Vibration and Acoustic Radiation from Orthogonally Stiffened Infinite Circular Cylindrical Shells in Water

Based on the motion differential equations of vibration and acoustic coupling system for thin elastic shells with ribs, by means of the Fourier integral transformation and the Fourier inverse transformation, as well as the stationary phase method, an analytic solution, which has satisfying computational effectiveness and precision, is derived for the solution to the vibration and acoustic radiation from a submerged stiffened infinite circular cylinder with both ring and axial ribs. It is easy to analyze the effect of stiffening supports in the acoustic radiation field by use of the formulas obtained by the presented method and corresponding numerical computation. It is shown that the axial-stiffeners can improve the mechanical and acoustical characteristics. Moreover, the present method can be used to study the acoustic radiation mechanism of the type of structure.

Strength Reliability Analysis of Stiffened Cylindrical Shells Considering Failure Correlation

The stiffened cylindrical shell is commonly used for the pressure hull of submersibles and the legs of offshore platforms. There are various failure modes because of uncertainty with the structural size and material properties, uncertainty of the calculation model and machining errors. Correlations among failure modes must be considered with the structural reliability of stiffened cylindrical shells. However, the traditional method cannot consider the correlations effectively. The aim of this study is to present a method of reliability analysis for stiffened cylindrical shells which considers the correlations among failure modes. Firstly, the joint failure probability calculation formula of two related failure modes is derived through use of the 2D joint probability density function. Secondly, the full probability formula of the tandem structural system is given with consideration to the correlations among failure modes. At last, the accuracy of the system reliability calculation is verified through use of the Monte Carlo simulation. Result of the analysis shows the failure probability of stiffened cylindrical shells can be gained through adding the failure probability of each mode.

Postbuckling of Imperfect Stiffened Cylindrical Shells Under Combined External Liquid Pressure and Axial Compression

posthuckling analysis is presented for the stilTened cylindrical shell of finite length subjected to combined loading of external liquid pressure and axial compression. The formulations are based on a boundary layer theory of shell buckling, which includes the effects of nonlinear prebuckling deformations, nonlinear large deflections in the postbuckling range and initial geometrical imperfections of the shell. The 'smeared stifl'cner' approach is adopted for the stiffencrs. In the analysis a singular perturbation technique is used (o determine the interactive buckling loads and the postbuckling paths. Numerical examples cover the performance of perfect and imperfect, stringer and ring stiffened cylindrical shells. Typical results arc presented in the dimcnsionless graphical form.

Effect prediction of stiffened-ring cylindrical shells subjected to drop mass impact

This study focuses on the effect of lateral mass impact on ring-stiffened thin-walled cylindrical shell.Cylindrical shells were fabricated to validate the numerical modeling and analytical techniques,and drop tests were performed using a rigid spherical indenter.Next,stiffened-ring cylindrical shells with various structural size parameters were simulated using ABAQUS software.The relationships between the impact force,deformation displacement,and rebound velocity were established,on the basis of impact mechanics theory and simulation results.It derived fitting functions to analyse the relationship between the maximum load and maximum displacement of ring-stiffened cylindrical shell under dynamic mass impact.Based on the validation of the simulation model,the fitting function data were compared with the simulation results,and the functions showed a good accuracy.Besides,the parameters,mass ratio and stiffened-ring mass ratio were used to reflect the effect of the mass change in the ring-stiffened cylindrical shell.Furthermore,parametric studies on ring-stiffened cylindrical shell models were conducted to analyse the progressive impact responses.

DYNAMIC BUCKLING OF STATICALLY PRELOADED RING-STIFFENED CYLINDRICAL SHELLS UNDER AXIAL FLUID-SOLID IMPACT LOADING

The Initial Imperfection Amplified Criterion is applied toinvestigate the geometric nonlinear dynamic buckling of staticallypreloaded ring-stiffened cylindrical shells under axial fluid-solidimpact. Tak- ing account of the effects of large deformation andinitial geometric imperfection, the governing equations are obtainedby the Galerkin method and solved by the Runge-Kutta method. Theeffects of static preloading (uniform external radial pressure) onthe buckling features and the load-carrying ability of ring-stiffenedcy- lindrical shells against axial impact are discussed.

