Although several studies have proven the accuracy of using a non-contact, air-coupled receiver in nonlinear ultrasonic (NLU) Rayleigh wave measurements, inconsistent results have been observed when working with narrow specimens. The objectives of this research are first, to develop a 3D numerical finite element (FE) model which predicts nonlinear ultrasonic measurements and second, to apply the validated model on the narrow waveguide to determine causes of the previously observed experimental issues. The commercial FE-solver ABAQUS is used to perform these simulations. Constitutive law and excitation source properties are adjusted to match experiments conducted, considering inherent effects of the non-contact detection, such as frequency dependent pressure wave attenuation and signal averaging. Comparison of “infinite” and narrow width simulations outlines various influences which impair the nonlinear Rayleigh wave measurements. When the wave expansion is restricted, amplitudes of the fundamental and second harmonic components decrease more significantly and the Rayleigh wavefronts show an oscillating interaction with the boundary. Because of the air-coupled receiver’s finite width, it is sensitive to these edge effects which alter the observed signal. Thus, the narrow specimen adversely affects key factors needed for consistent measurement of material nonlinearity with an air-coupled, non-contact receiver.

Le thème central de cette thèse est l'étude des résonances pour le problème intérieur en élastodynamique (géométries elliptique et sphéroïdale), et pour le problème de diffusion en acoustique (géométrie elliptique). On s'intéresse en particulier à la levée de dégénérescence des résonances liée à la brisure de symétrie de l'objet lors de la transition du disque circulaire vers le disque elliptique (2D), et de la sphère vers le sphéroïde (3D). Ce phénomène est étudié et interprété d'un point de vue théorique en prenant en compte les symétries de l'objet à l'aide de la théorie des groupes. Cette approche est complétée par une modélisation numérique et une partie expérimentale. En 2D, nous étudions le problème intérieur pour un disque elliptique élastique (étude des modes résonants) et le problème de la diffusion acoustique par des cylindres elliptiques élastiques. Ils sont traités à partir du formalisme modal combiné à la théorie des groupes dans le contexte vectoriel de l'élastodynamique. La levée de dégénérescence est observée théoriquement mais aussi expérimentalement en diffusion. La méthode simplifie considérablement le traitement numérique des problèmes étudiés, fournit une classification des résonances selon les 4 représentations irréductibles du groupe de symétrie C2v (associé à la géométrie elliptique) et donne une interprétation physique de la levée de dégénérescence en termes de brisure de symétrie. Une partie expérimentale en spectroscopie ultrasonore vient compléter l'étude théorique du problème de diffusion. Une série d'expériences en cuve est menée dans le cas de cylindres elliptiques de différentes excentricités en aluminium immergés dans l'eau, dans la bande de fréquence 0 ≤ kr ≤ 50, où kr est le nombre d'onde réduit dans le fluide. Les résultats expérimentaux présentent un très bon accord avec les résultats théoriques, la levée de dégénérescence est observée expérimentalement sur des fonctions de forme et mise en évidence sur des diagrammes angulaires. Le problème intérieur en 3D est traité expérimentalement à partir de la génération et la détection optiques d'ondes élastiques. Une série d'expérimentations sur des objets tridimensionnels (sphère, sphéroïdes oblates et prolates de différentes excentricités) en aluminium est réalisée. Ils sont mis en vibration par impacts laser et les mesures de vitesse et de fréquence s'effectuent par vibrométrie laser. On réalise ainsi une comparaison qualitative entre la théorie 2D et l'expérience 3D. Les mesures sont menées à la fois dans les domaines temporel et fréquentiel pour mettre en évidence la levée de dégénérescence d'une part, et l'onde de Rayleigh qui se propage sur la surface des objets d'autre part. Nous identifions deux trajets pour cette onde en géométrie sphéroïdale, l'un circulaire et l'autre elliptique.Enfin, dans le cadre des problèmes intérieurs 2D et 3D, on donne une interprétation en termes de rayons à travers la dualité entre le spectre des résonances et le spectre des longueurs des orbites périodiques (OPs), avec