Teses / dissertações sobre o tema "Propagative waves"
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Lalloz, Samy. "De la diffusion à la propagation d'ondes en magnétohydrodynamique bas-Rm : études théorique et expérimentale". Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALI020.
Texto completo da fonteThe thesis aims to clarify the conditions for Alfvén waves to propagate in a closed liquid metal domain. A first part of the research work presented is dedicated to a linear study of Alfvén waves in the low-Rm approximation and under the inertia-less limit. The second part is the experimental investigation of an electrically-induced oscillating flow subjected to an axial, static and uniform magnetic field and confined between two electrically insulating and no-slip horizontal walls.The theoretical study is itself split into two sub-parts. The first one aims to discuss the dispersion relation which contains the Alfvén wave dynamics. It presents the consequences of (mechanical and magnetic) gradients perpendicular to the imposed magnetic field. As such transverse gradients tend to impede the wave propagation. In the second sub-part an axisymmetric vortex confined between to electrically insulated and no-slip horizontal walls is magnetically forced at a given frequency. This forcing is radially dependent so as to study the impact of transverse gradients on the flow dynamics. A semi-analytical investigation of the flow dynamics is again carried out in the low-Rm approximation and under the inertia-less limit. This investigation is performed by varying the forcing frequency and the magnetic field intensity. This brings to emphasize two very distinct regimes for the oscillating vortex:- an oscillating-diffusive regime governed by the competition between pseudo-diffusive effects of the Lorentz force and the unsteady term of the momentum- a truly propagative regime, obtained for higher forcing frequencies, found definitelygoverned by Alfvén waves.The study also highlights how the propagative regime can be affected by transverse gradients. In addition to over-damping the waves, transverse gradients are found to modify the natural frequencies for which wave resonance peaks result from the superimposition of incident and reflected waves in the container.Beside this theoretical work, a setup has been designed in order to experimentally investigate the dynamics of oscillating flows under a strong magnetic field (up to 10T). A flow was forced in a cuboid vessel 15 cm x 15 cm x 10 cm by means of AC currents injected through a cartesian grid of four electrodes located at the bottom plate. Using instrumentation based on the measurement of local electric potential differences at the top and bottom horizontal (Hartmann) plates, we validate model's prediction. More precisely, a propagative dynamics in the presence of transverse gradients is recovered. The oscillating-diffusive regime is also recovered from experiments performed at small enough forcing frequency.In addition to results obtained at the forcing frequency, a first insight of signals obtained at other frequencies is shown. Frequency peaks obtained, eg the harmonics of the forcing frequency, are demonstrated not to be explained by a linear approach. We suggest that Alfvén wave non-linear interactions are a good candidate to explain these peaks. A preliminary study further shows that peaks at the first harmonic are likely to be Alfvén waves
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.
Texto completo da fonteKil, Hyun-Gwon. "Propagation of elastic waves on thin-walled circular cylinders". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/15967.
Texto completo da fonteFu, Y. "Propagation of weak shock waves in nonlinear solids". Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384589.
Texto completo da fonteGandhi, Navneet. "Determination of dispersion curves for acoustoelastic lamb wave propagation". Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37158.
Texto completo da fontePack, Jeong-Ki. "A wave-kinetic numerical method for the propagation of optical waves". Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/104527.
Texto completo da fonteZandi, Bahram. "Propagation of optical waves in tapered fibers and metallic wave guides". PDXScholar, 1986. https://pdxscholar.library.pdx.edu/open_access_etds/2693.
Texto completo da fonteReese, Owein. "Homogenization of acoustic wave propagation in a magnetorheological fluid". Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-101629.
Texto completo da fonteLane, Ryan Jeffrey. "Study of Wave Propagation in Damaged Composite Material Laminates". Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/86366.
