Mechanical Engineering Commons^™

Field-Assisted Post-Processing Of Cold-Sprayed Pure Copper, Alan Hensley

Theses and Dissertations--Mechanical and Aerospace Engineering

The properties of materials processed through cold spray, and many other AM processes, are non-uniform and unpredictable. In most cases, post-processing is required to achieve desired properties and better uniformity. In cold spray, the typical method is an annealing heat treatment (AHT), which can improve bond strength, reduce porosity, and restore ductility, among other effects. AHT alone, however, is unable to completely remedy any of the unfavorable properties. In addition, long treatments at high temperatures are often needed for satisfactory results. This increases energy consumption and extends production times for products made by the process. For these reasons, numerous investigations …

Multiphysics Transport In Porous Thermal Protection Systems: Experimental Characterization Of Gas Permeability And Radiative Properties, Yejajul Hakim

Theses and Dissertations--Mechanical and Aerospace Engineering

Porous thermal protection systems (TPS) used in hypersonic vehicles exhibit coupled gas and radiative transport across multiple regimes and length scales. Accurate performance prediction requires reliable characterization of permeability, slip-flow behavior, and radiative transport properties, particularly for low-permeability and charred materials where existing data are limited. This dissertation presents experimental methods for characterizing multiphysics transport in porous TPS materials. A modular flow system was developed to measure permeability and slip behavior in both virgin and charred materials under relevant environments. A transient pressure decay method enables accurate permeability estimation in low-permeability regimes and provides insight into effective pore structure. Results …

Reciprocity-Based Transfer Function Techniques For Acoustic Source Reconstruction, Spring Isolator Characterization And Structural Damping Assessment, David Pum Thian Lal Paite Neihguk

Theses and Dissertations--Mechanical and Aerospace Engineering

Reciprocity implies that a system responds identically when the source and receiver positions are interchanged. This dissertation applies this principle to address three practical challenges in noise and vibration characterization, where conventional approaches are limited by inaccessible interfaces, constrained excitation conditions, or metrics that do not fully capture vibroacoustic behavior.

The first study develops and validates an inverse method to characterize ducted acoustic sources using acoustic free velocity. Acoustic reciprocity is applied to simplify transfer function measurements. The method is extended to large cross-section ducts, where the source is reconstructed as a collection of point sources along a plane. Validation …

Process-Guided Learning Via Data-Driven Modeling And Controller Synthesis, Benton Clark

Theses and Dissertations--Mechanical and Aerospace Engineering

This work introduces process-guided learning, a framework in which process characteristics and learning algorithms are combined in the modeling process of engineering applications with the aim of uniting traditional and data-driven modeling and control techniques. Traditional engineering methods using simplified analytic models fail to capture the increasing complexities of engineering problems with sufficient accuracy to achieve modern requirements. More advanced modeling and control techniques using high-fidelity models often produce a computational burden that is infeasible for real-time solutions. Data-driven modeling offers a simple and flexible algorithm for producing real-time capable, high-fidelity models, but naive implementations lack the physical constraints of …

Analysis Of Ptfe Radial Lip Seals For Wheel Bearing Applications, Madison Vogt

Theses and Dissertations--Mechanical and Aerospace Engineering

A numerical analysis was conducted to investigate the viscoelastic effects of nonlinear materials on the sealing zone and contact pressure distribution of radial lip seals in a conventional geometric topology. The use of nonlinear materials in radial lip seal applications is desirable to improve operation and reliability of rotating machinery due to their high operating temperatures, chemical compatibility, and low friction coefficients. Examples include, but are not limited to, seals within industrial air compressors, turbine engines, aircraft landing systems, chemical processing equipment, and Freon pumps. This work focuses on analyzing the nonlinear viscoelastic response of pure Polytetrafluoroethylene (PTFE) and PTFE …

Simplified Molecular Diagnostics Methods For Environmental Testing Of Pathogens And Other Applications, Mohammad Dehghan Banadaki

Theses and Dissertations--Mechanical and Aerospace Engineering

Environmental Surveillance (ES) has emerged as a powerful tool to monitor the emergence and persistence of a pathogen within a facility or community using wastewater/water analysis. Over the past four years, implementation of ES has experienced an explosive acceleration, driven by efforts to monitor the spread of SARS-CoV-2, which has made ES a routinely used public health tool in many locations. We can now use ES to measure the emergence/presence/abundance of different viruses (e.g., SARS-CoV-2, influenza, mpox), bacteria (e.g., E. coli, V. cholerae, antibiotic-resistant strains), fungi (e.g., C. auris), and other biological markers indicative of infectious diseases. However, its broad …

