Tesi sul tema "Vibration of shells (engineering)"
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1
McDaniel, James Gregory. "A new higher-order shell theory for vibration and viscoelastically-coated circular cylindrical shells". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/15825.
Testo completo
2
Xu, Bo. "Vibration and stability analysis of toroidal shells". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/MQ45257.pdf.
Testo completo
3
Li, Nong. "Vibration of laminated orthotropic composite plates and shells". Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6946.
Testo completoAbstract (sommario):
Almost all of the analytical solution techniques presented for composite plates and shells deal with either simply supported conditions or boundary conditions with at least a pair of opposite edges simply supported. In the present study, an alternative general approach, combining superposition and state space techniques is developed for the free vibration analysis of laminated orthotropic composite plates and shells having arbitrary boundary conditions. This study concentrates on the antisymmetric angle-ply laminated plates and cross-ply laminated plates and shells. Three commonly adopted theories, i.e., classical theory, first-order shear deformation theory and third-order shear deformation theory, have been employed and compared with one another to investigate the influence of transverse shear deformation, structural aspect ratio, length-to-thickness ratio, degree of anisotropy and the number of layers on natural frequency. Convergence tests have been carried out to guarantee the accuracy of the closed-form solutions. Wherever possible, numerical results generated by the present approach are compared with those reported in the published references. Accurate non-dimensional fundamental frequencies are presented for laminated plates and shells with two adjacent edges, three edges and four edges clamped and other edges simply supported. Such analyses have not been reported in the literature previously. Also, vibration analysis of a cantilever angle-ply antisymmetric plate with a point support is conducted to demonstrate the applicability of the present technique. It has been shown that the method works extremely well and excellent agreements are found between the present results and those generated by previous researchers. It has also been shown that more complicated boundary-value problems can be solved by this technique without any difficulty.
4
Alizadeh, Y. "Free vibration of partially supported plates and shells". Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/10751.
Testo completoAbstract (sommario):
First-order transverse shear-deformation Mindlin theory has been used to predict the free vibration frequencies and modal shapes for isotropic, laminated and composite plates or shells. A finite element model based on the small deflection linear theory has been developed to obtain numerical solutions for this class of problems. The results for some of the degenerate cases are compared with other results available in the literature. These analyses involve a wide number of variables, namely; material properties, aspect ratios, support conditions and also radius to base ratio. The cracked base plates, shells and blades are idealized as partially supported models with varying support lengths. The effects of the detached base length on natural frequencies, modal shapes and nodal lines of these types of structures are investigated. Although the expected decrease in frequency with increase in the detached base length is observed almost for all modes it is seen that this behavior is very pronounced for higher modes in both plates and shells. Analysis also showed that the variation of the detached base length has a small effect on the natural frequencies of plates and shells with large aspect ratios ( b/a > 2, r/a > 2).
5
Shaw, Christopher Edward. "The effects of imperfections on the acoustic scattering of a coated shell". Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/17903.
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6
Du, Hung-Yih Isaac. "Vibration and buckling of geometrically imperfect laminated cylindrical shells /". The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487326511716282.
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7
Qatu, Mohamad-Subhi Khalil. "Free vibration and static analysis of laminated composite shallow shells /". The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487670346875409.
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8
Qatu, Mohamad Subhi Khalil. "Free vibration and static analysis of laminated composite shallow shells". The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1392112808.
Testo completo
9
Wang, X. H. "Free vibration and stability of complete orthotropic circular toroidal shells". Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26799.
Testo completoAbstract (sommario):
This study makes contributions in the areas of vibration and stability analysis of complete orthotropic circular toroidal shells. It is conducted in four main parts. A literature survey is first carried out indicating the new and continuing uses of toroidal shells in engineering structures. Secondly, theory is developed for the free vibration analysis of toroidal shells using the differential quadrature method. Numerical results are determined using the method for shells with small bend to cross-section radius ratios, and compared with finite element results. Thirdly, theory is developed using the Rayleigh-Ritz method for the free vibration analysis of toroidal shells having large bend to cross-section radius ratios. A parametric study of such shells including orthotropic and ring-stiffened isotropic ones is conducted using the finite element method. Finally, theory is developed using the Rayleigh-Ritz method for the linearized buckling analysis of toroidal shells with large bend to cross-section radius ratios. Numerical results are found for orthotropic and ring-stiffened isotropic shells using the finite element method. All theoretical work is carried out within the confines of the first-order Sanders-Budiansky shell theory. The work ends with an appropriate set of conclusions.
10
Young, Andrew J. "Active control of vibration in stiffened structures". Title page, contents and abstract only, 1995. http://hdl.handle.net/2440/37722.
