Dissertations / Theses on the topic 'A Rayleigh wave'
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Morlock, Merlin B. "Nonlinear mixing of two collinear Rayleigh waves." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50280.
Full textOoi, Eng Seng. "Rayleigh wave interactions with tribological contacts." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/9963/.
Full textMalladi, Subrahmanya Sastry Venkata. "Modeling and Algorithm Performance For Seismic Surface Wave Velocity Estimation." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1194630399.
Full textMorgan, Robert Vaughn. "Experiments on the Rarefaction Wave Driven Rayleigh-Taylor Instability." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/337302.
Full textBlake, Richard John. "Numerical models for Rayleigh wave scattering from surface features." Thesis, University College London (University of London), 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282401.
Full textHorne, Michael R. "Rayleigh Wave Acoustic Emission during Crack Propagation in Steel." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28780.
Full textPh. D.
Richmond, Rachelle Marie. "Ambient noise surface wave tomography across Europe: Rayleigh wave group and phase speed measurements." Connect to online resource, 2008. 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:1453514.
Full textHuang, Chi-Luen. "Effect of beam diffraction on nonlinear Rayleigh surface wave measurement." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47537.
Full textSelby, Neil D. "Rayleigh wave amplitudess and the attenuation structure of the earth." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365757.
Full textBashir, Hussam. "Calculation of Wave Propagation for Statistical Energy Analysis Models." Thesis, Uppsala universitet, Tillämpad mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267928.
Full textZeighami, Farhad. "Sub-wavelength resonators as seismic Rayleigh waves shield." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textFan, Yichao. "The analysis of surface defects using the ultrasonic Rayleigh surface wave." Thesis, University of Warwick, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495017.
Full textKafle, Durga N. "Rayleigh-Lidar Observations of Mesospheric Gravity Wave Activity above Logan, Utah." DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/466.
Full textFreed, Shaun L. "High Resolution Ultrasonic Rayleigh Wave Interrogation of a Thermally Aged Polymeric Surface." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1291685460.
Full textGross, Johann. "Evaluation of near surface material degradation in concrete using nonlinear Rayleigh surface waves." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45810.
Full textMcLellan, Morgan. "Structure and Deformation of the Northern Canadian Cordillera: Insights from Rayleigh Wave Tomography." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35383.
Full textSethi, Shipra. "Secondary microseisme Love wave generation." Thesis, Université de Paris (2019-....), 2019. https://theses.md.univ-paris-diderot.fr/SETHI_Shipra_va2.pdf.
Full textSeismic noise is the continuous oscillation of the Earth recorded at every station in the absence of earthquakes . The interaction of atmosphere, ocean waves and earth creates them. The dominant signal, called secondary microseisms in the frequency band 0.1-0.3 Hz have known to be formed due to the non-linear interaction between two oppositely traveling ocean gravity waves. The resulting pressure fluctuations close to the ocean surface generates a seismic signal which is dominantly Rayleigh waves (R). Many authors reported the observations of Love wave content (L) in the seismic signal. However the L/R amplitude ratio is shown to vary depending on the area investigated. The generation mechanism of Rayleigh waves due to these noise sources interacting with the sea-bottom is well understood and modeled. The explanation why Love waves are generated is unclear because the source in the ocean cannot generate shear motion. We have shown the existence of Rayleigh and Love waves recorded by the Alaska and California network. We then investigate the effect of ocean-continental slope boundary on the seismic noise amplitude of secondary microsiesm and quantify the Rayleigh-to-Love wave conversion. In order to do that, we use the spectral element method to numerically simulate the seismic wave field in 3D media. The primary focus of this study is on investigating several factors that can influence the seismic noise amplitude recorded on the continent in the frequency band 0.1-1 Hz. Those factors are a) the ocean-thickness, b) the source-site effect i.e., source close to the boundary and far from the boundary, c) the sedimentary layer beneath the sea-bottom and d) the effect of ocean-continental slope angle. We observe that Love waves can be generated at the ocean-continental boundary, however the amplitude change is frequency dependent. We observe energy in the transverse direction in a model that cannot generate Love waves as a result of conversion at the ocean-continental slope boundary. The strongest Love wave amplitude is recorded in a model with 6 km deep ocean at resonant frequencies in the ocean when the source is far from the coast. However at other frequencies, shallow oceans and source close to the boundary generates highest Love wave amplitude. In the presence of sediments, the amplification of Love waves is higher at shorter periods for both sources. The reduction in slope angle diminishes the Love wave amplitude. For both source close and far from the boundary, the L/R amplitude ratio vary strongly with frequency and ocean thickness. Among all the factors, highest L/R amplitude ratios are generated due to sediments when the source is close to the boundary
Yoon, Sungsoo. "Array-Based Measurements of Surface Wave Dispersion and Attenuation Using Frequency-Wavenumber Analysis." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7246.
