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1
Swisher, Nora. "Data Analysis of Rayleigh-Taylor Unstable Flows." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/988.
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Rayleigh-Taylor and Richtmyer-Meshkov instabilities (RTI and RMI) occur when afluid interface between fluids of different densities is accelerated against the density gradient. RTI/RMI plays an important role in the dynamics of fluids and plasmas on microscopic scales, such as inertial confinement fusion, through astronomical scales, such as supernova explosions. These problems have been studied for decades, yet it remains a challenge to observe, model, and describe RTI/RMI mathematically. Without the tools used to analyze stable equilibrium, we must find more robust analyses. This work uses robust data analysis techniques to systematically study RT unstable flows. We report a thorough analysis of experimental data in supernova experiments conducted at high powered laser facilities, evaluating what information experiments and simulations may tell us about the fundamentals of RTI and RT mixing in high energy density plasmas by comparing the data with rigorous theoretical approaches. We investigate the statistically unsteadiness of RT mixing by numerically modeling the set of stochastic nonlinear differential equations which govern the rate of change of momentum in a packet of fluid undergoing RT instability. By analyzing the modeled solutions, we measure the influence of fluctuations on measurable quantities, find new characteristic values which may be used as to diagnose the regime of an experiment or simulation, and measure the spectra of fluctuations as they propagate throughout the system. We study the effect of the initial perturbation amplitude on the RMI interfacial dynamics using Single Particle Hydrodynamics simulations. The compound motion of the interface and bulk fluid ow is measured, an empirical model is found to describe data, and we find an upper bound for the amount of energy deposited to the interface. There exists a plethora of data that may still be analyzed systematically, as exemplified in this thesis. Future work may improve the fits of experimental data by exploring well designed parameter spaces, model additional stochastic effects, and measure small scale features of ow quantities in simulations.
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Rao, Chaitanya Kumar Hassibi Babak Hassibi Babak. "Asymptotic analysis of wireless systems with Rayleigh fading /." Diss., Pasadena, Calif. : Caltech, 2007. http://resolver.caltech.edu/CaltechETD:etd-04252007-122857.
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Bashir, 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.
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This thesis investigates the problems of applying Statistical Energy Analysis (SEA) tomodels that include solid volumes. Three wave types (Rayleigh waves, Pressure wavesand Shear waves) are important to SEA and the mathematics behind them is explainedhere. The transmission coefficients between the wave types are needed for energytransfer in SEA analysis and different approaches to solving the properties of wavepropagation on a solid volume are discussed. For one of the propagation problems, asolution, found in Momoi [6] is discussed, while the other problem remains unsolveddue to the analytical difficulties involved.
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Mckay, Mark. "Finite element analysis of isotropic and anisotropic loaded ridge waveguide." Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/618.
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Fan, 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.
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Surface defects, such as rolling contact fatigue (RCF) cracking, can be a difficult class of surface defects for existing on-line non-destructive testing techniques to detect and size accurately at high speed. Gauge corner cracking on the running surface of the railway track is a type of RCF defect. There are economic and safety benefits to have an accurate, fast and reliable NDT technique to detect such defects. The EMAT pitch-catch ultrasonic testing technique, using the Rayleigh surface wave developed at the laser ultrasound group, has been shown to be able to detect and size surface defects. The pitch-catch geometry also allows this technique to be used at high speed, for on-line NDT applications.
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Yildirim, Cihan. "Numerical Study Of Rayleigh Benard Thermal Convection Via Solenoidal Bases." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613128/index.pdf.
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Numerical study of transition in the Rayleigh-B'enard problem of thermal convection between rigid plates heated from below under the influence of gravity with and without rotation is presented. The first numerical approach uses spectral element method with Fourier expansion for horizontal extent and Legendre polynomal for vertical extent for the purpose of generating a database for the subsequent analysis by using Karhunen-Lo'
eve (KL) decomposition. KL decompositions is a statistical tool to decompose the dynamics underlying a database representing a physical phenomena to its basic components in the form of an orthogonal KL basis. The KL basis satisfies all the spatial constraints such as the boundary conditions and the solenoidal (divergence-free) character of the underlying flow field as much as carried by the flow database. The optimally representative character of the orthogonal basis is used to investigate the convective flow for different parameters, such as Rayleigh and Prandtl numbers. The second numerical approach uses divergence free basis functions that by construction satisfy the continuity equation and the boundary conditions in an expansion of the velocity flow field. The expansion bases for the thermal field are constructed to satisfy the boundary conditions. Both bases are based on the Legendre polynomials in the vertical direction in order to simplify the Galerkin projection procedure, while Fourier representation is used in the horizontal directions due to the horizontal extent of the computational domain taken as periodic. Dual bases are employed to reduce the governing Boussinesq equations to a dynamical system for the time dependent expansion coefficients. The dual bases are selected so that the pressure term is eliminated in the projection procedure. The resulting dynamical system is used to study the transitional regimes numerically. The main difference between the two approaches is the accuracy with which the solenoidal character of the flow is satisfied. The first approach needs a numerically or experimentally generated database for the generation of the divergence-free KL basis. The degree of the accuracy for the KL basis in satisfying the solenoidal character of the flow is limited to that of the database and in turn to the numerical technique used. This is a major challenge in most numerical simulation techniques for incompressible flow in literature. It is also dependent on the parameter values at which the underlying flow field is generated. However the second approach is parameter independent and it is based on analytically solenoidal basis that produces an almost exactly divergence-free flow field. This level of accuracy is especially important for the transition studies that explores the regions sensitive to parameter and flow perturbations.
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Orozco, M. Catalina (Maria Catalina). "Inversion Method for Spectral Analysis of Surface Waves (SASW)." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5124.
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This research focuses on estimating the shear wave velocity (Vs) profile based on the dispersion curve obtained from SASW field test data (i.e., inversion of SASW data). It is common for the person performing the inversion to assume the prior information required to constrain the problem based on his/her own judgment. Additionally, the Vs profile is usually shown as unique without giving a range of possible solutions. For these reasons, this work focuses on: (i) studying the non-uniqueness of the solution to the inverse problem; (ii) implementing an inversion procedure that presents the estimated model parameters in a way that reflects their uncertainties; and (iii) evaluating tools that help choose the appropriate prior information.
One global and one local search procedures were chosen to accomplish these purposes: a pure Monte Carlo method and the maximum likelihood method, respectively. The pure Monte Carlo method was chosen to study the non-uniqueness by looking at the range of acceptable solutions (i.e., Vs profiles) obtained with as few constraints as possible. The maximum likelihood method was chosen because it is a statistical approach, which enables us to estimate the uncertainties of the resulting model parameters and to apply tools such as the Bayesian criterion to help select the prior information objectively.
The above inversion methods were implemented for synthetic data, which was produced with the same forward algorithm used during inversion. This implies that all uncertainties were caused by the nature of the SASW inversion problem (i.e., there were no uncertainties added by experimental errors in data collection, analysis of the data to create the dispersion curve, layered model to represent a real 3-D soil stratification, or wave propagation theory). At the end of the research, the maximum likelihood method of inversion and the tools for the selection of prior information were successfully used with real experimental data obtained in Memphis, Tennessee.
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Thiele, Sebastian. "Air-coupled detection of Rayleigh surface waves to assess material nonlinearity due to precipitation in alloy steel." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50276.
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Nonlinear ultrasonic waves have demonstrated high sensitivities to various microstructural changes in metal including coherent precipitates; these precipitates introduce a strain field in the lattice structure. The thermal aging of certain alloy steels leads to the formation of coherent precipitates, which pin dislocations and contribute to the generation of a higher harmonics in an initially monochromatic wave.
The objective of this research is to develop a robust technique to perform nonlinear Rayleigh wave measurements in metals using a non-contact receiving transducer. In addition a discussion about the data processing based on the two-dimensional diffraction and attenuation model is provided in order to calculate the relative nonlinearity parameter.
A precipitate hardenable material, 17-4 PH stainless steel, is used to obtain different precipitation stages by thermal treatment and the influence of precipitates on the ultrasonic nonlinearity is assessed.
Conclusions about the microstrucutural changes in the material are drawn based on the nonlinear Rayleigh surface wave measurement and complementary measurements of thermo-electric power, mircohardness and ultrasonic velocity.
The results show that the nonlinearity parameter is sensitive to coherent precipitates in the material and moreover that precipitation characteristics can be characterized based on the obtained experimental data.
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Seet, Siong Leng Henry. "Analysis of noncoherent orthogonal modulation for mobile computing." Thesis, Monterey, California. Naval Postgraduate School, 2010. http://hdl.handle.net/10945/55206.
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Approved for public release; distribution is unlimited.Wireless communication is employed to connect mobile computers in a networked environment for information exchange. In a tactical space, sensors and computers typically need to operate on-the-move while transmitting data over both short and long distances in different terrain and conditions. The wireless communication is thus susceptible to effects of Doppler shift and channel fading. In addition, when security and anti jamming features are required, such as frequency-hopping techniques, then coherent signal detection is difficult and noncoherent modulation is used instead. Our study will focus on the bit error rate (BER) performance analysis of noncoherent orthogonal modulation, specifically M-ary frequency-shift keying (MFSK) and code-shift keying (CSK) modulation, in both additive white Gaussian noise (AWGN) and for a Rayleigh fading channel with Doppler shift. The potential applications include communications between mobile computer-sensor devices, such as a mobile ground control station maintaining a datalink with UAV.
