Dissertations / Theses on the topic 'Shell vibration'
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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.
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Ustundag, Burak. "On the free vibration behavior of cylindrical shell structures." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67717.
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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.
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Mustafa, B. A. J. "Free vibration analysis of stiffened circular shells." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/14141.
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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.
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Dewi, Fata Dwi Endyana Jr. "Three-Dimensional Analysis of Wave Attenuation by Anchored Hemicylindrical Shell." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35761.
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The performance of a flexible structure as a breakwater is investigated numerically. The structure is a hemicylinder and is filled with water of uniform pressure. It is anchored along the sides. Only flexural modes are present.
The structure is modeled as an elastic shell using the finite element program ABAQUS. The fluid is assumed to be inviscid and incompressible. The fluid flow is analyzed using a boundary integral method and the integral equation is solved numerically by a panel method.
The vibration characteristics of the structure are analyzed both in the absence and presence of water. The hydrodynamic coefficients, forces, and the dynamic response of the structure in waves are obtained as a function of the wave number. Two different water depths of 5 m and 6 m are considered. For each water depth, normal and oblique incident waves are considered. The free surface elevation in front of and behind the structure is evaluated for different wave frequencies and directions. The results indicate that the flexible structure is effective in reducing the incident wave intensity over a wide range of frequencies.Master of Science
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Van, Zyl Marilize. "Prediction of flow-induced vibration in shell-and-tube heat exchangers." Diss., University of Pretoria, 2004. http://hdl.handle.net/2263/28055.
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Please read the abstract (Summary) in the 00front part of this documentDissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006.
Mechanical and Aeronautical Engineering
unrestricted
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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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Nasir, Azhar Mahmood. "Axisymmetric shell structures for multi-use." Thesis, Queensland University of Technology, 2002. https://eprints.qut.edu.au/36147/1/36147_Digitised%20Thesis.pdf.
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Shell structures find use in many fields of engineering, notably structural, mechanical, aerospace and nuclear-reactor disciplines. Axisymmetric shell structures are
used as dome type of roofs, hyperbolic cooling towers, silos for storage of grain, oil and industrial chemicals and water tanks. Despite their thin walls, strength is derived due to the curvature. The generally high strength-to-weight ratio of the shell form, combined with its inherent stiffness, has formed the basis of this vast application. With the advent in computation technology, the finite element method and optimisation techniques, structural engineers have extremely versatile tools for the optimum design of such structures.
Optimisation of shell structures can result not only in improved designs, but also in a large saving of material.
The finite element method being a general numerical procedure that could be used to treat any shell problem to any desired degree of accuracy, requires several runs in order to obtain a complete picture of the effect of one parameter on the shell structure. This redesign I re-analysis cycle has been achieved via structural optimisation in the present research, and MSC/NASTRAN (a commercially available finite element code) has been used in this context for volume optimisation of axisymmetric shell structures under axisymmetric and non-axisymmetric loading conditions.
The parametric study of different axisymmetric shell structures has revealed that the hyperbolic shape is the most economical solution of shells of revolution. To establish this, axisymmetric loading; self-weight and hydrostatic pressure, and non-axisymmetric loading; wind pressure and earthquake dynamic forces have been modelled on graphical pre and post processor (PATRAN) and analysis has been performed on two finite element codes (ABAQUS and NASTRAN), numerical model verification studies are performed, and optimum material volume required in the walls of cylindrical, conical, parabolic and hyperbolic forms of axisymmetric shell structures are evaluated and reviewed. Free vibration and transient earthquake analysis of hyperbolic shells have been performed once it was established that hyperbolic shape is the most economical under all possible loading conditions. Effect of important parameters of hyperbolic shell structures; shell wall thickness, height and curvature, have been evaluated and empirical relationships have been developed to estimate an approximate value of the lowest (first) natural frequency of vibration.
The outcome of this thesis has been the generation of new research information on performance characteristics of axisymmetric shell structures that will facilitate improved designs of shells with better choice of shapes and enhanced levels of economy and performance.
Key words; Axisymmetric shell structures, Finite element analysis, Volume Optimisation_ Free vibration_ Transient response.
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Huang, He. "Large-Amplitude Vibration of Imperfect Rectangular, Circular and Laminated Plate with Viscous Damping." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1924.
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Large-amplitude vibration of thin plates and shells has been critical design issues for many engineering structures. The increasingly more stringent safety requirements and the discovery of new materials with amazingly superior properties have further focused the attention of research on this area. This thesis deals with the vibration problem of rectangular, circular and angle-ply composite plates. This vibration can be triggered by an initial vibration amplitude, or an initial velocity, or both. Four types of boundary conditions including simply supported and clamped combined with in-plane movable/immovable are considered.
To solve the differential equation generated from the vibration problem, Lindstedt's perturbation technique and Runge-Kutta method are applied. In previous works, this problem was solved by Lindstedt's Perturbation Technique. This technique can lead to a quick approximate solution. Yet based on mathematical assumptions, the solution will no longer be accurate for large amplitude vibration, especially when a significant amount of imperfection is considered. Thus Runge-Kutta method is introduced to solve this problem numerically. The comparison between both methods has shown the validity of the Lindstedt's Perturbation Technique is generally within half plate thickness. For a structure with a sufficiently large geometric imperfection, the vibration can be represented as a well-known backbone curve transforming from soften-spring to harden-spring. By parameter variation, the effects of imperfection, damping ratio, boundary conditions, wave numbers, young's modulus and a dozen more related properties are studied. Other interesting research results such as the dynamic failure caused by out-of-bound vibration and the change of vibration mode due to damping are also revealed.