Full textOlsson, Daniel. "Numerical simulations of energy absorbing boundaries for elastic wave propagation in thick concrete structures subjected to impact loading." Thesis, Umeå universitet, Institutionen för fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-58015.
Full textMånga av världens kärnkraftverk närmar sig slutet på sin beräknade livslängd och ett behov uppstår då att kunna utvärdera de komponenter som är väsentliga för säkerheten på dessa verk. Reaktoromslutningen i betong är en av dessa komponenter och oförstörande provning (NDT) är en attraktiv metod för att bedöma dess tillstånd. Traditionellt har utvärdering av betongkonstruktioner bestått av stresstester på borrprover men p.g.a. den radioaktiva miljön på insidan av omslutningen är denna metod ej att föredra. NDT är självklart möjligt att använda på allsköns betongkonstruktioner då det ger både konstruktionsmässiga och estetiska fördelar. NDT metoden som rör denna studie kallas impact echo och går ut på att man med en hammare slår till en punkt på väggen och mäter responsen en bit därifrån. Lasten ger upphov till vågor i form av deformation som propagerar i väggen och dessa ger i sin tur upphov till Lamb moder. Lamb moderna är strukturella oscillationer av väggen och genom att studera dess frekvenser kan väggens tjocklek bestämmas. Elastiska egenskaper i väggen erhålls utifrån de olika vågornas propageringshastigheter. Impact echo metoden kan även användas för att finna strukturella oegentligheter inuti väggen så som sprickor och delaminering. För att utföra numeriska simuleringar av dynamiska system med NDT-metoder är finita elementmetoden (FEM) användbar. Syftet med denna studie är att bedöma vilka möjligheter som finns för att implementera absorberande ränder med ökande dämpning (ALID) i datamodeller för att minska beräkningstiden av FEM-analyser. ALID används vid kanterna för att simulera ett oändligt system, dess uppgift är att dämpa bort inkommande vågor så att dessa ej reflekteras tillbaka och stör mätningarna. Samtliga modeller i denna studie är två-dimensionella med antagen oändligt liten spänning i normalriktningen. Vinsten i beräkningstid av att använda ALID är stor och ökar ytterligare om modellen utökas till tre dimensioner. Ett ALID definieras genom dess längd och maximala massproportionerlig Rayleigh-dämpning (CMmax). I denna rapport har längderna 0.5, 1.5 and 4.5 m använts med CMmax i intervallet från 103 till 2*105 Ns/m. Dämpningen ökar med ökat avstånd in i ALID med det specificerade maxvärdet vid den bakre kanten. Det bör noteras att skillnad i dämpning mellan element leder till skillnad i impedans; reflektioner av vågorna uppstår vid övergång från ett element med lägre impedans till ett med högre impedans. Ett ALID måste således vara definierat så att det dämpar bort tillräckligt av de inkommande vågorna utan att oönskade reflektioner i ALID uppstår. Studien pekar på att ett 0.5 m långt ALID inte åstadkommer önskvärda resultat för något av valen för CMmax som använts i denna rapport. Både det 1.5 och 4.5 m långa ALID har däremot get bra resultat; ett 1.5 m långt ALID bör ha 2*104 < CMmax <5*104 Ns/m och ett 4.5 m långt ALID 5*103 < CMmax < 104 Ns/m. Förhoppningen med studien är att resultaten skall underlätta utvecklingen av NDT-metoder som kan användas vid konstruktion och underhåll av reaktoromslutningar och andra tjocka betongkonstruktioner.
