In an extensive outdoor propagation study, low antenna heights of 1.7 m are used at both the transmitter and the receiver to measure over 3500 wideband power-delay profiles (PDPs) of the channel for a peer-to-peer communications system. Rural and urban areas are studied in 22 different transmitter-receiver links. The results are used to characterize the narrowband path loss, mean delay, root-mean-square (RMS) delay spread, and timing jitter of the peer-to-peer wideband channel. Small-scale fading characteristics are measured in detail by measuring and analyzing 160 PDPs within each local area. This thesis shows the measurement setup for the calculation of fading rate variance and angular spread and reports the first known attempt to calculate angular spread from track power measurements. New analysis presented in this thesis shows the effect of measurement error in the calculation of angular spread. The expected characteristics of angular spread are derived using two different angle-of-arrival (AOA) models from the literature. Measurement results show initial validation of Durgin's angular spread theory. A new measurement-based algorithm for simulating wideband fading processes is developed and implemented. This simulation technique shows promise in the simulation of high-bit rate peer-to-peer radio communication systems. / Master of Science

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

Wave propagation is a phenomenon resulting from high transient loadings where the duration of the load is in µ seconds range. In aerospace and space craft industries it is important to gain knowledge about the high frequency characteristics as it aids in structural health monitoring, wave transmission/attenuation for vibration and noise level reduction. The wave propagation problem can be approached by the conventional Finite Element Method(FEM); but at higher frequencies, the wavelengths being small, the size of the finite element is reduced to capture the response behavior accurately and thus increasing the number of equations to be solved, leading to high computational costs. On the other hand such problems are handled in the frequency domain using Fourier transforms and one such method is the Spectral Finite Element Method(SFEM). This method is introduced first by Doyle ,for isotropic case and later popularized in developing specific purpose elements for structural diagnostics for inhomogeneous materials, by Gopalakrishnan. The general approach in this method is that the partial differential wave equations are reduced to a set of ordinary differential equations(ODEs) by transforming these equations to another space(transformed domain, say Fourier domain). The reduced ODEs are usually solved exactly, the solution of which gives the dynamic shape functions. The interpolating functions used here are exact solution of the governing differential equations and hence, the exact elemental dynamic stiffness matrix is derived. Thus, in the absence of any discontinuities, one element is sufficient to model 1-D waveguide of any length. This elemental stiffness matrix can be assembled to obtain the global matrix as in FEM, but in the transformed space. Thus after obtaining the solution, the original domain responses are obtained using the inverse transform. Both the above mentioned manuscripts present the Fourier transform based spectral finite element (FSFE), which has the inherent aliasing problem that is persistent in the application of the Fourier series/Fourier transforms. This is alleviated by using an additional throw-off element and/or introducing slight damping in to the system. More recently wave let transform based spectral finite element(WSFE) has been formulated which alleviated the aliasing problem; but has a limitation in obtaining the frequency characteristics, like the group speeds are accurate only up-to certain fraction of the Nyquist(central frequency). Currently in this thesis Laplace transform based spectral finite elements(LSFE) are developed for sandwich members. The advantages and limitations of the use of different transforms in the spectral finite element framework is presented in detail in Chapter-1. Sandwich structures are used in the space craft industry due to higher stiffness to weight ratio. Many issues considered in the design and analysis of sandwich structures are discussed in the well known books(by Zenkert, Beitzer). Typically the main load bearing structures are modeled as beam sand plates. Plate structures with kh<1 is analysed based on the Kirch off plate theory/Classical Plate Theory(CPT) and when the bending wavelength is small compared to the plate thickness, the effect of shear deformation and rotary inertia needs to be included where, k is the wave number and h is the thickness of the plate. Many works regarding the wave propagation in sandwich structures has been published in the past literature for wave propagation in infinite sandwich structure and giving the complete description of dispersion relation with no restriction on frequency and wavelength. More recently exact analytical solution or simply supported sandwich plate has been derived. Also it is seen by comparison of dispersion curves obtained with exact (3D formulation of theory of elasticity) and simplified theories (2D formulation as generalization of Timoshenko theory) made on infinite domain and concluded that the simplified theory can be reliably used to assess the waveguide properties of sandwich plate in the frequency range of interest. In order to approach the problems with finite domain and their implementation in the use of general purpose code; finite degrees of freedom is enforced. The concept of displacement based theories provides the flexibility in assuming different kinematic deformations to approach these problems. Many of the displacement based theories incorporate the Equivalent Single Layer(ESL) approach and these can capture the global behavior with relative ease. Chapter-2 presents the Laplace spectral finite element for thick beams based on the First order Shear Deformation Theory (FSDT). Here the effect of different choices of the real part of the Laplace variable is demonstrated. It is shown that the real part of the Laplace variable acts as a numerical damping factor. The spectrum and dispersion relations are obtained and the use of these relations are demonstrated by an example. Here, for sandwich members based on FSDT, an appropriate choice of the correction factor ,which arises due to the inconsistency between the kinematic hypothesis and the desired accuracy is presented. Finally the response obtained by the use of the element is validated with experimental results. For high shock loading cases, the core flexibility induces local effects which are very predominant and this can lead to debonding of face sheets. The ESL theories mentioned above cannot capture these effects due to the computation of equivalent through the thickness section properties. Thus, higher order theories such as the layer-wise theories are required to capture the local behaviour. One such theory for sandwich panels is the Higher order Sandwich Plate theory (HSaPT). Here, the in-plane stress in the core has been neglected; but gives a good approximation for sandwich construction with soft cores. Including the axial inertial terms of the core will not yield constant shear stress distribution through the height of the core and hence more recently the Extended Higher order Sandwich Plate theory (EHSaPT) is proposed. The LSFE based on this theory has been formulated and is presented in Chapter-4. Detailed 3D orthotropic properties of typical sandwich construction is considered and the core compressibility effect of local behavior due to high shock loading is clearly brought out. As detailed local behavior is sought the degrees of freedom per element is high and the specific need for such theory as compared with the ESL theories is discussed. Chapter-4 presents the spectral finite element for plates based on FSDT. Here, multi-transform method is used to solve the partial differential equations of the plate. The effect of shear deformation is brought out in the spectrum and dispersion relations plots. Response results obtained by the formulated element is compared and validated with many different experimental results. Generally structures are built-up by connecting many different sub-structures. These connecting members, called joints play a very important role in the wave transmission/attenuation. Usually these joints are modeled as rigid joints; but in reality these are flexible and exhibits non-linear characteristics and offer high damping to the energy flow in the connected structures. Chapter-5 presents the attenuation and transmission of wave energy using the power flow approach for rigid joints for different configurations. Later, flexible spectral joint model is developed and the transmission/attenuation across the flexible joints is studied. The thesis ends with conclusion and highlighting futures cope based on the developments reported in this thesis.