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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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Lo, Hung-Chieh. "Vibration Characteristics of Thin-Walled Noncircular Composite Cylinders." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77207.
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The lowest natural frequencies of thin-walled noncircular fiber-reinforced composite cylinders, specifically cylinders with elliptical cross sections, are investigated. Of interest is the variation of the lowest natural frequency, the so-called fundamental frequency, as a function of wall laminate properties, cross-sectional eccentricity and other cylinder geometric parameters. Both simple and clamped support boundary conditions are investigated. Laminate properties that are uniform with circumferential location and laminate properties that vary with circumferential location, by way of varying laminate fiber angle with circumferential location, are considered. As the radius of curvature of a noncircular cylinder varies with circumferential location, it is logical to consider the influence of circumferentially varying fiber orientation on the fundamental frequency. The analysis for predicting the fundamental frequency is based on Donnell shell theory, linear elastic properties, and the use of Hamilton's Principle in conjunction with the Rayleigh-Ritz technique. By use of a so-called shape factor, the magnitude of cylinder normal displacements are modulated to be larger in the regions of the cross section with the largest radius of curvatures and smaller in the regions with the smallest radius of curvature. The final equations for predicting the fundamental frequency are quite complex, but a series of approximations results in a hierarchy of simpler equations, the simplest being referred to as Lo's approximation. The prediction of the fundamental frequencies is spot checked by comparing the results as predicted by the various levels of approximation with predictions of a shell-based finite element model. Considering uniform laminate properties, comparisons between the developed analysis and the finite element model are good for all levels of simpler equations, and excellent in some cases. The developed analysis is subsequently used for parameter studies. It is found that compared to a circular cylinder of the same circumference and with uniform laminate properties, the fundamental frequency of an elliptical cylinder is always less. Surprisingly, based on the results obtained, it appears that for a given cylinder geometry the fundamental frequency is not particularly sensitive to wall lamination sequence, though the wave number in the circumferential direction of the mode shape associated with the fundamental frequency is sensitive to lamination sequence. Considering cylinders with circumferentially varying fiber orientation, comparisons between the developed analysis and the finite element model for most of the cases studied are good. However, the developed equations are limited since it is difficult to find a set of known functions to describe the deformation of an arbitrary lamination sequence when applying the Rayleigh-Ritz technique. In general, in can be concluded that the effect of varying fiber orientation on the fundamental frequency is much less than the influence of cylinder aspect ratio. It can also be concluded that the developed analysis would be an excellent tool for design purposes, as the calculation of the fundamental frequency is done quickly, and design trade-offs studies would be easy.Ph. D.
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Jha, Akhilesh K. "Vibration Analysis and Control of an Inflatable Toroidal Satellite Component Using Piezoelectric Actuators and Sensors." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/28243.
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Inflatable structures have been a subject of renewed interest in recent years for space applications such as communication antennas, solar thermal propulsion, and entry/landing systems. This is because inflatable structures are very lightweight and on-orbit deployable. In addition, they have high strength-to-mass ratio and require minimal stowage volume, which makes them especially suitable for cost-effective large space structures. An inflated toroidal structure (torus) is often used there in order to provide structural support. For these structures to be effective, their vibration must be controlled while keeping the weight low. Piezoelectric materials have become strong candidates for actuator and sensor applications in the active vibration control of such structures due to their lightweight, conformability to the host structure, and distributed nature. In this study, our main focus is to understand the dynamic characteristics of an inflatable torus and to control its vibration using piezoelectric actuators and sensors.
The first part of this study is concerned with theoretical formulations. We use Sanders' shell theory to derive the governing equations of motion for a shell subjected to pressure. To take into account the prestress effects of internal pressure, we use geometric nonlinearity, and to model the follower action of pressure force, we consider the work done by internal pressure during the vibration of the shell. These equations are then specialized to obtain approximate equations presented by previous researchers. We extend this analytical formulation to derive the equivalent forces due to piezoelectric actuators in unimorph and bimorph configurations and include their mass and stiffness effects in the governing equations. A sensor equation is also developed for the shell. The actuator and sensor equations are then written in terms of modal displacements and velocities so as to evaluate their interactions with different vibratory modes.
In the second part, we focus on numerical studies related to an inflated torus. At first, we perform a free vibration analysis of the inflated torus using Galerkin's method. We study how different parameters (aspect ratio, internal pressure, and wall-thickness) of the inflated torus affect the natural frequencies and mode shapes of the inflated torus. We compare the results obtained from the theory used in this research with the results from different approximate theories and commercial finite element codes. The results suggest that the use of an accurate shell theory and pressure effect is very important for the vibration analysis of an inflated torus. Next, the modal behaviors of piezoelectric actuator and sensor are analyzed. A detailed study is done in order to understand how the size and location of actuator and sensor affect the modal forces, the modal sensing constants, and the overall performance for all the considered modes. In order to determine the optimal locations and sizes of actuators and sensors, we use a genetic algorithm. Natural frequencies and mode shapes are calculated considering the passive effects of actuators and sensors. Finally, we attempt the vibration control of the inflated torus using the optimally designed actuators and sensors and sliding mode controller/observer. The numerical simulations show that piezoelectric actuators and sensors can be used in the vibration control of an inflatable torus. The robustness properties of the controller and observer against the parameter uncertainty and disturbances are verified.Ph. D.
