Dissertations / Theses: 'Elastic rods and waves'

1

Durickovic, Bojan. "Waves on Elastic Rods and Helical Spring Problems." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202750.

Full text

Abstract:

This work examines problems in the statics and traveling wave propagation on uniform elastic rods with constant curvature and torsion, i.e. a straight rod and a helical rod. The first set of problems concerns planar traveling loop-like waves on intrinsically straight rods. It is shown that loops with compact support can exist on homogeneous rods with a nonlinear constitutive relation, where the strain-energy density contains a quartic term. Next, the effect of heterogeneity in the material properties on the shape of the loop is examined using a homogenization method. The second set of problems deals with a system consisting of a helical spring with a force and a torque applied along the helix axis. First, an overview is presented of problems of finding the stresses given the strains, or vice-versa, assuming that the elastic parameters of the spring are known. Then, the inverse problem is examined, where both stresses and strains are measured, and optimal elastic parameters within the linear consitutive model are sought. Various forms of measured strains are considered. Finally, the special problem with zero axial torque is considered, and criteria when the spring overwinds with a tensile axial force applied are established.

APA, Harvard, Vancouver, ISO, and other styles

2

Fu, Tuan-Chun. "FEM simulation of ultrasonic wave propagation in solid rods." Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3452.

Full text

Abstract:

Thesis (M.S.)--West Virginia University, 2004.
Title from document title page. Document formatted into pages; contains x, 82 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-81).

APA, Harvard, Vancouver, ISO, and other styles

3

Cazzolli, Alessandro. "Snapping and Fluttering of Elastic Rods." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/259120.

Full text

Abstract:

The exact solutions for planar rods undergoing large rotations and subject to kinematically controlled ends are presented in the first part of the thesis. In particular, the equilibrium equations for a rod subject to Dirichlet boundary conditions and to isoperimetric constraints are derived through variational principles for both the Euler's elastica and the Reissner beam, while the related closed-form solutions are obtained in terms of the Jacobi elliptic functions. The study of stability of the Euler's elastica is addressed in the second part of the thesis through a modified version of the conjugate points method, thus disclosing the existence of a universal snap surface that represents the whole set of "saddle points" of the total potential energy, and therefore corresponding to snapping configurations. These theoretical findings allow for the prediction of snapping instabilities along any equilibrium path involving variations in the boundary conditions and are confirmed by numerical and experimental data. The universal snap surface is also exploited towards the realization of the elastica catastrophe machine, as the first extension of the classical Zeeman's machine to continuous elastic elements. Two families of the elastica catastrophe machine are presented and the theoretical model is fully validated through a prototype designed and tested at the Instability Lab of the University of Trento. Finally, the equations of motion of a pre-stressed planar rod and of its discretized counterpart subject to non-holonomic constraints are obtained in the last part. The analysis of the linearized stability surprisingly proves the existence of flutter instabilities despite the conservative nature of the considered systems. Moreover, Hopf bifurcations and destabilization paradoxes in the presence of dissipative forces are found. The non-linear equations of the proposed discretized model are also numerically solved, thus confirming the predicted stability properties and revealing the birth of periodic stable solutions.

APA, Harvard, Vancouver, ISO, and other styles

4

Miller, James Thomas Ph D. Massachusetts Institute of Technology. "Mechanical behavior of elastic rods under constraint." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/88280.

Full text

Abstract:

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.
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 (pages 213-223).
We present the results of an experimental investigation of the mechanics of thin elastic rods under a variety of loading conditions. Four scenarios are explored, with increasing complexity: i) the shape of a naturally curved rod suspended under self-weight, ii) the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint, iii) the mechanical instabilities arising when a rod is progressively injected into a horizontal cylinder, and iv) strategies for mitigation of these instabilities by dynamic excitation of the constraint. First, we consider the role of natural curvature in determining the shape of a hanging elastic rod suspended under its own weight. We categorize three distinct configurations: planar hooks, localized helices, and global helices. Experimental results are contrasted with simulations and theory and the phase diagram of the system is rationalized. Secondly, in what we call the classic case experiment, we study the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint. Under imposed displacement, the initially straight rod buckles into a sinusoidal mode and eventually undergoes a secondary instability into a helical configuration. The critical buckling loads are quantified and found to depend strongly on the aspect ratio of the rod to pipe diameter. Thirdly, we inject a thin elastic rod into a horizontal cylinder under imposed velocity in the real case experiment. Friction between the rod and constraining pipe causes an increasing axial load with continued injection. Consecutive buckling transitions lead to straight, sinusoidal, and helical configurations in a spatially heterogeneous distribution. We quantify critical lengths and loads for the onset of the helical instability. The geometric parameters of the system strongly affect the buckling and post-buckling behavior. Finally, we explore active strategies for delaying the onset of helical buckling in the real case. Distributed vertical vibration is applied to the cylindrical constraint, which destabilizes frictional contacts between the rod and pipe. Injection speed, peak acceleration of vibration, and vibration frequency are all found to affect the postponement of helical initiation. The process is rationalized and design
by James T. Miller.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

5

Khalid, Jawed Mohammad. "Coiling of elastic rods on rigid substrates." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93774.

Full text

Abstract:

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
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 (pages 115-120).
We investigate the deployment of a thin elastic rod onto a rigid substrate and study the resulting coiling patterns. In our approach, we combine precision model experiments, scaling analyses, and computer simulations towards developing predictive understanding of the coiling process. Both cases of deposition onto static and moving substrates are considered. We construct phase diagrams for the possible coiling patterns, e.g. meandering, stretched coiling, alternating loops, and translated coiling, and characterize them as a function of the geometric and material properties of the rod, as well as the height and relative speeds of deployment. The various modes selected and their characteristic length-scales are found to arise from a complex interplay between gravitational, bending, and twisting energies of the rod, coupled to the geometric nonlinearities intrinsic to their large deformations. We give particular emphasis to the first sinusoidal mode of instability, which we find to be consistent with a Hopf bifurcation, and rationalize the meandering wavelength and amplitude. Throughout, we systematically vary natural curvature of the rod as a control parameter, which has a qualitative and quantitative effect on the pattern formation, above a critical value that we determine. Upon establishing excellent quantitative agreement between experiments and simulations with no fitting parameters, we perform a numerical survey to relate the pattern size to the relevant length-scales arising from material properties and the setup geometry, and quantify the typical strain levels in the rod. The universality conferred by the prominent role of geometry in the deformation modes of the rod suggests using the gained understanding as design guidelines, in the original applications that motivated the study. These include the coiling of carbon nanotubes and the deployment of submarine cables and pipelines onto the seabed.
by Mohammad Khalid Jawed.
S.M.

