含环向表面裂纹圆柱壳的波传播特性研究

研究了振动波在含有环向表面裂纹的无限长圆柱壳中的传播特性.圆柱壳体的振动用Flügge方程来描述.运用线弹性断裂力学的理论,考虑到裂纹的张开、滑移和撕裂3种模式以及它们相互之间的耦合,利用分布的线弹簧来模拟裂纹并建立了裂纹所在区域的局部柔度矩阵,得到由此引起的附加位移和壳体中内力之间的关系.在入射波已知的情况下,根据裂纹两侧区域的位移和内力的连续性条件得到了反射和透射波的幅值系数.分析了入射波通过裂纹后的透射、反射系数与激励频率和裂纹尺寸之间的关系.为基于振动功率流方法识别圆柱壳表面损伤提供了理论基础.     

水下环向双周期加肋圆柱壳体的自由振动

以浸没于水中的弹性环向双周期加肋薄圆柱壳为研究对象，考虑介质与结构振动的耦合效应，研究流固耦合系统的自由振动。基于Kennard薄壳理论、Helmholtz方程以及壳壁外表面的运动协调条件，并借助Dirac-δ函数引进肋骨对壳体的作用，从而建立耦合系统的运动方程。通过富氏积分变换、引进算子，并利用算子的周期性，得到系统的频率方程。采用沿实波数轴搜索求根的方法，重点计算了水下无限长环向双周期加肋柱壳的自由传播波频率系数，并进一步研究了流场和肋参数对壳体固有频率的影响。     

水压下加筋圆柱壳自由振动—离散法

(一)前言在真空中,环加筋薄壳自由振动已由Ganetly,Bleich,Gondikas,Michalopoulos等人作了大量的研究。近一些年来,潜浸在流体中的圆柱壳的振动分析得到了重视。流体对浸入其中壳体自由振动的影响不外乎有二; ①流体静压力的影响。②流体与壳体相互偶合效应。文献[4]仅仅处理了未加强圆柱壳在流体静压下的振动。至于流体与壳体之间相互偶合作用,已有      

可渗透圆柱壳流固耦合问题的流场与内力分析

在弹性薄壳的非线性理论和流体力学基本方程的基础上,研究了可渗透圆柱壳的流固耦合问题.假定壳体具有均布孔隙且孔的面积很小,不考虑其阻力,忽略对弯曲刚度和壳体腔内流体微小运动影响,应用相容欧拉--拉格朗日法建立了带孔的圆柱壳在流体中相互作用的基本方程.通过具体算例求解,给出了流场速度与压力的变化、圆柱壳的变形及内力分布,并对相关参数进行了讨论.     

含裂纹圆柱薄壳的动态特性试验研究

 利用时间平均法分别拍摄了含轴向和环向裂纹圆柱薄壳的激光 全息振型图，讨论了裂纹对圆柱薄壳振型及固有频率的影响，把含裂 纹壳体的振型分为三个区，即：裂纹周围的局部振动区，壳体原振动 区和过渡区. 并着重分析了局部振动的特征，得出了局部振动有着自 己的独有振形和固有频率的结论，从而很好解释了含裂纹圆柱薄壳的 复杂振型图及固有频率的反常变化.     

弯载下中长圆柱壳表面裂纹的线弹簧模型解

针对含环向表面裂纹的中长圆柱壳,基于薄壳半膜力理论和线弹簧模型,导出了其在弯载作用下的解析解,并给出了相应的表面裂纹前缘的应力强度因子的计算公式以及表面裂纹存在对整个圆柱壳柔度的影响的表达式。研究表明,对于中长圆柱壳中的较长裂纹,裂纹前缘最深点处的应力强度因子对裂纹前缘的形状并不敏感;相应的数值计算结果表明,本文的解与有限元结果的误差不超过3%。     

带频率约束的浸水圆柱壳结构优化设计

与干结构相比，流固耦合系统属于非经典问题，其动态设计要复杂得多。本文基于流固耦合分析，主要探讨了浸水圆柱壳在频率，重量等约束条件下的优化设计问题。针对圆柱壳的结构特点，对壳体，流场分别采用有限条，边界元法进行分析以减小计算量。充分利用系统的灵敏数度信息，采用多目标优化方法对浸水圆柱壳进行了优化设计。通过具体算例证明了本文方法的可行性。     

受谐激励的带压电层充液圆柱容器稳态解

基于线性压电理论和可压缩无粘流场运动方程,推导出无限长带压电圆柱体流固耦合稳态解,由于流固耦合与力电耦合的复杂性,文中只考虑轴对称问题,研究了流固耦合智能结构在不同电压作用下位移、应力、流体压力的分布情况,为振动噪声控制奠定基础。     

充液圆柱壳的自振特性

文内含液圆柱壳的自由振动方程组以力矩理论为基础,壳面位移用梁函数逼近。壳内的流体力学方程用有限Hankel变换分段求解,结果能满足全流场条件。用广义液动压力表示流体与结构的相互作用,从而把充液圆柱壳的自由振动归结为广义代数特征值问题。为了比较方法的精度,以两端简支、端头有刚性平面限制的圆柱壳为例,计算了空壳和充液壳的频率,初步讨论了各阶频率与周波数的关系,最易激发周波数的变化规律。理论计算的频率值与实验结果一致。     

