夹芯圆柱壳在水下爆炸载荷作用下的抗冲击特性

采用声固耦合方法对夹芯圆柱壳和等质量的普通圆柱壳在爆炸载荷作用下的应变、速度和加速度进行有限元计算。结果表明:夹芯防护层对爆炸冲击波可起到较好的衰减作用,即通过芯层的塑性变形,耗散了冲击过程中产生的大部分能量,对里面的圆柱壳体起到较好的保护作用,由于夹芯防护层的存在,与等质量的普通圆柱壳相比,夹芯圆柱壳能够承受更强的爆炸冲击波,降低结构的整体变形。     

The exact solution for thick laminated cantilever cylindrical shell

Discarding any assumption regarding displacement or stress models, the state equation for orthotropy is established in a cylindrical system. The exact solution is presented for the statics of thick closed laminated cantilever cylindrical shells. Every equation of elasticity can be satisfied and all the elastic constants are taken into account. Arbitrary precision of a desired order can be obtained. Project supported by the National Natural Science Foundation of China     

A diffusion problem with chemical reaction

Summary A substance is subjected to cylindrical Poiseuille flow, diffusion and a chemical reaction. In this paper the stationary state will be considered. It is assumed that the axial component of the diffusion can be neglected. Then the problem can be reduced to an eigenvalue problem determining an orthogonal set of eigenfunctions. Also a simplified model will be considered where the cylindrical wall is replaced by a flat wall. This problem can be solved by means of Laplace transformation. An explicit solution for the concentration at the wall has been obtained.     

基于能量原理的双稳态各向同性柱壳力学特性研究

双稳态结构可以在伸展和卷拢两种状态下均保持稳定,作为一种新型可展开空间结构,其在航空航天等领域具有广阔的应用前景。选取各向同性材料作为研究对象,并假定该材料为理想弹塑性材料。建立柱壳的力学计算模型,推导结构变形时应变能的解析表达式,基于能量原理导出柱壳在两个稳定状态下的卷曲半径。结果表明,基于全量理论和增量理论的模型均能反映结构的双稳态特性,但后者能更准确地预测两个稳态对应的卷曲半径的大小。对于文中给定的柱壳,全量理论导出的卷曲半径R3x相对于增量理论结果误差为5.2%~11.6%,R5y相对误差为29.8%~41.3%。另外,应用有限元软件ABAQUS对各向同性柱壳结构的双稳态过程进行数值模拟,数值结果与增量理论结果的相对误差为0.9%~13.2%,二者吻合较好。     

非圆柱壳在各种边界条件下的自由振动分析

本文用一种特殊的坐标变换将具有复杂截面形状的柱壳映射成圆柱壳,然后只需对变换后的圆柱壳作振动分析就可获得非圆柱壳在各种边界条件下的固有频率与振型。文中首次系统地给出了椭圆柱壳在各种边界条件下的频率系数,研究了拱预平底截面形状柱壳的自由振动问题。最后讨论了截面形状和边界条件变化对固有频率的影响,并和前人的研究结果作了比较,表明本方法是正确的。     

层叠式PVDF压电作动器及圆柱壳的振动主动控制

设计了一个层叠式PVDF压电作动器用于壳结构的振动控制。考虑压电层、粘接层、壳体耦合关系,推导了表面局部粘贴层叠式PVDF压电作动器的圆柱壳的振动控制方程,给出了作动力与压电层和粘接层层数、厚度之间的关系以及作动力与作动器粘贴位置之间的关系。针对一端固定、另一端自由的圆柱壳,进行了振动控制仿真。结果表明层叠式PVDF压电作动器作动力与作动器层数近似成线性关系,增大作动器层数能有效增大作动力,在低控制电压下能显著抑制圆柱壳振动,作动器周向不完全粘贴时,在径向产生的径向作动力对壳体横向振动控制非常有利。说明了层叠式PVDF压电作动器是一种可用于壳体结构振动并具有良好作动效果的作动器。     

