靶板在弹丸低速冲击作用下的弹性恢复规律

为了对不同靶板被尖头弹丸低速侵彻条件下的弹性恢复机理进行研究,同时考虑弹丸低速冲击靶板过程中靶板整体塑性变形及弹性变形恢复,更好地反映弹丸对靶板低速侵彻过程中的变形及材料失效问题,使用非线性动力学分析软件ANSYS/LS-DYNA计算分析了弹丸以相同速度冲击不同边长、厚度靶板时,弹丸反弹速度以及靶板回弹速度随着靶板厚度...     

一类可压缩超弹性圆柱体轴线上的空穴现象

对于由一类均匀各向同性可压缩的广义Varga材料组成的实心圆柱体,研究其在给定的外表面拉伸和轴向拉伸或压缩共同作用下的轴对称变形问题.利用能量变分原理得到了问题的控制方程和边界条件,并求得了描述柱体径向对称变形的参数型解析解和描述圆柱体轴线上空穴生成和增长的空穴分岔解.给出了与泊松比和轴向伸长相关的径向临界伸长的表达式和空穴生成后的应力表达式;并通过数值算例讨论了这些参数对圆柱体轴线上空穴生成和增长、圆柱体的径向位移以及应力的集中和突变的影响,同时给出了相应的数值模拟.     

基于应力比值法的V形切口应力强度因子分析

本文基于有限元分析技术建立了一种应力比值方法,用于计算V形切口的应力强度因子。该方法不需要在V形切口尖端采用反映应力奇异性的奇异单元。求解时,首先给定参考问题的广义应力强度因子,然后利用待求问题的应力值与参考问题的应力值之间的比值来求解待求问题的广义应力强度因子。算例采用切口尖端应力方法分析了平板的V形切口问题。计算结果表明,该方法计算精度较高,能够方便地用于求解相关的工程问题。     

Elastically restrained Bernoulli-Euler beams applied to rotary machinery modelling

Facing the lateral vibration problem of a machine rotor as a beam on elastic supports in bending,the authors deal with the free vibration of elastically restrained Bernoulli-Euler beams carrying a finite number of concentrated elements along their length.Based on Rayleigh's quotient,an iterative strategy is developed to find the approximated torsional stiffness coefficients,which allows the reconciliation between the theoretical model results and the experimental ones,obtained through impact tests.The mentioned algorithm treats the vibration of continuous beams under a determined set of boundary and continuity conditions, including different torsional stiffness coefficients and the effect of attached concentrated masses and rotational inertias, not only in the energetic terms of the Rayleigh's quotient but also on the mode shapes,considering the shape functions defined in branches.Several loading cases are examined and examples are given to illustrate the validity of the model and accuracy of the obtained natural frequencies.     

地基与海洋建筑物相互作用——以最近西班牙海岸线建筑物内部损坏为例

海洋工程通常是一个细长的线。我们通常看到的仅仅是建筑物狭长的表面,而不分析支撑他们的大量水下材料。毋庸置疑,海底地基将承受来自于海洋的周期性和交替的静力以及变化的动力。外部和内部的海上工程均在复杂的环境中运行。固态颗粒(防波堤)可以吸入入射水流,并且通过颗粒之间的间距吸收海浪的能量。回流试图从固态颗粒中抽离物质,这样一个遵从太沙基原理的基于有效拉力和中性拉力之间的平衡建立起来。 在某些情况下,防护层的液化已经造成了防波堤崩溃(Sines,葡萄牙,1978年2月)。在其他情况下,虹吸作用或液化导致巨石(垂直的防波堤)毁坏或崩溃(新巴塞罗那港口,西班牙,2001年11月)。结合复合设计工具的地基-作用力——结构相互作用的过程是一个复杂的分析,关于其研究刚刚开始。 本文介绍了最近发生在西班牙的、由于地基失效导致的海上工程内部损坏的两个例子(马拉加,2004年7月,巴塞罗那,2007年1月),分析了其成因。     

Thermomagnetic viscoelastic responses in a functionally graded hollow structure

This paper presents an analytical solution for the interaction of electric potentials,electric displacements,elastic deformations,and thermoelasticity,and describes electromagnetoelastic responses and perturbation of the magnetic field vector in hollow structures(cylinder or sphere),subjected to mechanical load and electric potential.The material properties,thermal expansion coefficient and magnetic permeability of the structure are assumed to be graded in the radial direction by a power law distribution.In the present model we consider the solution for the case of a hollow structure made of viscoelastic isotropic material,reinforced by elastic isotropic fibers,this material is considered as structurally anisotropic material.The exact solutions for stresses and perturbations of the magnetic field vector in FGM hollow structures are determined using the infinitesimal theory of magnetothermoelasticity,and then the hollow structure model with viscoelastic material is solved using the correspondence principle and Illyushin’s approximation method.Finally,numerical results are carried out and discussed.     