Texto completo da fonteMaster of Science
The physical properties of high strength and low weight and the economic benefits of carbon fiber composites has resulted in these materials replacing metals in several industries. It is important, however, to be aware that the change in materials used impacts the different types of damage composites experience compared to conventional metals. One type of damage that could cause a composite part to fail is a delamination or a separation of layers. In order to identify if this damage has occurred, it is beneficial to have an inspection technique that will not damage the part. In this study, a technique was tested that involved breaking a piece of pencil lead on a plate in order to generate multiple wave modes that would propagate in the plate. Based on boundary conditions caused by the damage in the plate, the speed of the wave and frequency content could be compared to an undamaged plate to identify a delamination. A model was created to compare experimental results and demonstrated that using wavespeed and frequency could identify a delamination. The experimental results compared well with the model dispersion curves for a plate with and without a delamination suggesting this approach could be placed into practice to provide routine testing to detect delamination for in-service, carbon fiber composite parts.
Iskandarani, Saad S. "Electromagnetic wave propagation in anisotropic uniaxial slab waveguide". Ohio : Ohio University, 1989. http://www.ohiolink.edu/etd/view.cgi?ohiou1182437230.
Texto completo da fontePodo, Smardie D. "Comparison of layering effects in the propagation of transient planar stress waves". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/18378.
Texto completo da fonteServin, Martin. "Nonlinear interaction and propagation of gravitational and electromagnetic waves in plasmas". Doctoral thesis, Umeå University, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-122.
Texto completo da fonteGravitational waves and electromagnetic waves are important as carriers of energy and information. This thesis is devoted to the study of the propagation and interaction of these waves in plasmas, with emphasis on nonlinear effects and applications within astrophysics.
The physical systems are described by the Einstein-Maxwell-fluid equations or Einstein-Maxwell-Vlasov equations, when a kinetic treatment is required. The small amplitude and high-frequency approximation is employed for the gravitational waves, such that perturbative techniques can be applied and space-time can be considered locally flat, with a gravitational radiation field superimposed on it. The gravitational waves give rise to coupling terms that have the structure of effective currents in the Maxwell equations and an effective gravitational force in the equation of motion for the plasma. The Einstein field equations describe the evolution of the gravitational waves, with the perturbed energy-momentum density of the plasma and the electromagnetic field as a source.
The processes that are investigated are gravitational waves exciting electromagnetic waves in plasmas, altering the optical properties of plasmas and accelerating charged particles. The thesis also deals with the propagation propertities of gravitational and electromagnetic waves, e.g. effects due to resonant wave-particle interactions, plasma inhomogeneties and nonlinear self-interactions. It is also shown that plasmas that are not in thermodynamical equilibrium may release their free energy by emitting gravitational waves.
Razo, López Luis Alberto. "Localisation des ondes électromagnétiques au-delà d'Anderson : rôle des corrélations, des symétries et de la topologie". Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ5013.
Texto completo da fonteIn a broad sense, the term wave localization refers to a phenomenon where waves are spatially confined in small regions of the space without any bounding material barriers.In this Thesis, we investigate (analytically, numerically and experimentally) different physical collective mechanisms to spatially localize, and therefore, to control electromagnetic waves. Specifically, we focus on the role of uncorrelated and correlated potentials, as well as of topological effects to achieve wave confinement. Analytical and numerical studies are accomplished in the framework of a recent approach in the modeling of Anderson localization called localization landscape theory. On the other hand, experiments are performed using a microwave platform composed by small dielectric cylinders placed inside a cavity made of two metallic plates. The cavity implements a propagative wave system, where we can efficiently control the local permittivity by means of the cylinders acting as scatterers, or as an analogic tight-binding system, where, in this case, the dielectric cylinders play the role of resonators.First, we extend the scope of the localization landscape approach to a wide class of one and two dimensional tight-binding systems in the presence of uncorrelated disorder, where localized eigenfunctions appear in both band-edges. We demonstrate how the landscape theory is able to predict accurately not only the locations, but also the energies of localized eigenfunctions in the low- and high-energy regimes. Later, by using our experimental cavity as a propagative system, we perform microwave transport experiments in two dimensional planar arrays. Experiments are carried out on a disordered lattice and on an aperiodic Vogel spiral from where we characterize the electromagnetic modal structures in real space. Our results reveals that aperiodic systems can carry a rich variety of long-lived modes—with Gaussian, exponential, and power law spatial decays—which are able to survive even in a three-dimensional environment. This is supported by different transport quantities such as the density of states, the characteristic decay time, and the Thouless conductance that are also experimentally accessible. On the contrary, we show that the eigenstates in traditional disordered media are always limited to exponential radial decays with leaking features beyond two-dimensions.Finally, we use the experimental tight-binding configuration to investigate the propagation of topological helical states. Particularly, we experimentally analyze a set of honeycomb-like structures built using a triangular lattice with an hexagonal unit cell, which are characterized by the Z_2 topological invariant. By recovering the modal structure in real space and the density of states, our results reveal the possibility to open a topological gap, dwelt by edge states that lives in the border of the structure.We demonstrate the unidirectional counterpropagative features of such helical edge states.Taken together, our results demonstrate that it is possible to model, control and localize electromagnetic waves not only within, but beyond Anderson's conception. Thanks to the crossroads we have taken, we have mapped out an itinerary that brings us closer to the main avenue leading perhaps to Anderson localization of three dimensional electromagnetic waves
Wang, Bingnan. "Wave propagation in photonic crystals and metamaterials surface waves, nonlinearity and chirality /". [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3389159.