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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.
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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.
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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.
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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.
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Molloy, Sean J. "Finite Element Analysis of a Pair of Leaning Pressurized Arch-Shells Under Snow and Wind Loads." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36608.
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A structure comprised of two arches that lean against each other at the apex is considered. The arches are thin shells with internal pressure. This type of structure with solid arches has been used in bridges, such as the Gateway Arch Bridge in Columbus, Indiana, U.S.A., the Monongahela River Bridge in Pittsburgh, Pennsylvania, U.S.A., and a pedestrian bridge at the Pacific Tower in Paris, France. A series of leaning arches was incorporated in the frame of the Museum of the Moving Image, a temporary structure in London, England, during 1992-1994. Pressurized arch-shells made of a flexible material have been utilized as part of the framework for some transportable tent-like structures.
The behavior of a pair of pressurized leaning arch-shells with various tilt angles, boundary conditions, and loads is investigated numerically. Several types of loads are considered, including uniformly-distributed vertical loads applied over all or half of the structure (representing snow), and wind loads on the structure. The arches are pinned or fixed to the ground. Deflections, vibrations, and stability of the structures are investigated using the finite element method. The effect of the tilt angle on the response is examined, and buckling may occur for some tilt angles under vertical loading. This type of structure has not been used widely, but may be effective for various applications.
Master of Science
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Caresta, Mauro Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Structural and acoustic responses of a submerged vessel." Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/44404.
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Excitation of the low frequency vibrational modes of a submerged vessel can generate significant radiated noise levels. Vibrational modes of a submarine hull are excited from the transmission of fluctuating forces through the shaft and thrust bearings due to the propeller rotating in an unsteady fluid. The focus of this work is to investigate the structural and acoustic responses of a submarine hull under axial excitation. The submarine hull is modelled as a cylindrical shell with internal bulkheads and ring stiffeners. The cylindrical shell is closed by truncated conical shells, which in turn are closed at each end using circular plates. The entire structure is submerged in a heavy fluid medium. The structural responses of the submerged vessel are calculated by solving the cylindrical shell equations of motion using a wave approach and the conical shell equations with a power series solution. The displacement normal to the surface of the structure in contact with the fluid medium was calculated by assembling the boundary/continuity matrix. The far field radiated sound pressure was then calculated by means of the Helmholtz integral. Results from the analytical model are compared with computational results from a fully coupled finite element/boundary element model. The individual and combined effects of the various influencing factors, corresponding to the ring stiffeners, bulkheads, conical end closures and fluid loading, on the structural and acoustic responses are characterised by examining the contribution by the circumferential modes. It is shown that equally spaced internal bulkheads generate a periodic structure thus creating a grouping effect for the higher circumferential modes, but do not have strong influence on the sound radiation. Stiffeners are found to have an important effect on both the dynamic and acoustic responses of the hull. The contribution of the conical end closures on the radiated sound pressure for the lowest circumferential mode numbers is also clearly observed. This work shows the importance of the bending modes when evaluating the sound pressure radiated by a submarine under harmonic excitation from the propulsion system.
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David, Claire. "Modélisation de coques composites multicouches." Cachan, Ecole normale supérieure, 1996. http://www.theses.fr/1996DENS0027.
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La mise en place d'un modèle théorique de coque composite multicouche est proposée. Parmi les objectifs du modèle, on retiendra: " la satisfaction exacte des conditions de continuité aux interfaces pour les déplacements et les contraintes, ainsi que des conditions aux limites ; " le raffinement des termes de membrane, de cisaillement transverse ; " l'amélioration du calcul des contraintes de cisaillement transverse, sans recours a des facteurs de correction. L'approche retenue est de type cinématique. Les raffinements des termes de membrane et de cisaillement sont pris en compte par l'intermédiaire de fonctions trigonométriques suivant la variable d'épaisseur, la continuité du champ de déplacement étant automatiquement assurée par l'introduction, dans le champ de cinématique, de la fonction de Heaviside. Les équations du mouvement et conditions aux limites sont déduites du principe de Hamilton. On ne conserve que cinq déplacements généralisés indépendants. La validité du modèle est testée sur des problèmes pour lesquels une solution tridimensionnelle exacte existe. La sensibilité aux effets de bord est également examinée. La comparaison avec des calculs éléments finis est effectuée. Enfin, l'application directe à des problèmes de dynamique est envisagée
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Nilsson, Carl-Magnus. "Waveguide Finite Elements Applied on a Car Tyre." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3812.
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Structures acting as waveguides are quite common withexamples being, construction beams, fluid filled pipes, railsand extruded aluminium profiles. Curved structures like cartyres and pipe-bends may also be considered as waveguides. Wavesolutions in such structures may be found by a method calledthe Waveguide Finite Element Method or WFEM. This method uses afinite element approach on the cross-section of a waveguide tomodel the vibro-acoustic response as a set of linear, coupled,one dimensional, wave-equations.
In this thesis six novel waveguide finite elements arederived and validated. These elements are, straight and curvedpre-stressed, orthotropic or anisotropic shell elements,straight and curved fluid elements, and straight and curvedfluid-shell coupling elements.