Testo completoAbstract (sommario):
Active control of vibration in structures has been investigated by an increasing number of researchers in recent years. There has been a great deal of theoretical work and some experiment examining the use of point forces for vibration control, and more recently, the use of thin piezoelectric crystals laminated to the surfaces of structures. However, control by point forces is impractical, requiring large reaction masses, and the forces generated by laminated piezoelectric crystals are not sufficient to control vibration in large and heavy structures. The control of flexural vibrations in stiffened structures using piezoceramic stack actuators placed between stiffener flanges and the structure is examined theoretically and experimentally in this thesis. Used in this way, piezoceramic actuators are capable of developing much higher forces than laminated piezoelectric crystals, and no reaction mass is required. This thesis aims to show the feasibility of active vibration control using piezoceramic actuators and angle stiffeners in a variety of fundamental structures. The work is divided into three parts. In the first, the simple case of a single actuator used to control vibration in a beam is examined. In the second, vibration in stiffened plates is controlled using multiple actuators, and in the third, the control of vibration in a ring-stiffened cylinder is investigated. In each section, the classical equations of motion are used to develop theoretical models describing the vibration of the structures with and without active vibration control. The effects of the angle stiffener(s) are included in the analysis. The models are used to establish the quantitative effects of variation in frequency, the location of control source(s) and the location of the error sensor(s) on the achievable attenuation and the control forces required for optimal control. Comparison is also made between the results for the cases with multiple control sources driven by the same signal and with multiple independently driven control sources. Both finite and semi-finite structures are examined to enable comparison between the results for travelling waves and standing waves in each of the three structure types. This thesis attempts to provide physical explanations for all the observed variations in achievable attenuation and control force(s) with varied frequency, control source location and error sensor location. The analysis of the simpler cases aids in interpreting the results for the more complicated cases. Experimental results are given to demonstrate the accuracy of the theoretical models in each section. Trials are performed on a stiffened beam with a single control source and a single error sensor, a stiffened plate with three control sources and a line of error sensors and a ring-stiffened cylinder with six control sources and a ring of error sensors. The experimental results are compared with theory for each structure for the two cases with and without active vibration control.Thesis (Ph.D.)--Mechanical Engineering, 1995.
11
Caille, Gary W. "The acoustic field scattered from some approximate pressure release materials coating a finite cylinder". Thesis, Monterey, Calif. : Naval Postgraduate School, 1988. http://handle.dtic.mil/100.2/ADA194768.
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12
Kil, Hyun-Gwon. "An automated scanning laser doppler system for vibration measurements and wave-vector analysis of vibration of shells". Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/16856.
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13
Ravish, Masti Sarangapany. "Vibration damping analysis of cylindrical shells partially coated withconstrained visco-elastic layers". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31242169.
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14
Ravish, Masti Sarangapany. "Vibration damping analysis of cylindrical shells partially coated with constrained visco-elastic layers". Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23000867.
Testo completo
15
Yavuzbalkan, Erdem. "Free Vibration Analysis Of Anisotropic Laminated Composite Shells Of Revolution". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12606505/index.pdf.
Testo completoAbstract (sommario):
In this thesis, the free vibration analysis of anisotropic laminated composite shells of revolution (ALCSOR) is studied. The governing equations are kinematic, constitutive, and motion equations. Geometrically linear strain-displacement equations of Reissner-Naghdi shell theory in combination with first-order shear deformation theory in which transverse shear and rotatory inertia effects are taken into consideration. The constitutive relations are for macrosopically ALCSOR in which statically equivalent force and moment resultants, instead of internal stresses for a single layer, are introduced. Equations of motion for the free vibration problem are obtained by the Hamilton’
s principle. The derived governing equations for the free vibration analysis of ALCSOR are initially formulated into a system of partial differential equations in terms of fundamental variables. Then, those partial differential equations are reduced to a system of first order ordinary differential equations by applying finite exponential Fourier Transform method resulting in a two point boundary value problem. It has been demonstrated that the application of the finite exponential Fourier transform made it possible to solve the governing equations, comprising the full anisotropic form of the constitutive equations, which was otherwise impossible to solve with the classical Fourier decomposition method. First, the boundary value problem formulated is reduced to a series of initial value problems, then the multisegment numerical integration is used in combination with the frequency trial method in order to find the critical modes within a given range of natural frequencies. A computer code DALSOR is written for the solution of the natural frequencies and mode shapes of mascroscopically ALCSOR. DALSOR is applicable to any general boundary condition at both ends of the shell, and allows for variation of all elastic and geometric properties in the meridional direction. Numerical results are presented, and mainly discussions on the method of solution and the effect of macroscopic anisotropy on modal characteristics, mainly natural frequencies, are made. Various case studies are performed primarily on cylindrical shells in order to investigate the effects of mainly fiber orientation angle, stacking sequence, arbitrary boundary conditions at the edges of the shell, thickness-to-radius ratio on the modal characteristics, mainly natural frequencies. Application of the method of solution has also been demonstrated for a truncated composite spherical shell.
16
Kang, Jae-Hoon. "Three-dimensional vibration analysis of thick shells of revolution with arbitrary curvature and variable thickness /". The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487945015615814.
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17
Chen, Pei-Tai. "Axisymmetric vibration, acoustic radiation, and the influence of eigenvalue veering phenomena in prolate spheroidal shells using variational principles". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/19407.
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18
Plattenburg, Joseph Allan. "Development of Refined Analytical Vibration Models for Plates and Shells with Combined Active and Passive Damping Treatments". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1460578500.
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19
Ghaeadi, Sirous K. "Control of vibrations of shells using piezoelectric actuators". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0018/NQ55333.pdf.
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20
Glandier, Christian Y. "Wave-vector analysis of the vibrations of thin cylindrical shells". Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/16797.
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21
Ibrahimoglu, Can Serkan. "Investigation Of The Effect Of Semi-geodesic Winding On The Vibration Characteristics Of Filament Wound Shells Of Revolution". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612378/index.pdf.