Civilian
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Shao, Xiaofei. "A receiver structure for frequency-flat time-varying rayleigh channels and performance analysis." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121487.
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This thesis proposes a receiver structure for frequency-flat time-varying Rayleigh channels, consisting of two parts: a receiver front-end and Maximum A-Posteriori (MAP) detector. Discretization of the received continuous time signal is an essential stage in the front-end, and for such application this thesis presents a new framework for discrete representation of continuous time signals. A key point of this framework is the representation of the fading autocorrelation function in the form of a finite dimensional separable kernel. The Fast Haar Transform (FHT) algorithm is used in the front-end to reduce complexity. Analysis of our receiver structure for slow-fading channels shows that it is optimal for certain modulation schemes. Computed and Monte-Carlo simulated performance results are presented for three binary modulation schemes over time-varying Rayleigh fading channels. By comparison with literature, it is shown that our receiver can achieve optimal performance for Time-Orthogonal modulation. For Minimum Shift Keying (MSK) modulation, our receiver using four basis functions can lower the error floor by more than one order of magnitude with respect to reported techniques of comparable complexity. Orthogonal Frequency Shift Keying (FSK) modulation can achieve the same performance as Time-Orthogonal for the slow-fading case but performs worse over fast-fading channels, and suffers from an error floor. However, compared to MSK, Orthogonal FSK has a better performance.Dans la présente thèse, nous proposons une structure de récepteur pour des canaux de Rayleigh à variation temporelle et à réponse uniforme en fréquences, comprenant deux parties : un étage d'entrée du récepteur et un détecteur a posteriori maximum (MAP, pour Maximum A-Posteriori). La discrétisation du signal reçu et continu dans le temps représente une étape essentielle de l'étage d'entrée et pour une telle application, nous présentons un nouveau cadre pour la représentation discrète des signaux continus dans le temps. L'un des aspects clés de ce cadre est la représentation de la fonction d'autocorrélation de l'évanouissement sous la forme d'un noyau séparable dimensionnel fini. On utilise l'algorithme de la transformée de Haar rapide (FHT, pour Fast Haar Transform) à l'étage d'entrée dans le but d'atténuer la complexité. Une analyse de notre structure de récepteur pour canaux à évanouissement graduel révèle que cette structure convient de façon optimale à certains schémas de modulation. Les résultats de rendement, simulés par ordinateur et à l'aide de la méthode de Monte-Carlo, sont présentés pour trois schémas de modulation binaire appliqués à des canaux à évanouissement de Rayleigh à variation temporelle. Une comparaison avec la littérature scientifique démontre que notre récepteur peut offrir un rendement optimum dans le cas de la modulation orthogonale temporelle. En ce qui concerne la modulation à déplacement minimum (MSK, pour Minimum Shift Keying), notre récepteur, qui fait appel à quatre fonctions de base, est en mesure d'abaisser le plancher d'erreur d'un ordre de grandeur pour ce qui est des techniques signalées présentant une complexité similaire. La modulation par déplacement de fréquence orthogonale (FSK, pour Frequency Shift Keying) peut offrir le même rendement que la modulation orthogonale temporelle dans le casdes canaux à évanouissement graduel, mais son rendement est médiocre avec des canaux à évanouissement rapide, en plus de subir les répercussions d'un plancher d'erreur. Par contre, comparativement à la modulation à déplacement minimum, la modulation par déplacement de fréquence orthogonale procure un rendement supérieur.
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Campbell, Thomas E. "Simulations of a short Rayleigh length 100 kW FEL and mirror stability analysis." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FCampbell.pdf.
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Cabras, Flaminia. "Forests as a natural seismic metabarrier: analysis of interaction between trees and Rayleigh waves." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15200/.
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The present thesis describes a sensitivity analysis over design parameters carried out through finite element simulations on seismic metamaterials, locally resonant structures able to affect the propagation of waves passing through them. Locally resonant metamaterials represent a particular type of resonant scattering, which is very powerful mean for stopping (bandgaps) and redirecting elastic waves at different length scales.
This work, carried out at the Imperial College London, is inserted as part of the the METAFORET project, a large-scale wave experiment, which aims to demonstrate the effectiveness of
metamaterials in geophysics. In particular, this project proved that a dense forest of tree can behave as a natural seismic metamaterial for Rayleigh surface waves. Thus creating anomalous dispersion curves and bandgap, frequency regions where the wave propagation is forbidden. These regions are associated with compressional and flexural resonances of the trees.
Therefore I studied the same phenomena with time-domain numerical simulations, implemented in MATLAB. In particular, the simulation is performed with the spectral element method, a popular and efficient formulation of the finite element method that provides a numerical solution of partial differential equations. I analyzed the interaction between seismic metamaterials and the Rayleigh waves in one-dimensional and two-dimensional domain, neglecting the horizontal component to maintain the physical and numerical complexity low. This method is really efficient to conduct a sensitivity analysis, in order to identify which parameters influence the behavior of metamaterials and drive benchmarks.
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Ossenfort, William J. Jr. "Megawatt class free electron lasers for naval application-short Rayleigh length and stability analysis." Thesis, Monterey, California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/3494.
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Approved for public release; distribution in unlimited.The free electron laser (FEL) is theoretically capable of scaling up to a MW class laser for naval point defense. At such high power levels, the FEL's optics could be damaged. An FEL operating with a short Rayleigh length reduces intensity at the mirrors; however, the performance of short Rayleigh length FELs is unknown. This thesis presents simulations of Thomas Jefferson Laboratories' proposed 100 kW FEL operating with a short Rayleigh length, and of a proposed 1 MW FEL undergoing shipboard induced mirror vibrations. In the 100 kW FEL, Rayleigh lengths of 0.1L to 0.5L (where L is the undulator length) were simulated. Weak field gain increases as Rayleigh length decreases, indicating that short Rayleigh length FELs will start from spontaneous emissions. Final FEL efficiency also increases as Rayleigh length decreases, with the exception of a spike at the typical Rayleigh length design value of 0.3L. For the 1 MW FEL system, the high operating current acts to stabilize the optical mode against vibrations that result in mirror tilts of 0 to 400 microradians, where final output power was reduced 80%. When used in conjunction with an active mirror alignment system, output power of the 1 MW FEL is unaffected.
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Zhu, Chao. "Performance Analysis of Minimum Selection GSC with Channel Estimation Errors in Rayleigh Fading Channels." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250184723.
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Ossenfort, William J. "Megawatt class free electron lasers for naval application-short Rayleigh length and stability analysis /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FOssenfort.pdf.
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Mazursky, Laurie Ann. "Three-Dimensional Analysis of Geosynthetic Reinforcement Used in Column-Supported Embankments." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/31223.
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A geotechnical composite foundation system that has become increasingly popular over the years is a column-supported, geosynthetic-reinforced embankment. This system consists of strong columns or piles placed in soft clay, a bridging layer of sand or sand and gravel, and one or more layers of geosynthetic reinforcement. It is often used in soft ground situations where there is a need for faster construction and/or where there are adjacent structures that would be affected by settlement caused by the new embankment. The geosynthetic reinforcement is placed in the bridging layer to help transfer the load to the columns and decrease the total and differential settlements. Current methods of analysis for this material are extremely simplified, and do not thoroughly model the behavior of the system. Therefore, a more comprehensive analysis needs to be conducted that will better predict the true effect of the geosynthetic layer or layers.
In this thesis, one geosynthetic layer was considered. Models were developed using two different computer programs: Mathematica and ABAQUS. In Mathematica, the Rayleigh-Ritz method was used to approximate the deflections and tensile forces in the membrane. This method considered the geosynthetic reinforcement as a plate and minimized the total energy of the system. In ABAQUS, a finite element modeling program, the membrane was analyzed as a shell, and results were compared with some results from Mathematica.
A parametric study was completed in Mathematica to determine the effects of different parameters. The parameters varied involved the geogrid properties (Poissonâ s ratio, modulus of elasticity, and thickness), the vertical load, the soil stiffness above the piles, the soil stiffness between the piles, the size of the piles, and the distance between the piles.Master of Science
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Sherar, P. A. "Variational based analysis and modelling using B-splines." Thesis, Cranfield University, 2004. http://hdl.handle.net/1826/125.
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The use of energy methods and variational principles is widespread in many fields of engineering of which structural mechanics and curve and surface design are two prominent examples. In principle many different types of function can be used as possible trial solutions to a given variational problem but where piecewise polynomial behaviour and user controlled cross segment continuity is either required or desirable, B-splines serve as a natural choice. Although there are many examples of the use of B-splines in such situations there is no common thread running through existing formulations that generalises from the one dimensional case through to two and three dimensions.
We develop a unified approach to the representation of the minimisation equations for B-spline based functionals in tensor product form and apply these results to solving specific problems in geometric smoothing and finite element analysis using the Rayleigh-Ritz method. We focus on the development of algorithms for the exact computation of the minimisation matrices generated by finding stationary values of functionals involving integrals of squares and products of derivatives, and then use these to seek new variational based solutions to problems in the above fields. By using tensor notation we are able to generalise the methods and the algorithms from curves through to surfaces and volumes.
