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Journal ArticleDOI

Vibration and damping analysis of cylindrical shells with constrained damping treatment - a comparison of three theories

01 Apr 1995-Journal of Vibration and Acoustics (American Society of Mechanical Engineers)-Vol. 117, Iss: 2, pp 213-219
Abstract: Cylindrical shells with a constrained damping layer treatment are studied using three theories The finite element method is made use of in the study The nondimensional frequencies and loss factors predicted by the three theories are compared and the theories are evaluated The importance of inclusion of the extensional effects in the core and its effect on the loss factor is brought out in this study more

Topics: Vibration (51%)
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Journal ArticleDOI
Abstract: A layout optimization of passive constrained layer damping (PCLD) treatment for minimizing the vibration response of cylindrical shells is presented with consideration of broadband transverse force excitation. The equations governing the displacement responses, relating the integrated out-of-plane displacement over the whole structural volume, i.e., the structural volume displacement (SVD), of a cylindrical shell to structural parameters of base structure and multiple PCLD patches, are derived using the energy approach and assumed-mode method. Genetic algorithm (GA) based penalty function method is employed to find the optimal layout of rectangular PCLD patches with aim to minimize the SVD of the PCLD-treated cylindrical shell. Optimization solutions of the locations of patches for PCLD treatment are obtained under the constraint of total amount of PCLD materials in terms of percentage added weight to the base structure. Effects due to number of patches, their aspect ratios, and total amount of added PCLD weight are also studied. Examination of the optimal layouts reveals that the patches tend to increase their coverage in the axial direction and distribute over the whole surface of the cylindrical shell for optimal SVD reduction. more

97 citations

Journal ArticleDOI
Amr M. Baz1, T. Chen2Institutions (2)
Abstract: Distributed-parameter modeling of thin cylindrical shells which are fully treated with active constrained layer damping (ACLD) is presented. Hamilton's principle is utilized to develop the shell/ACLD model as well as the associated boundary conditions. A globally stable boundary control strategy is developed to damp out the vibration of the shell/ACLD system. The devised boundary controller is compatible with the operating nature of the ACLD treatments where the strain induced, in the active constraining layer, generates a control force acting at the boundary of the treated shell. As the boundary control strategy is based on a distributed-parameter model of the shell/ACLD system, the classical spillover problems resulting from using “truncated” finite element models is eliminated. Also, such an approach makes the boundary controller capable of controlling all the modes of vibration of the shell/ACLD and guarantees that the total energy norm of the system is continuously decreasing with time. Numerical examples are presented to demonstrate the effectiveness of the ACLD in damping out the vibration of cylindrical shells. Such effectiveness is determined for different control gains and compared with the performance of conventional passive constrained layer damping (PCLD). The results obtained demonstrate the high damping characteristics of the boundary controller particularly over broad frequency bands. more

47 citations

Journal ArticleDOI
Abstract: Vibration is normally viewed as undesirable, not only owing to the resulting unpleasant motions, noise, and dynamic stresses possibly leading to fatigue and failure of the structure or machine, but also owing to the energy losses and degraded performance. Technological advances have further enhanced the means of controlling vibration in mechanical engineering, aerospace engineering, civil engineering and related applications. The feasibility of developing a viscoelastic damping material of structures for vibration damping has received extensive interest. Surface treatment uses high damping viscoelastic materials firmly attached to the surface of structural elements. Optimal design depends on the ability to accurately predict and effectively control the vibration of a structure with viscoelastic damping treatment. Understanding the damping characteristics of viscoelastically damped structures becomes necessary. This study analyzes the design parameters for constrained layer damping structures by employing the Ross–Kerwin–Ungar (RKU) model. The effects of temperature, frequency and the dimensions of damped structures on vibration damping characteristics are also discussed. more

44 citations

Journal ArticleDOI
Y. S. Jeung1, I. Y. Shen2Institutions (2)
01 Jan 2001-AIAA Journal
Abstract: An isoparametric, degenerate element for constrained layer damping treatments is presented The element is valid for either plate or shell structures The element is an 18-node degenerate element with nine nodes located on the base shell (or plate) structure and nine nodes on the constraining layer Each node has five degrees of freedom: translations in x,y, and z and bending rotations α and β about the midsurface where the node is located The displacement field of the viscoelastic layer is interpolated linearly from the nodal displacements; therefore, the viscoelastic layer allows both shear and normal deformations The base shell (or plate) structure and the constraining layer can be linearly elastic or piezoelectric for passive or active applications The viscoelastic layer is assumed to be linearly viscoelastic The equation of motion is derived through use of the principle of virtual work For thin plate structures, numerical results show that the isoparametric element can predict natural frequencies, loss factors, and mechanical impedances that are as accurate as NASTRAN with substantially fewer elements For thin shell structures, locking and spurious modes need to be resolved to yield reasonable results more

34 citations

Journal ArticleDOI
Farough Mohammadi1, Ramin Sedaghati1Institutions (1)
Abstract: Damping characteristics of three-layered sandwich cylindrical shell for thin and thick core viscoelastic layers are studied using semi-analytical finite element method. The finite element method is developed based on the linear and nonlinear variations of the displacement distribution through the thickness of the core layer. Transient vibration has been conducted using the developed linear and nonlinear models and shown that the nonlinear formulation exhibits more damping property than the linear model. The effect of geometric nonlinearity due to the large deformation of the shell has also been considered assuming small strain and moderate rotation. Different assumptions based on the continuity and discontinuity in transverse shear stresses and slope of in-plane displacements are considered in the finite element formulation and their effects have been investigated. Considering nonlinearity of eigenvalue problem due to the frequency dependent property of viscoelastic material, an efficient algorithm has been developed to find the natural frequencies and loss factors of the viscoelastic cylindrical shell considering large deformation. The effect of imperfect bonding between the layers has also been investigated in the modeling and it is shown that slippage between layers at the interfaces leads to reduction in loss factor at the majority of modes. more

