Finite Length Cylindrical Shells Research Articles

Analysis of electromagnetic vibration of submerged tubular linear motors based on wave propagation approach

This paper presents the properties of electromagnetic vibration in a submerged tubular linear induction motor through an analytical model. Firstly, the spatial and temporal characteristics of electromagnetic force acting in the stator are analyzed. Subsequently, based on the wave propagation approach, an analytical model is established to calculate the vibration response of the stator, which is simplified as a finite-length cylindrical shell. The accuracy of the proposed model is verified by comparing natural frequencies of axial breathing modes and frequency response with the finite element method. Finally, the effects of the position of electromagnetic force, the spatial distribution of electromagnetic force, radial static pressure and structure parameters on vibration response are investigated and discussed. Some conclusions are outlined, which is of great importance to reduce electromagnetic vibrations by optimizing the structure design of the motor.

Investigation of sound transmission through a finite length cylindrical shell in the presence of an exterior turbulent boundary layer

This paper studies sound transmission through a thin cylindrical shell of finite length. The structure is subjected to an exterior turbulent boundary layer (TBL) excitation and the boundary conditions of its two ends are considered as simply-supported. The classical shell theory (CST) is employed to derive wave propagation in the cylindrical shell, and the Corcos model is applied to describe pressure fluctuation due to TBL. According to the existence of two axial and radial modes, a complete convergence study is presented. To examine sound transmission through the structure, a comprehensive parameters study is provided on the resulting power spectral density (PSD) of the kinetic energy. To validate the results of the present method, the statistical energy analysis (SEA) method is used. For this purpose, modeling is performed by SEA in VA One software, which shows the high accuracy of the results of the present method. The analytical predictions suggest that the sound insulation performance of such a finite length structure is enhanced considerably by increasing the thickness of the shell in a broad-band frequency range. Similar effects on sound transmission are observed for Young’s modulus and density of the shell particularly in the low and high-frequency ranges, respectively. Whereas, enhancing the turbulent pressure and freestream velocity adversely affects sound radiation into the structure.

Influence of the Position of Artificial Boundary on Computation Accuracy of Conjugated Infinite Element for a Finite Length Cylindrical Shell

Structural finite element coupled with the conjugated infinite element method is an efficient numerical technique for solving the acoustic radiation problem due to the vibration of underwater objects. However, for large complex structures, the total acoustic mesh would become very large if the artificial boundary is too far away from the structural wetted surface. Thus, the calculation time can become too long to confine the application of the conjugated infinite element method. On the other hand, if the artificial boundary is close to the structural wetted surface, it will lead to computation accuracy losing due to the near-field effects. Consequently, it is essential to present some guidelines based on the physical mechanism of structural acoustics to choose a suitable artificial boundary that optimizes calculation accuracy and efficiency. In present work, the evanescent wave theory of an infinite length cylindrical shell is adopted to theoretically analyze the decay characteristic of evanescent waves in near field. Then, the effect of the position of artificial boundary on computation accuracy of conjugated infinite element for a finite length ring-stiffened cylindrical shell is numerically investigated. Results suggested that for the cylindrical shell mentioned in this study, the artificial boundary can be placed at least 0.4 times the acoustic wavelength away from the structural wetted surface. What’s more, for high frequencies or large-scale structures, the required non-dimensional distance between the artificial boundary and the structural wetted surface increases.

Strain Growth in a Finite-Length Cylindrical Shell Under Internal Pressure Pulse

Strain growth is a phenomenon observed in the elastic response of containment vessels subjected to internal blast loading. The local dynamic response of a containment vessel may become larger in a later stage than its response in the earlier stage. In order to understand the possible mechanisms of the strain growth phenomenon in a cylindrical vessel, dynamic elastic responses of a finite-length cylindrical shell with different boundary conditions subjected to internal pressure pulse are studied by finite-element simulation using LS-DYNA. It is found that the strain growth in a finite-length cylindrical shell with sliding–sliding boundary conditions is caused by nonlinear modal coupling. Strain growth in a finite-length cylindrical shell with free–free or simply supported boundary conditions is primarily caused by the linear modal superposition, possibly enhanced by the nonlinear modal coupling. The understanding of these strain growth mechanisms can guide the design of cylindrical containment vessels.

Study on Applicability of Sound Radiation Characteristics of Thin Finite Length Cylindrical Shells Using Wave Propagation Approach

Based on Donnell’s thin shell theory and basic equations, the wave propagation method is discussed here in detail, which is used to investigate the vibration and sound radiation characteristics of thin finite length circular cylindrical shells and ring stiffened shells under various boundary conditions. The effects of boundary conditions, mode truncation, shell’s length, thickness and rings on the acoustic radiation are explored. It is shown that the wave propagation method is more effective for the long cylindrical shell, and the mode truncation can satisfy the calculation accuracy. The conclusion is drawn that the stiffeners have a great influence on the total mechanical impedance while have a slight influence on radiation impedance. The work will give some guidelines for noise reduction of this kind of shell.