YAN, ZHONGYU. "ENHANCED CRACK DETECTION BY COMBINATION OF LASER AND ULTRASONIC TECHNIQUES." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin996087800.
Full textUhrig, Matthias Pascal. "Numerical simulation of nonlinear Rayleigh wave beams evaluating diffraction, attenuation and reflection effects in non-contact measurements." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54368.
Full textCarpi, Isotta. "Seismic Metamaterials for Rayleigh waves attenuation: analytical and numerical survey on the effect of soil stratification." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textPandey, Shantanu [Verfasser]. "High resolution 3D Rayleigh wave velocity model of China and surrounding area / Shantanu Pandey." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1031100822/34.
Full textGerasik, Vladimir. "Consolidation and wave propagation in a porous medium." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2950.
Full textTwo-dimensional boundary value problems for a porous half-space, described by the widely recognized Biot's equations of poroelasticity, including inertia effects is discussed. In this poroelastic version of Lamb's problem in the classical theory of linear elastic waves, the surface of a porous half-space is subjected to a prescribed line traction. The following two broadly applicable cases are considered: 1) A steady state harmonic load, 2) An impulsive load (Dirac delta function time dependence). A general analytical solution of the problem in the Fourier -- Laplace space was obtained by the application of the standard Helmholtz potential decomposition, which reduces the problem to a system of wave equations for three unknown potentials, which correspond to three types of motion: P1, slow P2 wave, and the shear wave S. The possibilities of, and procedure for, obtaining analytic solutions in the physical space subsequently are discussed in detail. When viscous dissipation effects are taken into account, a steady-state harmonic line traction solution can be represented in the form of well convergent integrals, while for the case when viscous dissipation is ignored, closed form analytic solutions can be obtained for impulsive forcing with the application of the Cagniard -- de Hoop inversion technique. Numerical studies of the dispersion relation of the Rayleigh, or surface, wave for cases in which the dissipation is not negligible are presented.
Gandhi, Navneet. "Determination of dispersion curves for acoustoelastic lamb wave propagation." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37158.
Full textCarter, Benjamin. "Water-wave propagation through very large floating structures." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/12031.
Full textVoloshin, Vitaly. "Moving load on elastic structures : passage through the wave speed barriers." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4614.
Full textPandey, Shantanu [Verfasser]. "High resolution 3D Rayleigh wave velocity model of China and surrounding area / Shantanu Pandey. Deutsches GeoForschungsZentrum GFZ." Potsdam : Deutsches GeoForschungsZentrum GFZ, 2013. http://nbn-resolving.de/urn:nbn:de:kobv:b103-13010.
Full textMahvelati, Shams Abadi Siavash. "Advancements in Surface Wave Testing: Numerical, Laboratory, and Field Investigations Regarding the Effects of Input Source and Survey Parameters on Rayleigh and Love waves." Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/589154.
Full textPh.D.
