The prediction of the noise generated by en-route aircraft is gradually gaining in importance as the number of aircraft increases over the last few decades. While the studies of outdoor sound propagation have been focused on near ground propagation, the case when the sound source is high above the ground has not attracted much attention. At the same time there has been a lack of high-quality aircraft acoustic validation data sets that contain detailed acoustic, meteorology, and source-receiver position data. The DISCOVER-AQ data set, which was collected by Volpe in support of the Federal Aviation Administration (FAA), has greatly helped with studying the directivity and the Doppler effect in the comparison between simulation results and measurements. <div><br>To provide a more accurate prediction of en-route aircraft noise, we derived the analytic asymptotic solution of the sound field above a non-locally reacting ground due to a moving point source and a line source using the methods of the steepest descent and a Lorentz transform. The model predicts a much more accurate result for sound field above "soft" grounds, such as a snow-covered ground and sand-covered ground. At the same time, we derived a fast numerical algorithm based on Levin’s collocation for the prediction of the sound field in the presence of a temperature gradient, which can be applied to a wide range of acoustic problems involving integration. The achievements recorded in this thesis can be used to predict the sound field generated by aircraft, trains, and vehicles with a subsonic moving speed. In addition,<br>the model can be used for detection and design of moving sound source. <br></div>

In the Maritime Works Engineering department of Saipem, studies have been carried out to design an extension to an existing LNG export facility. The scope of work comprises the design of a jetty on piles. For this purpose, wave propagation and ship mooring computations have been performed, as well as shore protection and abutment studies. These studies were preceded by meteocean site data and bathymetry analysis.

This thesis concerns the applications and analysis of the Heterogeneous Multiscale methods (HMM) for Multiscale Elliptic and Hyperbolic Partial Differential Equations. We have gathered the main contributions in two papers. The first paper deals with the cell-boundary error which is present in multi-scale algorithms for elliptic homogenization problems. Typical multi-scale methods have two essential components: a macro and a micro model. The micro model is used to upscale parameter values which are missing in the macro model. Solving the micro model requires, on the other hand, imposing boundary conditions on the boundary of the microscopic domain. Imposing a naive boundary condition leads to $O(\varepsilon/\eta)$ error in the computation, where $\varepsilon$ is the size of the microscopic variations in the media and $\eta$ is the size of the micro-domain. Until now, strategies were proposed to improve the convergence rate up to fourth-order in $\varepsilon/\eta$ at best. However, the removal of this error in multi-scale algorithms still remains an important open problem. In this paper, we present an approach with a time-dependent model which is general in terms of dimension. With this approach we are able to obtain $O((\varepsilon/\eta)^q)$ and $O((\varepsilon/\eta)^q  + \eta^p)$ convergence rates in periodic and locally-periodic media respectively, where $p,q$ can be chosen arbitrarily large.      In the second paper, we analyze a multi-scale method developed under the Heterogeneous Multi-Scale Methods (HMM) framework for numerical approximation of wave propagation problems in periodic media. In particular, we are interested in the long time $O(\varepsilon^{-2})$ wave propagation. In the method, the microscopic model uses the macro solutions as initial data. In short-time wave propagation problems a linear interpolant of the macro variables can be used as the initial data for the micro-model. However, in long-time multi-scale wave problems the linear data does not suffice and one has to use a third-degree interpolant of the coarse data to capture the $O(1)$ dispersive effects apperaing in the long time. In this paper, we prove that through using an initial data consistent with the current macro state, HMM captures this dispersive effects up to any desired order of accuracy in terms of $\varepsilon/\eta$. We use two new ideas, namely quasi-polynomial solutions of periodic problems and local time averages of solutions of periodic hyperbolic PDEs. As a byproduct, these ideas naturally reveal the role of consistency for high accuracy approximation of homogenized quantities. / <p>QC 20130926</p>

This thesis aims to study how flat dielectric lenses can be designed. The usage of flat lenses is steadily increasing as they are smaller and less bulky than traditional convex lenses. Instead of a lens with a curved surface the permittivity in the lens is varied to achieve the same effect. Two different computational methods were investigated when approaching this problem: physical and geometrical optics. In physical optics the incoming radio waves are treated as waves in contrast to geometrical optics where it is considered as rays. Both methods are used as approximations of Maxwell's equations. The variation of permittivity in the lens was formulated as an optimisation problem where the lens' focusing abilities were maximised. The optimisation was implemented with an interior point method. Both arbitrary permittivity distributions as well as predetermined distributions were examined in this work. All optimised lens models were then simulated in a full wave commercial simulation software to verify and compare the two. The simulations showed that both approaches gave promising results as they focused the electromagnetic wave in a satisfying way. However the physical optics approach was more prominent as the focused radio waves had a much higher magnitude than the approach based on geometrical optics. The conclusion was therefore that physical optics is the preferred approach.