la mise en évidence du phénomène de conversion de mode et l'identification de l'onde de Rayleigh. Un phénomène, nouveau à notre connaissance, vient s'ajouter au phénomène de bifurcation de certaines orbites. Au cours de la déformation vers le disque elliptique, les orbites avec conversion de mode du disque circulaire se séparent en deux orbites dont les longueurs sont associées aux trajets minimal et maximal qu'elles parcourent. Cette observation s'interprète comme une conséquence du théorème de Fermat. Dans le cas du sphéroïde, on retrouve les orbites du disque circulaire dans le plan équatorial et celles du disque elliptique dans le plan méridien. Nous mettons également en évidence les pics associés aux deux trajets parcourus par l'onde de Rayleigh sur le spectre des OPs. / Resonances for the interior problem in elastodynamics and the acoustic scattering problem are considered in elliptical and spheroidal geometries. Interest is focused on the splitting up of resonances which occurs when the symmetry is broken in the transition from the circular disc to the elliptical one (2D), and from the sphere to the spheroid (3D). From the theoretical point of view, this physical phenomenon is studied and interpreted taking into account the symmetries of the object with the help of group theory. This approach is completed by a numerical modeling and an experimental part. As far as the two dimensional problems are concerned, the interior problem for an elliptical elastic disc (study of resonant modes) and the acoustic scattering problem for infinite elliptical elastic cylinders are studied combining modal formalism and group theory in the vectorial context of elastodynamics. The splitting up of resonances due to the circular symmetry breaking is not only theoretically observed but also experimentally for the scattering problem. The method significantly simplifies the numerical treatment of the problems studied, provides a full classification of resonances over the 4 irreducible representations of the symmetry group C2v (associated with the elliptical geometry) and gives a physical interpretation of the splitting up in terms of symmetry breaking of the symmetry group O(2) (invariance under rotation). An experimental part based on ultrasonic spectroscopy complements the theoretical study of the scattering problem. A series of tank experiments is carried out in the case of aluminum elliptical cylinders immersed in water, in the frequency range 0 ≤ kr ≤ 50, where kr is the reduced wave number in the fluid. The experimental results provide a very good agreement with the theoretical ones, the splitting up is observed on experimental form functions and the split resonant modes are identified on angular diagrams. The interior problem in 3D is studied by means of an experimental approach based on the optical generation and detection of elastic waves. A series of experiments is performed on three-dimensional objects in aluminium. These objects (sphere, prolate and oblate spheroids of various eccentricity) are excited by laser impacts, and the velocity and frequency measurements are carried out by laser vibrometry. Theory and experiments are qualitatively compared. The measurements are performed in both the frequency and time domains to highlight the splitting up of resonances on one hand, and the Rayleigh wave propagating on the surface of the objects on the other hand. We emphasize two paths for this surface wave in spheroidal geometry: a circular one in the equatorial plane and an elliptical one in the meridian plane. Finally, in the context of the interior problems in 2D and 3D, a physical interpretation of resonances in terms of geometrical paths is provided. Mode conversion is highlighted and the Rayleigh wave is identified on the periodic orbits lengths spectrum.In addition to the bifurcations of some periodic orbits, a phenomenon, new to our knowledge, appears. The orbits with mode conversion of the circular disc split in two orbits when the transition to the elliptic disc occurs. The lengths of these orbits are associated with the minimal and maximal travel paths. This observation is interpreted from Fermat's theorem.For the spheroid, orbits of the circular disc and those of the elliptical disc are recovered in the equatorial and meridian planes respectively. We also emphasize the peaks associated with the travel paths of Rayleigh wave in spheroidal geometry appearing on the periodic orbits spectrum.