The Multichannel Analysis of Surface Waves (MASW) method has been widely used to evaluate the subsurface in engineering applications since late 1990’s. In MASW, surface waves are introduced into the subsurface and recorded by sensors along the ground surface. The characteristics of the propagating surface wave are influenced by the subsurface stratification, the manner in which the surface waves are input into the ground, and the survey parameters to acquire data. Rayleigh waves are typically generated by vertical strikes on a metallic plate which serves as a coupler between the active input source (e.g., a sledgehammer) and the ground surface. It has been suggested that plastic-type base plates can improve the low-frequency energy of Rayleigh waves and therefore, can increase the depth of investigation among other potential improvements. However, very little studies exist in the literature that evaluate the role of base plate material, especially plastic materials. In addition to Rayleigh surface waves, seismic surface waves can also be generated with horizontal impacts (i.e., Love waves) using specialized base plates. In this regard, much less is available in the literature regarding Love waves as sources in MASW testing which means that optimum field survey parameters, the effects of near-field, and the role of seismic source have not been thoroughly investigated yet for Love waves. Given the aforementioned gaps in the literature, two aspects of MASW have been investigated. First, the role of base plate material, specifically plastic-type plates, has been studied. Field data collected from six sites along with the data from laboratory experiments and numerical simulations of hammer-plate impact were studied. The results showed that softer base plates improve the energy transfer by as much 20% and lead to minor improvements, typically one-digit numbers in relative changes, in other signal characteristics such as signal bandwidth and signal-to-noise ratio. These results were corroborated with laboratory testing and numerical models of wave propagation with different base plate materials. The second goal was to improve understanding of Love wave propagation, particularly as related to resolution capabilities from survey parameters. Rayleigh and Love waveforms were collected with multiple active seismic sources at three sites and a systematic comparison was made between the two types of waves. Also, seismic wave propagation was simulated using the research community code SPECFEM2D to further investigate their differences. The results revealed critical new information about the depth of investigation, the effects of bedrock location on near-field effects, and the role of the different survey parameters on Rayleigh and Love wave data. The depth of investigation of Love wave MASW was deeper by about 2-9 m than that of Rayleigh MASW as a result of improved minimum frequency. The minimum source offset to avoid near-field effects was comparable for both Rayleigh and Love waves (0.3-0.4 of maximum wavelength). At closer source offset locations, Rayleigh waves were more affected by near-field effects and showed an additional 10% underestimation of planar phase velocities. Overall, the results from both parts of this study provides new practical insights about some of the unexplored aspects of surface wave testing using MASW.
Temple University--Theses
Duquennoy, Marc. "Analyse ultrasonore des contraintes résiduelles dans les alliages d'aluminium par ondes de Rayleigh." Valenciennes, 1997. https://ged.uphf.fr/nuxeo/site/esupversions/a6bea93f-dcf7-4b3a-9275-e1aaeb5e6a12.
Full textBen, Khalifa Warida. "Modélisation de la propagation et de la réception des ondes élastiques émises par un défaut sous contrainte. Application à la simulation des contrôles non destructifs par émission acoustique." Thesis, Valenciennes, 2013. http://www.theses.fr/2013VALE0007/document.
Full textAE Non-destructive testing is used in many fields such as nuclear energy, oil and gas, civil engineering or mechanical engineering to check the integrity of structures under stress. Depending on the ratio of structure thickness to wavelength, the energy released by a crack under stress can propagate either as guided waves (in thin structures) or as Rayleigh wave (in thick structures). The analysis of signals resulting from this ultrasonic "passive" method is particularly difficult due to the complexity of typically measured signals. The objective of this thesis is to develop models to enable the simulation of AE testing experiments in the case of thick or thin structure. The developed models rely on the coupling between an AE source model, wave propagation models and an AE Sensor model. In the case of thick structures two 2D models (for plane and cylindrical surfaces) and a 3D model (for plane surface) have been developed to predict the signal corresponding to the Rayleigh wave emitted by a crack under stress. In the case of thin structures, a 2D model has been developed to predict the signal corresponding to the guided modes emitted by a crack under stress. Several parametric studies have been conducted to determine the influence of the different model input data on the AE signals and thus help to interpret AE testing results
Apaza, Marco Aurelio Flores. "Determinação do Gmáx através do método de análise espectral de ondas superficiais." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3145/tde-21082009-165223/.
Full textThis dissertation presents the spectral-analysis-of-surface-waves (SASW) method as a tool for obtaining the variations in the modulus shear (Gmax) with depth in the field of very small strains (below 0,001%). The SASW method is a nondestructive in situ seismic method, based on the generation and measurement of Rayleigh wave and on its dispersive characteristic nature. Throughout the implementation of an impact on the soil surface and the detection of the wave at various points by two receptors a dispersion curve is constructed (phase velocity versus wave-length). This dispersion curve is then inverted. Inversion is an analytical process for reconstructing the shear wave velocity profile from the experimental field. The shear modulus of each layer is readily obtained from the shear wave velocity profile. The theoretical content of the dissertation presents dynamic properties of the soils and is described in the equations that dominate the propagation of elastic waves, both in homogeneous media and in stratified media. The methodology developed to obtain the dispersion curves through the implementation of SASW test is defined, and results from tests carried out at the University Campus in São Paulo are presented and compared with values obtained from correlations based on SPT tests. These comparisons indicate that the SASW method is a good alternative to determine the profile of stiffness (Gmax) of the soil, agreeing with the level of deformation involved in the tests. Studies on the methods sensitivity are developed to verify the influence on the changing of the parameters given (natural unit weight, Poisson coefficient and thickness of layers) in reduction of data (inversion) on the final profile of VS. The conclusion is that the Poisson coefficient is the parameter with greater influence.