双股燃气射流在充液室内扩展特性的实验研究

为了探索高温高压双股燃气射流在整装式液体工质中的扩展特性,设计了五级圆柱渐扩型观察室和圆柱型观察室,借助数字高速录像系统,观察了双股燃气射流在充液室中的扩展过程,对比了不同的观察室边界以及不同的参数条件对双股燃气射流扩展过程的影响。实验结果表明,圆柱渐扩型观察室结构更有助于改善气液的掺混特性,通过参数的合理匹配可以一定程度上控制双股燃气射流在三维充液室中的扩展过程。     

Tensile stability of cylindrical membranes

The tensile stability of rotationally symmetric thin membranes composed of isotropic, incompressible and elastic materials is considered by investigating under what conditions the initial equilibrium configuration can bifurcate to another rotationally symmetric equilibrium mode.The general equilibrium equations of a rotationally symmetric membrane are first derived in cylindrical coordinates. The initially cylindrical membrane is studied. The classic solution, which assumes homogeneous deformations, is shown to be a special case of the general equations. Perturbation theory is employed to find the bifurcation points from the homogeneous mode.This study shows that, for the chosen boundary conditions, no rotationally symmetric equilibrium mode exists near the cylindrical mode except the cylindrical mode itself. This corresponds to all experimental data that the author is aware of. The initially cylindrical membrane either remains cylindrical or goes into a non-rotationally symmetric mode.     

封闭圆柱腔内旋转点声源声压的近场频域解

在圆柱腔壁面为声学硬壁面的假定下，利用圆柱腔体空间内的格林函数导出了圆柱腔内旋转运动点声源空间声压的近场频域解；进而利用该频域解计算分析了旋转简谐单极子点源的声学特性。计算分析表明：由于考虑了壁面的影响，在圆柱腔体内，点声源旋转频率和源频率的变化将改变声压的空间指向性；源频率和旋转频率的增加伴随明显的多普勒效应，同时基频声压沿圆柱腔体轴线的分布从比较平缓变为明显波动；沿半径方向基频声压也波动变化。     

小波分析在圆柱壳结构损伤检测中的应用研究

为了检测出圆柱壳中的裂纹引起的损伤,利用sym4小波,对含裂纹圆柱壳的应变能曲线进行连续小波变换和多分辨分析,从小波系数出现局部模极大值来识别损伤的存在以及裂缝位置。通过分析和计算获得满意结果,表明此方法在圆柱壳结构损伤诊断中具有较高的应用价值。     

圆柱薄壳稳定性的一个修正理论

著名的唐乃尔(Donnell)——穆什塔利的简化壳体理论只能较精确地适用于较短圆柱壳稳定性计算.其近似性误差随长度与半径之比的增加而增大.本文考虑了横向切力的影响,对非完善型圆柱壳体推导了几何非线性理论的基本方程,建立了对各种长度半径比的圆柱壳体稳定性均适用的修正理论.     

ACTIVE CONTROL OF THE PIEZOELASTIC LAMINATED CYLINDRICAL SHELL''''S VIBRATION UNDER HYDROSTATIC PRESSURE

IntroductionDuetotheintrinsicdirectandconversepiezoelectriceffects,piezoelectricmaterialscanbeeffectivelyusedtoproducesensorsoractuatorsfortheactiveshapeorvibrationcontrolostructures.Therefore,theuseofpiezoelectricmaterialsinintelligentstructuresattractedmanyattentionsinrecentyears.Thedesignofsuchactivesystemsrequiresgoodunderstandingofthemechanical_electricinteractionbetweenthestructuresandpiezoelectricmaterials.Manyinvestigationshavebeendoneinthisfield[1].However,mostofthesestudiesarebasedo…     

Determination of surface heat transfer coefficients from measured temperature data for spherical and cylindrical bodies during cooling

In this paper which is a combination of the methodological and experimental aspects, models were developed for determining surface heat transfer coefficients for spherical and cylindrical bodies from their center temperature measurements during forced-cooling. Experiments involved the cooling of the individual spherical and cylindrical products as test samples in the air flow. The cooling parameters in terms of the cooling coefficients and lag factors were also determined to use in the present models. The results show that the surface heat transfer coefficients of the individual spherical and cylindrical products increased with an increase in the flow velocities from 1 to 2 m/s. It can be concluded that the present models have the capabilities of determining the surface heat transfer coefficients for spherical and cylindrical bodies with a single transient experiment.     