33 citations

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Journal ArticleDOI
Ahmed K. Noor1, W. Scott Burton1Institutions (1)
Abstract: A review is made of the different approaches used for modeling multilayered composite shells. Discussion focuses on different approaches for developing two-dimensional shear deformation theories; classification of two-dimensional theories based on introducing plausible displacement, strain and/or stress assumptions in the thickness direction; first-order shear deformation theories based on linear displacement assumptions in the thickness coordinate; and efficient computational strategies for anisotropic composite shells. Extensive numerical results are presented showing the effects of variation in the lamination and geometric parameters of simply supported composite cylinders on the accuracy of the static and vibrational responses predicted by eight different modeling approaches (based on two-dimensional shear deformation theories). more

432 citations

Journal ArticleDOI
T. P. Khatua1, Y.K. Cheung1Institutions (1)
Abstract: A finite element displacement analysis of multilayer sandwich beams and plates, each with n stiff layers and n−1 weak cores, is presented. Each layer of the sandwich structure may have individual orthotropic properties of its own and the bending rigidities of the stiff layers are taken into account while direct stresses in cores are neglected in the analysis. The condition of common shear angle for all cores, which has been used by several authors is not implied in the formulation. Several examples on bending problems have been solved using lower-order elements and the accuracy of the results has been shown to be excellent. Two higher-order elements have also been developed but have not been found to yield much better results. The free vibration problems of multilayer sandwich structures have also been solved, and good accuracy is demonstrated. more

141 citations

Journal ArticleDOI
Mohan D. Rao1, Shulin He1Institutions (1)
01 Apr 1993-AIAA Journal
Abstract: This paper describes the formulation of a theory for the prediction of damping and natural frequencies of laminated composite beams with multiple viscoelastic damping layers. The damping layers are constrained (or sandwiched) by anisotropic laminates. The in-plane shear strains of the damping layers and the constraining layers are included in the model. Closed-form solutions for the resonance frequencies and modal loss factors of the composite beam system under simple supports are derived using the energy and Ritz method. A parametric study has been conducted to study the variation of dynamic stiffness and modal loss factor of the system with structural parameters (e.g., the ply orientations of laminas, thickness of the damping layers and the laminates), operating temperature, and damping material properties. The design of composite beams for maximizing the damping capacity is also presented in this paper which includes the determination of operating temperature range corresponding to given structural parameters and finding optimal structural parameters corresponding to given temperature range. Finally, some experimental results are compared with theory for the cases of single and double damping layer beam systems that show good agreement between predicted and measured natural frequencies. more

108 citations

Journal ArticleDOI
Naiyar Alam1, N. T. Asnani2Institutions (2)
01 Jun 1984-AIAA Journal
Abstract: The governing equations of motion for the nonaxisymmetric and axisymmetric variational of a general multilayered cylindrical shell having an arbitrary number of orthotropic material layers have been derived using variational principles. The refined analysis considers bending, extension, and shear deformations in all layers of a multilayered cylindrical shell, including rotary and longitudinal translatory as well as transverse inertias. The solution for a radially simply supported shell has been obtained and the procedure for determining the damping effectiveness in terms of the system loss factor for all families of the modes of vibration in a multilayered shell with elastic and viscoelastic layers is reported. Numerical results are reported in Part II of the paper. more

67 citations

Journal ArticleDOI
Dimitris A. Saravanos1, J. M. Pereira1Institutions (1)
01 Dec 1992-AIAA Journal
Abstract: Integrated damping mechanics for composite plates with constrained interlaminar layers of polymer damping materials are developed. Discrete layer damping mechanics are presented for composite laminates with damping layers, in connection with a semianalytical method for predicting the modal damping in simply supported specialty composite plates. Correlations between predicted and measured response in graphite/epox y plates illustrate the accuracy of the method. Additional application cases for graphite/epoxy plates of various laminations demonstrate the potential for higher damping than geometrically equivalent aluminum plates. The effects of aspect ratio, damping layer thickness, and fiber volume ratio on static and dynamic characteristics of the composite plate are also investigated. AMPING is a significant dynamic parameter for vibration and sound control, dynamic stability, positioning accu- racy, fatigue endurance, and impact resistance. Many current structural applications (e.g., large space structures, engine blades, and high-speed machinery) require light weight and high dynamic performance. Therefore, candidate sources of passive damping should add minimal parasitic weight and be compatible with the structural configuration. Two potential damping sources satisfying the previous re- quirements are the constrained damping layer approach and the damping capacity of composites. Constrained damping layers in isotropic metallic structures have been widely applied and investigated.1 They provide high damping, but tend to increase the structural weight and offer limited means for damping tailoring. The inherent damping capacity of compos- ite materials also seems promising. Although the damping of composite structures is not very high, it is significantly higher than that for most common metallic structures. Moreover, composites are the materials of preference in many cases, since they readily provide high specific stiffness and strength. More importantly, research on the damping mechanics of composite laminates2'4 and structures5'6 has shown that composite damp- ing is anisotropic, highly tailorable, and depends on an array of micromechanic al, laminate, and structural parameters. It has been further demonstrated that optimal tailoring may significantly improve the damped dynamic performance of composite structures.7 It seems likely that the combination of both approaches (i.e., composite structures with interlaminar damping layers) will offer the advantages of high damping, damping tailoring, good mechanical properties, and low weight addition. In addi- tion, the interlaminar damping concept is highly compatible with the laminated configuration of composite structures and their fabrication techniques. In contrast to isotropic materials, the variations in anisotropy and elastic properties of each more

65 citations

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