ANALYSIS OF SOUND TRANSMISSION THROUGH PERIODICALLY STIFFENED PANELS BY SPACE-HARMONIC EXPANSION METHOD

An analysis method is developed to study sound transmission characteristics of a thin plate stiffened by equally spaced line stiffeners. The dynamic equation that describes the vibro-acoustic response of the system is derived by expanding the structural and acoustic responses in terms of the space harmonics and by using the virtual energy method. The series solution can be considered as the exact solution because the structural and acoustic-structural coupling effects in the system are fully considered and the solution converges. Parameter studies are conducted for major design parameters to understand the characteristics of the system.     

ANALYSIS AND MEASUREMENT OF SOUND TRANSMISSION THROUGH A DOUBLE-WALLED CYLINDRICAL SHELL

Sound transmission through a double-walled cylindrical shell is studied. The solution that describes the system response is obtained by combining the solutions of two different models of the system. The first model, which describes the sound transmission due to the interaction between the acoustic waves and the bending waves in the shells, is formulated by three acoustic wave equations and two shell vibration equations. The second model describes the sound transmission by one-dimensional waves propagating through the layers of the shells and the air-gap. The transmission losses calculated from the two models are combined to represent the system response in the entire frequency range. Analytical solutions are compared to corresponding measured results, which shows reasonable agreements if the extent of the simplifications used in the analytical model is considered. The effects of important design parameters such as the air-gap size and the thickness ratio are studied using analytical solutions.     

SOUND TRANSMISSION THROUGH ELASTOMERIC BULB SEALS

The sound barrier performance of elastomeric vehicle weather seals was investigated. Experiments were performed on a single bulb seal specimen using a reverberation room method. The seal wall velocity was measured using a laser Doppler vibrometer. The sound pressure near the velocity measurement location was measured simultaneously, which allowed the sound intensity on both sides of the seal and the sound transmission loss to be determined. The vibration response and the sound transmission loss of the bulb seal were then computed using finite element analysis. Acoustic-structure interactions were considered for a partially coherent spatially distributed pressure excitation. The experimental data obtained using the reverberation room method allowed the validation of the numerical models. The resonance frequency due to the mass-air-mass mode of vibration was accurately predicted. The model was then used to numerically investigate the influence of various design parameters. It was found that the elastic modulus significantly affects the bulb seal resonance frequency, and that the loss factor of the material has major effects on the sound transmission loss around resonance.     

ON THE FREE VIBRATION OF STIFFENED SHALLOW SHELLS

A finite element analysis for free vibration behaviour of doubly curved stiffened shallow shells is presented. The stiffened shell element is obtained by the appropriate combinations of the eight-/nine-node doubly curved isoparametric thin shallow shell element with the three-node curved isoparametric beam element. The shell types examined are the elliptic and hyperbolic paraboloids, the hypar and the conoidal shells. The accuracy of the formulation is established by comparing some of the authors' results of specific problems with those available in the literature. Numerical results of additional stiffened shells are also presented to study the effects of various parameters of shells and stiffeners such as orientation (i.e., along x -/y -/both x and y directions), type (concentric, eccentric at top and eccentric at bottom) and number of stiffeners, stiffener depth to shell thickness ratio, and aspect ratio, shallowness and boundary conditions of shells on free vibration characteristics.     

在均匀外压力作用下柱壳的蠕变

 文中描述了对柱壳在蠕变到断裂条件下的形变实验研究，进行了三个系列的实验研究：第一个实验为，用X18H10T材料制造的长为380 mm的圆柱壳，在温度为850 ℃的情况下，加载到发生蠕变的状态下，测量发生断裂的时间和圆柱的椭圆度。第二个实验为，用Xastell-X合金，在800 ℃和900 ℃的情况下进行的，作者并对六个不同作者和模型的计算结果进行了比较。第三个实验为，用Xastell-X合金在700 ℃温度下，由西德Cooper进行的。作者应用三种理论模型和实验结果进行了比较，均在误差范围之内。     