Testo completoAbstract (sommario):
In this thesis, the effect of semi-geodesic winding on the free vibration characteristics of filament wound composite shells of revolution with variable radii of curvature is studied. The analysis is performed by a semi-analytical solution method which is based on the numerical integration of the finite exponential Fourier transform of the fundamental shell of revolution equations. The governing equations for the free vibration analysis are initially obtained in terms of fundamental shell variables, and they are reduced to a system of first order ordinary differential equations by the application of finite exponential Fourier Transform, resulting in a two point boundary value problem. The boundary value problem is then reduced to a series of initial value problems, and the multisegment numerical integration technique is used in combination with the frequency trial method in order to extract the natural frequencies and determine the mode shapes within a given range of natural frequencies. Previous studies on geodesic winding is extended such that the effect of semi-geodesic winding which rely on the preset friction between the fiber and the mandrel surface on the stiffness and vibration characteristics of filament wound shells of revolution is investigated. Additionally, finite element analysis is employed to compare the results obtained from semi-analytical model solved by numerical integration and finite element model solved by finite element method. Sample results are obtained for filament wound truncated conical and spherical shells of revolution and the effect of the winding pattern on the vibration characteristics of shells of revolution is investigated thoroughly.
22
Xu, Mubing. "Adaptive-passive and active control of vibration and wave propagation in cylindrical shells using smart materials". Akron, OH : University of Akron, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1123211712.
Testo completoAbstract (sommario):
Dissertation (Ph.D.)--University of Akron, Dept. of Mechanical Engineering, 2005."August, 2005." Title from electronic dissertation title page (viewed 12/27/2005) Advisor, Pizhong Qiao; Co-Advisor, Gangbing Song; Committee members, Wieslaw K. Binienda, Kevin L. Kreider, Paul C. K. Lam, Dane Quinn; Department Chair, Celal Batur, Wieslaw K. Binienda; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome Includes bibliographical references.
23
Shute, Marcus William Sr. "Polarization-maintaining optical fiber as a sensor of shell vibrations". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17915.
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24
Ustundag, Burak. "On the free vibration behavior of cylindrical shell structures". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67717.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 105-106).
Shell structures, especially cylindrical shells, are widely used in aerospace and naval architectural industries. Submarine hulls and aircraft bodies can be idealized as cylindrical shell structures. The study of vibrations of cylindrical shells is an important aspect in the successful applications of the cylindrical shells. The free vibration characteristics of a submarine hull have an important influence on the noise signature of the submarine. That makes the free vibration problem of the submarine hull a particular interest for the submarine community. The natural frequencies of cylindrical shells are clustered in a very narrow band and they are thus more prone to becoming involved in resonant vibrations. The determination and control of these frequencies is significant to manage the acoustic signature of the submarine. This thesis focuses on the free vibration characteristics of stiffened and unstiffened cylindrical shells. The analysis is carried out mainly in two parts. First, the unstiffened cylindrical shell is modeled and the free vibration problem is analyzed as the shell thickness decreases. Then the cylindrical shell is stiffened with ring stiffeners and the free vibration problem of the stiffened cylindrical shell is studied. The vibration modes of the unstiffened cylindrical shell are studied for four shells with different thicknesses. Initial tensile and compressive membrane stresses are applied separately to the shells to study the effect of the initial stresses on the free vibration modes. The vibration modes of the stiffened cylindrical shell are studied in two steps. First, the influence of the positions of two ring stiffeners on the fundamental frequencies is studied; second, the free vibration modes of the stiffened cylindrical shell are studied. Two cylindrical shells with different thicknesses are used and they are stiffened with different numbers of ring stiffeners, which are uniformly distributed along the longitudinal axis of the shell. The results are compared with available analytical results and finite element solutions of similar problems from the literature.
by Burak Ustundag.
S.M.
25
Gao, Yong. "Nonlinear vibrations of axially-loaded anti-symmetric cross-ply cylindrical shells". Thesis, University of Macau, 1999. http://umaclib3.umac.mo/record=b1445030.
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26
Martini, Jose Nilton. "Analise elasto-acustica de casos axi-simetricas". [s.n.], 1996. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265164.
Testo completoAbstract (sommario):
Orientador: Renato PavanelloDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-21T22:55:45Z (GMT). No. of bitstreams: 1 Martini_JoseNilton_M.pdf: 7982573 bytes, checksum: 32a2da76b3073d915b207aea2000e10e (MD5) Previous issue date: 1996
Resumo: Neste trabalho estuda-se o problema elasto-acústico de cascas axisimétricas interagindo com fluido interior. Os modelos matemáticos para casca axi-simétrica, para fluido e para acoplamento são apresentados na forma de equações diferenciais. A partir das equações diferenciais são obtidas formas integrais associadas, utilizando o método dos resíduos ponderados. Assume-se uma solução harmônica para o problema. O Método dos Elementos Finitos, (MEF), aplicado as equações integrais, é utilizado para aproximação da solução. O problema é implementado computacionalmente utilizando os conceitos de programação orientada para objetos. São realizados testes para validação dos modelos obtidos e dos códigos computacionais desenvolvidos. Como resultado são obtidas as freqüências e os modos naturais de vibração dos sistemas desacoplados e do sistema acoplado. As soluções obtidas são comparadas com soluções analíticas e numéricas, bem como com resultados experimentais. Finalmente, realiza-se uma análise dos resultados obtidos e propõe-se trabalhos que darão continuidade ao tema
Abstract: This work presents a study of the elasto-acoustic problem for axisymmetric shells. The structure and the fluid are modeled by differential equations. The interface conditions between fluid and structure are presented. The derivation of the finite element formulation is based on the weak solution of differential equations presented and on the Galerkin method. A symmetric and a non-symmetric finite element formulation are derived. The Object Oriented Programming (OOP) technique are used to codify the problem. Some test cases to validade formulation and computacional codes are shown. The natural frequencies and natural modes of vibration ofaxi-symmetric shells, acoustic cavities and the coupled problem are presented. The solutions obtained from this formulation are compared to analytical, numerical and experimental data
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
27
Mustafa, B. A. J. "Free vibration analysis of stiffened circular shells". Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/14141.
