Some problems associated with the disturbed matrix Lyapunov equation for linear time-invariant discrete systems

Both the Lyapunov stability and popov’s hyperstability ofdiscrete linear time-invariant system in case of system para-meter disturbance are discussed in this paper.The allowabledisturbance ranges are given so that the maintenance of theLyapunov stability and the popov’s hyperstability of a dis-crete linear system is guaranteed.The results find theirsignificance in the MRAC.     

A nonsimilar boundary layer on a moving wall

This paper is concerned with an analysis of viscous flow through a varying cross sectional area, typical of application in a Wankel Engine. The analysis models flow past a variable moving boundary. Dimensionless temperature, velocities, friction factor and Nusselt numbers are obtained and evaluated for the inside of a Wankel engine channel for different fluid properties. Research has indicated such application has not been previously performed.     

Finite amplitude elastic waves due to non-uniform traction at the surface of a cylindrical cavity

This paper is concerned with two spatial dimension, finite amplitude wave propagation emanating from the surface of an initially circular cylindrical cavity in an unbounded isotropic compressible isotropic hyperelastic solid. The solid is initially in the natural reference configuration and the wave propagation is due to an azimuthally non-uniform, sudden application of compressive nominal traction at the surface of the cavity. Governing equations for the problem are obtained in Lagrangian form in terms of cylindrical polar coordinates and two different classes of strain energy functions are considered. Numerical solutions, for a particular application of traction, are obtained from a fully explicit finite difference scheme. It was found that the responses to the particular application of traction differed negligibly for the various strain energy functions considered.     

The effect of path cut on Somigliana ring dislocations in a half-space

This paper provides solutions for the stress and displacement fields induced in a half-space by an edge dislocation of constant magnitude, where the dislocation line is a circular ring lying in a plane parallel with the free surface. Two types of edge dislocations are considered; the prismatic form with a displacement discontinuity vector normal to the surface and cases with radial dislocation vectors. The latter are not true Volterra dislocations and produce different results for different path cuts these effects are investigated in some detail. The primary application of these results is for analysis of axisymmetric problems – the radial dislocations would be impossible in finite material.     

爆破振动全历程预测及主动控制研究进展

爆破振动为爆破公害之首, 工程上需要对其进行控制. 基于爆破振动全历程预测的爆破振动控制方法是一种主动的控制方法, 且具有良好的应用前景, 本文阐述了爆破振动全历程预测的研究进展与应用, 并对各种预测模型的优缺点进行了比较. 介绍了两种典型的爆破振动主动控制方法-----干扰降振法和频谱控制法的理论试验研究及其在工程中的应用, 并重点分析了爆破振动控制在电子起爆条件下的优势及一些应用实例. 最后指出了今后需要进一步研究的问题.      

Micromechanical analysis of polymer composites reinforced by unidirectional fibres: Part II – Micromechanical analyses

This paper presents the application of a new constitutive damage model for an epoxy matrix on micromechanical analyses of polymer composite materials. Different representative volume elements (RVEs) are developed with a random distribution of fibres. Upon application of periodic boundary conditions (PBCs) on the RVEs, different loading scenarios are applied and the mechanical response of the composite studied. Focus is given to the influence of the interface between fibre and matrix, as well as to the influence of the epoxy matrix, on the strength properties of the composite, damage initiation and propagation under different loading conditions.     

减振阻尼材料设计方法研究

减振阻尼材料可以改变结构的阻尼特性从而降低振动响应和声辐射水平,因而被广泛应用于飞机结构的减振降噪。本文针对减振阻尼材料的设计和应用开展了一系列试验研究,首先通过材料改性得到了不同主基料下材料的配方对阻尼性能的影响;其次配制了三种不同的约束阻尼结构,通过DMA测试对比了三种约束阻尼结构的最佳使用温度和频率范围;最后对约束阻尼结构的减振效果和粘贴布局应用进行了试验,试验结果表明,约束阻尼结构具有良好的减振效果。通过研究掌握了减振阻尼材料在材料改性、约束阻尼结构设计、粘贴布局应用等方面的一些设计方法,可为后续的进一步研究提供技术支持和参考。     