Geophysical research has long been interdisciplinary, with many phenomena on the Earth's surface involving multiple, linked processes that are best understood using a combination of techniques. This is particularly true in the case of grain flows on sand dunes, in which the sedimentary stratification with which geologists are concerned arises from the granular processes investigated by physicists and engineers, and the water permeation that interests hydrologists and soil scientists determines the seismic velocities of concern to exploration geophysicists. In this dissertation, I describe four projects conducted for the degree of Doctor of Philosophy, using a combination of laboratory experimentation, fieldwork, numerical simulation, and mathematical modelling to link avalanching on dunes to its effects on stratification, on the permeation of water, and on seismic surveys. Firstly, I describe experiments on erodible, unbounded, grain piles in a channel, slowly supplied with additional grains, and I demonstrate that the behaviour of the consequent, discrete avalanches alternates between two regimes, typified by their size statistics. Reconciling the `self-organised criticality' that several authors have predicted for such a system with the hysteretic behaviour that others have observed, the system exhibits quasi-periodic, system-spanning avalanches in one regime, while in the other avalanches pass at irregular intervals and have a power-law size distribution. Secondly, I link this power-law size distribution to the strata emplaced by avalanches on bounded grain piles. A low inflow rate of grains into an experimental channel develops a pile, composed of strata in which blue-dyed, coarser grains overlie finer grains. Associating stopped avalanche fronts with the `trapped kinks' described by previous authors, I show that, in sufficiently large grain piles, mean stratum width increases linearly with distance downslope. This implies the possibility of interpreting paleodune height from the strata of aeolian sandstones, and makes predictions for the structure of avalanche-associated strata within active dunes. Thirdly, I discuss investigations of these strata within active, Qatari barchan dunes, using dye-infiltration to image strata in the field and extracting samples across individual strata with sub-centimetre resolution. Downslope increases in mean stratum width are evident, while measurements of particle size distributions demonstrate preferential permeation of water along substrata composed of finer particles, explaining the strata-associated, localised regions of high water content discovered by other work on the same dunes. Finally, I consider the effect of these within-dune variations in water content on seismic surveys for oil and gas. Having used high performance computing to simulate elastic wave propagation in the vicinity of an isolated, barchan sand dune, I demonstrate that such a dune acts as a resonator, absorbing energy from Rayleigh waves and reemitting it over an extensive period of time. I derive and validate a mathematical framework that uses bulk properties of the dune to predict quantitative properties of the emitted waves, and I demonstrate the importance of internal variations in seismic velocity, resulting from variations in water content.

Sur l’île de Majorque (Espagne), l’exploitation en continue de la nappe aquifère a favoriséla formation d’un biseau salé et l’épuisement de la ressource en eau potable. En 2002, un projet nommé ALIANCE, financé par l’Union européenne, a été lancé pour permettre une meilleure caractérisation des réservoirs. L’objectif est de concevoir un plan de gestion durable des ressources en eau dans les zones côtières aquifères sujets aux problèmes d’intrusion d’eau salée. Dans cet optique, un site expérimental près de la ville de Campos (Majorque) a été créé, avec la mise en place de plusieurs puits au sein d’un milieu karstique carbonaté. Des études pétrophysiques sur des échantillons ont été réalisées ainsi que différentes prospections géophysiques dans la zone saturée (tomographie puits à puits). Ce type d’études est utile pour déterminer certaines propriétés réservoirs telles que la porosité, mais sont limitées à la zone saturée au voisinage des puits. Ainsi, une étude sismique 3D haute résolution a été réalisée pour localiser les principaux réflecteurs, leurs répartitions sur la zone et imager les hétérogénéités du réservoir dans la zone non saturée. L’acquisition et le traitement de données sismiques lors de prospection de subsurface est une tâche difficile en raison de plusieurs facteurs, notamment logistique et technique. Cependant, cette acquisition 3D haute résolution a été optimisée pour imager une structure peu profonde, à savoir une centaine de mètres. Différentes stratégies de traitement de données ont été appliquées pour éliminer de manière efficace le bruit sur les données, et une technique de calcul de correction statique, basée sur l’inversion des temps de premières arrivées, a été mise au point. Différents