Determination And Limitations Of Blocked Forces In Industrial Settings, Matthew Smither

Theses and Dissertations--Mechanical and Aerospace Engineering

Transfer path analysis methods have been used for decades to determine noise and vibration paths emanating from machinery. In its advent, the machinery source had to be disconnected from the receiver it was attached to in order to gain useful information about each. Further advances in methodology allowed for determining machinery input forces without decoupling them from the structures they were attached to. However, these methods were limited in that the machinery and structures were required to be treated as a system. Thus, any force data obtain was only useful in the configuration it was measured in. Finally, a method …

In-Situ Characterization Of Damage Mechanisms In Ceramic Matrix Composites, Cle' E. Sanchez

Theses and Dissertations--Mechanical and Aerospace Engineering

Ceramic Matrix Composites have many advantages, attracting the nuclear, aerospace, and automotive industries with their high heat stability, strength, and oxidation resistance. However, challenges are presented when machining these materials due to the brittle properties and complicated microstructure. The objective of this project was to identify damage mechanisms that occur when a CMC is orthogonally machined and the cutting mechanics are observed in-situ, followed by post-cut characterization of the as-machined surface morphology. In this analysis, the main variable is the feed rate, which can influence the damage mechanisms, such as matrix failure (matrix cracking) or fiber failure (pullout). Through this …

In Situ Bourbon Barrel Measurements Of Alcohol By Volume And Liquid Depth Using Borosilicate Glass Probes And Near Infrared Absorption Spectroscopy, Trent T. Reed

Theses and Dissertations--Mechanical and Aerospace Engineering

In pursuit of measuring different variables present in bourbon barrels, absorption spectroscopy was utilized to ensure that different ethanol and water concentrations can be differentiated using a broadband light source and near infrared spectrometer in a simple cuvette-based testing setup. The intensity and absorption plots gathered of different ethanol and water mixtures were then analyzed using proper orthogonal decomposition (POD) to break down the data into modes which represent specific variables of interest, specifically ethanol concentration or alcohol by volume (ABV). The modes were then utilized to find mode constants to represent the data taken from cuvette samples which were …

Numerical Investigation Of Wind Disturbance Around A Multirotor Uav In Crosswind And Vertical Flight, Garrison Page

Theses and Dissertations--Mechanical and Aerospace Engineering

Uncrewed Aerial Vehicles (UAVs) are being increasingly utilized in a wide range of research applications, especially in meteorology. This is due to such factors as their ease of use, maneuverability compared to other forms of data collection, and for rotor- craft, the ability to hover. However, the rotorwash generated by UAVs can introduce significant disturbances, potentially affecting measurement accuracy from sensors. While several studies have investigated the rotorwash of individual UAVs utilizing Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD), there is limited exploration into how different rotor configurations and external wind conditions influence regions of turbulent flow around …

Growth Kinetics And Stability Of Metal Halide Perovskite Nanocrystals: Influence Of Stirring Speed And Water Exposure, You-Lin Huang

Theses and Dissertations--Mechanical and Aerospace Engineering

Cesium lead bromide (CsPbBr₃) perovskite nanocrystals (NCs) have garnered significant interest due to their exceptional optoelectronic properties, including high photoluminescence quantum yield, tunable bandgap, and excellent carrier dynamics. These attributes make them promising candidates for applications in light-emitting diodes, photovoltaics, and sensing technologies. However, optimizing their synthesis and improving their environmental stability remain critical challenges. This dissertation explores the growth kinetics of CsPbBr₃ NCs, focusing on the effects of stirring speed and water exposure on their structural and optical properties.

The synthesis of CsPbBr₃ NCs was performed using both mechanochemical (MC) and antisolvent methods, enabling an …

Acoustic Characterization Of A Quadcopter Using A Test Stand, Jared Schmal

Theses and Dissertations--Mechanical and Aerospace Engineering

Unmanned Aerial Vehicles (UAVs) with multirotor propulsion and control, commonly called drones or multicopters, generate a complex acoustic field that is not entirely understood. Many components and their interactions contribute to the overall noise level and behavior of the acoustic field. However, performing acoustic measurements on a multicopter in a confined space, such as a small anechoic chamber, can be an extremely difficult and time-consuming process. A test stand was developed to allow for rapid and safe acoustic measurements in a controlled environment. The design, development, and initial measurements are discussed. The performance and acoustic response are assessed to examine …