Testo completoAbstract (sommario):
This thesis is concerned with the free vibration analysis of stiffened circular cylindrical and conical shells. The study was carried out with a view to improving the accuracy and efficieny of various modelling techniques for the prediction of the stiffened shells natural frequencies and mode shapes. A review of the existing literature covering various aspects of the shell vibrations problem and modelling techniques has been given at the beginning of each chapter with a critical appraisal of the assumptions made and results obtained. Initially the continuum energy approach was used for the analysis. The developed method allows for discrete consideration of stiffeners having arbitrary location and properties. Energy of bending in two planes and rotary inertia have been included in the analysis. Various types of stiffened shells with shear diaphragm ends condition were analysed using this method for the prediction of their natural frequencies. The predicted results have been compared with published experimental results. The finite element technique was also used for the prediction of natural frequencies and mode shapes of stiffened shells. Axisymmetric shell of revolution element, Facet shell element, semi-100f element and various types of beam elements, which are available within the PAFEC 75 suite of programs, were used for these studies. An efficient modelling technique has been introduced for ring stiffened cylindrical and conical shells by the use of the shell of revolution element. For improved accuracy of the predicted frequencies and a more economical model, shell symmetry was utilized for the free vibration analysis of unstiffened and stiffened shells. Half, quarter and one eighth models were studied by developing the appropriate boundary conditions and are discussed here. The free vibration characteristics of orthogonally stiffened cylindrical shells and an orthogonally stiffened cylindrical panel have been studied. An eight noded stiffened super shell element was developed for this study. This element was used for modelling various other types of stiffened shells and the predicted natural frequencies have been compared with known published experimental and theoretical results. Experimental verification of theoretical predictions of natural frequencies and mode shapes of an orthogonally stiffened cylindrical panel was carried out and is reported here.
28
CAVALCANTI, LILIAN DE VASCONCELLOS. "BUCKLING AND VIBRATION ANALYSIS OF SHALLOW CONOIDAL SHELLS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=24636@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROEstruturas de cascas delgadas descritas por superfícies regradas têm sido frequentemente utilizadas em engenharia civil, devido ao fato de que elas são uma das soluções estruturais mais econômicos para cobrir grandes vãos. Superfícies regradas são obtidas pelo movimento de uma ou mais linhas ao longo de uma ou mais curvas. Sendo assim, elas são fáceis de construir, o que justifica a sua escolha em muitos casos. Por razões estéticas e estruturais, estas estruturas são geralmente superfícies abatidas, o que leva, como no caso de arcos abatidos, a uma forte não linearidade geométrica. Entre as cascas descritas por superfícies regradas, as cascas conoidais são frequentemente favorecidas para coberturas de grandes áreas livres de colunas, pela facilidade de construção, elegância estética e pelo bom fornecimento de luz natural. Uma casca conoidal é um caso especial de cilindróide, pertencente às superfícies de Catalan, e é gerada por uma linha reta em movimento paralelo a um plano, conhecido como o plano diretor, com uma de suas extremidades em uma curva plana e a outra em uma linha reta. Por vezes, uma parte da superfície conoidal no extremo reto é suprimida dando origem a uma configuração truncada. O objetivo deste trabalho é analisar, utilizando uma formulação de elementos finitos, as características de flambagem e vibração desta forma estrutural. Uma análise paramétrica detalhada é realizada para compreender a influência das condições de contorno e dimensões físicas da casca no seu comportamento estático e dinâmico. São apresentadas conclusões específicas no final do trabalho, para resumir os resultados do presente estudo, que pretende servir como importante subsídio para os engenheiros envolvidos na construção de estruturas similares.
Slender shell structures described by ruled surfaces have been frequently used in civil engineering due to the fact that they are one of the most economical structural solutions to cover large spans. Ruled surfaces are obtained by the movement of one or more lines along one or more curves. So they are easy to cast, which justifies their choice in many cases. For aesthetic and structural reasons these structures are usually shallow surfaces, which leads, as in the case of shallow arches, to a strong geometric nonlinearity. Among the shells described by ruled surfaces, conoidal shells are frequently favored as roofing units to cover large column-free areas due to the ease of fabrication, aesthetic elegance and good provision of natural light. A conoidal shell is a special case of cylindroids belonging to Catalan’s surfaces and is generated by a variable straight line moving parallel to a plane, known as the director plane, with one of its ends on a plane curve and the other on a straight line. Sometimes a part of the conoidal surface at the straight end is cut off giving a truncated configuration. The objective of this work is to analyze, using a finite element formulation, the buckling and vibration characteristics of this structural form. A detailed parametric analysis is conducted to understand the influence of boundary conditions, different spans, widths, and other physical dimensions on the static and dynamic characteristics of the structure. Specific conclusions are drawn at the end, to summarize the contributions of the present investigation, which are expected to serve as important design aids to engineers engaged in shell construction.
29
Chern, Yi-Tzong. "Forced vibration analysis of plates and shallow shells". The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1236861764.
Testo completo
30
Woolfe, Katherine. "A scaled physical model for underwater sound radiation from a partially submerged cylindrical shell under impact". Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44874.
