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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigation of Ultrasonic Wave Scattering Effects using Computational Methods

Campbell Leckey, Cara Ann 01 January 2011 (has links)
Advances in computational power and expanded access to computing clusters has made mathematical modeling of complex wave effects possible. We have used multi-core and cluster computing to implement analytical and numerical models of ultrasonic wave scattering in fluid and solid media (acoustic and elastic waves). We begin by implementing complicated analytical equations that describe the force upon spheres immersed in inviscid and viscous fluids due to an incident plane wave. Two real-world applications of acoustic force upon spheres are investigated using the mathematical formulations: emboli removal from cardiopulmonary bypass circuits using traveling waves and the micromanipulation of algal cells with standing waves to aid in biomass processing for algae biofuels. We then move on to consider wave scattering situations where analytical models do not exist: scattering of acoustic waves from multiple scatterers in fluids and Lamb wave scattering in solids. We use a numerical method called finite integration technique (FIT) to simulate wave behavior in three dimensions. The 3D simulations provide insight into experimental results for situations where 2D simulations would not be sufficient. The diverse set of scattering situations explored in this work show the broad applicability of the underlying principles and the computational tools that we have developed. Overall, our work shows that the movement towards better availability of large computational resources is opening up new ways to investigate complicated physics phenomena.
2

Use of Pattern Classification Algorithms to Interpret Passive and Active Data Streams from a Walking-Speed Robotic Sensor Platform

Dieckman, Eric Allen 01 January 2014 (has links)
In order to perform useful tasks for us, robots must have the ability to notice, recognize, and respond to objects and events in their environment. This requires the acquisition and synthesis of information from a variety of sensors. Here we investigate the performance of a number of sensor modalities in an unstructured outdoor environment, including the Microsoft Kinect, thermal infrared camera, and coffee can radar. Special attention is given to acoustic echolocation measurements of approaching vehicles, where an acoustic parametric array propagates an audible signal to the oncoming target and the Kinect microphone array records the reflected backscattered signal. Although useful information about the target is hidden inside the noisy time domain measurements, the Dynamic Wavelet Fingerprint process (DWFP) is used to create a time-frequency representation of the data. A small-dimensional feature vector is created for each measurement using an intelligent feature selection process for use in statistical pattern classification routines. Using our experimentally measured data from real vehicles at 50 m, this process is able to correctly classify vehicles into one of five classes with 94% accuracy. Fully three-dimensional simulations allow us to study the nonlinear beam propagation and interaction with real-world targets to improve classification results.
3

An Indicating Meter for Measuring Intensity Level of Sound

Foster, Walter Sanders 01 January 1936 (has links)
No description available.
4

Co-Simulation of Active Magnetic Bearing Rotors using Adams, MSC Apex, and Simulink

Charkowsky, Shea A 01 August 2023 (has links) (PDF)
Apex-Adams-Simulink co-simulation is applied to active magnetic bearing (AMB) rotors, demonstrating results unshown in literature, including continuous frequency response, and unavailable in known rotor dynamics software, including touchdown bearing impact. AMBs levitate rotors without contact, so they involve no friction, wear, lubrication, pollution, or shaft speed limits and are thus valuable for large, high-speed applications. Modeling of such rotors, necessary for safety and performance, simultaneously requires flexible body dynamics and advanced control design, but simulation programs tend to specialize in only one or the other. The co-simulation method combines multiple such programs—MSC Apex (finite element modeling), Adams (multibody dynamics), and Simulink (graphical control design) with MATLAB (visualization tools)—expanding the design space for AMB rotor modeling beyond that of available commercial software. In this work, accuracy of co-simulation to theory is validated through a rigid AMB rotor and a hanging disk on a steel wire, and new results are shown for a flexible anisotropic rotor and a simplified touchdown bearing impact test.
5

Ultrasonic guided wave interpretation for structural health inspections

Bingham, Jill Paisley 01 January 2008 (has links)
Structural Health Management (SHM) combines the use of onboard sensors with artificial intelligence algorithms to automatically identify and monitor structural health issues. A fully integrated approach to SHM systems demands an understanding of the sensor output relative to the structure, along with sophisticated prognostic systems that automatically draw conclusions about structural integrity issues. Ultrasonic guided wave methods allow us to examine the interaction of multimode signals within key structural components. Since they propagate relatively long distances within plate- and shell-like structures, guided waves allow inspection of greater areas with fewer sensors, making this technique attractive for a variety of applications.;This dissertation describes the experimental development of automatic guided wave interpretation for three real world applications. Using the guided wave theories for idealized plates we have systematically developed techniques for identifying the mass loading of underwater limpet mines on US Navy ship hulls, characterizing type and bonding of protective coatings on large diameter pipelines, and detecting the thinning effects of corrosion on aluminum aircraft structural stringers. In each of these circumstances the signals received are too complex for interpretation without knowledge of the guided wave physics. We employ a signal processing technique called the Dynamic Wavelet Fingerprint Technique (DFWT) in order to render the guided wave mode information in two-dimensional binary images. The use of wavelets allows us to keep track of both time and scale features from the original signals. With simple image processing we have developed automatic extraction algorithms for features that correspond to the arrival times of the guided wave modes of interest for each of the applications. Due to the dispersive nature of the guided wave modes, the mode arrival times give details of the structure in the propagation path.;For further understanding of how the guided wave modes propagate through the real structures, we have developed parallel processing, 3D elastic wave simulations using the finite integration technique (EFIT). This full field, numeric simulation technique easily examines models too complex for analytical solutions. We have developed the algorithm to handle built up 3D structures as well as layers with different material properties and surface detail. The simulations produce informative visualizations of the guided wave modes in the structures as well as the output from sensors placed in the simulation space to mimic the placement from experiment. Using the previously developed mode extraction algorithms we were then able to compare our 3D EFIT data to their experimental counterparts with consistency.
6

