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1
Makulsawatudom, Prasit. "Elastic and elastic-plastic analysis of thick cylindrical vessels with crossholes." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401319.
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Lawrie, Jane Barbara. "Interaction of sound with cylindrical elastic shells." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47151.
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Zhang, Jin. "Elastic/plastic buckling of cylindrical shells with elastic core under axial compression." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66952.
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Elastic as well as plastic buckling of circular cylindrical shells filled with a core material is analyzed under axial compressive loading. A practical example of this situation is the buckling of concrete filled steel tubular (CFT) columns used widely in high-rise buildings. The theoretical problem is modeled as the bifurcation buckling of a perfect "infinitely" long circular cylindrical shell under uniform compression, constrained by a one-way (tension-less) foundation. An important and useful novelty is that the shell material is allowed to undergo strain-hardening plasticity before buckling. For simplicity, the core material is assumed to remain elastic. The approach is analytical. The governing equations are solved exactly to obtain buckling loads, and wavelengths in contact and nocontact regions. The theoretical results, when applied to CFT columns, are found to be in very good agreement with the experimental buckling loads of other researchers.Le flambage élastique ainsi que plastique de coquilles cylindriques remplis d'un matériel sont analysé sous le chargement de la compression axiale. Un exemple pratique de cette situation est le flambage de colonnes tubulaires en acier remplis de béton (CFT) qui sont largement utilisées dans les immeubles de grande hauteur. Le problème théorique est modélisé comme le flambage par bifurcation d'une coquille parfaite cylindrique de longueur "infinie" sous la compression uniforme, en présence d'une contrainte à sens unique. Une nouveauté importante et utile est que le matériel de coquille est sollicitée dans le domaine post-élastique avant de flambement. Pour simplifier, le matériel remplis est supposé rester élastique. L'approche est analytique. Les équations régissants sont résolus exactement à obtenir les charges de flambage, et les longueurs d'onde en contact et sans contact régions. Les résultats théoriques, aux applications de CFT colonnes, se trouvent en très bon accord avec des charges de flambage d'autres chercheurs.
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Abdel-Fattah, Mohamed Thabit. "Nonlinear behaviour of cylindrical shells containing elastic solids." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58196.pdf.
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Karam, Gebran Nizar. "Elastic stability of cylindrical shells with soft elastic cores : biomimicking natural tubular structures." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12236.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1994.Vita.
Includes bibliographical references (leaves 76-77).
by Gebran Nizar Karam.
Ph.D.
6
Fajuyitan, Oluwole Kunle. "Length effects in elastic imperfect cylindrical shells under uniform bending." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/64813.
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Recent computational investigations into the buckling behaviour of perfect elastic thin-walled cylindrical shells under uniform bending, a ubiquitous reference structural system that enjoys wide practical applications, have demonstrated that the stability behaviour of this shell system depends largely on the length. Consequently, four distinct length domains – short, medium, transitional and long – were introduced to categorise the response of the system based on the relative influence of end boundary restraint and cross-sectional ovalisation. However, most investigations on this particular shell system have only focussed on near-perfect geometric cases despite the vast research efforts that were made on the subject of imperfection sensitivity in a related reference system of cylindrical shells under uniform axial compression. Furthermore, the potential coupling between length and imperfection sensitivity has never been studied for any shell system. This research thus seeks to understand and characterise the effect of length on the elastic stability of imperfect cylindrical shells under uniform bending, considering diverse forms of geometric imperfections. The stability investigations were performed over a wide parametric variation of length, radius-to-thickness ratio, end boundary condition, form and amplitude of geometric imperfection, using a combination of modern finite element analysis software and programming languages. It was confirmed that there exists a relationship between the length of the shell system and imperfection sensitivity and this relationship was characterised into realistic, but conservative closed-form, algebraic expressions as a proxy to undertaking further computational investigations by analysts. The study also offers an efficient computational strategy that may be adopted in managing large computational analyses through most modern finite element suites and it is envisaged that this strategy will appeal to computational analysts who are encouraged to adopt the automation methodology described herein to explore other structural systems.
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Brévart, Bertrand J. "Active control of coupled wave propagation in fluid-filled elastic cylindrical shells /." This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-10032007-171658/.
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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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Chen, Zi Qi. "Delamination buckling of pressure-loaded laminated cylindrical shells and panels." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/21227.
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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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Brevart, Bertrand J. "Active control of coupled wave propagation in fluid-filled elastic cylindrical shells." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/39559.