APA, Harvard, Vancouver, ISO, and other styles

6

Guo, Hanfen. "Quasi-static universal motions of homogeneous monotropic elastic rods." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq23326.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Beretta, Robert K. (Robert Kneeland). "A geometrically exact dynamic model for spatial elastic rods." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38117.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Gong, Chen. "Surface waves in elastic material." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-227640.

Full text

Abstract:

A finite volume method based solver for Rayleigh waves in two dimensional elastic materials is constructed by using the Conservation Laws Package (Clawpack). The Lax-Wendroff scheme is implemented and only first-order accuracy is achieved for the Rayleigh wave problems by the default elastic wave solver in Clawpack. A Lamb's problem is solved by Clawpack and some instabilities occur in the cases of almost incompressible materials. The Rayleigh wave problem in complex geometries is transformed by a smooth mapping function and solved by using a fourth-order summation-by-parts (SBP) operators with a simultaneous approximation term (SAT) method. The stability is proved by the energy method in the continuous and discrete form. The numerical experiment shows that the curved boundary has influences on the magnitude and phase of the Rayleigh waves.

APA, Harvard, Vancouver, ISO, and other styles

9

Dreyer, Daniel 1975. "Application of the Element Free Galerkin Method to elastic rods." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/80918.

Full text

Abstract:

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2000.
"February 2000."
Includes bibliographical references (p. 115-119) and index.
by Daniel Dreyer.
S.M.

APA, Harvard, Vancouver, ISO, and other styles

10

Connell, I. J. "Large elastic deformations of tubes, wires and springs." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376636.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Manohara, Ranganath Draksharam. "Modelling of Elastic Ship in Waves." Thesis, KTH, Marina system, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119768.

Full text

Abstract:

Ships in the seas undergo different distortions like bending, twisting or combined bending and twisting. The demand for increase in length and speed of the ships is increasing due to this the study for flexibility of structures is becoming important. Usually the structural excitations or natural frequencies of structure are given less priority since the natural frequencies of the structure are higher than encounter frequencies but since the length and speeds are increasing the encounter frequencies are closer to the fundamental frequencies. The structural behavior can be analyzed by semi-empirical formulation developed by classification societies but the flexibility of its application is limited. The present thesis work deals with the vertical motions of the ship structure. The thesis work is divided in to two parts the first part deals with the literature review of the global loads and Hydroelasticity and the second part deals with the modeling of the structural dynamic problem. In the modeling part Hydro-elasticity theory proposed by Bishop and Price on Euler Bernoulli beam is used for solving the structural dynamic problem and the illustration of springing and whipping is presented. An attempt has also been made to study the dynamic structural responses for a particular hull with the hydrodynamic forces and added mass from high speed strip program developed at KTH and the study has been performed to analyze the influence of various parameters like added mass, damping and stiffness.

APA, Harvard, Vancouver, ISO, and other styles

12

Draksharam, Manohara Ranganath. "Modelling of Elastic Ship in Waves." Thesis, KTH, Marina system, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121311.

Full text

Abstract:

Ships in the seas undergo different distortions like bending, twisting or combined bending and twisting. The demand for increase in length and speed of the ships is increasing due to this the study for flexibility of structures is becoming important. Usually the structural excitations or natural frequencies of structure are given less priority since the natural frequencies of the structure are higher than encounter frequencies but since the length and speeds are increasing the encounter frequencies are closer to the fundamental frequencies. The structural behavior can be analyzed by semi-empirical formulation developed by classification societies but the flexibility of its application is limited.The present thesis work deals with the vertical motions of the ship structure. The thesis work is divided in to two parts the first part deals with the literature review of the global loads and Hydroelasticity and the second part deals with the modeling of the structural dynamic problem. In the modeling part Hydro-elasticity theory proposed by Bishop and Price on Euler Bernoulli beam is used for solving the structural dynamic problem and the illustration of springing and whipping is presented. An attempt has also been made to study the dynamic structural responses for a particular hull with the hydrodynamic forces and added mass from high speed strip program developed at KTH and the study has been performed to analyze the influence of various parameters like added mass, damping and stiffness.

APA, Harvard, Vancouver, ISO, and other styles

13

Punjani, Minaz. "Crack characterisation using ultrasonic elastic waves." Thesis, University College London (University of London), 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267567.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Spillmann, Jonas. "CORDE: Cosserat rod elements for the animation of interacting elastic rods." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:25-opus-57751.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Anakok, Isil. "A Study on Steady State Traveling Waves in Strings and Rods." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/83890.

Full text

Abstract:

The main focus of this present work is to study how mechanical steady state traveling waves can be generated and propagated through one dimensional media by applying forces. By steady state traveling waves we refer to propagating mechanical waves in a finite medium that never exhibit reflections at the boundaries and continuously move from one end of the structure to the other. Mechanical waves can be classified as traveling, standing and hybrid waves that are the results of the interplay of excitation forces, applied force locations, and the boundary conditions of the structure. Traveling waves carry energy through a defined medium while standing waves keep energy at certain areas that are associated with the modes of excitation. To understand the interaction of systems that exhibit traveling waves with their surrounding media (i.e., swimming flagella, manta ray locomotion), it is crucial to first understand the wave propagation and what is desired in these structural systems. The parameters that affect the generation and propagation of waves should be welldefined to control and manipulate the desired system’s response. One-dimensional string and rod equations are studied with various boundary conditions to generate steady-state traveling waves in a string and longitudinal traveling waves in a rod. Two excitation forces are applied to a string and a rod near the boundaries to understand the generation and propagation of traveling and standing waves at various frequencies. The work examines the quality of the wave propagation in a string, and in a rod. A cost function approach is applied to identify the quality of such waves. Furthermore, steady-state square traveling waves are generated in a string and in-plane in a rod, both theoretically and experimentally. To the authors’ knowledge this is the first time this has been attempted in the literature. Determining the quality of traveling waves and understanding the parameters on the wave propagation of a string and rod can lead to further understand and leverage various engineering disciplines such as mechanical actuation mechanisms, propulsion of flagella, and the basilar membrane in the ear’s cochlea.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

16

Owen, Nicholas C. "Existence and stability of drawing and necking deformations for nonlinearly elastic rods." Thesis, Heriot-Watt University, 1986. http://hdl.handle.net/10399/1605.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Rodrigues, Ferreira Elizabete. "Finite-amplitude waves in deformed elastic materials." Doctoral thesis, Universite Libre de Bruxelles, 2008. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210464.

Full text

Abstract:

Le contexte de cette thèse est la théorie de l'élasticité non linéaire, appelée également "élasticité finie". On y présente des résultats concernant la propagation d'ondes d'amplitude finie dans des matériaux élastiques non linéaires soumis à une grande déformation statique homogène. Bien que les matériaux considérés soient isotropes, lors de la propagation d'ondes un comportement anisotrope dû à la déformation statique se manifeste.