Radiation Sound Field Performance in Finite Length Cylindrical Shell by Active Point Excitation

Radiation sound field performance of single-point and multi-point excitation on finite length cylindrical shell is studied theoretically.Donnell shell theory and modal analysis method are used to establish mathematical models of single-point and multi-point excitation on finite length cylindrical shell of sound radiation.Calculation and analysis of low frequency sound radiation characteristics of near-field and far-field on the single-point and multi-point excitation cylindrical shell are based on sound radiation mathematical model.Results show that with the increasing of the excitation force frequency,sound radiation power and efficiency of cylindrical shell increase,radiation sound pressure enhances,and the direction of sound energy radiation is same as excitation force acting direction;at the near-field,the sound pressure attenuates quickly as the frequency falls and has certain fluctuation characteristics;at the far-field,the rules of sound pressure changing are different on different radiation directions,and the attenuation of sound pressure are approximate to spherical wave attenuation.

Acoustic modes of finite length homogeneous and layered cylindrical shells: Single and multiwall carbon nanotubes

We present a numerical study of the normal modes of vibration of both homogeneous and heterogeneous finite length cylindrical shells of arbitrary wall thickness with applications toward single and multiwall carbon nanotubes in the continuum limit. The method is checked by comparison of computed and measured resonance spectra for a machined aluminum cylindrical shell. The dependence of the natural frequencies of various radial modes with the length and radius of single wall tubes is investigated and compared to atomistic models and Raman spectroscopy data. The radial dependence for the radial breathing mode and four harmonics of the squash mode are found to be well fitted by power laws and agree with analytical solutions in the thin wall limit. A general model for an elastically heterogeneous layered cylindrical shell is applied to multiwall tubes with graphene sheets and gaps between the sheets represented by two different materials. The frequency dependence on length and diameter is investigated for tubes composed of two to four concentric shells.

Study on applicability of modal analysis of thin finite length cylindrical shells using wave propagation approach

Donnell’s thin shell theory and basic equations based on the wave propagation method discussed in detail here, is used to investigate the natural frequencies of thin finite length circular cylindrical shells under various boundary conditions. Mode shapes are drawn to explain the circumferential mode numbern and axial mode numberm, and the natural frequencies are calculated numerically and compared with those of FEM (finite element method) to confirm the reliability of the analytical solution. The effects of relevant parameters on natural frequencies are discussed thoroughly. It is shown that for long thin shells the method is simple, accurate and effective.

Study on applicability of modal analysis of thin finite length cylindrical shells using wave propagation approach

Study on applicability of modal analysis of thin finite length cylindrical shells using wave propagation approach

Nonlinear bending response and buckling of ring-stiffened cylindrical shells under pure bending

Abstract In this paper, the nonlinear bending response of finite length cylindrical shells with stiffening rings is investigated by using a modified Brazier approach. The basic assumptions for the present study are that the deformation of a shell subjected to pure bending can be simplified into a two-stage process. One is that the shell ovalizes but its axis remains straight; the other is that the bending of the shell is regarded as a beam with nonuniform ovalization. The nonlinear bending response is derived by applying the minimum potential energy principle and the corresponding critical moment, associated with local buckling, is determined by employing the Seide–Weingarten approximation. Numerical results are shown and compared with those obtained from other methods, which demonstrates that the assumptions used in the present study are reasonable.

Acoustic radiation from a finite length cylindrical shell excited by an internal acoustic source : Solution based on a boundary element method and a matched asymptotic expansion

This paper deals with acoustic radiation by a thin elastic shell, closed by two perfectly rigid discs, immersed in water and filled with air. The system is driven by an internal acoustic source. The shell has a length L, is clamped along one of its boundaries and is freely supported along the other boundary.

Transient axisymmetric response of a finite cylindrical shell with internal fluid loading. Part 2. Comparison of theory and experiment

An experimental investigation addressing the transient axisymmetric response of a finite length cylindrical shell with a base plate and internal fluid loading is presented. The configuration consists of a steel cylindrical shell with a circular base plate welded to one end. The shell and base plate contain an internal volume of water with a free surface. Data are presented for the special case of an axisymmetric transient excitation due to a force impulse hammer acting on the base plate. The in-vacuo and fluid-loaded response of the shell and base plate measured with an accelerometer will be presented and compared with numerical results. Transient field point pressure measurements taken with a hydrophone will also be presented and compared with numerical results. The agreement between experiment and numerical results is noted to be excellent.

The response behaviour of a submerged cylindrical shell using the doubly asymptotic approximation method (DAA)

This paper presents experimentally measured and theoretically calculated responses of a flexible cylindrical shell subjected to an impulsive excitation in air and in water. The flat-ended, thin cylindrical shell of overall length 1284 mm, external radius 180 mm, thickness 3 mm is made of mild steel. The predicted responses are derived from a method using the doubly asymptotic approximation (DAA) models in order to uncouple the motion of the fluid from that of the structure. The DAAs enable the radiated pressure to be specified in terms of surface motion of the structure. The method, which employs the DAAs, is applied to determine the responses, i.e. acceleration, velocity and displacement, of the finite length cylindrical shell excited by an impulsive mechanical force. The calculated acceleration responses are compared with the experimental measurements.

Stability and Vibrations of Compressed, Aeolotropic, Composite Cylindrical Shells

A general method of solution, based on a complex finite Fourier transform, is adopted for the stability and vibration analysis of compressed, aeolotropic, composite cylindrical shells. A major feature of the solution method is its ability to handle both uniform and nonuniform conditions that hold at the boundaries of finite-length cylindrical shells. For the various shells investigated, an optimum winding angle was found for which a maximum frequency response and highest critical buckling load is attainable. Similar optimization was also discovered to be possible by controlling both/either shell heterogeneity and/or fiber orientation.