Testo completoAbstract (sommario):
The motivation for this study is to create a scaled laboratory model of a steel construction pile being driven by an impact hammer, which can provide controlled data to aid understanding and development of a structural acoustics numerical model simulating full-scale impact pile driving. The scaled model is approximately thirty times shorter than a typical 30-meter long Cast-in-Shell-Steel (CISS) pile. The relationship between the impact force, structural vibrations, and radiated sound field is analyzed. The time-domain acoustic intensity in the radial direction is found to be predominately negative immediately following excitation by the impact force. Analysis of the radial intensity shows that during the hammer strike, there is a net flow of energy from the structure into the water; however, because the structure and water are acoustically coupled a significant portion of the energy immediately flows back into the cylinder following hammer impact. This fluid-structure interaction results in a highly damped acoustic pulse in the water that propagates to the far field. In addition, the frequency spectra of the impact force, model pile wall acceleration in the radial direction in air and water, and underwater acoustic pressure are analyzed to find transfer functions between these variables. The transfer function between impact force and sound pressure is of particular interest because it can be used to calculate the system response for any other applied hammer force. This transfer function analysis has potential applications in mitigating noise generated by impact pile driving.
31
JAREK, AMANDA. "ENRICHED FINITE ELEMENTS FOR BUCKLING AND VIBRATION OF SHELLS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10410@1.
Testo completoAbstract (sommario):
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO presente trabalho avalia a utilização de elementos enriquecidos para obtenção de cargas críticas, freqüências de vibração e seus respectivos modos de peças estruturais bidimensionais (flexão de placas retangulares sujeitas a compressão em seu plano). O método de aproximação empregado foi o de Rayleigh-Ritz voltado para o uso de elementos finitos convencionais enriquecidos com funções de deslocamentos adicionais internas e de contorno. As funções ditas internas são desenvolvidas de forma a não envolver deslocamentos e rotações nodais e no contorno. Já as funções ditas de contorno são concebidas de forma a envolver apenas deslocamentos internos e ao longo de um lado apenas, sem deslocamentos generalizados nodais. Para este estudo foram desenvolvidas duas famílias de funções, uma com termos adicionais trigonométricos e outra com termos adicionais polinomiais. Para o cálculo de cargas críticas e freqüências são utilizadas as matrizes de rigidez elástica, rigidez geométrica e de massa, introduzidas em problemas generalizados de autovalores. Resultados numéricos são obtidos através de procedimentos computacionais utilizando o software Maple. Verifica-se que as funções adicionais trigonométricas, embora mais satisfatórias que as polinomiais quanto à convergência, exigem maior esforço computacional. São comparados resultados de elementos para placas esbeltas (teoria de Kirchhoff), com três e quatro graus de liberdade por nó, onde o quarto grau de liberdade corresponde à derivada mista (torção). Mostra-se que as funções adicionais, não-nodais, requerem o uso do elemento com quatro graus de liberdade por nó, para se ter convergência no cálculo das cargas críticas e freqüências em situações gerais. Outros exemplos abordam preliminarmente a inclusão de efeitos de dano e ortotropia no material, visando a modelagem de lajes comprimidas e pilares com seções retangulares alongadas. Esta modelagem envolvendo combinação de funções adicionais gerais e elementos convencionais representa um passo no desenvolvimento de uma técnica aplicável à combinação de modos globais e localizados de instabilidade
The focus of the present work is to developand evaluate enriched elements used to obtain critical loads, frequencies of vibration and respective modes for two-dimensional structural components (rectangular plates in bending under inplane compressive loading). The Rayleigh-Ritz approximation method has been employed, directed to the use of conventional finite elements enriched by internal and boundary additional displacements functions. The socalled internal functions are do not involve nodal and boundary displacements and rotations. The boundary functions are conceived to include displacements within the element and along one side, without involving any generalized nodal displacements. Two displacement function families were developed, the first with trigonometric additional terms and the second with polynomial additional terms. Critical loads and frequencies, and respective modes, are obtained by the use of elastic stifiness, geometric, and mass matrices, introduced in generalized eigenvalue problems. Numerical results are obtained by computational procedures using Maple software. The trigonometric additional functions, in spite of better convergence properties, demand greater computational effort. The basic elements are classical thin plate elements (Kirchhoff's theory) with three or four degrees of freedom per node, where the fourth degree of freedom corresponds to the mixed derivative (torsion). The results indicate that non- nodal additional functions require the use of elements with four freedom degrees by node to obtain convergence of critical loads and frequencies convergence in general situations. Other examples consist of preliminary approaches to include damage effects, in reinforced orthotropic plates, as modeling columns with wide rectangular sections and compressed slabs. The use of general additional functions combined with conventional elements represents a step on the development of a technique applicable to global and localized instability modes.
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El-Mously, Mohey El-Deen Mahmoud. "Free vibration of cylindrical and hyperboloidal cooling-tower shells". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627437.
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Bardell, N. S. "Wave propagation in periodically stiffened plates and shells". Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256281.
Testo completo
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Fégeant, Olivier. "Noise from wind turbines". Doctoral thesis, KTH, Byggnader och installationer, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3100.