泡沫铝缓冲吸能评估及其特性

对泡沫铝缓冲吸能特性的评估方法进行了比较分析 ,明确了吸能效率曲线与理想吸能效率曲线的应用范围 ,为缓冲器的选材与设计提供了依据。同时还对四种密度的泡沫铝在动静态下的缓冲吸能特性进行了评估 ,研究表明 ,泡沫铝是一种优良的吸能材料。     

功能梯度压电夹层结构中SH波的传播

研究了功能梯度压电上、下半空间和均匀压电层组成的夹层结构中SH波的传播性能,上、下功能梯度半空间的材料性能沿垂直于界面方向以指数函数形式变化。首先推导了SH传播时电弹场的解析解,然后利用界面条件得到了行列式形式的频散方程。基于推导的频散方程,通过数值算例表明了材料性能梯度变化、压电层厚度和材料组合方式对相速度的影响,结果对功能梯度压电材料在声波器件中的应用有参考价值。     

涂布流动的非线性阈值问题

本文研究了沿斜面流动薄层液体的非线性稳定性,即涂布流动的非线性稳定性问题。我们将周恒对平面Poiseuille流提出的弱非线性理论应用于涂布流动。文中对自由表面的世界条件提出了一个合理的简化方法,对亚临界时不同Reynolds数及扰动频率,求出了有限扰动的阈值。     

Detection and description of non-linear phenomena in experimental modal analysis via linearity plots

Ground vibration tests (GVTs) on aircraft prototypes are mainly performed to experimentally identify the structural dynamic behaviour in terms of a modal model. This assumes a linear dynamic behaviour of the structure. However, in the practice of ground vibration testing it is often observed that structures do not behave in a perfectly linear manner. Non-linearities can be determined, for example, by free play in junctions, hydraulic systems in control surfaces, or friction. This paper compiles measured, typical, non-linear phenomena from various GVTs on large aircraft. The standard procedure in GVTs nowadays is the application of the Harmonic Balance method which linearizes the dynamic behaviour on the level of excitation. The procedure requires a harmonic excitation of the structure which is usually performed during phase resonance testing. The non-linear behaviour is investigated in terms of linearity plots in which the resonance frequency of a mode is plotted as a function of the excitation level. The experimental data is then compatible with all post-processing procedures for the measured results, e.g. updating of the finite element model or flutter calculations. This paper shows measured linearity plots for some typical non-linear phenomena. In the second part of the paper analytical linearity plots for different non-linear stiffness and damping models are considered in order to investigate whether the type of non-linearity can be identified from measured linearity plots. The analytical linearity plots are discussed with respect to their application limits. The analytical linearity plots are used to interpret the experimental linearity plots stemming from various GVTs on different aircraft prototypes. Finally, the observability of non-linear stiffness and non-linear damping characteristics via linearity plots is assessed.     

Displacements and stresses in composite multi-layered media due to varying temperature and concentrated load

This paper deals with the determination of the thermo-elastic displacements and stresses in a multi-layered body set up in different layers of different thickness having different elastic properties due to the application of heat and a concentrated load in the uppermost surface of the medium. Each layer is assumed to be made of homogeneous and isotropic elastic material. The relevant displacement components for each layer are taken to be axisymmetric about a line, which is perpendicular to the plane surfaces of all layers. The stress function for each layer, therefore, satisfies a single equation in absence of any body forces. The equation is then solved by integral transform technique. Analytical expressions for thermo-elastic displacements and stresses in the underlying mass and the corresponding numerical codes are constructed for any number of layers. However, the numerical comparison is made for three and four layers.     

A penny-shaped crack in a filament-reinforced matrix—I. The filament model

This study deals with the elastostatic problem of a penny-shaped crack in an elastic matrix which is reinforced by filaments or fibers perpendicular to the plane of the crack. An elastic filament model is developed in the first paper. The second paper considers the application of the model to the penny-shaped crack problem in which the filaments of finite length are symmetrically distributed around the crack. The reinforcement problem for the cracked matrix with elastic fibers of different diameter, modulus, and relative location is considered in the third paper. Since the primary interest is in the application of the results to studies relating to the fracture of fiber or filament-reinforced composites and reinforced concrete, the main emphasis of the study will be on the evaluation of the stress intensity factor along the periphery of the crack, the stresses in the filaments or fibers, and the interface shear between the matrix and the filaments or fibers.     