圆柱圆锥状空腔声共振频率的测量

提出一种测量圆柱和圆锥状空腔声共振频率的方法,由微机和信号处理板配合构成的系统完成频响曲线的测量和运算,实验得到的数据和理论计算值相吻合。     

TRANSIENT ANALYSIS OF RING-STIFFENED COMPOSITE CYLINDRICAL SHELLS WITH BOTH EDGES CLAMPED

A theoretical method is developed to investigate the effects of ring stiffeners on vibration characteristics and transient responses for the ring-stiffened composite cylindrical shells subjected to the step pulse loading. Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The ring stiffeners are laminated with a composite material and have a uniform rectangular cross-section. The Rayleigh-Ritz procedure is applied to obtain the frequency equation. The modal analysis technique is used to develop the analytical solutions of the transient response. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The theoretical results are verified by comparison with FEM results.     

DYNAMICS BEHAVIOR OF AXISYMMETRIC AND BEAM-LIKE ANISOTROPIC CYLINDRICAL SHELLS CONVEYING FLUID

The flow-induced vibration characteristics of anisotropic laminated cylindrical shells partially or completely filled with liquid or subjected to a flowing fluid are studied in this work for two cases of circumferential wave number, the axisymmetric, where n=0 and the beam-like, where n=1. The shear deformation effects are taken into account in this theory; therefore, the equations of motion are determined with displacements and transverse shear as independent variables. The present method is a combination of finite element analysis and refined shell theory in which the displacement functions are derived from the exact solution of refined shell equations based on orthogonal curvilinear co-ordinates. Mass and stiffness matrices are determined by precise analytical integration. A finite element is defined for the liquid in cases of potential flow that yields three forces (inertial, centrifugal and Coriolis) of moving fluid. The mass, stiffness and damping matrices due to the fluid effect are obtained by an analytical integration of the fluid pressure over the liquid element. The available solution based on Sanders' theory can also be obtained from the present theory in the limiting case of infinite stiffness in transverse shear. The natural frequencies of isotropic and anisotropic cylindrical shells that are empty, partially or completely filled with liquid as well as subjected to a flowing fluid, are given. When these results are compared with corresponding results obtained using existing theories, very good agreement is obtained.     

OPTIMIZATION OF ANISOTROPIC SANDWICH BEAMS FOR HIGHER SOUND TRANSMISSION LOSS

This paper presents a study on the optimization of sound transmission loss across anisotropic sandwich beams. It has been found in earlier studies that there is a significant increase in the sound transmission loss for sandwich beams with anisotropic materials compared to those with isotropic ones. The optimization studies presented in this work further validate this concept. The material and geometric properties of the structure are treated as the design variables with the objective to maximize the sound transmission loss across the beam. Appropriate constraints are imposed to maintain material and structural integrity.     

X射线在毛细导管中传输的理论研究

给出了X射线在毛细导管中传输特性的简明而系统的理论描述.在这个理论描述的基础上,建 立了X射线在毛细导管中传输的计算模型,编制了X射线在毛细导管中传输的计算程序.利用 编制的X射线在毛细导管中传输计算程序得到的数值结果和实验结果符合得很好. 关键词： 毛细导管 X射线 传输模型     

VIBRATIONAL POWER TRANSMISSION FROM A MACHINE TO ITS SUPPORTING CYLINDRICAL SHELL

Power flows from a vibratory machine to its supporting structure are of primary concern in a passive or active isolation system design. Although in the literature there is a fair number of investigations on the power inputs to beams, plates or the like, few attempts have been made for other commonly used structures such as cylindrical shells. In this paper, the vibratory power flows from a rigid-body machine to an elastic cylindrical shell are studied considering the contributions of the non-radial (tangential and axial) displacements and forces. In particular, it is argued that the notion that the motion of a thin shell is primarily radial does not necessarily dictate that the power transmissions are predominantly carried out by the radial displacement. This point is subsequently illuminated through numerical examples. Another issue discussed here is concerned with the effects on the power flows of the cross couplings of the (different) displacement components. It is shown that even though the contributions of the cross couplings are usually insignificant, they may become important if the vibration isolators are substantially hard as compared with the local shell stiffness or impedance. This assertion is particularly useful when an experimental technique is used to measure the vibratory power flows into a supporting structure.     