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The vibrational energy propagating in straight fluid-filled elastic pipes is carried by the structure as well as by the internal fluid. Part of the energy in the system may also transfer from one medium to the other as propagation occurs. For various types of harmonic disturbance, this study demonstrates that, whether the
propagating energy is predominantly conveyed in the shell or in the fluid, large attenuations of the total power flow may be achieved by using an active control approach. As the shell and fluid motions are fully coupled, the implementation of intrusive sources/sensors in the acoustic field can be also avoided. The approach is based on using radial control forces applied to the outer shell wall and error sensors observing the structural motion.
A broad analytical study gives insight into the control mechanisms. The cylindrical shell is assumed to be infinite, in vacuo or filled with water. The first disturbance source investigated is a propagating free wave of circumferential order n=O or n= 1. The control forces are appropriate harmonic line forces radially applied
to the structure. The radial displacement of the shell wall at discrete locations downstream of the control forces is minimized using linear quadratic optimal control theory. The attenuation of the total power flow in the system after control is used to study the impact of the fluid on the performance of the control approach. Results for the shell in vacuo are presented for comparison. Considering the breathing
mode (n=O), the fluid decreases the control performance when the disturbance is a structural-type incident wave. Significant reductions of the transmitted power flow can be achieved when the disturbance is a fluid-type of wave. Regarding the beam mode (n=1), the fluid increases the control performance below the first acoustic cut-off frequency and decreases it above this frequency.Ph. D.
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Doherty, Christopher Gilles. "Elastic Response of Acoustic Coating on Fluid-Loaded Rib-Stiffened Cylindrical Shells." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78288.
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Reinforced cylindrical shells are used in numerous industries; common examples include undersea vehicles and industrial piping. Current models typically incorporate approximate theories to determine shell behavior, which have limitations in terms of both thickness and frequency. In addition, many applications feature coatings on the shell surface that normally have thicknesses which must also be considered. To increase the fidelity of such systems, this work develops an analytical model of an elastic cylindrical shell featuring periodically spaced ring stiffeners with an acoustic coating applied to the outer surface. There is an external fluid environment. Beginning with the equations of elasticity for a solid, spatial-domain displacement field solutions are produced incorporating unknown wave propagation coefficients. These fields are used to determine stresses at the boundaries of the shell and coating, which are then coupled with stresses from the stiffeners and fluid. The stress boundary conditions contain double-index infinite summations, which are decoupled, truncated, and recombined into a global matrix equation. The solution to this global equation results in the displacement responses of the system as well as the scattered pressure field. Two distinct loadings are considered: a ring loading and an incident acoustic wave. Thin-shell reference models are used for validation, and the acoustic response of the system is examined. It is shown that the reinforcing ribs and acoustic coating have a considerable effect on system behavior.Master of Science
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Bao, Chunyan. "Acoustic scattering by cylindrical scatterers comprising isotropic fluid and orthotropic elastic layers." Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32847.
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Doctor of PhilosophyDepartment of Mechanical and Nuclear Engineering
Liang-Wu Cai
Acoustic scattering by a cylindrical scatterer comprising isotropic acoustic and orthotropic elastic layers is theoretically solved. The orthotropic material is used for the scattering problem because the sound speeds along radial and tangential axes can be different; which is an important property for acoustic cloaking design. A computational system is built for verifying the solutions and conducting simulations. Scattering solutions are obtained based on two theoretical developments. The first one is exact solutions for elastic waves in cylindrically orthotropic elastic media, which are solved using Frobenius method. The second theoretical development is a set of two canonical problems for acoustic-orthotropic-acoustic media. Based on the two theoretical developments, scattering by three specially selected simple multilayer scatterers are analyzed via multiple-scattering approach. Solutions for the three scatterers are then used for solving a “general” multilayer scatterer through a recursive solution procedure. The word “general” means the scatterer can have an arbitrary number of layers and each layer can be either isotropic acoustic or orthotropic elastic. No approximations have been used in the process. The resulting analytically-exact solutions are implemented and verified. As an application example, acoustic scattering by a scatterer with a single orthotropic layer is presented. The effects on the scattering due to changing parameters of the orthotropic layer are studied. Acoustic scattering by a specially designed multilayer scatterer is also numerically simulated. Ratios of the sound speeds of the orthotropic layers along r and θ directions are defined to satisfy the requirement of the Cummer-Schurig cloaking design. The simulations demonstrate that both the formalism and the computational implementation of the scattering solutions are correct.
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Anastasiadis, John S. "Stability of cylindrical laminates by highter order shear deformable theories." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/12376.
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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.
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Kumar, Pravin. "Large deflection elastic-plastic analysis of cylindrical shells using the finite strip method." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/27896.
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A transversely-curved finite strip formulation for the static analysis of circular cylindrical shells is presented. The finite strip analysis is carried out by using one or two analytical modes in the longitudinal direction to determine the response of cylindrical shells subjected to uniform loads. Both linear and quadratic variation of membrane displacements in the curved direction are investigated and it is found that the quadratic variation is far superior.