The algorithms developed can be applied to other fields where a variational form of the
problem exists and where such tensor product B-spline functions can be specified as potential
solutions.
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Goh, Julian Kok Seng. "Analysis of Pressurized Arch-Shells." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/35576.
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A pressurized arch-shell structural component made of flexible material is considered.
The component is inflated with high internal pressure. The behavior of similar types
of structures, such as a pair of leaning pressurized arches and pressurized arch-supported
membrane shelters, has been investigated in the past. More recently, several types of
pressurized structures have been incorporated as part of the framework for a variety of
structural systems. Particularly, the U.S. Army has been investigating the use of large
lightweight and transportable pressurized arch-shell structures to be used as maintenance
shelters for vehicles, helicopters, and airplanes.
The formulated equations using thin shell theory are applied to a pressurized arch-shell
component. A numerical investigation based on the Rayleigh-Ritz method is utilized to
determine the behavior of arch-shells under various types of loading. The types of loading
include a uniformly distributed vertical load representing snow, a wind load, and a
horizontal side load distributed along the arc length. Deflections, stress resultants, and
moments at various locations are computed for two types of shapes: circular and non-circular
arch-shells.Master of Science
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Langrock, Stefanie. "Measurement of the Rayleigh scattering length and background contributions during early data taking phases at SNO+." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24647.
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SNO+ is a multipurpose neutrino experiment located at SNOLAB. Its key purpose is investigating the neutrinoless double beta decay of 130Te, amongst other physics goals such as solar and reactor neutrino oscillations. The success of the experiment depends on the understanding of the optical properties of the detection materials, as well as a good understanding of potential background contributions. The calibration system used to study the Rayleigh scattering properties of the detector is presented and methods to model the system in Monte Carlo simulations based on commissioning run data are introduced. Furthermore, the analysis of the scattering length in a water-filled detector is described and demonstrated on a fake water-fill data set with an accuracy of the measured scattering length scaling factor of 1:1 %. The evaluation of the systematic uncertainties is presented. The background contributions originating from the 238U and 232Th decay chains during early SNO+ run phases are constrained using 214Bi214Po and 212Bi212Po delayed coincidences. The methods to identify these coincidences are presented and the challenges to apply them to an intermediate partial water-scintillator phase are discussed. It is shown that for the current target background rates the 238U and 232Th chain contents can be determined with an uncertainty of 4:1% and 27:6%.
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Manin, Julien Luc. "ANALYSIS OF MIXING PROCESSES IN LIQUID AND VAPORIZED DIESEL SPRAYS THROUGH LIF AND RAYLEIGH SCATTERING MEASUREMENTS." Doctoral thesis, Universitat Politècnica de València, 2011. http://hdl.handle.net/10251/10189.
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Desde su introducción, los motores de combustión interna alternativos han sido desarrollados con el fin de reducir el consumo y mejorar el rendimiento y facilidad de conducción. Con el tiempo, la contaminación se ha convertido en un factor crítico para los gobiernos y como consecuencia se han introducido regulaciones para reducir las emisiones contaminantes de los motores.
Con el constante progreso tecnológico requerido por las normas contra la contaminación, la inyección directa se ha vuelto indispensable en cuanto a los motores Diesel. La introducción de combustible en la cámara de combustión permite un alto nivel de control sobre la liberación de energía del proceso de combustión. Con las novedosas estrategias de combustión empleadas, el proceso de inyección se ha convertido en el tema principal y el chorro es el factor principal.
El trabajo realizado a lo largo de este estudio para analizar el proceso de mezcla aire-combustible se basa en el desarrollo de técnicas láser de diagnóstico. Inicialmente, la inyección de Diesel se ha estudiado en una atmósfera isoterma para evitar la evaporación del combustible (dodecano) a través del uso de una iluminación estructurada para medir la distribución de la mezcla mediante el control de la dispersión de Mie. La aplicación de la dispersión de Rayleigh en la parte evaporada del chorro inyectado en una cámara a alta temperatura ha permitido la obtención de la distribución de combustible en una situación equivalente a la existente en un motor real.
El análisis y comparación de los distintos parámetros del chorro inyectado en condiciones de baja o alta temperatura da la posibilidad de entender mejor lo que es el proceso de mezcla en los motores Diesel. Por otra parte, según el estado del fluido inyectado, líquido o gaseoso, las condiciones experimentales tendrán diferentes efectos y la mezcla aire-combustible también tendrá un comportamiento distinto.Manin ., JL. (2011). ANALYSIS OF MIXING PROCESSES IN LIQUID AND VAPORIZED DIESEL SPRAYS THROUGH LIF AND RAYLEIGH SCATTERING MEASUREMENTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10189
Palancia
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Said, Nezar Ali. "Performance analysis of multi-carrier code division multiple access system in multipath fading channels." Ohio : Ohio University, 1998. http://www.ohiolink.edu/etd/view.cgi?ohiou1176401917.
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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.
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Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods.
Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented.
Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve.
The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a traditional estimation method and a frequency-wavenumber method utilizing sub-arrays were investigated using displacement data from numerical simulations, focusing on near-field and ambient noise effects. Detailed procedures for the frequency-wavenumber estimation method are developed based on a study of the primary factors affecting attenuation estimates. The two methods are also evaluated using experimental displacement data obtained from surface wave field measurements with three different arrays.
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Conka, Tahir. "Performance analysis of noncoherent differential phase shift keying using Post-Detection Selection Combining over a Rayleigh fading channel." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA346398.
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Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, June 1998.Thesis advisor(s): Tri T. Ha, Ralph D. Hippenstiel. "June 1998." Includes bibliographical references (p. 77). Also available online.
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LI, XIANGTAO. "PERFORMANCE ANALYSIS OF DECORRELATING DETECTORS FOR DUAL-RATE SYNCHRONOUS DS/CDMA SYSTEMS OVER FREQUENCY-SELECTIVE RAYLEIGH FADING CHANNELS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1028644891.
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Wei, Haoran. "Surface-Enhanced Raman Spectroscopy for Environmental Analysis: Optimization and Quantitation." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/93204.
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Fast, sensitive, quantitative, and low-cost analysis of environmental pollutants is highly valuable for environmental monitoring. Due to its single-molecule sensitivity and fingerprint specificity, surface-enhanced Raman spectroscopy (SERS) has been widely employed for heavy metal, organic compound, and pathogen detection. However, SERS quantitation is challenging because 1) analytes do not stay in the strongest enhancing region ("hot spots") and 2) SERS reproducibility is poor. In this dissertation, gold nanoparticle/bacterial cellulose (AuNP/BC) substrates were developed to improve SERS sensitivity by increasing hot spot density within the laser excitation volume. Environmentally relevant organic amines were fixed at "hot spots" by lowering solution pH below the analyte pKa and thus enabling SERS quantitation. In addition, a new SERS internal standard was developed based upon the electromagnetic enhancement mechanism that relates Rayleigh (elastic) and Raman (in-elastic) scattering. Rayleigh scattering arising from the amplified spontaneous emission of the excitation laser was employed as a normalization factor to minimize the inherent SERS signal variation caused by the heterogeneous distribution of "hot spots" across a SERS substrate. This highly novel technique, hot spot-normalized SERS (HSNSERS), was subsequently applied to evaluate the efficiency of SERS substrates, provide in situ monitoring of ligand exchange kinetics on the AuNP surface, and to reveal the relationship between the pKa of aromatic amines and their affinity to citrate-coated AuNPs (cit-AuNPs). Finally, colloidally stable stable pH nanoprobes were synthesized using co-solvent mediated AuNP aggregation and subsequent coating of poly(ethylene) glycol (PEG). These nanoprobes were applied for pH detection in cancer cells and in phosphate buffered aerosol droplets. The latter experiments suggest that stable pH gradients exist in aerosol droplets.PHD
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Bammou, Lahcen. "Instabilité thermoconvective d'un écoulement Poiseuille-Rayleigh-Bénard-Marangoni en canal ouvert à surface libre." Thesis, Pau, 2012. http://www.theses.fr/2012PAUU3030/document.