Texto completo da fonteTaouk, Habib. "Wave propagation in general anisotropic media". Ohio : Ohio University, 1986. http://www.ohiolink.edu/etd/view.cgi?ohiou1183380228.
Texto completo da fonteCasadei, Filippo. "Multiscale analysis of wave propagation in heterogeneous structures". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44889.
Texto completo da fonteXie, Zhongqiang. "Fourth-order finite difference methods for the time-domain Maxwell equations with applications to scattering by rough surfaces and interfaces". Thesis, Coventry University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369842.
Texto completo da fonteClavica, Francesco. "Computational and experimental time domain, one dimensional models of air wave propagation in human airways". Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/9622.
Texto completo da fonteGuddati, Murthy Narasimha. "Efficient methods for modeling transient wave propagation in unbounded domains /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Texto completo da fonteDrazin, William. "Blast propagation and damage in urban topographies". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274900.
Texto completo da fonteHurlebaus, Stefan. "Laser generation and detection techniques for developing transfer functions to characterize the effect of geometry on elastic wave propagation". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/20742.
Texto completo da fonteGeldenhuis, Andre. "The Atmospheric Gravity Wave Transfer Function above Scott Base". Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/3698.
Texto completo da fonteSrikasem, Suthum. "Wave reflection in uniaxially anisotropic media". Ohio : Ohio University, 1987. http://www.ohiolink.edu/etd/view.cgi?ohiou1183062033.
Texto completo da fonteOrszaghova, Jana. "Solitary waves and wave groups at the shore". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:5b168bdc-4956-4152-a303-b23a6067bf42.
Texto completo da fonteAyers, James Thomas. "Structural damage diagnostics via wave propagation-based filtering techniques". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34723.
Texto completo da fonteKreuzinger, Tobias. "Digital Signal Processing Methods for Source Function Extraction of Piezoelectric Elements". Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4792.
Texto completo da fonteLOPES, DANIEL T. "Caracterização de estruturas de ondas lentas helicoidais para utilização em, TWT de potência". reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11596.
Texto completo da fonteMade available in DSpace on 2014-10-09T13:58:44Z (GMT). No. of bitstreams: 0
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
FAPESP:05/03612-0
Johnson, Mark Alden Misra Anil. "The effect of normal and shear stresses on wave propagation through a fracture". Diss., UMK access, 2007.
Encontre o texto completo da fonte"A dissertation in engineering and physics." Advisor: Anil Misra. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed July 30, 2008. Includes bibliographical references (leaf 93 ). Online version of the print edition.
Ray, Timothy Allen. "Wave propagation over complex bathymetry". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FRay.pdf.
Texto completo da fonteThesis advisor(s): Thomas H.C. Herbers, Edward B. Thornton. Includes bibliographical references (p. 37). Also available online.
Muirhead, Matthew. "Interior wave propagation". Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289312.
Texto completo da fonteCowan, Michael L. "Strong scattering of ultrasonic waves in fluidized suspensions, wave propagation, spectroscopy techniques and particle dynamics". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq62630.pdf.