Testo completoAbstract (sommario):
A rapid growth of installed wind power capacity is expectedin the next few years. However, the siting of wind turbines ona large scale raises concerns about their environmental impact,notably with respect to noise. To this end, variable speed windturbines offer a promising solution for applications in denselypopulated areas like the European countries, as this designwould enable an efficient utilisation of the masking effect dueto ambient noise. In rural and recreational areas where windturbines are sited, the ambient noise originates from theaction of wind on the vegetation and about the listener's ear(pseudo-noise). It shows a wind speed dependence similar tothat of the noise from a variable speed wind turbine and cantherefore mask the latter for a wide range of conditions.However, a problem inherent to the design of these machines istheir proclivity to pure tone generation, because of theenhanced difficulty of avoiding structural resonances in themechanical parts. Pure tones are deemed highly annoying and areseverely regulated by most noise policies. In relation to thisproblem, the vibration transmission of structure-borne sound tothe tower of the turbine is investigated, in particular whenthe tower is stiffened at its upper end. Furthermore, sincenoise annoyance due to wind turbine is mostly a masking issue,the wind-related sources of ambient noise are studied and theirmasking potentials assessed. With this aim, prediction modelsfor wind-induced vegetation noise and pseudo-noise have beendeveloped. Finally, closely related to the effect of masking,is the difficulty, regularly encountered by local authoritiesand wind farm developers, to measure noise immission from windturbines. A new measurement technique has thus been developedin the course of this work. Through improving thesignal-to-noise ratio between wind turbine noise and ambientnoise, the new technique yields more accurate measurementresults. Keywords: Masking, vibration transmission, diffraction,ambient noise, pseudo-noise, cylindrical shell, perturbationmethods, structural mobility, acoustic outdoor measurement.QC 20100616
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Kang, Lan. "Linear and non-linear free vibration analysis of plates and shallow shells". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0025/MQ30714.pdf.
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SILVA, FREDERICO MARTINS ALVES DA. "LOW DIMENSIONAL MODELS FOR NONLINEAR VIBRATION ANALYSIS AND STABILITY OF CYLINDRICAL SHELLS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2008. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=11688@1.
Testo completoAbstract (sommario):
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORNesta tese, as vibrações não-lineares e a estabilidade de uma casca cilíndrica contendo um fluido são estudadas com base em modelos de dimensão reduzida, isto é, modelos com um número reduzido de graus de liberdade. A partir dos funcionais de energia potencial e cinética de uma casca cilíndrica, deduzem-se suas equações de movimento. O campo de deformações da casca cilíndrica segue a teoria não- linear de Donnell para cascas abatidas. O fluido é considerado interno à casca irrotacional, não-viscoso e incompressível, sendo descrito a partir de um potencial de velocidade que leva em consideração a interação entre o fluido e a estrutura. Para resolver o sistema de equações de equilíbrio da casca, desenvolve-se um procedimento analítico que permite obter os campos de deslocamento axial e circunferencial em função dos deslocamentos laterais, além de atender as condições de contorno do problema. Desta forma, reduz-se o sistema de equações de equilíbrio a uma única equação diferencial parcial que é resolvida com o método de Galerkin. A determinação dos deslocamentos laterais é feita a partir de técnicas de perturbação que ordena os modos não-lineares de acordo com sua importância na solução da casca cilíndrica. Comprova-se essa ordenação através do método de Karhunen-Loève que fornece, também, uma expansão ótima para os deslocamentos laterais. Além dessas técnicas, apresenta-se uma redução polinomial que relacionam as amplitudes dos modos não-lineares com a amplitude do modo linear, criando uma expansão modal com 1 GDL. Apresentam-se respostas no tempo, fronteiras de instabilidade e diagramas de bifurcação para uma casca cilíndrica submetida a dois tipos de carregamentos harmônicos, pressão lateral e carga axial. A seguir, são propostos alguns critérios para a análise da a integridade do sistema dinâmico tanto para um sistema com 1 GDL quanto para um sistema multidimensional através da evolução e erosão das bacias de atração. Por fim, estuda-se o comportamento de cascas cilíndricas parcialmente cheias, mostrando a influência da altura do fluido nas fronteiras de instabilidade e curvas de ressonância da casca cilíndrica.
The nonlinear vibrations and stability of a fluid-filled cylindrical shell is investigated using reduced order models. First, the nonlinear equations of motion of the cylindrical shell are deduced based on the expressions for the potential and kinetic energy, which are obtained using Donnell shallow shell theory. The internal fluid is considered to be irrotational, non- viscous and incompressible. It is described by a velocity potential that takes into account the fluid-shell interaction. A procedure is proposed to obtain analytically the axial and circumferential displacements of the shell, satisfying the in-plane equations of motion and the associated boundary conditions. So, the problem is reduced to one partial differential equation of motion which is solved by the Galerkin method. The transversal displacement field is obtained by perturbation techniques. This enables one to identify the relevance of each term in the nonlinear expansion of the vibration modes. Then, the Karhunen-Loève method is employed to investigate de relative importance of each mode obtained by the perturbation analysis on the nonlinear response and to deduce optimal interpolation function to be used in the Galerkin procedure. A SDOF model is also obtained by relating the modal amplitudes of the nonlinear modes to the vibration amplitude of the linear mode. Time responses, instability boundaries and ifurcation diagrams are obtained for cylindrical shells subjected to harmonic lateral and axial loads. Different procedures for the analysis of the shell integrity are proposed based on the evolution and erosion of the basins of attraction in state-space. Finally, the influence of the fluid height on the stability boundaries and resonance curves is studied.
37
Loukaides, Evripides George. "Elementary morphing shells". Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/269724.
