body problem written in terms of rotating coordinate systems whose angular motion is described by the rotation quaternions (Euler (Rodrigues–Hamilton) parameters) are considered; and the differential equations for angular momenta in the restricted three-body problem are given.Local regular quaternion differential equations of perturbed spatial restricted three-body problem in the Kustaanheimo–Stiefel variables, i.e., equations regular in a neighborhood of the first and second body of finite mass, are obtained. The equations are systems of nonlinear nonstationary eleventhorder differential equations. These equations employ, as additional dependent variables, the energy characteristics of motion of the body under study (a body of a negligibly small mass) and the time whose derivative with respect to a new independent variable is equal to the distance from the body of negligibly small mass to the first or second body of finite mass.The equations obtained in the paper permit developing regular methods for determining solutions, in analytical or numerical form, of problems difficult for classicalmethods, such as the motion of a body of negligibly small mass in a neighborhood of the other two bodies of finite masses.     

样条配点法分析结构动力响应的无条件稳定计算格式

本文以三次B样条函数作为位移时域函数,应用配点法,在任一时间步长中列出两个时刻的结构物运动方程式残值为零的条件并使结果满足了稳定条件得到一个计算结构物动力响应无条件稳定的计算格式。 这个计算格式于参数θ符合0.15<θ<0.05时是绝对无条件稳定的,研究证明,本文所提出的格式的精度根据三项指标:振幅衰减率 AD,周期伸长率 PE 及算法阻尼比都比较Wilson-θ法,Newmark法及Houbolt法的为优,例题计算也证明此点,即本文方法精度较上述三法为高,本文格式简单,准确,工作量不多,可以作为计算结构动力响应有效方法之一。