非饱和土-隧道系统动力响应计算的波函数法

针对非饱和地基土中埋置隧道的三维动力响应计算问题, 提出了波函数法.采用无限长的Flügge薄壁圆柱壳模拟圆形隧道衬砌,采用流、固、气组成的三相介质模拟非饱和地基土体.分别采用分离变量法以及Helmholtz矢量分解定理求解薄壁圆柱壳的振动控制方程与非饱和土的波动方程.根据隧-土交界面与地表面处的应力、位移以及孔隙流体压力等边界条件,利用平面波与柱面波的转换性质,实现了隧道内作用单位简谐载荷时隧道衬砌与土体系统动力响应的耦合求解.通过与既有单相弹性介质2.5维有限元-边界元法、两相饱和多孔介质2.5维有限元-边界元法以及三相非饱和介质Pip in Pip半解析法的计算结果进行对比, 验证了本文计算方法的可靠性. 最后,基于该方法, 通过算例分析了不同饱和度下非饱和土-隧道系统的动力响应特征.结果表明, 饱和度对土体动位移与超孔隙水压力的幅值响应有较大影响.该方法的非饱和地基土参数退化后,也可用来计算和分析饱和地基土或单相弹性地基土与隧道系统的动力响应.      

Geometrically nonlinear vibration of laminated composite cylindrical thin shells with non-continuous elastic boundary conditions

The geometrically nonlinear forced vibration response of non-continuous elastic-supported laminated composite thin cylindrical shells is investigated in this paper. Two kinds of non-continuous elastic supports are simulated by using artificial springs, which are point and arc constraints, respectively. By using a set of Chebyshev polynomials as the admissible displacement function, the nonlinear differential equation of motion of the shell subjected to periodic radial point loading is obtained through the Lagrange equations, in which the geometric nonlinearity is considered by using Donnell’s nonlinear shell theory. Then, these equations are solved by using the numerical method to obtain nonlinear amplitude–frequency response curves. The numerical results illustrate the effects of spring stiffness and constraint range on the nonlinear forced vibration of points-supported and arcs-supported laminated composite cylindrical shells. The results reveal that the geometric nonlinearity of the shell can be changed by adjusting the values of support stiffness and distribution areas of support, and the values of circumferential and radial stiffness have a more significant influence on amplitude–frequency response than the axial and torsional stiffness.

     

面向对象的土石坝参数随机反演程序设计

将储液容器流固耦合系统中的液体和容器分别视为理想可压缩流体和线弹 性固体，采用流体压力单元和固体壳单元对流固耦合系统进行有限元离散，得到一个非对称 的大型流固耦合有限元方程. 采用Arnoldi方法求解上面这个大型有限元方程的非对称特征 值问题，以得到储液容器的动力特性. 通过移频技术避免了处理零频问题，并构造了迭代格 式计算Arnoldi向量. 数值算例表明所用解法对于流固耦合系统都是非常有效的.     

同轴圆柱壳流固耦合附加质量研究

论文根据堆本体内窄间隙同轴设备支承筒的结构特征、边界条件和窄间隙环腔内流体流速,将结构简化为一端固定一端自由的同轴圆柱壳,将圆柱壳内外的流体简化为无旋、无黏、不可压缩流体.同轴圆柱壳通过流体压力场实现耦合,其径向位移模态决定了窄间隙流体域的压力场,故采用级数形式的圆柱壳径向正交位移模态构建既满足一端固定一端自由边界条件...     

Active sloshing control in a smart flexible cylindrical floating roof tank

An exact three dimensional fully-coupled hydro-elastic analysis for transient liquid sloshing in a partially-filled vertically-standing flexible circular cylindrical shell container fitted with a freely floating smart piezo-sandwich thin elastic circular plate is presented. The problem formulation is based on the linear water wave theory, the classical (Kirchhoff/Sanders) thin plate and shell models, Maxwell's equations of electrodynamics, Stokes’ transformation, and eigen-function expansions in cylindrical coordinates. The control action is achieved by combined volume displacement and volume velocity feedbacks (VDF, VVF) implemented in a second order active damping (AD) compensator via two competent evolutionary heuristic optimization techniques that systematically tune the controller gain parameters while constraining the floating panel displacement and control voltage. The uncontrolled and controlled transient responses of the coupled hydro-elastic system under various external disturbances (i.e., a harmonic base excitation, a real seismic event, a severe launch vehicle liftoff event, and a distributed impulsive transverse load on the floating panel) are calculated by means of Durbin's numerical inverse Laplace transform scheme. Moreover, the free vibration characteristics of the coupled fluid/structure interaction (FSI) system are briefly studied. The superior performance of the proposed active floating roof control configuration in effective suppression of the key hydro-elastic parameters (panel displacement, and shell displacements/stresses) is demonstrated. It is also found that, in the current FSI control problem, the Multi-objective Particle Swarm Optimization (MOPSO)-based ADC outperforms the Non-dominated Sorting Genetic Algorithm (NSGA-II)-based method, in terms of convergence rate and computational effort. Limiting cases are examined and the precision of results is verified by comparisons with the existing data as well as with the results produced by a commercial finite element package.     