Forced response and input power calculations for infiniteand periodic waveguides are presented. The assembled waveguidemodels can also serve as input for the Super Spectral FiniteElement Method, which enables forced response calculations formore complex boundaries. Furthermore, several properties ofdamped and undamped wave solutions are investigated.
Finally, a car tyre model, encompassing for the highlyanisotropic material and the air cavity inside the tyre is setforth. A number of forced response calculations for this modelare presented and compared with measurements with goodagreement.
Keywords:wave equation, wave solution, waveguide,finite element, spectral finite element, tyre noise, tyrevibration, input power, shells, pre-stress, fluid-shellcoupling axi-symmetric, two-and-half-dimensional
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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.
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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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Martinet, Quentin. "Étude des effets environnementaux sur les modes acoustiques confinés de nanoparticules par diffusion inélastique de la lumière." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1152/document.
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Au cours des vingt dernières années, la diffusion inélastique de la lumière par les modes propres de vibration des nanoparticules, appelés modes de Lamb, s’est avérée être une méthode très efficace pour caractériser la taille et les propriétés mécaniques des nano-objets. La fréquence de résonance d’une nano-sphère, dans la gamme du gigahertz, est donnée, en première approximation, par le ratio de la vitesse acoustique du matériau massif et la taille du confinement. Les raffinements du modèle théorique permettent d’obtenir, à partir de ces modes de vibration, des informations essentielles sur la géométrie et l’environnement local des nano-objets. L’objectif de cette thèse est de sonder le domaine de validité du modèle de Lamb, d’analyser les différents impacts de l’environnement sur ces modes de vibration et de développer de nouvelles méthodes pour les mesurer. Plusieurs aspects de l’interaction avec le milieu extérieur peuvent ainsi être pris en considération selon le type de système étudié. D’une part, la délocalisation de l’onde acoustique dans le cas de systèmes cœur-coquille, qui est gouvernée par les impédances acoustiques respectives du cœur et de la coquille, et qui se traduit par un couplage mécanique. D’autre part, l’effet de masse inertielle induite par la présence de ligands organiques à la surface de la particule qui modifie la fréquence de résonance. La validité de ces deux approches est ainsi discutée en fonction de la configuration des objets considérés, puis ces modèles théoriques sont appliqués à des cas réels tels que des nanoparticules cœur-coquille et des nano-plaquettes de semi-conducteurs ou des agrégats métalliques colloïdaux. L’effet de masse inertielle s’avère non négligeable pour des objets de petites tailles et il est ainsi montré la faisabilité de réaliser des nano-balances ultra-sensibles capable de sonder l’environnement proche des nano-objets. Par ailleurs, dans le cas des agrégats d’or, cette approche permet de discuter les limites du modèle de Lamb, basé sur la théorie des milieux continus, sur des vibrations n’impliquant que six atomes. Ainsi, grâce à la spectroscopie Raman basses fréquences, il apparait que les résultats expérimentaux des vibrations de ces objets s’accordent à la fois avec l’approche des milieux continus en considérant l’effet de masse inertielle et aussi avec les calculs de dynamique moléculaire. Finalement, le développement expérimental d’un montage optique capable de mesurer ces modes Raman basses fréquences sur une particule unique en milieu liquide est présenté. Cette approche nécessite de localiser une particule en milieu liquide à l’aide de nano-pinces plasmoniques puis d’exalter le signal Raman basses fréquences en stimulant les modes de vibration par électrostriction. Les perspectives étant d’appliquer cette méthode à l’étude de la dynamique vibrationnelle de nano-objet unique tel que des virus ou des protéinesOver the past twenty years, inelastic light scattering by vibrational eigenmodes of nanoparticles, called Lamb modes, has proven to be an effective method for characterizing the size and mechanical properties of nano-objects. The resonant frequency of a nano-sphere, in the gigahertz range, is given, as a first approximation, by the ratio of the acoustic velocity of the bulk material and the size of confinement. The refinements of the theoretical model allow to obtain, from these eigenmodes, information on the shape and local environment of nano-objects.The objective of this thesis is to probe the domain of validity of the Lamb model, to analyze the different impacts of the environment on eigenmodes and to develop a new strategy to measure them. Several aspects of interaction with the external medium can be considered depending on the system studied. On the one hand, the delocalization of the acoustic wave in the case of core shell systems is ruled by the acoustic impedance of the core and the shell and leads to a mechanical coupling. On the other hand, the inertial mass effect induced by the presence of organic ligands on the surface of the particle modifies the resonant frequency. The validity of both approaches is discussed according to the configuration and these models are applied to real cases, such as semiconductor core shell nanoparticles and nanoplatelets, or gold colloidal clusters. The inertial mass effect is significant for small objects and it is shown the feasibility to realize ultra-sensitive nano-balance capable of probing the local environment of nano-objects. Furthermore, in the case of gold clusters, this approach makes it possible to discuss the limit of the Lamb model, based on continuum mechanics, to interpret vibrations involving only six atoms. Thanks to low frequency Raman spectroscopy, it appears that the experimental results are in good agreement with both the continuum mechanics approach, by considering the inertial mass effect, and also with density functional theory (DFT) calculations. Finally, the experimental development of an optical set-up capable of measuring low frequency Raman modes on a single nanoparticle in a liquid medium is presented. This technic requires to localize a nanoparticle in a liquid medium with plasmonic tweezers and to enhance the low frequency Raman signal by stimulating vibrational modes with electrostriction. The perspectives are to apply this method to the dynamical study of a single object such as viruses or proteins
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Talmant, Maryline. "Retrodiffusion d'une impulsion ultrasonore breve par une coque cylindrique a paroi mince." Paris 7, 1987. http://www.theses.fr/1987PA077164.