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Plusieurs études tant numériques qu’expérimentales font état de la présence d’instabilités thermiques dans des films liquides chauffés uniformément par le bas pour des conditions aux limites et d’écoulements particuliers. La présence de ces instabilités modifiera les transferts thermiques associés. Le sujet de ce travail de thèse consiste à étudier numériquement les instabilités thermoconvectives d’un écoulement laminaire tridimensionnel de convection mixte dans un canal horizontal à surface libre. Les variations de la tension de surface avec la température (effet Marangoni ou effet thermocapillaire) sont prises en compte. Bien que d’un intérêt certain pour de nombreuses applications industrielles, cette situation a été très peu étudiée d’un point de vue académique dans la configuration considérée ici. Dans cette de configuration plusieurs types de structures thermoconvectives sont susceptibles d’apparaître. Lorsque les forces induites par les courants de convection naturelle, forcée et thermocapillaire sont du même ordre de grandeur, les premiers résultats montrent un développement des instabilités sous forme de rouleaux convectifs longitudinaux stationnaires semblables à ceux rencontrés pour des écoulements de type Poiseuille-Rayleigh-Bénard. A notre connaissance, c’est la première fois que l’écoulement de convection de type Poiseuille-Rayleigh-Bénard associé aux effets Marangoni est étudié. Le nombre et la distribution spatiale des rouleaux convectifs le long du canal dépendent des conditions de l’écoulement. Nous proposons une étude numérique pour ces conditions particulières d’écoulement pouvant conduire à des instabilités avec une évaluation de leur effet sur les transferts de chaleur. Les équations de Navier-Stokes et de l’énergie sont résolues numériquement par la méthode de volumes finis en prenant en compte les effets thermocapillaires. Les résultats présentés concernent l’influence des paramètres contrôlant l’écoulement (nombres de Reynolds, de Rayleigh, de Biot, de Marangoni et le rapport de forme) sur les motifs de l’écoulement et les échanges thermiques. Dans une seconde partie du travail, complémentaire à la première, une analyse de stabilité linéaire de l’écoulement dans un canal ouvert à surface libre d’extension latérale infinie est réalisée en utilisant la méthode spectrale de type collocation Chebyshev pour résoudre un système aux valeurs propres. Les diagrammes de stabilité déterminant les seuils des paramètres conduisant à l’instabilité thermoconvective ont été obtenus et analysés, ainsi que les structures spatiales associéesSeveral studies both numerical and experimental have reported the presence of thermal instabilities in liquid films uniformly heated from below for specific boundary conditions and flows. The presence of these instabilities modifies the associated heat transfer. The subject of this PhD thesis is to study numerically the instability of three-dimensional laminar mixed convection within a liquid flowing on a horizontal channel heated uniformly from below. The upper surface is free and assumed to be flat. The variations of the surface tension with the temperature (Marangoni effect or thermocapillary effect) are taken into account. Although of great interest for many industrial applications, this problem has received little attention from an academic point of view. In this configuration, several types of thermoconvective structures may appear. When the strength of the buoyancy, thermocapillary effects and forced convective currents are comparable, the results show the development of instabilities in the form of steady longitudinal convective rolls similar to those encountered in the Poiseuille-Rayleigh-Bénard flow. To our knowledge, this is the first time that the Poiseuille-Rayleigh-Bénard flow associated to the Marangoni effects has been investigated. The number and spatial distribution of the convective rolls along the channel depend on the flow conditions. We propose a numerical study on the flow conditions that could lead to thermal instabilities with an evaluation of their effect on the heat transfer. The coupled Navier-Stokes and energy equations are solved numerically by the finite volume method taking into account the thermocapillary effects. The results presented concern the influence of several control parameters (the Reynolds, Rayleigh, Biot and Marangoni numbers and the aspect ratio of the channel) on the flow patterns and heat transfer characteristics. In the second part of this work, complimentary to the first, a linear stability analysis of a horizontal liquid film flowing in an open channel, with infinite lateral extension and uniform heating from below, is carried out. An eigenvalue problem is obtained in the course of this analysis which is solved numerically using the Chebyshev collocation spectral method. The stability diagrams determining the threshold parameters leading to thermoconvective instabilities were obtained and analyzed as well as the associated spatial patterns
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Tahseen, Muhammad Mustafa, MatiUllah Khan, and Farhan Ullah. "Analysis of OSTBC in Cooperative Cognitive Radio Networks using 2-hop DF Relaying Protocol." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-2510.
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To achieve cooperative diversity in cognitive radio network, Decode and Forward (DF) protocol is implemented at Cognitive Radios (CRs) using Orthogonal Space Time Block Coding (OSTBC). The 2-hop communication between source and destination is completed with the help of Cognitive Relays (CRs) using Multiple Input Multiple Output (MIMO) technology within the network. To achieve spatial diversity and good code rate Alamouti 2×2 STBC is used for transmission. CR is using the decoding (Decode and Forward (DF)) strategy and without amplifying ability before forwarding data towards destination provide better performance. The main objective of this thesis is to detect Primary User (PU) spectrum availability or non-availability for the use of Secondary Users (SU). The Alamouti STBC encoded data is broadcasted to wireless Rayleigh faded channel through transmitter having two transmitting antennas. The CRs are preferred to place close with PU to detect transmitted signal and because of having decoding capability CRs decode the collected data using Maximum Likelihood (ML) decoding technique then re-encode the decoded data for further transmission towards receiver. The energy of PU signal received at relays is calculated using energy detector used at cognitive controller having authority to make final decision about presence or absence of PU signal within the spectrum by comparing calculated energy of PU received signal with a predefined value. If the calculated signal energy is less than threshold value it is pretended as the absence of PU and in the other case spectrum is assumed as occupied by PU. Decoding PU signal at relays before forwarding towards destination provide better performance in terms of detection probability and decreasing probability of false alarming as the Signal to Noise (SNR) increases. The proposed cooperative spectrum sensing using DF protocol at cognitive relays with Alamouti STBC is implemented and results are validated by MATLAB simulation.+46 455 38 50 00
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Dietze, Kai. "Analysis of a Two-Branch Maximal Ratio and Selection Diversity System with Unequal Branch Powers and Correlated Inputs for a Rayleigh Fading Channel." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/32412.
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This report, presents an analytical framework for analyzing two-branch diversity systems for a Rayleigh fading channel. In many cases the fading received at both branches (i.e. a two-antenna element system) is correlated because of the proximity of the antenna elements to each other. It is also not uncommon for a diversity system to use antennas with different patterns or polarizations, this usually results in differences in average signal-to-noise ratios at both branches depending on which element is better matched to the signal environment. As will be shown, the performance of a diversity system depends greatly on the envelope correlation, average power imbalance and the combining scheme used on both branches.
An analytical expression for the probability density function of the signal-to-noise ratio at the output of a two-branch maximal ratio and selection diversity system is developed in this report. The two branches are assumed to be Rayleigh fading, correlated, as well as of unequal signal-to-noise ratios. Measurements were made in Rayleigh fading channels and compared to the analytical results. The analytical cumulative distribution functions (derived using probability distributions) were found to be within 1 dB of the measured results (statistics obtained from time combining) for both maximal ratio and selection diversity attesting to the validity of the analytic results. Also developed in this report are the exact analytical average probabilities of symbol error for coherent BPSK and coherent QPSK before and after maximal ratio combining for this environment. The diversity gain for selection, maximal ratio, and equal gain combining for the 10% probability level is presented as a function of power imbalance and correlation between branches for a two-branch Rayleigh diversity systemMaster of Science
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Pertsch, Alexander Thomas. "An intelligent stand-alone ultrasonic device for monitoring local damage growth in civil structures." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31716.
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Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.Committee Chair: Jacobs, Laurence J.; Committee Co-Chair: Wang, Yang; Committee Member: Kim, Jin-Yeon. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Vanpouille, David. "Développement de modèles de turbulence adaptés à la simulation des écoulements de convection naturelle à haut nombre de Rayleigh." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0041/document.
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Un nouveau modèle de turbulence adapté aux écoulements turbulents soumis à laflottabilité a été développé en utilisant la configuration du canal plan vertical différentiellementchauffé comme référence. L’étude des DNS disponibles pour chacun des régimes de convection amontré les défauts des relations constitutives classiques conduisant à la mauvaise représentationdes écoulements de convection naturelle. Ces modèles ne prennent en compte ni le couplage deschamps thermique et dynamique ni l’anisotropie de l’écoulement, tout deux induits par la flottabilité.Une approche algébrique a donc été utilisées. L’hypothèse d’équilibre local a été validéedans une large partie du canal sauf dans la région de paroi et au voisinage d’un gradient devitesse nul, quel que soit le régime de convection. Les modèles homogènes et pariétaux pour lescorrélations de pression ont été étudiés et sélectionnés. Deux modèles EARSM et EAHFMprenant en compte les termes de flottabilité ont été développés. Ces modèles intègrent aussi destraitements spécifiques à la paroi reposant sur la pondération elliptique. Ils sont couplés à unmodèle corrigé pour mieux représenter le pic d’énergie cinétique turbulente prèsde la paroi. Le modèle complet a été confronté aux DNS sur la configuration du canal pourchacun des régimes de convection à travers des tests a priori et des calculs complets montrantdes résultats très encourageants et de meilleures prévisions que les modèles classiquesA new turbulence model dedicated to buoyant flows is developped using the differentiallyheated vertical plane channel flow configuration as test case. For each convection regime,the examination of available DNS databases pointed out the failure of classical modeling topredict buoyant flows. Neither the coupling between thermics and dynamics nor the anisotropy,both due to the buoyancy, are considered by these models. So, algebraic models are used. Theweak equilibrium assumption is validated in a large part of the channel except in the wall regionand close to zero velocity gradient whatever the convection regime. The wall and homogeneousmodels for the pressure terms are investigated and selected. Then, an EARSM and an EAHFMare developped to include the buoyant terms. These models both include wall treatments. Theyare coupled with a model modified to improve the representation of the turbulentkinetic energy maximum close to the wall. The complete model is finally compared to theDNS on the channel flow configuration for all convection regime thanks to a priori tests andcomplete computations, showing encouraging results and better predictions than classical models
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Ghosh, Kaushik. "Downlink W-CDMA performance analysis and receiver implmentation on SC140 Motorola DSP." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969/169.
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Mehmood, Faisal, and Muneeb Ejaz. "Performance Analysis of 3-hop using DAF and DF over 2-hop Relaying Protocols." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-4229.