La transformation d'espace (TE) a été développée par J. B. Pendry et U. Leonhardt en 2006 et suscite un énorme intérêt depuis la démonstration expérimentale de la première cape d'invisibilité en micro-ondes. Cette technique permet de contrôler la propagation des ondes en modifiant les propriétés électromagnétiques de l'espace. Malgré quelques limitations liées à la bande passante ou aux pertes consécutives à l'utilisation de métamatériaux pour les dispositifs TE, cette technique a attiré l'attention de nombreux domaines (optique, microondes, acoustique, etc). L'objectif de cette thèse est de développer des applications de la TE dans le domaine antennaire à l'aide de matériaux conventionnels lorsque cela est possible et aussi d'ouvrir de nouvelles voies dans le contrôle du rayonnement des antennes. Trois applications ont été étudiées: le réflecteur « parabolique plat »; un superstrat tout diélectrique pour contrôler l'ouverture angulaire d'une antenne patch; et finalement un superstrat permettant de modifier drastiquement le rayonnement d'une antenne. Ce travail a été financé par les agences de défense du Royaume Uni et de la France (DSTL et DGA respectivement), dans le cadre du projet MIMiCRA (Metamaterial Inspired Microwave Conformai Radar Antennas). / Transformation Electromagnetics technique was introduced by J. B. Pendry and U. Leonahrdt in 2006 and it has become an emerging research field in physics and engineering in the last few years after the concept was validated experimentally with a invisibility cloak in microwave regime. This technique claims the possibility of an unprecedented technique to control electromagnetic waves interaction with engineered materials to achieve exotic electromagnetic behaviour. Despite some issues about narrow bandwidth or excessive dispersive losses related to the use of metamaterials for realization of TE devices, this technique caught the attention in many research fields (optics microwave, acoustics, etc). The final purpose of this these is to explore and propose applications of Transformation Electromagnetics in the antenna design field by using standard materials with the purpose of controlling the radiation pattern of an antenna. More precisely, three applications were explored : a fiat "parabolic reflector", an all-dielectric superstrate to control the half power beamwidth of a patch antenna and finally a superstrate that allows to control drastically the radiation pattern of a planar antenna This work was funded by France and UK defence agencies (DSTL and DGA respectively), within the framework of MIMiCRA project (Metamateriallnspired Microwave Conformai Radar Antennas).

A series of small- to moderate-sized earthquakes occurred in Arkansas, Oklahoma and Texas from 2010 to 2012, coinciding with the arrival of the EarthScope Transportable Array (TA). The data the TA recorded from those earthquakes provide a unique opportunity to study attenuation of the Lg phase in the mid-continent and Gulf Coastal region. The TA data reveal previously unrecognized regional variability of ground motion propagation in the central United States. A study of the Fourier amplitude spectra shows the Lg phase exhibiting strong attenuation for ray paths from Arkansas, southwest through the Ouachita Orogenic Belt and into central Texas, and south into the Gulf Coastal region. Less attenuation is seen in central Texas for ray paths extending directly south from Oklahoma, though attenuation remains strong along the Gulf Coast. In contrast, ray paths to the north, regardless of source location, exhibit very little attenuation, especially in northern Missouri and southern Iowa. Regression models that incorporate near-receiver (distance-independent) attenuation due to thick sediments in the Gulf Coastal Plain successfully reduce path-related bias in the regression residuals for stations near the Gulf Coast. Dividing the central United States into three regions (the Gulf Coastal Plain, the Great Plains and the Midwest) further reduced bias, and allowed for the development of Q models in the Gulf Coastal Plain and the Great Plains. In the Gulf Coastal Plain, the Q model for that part of the ray path through the basement, from the earthquake to the base of the sediment deposits below the receiver, was found to be Q=(295±11)*f^(0.645±0.029). The model for attenuation in the sediment section near the receiver in the Gulf Coastal Plain is Q=(72±6.7)*f^(0.32±0.06) (velocity through the sediments is unconfirmed but thought to be approximately 1 km/s). The Q model for the Great Plains is  Q=(692±61.3)*f^(0.43±0.07). The Midwest region exhibited extremely complicated behavior: the data indicate little or no attenuation of amplitudes in the frequency band from approximately 0.7 to 2.0 Hz. As a consequence, Q in the Midwest region in that frequency range could not be realistically determined. / Master of Science

