Boundary element method for model analysis of 2-D composite structure

The boundary element method is used for the modal analysis of free vibration of 2-D composite structures in this paper. Since the particular solution method is used to treat the terms of body forces (inertial forces) in the equation of motion, only static fundamental solutions are needed in solving the problem. For an isotropic cantilever beam, the numerical results obtained by using the BEM presented in this paper are in good agreement, with, those of using FEM or other BEM, but this BEM can also be used to analyze problems for anisotropic materials. For simply supported composite laminated beams, the comparisons of the numerical reslts obtained by this method with the analytical results obtained by 1-D laminated beam theory indicate that if the ratio of length/thickness is greater than 20, the results of the two methods are in good agreement, but if the ratio of length/thickness is less than 20, big errors will occur for 1-D laminated beam theory.     

二维复合材料结构模态分析的边界元法

将边界元方法用于分析二维复合材料结构的自由振动模态，利用特解处理体积力（惯性力）仅需静态基本解就可求解问题，对一各向同性悬臂梁，用该法得到的结果与用有限元或各向性边界元法得到的结果符合得很好，但该法可解各向异性问题，对层状复合材料简支梁，用该法得到了数值结果与用一维层状复合材料梁的理论解的比较表明，当结构的长厚比大于２０时，二者符合得很好，当结构的长厚比小于２０时，一维层状材料梁的理论将产生很大的     

Three-dimensional vibrations of annular thick plates with linearly varying thickness

The free vibration of annular thick plates with linearly varying thickness along the radial direction is studied, based on the linear, small strain, three-dimensional (3-D) elasticity theory. Various boundary conditions, symmetrically and asymmetrically linear variations of upper and lower surfaces are considered in the analysis. The well-known Ritz method is used to derive the eigen-value equation. The trigonometric functions in the circumferential direction, the Chebyshev polynomials in the thickness direction, and the Chebyshev polynomials multiplied by the boundary functions in the radial direction are chosen as the trial functions. The present analysis includes full vibration modes, e.g., flexural, thickness-shear, extensive, and torsional. The first eight frequency parameters accurate to at least four significant figures for five vibration categories are obtained. Comparisons of present results for plates having symmetrically linearly varying thickness are made with others based on 2-D classical thin plate theory, 2-D moderate thickness plate theory, and 3-D elasticity theory. The first 35 natural frequencies for plates with asymmetrically linearly varying thickness are compared to the finite element solutions; excellent agreement has been achieved. The asymmetry effect of upper and lower surface variations on the frequency parameters of annular plates is discussed in detail. The first four modes of axisymmetric vibration for completely free circular plates with symmetrically and asymmetrically linearly varying thickness are plotted. The present results for 3-D vibration of annular plates with linearly varying thickness can be taken as benchmark data for validating results from various plate theories and numerical methods.     

磁耦合悬臂梁双稳动力学分析与实验

研究了一个自由端附加小磁铁的悬臂梁在磁力作用下的双稳态动力学行为．首先,利用Hamilton原理和Euler-Bernoulli梁的基本方程建立了系统在非零平衡点处做微幅振动的动力学方程．其次,利用多尺度法对建立的模型进行理论分析,得到悬臂梁在非零平衡点处振动的幅频方程和位移解,并对解进行了稳定性分析．最后,通过建立实验装置,得到悬臂梁不同运动形式下的参数平面分类和悬臂梁在非零平衡点处振动的幅频关系,通过观察系统在非零平衡点处振动的理论预测,实验结果验证了非零平衡点处振动的理论分析的正确性．对照理论、实验和数值结果得到：在不同的外激励幅值和频率作用下,悬臂梁有三种不同的运动形式：在非零平衡点处的微幅振动;大范围往返运动;在两个非零平衡点之间的无规律运动．     

A new meshless method for steady-state heat conduction problems in anisotropic and inhomogeneous media

Summary A new meshless method is developed to analyze steady-state heat conduction problems with arbitrarily spatially varying thermal conductivity in isotropic and anisotropic materials. The analog equation is used to construct equivalent equations to the original differential equation so that a simpler fundamental solution of the Laplacian operator can be employed to take the place of the fundamental solutions related to the original governing equation. Next, the particular solution is approximated by using radial basis functions, and the corresponding homogeneous solution is solved by means of the virtual boundary collocation method. As a result, a new method fully independent of mesh is developed. Finally, several numerical examples are implemented to demonstrate the efficiency and accuracy of the proposed method. The numerical results show good agreement with the actual results.This work was supported by the National Natural Science Foundation of China (No. 10472082) and Australian Research Council.     