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In wireless Communication, the need of radio spectrum increases nowadays. But in the system we are losing approximately 82-86% of spectrum most of the time due to the absence of Primary User (PU). To overcome this issue Cognitive Radio (CR) is an admirable approach. The concept of cooperative communication needs to be considering because high data rate is the demand for wireless services. Cooperative diversity in the network realized by 3-hop Decode, Amplify and Forward (DAF) and Decode and Forward (DF) and in 2-hop DF and Amplify and Forward (AF) Protocols implemented in cognitive radio communication network using Orthogonal Space Time Block Coding (OSTBC). The communication between end points is accomplished by using Multiple Input and Multiple Output (MIMO) antenna arrangement. During the Propagation, Alamouti Space Time Block Coding is used to accomplish spatial diversity and the encoded data is transmitted through Rayleigh fading channel. CR decodes the transmitted signal using Maximum Likelihood (ML) decoding method. Afterward signal broadcast toward the destination. To check the energy level of signal, energy detection technique applies at the Cognitive Controller (CC). Finally, CC will take ultimate decision for the presence of primary user if the energy level of signal is greater than predefined threshold level, it means PU is present otherwise it is absent. The main objective of this thesis is to analyze the performance of 3-hop and 2-hop communication network using relays. The performance is compared on the bases of two parameters i.e. Bit Error Rate (BER) and Probability of Detection (PD). The results are processed and validated by MATLAB simulation.
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Brittenden, Ashley Edward. "Critical Speeds of an HJ364 Water Jet Assembly." Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/7551.
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With a new range of water jet assemblies under development, CWF Hamilton & Co. Ltd. highlighted the need to establish a validated model for predicting critical speeds. A review of the relevant literature revealed a significant lack of information concerning the operating properties of a lightly loaded, water lubricated marine bearing. Therefore, an instrumented test rig based on a CWF Hamilton & Co. Ltd. ‘HJ364’ water jet assembly was established to evaluate critical speeds and validate the predictive models.
A number of analytical and numerical models for predicting critical speeds were investigated. Geometric modifications were made to the test rig and the changes in critical speeds were observed. The ability of the predictive models to measure these observed critical speeds was examined.
Driveline mass and driveline overhang were found to have the most significant effects on critical speeds. Modifications to the thrust bearing housing, the impeller mass, the tailpipe stiffness and the marine bearing resulted in no significant shift in critical speeds. However, a change to the geometry of the thrust bearing resulted in a significant shift. This indicated that the thrust bearing was not performing ideally in the test rig.
All three models predicted changes in critical speeds relatively accurately. However, the estimates of the critical speeds themselves were somewhat conservative; approximately 10 to 15 percent lower than those measured. Linearisation of the thrust bearing geometry is recommended if greater accuracy is to be achieved. Of all the predictive methods, the Myklestad-Prohl transfer-matrix and the Isolated-Mainshaft finite-element were deemed to be the most flexible and suitable for CWF Hamilton & Co. Ltd.
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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/.
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Esta dissertação apresenta o método de análise espectral de ondas superficiais (SASW) para a obtenção das variações do módulo cisalhante (Gmáx) com a profundidade, no domínio das deformações muito pequenas (abaixo de 0,001%). O SASW é um método sísmico in situ, não destrutivo, baseado na geração e detecção de ondas Rayleigh e na natureza dispersiva desta onda. Pela aplicação de um impacto na superfície do solo e detecção da onda em vários pontos, através de dois receptores, é construída uma curva de dispersão (velocidade de fase versus comprimento de onda). Esta curva de dispersão é, então, invertida. A inversão é um processo analítico para a reconstrução do perfil de velocidade de onda de cisalhamento (VS), partindo-se da curva de dispersão experimental de campo. O módulo de cisalhamento máximo de cada camada é facilmente obtido a partir do perfil de VS. No conteúdo teórico da dissertação discutem-se propriedades dinâmicas dos solos e descrevem-se as equações que dominam a propagação das ondas elásticas, tanto em meios homogêneos como em meios estratificados. A metodologia desenvolvida para a obtenção das curvas de dispersão, através da realização de ensaios SASW, apresenta os resultados obtidos em ensaios realizados na Cidade Universitária em São Paulo, sendo esses resultados comparados com estimativas feitas a partir de correlações baseadas em ensaios SPT existentes. Essas comparações permitem concluir que a metodologia SASW é uma boa alternativa para a determinação do perfil de rigidez (Gmáx) do solo, concordando com o nível de deformação envolvido nos ensaios. São desenvolvidos estudos de sensibilidade do método para verificar a influência na mudança dos parâmetros assumidos (peso específico, coeficiente de Poisson e espessuras das camadas) no processo de redução de dados (inversão) sobre o perfil final de VS, concluindo-se que o parâmetro que apresenta maior influência é o coeficiente de Poisson.This 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.
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Hanafi, Effariza binti. "Quickest spectrum sensing with multiple antennas: performance analysis in various fading channels." Thesis, University of Canterbury. Electrical and Computer Engineering, 2014. http://hdl.handle.net/10092/9642.
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Traditional wireless networks are regulated by a fixed spectrum assignment policy. This results in situations where most of the allocated radio spectrum is not utilized. In order to address this spectrum underutilization, cognitive radio (CR) has emerged as a promising solution. Spectrum sensing is an essential component in CR networks to discover spectrum opportunities. The most common spectrum sensing techniques are energy detection, matched filtering or cyclostationary feature detection, which aim to maximize the probability of detection subject to a certain false alarm rate. Besides probability of detection, detection delay is also a crucial criterion in spectrum sensing. In an interweave CR network, quick detection of the absence of primary user (PU), which is the owner of the licensed spectrum, allows good utilization of unused spectrum, while quick detection of PU transmission is important to avoid any harmful interference.
This thesis consider quickest spectrum sensing, where the aim is to detect the PU with minimal detection delay subject to a certain false alarm rate. In the earlier chapters of this thesis, a single antenna cognitive user (CU) is considered and we study quickest spectrum sensing performance in Gaussian channel and classical fading channel models, including Rayleigh, Rician, Nakagami-m and a long-tailed channel. We prove that the power of the complex received signal is a sufficient statistic and derive the probability density function (pdf) of the received signal amplitude for all of the fading cases. The novel derivation of the pdfs of the amplitude of the received signal for the Rayleigh, Rician and Nakagami-m channels uses an approach which avoids numerical integration. We also consider the event of a mis-matched channel, where the cumulative sum (CUSUM) detector is designed for a specific channel, but a different channel is experienced. This scenario could occur in CR network as the channel may not be known and hence the CUSUM detector may be experiencing a different channel. Simulations results illustrate that the average detection delay depends greatly on the channel but very little on the nature of the detector. Hence, the simplest time-invariant detector can be employed with minimal performance loss.
Theoretical expressions for the distribution of detection delay for the time-invariant CUSUM detector, with single antenna CU are developed. These are useful for a more detailed analysis of the quickest spectrum sensing performance. We present several techniques to approximate the distribution of detection delay, including deriving a novel closed-form expression for the detection delay distribution when the received signal experiences a Gaussian channel. We also derive novel approximations for the distribution of detection delay for the general case due to the absence of a general framework. Most of the techniques are general and can be applied to any independent and identically distributed (i.i.d) channel. Results show that different signal-to-noise ratio (SNR) and detection delay conditions require different methods in order to achieve good approximations of the detection delay distributions. The remarkably simple Brownian motion approach gives the best approximation for longer detection delays. In addition, results show that the type of fading channel has very little impact on long detection delays.
In later chapters of this thesis, we employ multiple receive antennas at the CU. In particular, we study the performance of multi-antenna quickest spectrum sensing when the received signal experiences Gaussian, independent and correlated Rayleigh and Rician channels. The pdfs of the received signals required to form the CUSUM detector are derived for each of the scenarios. The extension into multiple antennas allows us to gain some insight into the reduction in detection delay that multiple antennas can provide. Results show that the sensing performance increases with an increasing Rician K-factor. In addition, channel correlation has little impact on the sensing performance at high SNR, whereas at low SNR, increasing correlation between channels improves the quickest spectrum sensing performance. We also consider mis-matched channel conditions and show that the quickest spectrum sensing performance at a particular correlation coefficient or Rician K-factor depends heavily on the true channel irrespective of the number of antennas at the CU and is relatively insensitive to the channel used to design the CUSUM detector. Hence, a simple multi-antenna time-invariant detector can be employed. Based on the results obtained in the earlier chapters, we derive theoretical expressions for the detection delay distribution when multiple receive antennas are employed at the CU. In particular, the approximation of the detection delay distribution is based on the Brownian motion approach.
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Erskine, Jon S. "Effects of welding on energy dissipation in a watertight bulkhead." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FErskine.pdf.
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Hobiger, 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.