Testo completoAbstract (sommario):
Multistable shells are not yet completely understood. Even under the widespread Uniform Curvature (UC) assumption, the limits of this behaviour have not been established and the influence of individual material and geometric parameters has not been described conclusively; this research explores these open questions. In addition, this project was motivated by the need for practical design guidelines and the pursuit of alternative construction and actuation methods for multistable shells. Our analysis is based on an expression for the strain energy of a shell under a set of simplifying assumptions— primarily the aforementioned UC assumption. We extend this concept beyond the work of previous authors by admitting a more diverse range of anisotropic materials. Furthermore, we take advantage of some aspects of the mathematical field of Catastrophe Theory (CT) to maximise the generality of available results. When appropriate, we examine aspects of our predictions by constructing relevant shell structures, with particular focus on material considerations. A commercial Finite Element Analysis package provides additional means of analysis and comparison. On the theoretical front, the influence of certain control parameters on the availability of multistability is described in closed-form while a unique graphical overview of the limits of this behaviour is provided. In the lab, a novel tristable shell is constructed from a laminate and the use of specialized materials is scrutinised. In a subsequent project, a bistable spherical cap made from a customized material is actuated by a magnetic field—the ensuing snap-through event is recorded with a high-speed camera, leading to valuable insights on the transition geometry. Furthermore, we confirm the possibility of bistability for developable, non-prestressed shells, composed of a single material, using grid shells and thin honeycomb shells.
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Shin, Haksik. "Nonlinear analysis of axisymmetric shells". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0017/MQ58505.pdf.
Testo completo
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Nosier, Asghar. "On vibration and stability problems of laminated plates and shells using shear deformation theories". Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/37868.
Testo completoAbstract (sommario):
This study deals with the vibration and stability analyses of laminated plates and shells, using classical, first-order and third-order equivalent single-layer theories and the layer-wise theory of Reddy. Analytical solutions of these theories for natural frequencies and critical buckling loads of plates and shells under various boundary conditions are developed using an improved analytical procedure. A solution for the transient response of viscously damped cross-ply laminated plates, subjected to a sonic-boom type loading, is developed using the third-order shear deformation plate theory of Reddy and the first-order shear deformation plate theory.
The nonlinear dynamic equations of the first-order shear deformation plate theory and the third-order shear deformation plate theory of Reddy are reformulated in terms of a pair of equations describing the interior and the edge-zone problems of rectangular plates laminated of transversely isotropic layers. The pure—shear frequencies of the plate in linear and nonlinear problems are identified from the edge—zone equation. For certain boundary conditions the original system of equations are reduced to three in number, as in the classical plate theory.
The frequency and buckling equations of symmetric plates laminated of transversely isotropic layers are obtained using the Levinson’s third—order shear deformation plate theory. Using the interior and the edge—zone equations, the frequency and buckling equations are also obtained according to the first—order shear deformation plate theory. The solution contribution of the edge—zone equation is analyzed. By introducing a mixed approach, the bending problem of laminated plates with various boundary conditions is studied according to the first—order and Reddy’s third-order shear deformation plate theories.Ph. D.
40
Mohamedien, Mohamed Ahmed. "The buckling of grid shells". Thesis, University of Bath, 1990. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254000.
Testo completo
41
Mseikeh, Camille Hanna. "Wrinkling of membranes, plates, and shells". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30343.pdf.
Testo completo
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Mesnil, Romain M. Eng Massachusetts Institute of Technology. "Stability of elastic grid shells". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82716.
Testo completoAbstract (sommario):
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 83-86).
The elastic grid shell is a solution that combines double curvature and ease of mounting. This structural system, based on the deformation of an initially at grid without shear stiffness was invented more than fifty years ago. The apparition of new materials such as GFRP increased the potential of such structures whose properties depend on the deformation, or equivalently pre-stress of an initial structure. Elastic grid shells seem particularly promising as shelters, lightweight roofs, or kinetic structures. Although fundamental to the behavior of the strucure, the influence of the pre-stress on the stability of elastic grid shells has yet to be studied. Understanding this phenomenon could allow engineers to design more efficiently elastic grid shells. This thesis studies the influence of pre-stress on the stability of elastic grid shells. The research conducts a parametric study that focuses both a pre-buckled arch and initially at circular elastic grid shells with dierent grid spacing and levels of pre-stress. Realistic values of the parameters are determined from existing projects. The buckling analysis as well as the form-finding of the different structures are performed using finite element analysis. The tools are validated with comparison of the shape and buckling capacity of a pre-buckled arch with existing experiments. The parametric studies lead to recommendations aiming to facilitate the design of elastic grid shells. Keywords Elastic grid shell, Low-Speed Dynamics, form-finding, linear buckling analysis
by Romain Mesnil.
M.Eng.
43
El-Kaabazi, Nihal. "Free vibration of cylindrical shells with constant and variable thickness using the Wittrick-Williams algorithm". Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/55072/.
Testo completoAbstract (sommario):
With the rapid development of computer programming and systems, complex analytical shell problems are being tackled more than ever before. Finite element analysis has been the most widely used numerical method in modelling shell structures. In this thesis a more reliable and accurate method is demonstrated, in which the dynamic stiffness is derived from the exact differential equations, resulting in fewer elements and reduced computing time. Free undamped vibration analysis for constant and variable thickness cylindrical shells is carried out by deriving the dynamic stiffness matrix directly from the three differential equilibrium equations after transforming them to three ordinary differential equations and using the boundary value solver COLSYS. The natural frequencies and mode shapes are determined by using the Wittrick-Williams algorithm. A method of handling the effect of fixed end member frequencies below a limiting trial frequency is presented. Numerical examples for beams with constant and variable thicknesses and shells with constant and variable thicknesses are shown, and the method is validated by convergence studies and the handling of fixed end frequencies. A comparison of shell problem results with those of other authors is given, and a parametric study is carried out by varying the length to radius, radius to thickness, and thickness variation ratios. Results are obtained for different circumferential and axial harmonic numbers. Mode shapes are explained, for different shell thickness ratios and end conditions, and significant conclusions are drawn. From all the study and results obtained in this thesis it is ascertained that using the Wittrick-Williams algorithm in combination with COLSYS is a successful approach, and good agreements are effectively achieved for free undamped vibration of cylindrical shells with constant and variable thickness.