Texto completo da fonteCompton, Christopher S. "Propagation of Alfvén waves in the WVU HELIX device". Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4525.
Texto completo da fonteTitle from document title page. Document formatted into pages; contains iv, 22 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 22).
Tshisaphungo, Mpho. "Validation of high frequency propagation prediction models over Africa". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.
Texto completo da fonteLehmann, Lutz. "Wave propagation in infinite domains : with applications to structure interaction /". Berlin [u.a.] : Springer, 2007. http://www.gbv.de/dms/bs/toc/523903820.pdf.
Texto completo da fonteChauvette, Sylvain. "SLOW-WAVE SLEEP : GENERATION AND PROPAGATION OF SLOW WAVES, ROLE IN LONG-TERM PLASTICITY AND GATING". Thesis, Université Laval, 2013. http://www.theses.ulaval.ca/2013/29523/29523.pdf.
Texto completo da fonteSleep is known to mediate several major functions in the brain and among them are the gating of sensory information during sleep and the sleep-related improvement in memory consolidation. Slow-wave sleep in particular is thought to be critical for both of these processes. However, their physiological mechanisms are unknown. Also, the electrophysiological hallmark of slow-wave sleep is the presence of large amplitude slow waves in the cortical local field potential and the alternation of periods of intense synaptic activity in which cortical neurons are depolarized and fire action potentials and periods of silence in which no firing occurs, cortical neurons are hyperpolarized, and very little synaptic activities are observed. First, in order to better understand the studies presented in this manuscript, a general introduction covering the thalamocortical system architecture and function is presented, which includes a description of the states of vigilance, followed by a description of the rhythms present in the thalamocortical system during slow-wave sleep, then by a description of the mechanisms of synaptic plasticity, and finally two hypotheses about how sleep might affect the consolidation of memory are presented. Then, three studies are presented and were designed to characterize the properties of the sleep slow oscillation. In the first study (Chapter II), we showed that periods of activity (and silence) occur almost synchronously in neurons that are separated by up to 12 mm. The activity was initiated in a focal point and rapidly propagated to neighboring sites. Surprisingly, the onsets of silent states were even more synchronous than onsets of active states. The working hypothesis for the second study (Chapter III) was that active states are generated by a summation of spontaneous mediator releases. Using different recordings in both anesthetized and non-anesthetized animals, we showed that no neuronal firing occurs in the neocortex during silent states of slow-wave sleep but some synaptic activities might be observed prior to the onset of active states, which was in agreement with our hypothesis. We also showed that layer V neurons were leading the onset of active states in most of the cycles but this would be due to probabilistic reasons; these cells being equipped with the most numerous synaptic contacts among cortical neurons. We also showed that slow-wave sleep and ketamine-xylazine shares many similarities. v Having used a combination of recordings in ketamine-xylazine anesthetized and non-anesthetized animals, and because ketamine-xylazine anesthesia is extensively used as a model of slow-wave sleep, we made quantitative measurements of the differences between the two groups of recordings (Chapter IV). We found that the slow oscillation was much more rhythmic under anesthesia and it was also more coherent between distant sites as compared to recordings during slow-wave sleep. Under anesthesia, slow waves were also of larger amplitude and had a longer duration as compared to slow-wave sleep. However, spindles and gamma were also affected by the anesthesia. In the following study (Chapter V), we investigated the role of slow-wave sleep in the formation of long-term plasticity in the thalamocortical system. Using pre-thalamic stimulations of the ascending somatosensory pathway (medial lemniscus fibers) in non-anesthetized animals, we showed that evoked potential recorded in the somatosensory cortex were enhanced in a wake period following a slow-wave sleep episode as compared to the previous wake episode and this enhancement was long-lasting. We also showed that rapid eye movement sleep did not play a significant role in this enhancement of response amplitude. Using whole-cell recordings in vitro, we characterized the mechanism behind this enhancement and it was compatible with the classical form of long-term potentiation, because it required an activation of both NMDA and AMPA receptors as well as the presence of calcium in the postsynaptic neuron. The last study included in this thesis (Chapter VI) was designed to characterise a possible physiological mechanism of thalamic sensory gating occurring during sleep. Spindles are characterized by the presence of low-threshold calcium spikes and calcium plays a critical role in the synaptic transmission. Using several experimental techniques, we verified the hypothesis that these calcium spikes would cause a local depletion of calcium in the extracellular space which would impair synaptic transmission. We showed that calcium channels responsible for calcium spikes were co-localized with synapses and that indeed, local extracellular calcium depletion occurred during spontaneous or induced low-threshold calcium spike, which was sufficient to impair synaptic transmission. We conclude that slow oscillation originate at a focal point and then propagate to neighboring cortical areas being almost synchronous even in cells located up to 12 mm vi apart. Active states of this oscillation originate from a summation of spike-independent mediator releases that might occur in any cortical neurons, but happens more often in layer V pyramidal neurons simply due to probabilistic reasons. Both experiments in ketamine-xylazine anesthesia and non-anesthetized animals showed several similar properties, but also some quantitative differences. We also conclude that slow oscillation plays a critical role in the induction of long-term plasticity, which very likely contributes to memory consolidation. Spindles, another oscillation present in slow-wave sleep, contribute to the thalamic gating of information.