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L'aléa sismique d'un site donné peut être largement influencé par des effets de site. Afin d'évaluer ces effets, la structure locale du sous-sol ainsi que les propriétés du champ d'onde doivent être étudiées. Les ondes de surface (ondes de Love et de Rayleigh) s'avèrent utiles, leurs propriétés (courbes de dispersion, ellipticité des ondes de Rayleigh) étant directement liées à la structure du sous-sol. Le paramètre clé pour l'identification du type d'onde est la polarisation. Dans la première partie de la thèse, de nouvelles méthodes pour l'estimation de paramètres de polarisation d'ondes de surface sont développées. Deux méthodes, DELFI et RayDec, estiment l'ellipticité des ondes de Rayleigh à partir d'enregistrements d'un seul capteur sismique. La troisième méthode, MUSIQUE, est basée sur la méthode MUSIC et utilise les enregistrements multi-composantes de réseaux sismiques afin de distinguer ondes de Love et ondes de Rayleigh et d'estimer leurs propriétés. Dans la deuxième partie de la thèse, une étude théorique de l'inversion de courbes d'ellipticité montre quelles parties de ces courbes véhiculent les informations importantes sur la structure du sol et comment l'inversion peut être améliorée. Le schéma d'inversion résultant est alors testé en l'appliquant à des données réelles mesurées pour 14 sites européens. Finalement, 22 séismes enregistrés par un réseau de capteurs dans la vallée de Santa Clara en Californie sont analysés par MUSIQUE. La répartition azimutale, les courbes de dispersion, la courbe d'ellipticité et les énergies des différents types d'ondes sont analysées et soulignent l'importance des ondes de surface diffractées dans le champ d'ondes enregistré.
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Bassam, Maya. "Étude de la stabilité de quelques systèmes d'équations des ondes couplées sur des domaines bornés et non bornés." Thesis, Valenciennes, 2014. http://www.theses.fr/2014VALE0034/document.
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La thèse est portée essentiellement sur la stabilisation indirecte d’un système de deux équations des ondes couplées et sur la stabilisation frontière de poutre de Rayleigh.Dans le cas de la stabilisation d’un système d’équations d’onde couplées, le contrôle est introduit dans le système directement sur le bord du domaine d’une seule équation dans le cas d’un domaine borne ou à l’intérieur d’une seule équation mais dans le cas d’un domaine non borné. La nature du système ainsi couplé dépend du couplage des équations et de la nature arithmétique des vitesses de propagations, et ceci donne divers résultats pour la stabilisation polynomiale ainsi la non stabilité.Dans le cas de la stabilisation de poutre de Rayleigh, l’équation est considérée avec un seul contrôle force agissant sur bord du domaine. D’abord, moyennant le développement asymptotique des valeurs propres et des vecteurs propres du système non contrôlé, un résultat d’observabilité ainsi qu’un résultat de bornétude de la fonction de transfert correspondant sont obtenus. Alors, un taux de décroissance polynomial de l’énergie du système est établi. Ensuite, moyennant une étude spectrale combinée avec une méthode fréquentielle, l’optimalité du taux obtenu est assuréeThe thesis is driven mainly on indirect stabilization system of two coupled wave equations and the boundary stabilization of Rayleigh beam equation. In the case of stabilization of a coupled wave equations, the Control is introduced into the system directly on the edge of the field of a single equation in the case of a bounded domain or inside a single equation but in the case of an unbounded domain. The nature of thus coupled system depends on the coupling equations and arithmetic Nature of speeds of propagation, and this gives different results for the polynomial stability and the instability. In the case of stabilization of Rayleigh beam equation, we consider an equation with one control force acting on the edge of the area. First, using the asymptotic expansion of the eigenvalues and vectors of the uncontrolled system an observability result and a result of boundedness of the transfer function are obtained. Then a polynomial decay rate of the energy of the system is established. Then through a spectral study combined with a frequency method, optimality of the rate obtained is assured
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Hammouch, Zohra. "Développement d’une méthode numérique pour les équations de Navier-Stokes en approximation anélastique : application aux instabilités de Rayleigh-Taylor." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112086/document.
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L’approximation dite « anélastique » permet de filtrer les ondes acoustiques grâce à un développement asymptotique deséquations de Navier-Stokes, réduisant ainsi le pas en temps moyen, lors de la simulation numérique du développement d’instabilités hydrodynamiques. Ainsi, les équations anélastiques sont établies pour un mélange de deux fluides pour l’instabilité de Rayleigh-Taylor. La stabilité linéaire de l’écoulement est étudiée pour la première fois pour des fluides parfaits, par la méthode des modes normaux, dans le cadre de l’approximation anélastique. Le problème de Stokes issu des équations de Navier-Stokes sans les termes non linéaires (une partie de la poussée d’Archiméde est prise en compte) est défini ; l’éllipticité est démontrée, l’étude des modes propres et l’invariance liée à la pression sont détaillés. La méthode d’Uzawa est étendue à l’anélastique en mettant en évidence le découplage des vitesses en 3D, le cas particulier k = 0 et les modes parasites de pression. Le passage au multidomaine a permis d’établir les conditions de raccord (raccord Co de la pression sans condition aux limites physiques). Les algorithmes et l’implantation dans le code AMENOPHIS sont validés par les comparaisons de l’opérateur d’Uzawa développé en Fortran et à l’aide de Mathematica. De plus des résultats numériques ont été comparés à une expérience avec des fluides incompressibles. Finalement, une étude des solutions numériques obtenues avec les options anélastique et compressible a été menée. L’étude de l’influence de la stratification initiale des deux fluides sur le développement de l’instabilité de Rayleigh-Taylor est amorcéeThe « anelastic » approximation allows us to filter the acoustic waves thanks to an asymptotic development of the Navier-Stokes equations, so increasing the averaged time step, during the numerical simulation of hydrodynamic instabilitiesdevelopment. So, the anelastic equations for a two fluid mixture in case of Rayleigh-Taylor instability are established.The linear stability of Rayleigh-Taylor flow is studied, for the first time, for perfect fluids in the anelastic approximation.We define the Stokes problem resulting from Navier-Stokes equations without the non linear terms (a part of the buoyancyis considered) ; the ellipticity is demonstrated, the eigenmodes and the invariance related to the pressure are detailed.The Uzawa’s method is extended to the anelastic approximation and shows the decoupling speeds in 3D, the particular casek = 0 and the spurius modes of pressure. Passing to multidomain allowed to establish the transmission conditions.The algorithms and the implementation in the existing program are validated by comparing the Uzawa’s operator inFortran and Mathematica langages, to an experiment with incompressible fluids and results from anelastic and compressiblenumerical simulations. The study of the influence of the initial stratification of both fluids on the development of the Rayleigh-Taylor instability is initiated
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Garcia-Lopez, Alicia. "Hybrid model for characterization of submicron particles using multiwavelength spectroscopy." Scholar Commons, 2005. http://scholarcommons.usf.edu/etd/2889.
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The area of particle characterization is expansive; it contains many technologies and methods of analysis. Light spectroscopy techniques yield information on the joint property distribution of particles, comprising the chemical composition, size, shape, and orientation of the particles. The objective of this dissertation is to develop a hybrid scattering-absorption model incorporating Mie and Rayleigh-Debye-Gans theory to characterize submicron particles in suspension with multiwavelength spectroscopy.Rayleigh-Debye-Gans theory (RDG) was chosen as a model to relate the particles joint property distribution to the light scattering and absorption phenomena for submicron particles. A correction model to instrument parameters of relevance was implemented to Rayleigh-Debye-Gans theory for spheres. Behavior of nonspherical particles using RDG theory was compared with Mie theory (as a reference).
A multiwavelength assessment of Rayleigh-Debye-Gans theory for spheres was conducted where strict adherence to the limits could not be followed. Reported corrections to the refractive indices were implemented to RDG to try and achieve Mies spectral prediction for spheres.The results of studies conducted for RDG concluded the following. The angle of acceptance plays an important role in being able to assess and interpret spectral differences. Multiwavelength transmission spectra contains qualitative information on shape and orientation of non-spherical particles, and it should be possible to extract this information from carefully measured spectra. There is disagreement between Rayleigh-Debye-Gans and Mie theory for transmission simulations with spherical scatterers of different sizes and refractive indices.
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Kurtuldu, Huseyin. "New methods of characterizing spatio-temporal patterns in laboratory experiments." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37121.
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Complex patterns arise in many extended nonlinear nonequilibrium systems in physics, chemistry and biology. Information extraction from these
complex patterns is a challenge and has been a main subject of research for many years. We study patterns in Rayleigh-Benard convection (RBC) acquired from our laboratory experiments to develop new characterization techniques for complex spatio-temporal patterns. Computational homology, a new topological characterization technique, is applied to the experimental data to investigate dynamics by quantifying convective patterns in a unique way. The homology analysis is used to detect symmetry breakings between hot and cold flows as a function of thermal
driving in experiments, where other conventional techniques, e.g., curvature and wave-number distribution, failed to reveal this asymmetry.
Furthermore, quantitative information is acquired from the outputs of homology to identify different spatio-temporal states. We use this information to obtain a reduced dynamical description of spatio-temporal chaos to investigate extensivity and physical boundary effects in RBC. The results from
homological analysis are also compared to other dimensionality reduction techniques such as Karhunen-Loeve decomposition and Fourier analysis.
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Kinclová, Radka. "Dynamická analýza mostní konstrukce." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227208.
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The objective of this diploma thesis is a dynamic analysis of a cable-stayed walkway. The RFEM structural analysis software is used for the calculation. Design principles of the structure are explained and analysis of the construction phases is then performed. The eigenmodes of the structure are calculated for various material combinations. The thesis examines the effects of moving loads and earthquake effects using several different methods. A comparison of the various loading effects on the structure and also the calculation methods is presented at the conclusion.
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Lo, Hung-Chieh. "Vibration Characteristics of Thin-Walled Noncircular Composite Cylinders." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77207.