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Une comparaison peut etre etablie entre les ondes circonferentielles se propageant a la surface du tube et les ondes de surface se propageant sur une plaque plane. L'analyse experimentale est fondee sur l'obtention des variations de la vitesse de groupe en fonction de la frequence des ondes circonferentielles ainsi que de leur reemission
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Gautier, François. "Contribution a l'etude du comportement vibroacoustique des instruments de musique a vent." Le Mans, 1997. http://www.theses.fr/1997LEMA1016.
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Il est aise de constater que le corps d'un instrument de musique a vent en fonctionnement vibre. L'influence de ces vibrations sur le son musical produit est aujourd'hui un sujet ouvert. En effet, certains musiciens leur attribuent un effet, difficile a decrire en termes objectifs, et souvent mis en relation avec la nature du materiau constituant l'instrument, tandis que nombre d'acousticiens affirment qu'il s'agit d'une effet d'ordre superieur. Cette etude apporte une contribution a cette discussion, en quantifiant cet effet a l'aide d'un modele analytique du comportement vibroacoustique d'un instrument de musique en situation de jeu. Dans l'approche proposee, le corps de l'instrument de musique est modelise par une coque cylindrique, en appui simple a ses deux extremites, constituee d'un materiau elastique. Le systeme excitateur de l'instrument est modelise par une source acoustique (vitesse acoustique imposee sur la section d'entree du tube) et mecanique (force ponctuelle appliquee a l'embouchure), excitant en regime force le systeme vibroacoustique constitue par la coque cylindrique et les fluides interne et externe. Trois types de couplage sont identifies : couplage coque/fluide interne, couplage coque/fluide externe, couplage inter-modal acoustique induit par le rayonnement de l'extremite ouverte du tube. L'etude montre que la puissance acoustique rayonnee par la section terminale du tube, quantite qui caracterise le son percu par l'auditeur, est legerement differente suivant que les parois du tube vibrent ou ne vibrent pas. Cette difference est interpretee en termes de decalages des frequences de resonances acoustiques induits par les vibrations de la coque. De faibles modifications du timbre de l'instrument, qui ne sont vraisemblablement pas perceptibles par l'oreille humaine sont associees a ces decalages frequentiels.
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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.
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Shahla, Wajih. "Finite element analysis of the statics of, and vibrations in, axisymmetric shells." Thesis, Aston University, 1985. http://publications.aston.ac.uk/16662/.
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The finite element process is now used almost routinely as a tool of engineering analysis. From early days, a significant effort has been devoted to developing simple, cost effective elements which adequately fulfill accuracy requirements. In this thesis we describe the development and application of one of the simplest elements available for the statics and dynamics of axisymmetric shells . A semi analytic truncated cone stiffness element has been formulated and implemented in a computer code: it has two nodes with five degrees of freedom at each node, circumferential variations in displacement field are described in terms of trigonometric series, transverse shear is accommodated by means of a penalty function and rotary inertia is allowed for. The element has been tested in a variety of applications in the statics and dynamics of axisymmetric shells subjected to a variety of boundary conditions. Good results have been obtained for thin and thick shell cases .
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Timarci, Taner. "Vibrations of composite laminated cylindrical shells." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283227.
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Calbris, Gaëtan. "Dynamique thermique et vibrationnelle de nanoparticules d'or et Au@SiO2 en régime femtoseconde : effet de la nanostructuration." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14213/document.
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Généralement, un bon conducteur thermique est aussi bon conducteur électrique (Wiedemann-Franz). Pour de nombreuses applications, il est impératif de pouvoir découpler ces deux propriétés. La nanostructuration permet de modeler les propriétés thermiques sans affecter les propriétés électriques. Lors de cette thèse, nous nous sommes intéressés à la synthèse et à la caractérisation d'un matériau initialement isolant dans lequel est insérée une assemblée de nanoparticules métalliques. Le nanocomposite élaboré est constitué de nanoparticules cœur@écorce (Au@SiO2 ou Au@Thiol) structurées en opale par méthode de type "Langmuir". Lorsque la concentration en nanoparticules est suffisante, une amplification du transfert thermique dans le nanocomposite est prédite par certains auteurs. Le couplage par rayonnement en champ proche, majoritairement plasmonique, constitue un nouveau mécanisme de transport de chaleur. Dans ce travail, nous avons étudié le transfert d'énergie au sein de nanoparticules isolées et sous forme de réseau. Dans un premier temps, nous présentons les techniques de synthèse chimique mises en œuvre pour la conception des nanocomposites et détaillons leurs propriétés optiques. Puis, nous présentons la conception du banc de mesure, il s'agit d'un banc d'imagerie pompe-sonde femtoseconde accordable en longueur d'onde permettant des études en réflexion et transmission. Les expériences que nous avons menées nous ont permis d'étudier la dynamique thermique électronique de nanoparticules d'or pour différents environnements et de mettre en évidence expérimentalement des modes de vibration acoustiques de systèmes cœur-écorce lorsqu'ils sont soumis à une excitation laser femtosecondeTypically, a good thermal conductor is also a good electrical conductor (Wiedemann-Franz). For several applications, it is imperative to be able to decouple these two properties. Nanostructuration allows for the modification of thermal properties without affecting electrical properties. This thesis is concerned with the synthesis and characterization of nanocomposites made from an insulating matrix impregnated with metallic nanoparticles. The elaborated nanocomposite is assembled from core@shell nanoparticles (Au@SiO2 or Au@Thiol) structured in an artificial opal by the "Langmuir" method. When the nanoparticle concentration is sufficiently high, certain authors predict an amplification of thermal transport in the nanocomposite. The radiative near-field coupling, largely plasmonic, constitutes a new mechanism for heat transport. In this work, we have studied the energy transfer within isolated nanoparticles and in arrays. First, we present chemical synthesis techniques used for the nanocomposites conception and detailed their optical properties. Then, we present the conception of the experimental set-up; a multicolor femtosecond pump-probe Imaging system permitting studies in reflection or transmission. These experiments permit us to study the electronic temperature dynamics of gold nanoparticles in different environments and to measure core@shell system's acoustic vibrational modes femtosecond laser excitation
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Li, Nong. "Vibration of laminated orthotropic composite plates and shells." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6946.