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Uzoegbo, Herbert Chidozie. "Propagation of acoustic waves in concrete". Thesis, King's College London (University of London), 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321500.
Texto completo da fonteKeane, Adam J. "Propagating waves and variable neural dynamics". Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16861.
Texto completo da fonteRatan, Naren. "Complex phase space representation of plasma waves : theory and applications". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:af5654e3-3137-4d9a-b41d-574cd72103b2.
Texto completo da fonteLöfås, Henrik. "Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode". Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121898.
Texto completo da fonteKim, 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.
Texto completo da fonteTaouk, Habib B. "Optical wave propagation in active media". Ohio : Ohio University, 1991. http://www.ohiolink.edu/etd/view.cgi?ohiou1173729381.
Texto completo da fonteKocaoglu, 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.
Texto completo da fonteAldurayhim, Abdullah Mohammed. "Propagating waves in reaction cross-diffusion systems". Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31129.
Texto completo da fonteAnanda, Agus A. "Propagation of Rayleigh waves in thin films". W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623914.
Texto completo da fonteParisi, Giuseppe M. S. P. "Propagation of electromagnetic waves in "Fishnet" metamaterials". Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3425440.
Texto completo da fonteRecentemente la fabbricazione e l'ottimizzazione di nano aperture periodiche attraverso strati di metalli nobili ha riscosso molta attenzione sia per l'interesse verso fenomeni fisici non comuni sia per le potenziali applicazioni alla nano-ottica e alla biosensoristica. In particolare i metamateriali composti da strati metallo-dielettrici sovrapposti e perforati da aperture periodiche, conosciuti come strutture a forma di spina di pesce, sono oggi tra i migliori candidati per studiare alcuni fenomeni fisici non comuni, come la rifrazione ad angolo negativo. La tesi di dottorato riassume lo studio della propagazione delle onde elettromagnetiche in strutture periodiche, in particolare nelle "Fishnet". La propagazione di onde elettromangetiche nelle Fishent genera una proprietà non comune: l"indice di rifrazione negativo. L'obbiettivo principale della tesi è quello di studiare l'origine dell'indice di rifrazione negativo e la sua dipendenza dai parametri geometrici a partire da strutture di base come la Fishnet a tre strati fino a strutture più evolute come la Fishnet a multi strato. Dei metodi e modelli effettivi per l'estrazione dei parametri complessi saranno inizialmente considerati per lo studio preliminale. Tuttavia per un'indagine più rigorosa verrà presentato un recente metodo modale adatto all'analisi di strutture omogenee fortemente accoppiate come le Fishnet a multistrato in cui anche i modi evanescenti, legati alla dissipazione del metallo, possono giocare un ruolo cruciale. Il metodo FEM di analisi modale è basato sull'equazioni di Elmholtz in forma debole e rappresenta un potente metodo di indagine per studiare l'evoluzione dei modi complessi, alla base dell'indice effettivo di rifrazione negativo (parte reale e complessa), da un punto di vista più fondamentale.