Intrustive Probe Measurements in a High-Temperature Mach Two Flow

Nelson, Sonya Renee 01 August 2007 (has links)
To acquire heat transfer measurements of a high temperature Mach two flow a water-cooled calorimeter was placed in the flow and the water temperature rise was used to calculate the heat transfer rate and the recovery temperature of the gas. In addition, a graphite rod with a stainless steel tube at its core was used to measure the total pressure of the flow. This pressure probe was swept through the flow for two test runs to acquire a stagnation pressure profile of the gas flow. All results were compared to NASA CEA computer simulation code results. The heat transfer and recovery temperature results agreed well with the computer simulation code, while the total pressure results from the probe data agree excellently with the computer simulation code. A sensitivity analysis on the results was also preformed on the results.
7

Intrustive Probe Measurements in a High-Temperature Mach Two Flow

Nelson, Sonya Renee 01 August 2007 (has links)
To acquire heat transfer measurements of a high temperature Mach two flow a water-cooled calorimeter was placed in the flow and the water temperature rise was used to calculate the heat transfer rate and the recovery temperature of the gas. In addition, a graphite rod with a stainless steel tube at its core was used to measure the total pressure of the flow. This pressure probe was swept through the flow for two test runs to acquire a stagnation pressure profile of the gas flow. All results were compared to NASA CEA computer simulation code results. The heat transfer and recovery temperature results agreed well with the computer simulation code, while the total pressure results from the probe data agree excellently with the computer simulation code. A sensitivity analysis on the results was also preformed on the results.
8

Parallel three-dimensional acoustic and elastic wave simulation methods with applications in nondestructive evaluation

Rudd, Kevin Edward 01 January 2007 (has links)
In this dissertation, we present two parallelized 3D simulation techniques for three-dimensional acoustic and elastic wave propagation based on the finite integration technique. We demonstrate their usefulness in solving real-world problems with examples in the three very different areas of nondestructive evaluation, medical imaging, and security screening. More precisely, these include concealed weapons detection, periodontal ultrasography, and guided wave inspection of complex piping systems. We have employed these simulation methods to study complex wave phenomena and to develop and test a variety of signal processing and hardware configurations. Simulation results are compared to experimental measurements to confirm the accuracy of the parallel simulation methods.
9

Objectively Measured Physical Activity Among Older Adults During the COVID-19 Pandemic

Choudhury, Renoa 01 January 2022 (has links) (PDF)
COVID-19 pandemic has caused a severely detrimental effect on the physical, psychological, and functional well-being of the older adults by limiting their social and out-of-home activities, which in turn is likely to affect their habitual physical activity level. Physical activity (PA) is vital for healthy aging and the health-related benefits of PA for older adults are well-established. In the current context of COVID-19 pandemic, the changes in PA level, resulting from physical distancing adherence and social isolation, can be a major health concern for the older adults, as they are more prone to physical inactivity than the younger population. Accurate PA assessment at population levels is necessary to understand the trend in PA and sedentary behavior among the older adults during the pandemic. Self-reported assessments can be inexpensive and easy to administer, but they are often subjected to measurement biases such as misinterpretations or deliberate alterations (social desirability bias) and participants having difficulty in remembering activities (recall bias). Accelerometer-based PA monitoring can overcome these limitations of self-reported assessment and objectively measure the amount and intensity of PA in a free-living environment. The objective of this study is to examine the PA levels in the older adults, who were living under the physical distancing guidelines during the COVID-19 pandemic, using an accelerometry-based assessment. The study also investigates how such objectively measured PA levels varied among the older adults based on different sociodemographic factors. In this cross-sectional study, 124 community-dwelling older adults (Age: 60–96 years) were recruited from the region of Central Florida between March 2021 and August 2021. The findings of this study can infer guidelines and/or interventions to promote physical activity and healthy aging among the older adults, particularly those who are susceptible to social isolation and disconnectedness due to COVID-19 pandemic.
10

The Effect of Dynamic Span Wise Bending on the Forces of a Pitching Flat Plate

Sargunaraj, Manoj Prabakar 01 January 2021 (has links) (PDF)
A novel experiment has been conducted to investigate the effect of dynamic spanwise bending on the formation of a dynamic stall vortex on a rapidly pitching flat plate. Experiments have been performed in a towing tank at different nondimensional pitch rates (Kp) in the range of 0.4112 < Kp < 0.8225, and four maximum pitch angles (30° , 45°, 60°, and 90°) at a Reynolds number of 12,000. Synchronized direct force measurements and particle image velocimetry (PIV) are used to characterize the effect of bending on the unsteady forces and the flow field. An unsteady analytical model based on the bending and pitching kinematics is used to model the lift force histories. It is found that a spanwise bending of a pitching wing alleviated the unsteady lift forces. However, the main contribution was found to come from the non-circulatory forces. The circulation and pressure analysis of the pitching wing revealed little or no sensitivity to the wing bending motions examined.

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