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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.
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Alizadeh, Y. "Free vibration of partially supported plates and shells." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/10751.
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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).
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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.
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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.
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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.
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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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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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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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Dressler, Bernhard. "Modélisation numérique des coques en grandes transformations : mise en oeuvre dans un environnement orienté objet." Châtenay-Malabry, Ecole centrale de Paris, 1997. http://www.theses.fr/1997ECAP0522.
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Ce mémoire est consacré à la dynamique des coques en grandes rotations. La théorie bidimensionnelle des coques est déduite du principe des travaux virtuels d'un milieu continu tridimensionnel en introduisant la cinématique de Mindlin. On obtient un système d'équations non-linéaires qui est linéarise par rapport aux déplacements de la surface moyenne ainsi que par rapport aux paramètres de rotation. La paramétrisation des grandes rotations par le vecteur de rotation est comparée à la paramétrisation directe par la matrice de rotation. En vue d'une discrétisation en éléments finis isoparamétriques on utilise des objets tensoriels intrinsèques qui sont ramenés a une configuration de référence aplatie. Cette configuration aplatie est identifiée à l'élément de référence. En dehors d'une loi de comportement hyper élastique on présente deux lois élastoplastiques en grandes transformations supposant que les déformations locales restent petites. Les efforts résultants sont obtenus ou par une intégration numérique dans l'épaisseur ou a partir d'une loi de comportement globale qui est directement formulée en efforts résultants. L’implémentation numérique est effectuée dans un environnement de programmation orientée objet qui a été développe pour l'analyse non-linéaire par la méthode des éléments finis. En particulier, on regarde le rôle des grandes rotations dans le calcul de la matrice de rigidité tangente. Des résultats numériques confirment l'efficacité de cette approche.
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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.
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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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Awrejcewicz, Jan, Lidiya Kurpa, and T. Shmatko. "Vibration of functionally graded shallow shells with complex shape." Thesis, Department of Automation, Biomechanics and Mechatronics, 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/37081.
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The method for studying the geometrically nonlinear vibrations of functionally graded shallow shells with a complex planform is proposed. Сomposite shallow shells made from a mixture of ceramic and metal are considered. In order to take into account varying of the volume fraction of ceramic the power law is accepted. Formulation of the problem is carried out using the refined geometrically nonlinear theory of shallow shells of the first order (Timoshenko’s type). The R-functions theory, variational Ritz’s method, procedure by Bubnov Galerkin and Runge-Kytta method are used in the developed approach. A distinctive feature of the proposed approach is the method of reducing the initial nonlinear system of equations of motion for partial derivatives to a nonlinear system of ordinary differential equations. According to the developed approach first it is necessary to solve linear vibration problem. Further to solve elasticity problems for inhomogeneous differential equations with right hand side, containing eigen functions. Obtained solutions of these problems are applied for representation of unknown functions of the nonlinear problem. Application of the theory of R-functions on every step allows us to extend the proposed approach to the shell with arbitrary shape of plan and different kinds of boundary condition. The proposed method is validated by investigation of test problems for shallow shells with rectangular and elliptical planform and applied to new vibration problems for shallow shells with complex planform.
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Vautier, Isabelle. "Influence du contact unilatéral sur le comportement vibratoire de coques soudées par points." Châtenay-Malabry, Ecole centrale de Paris, 1994. http://www.theses.fr/1994ECAP0363.