BUCKLING AND POSTBUCKLING OF STIFFENED CYLINDRICAL SHELLS UNDER AXIAL COMPRESSION

Buckling and postbuckling behaviors of perfect and imperfect, stringer and ortho/ropically stiffened cylindrical shells have been studied under axial compression. Based on the boundary la ver theory for the buckling oj thin elastic shells suggested in ref. [1], a theoretical analysis is presented. The effects of material properties of stiffenefs and skin, which are made of different materials, on the huckling load and postbuckling behavior of stiffened cylindrical shells have also been discussed.

POSTBUCKLING OF IMPERFECT STIFFENED CYLINDRICAL SHELLS UNDER COMBINED EXTERNAL PRESSURE AND HEATING

A postbuckling analysis is presented for a stiffened cylindrical shell of finite length subjected to combined loading of external pressure and a uniform temperature rise. The formulations are based on a boundary layer theory of shell buckling, which includes the effects of nonlinear prebuckling deformations, nonlinear large deflections in the postbuckling range and initial geometrical imperfections of the shell. The 'smeared stiffener' approach is adopted for the stiffeners. The analysis uses a singular perturbation technique to determine the interactive buckling loads and the postbuckling equilibrium paths. Numerical examples cover the performances of perfect and imperfect, stringer and ring stiffened cylindrical shells. Typical results are presented in dimensionless graphical form.

KOITER-BOUNDARY LAYER SINGULAR PERTURBATION METHOD FOR AXIAL COMPRESSED STIFFENED CYLINDRICAL SHELLS

The double singularities induced by bifurcation point and boundary layer in non-dimensionalized nonlinear boundary-layer Karman-Donnell equations for axially compressed stiffened cylindrical shells can be treated by Koiter-boundary layer singular perturbation method in this paper. It is demonstrated that the method has high computing efficiency and accuracy based on the analysis of AS-2 shell, and some new conclusions can be directly obtained from the perturbation formulas which are very well in agreement with experimental phenomenon of axially compressed stiffened cylindrical shells.

New matrix method for response analysis of circumferentially stiffened non-circular cylindrical shells under harmonic pressure

Based on the governing equation of vibration of a kind of cylindrical shells written in a matrix differential equation of the first order, a new matrix method is presented for steady-state vibration analysis of a noncircular cylindrical shell simply sup- ported at two ends and circumferentially stiffened by rings under harmonic pressure. Its difference from the existing works by Yamada and Irie is that the matrix differential equation is solved by using the extended homogeneous capacity precision integration＇ approach other than the Runge-Kutta-Gill integration method. The transfer matrix can easily be determined by a high precision integration scheme. In addition, besides the normal interacting forces, which were commonly adopted by researchers earlier, the tangential interacting forces between the cylindrical shell and the rings are considered at the same time by means of the Dirac-δ function. The effects of the exciting frequencies on displacements and stresses responses have been investigated. Numerical results show that the proposed method is more efficient than the aforementioned method.

ANALYTICAL SOLUTION OF RADIATED SOUND PRESSURE OF RING－STIFFENED CYLINDRICAL SHELLS IN FLUID MEDIUM

In this paper, analytical formularions of radiated sound pressure of ring-stiffenedcylindrical shells in fluid medium are derived by means of Hamilton's principleHuygens principle and Green function . These formulations Can be used to compute the sound pressure of the shell's surface nearfield and farfield.

Mechanical and thermal postbuckling of FGM thick circular cylindrical shells reinforced by FGM stiffener system using higher-order shear deformation theory

The postbuckling of the eccentrically stiffened circular cylindrical shells made of functionally graded materials （FGMs）, subjected to the axial compressive load and external uniform pressure and filled inside by the elastic foundations in the thermal environments, is investigated with an analytical method. The shells are reinforced by FGM stringers and rings. The thermal elements of the shells and stiffeners in the fundamental equations are considered. The equilibrium and nonlinear stability equations in terms of the displacement components for the stiffened shells are derived with the third-order shear deformation theory and Leckhniskii smeared stiffener technique. The closed-form expressions for determining the buckling load and postbuckling load-deflection curves are obtained with the Galerkin method. The effects of the stiffeners, the foundations, the material and dimensional parameters, and the pre-existent axial compressive and thermal load are considered.