The effect of large deformations is incorporated in the present analysis by including the first order non-linearities in the strain-displacement relations. The material behavior is assumed to be isotropic elastic-plastic. The plasticity portion uses the von-Mises yield criteria, and the associated flow rule. For the examples considered, a bi-linear stress-strain relation is assumed. Numerical integration of the virtual work equations is carried out using Gaussian Quadrature. The number of integration points in a given direction is determined by observing the individual terms in the integration or by past experience. The resulting set of non-linear equations is solved iteratively by employing the Newton-Raphson scheme.
Numerical investigations of the method are carried out by modelling cylindrical shells subjected to self-weight or pressure load. These investigations compare the results for laterally loaded cylindrical shells with simply supported or clamped boundaries with analytical and numerical results. The results show that employing one bending mode and one or two membrane modes is sufficient to yield engineering accuracy for design purposes.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Al, lawati Hussain Ali Redha Mohammed. "The buckling of axially compressed cylindrical shells under different conditions." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25723.
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Civil Engineering thin cylindrical shells such as silos and tanks are normally subjected to axial compression that arises from a stored solid, wind, earthquake, self-weight or roof loads. The walls of these shells are very thin, generally of the order of 6 to 25 mm, and massively less than the radius, which is typically 5 to 30 m. They are thus very thin shell structures, like those of rockets, spacecraft, motor vehicles and aircraft. The commonest failure mode is elastic buckling under axial compression. It has long been known that the buckling strength of a thin cylindrical shell under axial compression is very sensitive to tiny deviations of geometry, reducing the buckling strength to perhaps 10 or 20% of the value for the perfect structure. A normal internal pressure usually accompanies the axial compression, caused by stored granular solids or fluids. At relatively low pressures, the elastic buckling strength under axial compression rises, but an elastic-plastic buckling phenomenon intervenes at higher pressures, causing a dramatic decrease in buckling resistance associated with an elephant’s foot collapse mode. To construct such large shells, the fabrication technique is generally the assembly of many rolled plates or panels, joined by short longitudinal welds and continuous circumferential welds. The process of welding produces a distinctive geometric imperfection form at each weld joint, which in turn is extremely detrimental to the shell axial buckling carrying capacity. The strength may be further reduced by slight misalignments between adjacent panels, or in bolted construction, by vertical and horizontal lap splices. Due to the pattern of loading, both the axial compression and internal pressure increase progressively down the wall. Accordingly, practical construction usually uses a stepped wall, formed from panels of uniform thickness, but with larger thicknesses at lower levels. Since the loading varies smoothly, but each panel has constant thickness, the critical location for buckling lies at the base of a panel. But the greater thickness of the lower panel can usefully enhance the buckling strength of the critical panel above it. This thesis presents an extensive computational study that examines all the above influences, divided into chapters that are outlined here. A full exploration of the effect of the cylinder length on the perfect and imperfect elastic buckling strength is presented in Chapter 3. In Chapter 4, the elastic-plastic buckling resistance of imperfect cylinders is described, including strain hardening. These lead to many capacity curves, for which the key parameters are extracted. The effect of internal pressure on the buckling resistance of imperfect elastic cylinders is explored in Chapter 5. Chapter 6 studies the effect of high pressures that produce elastic-plastic elephant’s foot buckling at circumferential welds in imperfect shells. Next, a step change in plate thickness is studied in Chapter 7 for imperfect butt jointed cylinders with and without the internal pressure. Chapter 8 presents an exploration of the effect of plate misalignments at a circumferential joint, as well as the full misalignment of a circumferential lap joint in bolted construction. These are investigated in both the elastic and elastic-plastic domains. The entire thesis is conceived in the context of EN 1993-1-6 (2007) and the ECCS Recommendations on Shell Buckling (2008). This research has shown significant weaknesses in both the concepts and the detailed rules of these standards. Many conditions are found where either the standard is unnecessarily conservative, or its safety margin may be too low. Thus, some new provisions are proposed for each of the above practical problems. These are expected to provide useful knowledge for the design of such structures against buckling in the future.
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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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Bencheikh, L. "Scattering of elastic waves by cylindrical cavities : Integral-equation methods and low-frequency matched asymptotic expansions." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376270.
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Laible, Henry A. "Wave scattering from cylindrical fluid inclusions in an elastic medium and determination of effective medium properties." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/39366.
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Engineer, Jeremy Cyrus. "A theoretical investigation into the interaction of sound waves with planar and cylindrical nonlinear elastic surfaces." Thesis, Keele University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334285.
