No description available.

No description available.

No description available.

No description available.

"The time-of-arrival (ToA)-based localization technique performs superior in line-of-sight (LoS) conditions, and its accuracy degrades drastically in proximity of micro-metals and human body, when LoS conditions are not met. This calls for modeling and formulation of Direct Path (DP) to help with mitigation of ranging error. However, the current propagation tools and models are mainly designed for telecommunication applications via focus on delay spread of wireless channel profile, whereas ToA-based localization strive for modeling of DP component. This thesis provides a mitigation to the limitation of existing propagation tools and models to computationally capture the effects of micro-metals and human body on ToA-based indoor localization. Solutions for each computational technique are validated by empirical measurements using Ultra-Wide-Band (UWB) signals. Finite- Difference-Time-Domain (FDTD) numerical method is used to estimate the ranging errors, and a combination of Uniform-Theory-of-Diffraction (UTD) ray theory and geometrical ray optics properties are utilized to model the path-loss and the ToA of the DP obstructed by micro- metals. Analytical UTD ray theory and geometrical ray optics properties are exploited to model the path-loss and the ToA of the first path obstructed by the human body for the scattering scenarios. The proposed scattering solution expanded to analytically model the path-loss and ToA of the DP obstructed by human body in angular motion for the radiation scenarios."

This thesis develops a Bayesian inversion algorithm for autonomous underwater vehicle localization, and carries out a study of several factors contributing to localization accuracy in an underwater acoustic positioning system. Specifically, a ray-based algorithm is described that estimates target position through the linearized inversion of transmission arrival time differences, and provides linearized uncertainty estimates for model parameters. Factors contributing to source localization uncertainty considered here included: (1) modelling transmission paths accounting for refraction due to a depth-varying SSP instead of using a constant sound-speed approximation and straight-line propagation, (2) inverting for a potential bias in the measured sound-speed profile, (3) accounting for errors in hydrophone position by including these positions as unknown parameters in the inversion, and (4) applying path-dependent timing correction factors to account for lateral variability in the sound-speed profile. In each case, nonlinear Monte Carlo analysis is applied in which a large number of noisy data sets are considered, to obtain statistical measures of the localization improvement that results by addressing these factors. / Graduate

Aircraft noise mitigation has been an ongoing challenge for the aeronautics research community. In response to this challenge, aircraft concepts have been developed in which the propulsion system is integrated with the airframe to shield the noise from the observer. These concepts exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and accurate modeling of these characteristics are essential to designing future low-noise aircraft. In this thesis, an alternative approach is created for predicting jet mixing noise that utilizes an acoustic analogy and the solution of the steady Reynolds-Averaged Navier-Stokes (RANS) equations using a two equation turbulence model. A tailored Green's function is used in conjunction with the acoustic analogy to account for the propagation effects of mixing noise due to a nearby airframe surface. The tailored Green's function is found numerically using a newly developed ray tracing method. The variation of the aerodynamics, acoustic source, and far- field acoustic intensity are examined as a large flat plate is moved relative to the nozzle exit. Steady RANS solutions are used to study the aerodynamic changes in the field-variables and turbulence statistics. To quantify the propulsion airframe aeroacoustic (PAA) installation effects on the aerodynamic source, a non-dimensional number is formed that can be used as a basic guide to determine if the aerodynamic source is affected by the airframe and if additional noise produced by the airframe surface is present. The aerodynamic and noise prediction models are validated by comparing results with Particle Image Velocimetry (PIV) and far-field acoustic data respectively. The developed jet noise scattering methodology is then used to demonstrate the shielding effects of the Hybrid Wing Body (HWB) aircraft. The validation assessment shows that the acoustic analogy and tailored Green's function provided by the ray tracing method are capable of capturing jet shielding characteristics for multiple configurations and jet exit conditions. / Master of Science

Just as water surface waves are found everywhere on the ocean's surface, internal waves are ubiquitous throughout the atmosphere. These waves constantly propagate and interact with other flows, but these interactions are difficult to observe due to inadequate current technology. Numerical simulations are often utilized in the study of internal waves. In this work, ray theory is used to numerically simulate the interaction of atmospheric internal waves with time-dependent and time-independent background flows, specifically the interaction of small-scale internal waves and large-scale inertial waves. Parameters such as initial wavenumbers and amplitudes of both small internal waves and inertial waves are determined that will cause the small waves to reach a turning point or critical level, or in the case of time-dependent flows, a wavenumber that reaches a critical value. Other parameters that may cause the waves to become unstable are included in the analysis, such as wave steepness and shear instability. These parameters are combined to determine the spectrum of waves that will experience instability during the interaction. Two principal interactions, small-scale internal waves propagating through an infinite wave train and small-scale internal waves propagating through an inertial wave packet, are simulated and compared. For the first interaction, the total frequency is conserved but is not for the latter. This deviance is measured and results show how it affects the outcome of the interaction. The interaction with an inertial wave packet compared to an inertial wave train results in a higher probability of reaching a Jones' critical level and a reduced probability of reaching a turning point, which is a better approximation of outcomes experienced by expected real atmospheric interactions.

No description available.

Title: Ray-based Born approximation Author: Libor Šachl Department: Department of Geophysics Supervisor: RNDr. Luděk Klimeš, DrSc. Supervisor's e-mail address: klimes@seis.karlov.mff.cuni.cz Abstract: One of the aims of this thesis was coding of program grdborn.for for computing the 2D and 3D ray-based Born approximation of the first order in an inhomoge- nous isotropic medium without attenuation. The computation of 3D amplitudes using the 2D Born approximation is based on the correction term, which is de- rived. The program is further used in computing the Born approximation in various models. We test its performance in three simple models. We study the effect of the discretization, the spurious waves introduced by the finite size of the grid etc. In the next step, we focus on the computations in more compli- cated models. We compute the Born seismograms in 2D heterogenous models. We study the diffracted waves, the effects of caustics etc. Keywords: Born approximation, ray theory, velocity model, perturbation 1