Vibration and Sound Radiation of Cylindrical Shell Covered with a Skin Made of Micro Floating Raft Arrays Excited by Turbulence

To reduce the vibration and sound radiation of underwater cylindrical shells,a skin composed of micro floating raft arrays and a compliant wall is proposed in this paper.A vibroacoustic coupling model of a finite cylindrical shell covered with this skin for the case of turbulence excitation is established based on the shell theories of Donnell.The model is solved with the modal superposition method to investigate the effects of the structural parameters of micro floating raft elements on the performance of reducing vibration and sound radiation of the cylindrical shell of this skin.The results indicate that increasing the stiffness ratio,damping ratio,mass ratio,or decreasing the interval betweenmicro floating raft elements can improve the vibration and sound radiation reduction performance of this skin over the frequency range 0∼2000 Hz.Moreover,the mean quadratic velocity level and sound radiation power level of the finite cylindrical shell with this skin can be reduced by 12.00 dB and 9.65 dB respectively compared to the finite cylindrical shell with homogeneous viscoelastic coating in the frequency range from0∼2000Hz,implying a favorable performance of this skin for reducing the vibration and sound radiation of cylindrical 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.

Research on vibration and near-field sound radiation of ring-ribbed cylindrical shell coated deadening and decoupling materials

The research on structural vibration and sound radiation of underwater ring-ribbed cylindrical shell, which is coated with a kind of deadening and decoupling materials, becomes a focus in recent years. This paper analyzes the problem on two aspects: model experiment and numerical calculation. The model experiment is carried out including three cases firstly, in which the structural vibration response and radiating acoustic field are measured respectively, and the results gained in these three cases are analyzed to discuss the effect of reducing structural vibration and radiating noise of the deadening and decoupling materials. The coupling FEM/BEM and the SEA methods are both used in numerical calculation, i.e. the arithmetic of the coupling FEM/BEM method is adopted to calculate the low frequency characteristics and the SEA method is adopted to calculate the medium-high frequencies characteristics of the model. By comparing experimental results with numerical calculation results, it is proved that the algorithm adopted in this paper is reasonable.

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.

THEORETICAL PREDICTION OF SOUND RADIATION FROM A HEAVY FLUID-LOADED CYLINDRICAL COATED SHELL

A theoretical model is developed to predict the sound radiation ability of a cylindrical thin elastic shell of finite length, covered with a damp layer and terminated with infinite cylindrical rigid baffles. This shell is immersed in a heavy fluid extending up to infinity, and excited by a constant point load continuously traveling along the circumferential direction. A frequency-domain representation of the rotating load and three equations of the vibroacoustic coupling problem are given. The equations are solved by means of modal analysis method and asymptotic expansion method. Also, a mathematical expression of modal amplitude of shell radial displacement is obtained. The sound radiation ability of this kind of shell is evaluated and the corresponding numerical results are given.

A General Method to Study the Sound Radiation of a Finite Cylindrical Shell Based on Elastic Theory

一个一般方法被建议与有弹性的理论学习有限的圆柱的壳的声音和颤动。这个方法通过有弹性的方程的分解和薄壳理论分析的有限的圆柱的壳的答案的结构获得的解开的 Helmholtz 方程的全面分析被开发。建议方法对壳和任何频率的任意的厚度理论上合适。另外，通过方法获得的结果能被用来决定薄壳理论的申请的范围。而且，建议方法能处理薄壳理论限制的问题。另外，方法能对象使硬戒指的圆柱的壳，抑制的圆柱的壳，和两倍圆柱的壳那样的复杂的圆柱的壳的几种类型合适。

Time-domain analysis for vibration and sound radiation of submerged spherical shell excited by force

The vibration and sound radiation of a submerged spherical shell are studied in the time-domain by Laplace transform method, where a CW pulse force acts at the apex of the shell. The numerical results for the case of long pulse show that the different vibrational modes and the resonant or beat radiated sound are excited for different carrier-frequencies, but litle sound is radiated for some vibrational modes. For the case of short pulse the waveforms of the pulse become widened and deformed, when the pulse propagates between apexes of the shell. Then, the Doubly Asymptotic Approximations (DAA2) and Kirchhoff's Retarded Potential Formulate (KRPF)are used to solve the same problem. It is shown that the results of DAA2 and KRPF method have a good agreement with the results of Laplace transform method.