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Schneider, William Frank. "Eigenvalue veering and mode localization in a hemispherically capped ciruclar cylindrical shell with an elastic bulkhead at midplate." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17956.
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Philobos, Mahera S. "Benchmark elasticity solution for the buckling of thick composite cylindrical shells under axial compression and combined external pressure and axial compression." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19549.
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Žák, Stanislav. "Pole napětí a deformace v okolí trhlin s komplikovanou geometrií čela zatížených ve smykových zátěžných módech." Doctoral thesis, Vysoké učení technické v Brně. CEITEC VUT, 2018. http://www.nusl.cz/ntk/nusl-390149.
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Tato závěrečná práce je shrnutím výzkumu smykově zatěžovaných trhlin, který proběhl v průběhu čtyř let doktorského studia jejich autora Ing. Stanislava Žáka (Středoevropský technologický institut, Vysoké učení technické v Brně). Předložená práce je zaměřena na prohloubení znalostí v oblasti pokročilé lomové mechaniky, konkrétně pro smykové zatěžování trhlin kombinované s případy geometrických odchylek trhlin od běžně používaných modelů. To mimo jiné znamená návrh nových přístupů a modelů a popis součinitelů intenzity napětí pro geometricky komplikované trhliny. První část práce je věnována shrnutí současných přístupů v lomové mechanice a dále i popisu numerických metod, použitých v dalších výpočtech. Kromě klasických přístupů se tato část textu zabývá i novějším výzkumem zaměřeným na smykové zatěžování trhlin, speciálně pro dva typy zkušebních těles – válcový vzorek s obvodovým vrubem a trhlinou zatížený prostým smykem nebo krutem a CTS těleso umožňující zatížení trhliny v módech I, II a také v jejich kombinaci I+II. Další část textu je zaměřena na konkrétní výpočty lomových parametrů při použití nových modelů s komplikovaným čelem trhliny. Teoretické řešení lomových parametrů pro oba výše zmíněné modely je porovnáno s experimentálními výsledky, získanými v navazujících projektech. U modelu válcového vzorku je popsána možnost zjednodušení budoucích modelů těles s podobným typem komplikované trhliny a současně je na něm popsán lokální vliv zubatosti čela trhliny na indukci lokálního zatížení v módu II při globálním zatížení v módu III. Tyto výsledky jsou přímo propojeny s experimentální kvantifikací únavového šíření lomu při zatížení v módu III. CTS těleso je použito k popisu vlivu drsnosti trhliny na součinitele intenzity napětí. Na tomto modelu je pozorován jak globální pokles hodnoty KII při zvyšující se drsnosti trhliny, tak i lokální změny v namáhání trhliny podél jednotlivých nerovností. Výsledky potvrzují, i pro dosud málo zkoumané smykové zatěžování, že mikrostruktura lomových ploch a čela trhliny má vliv na lomové parametry. Rozšiřují tak současné znalosti v oboru lomové mechaniky popisem geometrického stínění čela trhliny pro zátěžné módy II a III.
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Arulchandran, Victor. "Edge and interfacial vibration of a thin elasic cylindrical panel." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/7804.
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Free vibrations of a thin elastic circular cylindrical panel localized near the rectilinear edge, propagating along the edge and decaying in its circumferential direction, are investigated in the framework of the two-dimensional equations in the Kircho↵-Love theory of shells. At first the panel is assumed to be infinite longitudinally and semi-infinite along its length of curvature (of course not realistically possible), followed by the assumption that the panel is then finite along its length of curvature and fixed and free conditions are imposed on the second resulting boundary. Using the comprehensive asymptotic analysis detailed in Kaplunov et al. (1998) “Dynamics of Thin Walled Elastic Bodies”, leading order asymptotic solutions are derived for three types of localized vibration, they are bending, extensional, and super-low frequency. Explicit representation of the exact solutions cannot be obtained due to the degree of complexity of the solving equations and relevant boundary conditions, however, computational methods are used to find exact numerical solutions and graphs. Parameters, particularly panel thickness, wavelength, poisson’s ratio, and circumferential panel length, are varied, and their e↵ects on vibration analyzed. This analysis is further extended to investigate localized vibration on the interface (perfect bond) of two cylindrical panels joined at their respective rectilinear edges, propagating along the interface and decaying in the circumferential direction away from the interface. An earlier, similar, localized vibration problem presented in Kaplunov et al. (1999) “Free Localized Vibrations of a Semi-Infinite Cylindrical Shell” and Kaplunov and Wilde (2002) “Free Interfacial Vibrations in Cylindrical Shells” is replicated for comparison with all cases. The asymptotics are similar, however in this problem the numerics highlight the stronger e↵ect of curvature on the decay of the super-low frequency vibrations, and to some extent on the leading order bending vibration.