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Nous présentons dans cette thèse une modélisation du contact unilatéral entre coques soudées en dynamique et donnons des informations qualitatives sur l'influence de ces phénomènes sur la réponse en fréquence des structures. Notre objectif est une meilleure compréhension des mécanismes de transmission des vibrations et des bruits dans les voitures. Le modèle de coques minces utilise est celui de Koiter, traité par une formulation mixte proposée par Ph. Destuynder et M. Salaun. Les soudures sont représentées comme des corps rigides. Le contact unilatéral, suppose sans frottement, est pris en compte par une méthode de dualité permettant d'éviter l'interpénétration des sous-structures nœud à nœud, le multiplicateur de Lagrange représentant l'effort de contact normal. Comme le phénomène est non linéaire, nous effectuons une résolution des équations dans le domaine temporel, suivie d'une analyse de Fourier. Les équations du contact sont résolues par un algorithme de points intérieurs très efficace du AJ. Herskovits, dans le cadre d'une intégration en temps par la méthode de Neuwmark. On présente également différentes formes d'excitations large bande permettant d'obtenir la réponse de la structure dans une gamme de fréquences donnée, et en particulier la technique du MLS. Divers outils de traitement du signal sont également adaptés ou construits en vue de l'interprétation quantitative des résultats ; un panorama rapide de quelques éléments de psycho-acoustique permet, quant à lui, d'obtenir des conclusions qualitatives en termes de gène auditive. L'implémentation des modèles est faite dans le code éléments finis Héraclès, qui est valide en statique et en dynamique sur des cas simples et sur des pièces industrielles. Nous observons alors que le contact unilatéral modifie de façon importante le spectre de réponse: renforcement de certaines composantes fréquentielles, création de nouvelles fréquences, apparition de bruit large bande, et modulations d'amplitudes de certaines fréquences, ce qui est gênant pour l'oreille
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Chiambaretto, Pierre-Louis. "Modèle vibratoire de réservoir cryotechnique de lanceur : définition d’un méta-matériau équivalent." Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0022/document.
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L’hydrogène liquide est un ergol utilisé en complément de l’oxygène liquide pour la propulsion de nombreux lanceurs en particulier ceux de la famille Ariane. Cependant, sa dangerosité interdit la réalisation d’essais, en particulier vibratoires, sur des réservoirs remplis. Cette thèse explore une piste d’étude permettant de réaliser ces essais vibratoires sur le réservoir rempli d’un matériau de substitution : un ensemble de billes pré-contraintes. L’objectif est d’obtenir un comportement modal similaire en termes de modes et de fréquences propres à celui du réservoir rempli d’hydrogène liquide pour l’étude des premiers modes. Pour répondre à cet objectif, cette étude est développée en deux parties. Dans la première partie, une approche analytique basée sur une méthode par équivalences fréquentielles est détaillée. Après avoir présenté les grandes lignes de la méthodologie utilisée et l’ensemble des modèles développés, la méthodologie est appliquée au cas étudié expérimentalement de manière à mettre en évidence l’influence des différents paramètres et de proposer une première méthode pour choisir un jeu de billes adapté. La seconde partie, traite principalement des aspects expérimentaux et numériques. Après avoir détaillé la caractérisation des billes utilisées, le montage expérimental conçu et réalisé pour effectuer des essais vibratoires sur un réservoir rempli de billes pré-contraintes est présenté. Les différents résultats obtenus avec ce montage sont étudiés au regard de l’approche analytique, mais aussi de modèles numériques utilisant des éléments-discrets et des éléments-finisLiquid hydrogen is a propellant alternatively used with liquid oxygen for the propulsion of many launchers, especially those of the Ariane family. However, its dangerousness prohibits vibration tests on filled tank. The aim of this PHD is to explore the possibility to carry out such vibration tests by filling these tanks with a substitute material : a set of pre-stressed balls. As further argued and developed in the report, the objective is to obtain a modal behavior similar in term of mode shapes and natural frequencies to those of the tank filled with liquid hydrogen for the first modes. In the first part, an analytical approach based on a method using frequency equivalences is detailed. After presenting the outlines of the methodology used and all the models developed, the methodology is applied to the experimentally studied case in order to highlight the influence of the different parameters as well as then to propose a first method to choose a set of well adapted balls. The second part deals mainly with experimental and numerical aspects. Firstly, the balls used in the thesis are characterized. Then, the experimental set-up designed and realized to carry out vibration tests on a tank filled with pre-stressed balls is presented. The different results obtained are compared with both analytical results and numerical based on discrete-elements and finite-elements results
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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.
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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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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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Landman, Irina M. "Asymptotic analysis of vibrations of thin cylindrical shells." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0016/MQ54326.pdf.
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SOARES, ALEXANDRE ANDRADE BRANDAO. "NONLINEAR FREE VIBRATIONS OF FUNCTIONALLY GRADED CYLINDRICAL SHELLS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=35622@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Cascas cilíndricas são usadas em muitas aplicações de engenharia e, devido a sua forma e capacidade de transporte de carga, são bastante usadas na indústria aeroespacial e em estruturas civis. Elas minimizam a quantidade de material do qual são fabricadas, tornando-se assim estruturas muito leves e esbeltas. Em décadas recentes tem se procurado criar novos materiais que conjuguem múltiplas propriedades como maior resistência, melhor proteção térmica, proteção contra corrosão e adequado nível de amortecimento, dentre outras. Uma classe de materiais que podem atender simultaneamente várias destas exigências é o chamado material com gradação funcional, onde as propriedades do material variam de forma contínua em uma ou mais direções. Materiais com gradação funcional são particularmente indicados para a construção de cascas. Como a maioria destas estruturas estão sujeitas a cargas dinâmicas, torna-se importante o estudo do comportamento dinâmico de cascas fabricadas com materiais com gradação funcional. O objetivo deste trabalho é estudar as vibrações não lineares de cascas cilíndricas esbeltas com gradação funcional. Para isto utiliza-se a teoria não linear de cascas de Sanders, considerada uma das teorias mais precisas para a análise de cascas esbeltas. Inicialmente, derivam-se as equações de movimento considerando um estado de tensões iniciais. Usando as equações linearizadas, obtêm-se às frequências naturais e as cargas críticas, sendo estes resultados comparados favoravelmente com resultados encontrados na literatura para materiais homogêneos e com gradação funcional. A seguir, usando uma expansão modal que atende as condições de contorno e continuidade, além de expressar os acoplamentos modais característicos de cascas cilíndricas no regime não linear, as equações de movimento são discretizadas usando-se o método de Galerkin. As equações algébricas resultantes são resolvidas pelo método de Newton-Raphson, sendo assim obtida a relação não linear frequência-amplitude. Finalmente, realiza-se uma análise paramétrica para estudar a influência da geometria da casca, da gradação do material funcional e dos modos de vibração no grau e tipo de não linearidade da casca cilíndrica, sendo esta a principal contribuição deste trabalho de pesquisa.