A FINITE ELEMENT/BOUNDARY ELEMENT——MODIFIED MODAL DECOMPOSITION METHOD FOR VIBRATION AND SOUND RADIATION FROM SUBMERGED SHELL OF REVOLUTION

A finite element / boundary element-modified modal decomposition method (FBMMD) is presented for predicting the vibration and sound radiation from submerged shell of revolution. Improvement has been made to accelerate the convergence to FBMD method by means of introducing the residual modes which take into accaunt the quasi -state contributiort of all neglected modes. As an example, the vibration and sound radiation of a submerged spherical shell excited by axisymmetric force are studied in cases of ka=l,2,3 and 4. From the calculated results we see that the FBMMD method shows a significant improvement to the accuracy of surface sound pressure, normal displacement and directivity patterns of radiating sound, especially to the directivity patterns.

Sound radiation of a functionally graded material cylindrical shell in water by mobility method

Based on the fundamental dynamic equations of functionally graded material (FGM) cylindrical shell, this paper investigates the sound radiation of vibrational FGM shell in water by mobility method. This model takes into account the exterior fluid loading due to the sound press radiated by the FGM shell. The FGM cylindrical shell was excited by a harmonic line radial force uniformly distributing along the generator. The FGM shell equations of motion, the Helmholtz equation in the exterior fluid medium and the continuity equation at fluid-shell interface are used in this vibroacoustic problem. The expressions of sound radiation efficiency and sound field of the FGM shell have been derived by mobility method. Radiation efficiency, modal mobility and the directivity pattern of the sound field are solved numerically. In particular, radiation efficiency and directivity pattern with various power law index are analyzed.

A NOVEL SEMI-ANALYTICAL METHOD FOR SOLVING ACOUSTIC RADIATION FROM LONGITUDINALLY STIFFENED INFINITE NON-CIRCULAR CYLINDRICAL SHELLS IN WATER

Based on the extended homogeneous capacity high precision integration method and the spectrum method of virtual boundary with a complex radius vector, a novel semi-analytical method, which has satisfactory computation efectiveness and precision, is presented for solving the acoustic radiation from a submerged infnite non-circular cylindrical shell stifened by longitudinal ribs by means of the Fourier integral transformation and stationary phase method. In this work, besides the normal interacting force, which is commonly adopted by some researchers, the other interacting forces and moments between the longitudinal ribs and the non-circular cylindrical shell are considered at the same time. The efects of the number and the size of the cross-section of longitudinal ribs on the characteristics of acoustic radiation are investigated. Numerical results show that the method proposed is more efcient than the existing mixed FE-BE method.

RESONANCE RADIATION OF SUBMERGED INFINITE CYLINDRICAL SHELL

The resonance sound radiation from submerged infinite elastic cylindricalshell, excited by internal harmonic line force, is investigated. The shell radiation power ispresented in terms of resonant modal radiation derived from resonance radiation theory (RRT). Theresonance radiation formulae are derived from classical Rayleigh normal mode solution, which areuseful for understanding the mechanism of sound radiation from submerged shells. As an example,numerical calculation of a thin steel cylindrical shell is done by using these two methods. It seemsthat the results of RRT solutions are in good agreement with that of Rayleigh normal modesolutions.

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.