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Nguyen, The Nguyen. "Flambage sous contact d’une coque cylindrique soumise à pression externe." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI070/document.
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Cette étude vise à analyser la coque qui est en contact avec un matériau qui la confine, et qu’elle subite une pression latérale externe. Les conditions de contact entre les deux corps, frottant ou pas, la rigidité du confinement ainsi que les conditions de chargement, la pression qui peut être directement appliquée à la coque comme elle peut être induite par le matériau de confinement qui par retrait ou retreint ou convergence radiale induit des contraintes, ceux sont là les paramètres qui nous paraissent essentiels à jauger pour la problématique du flambage avec contact d’une coque sous pression externe. Une campagne expérimentale où plusieurs configurations de confinement sont considérées. La nature du milieu extérieur associé au confinement et donc sa rigidité, le type de confinement, discret ou locale au bien total (surface entière de la coque), sont évalués. Une instrumentation adéquate, couplant des mesures ponctuelles et de champ nous a permis de correctement mettre en exergue la phénoménologie. Les simulations numériques par éléments finis à l’aide du code de calcul Abaqus/Standard 6.12-3 intègrent les différentes non linéarité mise en musique dans ce problème, les grands déplacements et rotations du fait du flambage, la non linéarité matériau. Ces travaux montrent que même pour un confinement externe avec une très faible rigidité de membrane, comme pour le sable ou le polystyrène expansé, un gain important de capacité portante est observé, le flambage est retardé. L’augmentation est substantielle dans le cas d’un confinement total, non négligeable et consistante dans le cas d’un confinement local. Nous avons aussi constaté que la charge de flambage et le mode associé dépendent de la configuration de contact, notamment de la rigidité à la flexion du confinementMotivated by practical engineering applications, thin-walled cylindrical shells are widely used as structural elements. Because of their low flexural strength, these structures are very sensitive to buckling when exposed to external pressur. Conventional stiffening which makes it possible to improve the bearing capacity is to add stiffening rings connected by axial stiffeners or axial stiffeners. In these configurations the stiffening elements are an integral part of the structure with a continuity of material. One can ask the question of the effect of contiguous but non-continuous adjacent external structures ensuring total or local surface external contact. These are real configurations, such as those of buried pipelines, pipelines, or the case of insulated structures. This study aims to analyze these cases where the shell is in contact with a material which confines it, and that it undergoes an external lateral pressure. The contact conditions between the two bodies, whether rubbing or not, the stiffness of the confinement as well as the loading conditions, the pressure which can be directly applied to the shell as it may be induced by the confinement material which by withdrawal or shrinkage or Radial convergence induces stresses, these are the parameters that we consider essential for gauging the problem of buckling with contact of an external pressure shell. To answer these questions, we conducted an experimental campaign where several configurations of confinement are considered. The nature of the external environment associated with the confinement and therefore its rigidity, the type of confinement, discrete local or the total property (entire surface of the shell), are evaluated. Appropriate instrumentation, coupling point and field measurements, has allowed us to correctly highlight the phenomenology. Numerical modeling is also carried out using finite element method by Abaqus/Standard 6.12-3 code. Numerical simulations integrate the different nonlinearities in this problem, large displacements and rotations due to buckling, nonlinearity material, in some cases the buckling is plastic, but also the nonlinearity induced by an evolutionary contact. The modeling is carried out in 2D and 3D mesh, and in the latter case either by means of shell elements or by massive elements, the first aim being to corroborate the experimental observations more or less precisely. This work shows that even for external confinement with very low membrane rigidity, as for sand or expanded polystyrene, a significant gain in bearing capacity is observed, the buckling is delayed. The increase is substantial in the case of a total confinement which is not negligible and consistent in the case of local confinement. We have also found that the buckling load and the associated mode depend on the contact configuration, in particular the flexural rigidity of the confinement
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Huang, Wei-chu, and 黃威築. "FDTD Simulation of Elastic Waves in Cylindrical Multi-layered Structures." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/02926431066548384768.