Nonlinear stability of functionally graded material(FGM)sandwich cylindrical shells reinforced by FGM stiffeners in thermal environment

In this paper, Donnell＇s shell theory and smeared stiffeners technique are improved to analyze the postbuckling and buckling behaviors of circular cylindrical shells of stiffened thin functionally graded material （FGM） sandwich under an axial loading on elastic foundations, and the shells are considered in a thermal environment. The shells are stiffened by FGM rings and stringers. A general sigmoid law and a general power law are proposed. Thermal elements of the shells and reinforcement stiffeners are considered. Explicit expressions to find critical loads and postbuckling load-deflection curves are obtained by applying the Galerkin method and choosing the three-term approximate solution of deflection. Numerical results show various effects of temperature, elastic foundation, stiffeners, material and geometrical properties, and the ratio between face sheet thickness and total thickness on the nonlinear behavior of shells.

ANALYSIS OF SOUND RADIATION FROM THE RING-STIFFENED CYLINDRICAL SHELL COATED WITH VISCOELASTIC LAYER IN FLUID MEDIUM

The Donnell theory of shell is applied to describe shell motion and layer motion is described by means of three-dimensional Navier equations.Using deformation harmonious condi- tions of the interface,the effects of stiffeners and layer are treated as reverse forces and moments acting on the cylindrical shell.In studying the acoustic field produced by vibration of the sub- merged ring-stiffened cylindrical coated shell,the structure dynamic equation,Helmholtz equation in the fluid field and the continuous conditions of the fluid-structure interface compose the cou- pling vibration equation of the sound-fluid-structure.The extract of sound pressure comes down to the extract of coupling vibration equation.By use of the solution of the equation,the influ- ences of hydrostatic pressure,physical characters and geometric parameters of the layer on sound radiation are discussed.

Nonlinear Buckling Analysis of Pre-stressed Ring-Stiffened Circular Cylindrical Shells Under External Pressure

This paper is concerned with the nonlinear buckling behavior of pre-stressed ring-stiffened thin circular cylindrical shells under external pressure.According to the geometrical nonlinearity,governing equations are derived by incorporating initial stresses based on Donnell-type shell theory.The "smeared stiffeners" approach is used for ring stiffeners.The numerical analyses are conducted by Gelerkin's method to obtain critical buckling loads of shells.This study shows effects of initial stresses on stability of shells.Moreover,effects of initial stresses on buckling modes of shells are discussed.

深海无人系统大长径比环肋圆柱壳结构设计与试验研究

环肋圆柱壳是深海无人系统广泛采用的一种耐压结构形式,保障其结构安全是系统研制过程中非常重要的一环。针对环肋圆柱壳的结构特征推导了组合结构重量关系式和结构参数简化估算方法,并以一种超长型深海无人系统耐压结构为例,围绕大长径比环肋圆柱壳的结构形式、设计计算、仿真分析、模型验证等开展研究。研究表明提出的大长径比环肋圆柱壳结构设计参数简化估算方法具有较好的适应性。相关计算和分析结果可以为该型深海无人系统结构设计提供技术支撑,也可以为其他类似耐压结构设计提供参考。

不同水下爆炸参数下双层加筋圆柱壳结构响应研究

本文采用声固耦合方法模拟水下中远场爆炸产生的冲击波载荷和气泡脉动对双层加筋圆柱壳的冲击响应。从不同工况水下爆炸载荷下的鞭状运动和关键部位冲击响应2个方面,研究了药量、爆距、水深、爆炸方位等参数对双层加筋圆柱壳结构响应的影响。研究表明,在中远场水下爆炸作用下,双层加筋圆柱壳在不同药量和爆距下鞭状运动的位移响应幅值和冲击环境谱加速度幅值变化较大,但其鞭状运动的位移响应曲线的周期变化不大。双层加筋圆柱壳在不同水深下,鞭状运动受到水下载荷周期性影响显著,但谱加速度幅值变化不大。双层加筋圆柱壳在不同爆炸方位下鞭状运动变化和冲击环境谱加速度分布受其影响显著。这项研究旨在为水下中远场爆炸作用下,水下航行体结构的抗冲击特性研究提供数据及理论支撑。