Ces travaux sont consacrés à l'étude de la déformation d'interfaces liquides planes par la pression de radiation acoustique. Deux configurations expérimentales sont étudiées, selon que la vitesse du son du liquide d'où vient l'onde est plus grande ou plus petite que la vitesse du son de la seconde phase liquide. Ces travaux de recherche fondamentale ont pour objectif de comprendre les différentes formes complexes observées : jets, déformations en forme de doigts, tétines. Cela est rendu possible par le développement d'un modèle de couplage entre la propagation de l'onde et la déformation de l'interface. Ce modèle est notamment utile pour la compréhension et la caractérisation de colonnes liquides à la fois créées et stabilisées par la pression de radiation acoustique. Pour chacune des études, un parallèle est fait entre les déformations d'interfaces par un faisceau ultrasonore focalisé et par un faisceau laser continu. / Acoustic radiation pressure allows us to remotely create and manipulate liquid objets. Using a highly focused transducer, which emitted field is studied, we can create large aspect ratio and complex liquid interface deformations. This fundamental research aims at understanding these various objects. For this purpose, we developed a theoretical model taking into account the coupling between the wave propagation and the deformation of the interface. This model allows us to predict the characteristics of liquid columns both formed and stabilized by the acoustic radiation pressure. A study of acoustic liquid jets is performed as well. Moreover, we characterize finger-shaped andpacifier-shaped objects as piles of acoustic waveguides. The acoustic wave creates a liquidobject self-adapted to its propagation. For each of these studies, we compare deformationsobtained via the acoustic radiation pressure and the electromagnetic radiation pressurefrom a continuous laser beam.

Approved for public release, distribution is unlimited / In urbanized terrain, radiowave propagation is subjected to fading on large-scales and smallscales that would impede on the quality and reliability of data link transmission. This would have implications in many military applications. One example is the performance of unmanned aerial vehicle (UAV) data and communications links in complex urban environments. The purpose of this research is to study the effectiveness of diversity techniques on the performance of urban UAV data and communications links. The techniques investigated were spatial, polarization, and angle diversities. The ray tracing software, Urbana Wireless Toolset, was used in the modeling and simulation process. The various combinations of diversity techniques were simulated using a realistic urban city model. For the few transmit-receive geometries examined, it was found that angle diversity with a directive antenna provided the greatest increase in signal strength relative to the no diversity case. / Civilian, Singapore DOD

La sonorité de l’échappement joue un rôle significatif sur le confort acoustique des occupants, ainsi que sur le caractère du véhicule. L’étude proposée porte sur la problématique industrielle suivante : « Description et quantification de la transmission du son entre la bouche d’échappement et l’intérieur du véhicule ». Physiquement la transmission sonore entre l’échappement et l’intérieur du véhicule s’effectue en trois étapes : Propagation des ondes sonores de la canule à la surface extérieure du véhicule et conversion en énergie vibratoire (1) ; Le bruit structurel se propage de la peau extérieure du véhicule à l’habillage intérieur (2) ; La surface intérieure du véhicule rayonne de l’énergie dans l’air à l’intérieur (3). Dans l’état de l’art proposé, la méthode de sous-structuration vibro-acoustique Patch Transfer Functions (PTF) est considérée comme une alternative viable à la problématique proposée. Cependant, avant d’appliquer la méthode sur un véhicule complet, la problématique suivante devait être résolue : « Caractérisation expérimentale d’un sous-système par des mesures sur un système couplé ». Ce manuscrit propose une méthode originale pour mesurer des fonctions de transfert d’un système découplé, sur la base de la réponse d’un système couplé. En raison de la nature mal posée du problème inverse, une méthode originale de régularisation a été proposée. La méthode a été validée pas des essais numériques, puis par un test physique. / Exhaust noise has a significant impact on acoustic comfort and the sound identity of a vehicle brand. The present study focuses on the: “Description and quantification of the sound transmission from the exhaust outlet into the interior of a vehicle”. Physically the noise propagation from the exhaust pipe to the cabin consists of three steps: The sound waves propagate through the air from the exhaust outlet to the external skin of the vehicle (1); the external skin vibrates and transmits its vibration to the internal skin (2); the internal skin radiates sound in the passengers’ cabin (3). The Patch Transfer Functions method, which is based on the framework of dynamic substructuring, allows for the consideration of this complex problem as simpler subproblems that consist of subsystem interactions. Yet the application of the method to a full vehicle requires addressing the problem: “Characterization of Patch Transfer Functions of a subsystem by means of measurement on a coupled system”. This dissertation presents an original inverse method for the measurement of Patch Transfer Functions. In industrial structures, this in-situ characterization is generally the only possible measurement method. Yet, due to the ill posed nature of the problem, the inversion process is difficult. An original regularization method is proposed. The method is tested through numerical simulations, and is validated with an experimental setup.

Este trabalho caracterizou os siltitos do Grupo Itararé, rocha branda proveniente da amostragem de pedreira localizada nas proximidades de futuro empreendimento brasileiro, o Trem de Alta Velocidade. Objetivou entender as causas da pronunciada e rápida alteração da rocha intacta, e simular, em condições controladas de laboratório, a degradação hidromecânica causada pela simples variação da umidade relativa do ar. Para tal, estabeleceu-se técnica de amostragem de testemunhos por meio da extração via seca com ar-comprimido, e processo de intemperismo artificial, composto por 4 ciclos de 2 etapas (secagem e umedecimento). O processo se deu em dessecadores, sendo a variação da umidade ocasionada pela técnica do vapor e sílica gel. O acompanhamento da degradação dos corpos de prova efetuou-se com duas técnicas não-destrutivas de propagação de ondas: o pulso ultrassônico e a excitação por impulso (sistema Sonelastic). Em paralelo, realizou-se a caracterização geotécnica dos siltitos em umidade natural, com ensaios mineralógicos, físicos, físico-mecânicos, físico-químicos e de alteração laboratorial. Por meio desta metodologia, foi possível estimar as minorações do módulo de deformabilidade e da resistência, além das causas físico-químicas da degradação. / This work characterized the siltstones of the Itararé Group, a soft rock sampled in a quarry located near a future Brazilian venture, the High Speed Train. It aims at understanding the causes of the pronounced and fast changes of the intact rock, and simulate in controlled laboratory conditions the hydro degradation process caused by simple variation of relative air humidity. Dry sampling technique with compressed air was used to extract samples from blocks, and the process of artificial weathering consisted on 4 cycles of 2 steps (drying and wetting). The process occurred in desiccators, where moisture variation was caused by the vapor technique and silica gel. The monitoring of the specimens degradation was performed with two non-destructive wave propagation techniques: the ultrasonic pulse and the impulse excitation (Sonelastic system). A geotechnical characterization of the siltstones in natural moisture condition was made in parallel, consisting on mineralogical, physical, physical-mechanical, physical-chemical and durability tests. By this methodology, it was possible to estimate the mitigation of the deformability modulus and strength besides the physical- chemical causes of degradation.

[pt] O efeito da atenuação por chuvas em enlaces satélites que operam em frequências acima de 10 GHz é decisivo no cálculo de desempenho do sistema. A evolução da tecnologia dos sistemas satélite e a necessidade de expansão dos serviços de comunicações móveis pessoais levaram ao uso de sistemas de comunicação com satélites de órbita baixa. Estes sistemas são particularmente interessantes para o oferecimento destes serviços por suas características de pequeno atraso de propagação e uso de potência de transmissão mais baixas que os sistemas geoestacionários. Satélites em órbita baixas (LEO) operam em altitudes de cerca de 1000km e possuem movimento em relação à estação terrena. Esta característica de mobilidade traz novas questões sobre o comportamento da atenuação por chuvas, em particular a necessidade de um modelo de previsão de atenuação para estes enlaces com ângulo de elevação variante no tempo. Neste trabalho um modelo para a previsão de atenuação em enlaces com ângulo de elevação fixo, mais preciso do que os existentes na literatura técnica, foi desenvolvido como primeiro passo para o tratamento do problema de enlaces com ângulo de elevação variável. A seguir foi feita uma simulação de medidas em enlaces LEO a partir do banco de dados de medidas de atenuação em enlaces fixos no Brasil, considerando um modelo de constelação de satélites. Foi implementado um método geral que utiliza o histograma dos ângulos de elevação do satélite como ponderação da distribuição cumulativa de atenuação em cada ângulo. O método foi testado contra os resultados obtidos com simulações para a constelação Globalstar sendo obtida muito boa concordância entre o modelo de predição desenvolvido e a simulação. / [en] Rain attenuation is the most important propagation effect to be taken into account in the performance calculation for satellite systems operation at frequencies above 10 GHz. The technological evolution of such systems and the need for personal communication systems with global coverage lead to the use of low earth orbit communication systems, that not only have shorter propagation delays but also allow the use of lower transmission power than the traditional geostationary systems. Low earth orbit (LEO) satellites have altitudes around 1.000 Km and are in motion relatively to the earth stations. This mobility requires a new approach to the problem of rain attenuation prediction, particularly the need for a prediction model that takes into account the elevation angle variability. In this work, an improved rain attenuation prediction method for the geostationary case has been developed as a starting point for the analysis of the nongeostationary case. Then, the rain attenuation in the a LEO system has been simulated using measured data from fixed system systems and the satellite constellation model. A general method for slant path rain attenuation prediction considering variable elevation angles is proposed. The method uses the histogram of the elevation angles to weight the distributions obtained for fixed elevation. The method has been tested with simulations performed for the Globalstar LEO system and a very good agreement was obtained.

There is an increasing interest in the deployment of wireless communication systems in vehicles. The motivation for this work is to provide a fundamental characterisation of the in-vehicle Electromagnetic (EM) wave propagation environment, and to demonstrate how this can be used to aid the deployment of wireless communication systems in vehicles. The fundamental characterisation of the in-vehicle EM wave propagation environment presented in this dissertation yields a number of useful outcomes. The instantaneous impulse response of the in-vehicle channel is characterised, which is presented in the form of a statistical model for arriving rays. Noticing that it is impractical to undertake a full statistical characterisation of the time-varying impulse response, the time variation of the in-vehicle channel is instead characterised as a Doppler spread. This approach provides parameters which are sufficient to perform an information theoretic analysis to lower bound the capacity of the in-vehicle channel. For typical operating conditions, it is found that the channel capacity is approximately equal to that of the same channel with perfect channel state information available at the receiver. Having established the fundamental EM wave propagation characteristics for a single in-vehicle wireless channel, the EM properties of the cavity itself are characterised. This is achieved through a thorough investigation into the analogy between vehicle cavities and reverberation chambers, specifically considering the quality factor (and hence time constant), EM isolation, and electric field uniformity of typical vehicle cavities. This approach yields the important insight that the root mean square delay spread is approximately the same for all wireless links in a typical vehicle cavity. Also, that the angular spread of energy received at any given location (away from the cavity boundaries) is approximately uniform, and that over short distances the coherence distance is well defined, and hence Multiple Input Multiple Output antenna arrays should work well in vehicles. To what extent a typical wireless system can exploit this characterisation depends on how well the parameters can be estimated by a typical wireless communication system. This is also addressed, specifically investigating the estimation of the cavity time constant, and channel time variation. It is found that both of these can be estimated well using a typical wireless sensor network system.

Les travaux de la présente thèse portent sur l’estimation d'erreur a posteriori pour les solutions numériques par éléments finis de l'équation des ondes élastiques dans les milieux hétérogènes. Deux types d’estimation ont été développés. Le premier considère directement l’équation élastodynamique et conduit à un nouvel estimateur d'erreur a posteriori explicite en norme L∞ en temps. Les principales caractéristiques de cet estimateur explicite sont l'utilisation de la méthode de résidus et le développement de reconstructions en temps et en espace selon les différentes régularités exigées par les différents termes contribuant à l’obtention d’une borne supérieure. L’analyse numérique de cet estimateur dans le cas des maillages uniformes montre qu’il assure bien une borne supérieure mais avec une propriété asymptotique qui reste à améliorer. Le deuxième type d’estimateur d’erreur est développé dans le contexte de la propagation des ondes à haute fréquence dans des milieux hétérogènes à l’échelle mésoscopique. Il s’agit d’une nouvelle erreur en résidus basée sur l'équation de transfert radiatif, qui est obtenue par un développement asymptotique multi-échelle de l'équation d'onde en utilisant la transformation de Wigner en espace-temps. Les résidus sont exprimés en termes de densités énergétiques calculés dans l’espace des phases pour les solutions d’onde numériques transitoires par éléments finis. L’analyse numérique de cette erreur appliquée aux milieux homogènes et hétérogènes en 1D a permis de valider notre approche. Les champs d’application visés sont la propagation des ondes sismiques dans les milieux géophysiques ou la propagation des ondes ultrasonores dans les milieux polycristallins. / This thesis work deals with a posteriori error estimates for finite element solutions of the elastic wave equation in heterogeneous media. Two different a posteriori estimation approaches are developed. The first one, in a classical way, considers directly the elastodynamic equation and results in a new explicit error estimator in a non-natural L∞ norm in time. Its key features are the use of the residual method and the development of space and time reconstructions with respect to regularities required by different residual operators contributing to the proposed error bound. Numerical applications of the error bound with different mesh sizes show that it gives rise to a fully computable upper bound. However, its effectivity index and its asymptotic accuracy remain to be improved. The second error estimator is derived for high frequency wave propagation problem in heterogeneous media in the weak coupling regime. It is a new residual-type error based on the radiative transfer equation, which is derived by a multi-scale asymptotic expansion of the wave equation in terms of the spatio-temporal Wigner transforms of wave fields. The residual errors are in terms of angularly resolved energy quantities of numerical solutions of waves by finite element method. Numerical calculations of the defined errors in 1D homogeneous and heterogeneous media allow validating the proposed error estimation approach. The application field of this work is the numerical modelling of the seismic wave propagation in geophysical media or the ultrasonic wave propagation in polycrystalline materials.