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碩士國立中山大學
光電工程學系研究所
103
In oil field exploration, various logging devices are put into the borehole structure during and after the drilling process and also after the well cementation job to check for the hydraulic isolation between different fluid layers. Ultrasonic transducers transmit acoustic signals and produce elastic waves in the geological structure. The reflected and scattered signals are then received and processed at the same time. By the sonic and ultrasonic measuring techniques, we may understand the compositions and orientations of the geological structure and confirm the isolation quality of the cementing layer. This work is part of the four-year cooperative education research program “Modeling of borehole ultrasonic measurement” between National Sun Yat-sen University and Halliburton Far East Pte Ltd. We begin with the review of the basic physics of elasticity, including definitions of stress, strain, and stiffness tensors. For continuous media, we may apply the Hooke''s law to linearly relate the strain and the stress tensors. This is followed by Newton''s second law of motion to obtain, VS-PDEs, the first-order (in time and space), velocity-stress coupled partial differential equations for elastic wave propagation in the continuum. These control equations can be shown to be equivalent to the standard second-order vector wave equations for elastic waves and the solutions are well known to include both compressional (P) waves and shear (S) waves. We use the FDTD method to discretize the first-order VS PDEs and perform numerical simulations on the MATLAB platform. The arrangement of unknown quantities is based on the standard staggered grid (in both space and time) layout. Simulations in FDTD will be implemented on standard rectangular grid in both the Cartesian and polar coordinate systems. The calculations in the cylindrical mesh are then mapped into a rectangular grid for cross verification with the calculations done in the Cartesian mesh. By selecting the appropriate simulation parameters, simulation results in rectangular grid and in cylindrical grid are nearly identical. We plot, from these simulation results, for both types of the stress and velocity components. From these results we are able to gain clear physical pictures regarding the distribution, propagation and scattering of the elastic waves in a cylindrical multilayer structure.
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Yen-JungChen and 陳彥蓉. "Cylindrical Bending Vibration of Multiple Graphene SheetSystems Embedded in an Elastic Medium." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/2m863n.
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碩士國立成功大學
土木工程學系
107
An asymptotic nonlocal elasticity theory for cylindrical bending vibration analysis of simply-supported, Nl-layered, and uniformly- or nonuniformly-spaced, graphene sheet (GS) systems embedded in an elastic medium is developed by using the Eringen nonlocal elasticity theory and multiple time scale method. Both the interactions between the topmost and bottommost GSs and their surrounding medium and the interactions between each pair of adjacent GSs are modelled as one-parameter Winkler models with different stiffness coefficients. In the formulation, the small length scale effect is introduced to nonlocal constitutive equations using a nonlocal parameter, and then the nondimensionalization, asymptotic expansion, and successive integration mathematical processes are performed for a typical GS. After assembling the motion equations for each individual GS to form those of the multiple GS system, recurrent sets of motion equations can be obtained for various order problems. Nonlocal multiple classical plate theory (CPT) is derived as a first-order approximation of the current nonlocal plane strain problem, and the motion equations for higher-order problems retain the same differential operators as those of nonlocal multiple CPT, although with different nonhomogeneous terms. Some nonlocal plane strain solutions for the natural frequency parameters of the multiple GS system with and without being embedded in the elastic medium and their corresponding mode shapes are presented to demonstrate the performance of the asymptotic nonlocal elasticity theory.
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Peng, Tzu-Huan, and 彭子桓. "Acoustic Wave Propagation in a Cylindrical Elastic Tube Filled with Inviscid Liquid." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/51846960145270535700.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
102
In this article, the acoustic wave propagation in the model “Cylindrical Elastic Tube Filled with Inviscid Liquid” is studied, for explaining special acoustic propagation phenomena in the cochlear － fast wave and slow wave, and traveling wave with well slow velocity. In the study of the model “Cylindrical Elastic Tube Filled with Inviscid Liquid”, the governing equations of tube and liquid with appropriate material parameters and boundary conditions, are solved by MATLAB to get the dispersion curve and the mode shapes. Investigation the dispersion curve and mode shapes of the model, it can be found that there’s no cutoff frequency in the 1st and 2nd mode, which originate from the plane wave of liquid and tube, and they also have well slow velocity just as the phase velocity plot showing. The characteristic in the model above can explain the wave propagation phenomena in the cochlear. Besides, it is found the modes of liquid appear significantly in the high frequency place. In these areas, the mode shape of the liquid part is larger and the group velocity is faster than those in the other areas.
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Boot, John C., Akbar A. Javadi, and Irina L. Toropova. "The structural performance of polymeric linings for nominally cylindrical gravity pipes." 2004. http://hdl.handle.net/10454/2837.
Full textAbstract:
NoThis paper considers both the linear elastic and creep buckling of polymeric pipe linings used for the rehabilitation of gravity pipes, for which external groundwater pressure has been identified as the prime source of loading. Theoretically perfect and imperfect conditions are considered, with the imperfections taken to be in the form of a concentric or eccentric annulus between the rigid host pipe (cylindrical constraint) and polymeric lining. Under these conditions two recently obtained mathematical procedures for the prediction of linearly and non-linearly elastic buckling are compared with the results of complementary laboratory testing. Linear elastic conditions are shown to be well approximated by undertaking short-term (¿30 min) testing under increasing pressure to failure. Controlled imperfections are introduced into the laboratory tests and excellent correlation with the theoretical predictions is obtained. In particular, the dominant geometrical imperfections are shown to be major influences on the obtained buckling pressure. The mathematical models are then adapted to simulate the creep buckling process under long-term constant pressure. The results obtained are again compared with those provided by complementary physical testing, and appropriate conclusions are made.