Wave propagation analysis in 1-D and 2-D composite structures is performed efficiently and accurately through the formulation of a User-Defined Element (UEL) based on the wavelet spectral finite element (WSFE) method. The WSFE method is based on the first order shear deformation theory which yields accurate results for wave motion at high frequencies. The wave equations are reduced to ordinary differential equations using Daubechies compactly supported, orthonormal, wavelet scaling functions for approximations in time and one spatial dimension. The 1-D and 2-D WSFE models are highly efficient computationally and provide a direct relationship between system input and output in the frequency domain. The UEL is formulated and implemented in Abaqus for wave propagation analysis in composite structures with complexities. Frequency domain formulation of WSFE leads to complex valued parameters, which are decoupled into real and imaginary parts and presented to Abaqus as real values. The final solution is obtained by forming a complex value using the real number solutions given by Abaqus. Several numerical examples are presented here for 1-D and 2-D composite waveguides. Wave motions predicted by the developed UEL correlate very well with Abaqus simulations using shear flexible elements. The results also show that the UEL largely retains computational efficiency of the WSFE method and extends its ability to model complex features. An enhanced cross-correlation method (ECCM) is developed in order to accurately predict damage location in plates. Three major modifications are proposed to the widely used cross-correlation method (CCM) to improve damage localization capabilities, namely actuator-sensor configuration, signal pre-processing method, and signal post-processing method. The ECCM is investigated numerically (FEM simulation) and experimentally. Experimental investigations for damage detection employ a PZT transducer as actuator and laser Doppler vibrometer as sensor. Both numerical and experimental results show that the developed method is capable of damage localization with high precision. Further, ECCM is used to detect and localize debonding in a composite material skin-stiffener joint. The UEL is used to represent the healthy case whereas the damaged case is simulated using Abaqus. It is shown that the ECCM successfully detects the location of the debond in the skin-stiffener joint.

No description available.

[pt] As teorias clássicas da propagação das ondas eletromagnéticas em presença da terra apresentam soluções gerais que, em vista da complexidade matemática, não se aplicam diretamente aos casos práticos. Desta forma, partindo destas soluções, procura-se determinar aproximações que simplifiquem os cálculos de propagação. Entretanto, devido às condições supostas na obtenção das soluções aproximadas, estas apresentam uma região de validade restrita e a sua aplicação indevida pode acarretar erros inaceitáveis. Este fato, no entanto, não tira o mérito das soluções aproximadas, que, quando empregadas corretamente, fornecem resultados bastante satisfatórios em comparação com os experimentais. O objetivo do presente trabalho é a análise das aproximações efetuadas na obtenção das expressões usualmente empregadas nos cálculos de propagação, onde se procurará evidenciar as limitações inerentes a cada caso particular. O efeito da ionosfera não será considerado, assim como as variações do índice de refração da atmosfera, responsáveis pelo mecanismo da tropodifusão. / [en] In view of the mathematical complexity, the rigorous solutions of the classical theories of radio wave propagation in the presence of the earth are not directly applied to practical problems. Hence, based on these rigorous solutions, approximate expressions are developed to simplify the eveluation of radio wave signal attenuation. However, due to assumptions considered in the derivation of such solutions, they have a limited range of validity and, if erroneously used, can lead to unacceptable errors. Nevertheless, this fact does not take out the merit of the approximate solutions, once when they are correctly employed the numerical results are in accordance with the experimental data. This dissertation intends to analyze the approximations usually carried out in radio wave propagation problems, pointing out limitations associated to each particular case. The effect of the ionosphere will not be considered, as well as, the variability of the refractive index of the troposphere responsibe by the scatter propagation mechanism.

The National Aeronautics and Space Administration maintains a challenging schedule of planned and on-going space exploration missions that extend to the outer reaches of our galaxy. New missions represent a huge investment, in terms of actual costs for equipment and support infrastructure, and personnel training. The success of a mission is critical considering both the monetary investment, and for manned missions, the lives which are put at risk. Tragedies involving Challenger, Columbia, Apollo 7, and the near tragedy of Apollo 13 exemplify that space exploration is a dangerous endeavor, posing extreme environmental conditions on both equipment and personnel. NASA, the National Science Foundation' and numerous independent researchers indicate that predictive simulations have the potential to decrease risk and increase efficiency and effectiveness in space exploration activity. Simulations provide the capability to conduct planning and rehearsal of missions, allowing risk reducing designs and techniques to be discovered and tested. Real-time simulations may improve the quality of the response in a real-time crisis situation. The US Army developed Layered Terrain Format (LTF) database is a uniquely architected database approach that provides high fidelity representation of terrain and specialized terrain query functions that are optimized to support real-time simulations. This dissertation investigates the question; can the unique LTF database architecture be applied to the general problem of celestial body representation? And if so, what benefits might it bring for mission planners and personnel executing the mission? Due to data limitations, this research investigates these questions through a lunar analog setting iv involving S band and Earth-bound communication signals as might be needed to conduct manned and/or robotic mission on the moon. The target terrain data set includes portions of the Black Point Lava Flow in Arizona which will be used for NASA's 2010 Desert RATS analog studies. Applied Research Associates Inc, the developer of the LTF product, generated Black Point databases and made limited modifications to the LTF Viewer tool, RAVEN, which is used for visualization of the database. Through the results attained during this research it is concluded that LTF product does provide a useful simulation capability which could be used by mission personnel both in pre-mission planning and during mission execution. Additionally, LTF is shown to have application an information system, allowing geospecific data of interest to the mission to be implemented within its layers. The Florida Space Research & Education Grant Program sponsored by FSGC, Space Florida and UCF provided a grant of $31,500 to perform this research.