Stability of a twisted and compressed clamped rod

We consider the problem of determining the stability boundary of an elastic rod clamped at both ends and loaded by a compressive force and a couple. The constitutive equations of the rod are such that both shear of the cross section and compressibility of the rod axis are considered. The stability boundary is given by the bifurcation points of a system of eight nonlinear first-order differential equations, obtained by using the first integrals. Depending on the parameter values the type of bifurcation is determined. The post-critical shape of the rod is obtained by the numerical integration of a system of 12 nonlinear first-order differential equations.     

Buckling of rotating compressed rods

Summary Stability of axially compressed rotating rods is studied as a two parameter bifurcation problem. A stability criterion is obtained for two types of boundary conditions. In one case the behaviour of the solution near the bifurcation point is examined by the use of the method of integral inequalities.With 4 Figures     

Vibrations of a rotating flexible rod clamped off the axis of rotation

Summary We consider a fourth-order boundary value problem associated with the small vibrations of a uniform flexible rod which is clamped at one end and rotates in a plane perpendicular to the axis of rotation. A significant feature is that the axis of rotation does not pass through the clamped end itself. For rapid rotation rates, the governing equation involves a small parameter and must be treated by singular perturbation techniques. A second parameter fixes the relative location of two turning points. For a range of this second parameter, consistent approximations to the characteristic equation are derived, and the limiting behavior of the eigenvalues is obtained.     

The influence of shear and extensibility on the stability of a heavy rotating rod

We determine the critical rotation speed for a heavy rod, fixed at one and free at the other end, that rotates with constant angular speed about its axis. The constitutive equations of the rod are taken in the form of generalized Bernoulli-Euler theory that takes into account extensibility of the rod axis and the influence of shear stresses. The type of bifurcation pattern at the lowest eigenvalue is determined. The post-critical shape of the rod is determined by numerical integration and a new, interesting property of the equilibrium equations is discovered     

钢坯吊具主连杆可靠性优化设计

应用摄动分析理论,论述了钢坯吊具主连杆结构的可靠性问题.在不确定变量分布形式未知情况下,利用Edgeworth级数,将任意分布的随机变量转化为标准的正态分布形式,建立其分布函数,结合摄动分析方法计算标准化正态变量及结构失效状态函数的均值和方差,得到结构的可靠度指标,可用于描述结构的可靠性程度.以可靠度指标为约束构建优化...     

Transverse shear effects in discrete optimization of laminated compressed cylindrical shells

This paper presents optimization problems of cylindrical shells subjected to buckling and ply failure constraints. The objective is to maximize failure load. The layers are assumed to be oriented at 0 °, 90 ° and ± 45 °, so that the locations of plies in the laminate (3^N variables) are design variables. The aim of the present work is to discuss the influence of various formulations of governing equations on optimal solutions including the effects of transverse shear deformations and to present the use of different variants of genetic algorithms, i.e. different selection, mutation and crossing. A series of numerical examples illustrates the discussed problem.     

Improved cuckoo search with particle swarm optimization for classification of compressed images

The need for a general purpose Content Based Image Retrieval (CBIR) system for huge image databases has attracted information-technology researchers and institutions for CBIR techniques development. These techniques include image feature extraction, segmentation, feature mapping, representation, semantics, indexing and storage, image similarity-distance measurement and retrieval making CBIR system development a challenge. Since medical images are large in size running to megabits of data they are compressed to reduce their size for storage and transmission. This paper investigates medical image retrieval problem for compressed images. An improved image classification algorithm for CBIR is proposed. In the proposed method, RAW images are compressed using Haar wavelet. Features are extracted using Gabor filter and Sobel edge detector. The extracted features are classified using Partial Recurrent Neural Network (PRNN). Since training parameters in Neural Network are NP hard, a hybrid Particle Swarm Optimization (PSO) – Cuckoo Search algorithm (CS) is proposed to optimize the learning rate of the neural network.     

负载模拟器弹性杆的结构优化与有限元分析

为提高电动负载模拟器中弹性杆的性能,对其进行结构优化与有限元分析。根据扭转强度条件,确定弹性杆的最小直径;根据电动负载模拟器的加载梯度,对弹性杆的长度进行优化设计;以减小弹性杆所受应力为原则,运用零阶优化算法对过渡圆角半径进行优化设计,得到最优解。利用ANSYS软件对弹性杆进行模态和疲劳寿命的有限元分析,仿真结果表明弹性杆的固有频率和疲劳寿命满足电动负载模拟器的使用要求。研究结果对弹性杆在电动负载模拟器中充分发挥作用以及进一步的优化设计具有指导意义。     

Genesis of Bimodal Distributions

Conditions for which the density function of a mixture of two normal distributions is bimodal are investigated. For fixed values of the variances σ₁ ² and σ₂ ² of the normal distributions if the difference between the means is sufficiently small, the distribution of the mixture will be unimodal, independent of the proportions p and 1 – p, 0 < p < 1. If the difference exceeds a critical value which depends on σ₁ ² and σ₂ ² the bimodality property then depends on p. Values of p sufficiently close to zero and one always exist for which the distribution is unimodal.     