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Boot, John C., Akbar A. Javadi, and Irina L. Toropova. "Predicting the creep lives of thin-walled cylindrical polymeric pipe linings to external pressure." 2004. http://hdl.handle.net/10454/3443.
Full textAbstract:
NoThis paper considers both the linear elastic and creep buckling of polymeric pipe linings used for the rehabilitation of gravity pipes, for which external groundwater pressure has been identified as the prime source of loading. Theoretically perfect and imperfect conditions are considered, with the imperfections taken to be in the form of a concentric or eccentric annulus between the rigid host pipe (cylindrical constraint) and polymeric lining. Under these conditions two recently obtained mathematical procedures for the prediction of linearly and non-linearly elastic buckling are compared with the results of complementary laboratory testing. Linear elastic conditions are shown to be well approximated by undertaking short-term (¿30 min) testing under increasing pressure to failure. Controlled imperfections are introduced into the laboratory tests and excellent correlation with the theoretical predictions is obtained. In particular, the dominant geometrical imperfections are shown to be major influences on the obtained buckling pressure. The mathematical models are then adapted to simulate the creep buckling process under long-term constant pressure. The results obtained are again compared with those provided by complementary physical testing, and appropriate conclusions are made.
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Hung-Liang-Tseng and 曾宏量. "The Scattering of a Vertical Transverse Isotropic Cylindrical Canyon Subjected to Time-Harmonic Elastic Wave." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/85611784979191904306.
Full textAbstract:
碩士國立臺灣大學
應用力學研究所
103
The objective of this research is to study the scattering of a vertically transversely isotropic cylindrical canyon subjected to the incidence of time harmonic plane elastic wave. The total displacement field of either the anti-plane or in-plane scattering problem can be decomposed into two parts, namely, free field as well as scattering filed part. The known free field part can be further separated into incident wave and reflected wave in order to satisfy the ground surface condition. While the unknown scattering field part is expanded into a series of n-th order outgoing singular solutions of Lamb’s problem with unknown amplitude which can be determined by boundary condition of canyon itself. The displacement field and stress field of each n-th order outgoing singular solutions of Lamb’s problem can only be expressed into a form of horizontal wave-number integral which can be evaluated efficiently in complex wave-number domain by using the so called steepest descend-stationary phase method. For in-plane scattering problem, the outgoing scattering field contains two kinds of wave field, namely, P wave and S wave, only two sheets of the four Riemann Surface are sufficient to describe the outgoing scattering field. In order to ensure the single value of a multi-value radical function in each Riemann sheet, the branch points and the associated branch cuts are carefully chosen according to the material considered. Least Square method is employed to solve the unknown coefficients of the expansion series of the scattering field. Once the coefficients are determined, the complete displacement field and stress field can be obtained.
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SHIH, MING-CHOU, and 施名洲. "Scattering Problem of a Vertical Transverse Isotropic Circular Cylindrical Cavity Subjected to Time-Harmonic Elastic Wave." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8r96d5.
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Nieh, Hsiang-Yu, and 聶祥宇. "The Dynamic Stress Concentration of a Vertical Transverse Isotropic Cylindrical Cavity Subjected to Time-Harmonic Elastic Wave." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/55763826867149727087.
Full textAbstract:
碩士國立臺灣大學
應用力學研究所
104
The objective of this thesis is to study the scattering as well as dynamic stress concentration phenomenon of a vertically transversely isotropic circular cylindrical cavity subjected to the obliquely incidence of time harmonic plane elastic wave. The total displacement field of either the anti-plane or in-plane scattering problem can be decomposed into two parts, namely, the incidence field as well as the scattering field part. We propose that the unknown scattering field part can be expanded into a series of n-th order wave function. Each wave function is defined by a trigonometric angular spectrum along a complex contour integral path with a kernel function which is non-trivial plane wave solution of the corresponding wave equation. The phase velocity of the plane wave kernel function varies with the phase angle. The trigonometric angular spectrum of each n-th order wave function can be further converted to infinite horizontal slowness integral which can be evaluated efficiently in complex slowness domain by employing the steepest descend-stationary phase method. In order to satisfy the boundary condition at each collocation point which allocate along the cavity surface, Least Square method is employed to solve the unknown coefficients of the expansion series of the scattering field. Once the coefficients are determined, the complete displacement field and stress field can be obtained. Thus, the dynamic stress concentration phenomenon of a vertically transversely isotropic circular cylindrical cavity subjected to the obliquely incidence of time harmonic plane elastic wave is thoroughly studied. Specially, for the anti-plane scattering problem of a circular cylindrical cavity embedded in a vertically transversely isotropic medium, In order to demonstrate the above proposed procedure is valid theoretically, through a coordinate transformation technique and recombination of the original expansion series, it can be shown that the original expansion series is identical to elliptic cylindrical wave function expansion for an isotropic medium, However, the original circular cylindrical cavity is transformed into an elliptic cylindrical cavity whose scattering problem can be solved analytically. From which the dynamic stress concentration phenomenon is thoroughly studied.
