This thesis examines the use of nonlinear ultrasound to evaluate sensitization, a precursor to stress corrosion cracking in austenitic stainless steel. Ultrasonic Rayleigh surface waves are generated on a specimen; as these waves pass through sensitized material, second harmonic generation (SHG) increases. In austenitic stainless steel with oven-induced sensitization, this increase is due only to the formation of chromium carbide precipitates, key products of the sensitization process. Weld-induced sensitization specimens demonstrate additional increases in SHG, likely caused by increased residual stress and dislocation density as a result of uneven heating. Experimental data are used to calculate the acoustic nonlinearity parameter, which provides a single value directly related to the quantity of micro- and nano-scale damage present within any given sample. Using this procedure, the effects of weld- and oven-induced sensitization are compared. Results demonstrate the feasibility of using nonlinear Rayleigh waves to detect and monitor stress corrosion susceptibility of welded material.

The goal of wind-waves research is to predict the waves field and its effect on the environment. That environment could be natural or imposed by human endeavour. The mechanism of wind generated waves is described in the present work as a wind-bulk flow interaction rather than as a mechanical process which only transfers the wind energy to the wave. In the light of this description, the generation and growth of surface waves are functions of the physical properties of the interface, density of the bulk flow perturbations and wind shear stress. While the present models for the prediction of surface growth and evolution show some consistence - in some cases - with observations that were conducted in laboratories and in real fields, the work presented in this thesis justifies and explains the inconsistency or contradictions in other cases between the observations and the predictions. Also, physical interpretations for observations, for example wave growth with fetch, are suggested in the present work. To illustrate the physical mechanism responsible for wave generation and growth under the effect of wind action, two approaches are used. The first involves studying the effect of the physical properties of the water surface on atmospheric input into the bulk and thus the effect on the formation and growth of capillary waves. The second involves studying the correlation between the wave formation and growth and the density of the bulk perturbations. Wide ranges of previous data are used to analyse the effect of the physical properties of the water surface on wave generation and growth mechanism for the first approach. Also, a group of experiments using the PIV system (Particle Image Velocimetry) were conducted to study the correlation between the wind speed, bulk flow evolution and wind-waves‟ generation and growth for the second approach. The main physical parameters which are responsible for the generation and growth of capillary waves are determined. The Ohnesorge number is modified to predict the generation and growth of surface waves. In the second part, additional physical parameters of the bulk flow are introduced to illustrate the correlation between the wind generated waves and bulk flow evolution. A new parameter is used to scale the transition of the bulk flow from laminar flow to turbulent flow or the transition of the water surface from an undisturbed surface to a fully disturbed surface. The history of wind-wave research is relatively short. Although there were basic developments in the 18th century, a concentrated effort really began as a result of the military imperative of the Second World War. These developments were however, largely empirical. A theoretical frame work began to develop with the studies of wind-wave generation in the last century. The present work is conducted to fill some gaps in wind generated surface waves research and to introduce new approaches to simplify understanding wind-waves field and its effect on the environment.

In this thesis, nondestructive surface wave measurements are presented for characterization of dynamic modulus and layer thickness on different pavements and cement concrete slabs. Air-coupled microphones enable rapid data acquisition without physical contact with the pavement surface. Quality control of asphalt concrete pavements is crucial to verify the specified properties and to prevent premature failure. Testing today is primarily based on destructive testing and the evaluation of core samples to verify the degree of compaction through determination of density and air void content. However, mechanical properties are generally not evaluated since conventional testing is time-consuming, expensive, and complicated to perform. Recent developments demonstrate the ability to accurately determine the complex modulus as a function of loading time (frequency) and temperature using seismic laboratory testing. Therefore, there is an increasing interest for faster, continuous field data evaluation methods that can be linked to the results obtained in the laboratory, for future quality control of pavements based on mechanical properties. Surface wave data acquisition using accelerometers has successfully been used to determine dynamic modulus and thickness of the top asphalt concrete layer in the field. However, accelerometers require a new setup for each individual measurement and are therefore slow when testing is performed in multiple positions. Non-contact sensors, such as air-coupled microphones, are in this thesis established to enable faster surface wave testing performed on-the-fly. For this project, a new data acquisition system is designed and built to enable rapid surface wave measurements while rolling a data acquisition trolley. A series of 48 air-coupled micro-electro-mechanical sensor (MEMS) microphones are mounted on a straight array to realize instant collection of multichannel data records from a single impact. The data acquisition and evaluation is shown to provide robust, high resolution results comparable to conventional accelerometer measurements. The importance of a perfect alignment between the tested structure’s surface and the microphone array is investigated by numerical analyses. Evaluated multichannel measurements collected in the field are compared to resonance testing on core specimens extracted from the same positions, indicating small differences. Rolling surface wave measurements obtained in the field at different temperatures also demonstrate the strong temperature dependency of asphalt concrete. A new innovative method is also presented to determine the thickness of plate like structures. The Impact Echo (IE) method, commonly applied to determine thickness of cement concrete slabs using an accelerometer, is not ideal when air-coupled microphones are employed due to low signal-to-noise ratio. Instead, it is established how non-contact receivers are able to identify the frequency of propagating waves with counter-directed phase velocity and group velocity, directly linked to the IE thickness resonance frequency. The presented non-contact surface wave testing indicates good potential for future rolling quality control of asphalt concrete pavements. / <p>QC 20170209</p>