A meshfree method for transverse vibrations of anisotropic plates

A meshfree approach, called displacement boundary method, for anisotropic Kirchhoff plate dynamic analysis is presented. This method is deduced from a variational principle, which uses a modified hybrid functional involving the generalized displacements and generalized tractions on the boundary and the lateral deflection in the domain as independent variables. The discretization process is based on the employment of the fundamental solutions of the static problem operator for the expression of the variables involved in the functional. The stiffness and mass matrices obtained for the dynamic model are frequency-independent, symmetric and positive definite and their computation involves boundary integrals of regular kernels only. Due to its features, the final resolving system can be solved with the classical approaches by using standard numerical procedures. To assess the formulation, the free vibrations of some anisotropic plates were calculated and the results compared with those obtained using other solution techniques. The present results are in good agreement with those found in the literature showing the accuracy and effectiveness of the proposed approach.     

On out-of-plane buckling of anisotropic elastic plate subjected to a simple shear

Out-of-plane buckling of anisotropic elastic plate subjected to a simple shear is investigated. From exact 3-D equilibrium conditions of anisotropic elastic body with a plane of elastic symmetry at critical configuration, the eqution for buckling direction (buckling wave direction) parameter is derived and the shape functions of possible buckling modes are obtained. The traction free boundary conditions which must hold on the upper and lower surfaces of plate lead to a linear eigenvalue problem whose nontrivial solutions are just the possible buckling modes for the plate. The buckling conditions for both flexural and barreling modes are presented. As a particular example of buckling of anisotropic elastic plate, the buckling of an orthotropic elastic plate, which is subjected to simple shear along a direction making an arbitrary angle of θ with respect to an elastic principal axis of materials, is analyzed. The buckling direction varies with θ and the critical amount of shear. The numerical results show that only the flexural mode can indeed exist. Project supported by the National Natural Science Foundation of China (No. 19772032).     

有面内张力和剪力的四边支承各向异性平行四边形板振动、屈曲和弯曲的精确解

给出了弹性地基上四边支承的各向异性平行四边形板在面内张力和剪力作用下自由振动、屈曲和弯曲问题的精确的解析解。此解是利用叠加法得到的重富立叶级数解。与现有结果的比较验证了解的精确性。并给出了一些固定边和简支边组合的多种倾斜角的平行四边形板的自由振动、屈曲和弯曲的数值结果。     

各向异性板的面导纳特性研究

目前在工程上各向异性结构中的振动问题和振动能量传递的问题越来越多,然而对各向异性结构导纳的研究还不充分,对各向异性板面导纳的研究也还处于萌芽状态.面导纳不仅反映结构的振动特性还能反映能量传递的特性,因此面导纳比点导纳在工程上更加贴合实际.论文根据理论公式获得了一般各向异性板面导纳的理论解,并与有限元模型的数值解对比发现...     

Theoretical statistical solution and numerical simulation of heterogeneous brittle materials

The analytical stress-strain relation with heterogeneous parameters is derived for theheterogeneous brittle materials under a uniaxial extensional load, in which the distributions of theelastic modulus and the failure strength are assumed to be statistically independent. This theoreticalsolution gives an approximate estimate of the equivalent stress-strain relations for 3-D heterogeneousmaterials. In one-dimensional cases it may provide comparatively accurate results. The theoreticalsolution can help us to explain how the heterogeneity influences the mechanical behaviors, Further, anumerical approach is developed to model the non-linear behavior of three-dimensional heterogeneousbrittle materials. The lattice approach and statistical techniques are applied to simulate the initialheterogeneity of heterogeneous materials. The load increment in each loading stage is adaptivelydetermined so that the better approximation of the failure process can be realized. When the maximumtensile principal strain exceeds the failure strain, the elements are considered to be broken, which canbe carried out by replacing its Young‘s modulus with a very small value. A 3-D heterogeneous brittlematerial specimen is simulated during a full failure process. The numerical results are in good agreementwith the analytical solutions and experimental data.     

High-order derivatives of Green’s functions in magneto-electro-elastic materials

Three-dimensional Green’s functions and their arbitrary order derivatives in general anisotropic magneto-electro-elastic materials are derived by using Fourier transform. They are analytical solutions expressed in line integral forms, and can be evaluated by a standard numerical integration method. With this method, we can obtain results with high accuracy. Besides, a numerical finite difference method is also given to evaluate the second-order derivatives quickly. When setting the appropriate material coefficients to zero, the piezoelectric, piezomagnetic, and purely anisotropic elastic Green’s functions and their derivatives can all be obtained from the current solutions.     

机电耦联系统余维3动态分岔研究

以r_{sl}, r_{f}以及x_{c}为分岔参数,对具有串补电容的单 机无穷大电力系统的失稳振荡问题,运用动态分岔理论进行了研究. 对系统同时出现有3对 纯虚根特征值的一类多参数高余维分岔情况,运用中心流行方法降维后得到约化方程,对此 强非线性约化方程的求解难点,运用多参数稳定性理论、谐波平衡法、归一化技术和Normal Form方法,得到了系统的解析解. 由分析得知,系统会出现3种Hopf分岔情况、二维环面 情况,以及三维环面分岔解,甚至会出现四维环面,或者更高维的环面分岔. 详细讨论 了系统各种分岔解的稳定性条件和稳定区域,并作了详细的数值分析加以验证.     