Après un rappel des équations de base de l'élasticité non linéaire (Chapitre 1), on considère tout d'abord la classe générale des matériaux incompressibles. Pour ces matériaux, on montre que la propagation d'ondes transversales polarisées linéairement est possible pour des choix appropriés des directions de polarisation et de propagation. De plus, on propose des généralisations des modèles classiques de "Mooney-Rivlin" et "néo-Hookéen" qui conduisent à de nouvelles solutions. Bien que le contexte soit tri-dimensionnel, il s'avère que toutes ces ondes sont régies par des équations d'ondes scalaires non linéaires uni-dimensionelles. Dans le cas de solutions du type ondes simples, on met en évidence une propriété remarquable du flux et de la densité d'énergie.

Dans les Chapitres 3 et 4, on se limite à un modèle particulier de matériaux compressibles appelé "modèle restreint de Blatz-Ko", qui est une version compressible du modèle néo-Hookéen.

En milieu infini (Chapitre 3), on montre que des ondes transversales polarisées linéairement, faisant intervenir deux variables spatiales, peuvent se propager. Bien que la théorie soit non linéaire, le champ de déplacement de ces ondes est régi par une version anisotrope de l'équation d'onde bi-dimensionnelle classique. En particulier, on présente des solutions à symétrie "cylindrique elliptique" analogues aux ondes cylindriques. Comme cas particulier, on obtient aussi des ondes planes inhomogènes atténuées à la fois dans l'espace et dans le temps. De plus, on montre que diverses superpositions appropriées de solutions sont possibles. Dans chaque cas, on étudie les propriétés du flux et de la densité d'énergie. En particulier, dans le cas de superpositions il s'avère que des termes d'interactions interviennent dans les expressions de la densité et du flux d'énergie.

Finalement (Chapitre 4), on présente une solution exacte qui constitue une généralisation non linéaire de l'onde de Love classique. On considère ici un espace semi-infini, appelé "substrat" recouvert par une couche. Le substrat et la couche sont constitués de deux matériaux restreints de Blatz-Ko pré-déformés. L'onde non linéaire de Love est constituée d'un mouvement non atténué dans la couche et d'une onde plane inhomogène dans le substrat, choisies de manière à satisfaire aux conditions aux limites. La relation de dispersion qui en résulte est analysée en détail. On présente de plus des propriétés générales du flux et de la densité d'énergie dans le substrat et dans la couche.

The context of this thesis is the non linear elasticity theory, also called "finite elasticity".

Results are obtained for finite-amplitude waves in non linear elastic materials which are first subjected to a large homogeneous static deformation. Although the materials are assumed to be isotropic, anisotropic behaviour for wave propagation is induced by the static deformation.

After recalling the basic equations of the non linear elasticity theory (Chapter 1), we first consider general incompressible materials. For such materials, linearly polarized transverse plane waves solutions are obtained for adequate choices of the polarization and propagation directions (Chapter 2). Also, extensions of the classical Mooney-Rivlin and neo-Hookean models are introduced, for which more solutions are obtained. Although we use the full three dimensional elasticity theory, it turns out that all these waves are governed by scalar one-dimensional non linear wave equations. In the case of simple wave solutions of these equations, a remarkable property of the energy flux and energy density is exhibited.

In Chapter 3 and 4, a special model of compressible material is considered: the special Blatz-Ko model, which is a compressible counterpart of the incompressible neo-Hookean model.

In unbounded media (Chapter 3), linearly polarized two-dimensional transverse waves are obtained. Although the theory is non linear, the displacement field of these waves is governed by a linear equation which may be seen as an anisotropic version of the classical two-dimensional wave equation. In particular, solutions analogous to cylindrical waves, but with an "elliptic cylindrical symmetry" are presented. Special solutions representing "damped inhomogeneous plane waves" are also derived: such waves are attenuated both in space and time. Moreover, various appropriate superpositions of solutions are shown to be possible. In each case, the properties of the energy density and the energy flux are investigated. In particular, in the case of superpositions, it is seen that interaction terms enter the expressions for the energy density and the energy flux.

Finally (Chapter 4), an exact finite-amplitude Love wave solution is presented. Here, an half-space, called "substrate", is assumed to be covered by a layer, both made of different prestrained special Blatz-Ko materials. The Love surface wave solution consists of an unattenuated wave motion in the layer and an inhomogeneous plane wave in the substrate, which are combined to satisfy the exact boundary conditions. A dispersion relation is obtained and analysed. General properties of the energy flux and the energy density in the substrate and the layer are exhibited.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

APA, Harvard, Vancouver, ISO, and other styles

18

Johnston, Clifton Reed. "Solitary waves in fluid-filled elastic tubes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq64866.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Wang, Wei. "Manipulation of Lamb waves with elastic metamaterials." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS414.

Full text

Abstract:

Nous développons des métamatériaux élastiques à piliers pour manipuler les ondes de Lamb. Dans un premier temps, les propriétés négatives associées aux résonances de flexion, de compression et de torsion dans deux structures constituées de piliers sur un seul côté d’une membrane sont examinées. Nous décrivons deux mécanismes différents des propriétés de double négativité. Le potentiel de ces structures pour la réfraction négative et le cloaking acoustique est démontré. Deuxièmement, nous présentons le transport protégé topologiquement des ondes de Lamb par analogie avec les effets Hall quantiques de spin et de vallée. En réorganisant les structures précédentes en un réseau en nid d'abeille, un cône de Dirac simple et un cône de Dirac double sont introduits. Nous discutons de l’apparition d’états de bord protégés topologiquement par une vallée dans une structure à piliers double face asymétrique. La propagation unidirectionnelle des états de bord est étudiée. De plus, nous considérons un système double face symétrique. Les états de bord protégés topologiquement sur le pseudospin et sur le pseudospin-vallée sont démontrés. Troisièmement, nous proposons une approche pour contrôler activement la transmission de l’onde de Lamb antisymétrique se propageant à travers une ligne infinie de piliers. Deux situations différentes avec les résonances de flexion et de compression respectivement séparées ou superposées sont étudiées. Une force de traction externe et une pression sont appliquées sur les piliers, ce qui permet de les coupler avec les vibrations de flexion et de compression. La transmission est étudiée en fonction de l’amplitude et de la phase relative des sources externes
We develop elastic pillared metamaterials to manipulate Lamb waves. Firstly, the negative properties associated with bending, compression and torsion resonances in two structures consisting of pillars on one side of a thin plate are examined. We describe in details two different mechanisms at the origin of doubly negative property. The potential of these structures for negative refraction of Lamb waves and acoustic cloaking is demonstrated numerically. Secondly, we present the topologically protected transport of Lamb waves by analogy with quantum spin and valley quantum Hall effects. By rearranging the previous structures into a honeycomb network, a single Dirac cone and a double Dirac cone are introduced. We discuss the appearance of topologically valley-protected edge states in an asymmetrical double-sided pillar structure. The unidirectional propagation of edge states on different domain walls is studied. In addition, we consider a symmetrical double-sided system allowing the separation of the symmetric and antisymmetric modes. Combined edge states protected topologically by pseudospin and pseudospin-valley degree of freedom are demonstrated. Third, we propose an approach to actively control the transmission of the antisymmetric Lamb wave propagating through an infinite line of pillars. Two different situations with bending and compression resonances respectively separated or superimposed are studied. External tensile force and pressure are applied to the pillars, which allows them to couple with the bending and compressive vibrations. The transmission is studied as a function of the amplitude and the relative phase of the external sources