attributs sismiques ont été extraits et utilisés pour la caratérisation du réservoir. La propagation des ondes sismiques est limitée par la nature des roches carbonatées et la création d’ondes de Rayleigh. Un obstacle majeur rencontré lors du traitement des données sismiques a été la présence d’ondes de Rayleigh de fortes amplitudes, d’une part due à l’utilisation d’une source en surface et d’autre part en raison des hétérogénéités de petite tailles. Un "mute" de ces ondes de surface a été réalisé avant d’imager la structure profonde. De multiples problèmes d’interférences sont également dus aux nombreuses hétérogénéités, à l’atténuation rapide du contenu hautes-fréquences des signaux et au contraste d’impédance avec les couches sous-jacentes. L’interprétation finale nous amène à observer que le réflecteur principal est très irrégulier sur une zone d’étude de petite taille à l’échelle d’un réservoir. L’analyse de différents attributs sismiques révèle clairement des structures et hétérogénéités typiques des systèmes karstiques. / Continuous water extraction and intrusion of salt water in the coastal aquifer of the islandof Mallorca (Spain) is depleting the fresh water aquifers. In 2002 a project named ALIANCE,funded by European Union, was initiated for better reservoir characterization and to devisethe sustainable management plan of the water resources in coastal aquifers suffering from salt water intrusion. For this purpose an experimental site near the Campos town on the island of Mallorca (Spain) was developed. Several wells on the site were drilled and cored. Extensive studies are carried out to characterize the reservoir by studying the well cores. Different geophysical tomographic studies are also carried out for these drilled wells in the saturated zone. Laboratory study of cores, petrophysical studies and several tomographic studies were helpful to construct the reservoir porosity system and other reservoir properties. But these all studies are restricted to saturated zone and in the vicinity of the wells. High resolution 3D seismic survey is carried out on this site to locate the different characteristic reflectors, their spatial presence over the area and reservoir heterogeneity in the unsaturated zone. Seismic data acquisition and processing for the shallow surveys is a difficult task due to number of factors including logistic and technical. Nonetheless high resolution 3D seismic survey is acquired with optimized parameters to image the required zone. Different data processing strategies are applied to get a noise free high resolution image. A technique for static correction calculation based on the delay time inversion is developed.Energy penetration in the subsurface was hampered due to carbonate rock nature and forced generation of Rayleigh waves. The processing of the seismic data was difficult due to overwhelming high amplitude Rayleigh waves that are generated partly due to use of the surface source and partly due to the small scale heterogeneities. Rayleigh wave muting is performed to obtain the meaningful image. Due to heterogeneities, attenuation of high frequency content of the signals and impedance contrast of the underlying layers result in interference. Different seismic attributes are extracted and used for reservoir characterization. From the interpretation of data it is evident that even for this small area the shape of the main reflector varies considerably in the area. Seismic attributes reveal karsts and other structural heterogeneities in the area.

Made available in DSpace on 2014-12-17T14:08:36Z (GMT). No. of bitstreams: 1 NisarRO.pdf: 2584049 bytes, checksum: f18a00826204d450659ba7d3316e358e (MD5) Previous issue date: 2009-05-08 / Among the many types of noise observed in seismic land acquisition there is one produced by surface waves called Ground Roll that is a particular type of Rayleigh wave which characteristics are high amplitude, low frequency and low velocity (generating a cone with high dip). Ground roll contaminates the relevant signals and can mask the relevant information, carried by waves scattered in deeper regions of the geological layers. In this thesis, we will present a method that attenuates the ground roll. The technique consists in to decompose the seismogram in a basis of curvelet functions that are localized in time, in frequency, and also, incorporate an angular orientation. These characteristics allow to construct a curvelet filter that takes in consideration the localization of denoise in scales, times and angles in the seismogram. The method was tested with real data and the results were very good / Dentre os diversos tipos de ru?dos existentes nos dados s?smicos terrestres est? o Ru?do de Rolamento Superficial tamb?m conhecido como ground roll que ? um tipo particular de ondas de Rayleigh com amplitude forte, freq??ncia baixa e velocidade baixa que gera um cone de grande mergulho no sismograma. O ru?do de rolamento superficial contamina os sinais relevantes e pode mascarar a informa??o desejada, trazidas por ondas espalhadas em regi?es mais profundas das camadas geol?gicas. Nesta disserta??o ser? apresentada uma ferramenta que atenua o ru?do de rolamento superficial baseada na transformada curvelet. A t?cnica consiste em decompor o sismograma em uma base de fun??es curvelets as quais s?o localizadas no tempo e na freq??ncia, al?m de incorporarem uma orienta??o angular. Tais caracter?sticas permitem a constru??o de um filtro curvelet que leva em considera??o a localiza??o do ru?do em escalas, limiares de corte dos coeficientes curvelets e dos ?ngulos no sismograma. O m?todo foi testado com dados reais e os resultados obtidos foram muito bons