Symplectic system based analytical solution for bending of rectangular orthotropic plates on Winkler elastic foundation

This paper analyses the bending of rectangular orthotropic plates on a Winkler elastic foundation.Appropriate definition of symplectic inner product and symplectic space formed by generalized displacements establish dual variables and dual equations in the symplectic space.The operator matrix of the equation set is proven to be a Hamilton operator matrix.Separation of variables and eigenfunction expansion creates a basis for analyzing the bending of rectangular orthotropic plates on Winkler elastic foundation and obtaining solutions for plates having any boundary condition.There is discussion of symplectic eigenvalue problems of orthotropic plates under two typical boundary conditions,with opposite sides simply supported and opposite sides clamped.Transcendental equations of eigenvalues and symplectic eigenvectors in analytical form given.Analytical solutions using two examples are presented to show the use of the new methods described in this paper.To verify the accuracy and convergence,a fully simply supported plate that is fully and simply supported under uniformly distributed load is used to compare the classical Navier method,the Levy method and the new method.Results show that the new technique has good accuracy and better convergence speed than other methods,especially in relation to internal forces.A fully clamped rectangular plate on Winkler foundation is solved to validate application of the new methods,with solutions compared to those produced by the Galerkin method.     

AN ACCURATE TWO-DIMENSIONAL THEORY OF VIBRATIONS OF ISOTROPIC,ELASTIC PLATES

An infinite system of two-dimensional equations of motion of isotropic elastic plates with edge and corner conditions are deduced from the three-dimensional equations of elasticity by expansion of displacements in a series of trigonometrical functions and a linear function of the thickness coordinate of the plate. The linear term in the expansion is to accommodate the in-plane displacements induced by the rotation of the plate normal in low-frequency flexural motions. A system of first-order equations of flexural motions and accompanying boundary conditions are extracted from the infinite system. It is shown that the present system of equations is equivalent to the Mindlin’s first-order equations, and the dispersion relation of straight-crested waves of the present theory is identical to that of the Mindlin’s without introducing any corrections. Reduction of present equations and boundary conditions to those of classical plate theories of flexural motions is also presented.     

WAVE PROPAGATION IN A TRANSVERSELY ISOTROPIC THERMOELASTIC SOLID CYLINDER OF ARBITRARY CROSS-SECTION

The wave propagation in an infinite, homogeneous, transversely isotropic solid cylinder of arbitrary cross-section is studied using Fourier expansion collocation method, within the frame work of linearized, three-dimensional theory of thermoelasticity. Three displacement potential functions are introduced, to uncouple the equations of motion and the heat conduction. The frequency equations are obtained for longitudinal and flexural (symmetric and antisymmetric) modes of vibration and are studied numerically for elliptic and parabolic cross-sectional zinc cylinders. The computed non-dimensional wave numbers are presented in the form of dispersion curves.     

基于弹性地基梁计算的Daubechies条件小波Ritz法研究

在现有的Daubechies小波Ritz法中,为方便边界条件的引入,借助于位移转换矩阵将Daubechies小波待定系数转换为节点位移。但该方法会降低计算精度,并且计算结果是多个离散的单点位移,不利于进一步解得弯矩、剪力、荷载集度。为寻求更为高效精确的弹性地基梁计算方法,对现有的Daubechies小波Ritz法进行改进,以避免位移转换矩阵的出现,从而提高了计算精度。结合广义变分原理,采用Lagrange乘子法,将边界条件作为附加条件引入自然变分条件下的泛函表达式,构造新的修正泛函。以该修正泛函的驻值条件建立求解矩阵方程组,进而解得未知场函数。此法称为Daubechies条件小波Ritz法。该法计算结果直接是小波基函数待定系数,单元内部任意点的位移均可通过小波基函数得到,也可进一步解得弯矩、剪力、荷载集度,因此比原有方法更为有效。最后,采用受均布荷载的两端铰支弹性地基梁算例,将Daubechies条件小波Ritz法计算结果与基于弹性地基梁理论的解析解进行比较,挠度值（保留小数点后6位小数）与解析解完全一致,弯矩值的相对误差为0.03%,说明Daubechies条件小波Ritz法具有较高计算精度。