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Xu, Xin, and 許昕. "Study on the pressure and flow propagation in a long cylindrical elastic tube with radial resonance theory." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/22937210828537524284.
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Lenhart, Richard David. "Development of a standing-wave apparatus for calibrating acoustic vector sensors." Thesis, 2014. http://hdl.handle.net/2152/26385.
Full textAbstract:
Underwater acoustic pressure transducers measure pressure fluctuations, a scalar parameter of the acoustic field. Acoustic vector sensors contain an omnidirectional pressure transducer (omni) and also bi- or tri-axial sensing elements that respond to either the particle velocity or pressure gradient of the acoustic field; which are vector quantities. The amplitude of the signal output of each directional channel of a vector sensor is proportional to the orientation relative to the direction of acoustic pressure propagation. The ratio of the signal amplitudes between two directional channels and the cross-spectra between the vector sensor omni and directional channels enable one to estimate the bearing to the source from a single point measurement. In order to accurately estimate the bearing across the usable frequency band of the vector sensor, the complex sensitivities of the omni and directional channels must be known. Since there is no standard directional reference transducer for a comparative calibration, the calibration must be performed in an acoustic field with a known relationship between the acoustic pressure and the acoustic particle velocity. Free-field calibrations are advantageous because this relationship is known for both planar and spherical wave fronts. However, reflections from waveguide boundaries present a practical limitation for free-field calibrations, especially at low frequencies. An alternative approach is to perform calibration measurements in a standing-wave field, where the relationship between pressure and particle velocity is also known. The calibration facility described in this thesis is composed of a laboratory-based, vertically-oriented, water-filled, elastic-walled waveguide with a piston velocity source at the bottom end and a pressure release boundary condition at the air/water interface at the top end. Some of the challenges of calibrating vector sensors in such an apparatus are discussed, including designing the waveguide to mitigate dispersion, mechanically isolating the apparatus from floor vibrations, understanding the impact of waveguide structural resonances on the acoustic field, and developing the calibration algorithms. Data from waveguide characterization experiments and calibration measurements are presented along with engineering drawings and calibration software.text
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Chun-ILin and 林峻毅. "Line-Focused PVDF Transducer and Defocusing Method for Measuring Cylindrically Guided Waves and Acousto-Elastic/Plastic Effects." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/92913285383689555120.
Full textAbstract:
博士國立成功大學
機械工程學系
102
Lens-less line-focused PVDF transducers and defocusing measurement method are applied to determine the dispersion curves of cylindrically guided waves, including Rayleigh-like cylindrical surface waves propagating along the circumferential direction of solid cylinders and layer-coated cylinders, as well as cylindrical Lamb waves on circular annuli. Conventional V(f,z) waveform processing method has been modified to cope with the non-linear relationship between the phase angle of wave interference and the defocusing distance. A cross correlation method is proposed to accurately extract the cylindrically guided wave velocity from measured data. Experiments have been carried out on: (1) stainless steel and glass cylinders, (2) Ni-coated stainless steel cylinders, and (3) cylindrically curved stainless steel sheets. The experimentally obtained dispersion curves are in very good agreement with their theoretical counterparts. Variation of cylindrically guided wave velocity due to the cylindrical curvature is quantitatively verified using this method. Line-focused PVDF transducers and its V(f,z) defocusing measurement system are also applied to determine the acoustoelastic and acoustoplastic effects of deformed polymethylmeth-acrylate (PMMA) samples, as well as silicon steel samples with permanent deformation. Different levels of strain or permanent deformation are formed in PMMA and silicon steel samples. Large plastic deformation ranging from 5% to 30% is created in the silicon steel samples using uni-axial tensile loading. The velocity changes of surface acoustic waves under different strain or plastic deformation are measured along various directions relative to the loading direction. The acoustoelastic coefficients of PMMA are successfully determined from measurement results. The acoustoplastic effects of PMMA and silicon steel samples are also measured and determined. The investigation on the acoustoelastic and acoustoplastic effects demonstrates an effective way for estimating applied and/or residual stresses in solid materials nondestructively using the line-focused PVDF transducer and its measurement method.