Un système microfluidique à onde élastique de surface a été développé dans le but de réaliser une réaction d'amplification de brins d'ADN par PCR. Nous avons principalement étudié la température et l'uniformité de l'échauffement des gouttes irradiées par des ondes de type Rayleigh. Ces dernières sont générées à la surface d'un substrat piézoélectrique de Niobate de Lithium (LiNbO3). Nous avons pensé un système consommant le moins d'énergie électrique possible pour atteindre les températures désirées et permettant une meilleure uniformité de la température des gouttes. Pour cela, un dispositif à transducteur enterré a été réalisé sous une couche isolante de silice. Les gouttes sont ainsi directement posées sur le transducteur ce qui limite les pertes et améliore la répartition de la chaleur au sein des gouttes. Nous avons ensuite vérifié que les réactifs de la PCR ne sont pas affectés par les ondes de Rayleigh ce qui laisse présager que la PCR peut être réalisée à l'aide d'un système d'échauffement par ondes de Rayleigh. Par ailleurs, le déplacement de goutte sur ce type de substrat de LiNbO3 est important pour des applications de type laboratoire sur puce. Ce substrat ayant des propriétés hydrophiles, des revêtements ont été développés afin de minimiser la force nécessaire à l'actionnement des gouttes. Dans ces travaux, nous proposons un nouveau type de couche à base de copolymère P(VDF-TrFe) dont la fabrication est simplement réalisée par dissolution et étalement par spin-coating. Nous avons montré que ce type de couche n'affecte que très peu la propagation des ondes de Rayleigh et les propriétés hydrophobes sont équivalentes à d'autres revêtements / In this work, a microfluidic system based on surface acoustic wave has been developed in order to achieve the amplification of DNA strands by temperature cycling (PCR). We studied mainly the temperature and the heat uniformity of microdroplets irradiated by Rayleigh waves. These waves are generated at the surface of a lithium niobate substrate. We propose a system allowing better temperature uniformity within microdroplets with an optimal energy consumption. For this, a device with buried transducer has been developed under an insulating layer (Silice). The droplets are then placed directly on the transducer which limits losses and improves the distribution of heat within the microdroplets. We then verified that the PCR reagents are not affected by the Rayleigh waves which suggests that PCR can be performed using a heating system by Rayleigh waves. Moreover, the move of microdroplets on this kind of LiNbO3 substrate is important for lab on chip applications. This substrate having hydrophilic properties, some coatings have been developed to minimize the required force to actuate the microdroplets. In this work, we developed a new hydrophobic layer based on copolymer P(VDF-TrFe) whose production is simply made by dissolving and spreading by spin-coating. We have shown that this kind of layer is compatible with Rayleigh waves and that the hydrophobic properties are equivalent to other coatings

Submitted Ph.D. thesis is concerning the application and interpretation of seismic surface waves in a broad range of frequencies and scales. Using surface waves as a supplement to the methods dealing with body waves seems to be worth the effort. Surface wave interpretation can be used to obtain new information about the studied medium and simultaneously it can overcome, in some cases, the limitations of other seismic techniques. Moreover, surface waves are usually present on measured records and hence for its usage it is not necessary to modify the standard measuring procedures. One of the results of this thesis is an original algorithm for dispersive waveform calculation. The program works in an arbitrary range of frequencies and scales. The input parameter for the calculation is the dispersion curve. In this point the algorithm differs from all other approaches used so far. Algorithm is based on a summation of frequency components with shifts corresponding to the velocity dispersion and distance. The resulting waveform only contains an individual dispersive wave of the selected mode, thus being particularly suitable for testing of methodologies for dispersive wave analysis. The algorithm was implemented into the program DISECA. Furthermore, a new procedure was designed to calculate the dispersion...