Analysis Of Closed-Loop Dynamical Systems Using Relu Nns, Pouya Samanipour

Theses and Dissertations--Mechanical and Aerospace Engineering

This thesis develops a framework for analyzing the stability and invariance properties of closed-loop dynamical systems whose dynamics are derived from neural networks with rectified linear units (ReLUs). The ReLU neural network defines continuous piecewise affine (PWA) functions, which makes them ideal for analysis using polyhedral geometry and optimization techniques. To begin, we introduce two exact algorithms for enumerating polytopic regions of affine behavior induced by ReLU networks: a half-space-based method that checks the feasibility of activation patterns and a geometric vertex-based method. Using these methods, we are able to perform precise region-wise analysis, and these methods serve as the …

In-Situ Informed Modeling And Characterization Of Friction And Built-Up Edge In Machining Of Aerospace Alloys, Avery Hartley

Theses and Dissertations--Mechanical and Aerospace Engineering

Machining is by no means a new manufacturing process. However, it is separated from other traditional deformation processes by its extreme temperatures and strain rates. The function and life of a multitude of products and mechanical components are dependent on the material properties induced by changing the surface through machining. Furthermore, the tools used within machining are often expensive and material reserves are sparse. The understanding the mechanics of the machining process, especially related to the friction of the tool and workpiece, helps to further the life of tools and parts to minimize economic and environmental impact.

Current friction modeling …

Engineering A Novel Solvent Regenerator That Leverages Electrochemically Induced Ph Swings For Direct Air Capture And Hydrogen Generation, Emmanuel Aluhunmile Ohiomoba

Theses and Dissertations--Mechanical and Aerospace Engineering

Direct Air Capture (DAC) is considered to be a key component for achieving global net-negative emissions. However, to capture CO₂ at the low concentrations in the atmosphere requires materials with high affinity for CO₂. This makes the solvent-based chemical approach for DAC more applicable compared to physical approaches. Nonetheless, regenerating the capture solvent presents a significant challenge due to high heat requirements for thermal decomposition of carbonates. Leveraging electrochemical principles provides an opportunity to simplify the regeneration process, thus, this work focuses on engineering an electrochemical solvent regenerator for recovering alkaline solvents for DAC, with co-production of …

Machining-Induced Residual Stress Modeling Using Physics-Informed Neural Networks, Md Mehedi Hasan

Theses and Dissertations--Mechanical and Aerospace Engineering

Process-induced residual stress (RS) plays a critical role in determining the structural integrity, fatigue life, corrosion resistance, and dimensional stability of manufactured components. Tensile residual stress can be harmful to the machined workpiece by lowering fatigue strength, while compressive residual stress helps to prevent such issues. Therefore, accurate prediction and control of machining-induced residual stresses are essential for optimizing manufacturing processes and enhancing component performance. However, existing modeling approaches—empirical, analytical, and numerical—often have limited predictive accuracy, demand extensive calibration, or involve high computational costs. Traditional finite element analysis (FEA) provides modeling insights but is constrained by its high computational cost …

Scaling Investigations Of Wall-Bounded Turbulent Flow, Nikolay Gustenyov

Theses and Dissertations--Mechanical and Aerospace Engineering

This dissertation investigates the scaling behavior, structural organization, and modeling of turbulence in wall-bounded flows across a wide range of Reynolds numbers and surface conditions. Through high-resolution experimental studies in zero-pressure- gradient turbulent boundary layers and pipe flows (2000 < Reτ < 38 200), the wall- dependence of turbulent length scales is examined with a focus on both small-scale dissipative motions and large-scale structures. When external intermittency is properly accounted for, dissipative motions are shown to obey inner scaling even in outer- scaled regions, while large-scale motions exhibit outer scaling behavior deep into the inner region. These findings are consistent across internal (pipe) and external (boundary layer) flows and are reflected in distinct features of the longitudinal wavenumber spectrum.

The dissertation also explores the development of a turbulent boundary layer transitioning from a smooth solid wall to a liquid surface. An internal boundary layer forms in response to stochastic surface waves, resulting in increased turbulence intensity and displaced momentum relative to solid-wall cases. Near the liquid surface, turbulence generation aligns with wavenumbers corresponding to the surface waves, introducing distinct small-scale …

Fluid Pathways For Enhanced Mass Transfer In The Micro Regime: Applications In Novel Pumpless Redox Flow Cell And Zinc Finger Protein-Based Dna Detection, Shaikh Al Mahmud Bhuiyan

Theses and Dissertations--Mechanical and Aerospace Engineering

Precise fluid transport through microscale geometries can help optimize electrochemical and biochemical processes by maximizing the mass transfer rate of reactants. By introducing intricate structural features inside microchannels, it is possible to manipulate the fluid motion and direct the flow towards any surface of interest. In this study, we have demonstrated that rationally designed fluid pathways can improve the performance of electrochemical and biochemical systems.