APA, Harvard, Vancouver, ISO, and other styles

20

Schlottmann, Robert Brian. "A path integral formulation of elastic wave propagation /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004372.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Arens, Tilo. "The scattering of elastic waves by rough surfaces." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311560.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Imhof, Matthias Georg. "Scattering of elastic waves using non-orthagonal expansions." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/54423.

Full text

Abstract:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.
Includes bibliographical references (p. 270-284).
by Matthias Georg Imhof.
Ph.D.

APA, Harvard, Vancouver, ISO, and other styles

23

Ahonsi, Bright. "On the propagation of stress waves in viscoelastic rods for Hopkinson bar studies." Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=182239.

Full text

Abstract:

The propagation of stress waves in long polymer rods forms the basis of two major experimental techniques. The first is a modified Split-Hopkinson pressure bar (SHPB) arrangement that employs polymer Hopkinson bars (as opposed to metallic bars) in order to determine the high strain-rate mechanical properties of soft materials. The second experimental technique consists of a group of methods for determining the viscoelastic properties of polymer rods within a frequency range of 20 Hz to 30 kHz. An experimental, analytical and finite element study of stress waves propagating in viscoelastic rods is reported. A propagation coefficient is used to account for the attenuation and dispersion of stress waves propagating in polymer rods. Through experimental investigations, an optimal experimental arrangement is used to determine the propagation coefficient of a PMMA rod with an improved level of accuracy in comparison with results available in the open literature. Analytical investigations show difficulties associated with experimental arrangements as well as the numerical procedure adopted which tend to reduce the accurate frequency range of the determined propagation coefficient. The FE analysis of stress waves propagating in polymer rods suggests end effects are important; these end effects are not accounted for in any analytical bar wave theory. The high strain-rate mechanical properties of Hydroxyl-terminated polybutadiene (HTPB) are measured via a viscoelastic SHPB set-up. A scheme for processing the strain signals from the tests that allows for large strain measurement (approximately 60%) is presented. The use of viscoelastic SHPB set-up is able to produce a more sensitive measurement when compared with test results in the literature which are obtained using conventional metallic bars. A Finite element model of a viscoelastic Hopkinson bar set-up is developed. The applicability of the model in viscoelastic SHPB testing is validated.

APA, Harvard, Vancouver, ISO, and other styles

24

Kim, Hyun Sil. "Instability of finite amplitude wave propagation in harmonically heterogeneous elastic solids." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/16437.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

De, Lima Washington Jose. "Harmonic generation in isotropic elastic waveguides /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004249.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Maboudi, Afkham Babak. "Modeling and Simulation of Elastic Rods with Intrinsic Curvature and Twist Immersed in Fluid." Thesis, KTH, Numerisk analys, NA, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-148168.

Full text

Abstract:

Understanding the dynamics of thin elastic rods that are immersed in fluid is fundamental in explaining many problems that arise in biology, physics and engineering. Solving the coupled system of rod-fluid in 3D is usually very costly, however in case of low Reynolds number, the three-dimensional problem can be reduced a one-dimensional problem on the centerline of the rod. In this thesis we examine the method of regularized Stokeslets which is a numerical algorithm for an elastic rod immersed in viscous, incompressible fluid at zero Reynolds number governed by Stokes equations. In this method, the elastic rod is represented by a space curve corresponding to the centerline of the rod. In addition, an orthonormal triad is varying along the curve, with one vector being tangent to the curve, and the others describing the material twist. The model that is used for the elastic forces based on this, allows for natural configurations for the rods that are far from straight, as described by curvature and torsion. In this way, the basic or equilibrium configuration for the rod can be e.g. a helix. The linearity of Stokes equations allows us to evaluate the linear and angular fluid velocity only at centerline of the rod. We also examine the dependency to the numerical parameters together with the accuracy and convergence properties of the method. As a bench mark, we compare the numerical result of this method to those produced by the non-local slender body method for the case of elastic rods with no intrinsic curvature and twist inside a planar shear flow. We also present the simulation of the extension of helical rods when they are placed within a constant background flow and we provide a fast converging formula for the periodic summation of the fundamental solutions to the Stokes equations.
Förståelsen för dynamiken hos tunna elastiska fibrer eller stavar inuti en vätska är fundamental för att förklara många problem som uppstår inom biologi, fysik och ingenjörsvetenskap. Att lösa det sammanbundna stav-vätska systemet i 3D är vanligtvis väldigt kostsamt; men vid ett lågt Reynoldstal kan det tredimensionella problemet reduceras till ett endimensionellt längs stavens centrumlinje. I det här arbetet har vi undersökt metoden med regulariserande Stokeslets, vilken är en numerisk algoritm som används på elastiska stavar inuti en viskös, inkompressibel vätska med Reynoldstal noll, modellerad med Stokes ekvation. I den här metoden så är den elastiska staven representerad av en kurva i rummet som beskriver stavens centrumlinje. Dessutom används en ortogonal triad som varierar längs kurvan, och som beskriver materialets vridning. Med den modell som används för de elastiska krafterna baserat på detta, så kan stavarnas naturliga konfiguration vara allt annat än raka, och beskrivas med kurvatur och torsion. På detta sätt kan grundläget för staven vara tex spiralformad. Lineariteten av Stokes ekvation möjliggör att vi kan beräkna både den linjära och vinkel-flödeshastigheten endast längs med stavens centrumlinje. Vi undersöker också hur metoden beror av de numeriska parametrarna och metodens noggrannhets- och konvergens-egenskaper. Som ett riktmärke jämför vi de numeriska resultaten av metoden med resultaten producerade av den så kallade ”non-local slender body” metoden som använts för elastiska stavar utan naturlig kurvatur och vridning som placeras i ett plant skjuvflöde. Vi presenterar också simuleringar av utsträckning av spiralformade stavar då dessa är placerade i ett konstant bakgrundsflöde, och dessutom så tillhandahåller vi en snabbt konvergerande formel för den periodiska summeringen av de fundamentala lösningarna till Stokes ekvation.