Au moyen d'une expérience d'excitation paramétrique d'onde de surface, nous mettons en évidence l'existence de nouveaux types d'ondes solitaires et stationnaires à la surface de l'eau. Ces ondes de grande amplitude sont très non-linéaires et l'étude théorique réalisée ne permet pas de rendre compte de la forme des vagues mais permet de comprendre l'origine du phénomène d'hystérésis observé qui est nécessaire à la compréhension des phénomènes observés. En effet, l'existence de ces ondes (dans notre configuration expérimentale) est conditionnée par la présence d'un domaine de bistabilité dans le plan amplitude d'excitation - amplitude des vagues au coeur duquel nous avons montré qu'il était possible d'avoir coexistence de deux solutions, une d'amplitude nulle et une d'amplitude non nulle. Ces expériences en géométrie Hele-Shaw ont aussi permis de mettre en évidence des ondes enveloppes qui ne sont encore décrit par aucun modèle existant. Il s'agit à notre connaissance de la première onde enveloppe stationnaire observé à la surface de l'eau. Nous mettons aussi en évidence des ondes de gravité de très grande amplitude, qui sont formées alternativement d'étoiles et de polygones. Nous montrons que la symétrie du motif (nombre de branche de l'étoile) est indépendante de la taille et de la forme du récipient vibré. Nous montrons qu'un mécanisme de couplage non-linéaire résonant à trois ondes peut expliquer cette géométrie, bien que cette possibilité fut rejetée pour des ondes purement gravitaire. / By means of the parametric excitation of water waves in a Hele-Shaw cell, we report the existence of two new types of highly localized, standing surface waves of large amplitude. They are respectively of odd and even symmetries. Both solitary waves oscillate subharmonically with the forcing frequency. They are highly nonlinear, and dier strongly from the other types of localized patterns. Moreover, to our knowledge, such a solitary waves of odd symmetry has never been reported hitherto. We report a new type of standing gravity waves of large amplitude, having alternatively the shape of a star and of a polygon. This wave is observed by means of a laboratory experiment by vibrating vertically a tank. The symmetry of the star (i.e. the number of branches) is independent of the container form and size, and can be changed according to the amplitude and frequency of the vibration. We show that this wave geometry results from nonlinear resonant couplings between three waves, although this possibility has been denied for pure gravity waves up to now.

This thesis investigates inversion techniques used to determine the geoacoustic properties of a shallow-water waveguide. The data used were obtained in the Shallow Water '06 Modal Mapping Experiment in which four buoys drifted over a system of subbottom channels. The method used was perturbative inversion using modal eigenvalues as input parameters, which were found using an autoregressive spectral estimator. This work investigates the differences between a "channel" region and a "no channel" region based on an inferred stratigraphic model. Inversions were performed on data from a single buoy both at individual frequencies and multiple frequencies simultaneously. Since the use of multiple frequencies and a certain set of constraints proved to be an effective method of inversion, the method was applied to data from the other three buoys as well. It is shown that the "channel" and "no channel" regions have significantly different sound speed profiles. / by Rebecca Weeks. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Sound propagation in a waveguide is greatly dependent on the acoustic properties of the boundaries. The effect of these properties can be described by a bottom reflection coefficient RB, and surface reflection coefficient RS. Two methods for estimating reflection coefficients are used in this research. The first, the ratio method, is based on the variations of the Green's function with depth utilizing the ratio of the wavenumber spectra at two depths. The second, the pole method, is based on the wavenumbers of the modal peaks in the spectrum at a particular depth. A method to invert for sound speed and density is also examined. Estimates of RB and RS based on synthetic data by the ratio method were very close to their predicted values, especially for higher frequencies and longer apertures. The pole method returned less precise estimates though with longer apertures, the estimates were better. Using experimental data, results of the pole method as well a geoacoustic inversion technique based on them were mixed. The ratio method was used to estimate RS based on the actual data and returned results close to the predicted phase of p. / by Alexander Conrad. / Vita. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