Analytical solution for axisymmetric problem of thick laminated closed cantilever shells in hamilton system

By giving up any assumptions about displacement models and stress distribution, the mixed state Hamilton equation for the axisymmetric problem of the thick laminated closed cantilever cylindrical shells is established. An identical analytical solution is obtained for the thin, moderately thick and thick laminated closed cantilever cylindrical shells. All equations of elasticity can be satisfied, and all elastic constants can be taken into account. This work is supported by the National Natural Science Foundation of China.     

弱粘结的斜交铺设层合圆柱壳的柱形弯曲

导出了两端简文的具有弱粘结界面的任意斜交铺设层合圆柱壳柱形弯曲问题的一个精确弹性理论解。分析中采用线性弹簧模型来表征界面的弱粘结特性。引进新的物理量改写了基本方程,导出了对应的状态空间列式,并利用变量替换技术将该状态方程转换成常系数状态方程,从而方便求解。最后给出了数值算例,并讨论了弱界面的影响。     

A closed-form solution procedure for circular cylindrical shell vibrations

A systematic procedure for obtaining the closed-form eigensolution for thin circular cylindrical shell vibrations is presented, which utilizes the computational power of existing commercial software packages. For cylindrical shells, the longitudinal, radial, and circumferential displacements are all coupled with each other due to Poissons ratio and the curvature of the shell. For beam and plate vibrations, the eigensolution can often be found without knowledge of absolute dimensions or material properties. For cylindrical shell vibrations, however, one must know the relative ratios between shell radius, length, and thickness, as well as Poissons ratio of the material. The mode shapes and natural frequencies can be determined analytically to within numerically determined coefficients for a wide variety of boundary conditions, including elastic and rigid ring stiffeners at the boundaries. Excellent agreement is obtained when the computed natural frequencies are compared with known experimental results.     

New matrix method for analyzing vibration and damping effect of sandwich circular cylindrical shell with viscoelastic core

Based on the linear theories of thin cylindrical shells and viscoelastic materials, a governing equation describing vibration of a sandwich circular cylindrical shell with a viscoelastic core under harmonic excitation is derived. The equation can be written as a matrix differential equation of the first order, and is obtained by considering the energy dissipation due to the shear deformation of the viscoelastic core layer and the interaction between all layers. A new matrix method for solving the governing equation is then presented With an extended homogeneous capacity precision integration approach. Having obtained these, vibration characteristics and damping effect of the sandwich cylindrical shell can be studied. The method differs from a recently published work as the state vector in the governing equation is composed of displacements and internal forces of the sandwich shell rather than displacements and their derivatives. So the present method can be applied to solve dynamic problems of the kind of sandwich shells with various boundary conditions and partially constrained layer damping. Numerical examples show that the proposed approach is effective and reliable compared with the existing methods.     

Free vibration analysis of a hung clamped-free cylindrical shell partially submerged in fluid

The free flexural vibration of a hung clamped-free cylindrical shell partially submerged in a fluid is investigated. The fluid is assumed to be inviscid and irrotational. The cylindrical shell is modelled by using the Rayleigh-Ritz method based on Sanders’ shell theory. The kinetic energy of the fluid is derived by solving the boundary-value problem related to the fluid motion. The natural vibration characteristics of the partially submerged cylindrical shell are discussed with respect to the added virtual mass approach. In this study, the nondimensionalized added virtual mass incremental factor for the partially submerged finite shell is derived. This factor can be readily used to estimate the change in the natural frequency of the shell due to the presence of a fluid.     

AN EXPERIMENTAL TECHNIQUE TO STUDY IMPULSE- WAVE PROPAGATION IN MATERIALS

A reliable experimental technique designed to study impulse-wave propagation in materials is described. This technique uses a mechanical shaker to subject vertically mounted cylindrical specimens to impulsive forces. The method is applicable to the study of impulse-wave propagation in cylindrical specimens when the length of the pulse is great compared to the diameter of the specimen, and the material is not stressed beyond its proportional elastic limit. The procedure is particularly suited for biomechanical measurements in which the specimen is to be subjected to repeated impulsive loading. Shockabsorption capacity of bone joints can be studied with this setup. The apparatus can also be used for modal analysis.