A novel construction of substitution box using a combination of chaotic maps with improved chaotic range

The influential application of substitution boxes in secure communication and multimedia security attracted researchers to construct more robust substitution boxes. The advantage of using chaos in the secure communication is to get additional unpredictability and randomness in data. In this paper, substitution boxes are constructed with the help of chaotic system and linear fractional transformation. The 256 distinct values of each substitution box are then checked with the help of different available algebraic and statistical analyses. These tests evaluate the strength and application of substitution boxes in different encryption techniques. The results indicate the strength of anticipated technique.

     

A new fibre optics illumination system for application to electronics holography

The practical application of electronic holography requires the use of fibre optics. The need of employing coherent fibre optics imposes restrictions in the efficient use of laser light. This paper proposes a new solution to this problem. The proposed method increases the efficiency in the use of the laser light and simplifies the interface between the laser source and the fibre optics. The paper will present the theory behind the proposed method. A discussion of the effect of the different parameters that influence the formation of interference fringes is presented. Results that can be achieved and limitations are given. An example of application is presented.     

层状地基轴对称问题的Mindlin解

本文在文献[1]的基础上,对层状地基应力和位移的计算方法做了一些创新的工作。首先作者提出求解传矩阵的逆矩阵的简便公式。并在应力、位移的计算上,对荷载作用面上下分别采用二种不同的传递矩阵。加快了计算速度,避免了层状体系计算中常见的溢出问题及大数减大数造成的计算困难。     

Analysis of gear rattle by means of a wavelet-based signal processing procedure

In the paper a wavelet-based signals processing technique for the experimental detection of the gear rattle produced by the teeth impacts in lightly loaded gears is proposed. The Discrete Wavelet Transform is used to decompose the signal of the angular relative motion of an helical gear pair, and the wavelet decomposition details are adopted to analyze the dynamic behavior under rattle condition. In particular the procedure permits to evaluate the quality of the impacts between the teeth, discriminating between the two different sides of teeth contacts when there is a double-sided rattle condition. This technique enables, moreover, to define new indices for metrics of gear rattle especially useful in order to conduct comparisons for different operative conditions. Some examples of application of the proposed technique are reported in the paper adopting experimental signals acquired by two high resolution incremental encoders on a specific gear pair test rig. The experimental investigations regard comparative analyses with respect to the speed fluctuations amplitude, the rattle frequency and the lubrication regime.     

Applications of experimental mechanics to plant fabricating-equipment problems

Representative field projects are described to illustrate different uses made of experimental-measurement techniques in problems relating to fabricating equipment and production processes in Alcoa plants. Typical areas of application for this work covered in the paper are: establishing optimum adjustment of equipment, determining forces for fabricating operations; determining strength and behavior of equipment; developing load-monitoring and control systems for fabricating equipment.     

A Frequency Method for Predicting Limit Cycle Bifurcations

The paper studies the bifurcations of limit cycles in a rather general class of nonlinear dynamic systems. Relying on the classical harmonic balance approach as applied in control engineering neat frequency conditions for such bifurcations are derived. These results, approximate in nature, make clear the structural mechanism of the considered phenomena and can be applied to predict the occurrence of bifurcations as a function of system parameters. The application to several examples of different complexity shows the simplicity and accuracy of the proposed method for solving complicated problems of nonlinear dynamics.     

Analysis of cantilever plates by the line-solution technique

Summary The application of the line-solution technique to the analysis of uniformly loaded cantilever plates is described in this paper. In this method, the two-dimensional partial differential equation of plate theory is reduced to a set of ordinary linear differential equations by replacing the derivatives in one direction by their finite-difference equivalents. The resulting equations are solved numerically by the matrix-progression technique.Three different approaches are suggested for the elimination of the corner forces which arise as a result of using Kirchhoff's boundary conditions. Numerical results are presented and compared with those of previous theoretical and experimental investigations.