The emergence of additive manufacturing has enabled rapid fabrication of robust structures with intricate features to guide fluid motion. However, their application in nonaqueous electrochemical systems has been limited due to their interaction with organic …

Direct Numerical Simulation Of Pulsating Flow In Curved Pipes: Insights Into Aortic Dissection In Humans, Gokul Anugrah Gopakumar

Theses and Dissertations--Mechanical and Aerospace Engineering

This dissertation investigates the hemodynamics of pulsating blood flow in curved vessels through direct numerical simulations (DNS), with the overarching aim of uncovering fluid dynamic mechanisms linked to the onset and progression of aortic dissection in humans. The work is structured in two parts: (i) fundamental studies in idealized geometries and (ii) preliminary investigations in patient-specific anatomies. In the first part, curved pipe models representing the aortic arch are used to isolate the effects of pulsation frequency, amplitude ratio, and curvature ratio on transitional and turbulent flow dynamics. The simulations reveal that curvature-driven centrifugal forces shift the peak velocity toward …

High-Altitude Balloon-Launched Uncrewed Aircraft System Measurements Of Atmospheric Turbulence And Qualitative Comparison With Infrasound Microphone Response, Anisa Haghighi

Theses and Dissertations--Mechanical and Aerospace Engineering

This study explores the use of a balloon-launched uncrewed aircraft system (UAS) to measure atmospheric turbulence in the troposphere and lower stratosphere using both wind velocity measurements and infrasonic acoustic energy. The UAS, a glider configured for autonomous descent along a predefined trajectory, had on board, in situ sensors to capture thermodynamic and kinematic atmospheric parameters. Additionally, it carried an infrasonic microphone to evaluate its potential for remotely detecting clear-air turbulence by capturing infrasonic waves. The system’s performance was assessed over the course of three test flights conducted in New Mexico, USA, in 2021. The descent enabled high-resolution profiling, with …

Simulation-To-Hardware Validation Of Mpc For Binary Thruster 2d Cubesat Control, Aevar Amundinusarson Oefjoerd

Theses and Dissertations--Mechanical and Aerospace Engineering

Small satellites must execute precise, fuel-limited maneuvers under strict actuation and operational constraints. Model Predictive Control (MPC) is a suitable approach because it optimizes future actions while explicitly enforcing these limits. This work evaluates (1) whether MPC can operate in real time using binary (on/off), asymmetric thrusters, and (2) whether a high-fidelity digital twin can be used to tune and validate the controller prior to hardware testing.

An MPC framework was implemented on a planar satellite prototype that floats on air bearings, operates at 16.7 Hz (60 ms period), and uses eight binary thrusters exhibiting up to 13.2% variation in …

Propagation Of Vibro-Acoustic Energy In Ducts: Measurement, Simulation, And Attenuation Studies, Caoyang Li

Theses and Dissertations--Mechanical and Aerospace Engineering

Vibro-acoustic energy propagates through heating, ventilating, and air conditioning (HVAC) systems through both airborne and structureborne paths. In this research, measurement and simulation studies are performed to better understand this propagation of energy and how to better attenuate the sound before it impacts building occupants.

First, a scaled-down experiment was developed to assist in the validation of numerical simulation models. A small source room was attached to a wooden duct with variable cross-sectional area. The sound power for both untreated and treated ductwork was measured using sound intensity scanning, and the insertion loss is the difference between untreated and treated …

Artificial Intelligence Enabled Machinery Fault Detection And Diagnosis Using Vibro-Acoustic Signals, Srinivasa Rao Ippili

Theses and Dissertations--Mechanical and Aerospace Engineering

In various industries, the early detection of faults in rotating machinery is crucial to prevent system failures and ensure customer satisfaction. Typically, vibration measurement and diagnosis are employed for fault detection, but this process faces challenges in automation due to the complexity of installing and maintaining accelerometers, particularly in end-of-line quality control or pre-installed machinery health assessments. Acoustic signals, as a form of mechanical wave, offer an alternative for monitoring machinery while in operation. Unlike accelerometers, acoustic transducers are non-contact and easy to set up, enabling real-time data collection without interrupting equipment operation. However, utilizing acoustic signals in manufacturing poses …

Measurement And Simulation Of Aeroacoustic Sources Generated By Elementary Muffler Components, Seth Donkin

Theses and Dissertations--Mechanical and Aerospace Engineering

Mufflers and silencers are commonly used to control noise from sources such as internal combustion engines and heating, ventilating, and air conditioning (HVAC) systems. In these applications, flow interacts with muffler components generating aeroacoustic noise sources. In order to measure these sources in a lab setting, specialized flow rigs are designed to isolate aeroacoustic noise sources. Flow sometimes compromises muffler performance. However, muffler performance is sometimes improved because flow can increase the attenuation of some muffler elements such as perforates. To better understand the complicated impact of flow, the University of Kentucky developed a muffler test rig to measure insertion …