APA, Harvard, Vancouver, ISO, and other styles

27

Xu, Liwei. "Computational methods for a class of problems in acoustic, elastic and water waves." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 203 p, 2009. http://proquest.umi.com/pqdweb?did=1833647381&sid=12&Fmt=2&clientId=8331&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Yi, Kaijun. "Controlling guided elastic waves using adaptive gradient-index structures." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC044/document.

Full text

Abstract:

Les matériaux à gradient d'indice de réfraction (GRIN) présentent des propriétés mécaniques variant en temps ou/et en espace. Ils ont été testés pour des applications prometteuses dans de nombreuses applications d'ingénierie, comme pour le contrôle santé structurale ou la surveillance de structure (SHM), le contrôle des vibrations et bruit, la récupération d'énergie, etc. D'un autre côté, les matériaux piézoélectriques offrent la possibilité de réaliser des cellules composites dont les propriétés mécaniques peuvent être contrôlées en ligne. Motivé par ces deux approches, cette thèse étudie la mise en œuvre de structures GRIN adaptatifs pour le contrôle des ondes élastiques. Deux types de structures GRIN adaptatifs sont étudiés dans ce travail. Le premier exemple concerne la mise en œuvre d'une lentille piézoélectrique dans une plaque. Il est composé de patchs piézoélectriques shuntés, collés périodiquement en surface du guide d'ondes. Les circuits de shunt utilisés permettent d'émuler une capacité négative (NC). En accordant les valeurs de NC on peut ajuster l'indices de réfraction du milieu à l'intérieur de la lentille piézoélectrique et pour satisfaire une fonction sécante hyperbolique. Les résultats numériques montrent que les lentilles piézoélectriques peuvent alors focaliser les ondes de flexion de la plaque sur les points focaux. La lentille piézoélectrique est efficace dans une grande bande de fréquences et efficace dans une grande plage de fonctionnement. Ainsi elle peut focaliser des ondes sur différent points par simple ajustement des valeurs de NC réalisés par le circuit. Cette focalisation adaptative la rend très intéressante pour de nombreuses applications comme la récupération d'énergie ou le SHM. La mise en œuvre de ces techniques pour la récupération d'énergie est discutée dans cette thèse. Le second exemple concerne l'étude d'une structure dont les propriétés mécaniques sont contrôlées en temps et en espace. En particulier, une modulation périodique permet de créer une onde artificielle se propageant dans la structure. L'interaction avec des ondes mécaniques entraîne une rupture de réciprocité visible dans un diagramme de bande non symétrique. De nombreux phénomènes inhabituels sont observés dans ce type de structures variables : fractionnement des fréquences, conversion d'ondes et transmission unidirectionnelles. Deux types de conversion fréquentielle sont démontrés et expliqués. Le premier est induit par la transmission d'énergie entre les différents modes Bloch et le second type est dû à la diffusion de Bragg dans les structures modulées. La transmission unidirectionnelle des ondes pourrait être exploitée pour réaliser des diodes dans des systèmes infinis ou semi-infinis. Cependant, la transmission unidirectionnelle n'existe pas dans les systèmes finis en raison des phénomènes de conversion de fréquence
GRadient INdex (GRIN) media are those whose properties smoothly vary in space or/and time. They have shown promising effects in many engineering applications, such as Structural Health Monitoring (SHM), vibration and noise control, energy harvesting, etc. On the other hand, piezoelectric materials provide the possibility to build unit cells, whose mechanical properties can be controlled on-line. Motivated by these two facts, adaptive GRIN structures, which can be realized using shunted piezoelectric materials, are explored in this dissertation to control guided elastic waves. Two types of adaptive GRIN structures are studied in this work. The first type is a piezo-lens. It is composed of shunted piezoelectric patches bonded on the surfaces of plates. To control the mechanical properties of the piezoelectric composite, the piezoelectric patches are shunted with Negative Capacitance (NC). By tuning the shunting NC values, refractive indexes inside the piezo-lens are designed to satisfy a hyperbolic secant function in space. Numerical results show that the piezo-lens can focus waves by smoothly bending them toward the designated focal point. The piezo-lens is effective in a large frequency band and is efficient in many different working conditions. Also the same piezo-lens can focus waves at different locations by tuning the shunting NC values. The focusing effect and tunable feature of piezo-lens make it useful in many applications like energy harvesting and SHM. The former application is fully discussed in this thesis. The focusing effect at the focal point results in a known point with high energy density, therefore harvesting at the focal point can yield more energy. Besides, the tunable ability makes the harvesting system adaptive to environment changes. The second type is the time-space modulated structure. Its properties are modulated periodically both in time and space. Particularly, the modulation works like a traveling wave in the structure. Due to the time-varying feature, time-space modulated structures break the reciprocity theorem, i.e., the wave propagation in them is nonreciprocal. Many unusual phenomena are observed during the interaction between waves and time-space modulated structures: frequency splitting, frequency conversion and one-way wave transmission. Two types of frequency conversion are demonstrated and explained. The first type is caused by energy transmission between different orders Bloch modes. The second type is due to the Bragg scattering effect inside the modulated structures. The one-way wave transmission could be exploited to realize one-way energy insulation in equivalent infinite or semi-inffnite systems. However, the one-way energy insulation fails in finite systems due to the frequency conversion phenomenon

APA, Harvard, Vancouver, ISO, and other styles

29

Kil, Hyun-Gwon. "Propagation of elastic waves on thin-walled circular cylinders." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/15967.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Fong, Ka Lok Jimmy. "A study of curvature effects on guided elastic waves." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421857.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Li, Xiaofan. "Scattering of elastic waves by heterogeneous and extended continua." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389961.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Haslinger, Stewart. "Mathematical modelling of flexural waves in structured elastic plates." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/16833/.