Dali-Ali, Mohamed. "Etude et caractérisation des ondes de Rayleigh dans les milieux non-piézoélectriques à l'aide de PVF2 et P(VF2-VF3)." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10127.
Full textCroquette, Vincent. "Etude des structures convectives de Rayleigh-Bénard en géométrie étendue." Paris 6, 1986. http://www.theses.fr/1986PA066050.
Full textOberhardt, Tobias. "A micromechanical model for the nonlinearity of microcracks in random distributions and their effect on higher harmonic Rayleigh wave generation." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54365.
Full textParmar, Biren Jagadish. "Development Of Point-Contact Surface Acoustic Wave Based Sensor System." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/279.
Full textTsarsitalidou, Christina. "Inversion of Rayleigh-wave dispersion curves using a finite-element eigenvalue/eigenvector solver, applied to the Alpine region and Italian peninsula." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18152/.
Full textLucena, Rodrigo Ferreira de. "Avaliações e testes dos métodos MASW e ReMi por meio do tratamento de dados empíricos e sintéticos em um programa de processamento e inversão desenvolvido em MATLAB e sua implicação em um problema geológico na Bacia de Taubaté." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/44/44138/tde-17062016-135652/.
Full textThe surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical information associated with geological information allowed the generation of an analytical profile of the study region with two geological interpretation confirming the suspect of neotectonic movements in the region wherein the geological contacts between the quaternary and tertiary deposits were identified and they agreed with the initial model of a hemi-graben with dip to Southeast.
Nicolson, Heather Johan. "Exploring the Earth's subsurface with virtual seismic sources and receivers." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5726.
Full textSu, Bei. "EFFECTS OF RAILROAD TRACK STRUCTURAL COMPONENTS AND SUBGRADE ON DAMPING AND DISSIPATION OF TRAIN INDUCED VIBRATION." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_diss/312.
Full textGnadjro, Dossou. "Nombres d'ondes, masses volumiques et modules effectifs de milieux composites formés d'une matrice poro-élastique contenant des inclusions de forme cylindrique." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMLH16/document.
Full textWe study the propagation of acoustic waves in a porous medium obeying the Biot theory and containing a random distribution of cylindrical cavities and that of an acoustic wave in a fluid containing a random polydisperse distribution of porous spheres. In the first case we use the generalization by Conoir-Norris of the Linton-Martin formula. It allows to take into account the phenomenon of the conversion between the three waves (two longitudinal and one transverse) naturally propagating in a porous Biot medium containing a random distribution of cavities. Analytical expressions are found for the effective wavenumbers of coherent waves in the Rayleigh limit (low frequency regime). The approximations of the densities and heterogeneous media modules are presented up to the order of c2 in concentration. The limiting case of random fluid cavities in an elastic matrix is also discussed. In the second case the effective wavenumbers, moduli and density are determined for polydisperse distributions of poroelastic spheres. To achieve this, the recent formulas of the effective wave number given by Linton and Martin in the dilute monodisperse case have been modified. Given the uncertainty for predicting the distribution in size of obstacles, three different probability densities are studied and compared: uniform, Schulz and lognormal. More precisely, the Rayleigh limit is taken into account when the wave lengths can be assumed to be very large compared to the size of the obstacles. Within this limit, simplified formulas for concentrations are provided depending on the parameter characterizing the size dispersion
Millon, Célia. "Contribution à l’inspection d’échantillons de fabrication additive métallique par ondes de Rayleigh au moyen d’une méthode ultrasons-laser." Thesis, Paris, CNAM, 2018. http://www.theses.fr/2018CNAM1195/document.