Fast Prediction of Acoustic Radiation from a Hemi-capped Cylindrical Shell in Waveguide

以便在波导从结构预言声学的放射，一个方法基于波浪重叠被建议，在哪个空间草地函数被用来匹配相等的来源的力量。另外，以便从边界忽视健全思考的效果，必要处理被进行，它使方法更有效。而且，这个方法与健全繁殖算法被相结合预言声音在波导从圆柱的壳放射了。数字模拟看思考怎么能被忽视的效果在结构和边界之间的距离是否超过结构的最大的线性尺寸。它也证明从波导的底部的思考能乘飞机被接近有条件地飘动。建议方法在计算更柔韧、有效，它能被用来在波导预言声学的放射。

部分浸没充液无限长圆柱壳声辐射特性研究

本文旨在研究圆柱壳的浸没和充液对其声辐射特征的影响,为界面附近充液壳体目标声学性能的评估和测量提供理论依据和研究方法。通过有限元数值仿真方法计算得到半充液无限长圆柱壳辐射声压的频率-浸没深度谱和半浸没无限长圆柱壳辐射声压的频率-充液高度谱,结果均呈现出两种明显的共振现象,分别由弯曲波和低阶流体附加波激发。根据相速度频散曲线推导出共振频率的预报公式,能够准确地预报辐射声场中出现的共振现象,可为系泊状态内部液舱结构振动声辐射线谱特征控制与评估提供理论支撑。

敷设分层梯度声学覆盖层的加肋圆柱壳声辐射特性研究

单壳体潜艇敷设声学覆盖层应具有机械噪声、水动力噪声和声目标强度控制的多功能特性,为此需要解决两个基本问题:其一,提高机械噪声低频控制效果;其二,实现覆盖层的多功能兼容性。本文从降低机械激励壳体声辐射角度出发,采用模态叠加法,建立无限大理想水介质中分层梯度声学覆盖层与有限长加肋圆柱壳的声振耦合及声辐射模型,基于声学覆盖层模态传递函数特性,计算分析声学覆盖层分层梯度分布及厚度、层数等参数对加肋圆柱壳辐射噪声影响的特征和规律,给出分层梯度声学覆盖层的特征声阻抗渐变参数分布并与敷设均匀声学覆盖层降噪特性比较。研究结果表明:加肋圆柱壳敷设内层至外层声阻抗逐渐递增,各分层取慢波速的声学覆盖层,具有比均匀声学覆盖层更有效地降低外表面振动位移的特性,可明显增加降噪效果,并扩展低频降噪范围。声学覆盖层的优化应增加声阻抗的内分层失配和外分层适配的效应,有利于降低加肋圆柱壳低频声辐射,并可兼顾降低声目标强度。

Edge-induced radiation force and torque on a cylindrically-radiating active acoustic source located near a rigid corner-space

This work examines the physical effect of the edge-induced acoustic radiation force and torque on an acoustically radiating infinitely-long circular cylindrical source,located near a rigid corner.Assuming harmonic(linear)radiating waves of the source,vibrating in monopole or dipole radiation modes near a rigid corner-space in a non-viscous fluid,the modal series expansion method in cylindrical coordinates,the classical method of images and the translational addition theorem are applied to obtain the mathematical expressions for the radiation force and torque components in exact partial-wave series.Computational results illustrate the theory,and examine some of the conditions where the radiation force and torque components vanish,which has the potential to achieve total motion suppression(i.e.,translation or rotation).Furthermore,depending on the size parameter of the source and the distances from the rigid corner space,these physical observables take positive or negative values,anticipating the prediction of pulling/pushing motions toward the corner space,and possible spinning of the source clockwise or counter-clockwise.The present analysis and its results may be useful in some applications related to underwater acoustical oceanographic engineering of submerged objects,cloaking and stealth technology development and the experimental design of elongated unmanned autonomous vehicles or submarines,as well as the manipulation of an active carrier or ultrasound contrast agents of elongated cylindrical shapes near a corner space or chamber walls at a right angle.