Antiplane Problems of Periodical Rigid Line Inclusions between Dissimilar Anisotropic Materials

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3-D numerical study on the bending of symmetric composite laminates

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无单元法求解正交各向异性板自由振动问题

无单元法是一种新出现的数值方法。本文对无单元法的数学基础—滑动最小二乘法进行了详细的研究,推导了无单元法的形函数,并对一些关键问题,如权函数的选取,正交基函数,边界条件,数值实现方法等得出了研究结论。用无单元法研究了正交各向异性板的自由振动问题,由动力学变分原理和滑动最小二乘法导出了正交各向异性板的无单元法质量矩阵和刚度矩阵,编制了相应的计算程序,通过计算实例验证了该方法的有效性。     

Robust control volume finite element methods for numerical wave tanks using extreme adaptive anisotropic meshes

Multiphase inertia-dominated flow simulations, and free surface flow models in particular, continue to this day to present many challenges in terms of accuracy and computational cost to industry and research communities. Numerical wave tanks and their use for studying wave-structure interactions are a good example. Finite element method (FEM) with anisotropic meshes combined with dynamic mesh algorithms has already shown the potential to significantly reduce the number of elements and simulation time with no accuracy loss. However, mesh anisotropy can lead to mesh quality-related instabilities. This article presents a very robust FEM approach based on a control volume discretization of the pressure field for inertia dominated flows, which can overcome the typically encountered mesh quality limitations associated with extremely anisotropic elements. Highly compressive methods for the water-air interface are used here. The combination of these methods is validated with multiphase free surface flow benchmark cases, showing very good agreement with experiments even for extremely anisotropic meshes, reducing by up to two orders of magnitude the required number of elements to obtain accurate solutions.     

Three-dimensional dynamics of a cantilevered pipe conveying fluid, additionally supported by an intermediate spring array

In this paper, the three-dimensional (3-D) non-linear dynamics of a cantilevered pipe conveying fluid, constrained by arrays of four springs attached at a point along its length is investigated. In the theoretical analysis, the 3-D equations are discretized via Galerkin's technique. The resulting coupled non-linear differential equations are solved numerically using a finite difference method. The dynamic behaviour of the system is presented in the form of bifurcation diagrams, along with phase-plane plots, time-histories, PSD plots, and Poincaré maps for five different spring configurations. Interesting dynamical phenomena, such as 2-D or 3-D flutter, divergence, quasiperiodic and chaotic motions, have been observed with increasing flow velocity. Experiments were performed for the cases studied theoretically, and good qualitative and quantitative agreement was observed. The experimental behaviour is illustrated by video clips (electronic annexes). The effect of the number of beam modes in the Galerkin discretization on accuracy of the results and on convergence of the numerical solutions is discussed.     

LONGITUDINAL SHEAR PROBLEMS OF COLLINEAR RIGID LINE INCLUSIONS IN ANISOTROPIC MATERIALS

ＬＯＮＧＩＴＵＤＩＮＡＬＳＨＥＡＲＰＲＯＢＬＥＭＳＯＦＣＯＬＬＩＮＥＡＲＲＩＧＩＤＬＩＮＥＩＮＣＬＵＳＩＯＮＳＩＮＡＮＩＳＯＴＲＯＰＩＣＭＡＴＥＲＩＡＬＳＪｉａｎｇｃｎｉ－ｐｉｎｇ（蒋持平）（ＤｅｐａｒｉｔｍｅｎｔｏｆＦｌｉｇｈｔＶｅｈｉｃｌｅＤｅｓ...     

粘弹层合板的自由振动和横向应力

Based on Reddy＇s layerwise theory, the governing equations for dynamic response of viscoelastic laminated plate are derived by using the quadratic interpolation function for displacement in the direction of plate thickness. Vibration frequencies and loss factors are calculated for free vibration of simply supported viscoelastic sandwich plate, showing good agreement with the results in the literature. Harmonious transverse stresses can be obtained. The results show that the transverse shear stresses are the main factor to the delamination of viscoelastic laminated plate in lower-frequency free vibration, and the transverse normal stress is the main one in higher-frequency free vibration. Relationship between the modulus of viscoelastic materials and transverse stress is analyzed. Ratio between the transverse stress＇s maximum value and the in-plane stress＇s maximum-value is obtained. The results show that the proposed method, and the adopted equations and programs are reliable.     

Subgrid modeling of flow processes in an anisotropic fractal medium

Equations are derived for the effective coefficients of random conductivity fields in the stationary problem of flow in an anisotropic medium. For the fields, lognormal statistics is assumed. The problem is solved using the subgrid modeling method. The results of theoretical calculations are compared with the results of direct three-dimensional numerical modeling. The results of numerical and theoretical calculations are shown to be in good agreement with each other.