Full textThis thesis contributes to the detection of flaws in laser metal deposition (LMD) additive manufacturing process samples towards an in situ control of the process. The in situ control foreseen concerns the last layers deposited by the process (316L and Inconel 718 steel) for which porosities and cracks may appear (~ 100 µm). The inspection is performed by laser-ultrasonics (LU), an all-optical and non-invasive technic. Experiments are conducted in thermoelastic mode. The LMD process gives rise to coarse grain microstructure and surface roughness, that make the control tricky. Indeed, those characteristics generate scattering elastic waves. Thus, this work contributes to the better comprehension of those phenomena and their effects of the detection on subsurface flaws which dimensions are close to the acoustic wavelength. Surface inspection has been optimized by designing an optical setup, improving the Rayleigh wave generation by using a thin laser line source (~200 µm). Hence, the spectral content has been increased until it reaches 10 MHz, that is to say a wavelength equals to 700 µm (λR). Then, the limits have been brought out through the inspection of LMD samples. Those samples include sided drilled holes and notches which dimensions are less than λR, on rough surface (multiple scattering of Rayleigh wave). Moreover, real subsurface flaws inspections have been studied. The flaws have been created by the instability of one of the process parameter: the hatch (distance between each layer), or by a bad powder quality. By intentionally deteriorating those parameters, the samples, then, have porosity rate (Φ) with ranging from 0.5% to 10%. Finally, two correlation methods have been studied to discriminate porosity rate: through the study of the normalized cross correlation function and by Principal Component Analysis (PCA). The first method, simple and fast to implement, does not allow distinguishing the porosity rates. Nevertheless, the PCA indicates that it is possible to discriminate all the flaws. Finally, preliminary tests have been carried out to show that LU measurements is feasible on rough surfaces, while keeping a good signal-to-noise ratio, without averaging, during an automated displacement
Mousselon, Laure. "Radio Wave Propagation Measurements and Modeling for Land Mobile Satellite Systems." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/10155.
Full textMaster of Science
Duan, Yuting. "Trapped modes and acoustic resonances." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/12860.
Full textAlcantara, Glaucio Pedro de 1974. "Estudo das propriedades acusticas do filme fino de TiO2 usando SAW." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/258792.
Full textDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: Este trabalho de dissertação apresenta o estudo e projeto dos elementos que compõem um sensor de gases baseado na tecnologia de Onda Acústica de Superfície (SAW), tais como, o oscilador colpitts SAW e um ressonador SAW de uma porta, os quais estão na malha de realimentação de um amplificador. Foi realizado também a deposição de diferentes espessuras de filme fino de TiO2 sobre o sensor, a fim de se estudar o efeito da atenuação da SAW na fronteira entre o cristal e o filme. É mostrado que atenuação da SAW acontece no filme na fina camada de aproximadamente 500 angstroms de espessura. A dependência de espessura com a mudança de freqüência e com fator Q do oscilador SAW e ressonador são apresentados, bem como a ssensitividade de massa do ressonador SAW para o filme de TiO2. Um modelo de oscilador SAW usando 2 caminhos acústicos, de melhor sensitividade que aquele de modo simples, foi estudado e proposto
Abstract: This thesis presents the study and design of the elements which compose a gas sensor based on Surface Acoustic Wave technology, such as, SAW Colpitts oscillator and the SAW one-port resonator that are presents in the feedback loop of an amplifier. It was done deposition of TiO2 thin film different thickness on the sensor, in order to study the effect of SAW attenuation on the border between the crystal and the film. It is shown that SAW attenuation takes place in the film in thin layer of about 500 angstroms thickness. Thickness dependence of frequency shift and Q-factor of SAW oscillator and resonator, as well as, the mass sensitivity of SAW resonator to TiO2 film are presented. The model of SAW oscillator which uses two acoustic paths, has been studied and proposed.
Mestrado
Mestre em Engenharia Elétrica
Dudchenko, Aleksandr. "Analyse numérique de l’interaction des ondes de Rayleigh en surface avec des barrières sismiques et des champs de pieux prenant en compte le comportement élastoplastique du sol." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI102/document.