复合材料多层圆柱壳振动和声辐射问题研究进展

鉴于复合材料优良的力学和声学性能,将其用于潜艇结构已成为未来的发展趋势和研究重点。而圆柱壳作为潜艇的主体结构形式,针对复合材料多层圆柱壳的振动和声辐射问题的研究已广泛开展。在满足水下承载能力的前提下,复合材料耐压圆柱壳趋于中厚壳,甚至厚壳,沿壳体厚度方向的横向剪切变形、压缩变形、截面翘曲变形不可忽略,这些因素直接决定了横向振动位移场描述的准确度,会进一步影响壳体周围声辐射场预报的准确性。现有的壳体理论主要有经典壳体理论、一阶剪切变形理论、高阶剪切变形理论、分层理论、锯齿理论和三维弹性理论等,这些理论发展比较成熟,但大多研究仍局限于正交各向异性薄壳结构的振动问题,涉及各向异性材料厚壳结构的声辐射研究较少,且目前对于这些壳体理论在复合材料圆柱壳的振动和声辐射问题的适用性方面缺乏系统的总结和研究。本文首先从复合材料的刚度特性出发说明其振动和声辐射问题求解的复杂性,然后从横向振动位移场的角度综述了这些理论的发展过程、研究现状以及各自的特点,最后给出了这些理论的适用范围和使用建议,并提出了有待进一步研究的问题,以期为复合材料多层圆柱壳结构的设计和振声性能分析提供参考。

圆柱壳振动声辐射Jacobi-Ritz时域半解析法及特性分析

针对圆柱壳结构瞬态声振特性分析研究不足,结合Newmark-β积分法和Kirchhoff时域边界积分方程,提出一种圆柱壳受迫振动声辐射Jacobi-Ritz时域半解析法。基于一阶剪切变形理论和微元法思想,建立了圆柱壳振动声辐射分析模型,采取Jacobi多项式和Fourier级数表示轴向和周向位移容许函数,基于Rayleigh-Ritz法和Newmark-β积分法计算圆柱壳的受迫振动时域响应,在此基础上,基于Kirchhoff积分方程求解辐射噪声时域响应,分析圆柱壳受迫振动声辐射特性。与有限元方法/边界元方法数值结果对比表明,该方法具备收敛性好、精度高等优点,圆柱壳结构声振响应峰值随边界条件的刚度变弱存在左移现象,振动声辐射响应随厚度的增加呈现下降趋势;当随机载荷峰值频率与结构固有频率接近时,结构声振响应出现强特征线谱。

有限长双层壳体声辐射理论及数值分析

研究流场中有限长加筋双层圆柱壳受径向点激励的振动和声辐射性能。壳体的振动用 Flügge壳体方程描述 ,将加强构件等价为对内外壳体的支持力 ,采用 Helmholtz波动方程、壳体表面的边界条件和傅氏变换方法求解声压的表达式 ,然后将其引入壳体振动方程 ,最后求解双层壳体声 -流体 -结构耦合方程 ,计算结果用辐射声功率、表面振动均方速度级和辐射效率的形式表示。讨论了有限长单、双层壳体声辐射性能的差别以及双层壳体壳间连接形式和实肋板参数的变化对其声辐射性能的影响 ,得出结论 :当内壳受激振动 ,通过外壳向外场辐射噪声时 ,其主要通道为连接内外壳壳体的实肋板 。

激励力对双层圆柱壳声辐射性能的影响

研究了不同激励力对流场中敷设阻尼材料的有限长加筋双层圆柱壳的振动和声辐射性能的影响。壳体的振动用Flügge壳体方程描述,将加强构件等价为对内外壳体的支持力,粘弹性阻尼层的运动用三维Navier方程描述,壳体受到的激励力可以归结成轴向力、周向力、径向力、轴向弯距、周向弯距和扭矩的作用,点激励用啄函数表示,然后将其引入壳体振动方程,最后求解双壳体声-流体-结构耦合方程,计算结果用辐射声功率和表面振动均方速度级的形式表示。在数值分析部分,讨论了六种不同性质激励力、两个力联合作用以及阻尼材料对双层圆柱壳的辐射声功率和表面振动速度级的影响。得出结论:同一位置受单位力激励时,Mx激励的声功率最高,Fr居第二,Fx最低;联合激励力产生的辐射声功率级和外壳振动速度级比单个力激励时都要大;阻尼材料能有效地抑制壳体的辐射噪声。