La tectonique actuelle et récente (~40 Ma) de la région Egée-Anatolie en fait un laboratoire naturel privilégié pour l'étude de la déformation continentale. L'analyse de la structure détaillée et de la déformation du manteau de cette zone de collision continentale immature constitue une étape indispensable pour comprendre les relations entre la cinématique de surface et la dynamique du manteau. La structure du manteau supérieur a été étudiée à l'échelle de la région en réalisant un modèle 3-D de la vitesse des ondes S par tomographie télésismique en ondes de surface. Les résolutions latérale (~100-200 km) et verticale (~50 km) des images obtenues, grâce à l'utilisation d'un réseau sismologique large bande composé de ~150 stations (permanentes et temporaires (expérience SIMBAAD), apporte de nouvelles contraintes sur la structure du manteau de la Grèce continentale à l'Anatolie centrale. Cette tomographie révèle notamment des corrélations verticales claires entre les géométries des déchirures affectant le slab Hellénique et celles des zones de cisaillement trans-tensives qui accommodent le mouvement rapide du bloc Egéen vers le SW. Le slab Chypriote est clairement imagé dans le modèle 3-D comme plissé et déchiré en plusieurs segments sous l'Anatolie. L'analyse de l'anisotropie azimutale par méthode de réseau sur les ondes de Rayleigh a permis de proposer l'existence de deux couches anisotropes dans le manteau supérieur. L'étude de variations latérales de l'anisotropie sous la région suggère que la déformation des slabs et la cinématique de surface sont contrôlées par des flux mantelliques toroïdaux de différentes échelles. / The last ~40 M.y. tectonics of the Aegean-Anatolia region has shaped a natural laboratory ideal to study the continental deformation processes. The detailed analysis of the mantle structure and deformation of this non-mature continental collision zone constitutes an essential step to investigate the contribution of mantle dynamics to surface kinematics. The upper mantle structure is investigated over the entire region through a new 3-D S-wave velocity model from surface-wave tomography. The model reveals remarkable vertical correlations between geometries of the Hellenic slab tears and geometries of shear zones which accommodate the rapid SW movement of the Aegean bloc. The Cyprus slab is clearly identified in the 3-D model as fold and torn in tree segments beneath Anatolia. The observed azimuthal anisotropy from Rayleigh-wave array analysis suggests the existence of two anisotropic layers in the upper mantle. The lateral variations of anisotropy beneath the region are interpreted as the indication of toroidal mantle flows at different scales governing the slabs deformation and the surface kinematics.

To determine the effect of body shape on the response of underwater vehicles to surface waves in shallow water, the wave radiation hydrodynamic forces are evaluated for a family of (i) prolate spheroidal hull forms and (ii) cylindrical bodies with hemispherical nose and conical tail sections by systematically varying the geometric parameters but keeping displacement constant. The added-mass and wave damping coefficients are determined using a frequency-domain, simple-source based boundary integral method. Results are obtained for a range of wave frequencies and depths of vehicle submergence all for a fixed water depth of 10 m. With the wave exciting force and moment determined using the Froude-Krylov theory, the response transfer functions for heave and pitch are then determined. The heave and pitch response spectra in actual littoral seas are then determined with the sea state modeled using TMA spectral relations. Results show that vehicle slenderness is a key factor affecting the hydrodynamic coefficients and response. The results show two characteristics that increase the radiation hydrodynamic forces corresponding to heave and pitch motions: namely, vehicle length and further-away from mid-vehicle location of the body shoulder. The opposite is true for the oscillatory surge motion. By utilizing these observed characteristics, one can design the lines for maximum radiation forces and consequently minimum hull response for the critical modes of rigid-body motion in given waters and vehicle missions. In the studies carried out in the thesis, a hull with a long parallel middle body with hemispherical nose and conical tail sections has better heave and pitch response characteristics compared prolate spheroid geometry of same volume. The methodology developed herein, which is computationally efficient, can be used to determine optimal hull geometry for minimal passive vehicle response in a given sea. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

