Analysis and optimization of laminated composite circular cylindrical shell subjected to compressive axial and transverse transient dynamic loads

Optimization is one of the important stages in the design process. In this paper the genetic algorithms method is applied for weight and transient dynamic response and two constraints including critical buckling loads and principle strains optimization of laminated composite cylindrical shells. The multi-objective function seeks the minimum structural weight and transient dynamic response. Nine design variables including material properties (fibre and matrix), volume fraction of fibre, fibre orientation and thickness of each layer are considered. In analytical solution, vibration of composite circular cylindrical shells are investigated based on the first-order shear deformation shell theory. The boundary conditions are assumed to be fully simply support. The dynamic response of the composite shells is studied under transverse impulse and axial compressive loads. The modal technique is used to develop the analytical solution of the composite cylindrical shell. The solution for the shell under the given loading conditions can be found using the convolution integrals. An example of simply supported laminated composite cylindrical shells is given to demonstrate the optimality of the solution obtained by the genetic algorithms technique. Results are shown that the weight coefficient of multi-objective function and the type of the constraints have considerable effect on the optimum weight and dynamic response.     

Dynamic buckling of stiffened cylindrical shells of revolution under a transient lateral pressure shock wave

A modal method of analysis is used to determine the response of an infinitely long stiffened cylindrical shell of revolution to a transient lateral pressure produced by an underwater explosion and propagating in an acoustic fluid. The shell is initially immersed, hence prestressed by the external hydrostatic pressure. A theory of dynamic buckling is then developed for cylindrical shells subjected to transverse pressure pulses of different durations.     

Free vibrations of fluid-filled cylindrical shells on elastic foundations

The free vibration characteristics of fluid-filled cylindrical shells on elastic foundations are presented by a semi-analytical finite element method. A shell is discretized into cylindrical finite elements where shell governing equations based shape functions in the longitudinal direction are used instead of the usual simple polynomials. Non-uniformities of the foundations in the circumferential and longitudinal directions are handled by the Fourier series and an element mesh strategy, respectively. The fluid domain is described by the potential flow theory. The hydrodynamic pressure acting on shells is derived from the condition for dynamic coupling of the fluid-structure. The effect of fluid in a shell, shell geometries, and foundation parameters on the dynamic behavior of fluid-containing shells is investigated. Numerical results based on the present method converge more rapidly than those obtained by the simple polynomial formulation. The method is suitable for the problem considered due to its generality, simplicity, and potential for further development.     

浅析湿陷性黄土地基的处理方法

阐述了湿陷性黄土的性质,介绍了几种湿陷性黄土地基的处理方法,包括垫层法、强夯法、灰土桩挤密法、化学加固法、预浸水法等,以提高人们对湿陷性黄土地基处理方法的认识。     

Static and transient response of cylindrical shells

Static and transient analysis of composite cylindrical shells is presented using a recently proposed shear deformation theory. The dynamic response is obtained by employing the numerical time integration scheme due to Newmark. The results obtained by using classical shell theory (CST) and Mindlin-type shear deformation theory (SDT) are compared with those obtained by using the proposed theory. The comparison studies reveal that the linear stress distribution, as assumed in CST and SDT, differs considerably from the predicted nonlinear distribution of the proposed theory.     

单层柱面索拉网壳结构动力特性分析

柱面索拉网壳是一种新型的玻璃采光顶支撑结构。讨论这种结构的动力特性,比较单层柱面索拉网壳和单层柱面网壳的自振频率及其相应振型。通过计算,分析长跨比、矢跨比、索截面、索初始预应力、钢杆件截面对柱面索拉网壳动力特性的影响。计算结果显示:单层柱面索拉网壳的动力特性优于单层柱面网壳;单层柱面索拉网壳的自振频率随着钢杆件及索截面的增大而增大,随长跨比的增大而减小。索的初始张拉力对索拉网壳的动力特性影响很大。     

Dynamic effects on buckling and energy absorption of cylindrical shells under axial impact

The crushing behaviour of aluminium and steel cylindrical shells, when subjected to an axial impact, is examined using a numerical simulation. The influence of the material properties, shell geometry, boundary conditions and loading techniques on the energy absorbed and the buckling shapes is explored. Various shell response characteristics, such as the peak load, fold lengths, axial compression and energy absorption are studied. An examination is also made of the influence of filtering on the accuracy of data obtained usually in dynamic tests.     