Droplet Analysis Of Spray Inside A Compact Column Gas Scrubber Through Shadowgraphy, Brandon Heller

Theses and Dissertations--Mechanical and Aerospace Engineering

The shadowgraphy imaging technique was adapted to analyze the droplet field from a spray nozzle inside the gas absorption section of a compact column gas scrubber. This technique in conjunction with a developed image processing technique was able to gain statistical size information at different distances from two types of spray nozzles. The gas scrubber then ran a parametric campaign of eight operating conditions and statistical size information was captured for each case with the goal of understanding how operating conditions affect the droplet field properties. Lastly, several simulations were completed to understand how the addition of recirculation zones would …

Microstructure-Based Modeling And Simulation Via A Nonlocal Multiphysics Discrete Approach, Donglai Liu

Theses and Dissertations--Mechanical and Aerospace Engineering

Many structures in engineering are subject to multiphysics loadings or environment. Computational modeling plays a significant role to predict or evaluate the performance of these structures, especially in the scenarios where the experimental investigation is cumbersome or prohibitively expensive. Microstructure-based modeling incorporates the information of microstructures of materials in numerical models, which can provide insights about the relationship between microstructures and mate- rial properties. This research developed a microstructure-based modeling framework for coupling diffusion-deformation simulation of solids. The model is based on a recent developed meshfree method referred to as lattice particle method in the literature. In the developed model, …

Provably Safe Control For Input-Constrained Robotic Systems, Pedram Rabiee

Theses and Dissertations--Mechanical and Aerospace Engineering

This dissertation addresses challenges in control design for safety-critical robotic systems with input constraints. It focuses on developing novel control barrier function (CBF) approaches to ensure safety while optimizing performance. The work is motivated by the limitations of traditional methods in handling nonlinear systems with multiple constraints and actuator limits.

Three main contributions are presented. First, a soft-minimum barrier function is introduced, utilizing finite-time horizon predictions to create control forward invariant subsets of the safe set while respecting actuator constraints. This method is extended to multiple backup controls, which can enlarge the safe operating region.

Second, a technique for composing …

High-Fidelity Coupling For Studies Of Ablative Materials At Hypersonic Conditions, Aleksander Zibitsker

Theses and Dissertations--Mechanical and Aerospace Engineering

The development of accurate models and robust numerical tools for simulating ablative thermal protection materials (TPMs) in hypersonic flows is crucial for advancing atmospheric entry and hypersonic technologies. Traditional methods for simulating ablative materials often rely on heavy assumptions, such as equal heat and mass transfer coefficients and chemical equilibrium in the boundary layer, leading to conservative thermal protection system (TPS) designs and insufficient accuracy for certain in-flight ablation phenomena.

This work presents a high-fidelity and versatile coupled framework between hypersonic flow and material response solvers. The flow domain is modeled with an innovative overset CHAMPS NBS-Cart solver, which features …

Multiscale Fiber Remodeling In The Heart Using A Finite Element Framework, Mohammad Mehri

Theses and Dissertations--Mechanical and Aerospace Engineering

The organization of myofibers and extra cellular matrix within the myocardium plays a significant role in defining cardiac function. When pathological events occur, such as myocardial infarction (MI) or hypertrophic cardiomyopathy (HCM), this organization can become disrupted, leading to alteration in pumping performance. The current study proposes a multiscale finite element (FE) framework to determine realistic fiber distributions in the left ventricle (LV). This is achieved by implementing a stress-based fiber reorientation law, which seeks to align the fibers with local traction vectors, such that contractile force and load bearing capabilities are maximized. By utilizing the total stress (passive and …

Attrition Study Of Copper-Supplemented Iron-Based Oxygen Carrier For Chemical Looping Combustion, Neng Huang

Theses and Dissertations--Mechanical and Aerospace Engineering

Chemical looping combustion (CLC) is a promising technology that can mitigate the carbon emissions for power generation. The cost of oxygen carriers (OCs) impedes the scale up of CLC. Compared to synthetic iron-based OCs, red mud (RM), an abundant iron-based solid waste from industry, is a cost-effective choice due to its intrinsic inclusion of both inert and catalytic phases that are crucial for CLC. It was anticipated that the addition of copper oxide to RM using a mechanical mixing method that can be easily scaled up would enhance both reactivity and oxygen transport capacity (OTC), and the heat of reaction …