O método da análise multicanal de ondas superficiais foi empregado em um estudo de caso no sítio controlado do Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo - IAG-USP, localizado no campus Butantã, São Paulo, em terrenos da bacia sedimentar de São Paulo. O estudo visou à investigação geológica rasa, ou seja, ao mapeamento dos estratos sedimentares presentes e do contato sedimentos-embasamento. Além disso, procurou-se, através de testes de diversos parâmetros de aquisição, chegar-se a uma rotina para a aquisição e tratamento dos dados provenientes de fontes ativas (marreta e queda de peso) e passivas (tráfego de veículos) que possa ser indicada para ensaios em outras áreas da cidade de São Paulo que apresentem condições semelhantes às da área estudada. Na aquisição com fontes ativas foram registrados dados com diversos offsets mínimos e na passiva foi aplicada a técnica Passive Roadside com o arranjo de geofones disposto próximo e paralelamente à via de tráfego. Foram realizadas as etapas de pré-processamento dos dados, geração das imagens de dispersão, extração das curvas de dispersão e inversão. A combinação de imagens geradas a partir de dados adquiridos com diferentes fontes resultou numa imagem com melhor razão sinal-ruído, e consequentemente na produção de melhores curvas que foram invertidas para a geração dos perfis 1D das velocidades da onda S. De modo geral, os perfis de velocidades obtidos a partir dos dados obtidos com o emprego de uma marreta para geração da onda mapearam as interfaces geológicas mais superficiais, já os perfis resultantes dos dados adquiridos com o uso de uma fonte tipo queda de peso alcançaram profundidades maiores, por vezes amostrando o embasamento. No caso das fontes passivas, as principais interfaces de contato foram imageadas, conseguindo-se com sucesso o mapeamento do embasamento, que na área está a mais de 50 metros de profundidade. Correlações com o perfil litológico e de dados de ensaios SPT de um furo de sondagem localizado no centro do arranjo revelaram que as diferenças na determinação da profundidade das interfaces foram menores do que 10%. Desta forma, o método mostrou ser uma ferramenta prática e eficiente nas aplicações geotécnicas, principalmente em ix áreas urbanas onde o ruído é elevado, o que muitas vezes inviabiliza o uso da investigação sísmica convencional (refração ou reflexão). / The multichannel analysis of surface waves (MASW) method was employed in a case study on the controlled site in the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG), University of São Paulo (USP), located on the campus Butantã, São Paulo, in the grounds of the sedimentary basin São Paulo. The study aimed to shallow geological investigation, in other words, mapping of sedimentary strata present and the sediment-basement contact. In addition, It is sought to, by testing with different acquisition parameters, to get a routine for the acquisition and processing of data from active sources (sledgehammer and drop weight) and passive (vehicle traffic) that can be suitable for testing in other areas of the city of São Paulo who have similar conditions of the study area. In the acquisition with active sources were registered data with many different offsets and passive acquisition has been applied to the Passive Roadside MASW technique with the conventional linear receiver array disposed near and parallel to the traffic lane. Were performed, pre-processing of the data, generation of images of dispersion, extraction of dispersion curves and inversion. The combination of images generated based on data acquired from various sources resulted in image with improved signal to noise ratio and consequently in the production of finest curves that have been inverted to generate the 1D shear-wave velocities profiles. In general, the velocity profiles obtained from the data were acquired with the use of a sledgehammer to the wave generation mapped shallowest geological interfaces, but the resulting profiles of the acquired data using a font type \"drop weight\" reached greater depths, sometimes sampling the basement. In the case of passive sources, the main contact interfaces were imaged, achieving successful mapping of the basement, which in this area is over 50 meters deep. Correlations with the lithological profile and SPT data from a borehole located in the center of the array revealed that the differences in the depth determination of the interfaces was less than 10%. Thus, the method showed to be an efficient and practical tool in geotechnical applications, especially in urban areas where the noise is high, which often prevents the use of conventional seismic survey (reflection or refraction).

We formulate a model for acoustic excitations in a magnetorheological fluid. Constitutive equations are derived for Navier-Stokes flow coupled with Maxwell's Equations. The viscosity of the fluid is modified to reflect the dependence of waves propagating within the fluid itself and in the case where they propagate along the network of particles.