Dynamic torsional buckling of cylindrical shells in Hamiltonian system

By considering the effect of stress waves in a Hamiltonian system, this paper treats dynamic buckling of an elastic cylindrical shell which is subjected to an impact torsional load. A symplectic analytical approach is employed to convert the fundamental equations to the Hamiltonian canonical equations in dual variables. In a symplectic space, the critical torsion and buckling mode are reduced to solving the symplectic eigenvalue and eigensolution, respectively. The primary influence factors, such as the impact time, boundary conditions and thickness, are discussed in detail through some numerical examples. It is found that boundary conditions have limited influence except free boundary condition in the context of the scope in this paper. The localization of dynamic buckling patterns can be observed at the free end of the shell. The new analytical and numerical results serve as guidelines for safer designs of shell structures.     

利用Hamilton函数分析圆柱壳动态扭转屈曲

在Hamilton函数中考虑应力波的影响,研究冲击扭转载荷作用下弹性圆柱壳的动态屈曲。采用辛方法将基本方程转化为对偶变量的Hamilton典型方程。在辛空间将临界扭转和屈曲模式分别简化为求解辛本征值和本征解问题。主要影响因素有冲击时间、边界条件和厚度等,通过数值算例对这些因素进行了详细讨论。研究结果表明,边界条件的影响有限(自由边界条件除外)。在壳体自由端能够观察到局部动态屈曲模式。新的分析和数值模拟结果可作为壳结构的安全设计准则。     

A numerical investigation of dynamic plastic buckling behaviour of thin-walled cylindrical structures with several geometries

In this study dynamic buckling behaviors of an aluminum alloy cylindrical shell with axial linear variable thickness, discontinuity and conical shaped have been numerically investigated for high velocity impact by means of finite element method. The validation of finite element model was provided by the results of previous studies in literature. Throughout study commerce finite element package program LS-DYNA3D was used and all simulations were fulfilled as explicitly. According to results obtained, the minor changes in the geometry are able to convert the dynamic plastic buckling into dynamic progressive buckling behavior. This study indicates that which of the dynamic buckling or progressive buckling mechanism will be dominant is sensitive to geometrical properties for cylindrical aluminum alloy shells under the high velocity impact.     

Transient vibrations of laminated composite cylindrical shells exposed to underwater shock waves

The problem of the transient vibration of an elastic laminated composite cylindrical shell with infinite length exposed to an underwater shock wave is solved approximately. The linear acoustic plane wave assumption and Sanders thin shell theory are adopted. The reflected-afterflow virtual-source (RAVS) procedure is used to model the fluid–structure interaction involved during the underwater shock event. For the validity of the present analysis, the response of a laminated cylindrical shell under step plane wave is first analyzed and compared with the numerical solution available in the literature. Detailed numerical results for the transient responses of the shells under an exponentially decaying underwater shock wave are presented, and the influences of fiber angle, shell radius and thickness upon the dimensionless radial velocity, mid-surface strain, 0th mode radial displacement and 1st mode radial velocity of the shells, are investigated.     

冲击荷载作用下带下部钢管柱单层球面网壳结构动力响应分析

为研究带下部钢管柱的单层球面网壳在冲击荷载下的动力响应,在ANSYS/LS DYNA中建立70 m跨度带下部钢管柱的K8型单层球面网壳与正方体冲击物的数值模型并进行数值分析。根据结构动力响应和最终变形,总结了结构在冲击荷载作用下的4种响应模式,并分析了各响应模式下的动力响应（冲击力、节点速度、节点位移、杆件应力）特点。通过改变冲击点位置以及下部柱高度等参数,分析这些参数对带下部钢管柱的单层球面网壳结构响应模式的影响,揭示了结构响应随各参数的分布规律。研究结果表明:水平侧向冲击作用下结构的冲击力主要为等腰三角形脉冲荷载;冲击柱顶点时,上部结构有杆件失效,结构的节点水平位移和杆件应力最大;冲击柱高度较低时,冲击力峰值较小,节点最大水平位移和杆件最大应力较大。     

单层柱面铝合金网壳结构强震失效机理及地震易损性

通过有限元分析软件ABAQUS建立了单层柱面铝合金网壳结构的有限元分析模型,利用增量动力分析方法（IDA）对网壳结构进行强震作用下动力响应全过程分析,获得了单层柱面铝合金网壳结构强震失效模式。基于模糊数学理论提出单层柱面铝合金网壳结构强震失效判别方法,结合结构损伤理论拟合网壳结构强震损伤因子,通过大规模参数分析定义适用于铝合金网壳结构的损伤程度分级,对铝合金网壳结构不同损伤状态进行划分。通过随机抽样选取一定数量的结构-地震样本,对铝合金网壳结构开展地震易损性分析,通过回归分析建立地震易损性函数,获得单层柱面铝合金网壳结构的概率地震易损性曲线。结果表明：通过结构地震易损性分析可以看出铝合金网壳结构具有良好的抗震性能,在强震作用下保持基本完好或仅有轻微破坏的概率较大。     