Two surface wave testing methods, namely, (i) the spectral analysis of surface waves (SASW), and (ii) the multi-channel analysis of surface waves (MASW), form non-destructive and non-intrusive techniques for predicting the shear wave velocity profile of different layers of ground and pavement. These field testing tools are based on the dispersive characteristics of Rayleigh waves, that is, different frequency components of the surface wave travel at different velocities in layered media. The SASW and MASW testing procedure basically comprises of three different components: (i) field measurements by employing geophones/accelerometers, (ii) generating dispersion plots, and (iii) predicting the shear wave velocity profile based on an inversion analysis. For generating the field dispersion plot, the complexities involved while doing the phase unwrapping calculations for the SASW technique, while performing the spectral calculations on the basis of two receivers’ data, makes it difficult to automate since it requires frequent manual judgment. In the present thesis, a new method, based on the sliding Fourier transform, has been introduced. The proposed method has been noted to be quite accurate, computationally economical and it generally overcomes the difficulties associated with the unwrapping of the phase difference between the two sensors’ data. In this approach, the unwrapping of the phase can be carried out without any manual intervention. As a result, an automation of the entire computational process to generate the dispersion plot becomes feasible. The method has been thoroughly validated by including a number of examples on the basis of surface wave field tests as well as synthetic test data. While obtaining the dispersion image by using the MASW method, three different transformation techniques, namely, (i) the Park’s wavefield transform, (ii) the frequency (f) -wavenumber ( ) transform and (iii) the time intercept ( -phase slowness (p) transform have been utilized for generating the multimodal dispersion plots. The performance of these three different methods has been assessed by using synthetic as well as field data records obtained from a ground site by means of 48 geophones. Two-dimensional as well as three-dimensional dispersion plots were generated. The Park’s wavefield transformation method has been found to be especially advantageous since it neither requires a very high sampling rate nor an inclusion of the zero padding of the data in a wavenumber (distance) domain. In the case of an irregular dispersive media, a proper analysis of the higher modes existing in the dispersion plots becomes essential for predicting the shear wave velocity profile of ground on the basis of surface wave tests. In such cases, the establishment of the predominant mode becomes quite significant. In the current investigation for Rayleigh wave propagation, the predominant mode has been computed by maximizing the normalized vertical displacements along the free surface. Eigenvectors computed from the thin layer approach (TLM) approach are analyzed to predict the corresponding predominant mode. It is noted that the establishment of the predominant mode becomes quite important where only two to six sensors are employed and the governing (predominant) modal dispersion curve is usually observed rather than several multiple modes which can otherwise be identified by using around 24 to 48 multiple sensors. By using the TLM, it is, however, not possible to account for the exact contribution of the elastic half space in the dynamic stiffness matrix (DSM) approach. A method is suggested to incorporate the exact contribution of the elastic half space in the TLM. The numerical formulation is finally framed as a quadratic eigenvalue problem which can be easily solved by using the subroutine polyeig in MATLAB. The dispersion plots were generated for several chosen different ground profiles. The numerical results were found to match quite well with the data available from literature. In order to address all the three different aspects of SASW and MASW techniques, a series of field tests were performed on five different ground sites. The ground vibrations were induced by means of (i) a 65 kg mass dropped freely from a height of 5 m, and (ii) by using a 20 pound sledge hammer. It was found that by using a 65 kg mass dropped from a height of 5 m, for stiffer sites, ground exploration becomes feasible even up to a depth of 50-80 m whereas for the softer sites the exploration depth is reduced to about 30 m. By using a 20 lb sledge hammer, the exploration depth is restricted to only 8-10 m due to its low impact energy. Overall, it is expected that the work reported in the thesis will furnish useful guidelines for (i) performing the SASW and MASW field tests, (ii) generating dispersion plots/images, and (iii) predicting the shear wave velocity profile of the site based on an inversion analysis.