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The lowest natural frequencies of thin-walled noncircular fiber-reinforced composite cylinders, specifically cylinders with elliptical cross sections, are investigated. Of interest is the variation of the lowest natural frequency, the so-called fundamental frequency, as a function of wall laminate properties, cross-sectional eccentricity and other cylinder geometric parameters. Both simple and clamped support boundary conditions are investigated. Laminate properties that are uniform with circumferential location and laminate properties that vary with circumferential location, by way of varying laminate fiber angle with circumferential location, are considered. As the radius of curvature of a noncircular cylinder varies with circumferential location, it is logical to consider the influence of circumferentially varying fiber orientation on the fundamental frequency. The analysis for predicting the fundamental frequency is based on Donnell shell theory, linear elastic properties, and the use of Hamilton's Principle in conjunction with the Rayleigh-Ritz technique. By use of a so-called shape factor, the magnitude of cylinder normal displacements are modulated to be larger in the regions of the cross section with the largest radius of curvatures and smaller in the regions with the smallest radius of curvature. The final equations for predicting the fundamental frequency are quite complex, but a series of approximations results in a hierarchy of simpler equations, the simplest being referred to as Lo's approximation. The prediction of the fundamental frequencies is spot checked by comparing the results as predicted by the various levels of approximation with predictions of a shell-based finite element model. Considering uniform laminate properties, comparisons between the developed analysis and the finite element model are good for all levels of simpler equations, and excellent in some cases. The developed analysis is subsequently used for parameter studies. It is found that compared to a circular cylinder of the same circumference and with uniform laminate properties, the fundamental frequency of an elliptical cylinder is always less. Surprisingly, based on the results obtained, it appears that for a given cylinder geometry the fundamental frequency is not particularly sensitive to wall lamination sequence, though the wave number in the circumferential direction of the mode shape associated with the fundamental frequency is sensitive to lamination sequence. Considering cylinders with circumferentially varying fiber orientation, comparisons between the developed analysis and the finite element model for most of the cases studied are good. However, the developed equations are limited since it is difficult to find a set of known functions to describe the deformation of an arbitrary lamination sequence when applying the Rayleigh-Ritz technique. In general, in can be concluded that the effect of varying fiber orientation on the fundamental frequency is much less than the influence of cylinder aspect ratio. It can also be concluded that the developed analysis would be an excellent tool for design purposes, as the calculation of the fundamental frequency is done quickly, and design trade-offs studies would be easy.Ph. D.
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Sprenger, Lisa. "Beeinflussung der thermomagnetischen Konvektion in Ferrofluidschichten durch den magnetischen Soret-Effekt." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-127792.
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Diese Arbeit stützt sich auf die theoretische und experimentelle Untersuchung der Thermodiffusion im Magnetfeld. Bei magnetischen Flüssigkeiten als kolloidalen Suspensionen versteht man unter der Thermodiffusion einen durch einen Temperaturgradienten angestoßenen unidirektionalen Partikeltransport, der zur Separation des Fluids führt. Beschrieben wird die Thermodiffusion theoretisch über das Konzentrationsprofil der Partikel in Abhängigkeit von Zeit und Ort in einer Fluidschicht. Die Experimente detektieren die Separation des Fluids über die Konzentrationsdifferenz zwischen zwei Fluidkammern. Die Bestimmung des Soret-Koeffizienten erfolgt über einen Datenfit zwischen experimentellen und theoretischen Daten. Für das kerosinbasierte Ferrofluid EMG905 wurden zwei Effekte festgestellt. Bei kleinen Magnetfeldstärken wandern die Partikel zum kalten Rand der Schicht (ST>0), bei steigenden Feldstärken kehrt sich diese Richtung um (ST<0). Die Ergebnisse der Untersuchungen zur Thermodiffusion gehen dann in eine lineare Stabilitätsanalyse einer Ferrofluidschicht bei anliegendem Temperaturgradienten und Magnetfeld ein. Dabei wird festgestellt, dass die kritische Rayleigh-Zahl als charakteristische Größe zum Einsetzen von Konvektion von dem Soret-Koeffizienten abhängt. Ist letzterer positiv, wird das Einsetzen von Konvektion begünstigt, ist er wiederum negativ, so kann Konvektion vollständig unterdrückt werden.
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Muñiz, Martín Ernesto. "Análisis dinámico de las tenso estructuras : propuesta de metodología de cálculo y software aplicado." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284961.
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Traditionally, the dynamic analysis of Multi degree Systems are based on the study of modal Shapes or energy balances given an established oscillation figure. The expert user of those methods could determine how resonance affects the dynamic behaviour of the analysed structure under time dependent variables as wind, moving loads, human steps, etc. or response spectrums (seismic).
This Doctoral thesis propases a calculus methodology whose purpose is to obtain the characteristic modal shapes and energy balances of a tensile structure. Thus, an idealized tensile structure which is modeled using beams with only axial forces could be analyzed in order to get its natural vibrations, modal shapes and tridimensional dynamic behaviour. The expert use of the obtained results conforms the base for the analysis of the most common dynamic situations that can be considered when a tensile structure is designed.
Proposed methodology is based on:
. Force density method.
. Classic analysis of dynamics of structures.
. Modal Spectrum Analysis .
. Energy balances: Rayleigh Ritz method.
Starting from these fundamentals, a sequence of physical and mathematical principies is used to obtain and verify the natural vibration modes for a given tensile structure. The highlights of . the procedure are:
. Deduction of the stiffness matrix using the force density method: an adaption of the general method is used to substantiate a stiffness relation among applied forces and displacements on movable nodes. This is possible due to a "static condensation" of part of the system and the deduction of a Dynamic Force Density for each beam that links load and length for a given prestressing level, taking in consideration section, materials and other corrections. Finally, it is concluded that geometry, loads on movable nodes, supports, prestressing loads and beam properties are linked to each other through a "dynamic stiffness matrix"
. Classic Dynamic Analysis and Modal Spectrum Methods: taking as the starting point the previous "dynamic stiffness matrix", a relation to the mass of the system (having into consideration geometry, loads and materials) is formulated.
Furthermore, it is possible to outline the classic eigenvalue's problem whose resolution is necessary to obtain the modal shapes of a system with multiple degrees of freedom . lt is important to consider the singularities of the problem because X, Y, and Z are independent variables. Synchronization among directions is required because it affects to the tridimensional analysis of the movement when the natural frequencies are studied and the total movement is composed.
. Energy balances: They are mostly used to verify results previously obtained.
The proposal contains a software as part of the Thesis, whose development is based in the exposed method. The software allows the simulation of the most common tensile structures, showing its modal shapes and natural frequenciesEl análisis dinámico de los sistemas de múltiples grados de libertad se plantea tradicionalmente estudiando sus Modos Propios de oscilación o mediante los balances de energia que se establecen sobre formas de oscilación supuestas. A partir de dichas técnicas el analista determinará la sensibilidad a la resonancia del sistema ante acciónes externas dinámicas (viento, circulación de vehículos, paso humano, etc ... ), o acotará el potencial comportamiento del sistema en base a los espectros de respuesta (sismo). Esta Tesis Doctoral propone una metodología de cálculo que permitirá obtener las diferentes formas modales y balances energéticos asociados a la dinámica de una malla tesa, de manera que para una tenso estructura idealizada en barras se determinarán sus frecuencias fundamentales, las formas características de los modos propios asociados a las diferentes frecuencias, así como la composición de la oscilación en "X, Y, Z". Con dicha información el analista tendrá la base con la cual interpretar el comportamiento dinámico potencialmente resultante en una malla tesa en las situaciones ingenierilmente más comunes. La metodologia propuesta se basa en los siguientes fundamentos del cálculo de estructuras. . Método de la Densidad de Fuerza. . Dinámica clásica de sistemas estructurales. . Análisis Modal Espectral. . Planteamiento Energético . Rayleigh Ritz. Partiendo de los fundamentos anteriormente expuestos realizaremos una secuenciada asociación de principios físicos y matemáticos que nos permitirá deducir y verificar las formas modales de vibración y las frecuencias asociadas a una tenso estructura dada. El proceso sigue la siguiente pauta: . Deducción de la rigidez dinámica a partir del método de la Densidad de Fuerza: Se realizará una adaptación del método general de cálculo que nos permitirá plantear para los nudos móviles del sistema una relación de rigidez entre los desplazamientos y las fuerzas aplicadas. Ello se logra gracias a la "condensación en X,Y,Z" de la parte del sistema asociada a los apoyos, y a la deducción de unas "densidades dinámicas de fuerza" que vinculan -para un pretensado determinado- la tensión y la longitud de la barra en equilibrio con la sección y el material correspondiente a la estructura real, incluyéndose además las pertinente correcciones asociadas al módulos de elasticidad Tangente. Se relacionan pues las coacciones externas, la geometría, el pretensado de equilibrio, y las propiedades de las barras que vinculan entre si a los nudos en la estructura real. Entendemos por nudo móvil del sistema aquellos que no son apoyos y que por tanto son susceptible de oscilación. . Dinámica clásica de sistemas estructurales y Análisis Modal: Planteada la citada "rigidez dinámica" estableceremos una asociación de masas (basada en la geometría, materiales y cargas actuantes) que nos permitirá desarrollar el problema clásico de análisis dinámico para múltiples grados de libertad, pero atendiendo a las singularidades del caso por ser un movimiento cuyo análisis se realiza de forma disociada en "X, Y, Z". Se deducirán de ello las formas y frecuencias modales de oscilación (idénticas para los distintos ejes por ser el movimiento forzosamente sincronizado en los ejes) y se analizará la influencia de la composición del movimiento "X, Y, Z" en la frecuencia. Principios energéticos: Realizaremos la verificación energética para los resultados obtenidos de la dinámica clásica. La propuesta se complementa con un software informático que materializa la aplicación del método.