Cylindrical shells are used in many engineering applications and, due to its shape and load carrying capacity, are frequently used in aerospace and civil structures. They minimize the amount of material from which they are manufactured, thus making it a very lightweight and slender structure. In recent decades, there has been a search for new materials that combine multiple properties such as increased strength, better thermal protection, corrosion protection and appropriate damping level, among others. A material that can meet several of these requirements simultaneously is the so called functionally graded material, where the material properties vary continuously in one or more directions. Functionally graded materials are particularly suitable for the construction of shells. As most of these structures are subjected to dynamic loads, it is important to study the dynamic behavior of shells made of functionally graded materials. The objective of this work is to study the nonlinear vibrations of slender functionally graded cylindrical shells. For this, the Sanders non-linear shell theory, which is considered one of the most precise theories for the analysis of slender shells, is adopted. Initially, the equations of motion are derived considering an initial stress state. Using the linearized equations of motion, the natural frequencies and critical loads are obtained. These results compare favorably with results reported in the literature for homogeneous and functionally graded shells. Then, using a modal expansion that satisfies the boundary and continuity conditions and expresses the modal couplings characteristic of cylindrical shells in the nonlinear regime, the equations of motion are discretized using the Galerkin method. The resulting algebraic equations are solved by the Newton-Raphson method, thus obtaining the nonlinear frequency-amplitude relation. Finally, a parametric analysis is conducted to study the influence of the geometry of the shell, the gradient of the functional material and vibration modes on the degree and type of nonlinearity of the cylindrical shell, which is the main contribution of this research work.
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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.
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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.
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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.
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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.
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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.
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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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Young, Andrew J. "Active control of vibration in stiffened structures." Title page, contents and abstract only, 1995. http://hdl.handle.net/2440/37722.
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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.
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Roberts, G. W. "Vibrations of shells and their relevance to musical instruments." Thesis, Bucks New University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376443.
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Alhazza, Khaled. "Nonlinear Vibrations of Doubly Curved Cross-PLy Shallow Shells." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/30042.
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The objective of this work is to study the local and global nonlinear vibrations of isotropic single-layered and multi-layered cross-ply doubly curved shallow shells with simply supported boundary conditions. The study is based-on the full nonlinear partial-differential equations of motion for shells. These equations of motion are based-on the von K\'rm\'{a}n-type geometric nonlinear theory and the first-order shear-deformation theory, they are developed by using a variational approach. Many approximate shell theories are presented.
We used two approaches to study the responses of shells to a primary resonance: a $direct$ approach and a $discretization$ approach. In the discretization approach, the nonlinear partial-differential equations are discretized using the Galerkin procedure to reduce them to an infinite system of nonlinearly coupled second-order ordinary-differential equations. An approximate solution of this set is then obtained by using the method of multiple scales for the case of primary resonance. The resulting equations describing the modulations of the amplitude and phase of the excited mode are used to generate frequency- and force-response curves. The effect of the number of modes retained in the approximation on the predicted responses is discussed and the shortcomings of using low-order discretization models are demonstrated. In the direct approach, the method of multiple scales is applied directly to the nonlinear partial-differential equations of motion and associated boundary conditions for the same cases treated using the discretization approach. The results obtained from these two approaches are compared.
For the global analysis, a finite number of equations are integrated numerically to calculate the limit cycles and their stability, and hence their bifurcations, using Floquet theory. The use of this theory requires integrating $2n+(2n)^2$ nonlinear first-order ordinary-differential equations simultaneously, where $n$ is the number of modes retained in the discretization. A convergence study is conducted to determine the number of modes needed to obtain robust results.
The discretized system of equation are used to study the nonlinear vibrations of shells to subharmonic resonances of order one-half. The effect of the number of modes retained in the approximation is presented. Also, the effect of the number of layers on the shell parameters is shown.
Modal interaction between the first and second modes in the case of a two-to-one internal resonance is investigated. We use the method of multiple scales to determine the modulation equations that govern the slow dynamics of the response. A pseudo-arclength scheme is used to determine the fixed points of the modulation equations and the stability of these fixed points is investigated. In some cases, the fixed points undergo Hopf bifurcations, which result in dynamic solutions. A combination of a long-time integration and Floquet theory is used to determine the detailed solution branches and chaotic solutions and their stability. The limit cycles may undergo symmetry-breaking, saddle node, and period-doubling bifurcations.Ph. D.