激光辐照下充压铝柱壳爆裂断口分析

分析了激光辐照下充压铝柱壳的断口特性, 在激光辐照区上裂纹的起裂、扩展和止裂机制均为韧性的, 断口以韧窝分布为主, 由于加载不同, 有的断口在壳壁厚度方向有明显的分层, 即外层的塑性变形层和内层的韧窝状断口。给出了柱壳上激光辐照区的应力分布与断裂的关系和整个断裂过程较为细微完整的物理图象。     

平行板-偏心圆柱耦合传输线的特性阻抗

提出用保角变换边界元组合法计算平行板-偏心圆柱耦合传输线的特性阻抗。通过对三种基本偏心结构的计算,获得平行板-偏心圆柱耦合传输线的特性阻抗数据。这些数据不仅可为平行板-偏心圆柱耦合传输线的准确设计提供理论依据,而且可为同轴传输线的加工制作精度提供理论参考。     

ELASTIC WAVE SCATTERING AND DYNAMIC STRESS CONCENTRATIONS IN CYLINDRICAL SHELLS WITH A CIRCULAR CUTOUT

In this paper, based on the theory of elastic wave motion for open cylindrical shell, wave scattering and dynamic stress concentrations in open cylindrical shells with a hole are studied by making use of small parameter perturbation methods and boundary-integral equation techniques. The boundary-integral equations and iterative imminent series of scattered waves around the cavity of the cylindrical shell are derived. By employing this method, the approximately analytical solutions of scattered waves on the edge of cutout are gained. The computational formula for getting the dynamic stress concentration factors on the contour of cavity is developed. As an example, the numerical results of these dynamic stress concentration factors are graphically presented and discussed. The analytical methods put forward in the present work have practical significances for solving the problem of elastic wave scattering and dynamic stress concentrations in cylindrical shells with a circular cutout.     

激光辐照下充压铝柱壳爆裂断口分析

 分析了激光辐照下充压铝柱壳的断口特性, 在激光辐照区上裂纹的起裂、扩展和止裂机制均为韧性的, 断口以韧窝分布为主, 由于加载不同, 有的断口在壳壁厚度方向有明显的分层, 即外层的塑性变形层和内层的韧窝状断口。给出了柱壳上激光辐照区的应力分布与断裂的关系和整个断裂过程较为细微完整的物理图象。     

WAVE PROPAGATION THROUGH A CYLINDRICAL BORE CONTAINED IN A MICROSTRETCH ELASTIC MEDIUM

Propagation of waves in a cylindrical bore filled with viscous liquid embedded in a microstretch elastic medium is investigated. Frequency equation for the surface wave propagation near the surface of the cylindrical bore is obtained, characterizing the dispersive nature of the wave. Significant effects of viscosity, microstretch and micropolarity are observed. Some special cases have been deduced.     

ON TRANSMISSION OF SOUND IN A NON-UNIFORM DUCT CARRYING A SUBSONIC COMPRESSIBLE FLOW

The differential equations governing the transmission of one-dimensional sound waves in a non-uniform duct carrying a subsonic compressible mean flow have been the subject of a recent debate [1, 2]. Of the two formulations presented, one is considered to be non-acoustical and the other as neglecting the spatial variation of the speed of sound. The present paper shows that both formulations are acoustical and represent valid approximations to correct conditions for isentropic sound propagation in a subsonic low Mach number duct. Each formulation is associated with an “error wave”, which is essentially a hydrodynamic wave when the mean flow Mach number is small. Three-port modelling is required, however, to capture this wave when the Mach number of the mean flow is relatively large and a numerical matrizant approach is described which can be used for this purpose.