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Trimble, A. Zachary. "Downhole vibration sensing by vibration energy harvesting". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39891.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 117).
This thesis outlines the design of a prototype electromagnetic induction vibration energy harvesting device for use in a downhole environment. First order models of the necessary components for a generic vibration energy harvester are presented and used to predict the most sensitive parameters for the design of energy harvesting systems. A subset of the design tools created in MATLAB and Excel for vibration energy harvester design and first order optimization is introduced and used to aid in the design of an energy harvester specific to the downhole environment. The manufacture of a prototype design is documented and recommendations for future manufacturing processes are given. The prototype is then tested against the models. Based on the results, final conclusions and recommendations for future refinements are made, and other applications are suggested.
by A. Zachary Trimble.
S.M.
45
Zhong, Hongzhi. "Behaviour of shells under localised impact". Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308648.
Testo completo
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Hiller, Jean-François 1974. "Finite element analysis of shells with layers". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29255.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.Includes bibliographical references (leaves 160-165).
It is well established that thin shell structures frequently feature narrow bands of strain concentration and localized displacement irregularities referred to as boundary and internal layers. It is crucial to capture these layers properly as they can be sources of structural failures. Unfortunately, while the absence of analytical solutions to most shell problems of practical interest has spawned the development of a variety of finite element formulations over the years, largely speaking these schemes were proposed without a rigorous and comprehensive testing procedure available. We are now faced with a wealth of existing formulations and little way to assess their ability to model boundary and internal layers. Most of the difficulties in assessing the performance of shell finite elements stem from the use of mixed formulations. These are necessary to alleviate the locking phenomenon present in bending-dominated problems when displacement-based formulations are used. We develop a new error measure approach that is physically-based and can be used to assess the performance of mixed-interpolated shell finite element formulations. We apply this approach to the MITC (Mixed Interpolation of Tensorial Components) family of shell elements, a widely-used mixed formulation. We focus in particular on the performance of these elements when employed to analyze problems featuring layers, and specifically we assess the effect of mesh refinement in the regions where layers are present.
(cont.) We demonstrate that the MITC elements are consistent with the basic shell model and find that local mesh refinement allows us to obtain optima order convergence of the MITC solution to the solution of the mathematical model even in the presence of layers. The proposed error measure can be easily extended to other mixed-formulated finite elements used for problems such as incompressible materials and fluids, beams or plates.
by Jean-François N. Hiller.
Ph.D.
47
Al-Rashed, Rashed Abdulazeez. "Buckling patterns on pre-stretched bilayer shells". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113759.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 59-63).
We introduce a new experimental system to study the effects of pre-stretch on the buckling patterns that emerge from the biaxial compression of elastomeric bilayer shells. After fabricating our samples, releasing the pre-stretch in the substrate by deflation places the outer film in a state of biaxial compression and yields a variety of buckling patterns. We systematically explore the parameter space by varying the pre-stretch of the substrate and the ratio of film stiffness to substrate stiffness. The phase diagram of the system exhibits a variety of buckling patterns: from the classic periodic wrinkle to creases, folds, and high aspect ratio ridges. Our system is capable of easily transitioning between these buckling patterns, a first for biaxial systems. We focus on the wrinkle to ridge transition, where we find that pre-stretch plays an essential role in ridge formation, and that the ridge geometry (width, height) remains approximately constant throughout the process. For the localized ridge patterns, we find that the propagation of the ridge tip depends strongly on both strain and stiffness ratio, in a way that is akin to hierarchical fracture of brittle coatings.
by Rashed Abdulazeez Al-Rashed.
S.M.
48
Fazzolari, Fiorenzo A. "Advanced dynamic stiffness formulations for free vibration and buckling analysis of laminated composite plates and shells". Thesis, City University London, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635315.
Testo completoAbstract (sommario):
In this thesis both static and dynamic analyses of composite thin-walled structures are carried out. Most notably, the Dynamic Stiffness Method (DSM) has been extensively exploited to develop advanced formulations for plates and shells. In particular, the. Dynamic Stiffness (DS) matrices have been developed for laminated composite plates and shells using Higher-order Shear Deformation Theory (HSDT) in order to investigate their free vibration behavior and buckling characteristics. First, the Governing Differential Equations (GDEs) of motion and associated natural Boundary Conditions (BCs) (Neumann-type) for the given displacement field are derived via Hamilton's principle for both composite plate and shell structures. In the case of composite plates, the DS matrices are formulated for both out-of-plane and in-plane deformations. The GDEs for each of the two cases are solved in Levy's form separately. Next the problems for both plates and shells are reduced to a system of ordinary differential equations which are then solved by using the classical exponential solution procedure.
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Kassegne, Samuel Kinde. "Layerwise theory for discretely stiffened laminated cylindrical shells". Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07282008-134249/.
Testo completo
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Kwok, Raymond Moon Keung. "Mechanics of damaged thin-walled cylindrical shells". Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/993/.
Testo completo