Full text

Abstract:

This thesis discusses properties of flexural waves in thin elastic plates that incorporate a structured system of gratings of defects. The defects may take the form of inclusions or masses, but we focus on circular inclusions, and in particular, holes with a clamped edge. We place the work in the relatively new field of platonics, which is the study of flexural waves in plates governed by the fourth-order biharmonic plate equation. By analogy with photonic and phononic crystals, the two-dimensional structures in thin elastic plates are known as platonic crystals. We present a novel analysis of trapped modes and transmission resonances in grating stacks, arising from the interaction with plane waves incident on the gratings. We show that the evanescent modes are important in demonstrating interesting and unusual filtering effects. In particular we analyse the previously unstudied effect of elasto-dynamically inhibited transmission (EDIT), where a resonance in transmission is cut in two by a resonant minimum arising from destructive interference. Similar destructive interference-induced phenomena have been observed in other settings, notably classical optical oscillators, metamaterials and plasmonics, but we are the first to do it for flexural plates. The phenomenon of EDIT is a central theme of this thesis, and is linked to the analysis of even and odd Bloch modes in the grating waveguides. We develop a method that identifies the parameters of the model, the relative separations η and lateral shifts ξ of the gratings, and the spectral parameter β and angle of incidence θi of the plane wave, to find EDIT efficiently. The method is powerful and universal, based on a recurrence procedure for the construction of reflection and transmission matrices. A multipole method is employed for circular scatterers and the limiting case of rigid pins, whereby the solutions are determined analytically. Recent developments have also been made with arbitrarily-shaped holes, and other future research is likely to focus on the association with Dirac-like cones that are linked to the standing modes arising in platonic crystals.

APA, Harvard, Vancouver, ISO, and other styles

33

Zhao, Jinfeng. "Phononic Crystals to Control the Propagation of Elastic Waves." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066098/document.

Full text

Abstract:

Ce travail de thèse concerne la focalisation des ondes élastiques se propageant dans une plaque mince ou à la surface d’un milieu semi-infini, au travers de lentilles acoustiques planes. Les dispositifs que nous avons étudiés sont basés sur des cristaux phononiques 2D, constitués d'inclusions d'air dans une matrice solide. Ces hétérostructures présentent un gradient de leurs propriétés élastiques le long d'une direction de la lentille. Le gradient d'indice est obtenu en modulant soit la taille des inclusions d'air, soit la distance entre deux inclusions consécutives. L’approche que nous avons adoptée est basée principalement sur la simulation numérique par éléments finis. Cependant une partie significative du travail concerne le calcul analytique de la trajectoire des rayons acoustiques ainsi que la vérification expérimentale des résultats théoriques.L’approche analytique a consisté à calculer la trajectoire des rayons acoustique dans la lentille, en tenant compte de l'anisotropie le long de chaque ligne d'inclusions. L'analyse analytique, appliquée à une onde de Lamb antisymétrique (A0), ainsi que les résultats numériques et les données expérimentales, expliquent parfaitement les caractéristiques du champ de déplacement dans la zone focale, y compris la position, la forme et les dimensions latérales de la tâche focale. Le formalisme s’applique quelle que soit la symétrie du cristal phononique et peut être étendu à des ondes élastiques présentant une autre polarisation. Nous montrons dans ce travail qu’une largeur à mi-hauteur aussi petite que 0.64 peut être obtenue lorsque la focalisation intervient au sein de la lentille.Le formalisme s’applique également à la focalisation derrière la lentille. Dans ce cas, la résolution au point focal est déterminée par le "nombre d'onde transversal maximal" à la sortie de la lentille, en bon accord avec les résultats numériques et expérimentaux. Ensuite, nous avons conçu une lentille à gradient d’indice avec des piliers résonnants érigés entre les inclusions d'air. L'analyse numérique prévoit une résolution légèrement au-delà de la limite de diffraction. Expérimentalement, nous mesurons une largeur à mi-hauteur de la tâche focale juste au-dessus de la limite de diffraction.Enfin, nous avons étudié la focalisation d’une onde de Rayleigh par une lentille à gradient d’indice. Nous avons trouvé un bon accord entre le calcul des trajectoires des rayons, les simulations numériques et les expériences. En outre, nous avons analysé la transmission de l’énergie élastique lorsque la focalisation intervient derrière la lentille
This manuscript is about the focusing of elastic beams propagating in a plate or on the free surface of a semi-infinite medium, using flat acoustical lenses. The devices we have studied are based onto 2D phononic crystals that are made of air inclusions in a solid matrix and featuring a gradient of their elastic properties along one direction of the lens. The gradient index (GRIN) is obtained by modulating either the size of the air inclusions or the distance between two consecutive inclusions.We primarily adopted a computational approach but a significant part of the work concerns the analytical calculation of the ray trajectories as well as the experimental check of the theoretical findings. The analytical approach consists to calculate the ray trajectories of an elastic waves within the lens while accounting for the anisotropy along each lines of inclusions. The analysis applied to the lowest-order flexural Lamb wave (A0), together with both the numerical results and the experimental data, well explains the features of the displacements field in the focus area, including the location, shape and lateral width. The formalism applies whatever the symmetry of the phononic crystal is and can be extended to other polarization of the elastic wave. We show in this work that FWHM as small as 0.64 may be obtained when focusing inside the lens.The formalism applies also to the focusing behind the lens. In that case, the resolution at the focus is determined by the “maximum transverse wavenumber” at the exit of lens, in good agreement with the numerical and experimental results. Then we designed a GRIN phononic lens featuring resonant pillars in addition to the constitutive air inclusions. The numerical analysis foresees the resolution at the focus beyond the diffraction limit, while experimentally we measured the resolution to be just above the diffraction limit. Lastly, we turned to the subwavelength focusing of Rayleigh waves through GRIN lenses. We found a good agreement between the ray trajectories calculation, the numerical simulations and the experiments. We further analysed the influence of energy transmission when the focus is located behind the lens

APA, Harvard, Vancouver, ISO, and other styles

34

Shearer, Tom. "Waves in nonlinear elastic media with inhomogeneous pre-stress." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/waves-in-nonlinear-elastic-media-with-inhomogeneous-prestress(39ffbda5-3510-4941-b092-208b854141b4).html.

Full text

Abstract:

In this thesis, the effect of inhomogeneous pre-stress on elastic wave propagation and scattering in nonlinear elastic materials is investigated. Four main problems are considered: 1. torsional wave propagation in a pre-stressed annular cylinder, 2. the scattering of horizontally polarised shear waves from a cylindrical cavity in a pre-stressed, infinite, nonlinear elastic material, 3. the use of pre-stress to cloak cylindrical cavities from incoming horizontally polarised shear waves, and 4. the scattering of shear waves from a spherical cavity in a pre-stressed, infinite, nonlinear elastic material.It is observed that waves in a hyperelastic material are significantly affected by pre-stress, and different results are obtained from those which would be obtained if the underlying stress was neglected and only geometrical changes were considered. In Chapter 3 we show that the dispersion curves for torsional waves propagating in an annular cylinder are strongly dependent on the pre-stress applied. A greater pressure on the inner surface than the outer causes the roots of the dispersion curves to be spaced further apart, whereas a greater pressure on the outer surface than the inner causes them to be spaced closer together. We also show that a longitudinal stretch causes the cut-on frequencies to move closer together and decreases the gradient of the dispersion curves, whilst a longitudinal compression causes the cut-on frequencies to move further apart and increases the gradient of the dispersion curves. In Chapter 4 we observe that pre-stress affects the scattering coefficients for shear waves scattered from a cylindrical cavity. It is shown that, for certain parameter values, the scattering coefficients obtained in a pre-stressed medium are closer to those that would be obtained in the undeformed configuration than those that would be obtained in the deformed configuration if the pre-stress were neglected. This result is utilised in Chapter 5 where the cloaking of a cylindrical cavity from horizontally polarised shear waves is examined. It is shown that neo-Hookean materials are optimal for this type of cloaking. A stonger dependence of the strain energy function on the second strain invariant leads to a less efficient cloak.We observe that, for a Mooney-Rivlin material, as S1 tends from 1 towards 0 (in other words, as a material becomes less dependent on the first strain invariant, and more dependent on the second strain invariant), there is more scattering from the cloaking region. For materials which are strongly dependent on the second strain invariant the pre-stress actually increases the scattering cross-section relative to the scattering cross-section for an unstressed material, hence these materials are unsuitable for pre-stress cloaking.Finally, in Chapter 6 we study the effect of pressure applied to the inner surface of a spherical cavity and at infinity on the propagation and scattering of shear waves in an unbounded medium. It is shown that the scattering coefficients and cross-sections for this problem are strongly dependent on the pre-stress considered. We observe that a region of inhomogeneous pre-stress can lead to some counterintuitive relationships between cavity size and scattering cross-sections and coefficients.

APA, Harvard, Vancouver, ISO, and other styles

35

Brevis, Vergara Rodrigo Ignacio. "Source time reversal methods for acoustic and elastic waves." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/152342.

Full text

Abstract:

Tesis para optar al grado de Doctor en Ciencias de la Ingeniería, Mención Modelación Matemática
Esta tesis estudia la detección y reconstrucción del término espacial de una fuente de variables separables en problemas de onda acústica y elástica. Para esto, estudiamos el método time-reversal mirror, el cual explota una invariancia intrínseca de la física a nivel microscópico que se observa también a nivel macroscópico en las ecuaciones de ondas. Esto significa que es posible recuperar la condición inicial de una ecuación de ondas homogénea revirtiendo la onda a través del tiempo. Para localizar y reconstruir el término espacial de la fuente, desarrollamos un método llamado source time reversal. La aplicación subyacente aquí es la detección de fuentes sísmicas en la minería. Es sabido que la actividad minera induce temblores dentro de las minas [50]. Esto se vuelve bastante peligroso si no se toman las precauciones adecuadas. Conocer sobre el origen de las actividades sísmicas puede ser utilizado para reducir el peligro de derrumbes y mejorar la seguridad dentro de las minas. Este trabajo se divide en tres capítulos; cada uno de ellos constituye un documento autocontenido para ser presentado como artículo. El primer capítulo aborda el problema de reconstrucción de fuente para ondas acústicas. Para esto introducimos el método source time reversal, la cual reconstruye el término espacial de una fuente de la forma f(x)g(t), donde f(x) entrega la forma y g(t) representa la distribución en tiempo de la fuente. Además, presentamos una estimación del error de la reconstrucción para el caso cuando f es una función de cuadrado integrable. Aquí, proponemos un método de regularización para implementar la reconstrucción de la fuente numéricamente. Adicionalmente, analizamos las principales características y limitaciones del método propuesto cuando se aplica a ondas acústicas. El capítulo dos estudia el problema de reconstrucción de fuente para ondas elásticas. Extendemos el método source time reversal para problemas elásticos. Además, introducimos un nuevo método de regularización para implementar la reconstrucción del término espacial de la fuente numéricamente para grandes volúmenes de datos. El nuevo método de regularización elimina las altas frecuencias presentes en la señal procesada, lo que permite utilizar mallas numéricas más gruesas y reduce el costo computacional. Finalmente, este capítulo presenta diversos experimentos numéricos para probar que el método es válido en el caso elástico. El último capítulo analiza un problema de reconstrucción de fuente diferente. Aquí consideramos una fuente compuesta por una suma finita de funciones de variable separable, donde cada término temporal de la fuente es una función delta de Dirac actuando a un tiempo diferente. Basado en una propiedad de tiempo reverso, la fuente puede ser localizada observando el desplazamiento y la velocidad de desplazamiento en el problema reverso [31]. Nosotros extendemos esta idea a sistemas de ondas elásticas. Adicionalmente, proponemos un algoritmo para la implementación numérica.
CONICYT, CMM - Conicyt PIA AFB170001 y el proyecto GEAGAM

APA, Harvard, Vancouver, ISO, and other styles

36

Kocaoglu, Argun H. "A new method for modeling surface wave propagation in heterogeneous media." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/25716.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Tie, An. "On scattering of seismic waves by a spherical obstacle." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/27988.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Dalo, Dominic N. "A finite element solution of thermal wave propagation in elastic media /." Online version of thesis, 1987. http://hdl.handle.net/1850/8821.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Liu, Zunping. "Three-dimensional multiple scattering of elastic waves by spherical inclusions." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/386.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Littles, Jerrol W. Jr. "Scattering of longitudinal elastic waves from a distribution of cracks." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19242.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Miniaci, Marco <1986&gt. "Behaviour and applications of elastic waves in structures and metamaterials." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6634/.

Full text

Abstract:

The present thesis focuses on elastic waves behaviour in ordinary structures as well as in acousto-elastic metamaterials via numerical and experimental applications. After a brief introduction on the behaviour of elastic guided waves in the framework of non-destructive evaluation (NDE) and structural health monitoring (SHM) and on the study of elastic waves propagation in acousto-elastic metamaterials, dispersion curves for thin-walled beams and arbitrary cross-section waveguides are extracted via Semi-Analytical Finite Element (SAFE) methods. Thus, a novel strategy tackling signal dispersion to locate defects in irregular waveguides is proposed and numerically validated. Finally, a time-reversal and laser-vibrometry based procedure for impact location is numerically and experimentally tested. In the second part, an introduction and a brief review of the basic definitions necessary to describe acousto-elastic metamaterials is provided. A numerical approach to extract dispersion properties in such structures is highlighted. Afterwards, solid-solid and solid-fluid phononic systems are discussed via numerical applications. In particular, band structures and transmission power spectra are predicted for 1P-2D, 2P-2D and 2P-3D phononic systems. In addition, attenuation bands in the ultrasonic as well as in the sonic frequency regimes are experimentally investigated. In the experimental validation, PZTs in a pitch-catch configuration and laser vibrometric measurements are performed on a PVC phononic plate in the ultrasonic frequency range and sound insulation index is computed for a 2P-3D phononic barrier in the sonic frequency range. In both cases the numerical-experimental results comparison confirms the existence of the numerical predicted band-gaps. Finally, the feasibility of an innovative passive isolation strategy based on giant elastic metamaterials is numerically proved to be practical for civil structures. In particular, attenuation of seismic waves is demonstrated via finite elements analyses. Further, a parametric study shows that depending on the soil properties, such an earthquake-proof barrier could lead to significant reduction of the superstructure displacement.

