Mechanical Engineering Commons^™

Experimental And Numerical Analysis Of Laminar And Transitional Flow Through Annular Corrugated Pipes, Joseph Russell Sargent

Theses and Dissertations

This dissertation presents studies on pressure loss through annular corrugated pipes to determine a friction factor coefficient using nitrogen. Ten different corrugated pipes’ geometries were evaluated via testing and experimentation. The ratio of corrugation height to inner diameter varied from 0.233 to 0.333 and the ratio of corrugation pitch to inner diameter varied from 0.181 to 0.446. Nitrogen flow rates between 0.25 to 94.4 standard liters per minute were used, resulting in Reynolds numbers, based on the corrugated pipe inner diameter, from 100 to 23,000. The experimental set-up was validated using smooth-pipe pressure loss measurements and the derived friction factor …

Path Planning Development Framework For Mobile Robots, Lauren-Ann Elizabeth Graham

Theses and Dissertations

Planetary exploration relies on methods of path planning to achieve autonomous navigation in hazardous environments. Simulating harsh terrain, real-time varying physics, and robotics applications is vital for testing control algorithms here on Earth. Robotics Operating System (ROS) is a set of software libraries and tools that allow you to build and simulate robotic applications. Utilizing ROS, Gazebo, and Blender, a rough terrain simulation framework is created to explore and compare path planning algorithms using various desired robots and maps. ROS supports multiple path planning algorithms given its open-source abilities. This research focuses on path planning implementation of Proportional-Integral-Derivative (PID) control …

Computational Study On The Acoustic Footprint Of Stenosis In Larger Arteries, Ahmed Abdelnabi

Theses and Dissertations

We identify a new (acoustic) frequency-stenosis relations whose frequencies fall within the recommended auscultation threshold for stethoscopy (< 120 Hz) in this study. We demonstrate that these relations can be used to extend the application of phonoangiography (the measurement of the degree of stenosis from bruits) to stethoscopes that are broadly available. The First relationship is successfully identified using an analysis limited to the acoustic signature of the von Karman vortex street, which we automatically isolate using a metric based on an area-weighted average of the Q-criteria for the post-stenotic region. Specifically, we conduct LES-CFD simulations on simplified 2D internal flow geometries that represent blood vessels with varying degrees of stenosis. Then, using the Ffowcs Williams-Hawkings (FW-H) equation, we extract their emitted acoustic signals, which we subtract from a pure signal (stenosis-free) at the same heart rate. Next, we transform this differential signal to the frequency domain and meticulously classify its acoustic signatures according to six stenosis-invariant flow phases of a cardiac cycle. Using our Q-criterion-based metric, we then automatically restrict our acoustic analysis to the noises emitted by the von Karman vortex street (phase 4). Our analysis of its acoustic signature demonstrates a strong linear relationship between the degree of steno- sis and its dominant frequency, which differs significantly from the break frequency and heart rate (previously identified dominant frequencies). For the Second relationship, we develop a frequency-stenosis scaling law for particularly supravalvular aortic stenosis that falls within the preferred frequency range (30-120 Hz) for echocardiography. We expand to 3D patient specific geometry using Simulia’s Living Heart Human Model (LHHM), which has an anatomically accurate aorta geometry. This LHHM geometry is modified with stenoses ranging from 30 to 80 percent (moderate to severe). For physiologically consistent hemodynamic boundary conditions, we expand the study to employ the Windkessel model, which has been implemented on Fluent using UDF. We demonstrate that physiological boundary conditions reduce simulation time significantly compared to static boundary conditions. The FW-H model extracted the flow-generated acoustic signal of the stenotic geometries and analysed it at clinically relevant receiver locations. A preferred receiver location consistent with clinical practise is determined, and a correlation between the degree of stenosis and the prevalent acoustic frequency (within the frequency range of 70-120 Hz) is established. The obtained second scaling law is shown to be clinically reliable in assessing stenotic severity. Future research will investigate incorporating the vibroacoustic role of adjacent organs and tissue to expand the clinical applicability of our findings. Expansion of clinical and numerical datasets will be pursued in future research to enhance the reliability of our scaling law, possibly by leveraging much-needed ML-based acceleration schemes.

Challenges And Signal Processing Of High Strain Rate Mechanical Testing, Barae Lamdini

Theses and Dissertations

Dynamic testing provides valuable insight into the behavior of materials undergoing fast deformation. During Split-Hopkinson Pressure Bar testing, stress waves are measured using strain gauges as voltage variations that are usually very small. Therefore, an amplifier is required to amplify the data and analyze it. One of the few available amplifiers designed for this purpose is provided by Vishay Micro-Measurements which limits the user’s options when it comes to research or industry. Among the challenges of implementing the Hopkinson technology in the industry are the size and cost of the amplifier. In this work, we propose a novel design of …

Torque Vectoring To Maximize Straight-Line Efficiency In An All-Electric Vehicle With Independent Rear Motor Control, William Blake Brown