Full textThe present work is focused on numerical simulation (FEM) and analysis of surface Rayleigh wave interaction with vertical seismic barriers (underground walls, screens, trenches, etc.) as well as pile fields within the framework of linear elastic and plastic mechanical material models. The aim of the research is to estimate the degree of protection that vertical barriers and pile fields provide against vibrations transferred by surface Rayleigh waves and generated by various sources. The main idea behind this type of protection is to prevent seismic waves form transmitting wave energy into the protected zone, decreasing the amplitude of displacements, velocities and accelerations at the points behind the barrier (pile field). The attention is paid to Rayleigh waves as they can be generated by both external (located on the Earth's surface) and internal (located beneath the Earth's surface) vibration sources and this type of waves can transfer a significant portion of vibration source energy.First, numerical simulations of Rayleigh wave interaction with vertical seismic barriers and pile fields are performed assuming the soil and barrier materials to behave according to the linearly-elastic constitutive law. This regards the vibrations that induce shear strains in the soil not exceeding 0.00001 during their propagation. Based on this, the principal dimensionless complexes are formulated. Geometrical along with mechanical parameters of the barrier (pile field), that determine vibration reduction effect, are identified. The obtained results reveal the validity of this way of vibration protection. In addition to that, the approach towards vertical seismic barrier optimization (which can also be extended to the pile field) is adopted in finite difference form to use for particular soil conditions and design vibration frequency.Several models of soil behaviour are analysed and their validity as well the applicability to approximate real dynamic soil behaviour along with the mechanism of vibration energy dissipation are identified. Based on this analysis, Mohr-Coulomb constitutive model is selected as it has a broad experimental database for various soils and appropriately reflects shear modulus reduction with an increase in the shear strain as well as energy dissipation effects. Afterwards, this model is used in the analysis of Rayleigh wave interaction with the vertical barriers and pile fields accounting for non-linear character of soil deformation at different shear strain level. As a results, the influence of shear strain level on the effectiveness of the considered ways of vibration protections is shown and the appropriate conditions to use these methods are identified within the scope of this research
Monfret, Tony. "Utilisation de la composante verticale du mode fondamental des ondes de rayleigh du manteau : etude de la source sismique et modelisation tri-dimensionnelle de la terre." Paris 7, 1988. http://www.theses.fr/1988PA077123.
Full textHobiger, Manuel. "Polarisation des ondes de surface : caractérisation, inversion et application à l'étude de l'aléa sismique." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00577887.
Full textSoltani, Fethi. "Caractérisation de la pâte de ciment par des méthodes ultrasonores." Phd thesis, Ecole Centrale de Lille, 2010. http://tel.archives-ouvertes.fr/tel-00685879.
Full textFaëse, Frédéric. "Génération d'ondes acoustiques de surface par différentes sources lasers : applications à la caractérisation sans contact de défauts." Thesis, Valenciennes, 2013. http://www.theses.fr/2013VALE0039/document.
Full textIndustries like aeronautics or iron and steel industry are more and more interested in laser ultrasonics, which is a cutting-edge technique used in non-destructive testing and evaluation. The main advantages of this acoustic wave generation and detection method are its noncontact feature and its ability to characterize high temperature and/or geometrically complex materials for which conventional methods implementation turns out to be difficult.During this thesis, we dealt with the propagation of surface acoustic waves (SAW) generatedby laser sources and their interaction with different flaws. As analytical models describing theinteraction between SAW and flaws are limited to a few special cases, the theoretical study was preferentially led thanks to the finite element method (FEM) that gave the different waves displacement fields. Experimental results first confirmed analytical models and FEM results suitability. Then, they consisted in studying the interaction between SAW and flaws for different flaw shapes and different thermoelastic sources.FEM results combined with experimental results especially led to an original characterizationmethod based on mode conversion giving both the flaw position and depth thanks to a singleA-scan. Unusual thermoelastic sources have also been implemented and their potentialities in non destructive testing and evaluation applications have been highlighted