APA, Harvard, Vancouver, ISO, and other styles

42

Captain, V. S. "The effect of inextensibility on elastic surface and interfacial waves." Thesis, University of East Anglia, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378895.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Prikazchikova, Liudmila A. "Small amplitude waves in a pre-stressed compressible elastic plate." Thesis, University of Salford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419310.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Garnier, Erell-Isis. "Long waves in water over a visco-elastic muddy seabed." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67613.

Full text

Abstract:

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 289-290).
The propagation of surface waves over a flat muddy seabed are studied. Mud is first considered as a Newtonian fluid. Water and mud equations are derived in order to obtain governing equation for surface and interface waves. By the method of multiple scales. nonlinear evolution equations are derived for the harmonic amplitudes. These equations are numerically solved for a finite number of harmonics to show the behavior of surface and interface motions. A drift current in mud is found at the second order., meaning that surface waves induce mud motion. Equation governing the total wave energy variation is derived and used to verify the accuracy of numerical solutions. The model is extended to viscoelastic mud, using the results of four experiments carried on different types of muds. These muds range from very elastic to rather viscous, allowing us to compare hie differences in behavior. Surface and interface variations. mud drift current and energy variations are plotted and compared to the results with Newtonian muds. A sloping muddy seabed is then considered. Mud is modeled as viscoelastic to avoid a constant static current that would happen with Newtonian mud. By the method of multiple scales and by introducing a space-dependent wavenumber, mud drift current and energy variation equations are derived again, taking into account the effect of the slope. An analytic stud v of the surface variations demonstrates that surface and interface waves, as well as drift current, exponentially decay to reach a zero value at the shore.
by Erell-Isis Garnier.
S.M.

APA, Harvard, Vancouver, ISO, and other styles

45

Drozdz, Mickael Brice. "Efficient finite element modelling of ultrasound waves in elastic media." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/7974.

Full text

Abstract:

The aim of the work presented in this thesis is to provide tools to extend modelling capacities and improve quality and reliability of bulk and guided wave propagation models using commercially available finite element (FE) packages. During the development process of NDT inspection techniques, the knowledge of the interaction of waves with defects is key to the achievement of robust and efficient techniques as well as identifying potential weaknesses. The reflection of ultrasound from cracks and notches of simple geometry anq'orientation is already well understood, but there are few results for more complex c~es. A discrete approach is needed to model how the waves interact with discontinuities, including structural features, cracks, corrosion or other forms of defects. FE methods have been used to model a wide range of bulk and guided waves problems and have successfully provided important information about wave interaction with discontinuities. In these studies, defects were strongly simplified. One reason for this is that initial work is bound to focus on the simplest cases, but many modellers are ready to go on to more complex problems. The reason that so little of that is happening is that, despite rapid growth in computer power, many of the more complex realistic problems are still beyond the capacity of the models. The more complex problems require much larger models than the simplified ones, and so have remained out of reach. This can be changed by using innovative techniques and improving the quality and reliability ofmodelling by taking the right decisions during the modelling process. Perfectly matched layers (pML) and absorbing layers using increasing damping (ALID) enabling a reduction in the model geometric size are implemented in commercially available FE packages. Analytical models are developed in order to facilitate the achievement of high computational efficiency. Demonstrator cases highlight the gains achieved by the use of these techniques. As the choice of mesh density is crucial in defining the resources necessary to solve a model, a study of the influence of meshing parameters for various element types and numerical schemes on the propagation velocity is performed. This provides information helping modellers to reach the right modelling compromises thanks to an improved understanding ofthe consequences of the decisions made. The accuracy of defect modelling is investigated for a range of situations and modelling strategy. The weight ofthe choice ofthe right strategies is demonstrated. The potential implementation of local mesh refinement in commercially available FE packages is considered and discussed in the context of the choices open to the modellers. The outcome of the use of the techniques and information presented in this thesis is a significant improvement in FE modelling of waves in elastic media.

APA, Harvard, Vancouver, ISO, and other styles

46

Liow, J. (Jeih-San). "A two dimensional finite-difference simulation of seismic wave propagation in elastic media." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/25781.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Burton, David A. "Slender elastic media and the gravitational field." Thesis, Lancaster University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322890.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Shu, Kun-Tien. "Multidimensional reflection and refraction of infinite amplitude stress waves in elastic solids." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17680.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Brookes, David William. "The existence of surface waves in piezoelectric half-spaces and of edge waves in elastic laminated plates." Thesis, Keele University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425970.

Full text

Abstract:

This thesis is concerned with determining the possibility of the existence of subsonic free surface waves in piezoelectric half-spaces, and of subsonic free edge waves in elastic laminated semi-infinite plates, where the material constants are not presumed to possess any particular special form of symmetry. By means of an introduction, standard analytical results are presented for the existence and uniqueness of surface waves and edge waves in isotropic elastic half-spaces and semi-infinite plates respectively, together with analytical expressions for the wave speeds. A re-analysis of the problem of determining the existence of surface waves in piezoelectric half-spaces is then presented. Lothe and Barnet [30] solved this problem using ideas from the Stroh formalism, whereas the work presented here arrives at the same conclusions by using different analytical methods. For the electrically open boundary condition it is shown that at most one surface wave may exist, and when the boundary condition is not electrically open then at least one and at most two surface waves may exist. A computer program was used to calculate the surface wave speeds for a variety of boundary conditions. The numerical results obtained are shown to be in agreement with the theory. Original theoretical work is then presented regarding the existence of waves propagating along the edge of an elastic laminated plate. The problem is resolved using an octet formalism, and it is shown that when a normal transonic state is present then at least one and at most two edge waves may exist. In the case where there is an exceptional transonic state, then it is possible that zero, one or two edge waves may exist. Numerical results relating to edge wave speeds are then obtained using another computer program, and are found not to conflict with the theory.

APA, Harvard, Vancouver, ISO, and other styles

50

Zhang, Jin E. Wu Theodore Y. T. Wu Theodore Y. T. "I. Run-up of ocean waves on beaches. : II. Nonlinear waves in a fluid-filled elastic tube /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-01072008-105605.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Elastic rods and waves'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles