Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 26 for “"Acoustic Wave Propagation"”.
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Effect of liner thickness on acoustic wave propagation in ducts
The acoustic characteristics of a point-reacting duct liner that consists of a porous facing sheet backed by cellular cavities are derived by examining the wave propagation within the liner. The relation between the derived expression for the liner acoustic admittance and a semi-empirical formula …
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Immersed Discontinuous Galerkin Methods for Acoustic Wave Propagation in Inhomogeneous Media
… element methods for one and two dimensional acoustic wave propagation problems in inhomogeneous media where elements are allowed to be cut by the material interface. The proposed methods use the standard discontinuous Galerkin finite element formulation with polynomial approximation on …
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Acoustic wave propagation and non-intrusive velocity measurements in highly concentrated suspensions
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1991.
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Impacts of short-time scale water column variability on broadband high-frequency acoustic wave propagation
Acoustical oceanography is one way to study the ocean, its internal layers, boundaries and all processes occurring within using underwater acoustics. Acoustical sensing techniques allows for the measurement of ocean processes from within that logistically or financially preclude traditional in-situ …
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An Investigation of Performance Limitations in Active Noise Reduction Headsets
… lag. Speaker dynamics, control hardware, and acoustic wave propagation from the control speaker to the error microphone all contribute to this phase lag. Understanding these sources of phase lag and their relative effects on performance allows for better design of an analog or digital ANR …
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Acoustic waves in crystals: I. Ultrasonic flux imaging and internal diffraction. II. Imaging phonons in superconducting niobium
Acoustic wave propagation is studied via imaging techniques in two regimes not previously amenable to such experiments. (I) The low-temperature phonon-imaging technique is extended to ultrasonic frequencies at room temperatures where it is used to study the anisotropic propagation of acoustic waves …
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Ultrasonic Real-Time Quality Monitoring Of Aluminum Spot Weld Process
… process and finite difference modeling of the acoustic wave propagation through the aluminum spot welds presented in this dissertation, revealed that the thermodynamics and hence the acoustic wave propagation through an aluminum and a steel spot weld differ significantly. For this reason, the …
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Design optimization of acoustic metamaterials and phononic crystals with a time domain method
… derivatives for shape optimizations of acoustic metamaterials and phononic crystals is presented. The gradient-based design procedure is suitable for large numbers of design variables, and results are shown on achieving effective material properties with a unit cell and the broadband …
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Applications of the Radon transform, Stratigraphic filtering, and Object-based stochastic reservoir modeling
… of the Radon transform, one aspect of acoustic wave propagation, and a pilot study of generating a stochastic reservoir model. The first three studies focus on the use of the Radon transform to enhance surface-recorded, controlled-source seismic data. First, the use of this transform …
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Experimental investigation of the flow field during combustion in narrow circular ducts
… quartz tubes yielded cycles of ignition, flame propagation, and extinction. This phenomenon was studied with the intent of determining the flow structure that underlay the observed oscillatory motion. The fluid motion during the oscillations was visualized by seeding TiO2 micron-sized particles. …
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Time-Domain Simulation of Sound Propagation in Frequency-Dependent Materials
This dissertation investigates sound propagation in frequency-dependent materials. The study provides an improved understanding of how to numerically model the porous impedance materials more accurately under the conditions of complicated geometries. The finite difference time-domain (FDTD) method …
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Frequency Domain Ultrasound Waveform Tomography Breast Imaging
… of disease. Using the principles of full waveform inversion, high-resolution quantitative sound speed and attenuation maps of the breast can be created. In this thesis, we introduce some basic principles of imaging breast disease and the formalism of sound wave propagation. We present …
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Power Transformer Partial Discharge (PD) Acoustic Signal Detection using Fiber Sensors and Wavelet Analysis, Modeling, and Simulation
… this work, we first analyze the behavior of the acoustic wave from the theoretical point of view using a simplified 1-dimensional model. The model was developed based on the conservation of mass, the conservation of momentum, and the state equation; in addition, the fluid medium obeys Stokes …
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Numerical evaluation of wavenumbers of the acoustic waves propagating in an ice-covered ocean
We consider acoustic wave propagation in a layered ocean waveguide covered by thick ice. The standard method of separation of variables leads to a Sturm-Liouville problem in the crosssection of the waveguide. We are specifically interested in the two leading modes, the separated solutions for the …
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Mechanical characterisation of soft biological tissue by using surface acoustic waves
… or disease progression tracking. Surface acoustic waves (SAWs) have been preliminarily used for the characterisation of tissue mechanical properties and it is increasingly becoming a topic of research interest as SAWs can provide more localised information in the tissue near-surface region …
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Green's function derivations for specific acoustic admittances and impedances
Impedance and admittance relationships in acoustics are commonly given in their frequency-domain representations. This is done for many reasons including the simplicity of the mathematics used to compute frequency-domain impedance functions. However, although the frequency-domain representations of …
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Optical transient grating measurements of micro/nanoscale thermal transport and mechanical properties
… and nanostructured semiconductors and surface wave propagation in a monolayer of micron sized spheres. In the transient grating technique two picosecond pulses are crossed to generate a spatially periodic intensity profile. The spatially periodic profile generates a material excitation with a …
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Imaging surface acoustic waves in anisotropic and periodic media
… has been developed for studying surface acoustic wave propagation. The technique, which uses non-contact immersion transducers to excite and detect ultrasound with frequencies between 1 and 20 MHz, allows convenient examination of surface waves traveling in arbitrary directions on a …
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A method for the numerical analysis of combustion instabilities with an application to afterburner screech
… the prediction of potentially damaging thermoacoustic oscillations in gas turbine combustion systems by computational means. A framework is laid out to predict numerically the frequency and stability of thermoacoustic oscillations, with focus on the high frequency screech instability of …
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