滚动轴承压缩故障信号的特征代理与凸优化重构算法EI北大核心CSCD

压缩采样可以有效缓解机械状态监测数据存储和传输的压力,但是压缩数据的感知重构一直是个难点。针对滚动轴承压缩信号的故障特征提取问题,提出一种基于特征代理与凸优化算法的故障信号重构方法。分析了滚动轴承局部故障信号的稀疏和卷积特性,学习得到故障冲击模式。对压缩得到的轴承观测信号,构造包含冲击时刻特征的代理,并对代理建立目标优化函数,采用快速迭代收缩阈值算法(Fast Iterative Shrinkage Threshold Algo⁃rithm,FISTA)直接从代理提取出稀疏系数,将学习模式与稀疏系数卷积重构出故障信号。与直接利用FISTA从压缩信号中提取冲击特征相比,所提方法在不降低求解精度的同时降低了计算复杂度。相比于常用的贪婪类重构算法,所提方法无需预先估计信号的稀疏度,且能得到全局最优解。通过滚动轴承仿真和实验信号进一步验证了所提方法的有效性。     

Structural optimization of rotating tapered laminated thick composite plates with ply drop-offs

In this study, structural optimization of rotating tapered thick laminated composite plates with ply drop-offs has been investigated numerically. The governing differential equations of motion of the tapered composite plate have been presented including the energy associated with the inertia force, coriolis force, displacement dependent centrifugal force and initial stress resultants due to steady state rotation. Four noded quadrilateral finite element has been formulated based on the first order shear deformation theory. Finite element analysis results are validated with experimental results for natural frequencies of the tapered plate with various configurations. Various cases of optimization problems are formulated with different objective functions in terms of maximization of natural frequencies and damping factors (individually and combined) and solved using genetic algorithm in order to obtain optimal ply sequence and ply orientation. It is shown that the optimization problem with maximization of fundamental modal damping factor without rotating condition yields the optimal layout as 90° for all the layers in the plate. It is also observed that maximization of the fundamental modal damping factor yields identical optimal orientation for uniform and all the configurations of a tapered composite plate.     

Thermal state of a plasma in a compressed layer

The results of an investigation of the thermal state of a plasma in a compressed layer under retardation conditions of the plasma flow of a coaxial Hall accelerator are reported and compared with analogous data for a free flow.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 108–111, July–August, 1994.     

Nonstationary heating of a conical rod

The Galerkin-Kantorovich method is used to obtain an approximate solution of the nonstationary problem of heat conduction for a thin conical rod.     

Distortion in a gradient-index rod

An algebraic formula is derived for the fifth-order distortion of a GRIN-rod lens. By measuring distortion, one can then determine the coefficients of the profile formula.     

Characterization and optimization of Yb-doped photonic-crystal fiber rod amplifiers using spatially resolved spectral interferometry

Spatially resolved spectral interferometry is used to measure the mode content of a Yb-doped photonic-crystal fiber rod amplifier with a 2300 μm(2) mode area. The technique, known as S(2) imaging, was adapted for the short fiber amplifier at full power and revealed a small amount of a copolarized LP(11) mode. Simulations illustrate the potential for weak mode suppression in this fiber and agree qualitatively with the measurements of S(2) and M(2). Higher-order-mode content depends on the alignment of the input signal at injection and ranged from -18 dB for optimized alignment to -13 dB when the injection alignment was offset along the LP(11) axis by 30% of the 55 μm mode-field diameter.     

Elastic-plastic torsion of a Cosserat-type rod

Summary Elastic-plastic torsion of a Cosserat-type rod of a solid circular cross-section is considered. The governing equations are linearised using a small parameter which is equal to the relative grain rize. The linearized problem is subjected to asymptotic analysis based on the singular perturbation technique. Qualitative features of the elastic-plastic state of the rod are discussed. Apparently, this is the first explicit asymptotic solution for the elastic-plastic Cosserat continuum.     

Unsteady MHD rotating flow over a rotating sphere near the equator

The unsteady rotating flow of a laminar incompressible viscous electrically conducting fluid over a rotating sphere in the vicinity of the equator has been studied. The fluid and the body rotate either in the same direction or in opposite directions. The effects of surface suction and magnetic field have been included in the analysis. There is an initial steady state that is perturbed by a sudden change in the rotational velocity of the sphere, and this causes unsteadiness in the flow field. The nonlinear coupled parabolic partial differential equations governing the boundary-layer flow have been solved numerically by using an implicit finite-difference scheme. For large suction or magnetic field, analytical solutions have also been obtained. The magnitude of the radial, meridional and rotational velocity components is found to be higher when the fluid and the body rotate in opposite directions than when they rotate in the same direction. The surface shear stresses in the meridional and rotational directions change sign when the ratio of the angular velocities of the sphere and the fluid ₀. The final (new) steady state is reached rather quickly which implies that the spin-up time is small. The magnetic field and surface suction reduce the meridional shear stress, but increase the surface shear stress in the rotational direction.     

Longitudinal vibrations of a rod with a coating

A solution is obtained to the problem of the longitudinal vibration of a rod with a coating. The solution is obtained in a refined formulation. The same theoretical model is also used to find the solution for the case of static tension. An analysis is made of the way in which the properties of a deformable rod are affected by the stiffness of the shear constraints, which is regarded as a physicomechanical characteristic of the coating-substrate system. A method is proposed for experimental determination of stiffness for both static and cyclic loading conditions. All of the relations needed to analyze the stress-strain state are presented, including those required for fatigue tests in tension-compression.Translated from Problemy Prochnosti, No. 10, pp. 68–75, October, 1994.