Monsalve, Gutiérrez Eduardo. "Études expérimentales des ondes à la surface de l'eau : effets non linéaires et absorption". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066027/document.
Texto completo da fonteThis thesis presents an experimental investigation on the propagation of nonlinear water waves. The first part focuses on the space-time measurements of nonlinear water waves, when it passes over a submerged step. The space-time resolved measurement allows us to separate the different components at the second order, which are compared with a theoretical nonlinear multi-modal model. The important contribution of the surface tension at higher orders is verified by measuring the beating length of the second harmonic. In the same conditions, the addition of a reflecting wall at the end of the channel sets a rectangular tank with submerged step, where the excitation of low-frequency modes yields a quasi-periodic dynamics. Concurrently, a research about aspects that have to be considered in small scale experiments of surface waves has been carried out. In shallow water, the damping of water waves is highly influenced by the bottom friction. This dependence was measured for randomly distributed waves, revealing the relative contribution of this effect. Moreover, the dynamic of the contact line plays a significant role when the wave-amplitude is small and the boundaries are near, both in relation to the capillary length. We observed experimentally how the wetting of the boundaries changes the reflection and the wave-front curvature. The final part covers the measurement of perfect wave absorption by a coupled resonator in a narrow waveguide. The trapped modes generated by a cylinder shifted from the channel axis were excited to generate the absorption
Forslund, Ola. "Scattering and propagation of electromagnetic waves in planar and curved periodic structures - applications to plane wave filters, plane wave absorbers and impedance surfaces". Doctoral thesis, KTH, Alfvén Laboratory, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3825.
Texto completo da fonteThe subject of this thesis is scattering of electromagneticwaves from planar and curved periodic structures. The problemspresented are solved in the frequency domain.
Scattering from planar structures with two-dimensionalperiodic dependence of constitutive parameters is treated. Theconstitutive parameters are assumed to vary continuously orstepwise in a cross section of a periodically repeating cell.The variation along a longitudinal coordinate z is arbitrary. Ageneral skew lattice is assumed. In the numerical examples, lowloss and high loss dielectric materials are considered. Theproblem is solved by expanding the .elds and constitutiveparameters in quasi-periodic and periodic functionsrespectively, which are inserted into Maxwells equations.Through various inner products de.ned with respect to the cell,and elimination of the longitudinal vector components, a linearsystem of ordinary di.erential equations for the transversecomponents of the .elds is obtained. After introducing apropagator, which maps the .elds from one transverse plane toanother, the system is solved by backward integration.Conventional thin metallic FSS screens of patch or aperturetype are included by obtaining generalised transmission andre.ection matrices for these surfaces. The transmission andre.ection matrices are obtained by solving spectral domainintegral equations. Comparisons of the obtained results aremade with experimental results (in one particular case), andwith results obtained using a computer code based on afundamentally di.erent time domain approach.
Scattering from thin singly curved structures consisting ofdielectric materials periodic in one dimension is alsoconsidered. Both the thickness and the period are assumed to besmall. The .elds are expanded in an asymptotic power series inthe thickness of the structure, and a scaled wave equation issolved. A propagator mapping the tangential .elds from one sideto the other of the structure is derived. An impedance boundarycondition for the structure coated on a perfect electricconductor is obtained.
Keywords:electromagnetic scattering, periodicstructure, frequency selective structure, frequency selectivesurface, grating, coupled wave analysis, electromagneticbandgap, photonic bandgap, asymptotic boundary condition,impedance boundary condition, spectral domain method,homogenisation
Su, Dan. "Microcrack damage and its effect on stress wave propagation". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 114 p, 2009. http://proquest.umi.com/pqdweb?did=1654487641&sid=6&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Texto completo da fonteDavis, Bradley A. "Propagation and Scattering of Waves by Terrain Features". Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/28137.
Texto completo da fontePh. D.
Banerjee, Sourav. "Elastic Wave Propagation in Corrugated Wave Guides". Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1182%5F1%5Fm.pdf&type=application/pdf.
Texto completo da fonte