螺旋加筋圆柱壳屈曲特性试验及数值研究

为研究均匀外压下,螺旋加筋圆柱壳的屈曲特性,制作2组螺旋加筋圆柱壳和不加筋圆柱壳,并对其开展几何测量和静水压力测试。其次,基于实测初始几何缺陷,对螺旋加筋圆柱壳和圆柱壳开展非线性数值分析,数值分析与试验结果具有良好一致性。最后,研究圆柱壳长度与肋骨螺距之比(长度螺距比)、肋骨截面类型对螺旋加筋圆柱壳屈曲载荷的影响规律。结果表明,螺旋加筋可使圆柱壳获得52.6%的极限载荷增益;随着长度螺距比增大,螺旋加筋圆柱壳的屈曲载荷也随之增大,但受缺陷幅值的影响也变大;L型截面的螺旋肋骨相较于矩形截面和工字型截面,屈曲载荷提升效果最优,最大提升14.6%。

附水复杂圆柱壳的声振分析及实验对比

提出了一种求解内部复杂结构的水下圆柱壳声振特性的计算方法,计算了含内部结构的加筋圆柱壳附水壳体的低频段振动响应及全频段声辐射特性,低频段采用有限元(FE)法,中、高频段采用统计能量分析(SEA)法,实验验证了有限元-统计能量分析(FE-SEA)方法的准确性。结果表明:低频段振动响应和全频段声辐射计算结果与实验结果吻合良好,FE和SEA方法分别在1~1000 Hz和1~10 kHz范围内可获得较准确的结果,说明FE-SEA方法求解含内部结构的圆柱壳的声振特性是可行的,但需要确定不同频段的计算方式。由于网格质量的限制,FE方法对中、高频的计算不具有优势,SEA方法关注结构平均功率流,无法获得具体位置振动响应。

水下双层加肋圆柱壳全空间收发分置散射声场快速预报方法

针对水下双层加肋圆柱壳的全空间收发分置散射声场求解,提出了一种快速预报方法。该方法将散射声场表示为声散射传递函数与声源密度函数的乘积,以目标表面网格信息、少量的仿真或测试多基地散射声压数据作为已知信息,借助数值积分、矩阵理论、最小二乘法对其他收发分置散射声场进行预报。分别以有限元仿真和试验测试的散射声压数据作为输入,对水下双层加肋圆柱壳的多基地散射声场进行了计算,并与完全采用有限元方法的计算结果进行了对比。结果表明:该方法在目标表面结构和部分散射声场数据已知条件下能对目标的全空间收发分置散射声场进行预报;已知散射声压数据量越多,计算频率越低,预报精度越高。

几何参数对加筋圆柱壳轴压屈曲折减因子的影响

加筋圆柱壳广泛应用于航天运载器结构中。受制造工艺影响,实际产品总是存在无法避免的几何缺陷,导致实际航天运载器结构的轴压承载力远低于理论解,需要引入一个0-1之间的折减因子乘上理论解来进行修正,令理论解在保证安全的同时尽可能接近实验值。当结构的几何参数在设计迭代过程中调整时,折减因子的值也可能会随之改变。厘清折减因子随结构几何参数发生改变时的变化规律,有助于便捷、准确地得到合适的折减因子值,从而保证结构安全、降低重量、缩短设计周期。介绍了基于边界扰动载荷法的实现过程,针对主要分析参数进行了收敛性考察,明确了分析参数的选取原则。基于该方法研究了结构的典型参数发生变化时折减因子相应的变化规律。结果表明,折减因子随蒙皮厚度的增加而线性增加,随纵筋截面面积的增加而线性减小,即蒙皮厚度越大、纵筋越是低而薄,则折减因子值越大、结构的缺陷敏感性也越低,而壳体高度的变化则对折减因子没有显著影响。