板锥柱面网壳结构的动力特性研究

考虑不同跨度、厚度、矢跨比等因素对网壳结构动力特性的影响，本文采用子空间迭代法，对板锥柱面网壳的动力特性进行了系统分析研究，在大量参数分析、计算的基础上，得出了板锥柱面网壳结构的自振规律，对板锥柱面网壳结构的抗震设计有重要的参考价值。     

Recent advances on postbuckling analyses of thin-walled structures: Beams, frames and cylindrical shells

The lateral postbuckling response of thin-walled structures such as bars and frames with members having steel rolled shapes as well as circular cylindrical shells under axial compression is thoroughly reconsidered. More specifically via a simple and very efficient technique it is found that beams with rolled shapes (symmetric or non symmetric) under uniform bending and axial compression exhibit a stable lateral-torsional secondary path with limited margins of postbuckling strength. New findings for the static and dynamic stability of frames with crooked steel members-due to the presence of residual stresses-are also reported. It is comprehensively established that the coupling effect due to initial crookedness and loading eccentricity may have a beneficial effect on the load-carrying capacity of the frames. Moreover, simple mechanical models are proposed for simulating the buckling mechanism of axially compressed circular cylindrical shells. Very recently Bodner and Rubin proposed an 1-DOF mechanical model whose buckling parameters correlated to those of the shells by using an empirical formula based on experimentally observed shell buckling loads. In the present analysis a new 2-DOF model for the static and dynamic buckling of axially compressed circular cylindrical shells, which can include mode coupling, is presented.     

某储仓三心圆柱面四角锥网壳结构设计

某储仓采用双层三心圆柱面四角锥网壳结构,从结构选型、动力响应、结构分析以及节点构造和防腐、防火设计等方面进行分析。利用SAP2000和3d3s结构分析软件对整体结构进行动力响应分析和静力计算,考虑各种工况的组合。分析表明各种参数指标均满足相应规范要求,可供同类工程参考。     

两种正四角锥形柱面网壳参数化建模

根据正四角锥形柱面网壳特点,采用ANSYS软件自带参数化设计语言APDL（ANSYS Parametric Design Language）,研制了正四角锥体系柱面网壳参数化建模宏程序;实现了给定柱面网壳跨度S、矢高F、跨度方向网格数m、长度方向网格数n参数下,该类柱面网壳的参数化建模。建模设计实例表明,该参数化建模宏程序简单、高效、实用,为采用ANSYS软件进行不同类型、不同几何参数下柱面网壳结构建模奠定了良好的基础。     

Dynamic elastic instability of long circular cylindrical shells under pure bending

The present paper studies the responses and instabilities of long circular cylindrical shells subjected to dynamic pure bending. The dynamic instability characteristics of the shells subjected to a sudden step bending load of infinite duration are explored. Analysis is performed using nonlinear finite element numerical methods. Critical dynamic moments are determined through the use of Budiansky and Routh's stability criterion. Numerical predictions for the dynamic instability are compared with those static results given earlier by Brazier. The effects of shell geometry on the dynamic stability of the shells are shown. It is found that the dominating factor to affect the shell stability is the ovalization of the shell cross-section in the centre of the shell.     

单层柱面网壳结构风振响应分析

风荷载在大跨度屋盖结构设计中常常起主要甚至决定性作用,这使得该类结构的风荷载及风致动力响应研究日益受到关注与重视。利用随机模拟时程分析方法对三向网格单层柱面网壳结构的风振性能进行了系统的参数分析,探讨了几何参数、气动参数、结构参数等因素对结构风振响应规律的影响,并在此基础上给出了可供单层柱面网壳结构抗风设计参考的风振系数。     

Buckling and postbuckling of cylindrical shells with one end pinned and the other end free

Using finite element analysis, this paper examines the linear bifurcation buckling loads, and nonlinear collapse loads, of cylindrical shells with one end pinned and the other end free, under a variety of axial and pressure load combinations. The pinned end is formulated so as to provide no axial restraint. For the bifurcation analysis, loads are related back to the classical solutions for cylinder buckling loads, to explain the very low values found for this set of boundary conditions.The nonlinear analysis includes both imperfections and material plasticity. In this analysis, it is found that cylindrical shells with pinned-free boundary conditions are notably imperfection insensitive, and for a range of geometries are able to reach collapse loads significantly greater than their bifurcation load. For other geometries, collapse loads very close to the bifurcation load are found. This unusual imperfection insensitivity for a cylindrical shell is explained in terms of the large flexibility engendered by the pinned-free boundary conditions and the oval buckling mode.