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Chalayer, Rénald. "Méthodes de projection pour des écoulements à seuil, incompressibles et à densité variable." Thesis, Université Clermont Auvergne (2017-2020), 2019. http://www.theses.fr/2019CLFAC089.
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Cette thèse traite de l'utilisation de méthodes de projection pour la simulation de fluides à seuil, incompressibles et à densité variable. Elle se découpe en trois parties. La première partie est consacrée à la présentation du modèle mathématique, à la construction du schéma de semi-discrétisation en temps du modèle, ainsi qu'à l'analyse du schéma ainsi obtenu. Pour construire le schéma, nous avons d'une part adapté un schéma de type pas de temps fractionné existant pour les écoulements newtoniens au cas des écoulements à seuil et d'autre part, nous avons utilisé une formulation en terme de projection pour le tenseur des contraintes qui nous permet de résoudre le couplage entre la vitesse et la contrainte dans l'équation de conservation de la quantité de mouvement avec une méthode de type Uzawa. Nous démontrons mathématiquement la stabilité et la convergence du schéma, et on obtient une estimation d’erreur en temps d’ordre un pour la vitesse, la densité, la viscosité ainsi que le seuil de plasticité. La deuxième partie est consacrée à la discrétisation en espace et à l’implémentation du schéma. La discrétisation en espace est effectuée à l’aide d’une méthode de type volumes finis sur grilles décalées. L’implémentation de l’algorithme a été réalisée à partir d’un code Fortran 90 parallélisé et utilisant les bibliothèques PetsC et MPI. La dernière partie de cette thèse est consacrée à la réalisation de simulations numériques à l'aide du code de calcul que l’on a ainsi construit. Dans la configuration de l’instabilité de Rayleigh-Taylor, on réalise des simulations en faisant varier le seuil de plasticité, en décrivant l’évolution de la position des deux phases et la localisation des zones rigides. Dans la configuration de rupture de barrage, nous mettons en oeuvre les conditions aux limites de type glissement à seuil, plus réalistes physiquement que les conditions de Dirichlet, et nous comparons les résultats obtenus à l’aide de notre nouveau schéma à la littérature existanteThis thesis deal with the use of projection methods for incompressible viscoplastic flows with a variable density. This manuscript is organized following three main lines. The first part is devoted to the mathematical model, the time-discretization of the model and the analysis of the numerical scheme. To construct the numerical scheme, on one side we adapt a time-stepping method already used for newtonian flows to viscoplastic flows and on the other side, we use a projection formulation of the stress tensor to solve the coupling between the velocity and the plastic part of the stress tensor in the momentum equation with an Uzawa-like method. Stability and error analysis of the numerical scheme are provided and a first-order estimate of the time error is derived for the velocity field, the density, the viscosity and the yield stress. The second part is devoted to the space discretization and the implementation of the scheme. A second-order cell-centred finite volume scheme on staggered grids is applied for the spatial discretization. The implementation of the numerical scheme has been performed using a Fortran 90 code and using the PetsC and MPI library The last part of the manuscript is devoted to numerical simulations. In the Rayleigh-Taylor instability configuration, we perform simulations by varying the yield stress, and describing the evolution of the interface and the localization of the rigid zones. In the dambreak configuration, we use Stick-Slip boundary conditions and we compare our results to the existing literature
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Bai, Yang. "Study of viscoelastic instabily in Taylor-Couette system as an analog of the magnetorotational instability." Thesis, Le Havre, 2015. http://www.theses.fr/2015LEHA0015/document.
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Cette thèse est consacrée à la vérification de l'analogie entre l'instabilité viscoélastique (VEI) et l'instabilité magnéto-rotationnel (MRI) dans un écoulement képlérien, afin de mieux comprendre le transport du moment dans les disques d'accrétion. Le discriminant de Rayleigh élasto-rotationnel est établi pour clarifier le rôle de l'élasticité dans le VEI. L'analyse de stabilité linéaire (LSA) avec le modèle d’Oldroyd-B est effectuée pour prédire les paramètres critiques des modes viscoélastiques. Il fait apparaître également l'influence de l'élasticité, la viscosité polymérique et d'autres paramètres de contrôle pour le VEI. Des expériences bien contrôlées avec des solutions aqueuses de polyoxyéthylène (POE) et de polyéthylène glycol (PEG) sont effectuées. Nous avons observé le mode stationnaire axisymétrique supercritique avec des solutions de faible élasticité et modes désordonnés sous-critiques avec des solutions de grande élasticité. Les formes et les valeurs critiques de ces modes sont en bon accord avec les prédictions théoriques de LSA. Selon l'analogie, le mode axisymétrique stationnaire est probablement l'analogue de MRI standard, tandis que le mode désordonné est probable que l'analogue de MRI hélicoïdale. La thèse contient aussi des résultats théoriques expérimentaux sur quatre autres régimes de rotation et un cas de limite d'élasticité infinieThis thesis is devoted to the verification of the analogy between the viscoelastic instability (VEI) and the magnetorotational instability (MRI) in a Keplerian flow, in order to get better understanding of the momentum transportation in accretion disks.The elasto-rotational Rayleigh discriminant is deduced to clarify the role of the elasticity in the VEI. The linear stability analysis (LSA) with Oldroyd-B model is performed to predict critical parameters of viscoelastic modes, and it reveals the influence of the elasticity, polymer viscosity on the VEI. Experiments with well controlled aqueous solutions of polyoxyethylene (POE) and polyethylene glycol (PEG) are conducted. We have observed supercritical stationary axisymmetric mode with solutions of small elasticity and subcritical disordered modes with solutions of large elasticity. Both the flow patterns and the critical values of these modes are in good agreement with the LSA predictions. According to the analogy, the stationary axisymmetric mode is likely the analog of the standard MRI while the disordered mode is likely the analog of the helical MRI. The thesis contains also theoretical and experimental results with four other rotation regimes and the limit case of infinite elasticity
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CASNER, ALEXIS. "Déformations, manipulations et instabilités d'interfaces liquides induites par la pression de radiation d'une onde laser." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2002. http://tel.archives-ouvertes.fr/tel-00001637.
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Ce travail est consacré à l'étude expérimentale des effets de la pression de radiation d'une onde laser continue sur une interface liquide. Les propriétés particulières du ménisque séparant deux phases liquides en coexistence au voisinage de leur point critique de démixtion nous ont permis de visualiser directement des déformations stationnaires d'interface de taille micrométrique. Au stade linéaire, i.e pour des intensités laser modérées, une loi d'échelle exprimant la hauteur des déformations a été validée, ceci pour les deux sens de propagation du faisceau relativement à l'interface. Pour des excitations laser plus élevées, une brisure de symétrie vis à vis du sens de propagation a été mise en évidence. On observe en effet la formation de doigts de grand rapport d'aspect, ou la brisure de l'interface suite à une instabilité optohydrodynamique, suivant que le faisceau se propage du milieu le moins réfringent au milieu le plus réfringent, ou inversement. Ces caractéristiques ont été exploitées pour créer et stabiliser sous champ laser des ponts liquides de rapports d'aspect bien supérieurs à la limite de l'instabilité de Rayleigh-Plateau des colonnes liquides. Les déformations thermocapillaires, engendrées par la faible élévation de température induite par le faisceau laser, ont également été caractérisées, afin de les distinguer sans ambiguité des déformations engendrées par la pression de radiation seule.
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Mériguet, Guillaume. "Structure et dynamique des colloïdes magnétiques : détermination expérimentale et modélisation brownienne." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2005. http://tel.archives-ouvertes.fr/tel-00069633.
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Les suspensions colloïdales magnétiques sont utilisées dans de nombreuses applications pratiques. Toutefois, leurs propriétés structurales et dynamiques, en particulier en présence d'un champ appliqué, restent mal connues. Dans ce but, nous avons adopté une approche qui couple une modélisation par simulation numérique de dynamique brownienne à plusieurs techniques expérimentales sur des dispersions aqueuses préparées «sur mesure». L'emploi de la diffusion de rayonnement, en particulier de neutrons, a permis d'une part, l'élucidation de la structure locale et d'autre part, l'examen de la dynamique de translation à plusieurs échelles. L'effet d'un champ extérieur a été mesuré et évalué parallèlement par la simulation numérique. De plus, la dynamique de rotation a été sondée par la relaxation de biréfringence magnéto-optique. La confrontation des résultats expérimentaux et de simulation numérique complète la compréhension du système, soulignant le rôle des interactions dipolaires.
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Toqeer, Muhammad. "Caractérisation de réservoir carbonaté par sismique réflexion 3D haute résolution." Thesis, Pau, 2012. http://www.theses.fr/2012PAUU3005/document.
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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 karstiquesContinuous 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