Modelling techniques for fluid–solid coupling dynamics of bundle tubes vibrating and colliding in fluids

Nonlinear vibrations that occur in such bundle structures caused collisions between tubes and cross flows of the surrounding fluid. This paper presents modeling techniques for simulating the FSI dynamics of bundle tubes vibrating and colliding in fluids. A typical configuration of a three-dimensional tube bundles submerged in fluid of a cylindrical container is studied. Coupling conditions of displacement, velocity and forces are considered on the fluid-structure coupling interfaces. Contacts boundary between tubes and topological domain changes of the fluid are also considered on the fluid-structure coupling interface. Modeling techniques and algorithm are then established for flow-induced vibrations of the tubes, and collisions between tubes in fluids. The examples are presented to demonstrate the effectiveness of the proposed techniques. It has confirmed that our code produces the correct physics of the FSI problem, and capable of revealing the complex nonlinear mechanism with solid-solid contacts together with fluid-solid interactions.     

Vibration characteristics of a spherical–cylindrical–spherical shell by a domain decomposition method

A domain decomposition method is used to analyze the free and forced vibration characteristics of a spherical–cylindrical–spherical shell, based on Reissner–Naghdi's thin shell theory. The joined shell is divided into some cylindrical and spherical shell segments along the meridional (longitudinal) direction. Double mixed series, i.e., Fourier series and Chebyshev polynomials, are employed as the admissible displacement functions to obtain the discretized equation of motion for the joined shell. Numerical comparisons with the results derived by FEM and those available in the previous literature are made to validate the present method. Moreover, the effects of length-to-radius and radius-to-thickness ratios on the natural frequencies are also investigated.     

Vibroacoustic comparisons of composite laminated cylindrical shells according to three shear deformation shell theories

Whether the first-order and Reddy third-order shear deformation shell theories are able to evaluate the vibroacoustic responses of laminated cylindrical shells with normal deformation in the high frequency range or not is examined by comparison with a 3D higher-order shear deformation shell theory. The implicit governing equations of arbitrary angle-ply laminated cylindrical shells are derived from the 3D higher-order and Reddy third-order shell theories, and solved on the basis of the Fourier transform. The Reddy third-order shell theory can be obtained as a special case from the 3D higher-order shell theory. The first-order and Reddy third-order shell theories almost give rise to the same vibrational and acoustic results. These two simple shear deformation shell theories can be used to study far-field acoustic radiation from laminated cylindrical shells from the low to high frequency range, but they show some differences from the 3D higher-order shell theory in high frequency vibration of shells. Nevertheless, the differences of vibrational responses seem not to be distinct. The helical wave spectra of the higher-order radial displacements are nearly separate from those of the low-order radial displacement and play a minor role in far-field acoustic radiation, which makes the two simple shell theories applicable in prediction of acoustic power of the cylindrical shells in the much higher frequency range. Moreover, it also results in the fact that far-field sound is least sensitive in comparison with near-field sound and vibration of shells.     

VIBRATIONS OF CIRCULAR CYLINDRICAL SHELLS WITH NONUNIFORM CONSTRAINTS,ELASTIC BED AND ADDED MASS. PART II: SHELLS CONTAINING OR IMMERSED IN AXIAL FLOW

The model introduced in Part I of the present study is extended to take into account a flowing fluid, a mean radial pressure and initial pre-stress in circular cylindrical shells. The axial flow can be external, internal or annular and is described by the potential theory for inviscid and incompressible fluid. The computer program DIVA has been developed. It takes into account all the following complicating effects on the vibrations of circular cylindrical shells: (i) nonuniform boundary conditions around the shell edges including elastic boundary conditions; (ii) fluid–structure interaction including both flowing and quiescent fluids; (iii) internal, external and annular fluids; (iv) effect of a mean radial pressure and initial pre-stress; (v) elastic bed of partial extension in circumferential and longitudinal directions; (vi) intermediate constraints; (vii) added masses. It can be considered the most complete computer program specifically dedicated to dynamics of circular cylindrical shells. The Flügge theory of shells is used to describe the shell deformations. The system has been proved to be conservative for any combination of boundary conditions with restrained displacement at the shell ends. Numerical results show that shells clamped at the upstream end and simply supported at the downstream end have a larger critical velocity than simply supported shells, solving the paradox of Horáček and Zolotarev.     

The Problem of Forced Nonlinear Vibrations of Cylindrical Shells Completely Filled with Liquid

The forced nonlinear vibrations of a thin cylindrical shell completely filled with a liquid are studied. A refined mathematical model is used. The model takes into account the nonlinear terms up to the fifth power of the generalized displacement of the shell. The Bogolyubov’Mitropolsky averaging method is used to plot amplitude’frequency response curves for steady-state vibrations. The steady-state vibrations at the frequency of principal harmonic resonance are analyzed for stability__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 52–59, February 2005.