Theses and Dissertations

BEVs are a critical pathway towards achieving energy independence and meeting greenhouse and pollutant gas reduction goals in the current and future transportation sector [1]. Automotive manufacturers are increasingly investing in the refinement of electric vehicles as they are becoming an increasingly popular response to the global need for reduced transportation emissions. Therefore, there is a desire to extract the most fuel economy from a vehicle as possible. Some areas that manufacturers spend much effort on include minimizing the vehicle’s mass, body drag coefficient, and drag within the powertrain. When these values are defined or unchangeable, interest is driven to …

Sound Propagation In Viscous Flows Using Piezoelectric Sensors And Non-Destructive Propagation Techniques And Its Applications, Ahmed M. Abdulkareem

Theses and Dissertations

Structural non-destructive evaluation techniques are applied to viscous flows to detect fluid property changes. The main operating principle consists of an actuator which provides a stimulus, and a sensor to receive a signal traveling to a fluid domain. The main challenge of the operating principle consists of investigating waves traveling in a viscous flow. Traveling waves utilizing a piezoelectric actuator-sensor pair are modeled and the results are validated experimentally. ANSYS models, coupled with a two-way fluid-solid interaction model, are built to investigate how far a signal travels and what frequency ranges are of interest. The numerical model includes modeling three …

Coding Strategies For Cochlear Implants Under Adverse Environments, Qudsia Tahmina

Theses and Dissertations

Cochlear implants are electronic prosthetic devices that restores partial hearing in patients with severe to profound hearing loss. Although most coding strategies have significantly improved the perception of speech in quite listening conditions, there remains limitations on speech perception under adverse environments such as in background noise, reverberation and band-limited channels, and we propose strategies that improve the intelligibility of speech transmitted over the telephone networks, reverberated speech and speech in the presence of background noise. For telephone processed speech, we propose to examine the effects of adding low-frequency and high- frequency information to the band-limited telephone speech. Four listening …

Covert Contrast: The Acquisition Of Mandarin Tone 2 And Tone 3 In L2 Production And Perception, Liya Mar

Theses and Dissertations

This dissertation investigates the occurrence of an intermediate stage, termed a covert contrast, in the acquisition of Mandarin Tone 2 (T2) and Tone 3 (T3) by adult speakers of American English. A covert contrast is a statistically reliable distinction produced by language learners that is not perceived by native speakers of the target language (TL). In second language (L2) acquisition, whether a learner is judged as having acquired a TL phonemic contrast has largely depended on whether the contrast was perceived and transcribed by native speakers of the TL. However, categorical perception has shown that native listeners cannot perceive a …

Power Maximization For Pyroelectric, Piezoelectric, And Hybrid Energy Harvesting, Murtadha A. Shaheen

Theses and Dissertations

The goal of this dissertation consists of improving the efficiency of energy harvesting using pyroelectric and piezoelectric materials in a system by the proper characterization of electrical parameters, widening frequency, and coupling of both effects with the appropriate parameters.

A new simple stand-alone method of characterizing the impedance of a pyroelectric cell has been demonstrated. This method utilizes a Pyroelectric single pole low pass filter technique, PSLPF. Utilizing the properties of a PSLPF, where a known input voltage is applied and capacitance C_p and resistance R_p can be calculated at a frequency of 1 mHz to 1 Hz. …

Increasing The Sensitivity Of Surface Acoustic Wave (Saw) Chemical Sensors And Other Chemical Sensing Investigations, Nina R. Smith

Theses and Dissertations

The work involves the fabrication and testing of three different surface acoustic wave (SAW) device designs, an investigation of nanowires sensitive to chemicals and preconcentrator prototypes to include with chemical sensors. The SAW chemical sensor designs include modifications to a basic SAW device to see if the sensitivity of the SAW device is increased. The modifications consist of etched trenches along the propagation field, coating the device with carbon nanotubes (CNTs) under the chemically sensitive layer and coating CNTs on top of the chemically sensitive layer. SAW devices are coated with Nafion®, a polymer sensitive to ethanol. The tests indicate …

Microelectromechanical Isolation Of Acoustic Wave Resonators, James R. Reid Jr.

Theses and Dissertations

Microelectromechainical systems (MEMS) is a rapidly expanding field of research into the design and fabrication of actuated mechanical systems on the order of a few micrometers to a few millimeters. MEMS potentially offers new methods to solve a variety of engineering problems. A large variety of MEMS systems including flip-up platforms, scanning micromirrors, and rotating micromirrors are developed to demonstrate the types of MEMS that can be fabricated. The potential of MEMS for reducing the vibration sensitivity of surface acoustic wave and surface transverse wave resonators is then evaluated. A micromachined vibration isolation system is designed and modeled. A fabrication …

Binaural Room Simulation, Brian A. Smith

Theses and Dissertations

Research in binaural and spatial hearing is of particular interest to the Air Force. Applications in cockpit communication, target recognition, and aircraft navigation are being explored. This thesis examines human auditory localization cues and develops a mathematical model for the transfer function of a sound signal traveling from an isotropic point source through a rectangular room to both ears of a listener. Using this model as a guide, non-head coupled binaural sound signals are generated in a binaural room simulation. Reflection and attenuation cues included in the computer generated signals are varied in order to determine which cues enhance the …