Mechanical Engineering Commons^™

Ultrasonic Non-Destructive Evaluation Of Additively Manufactured Polymer-Ceramic Composites, Christian Alexander Ruiz

Open Access Theses & Dissertations

Digital light processing (DLP) is an attractive additive manufacturing technique due to its ability to create ceramic parts with complex geometries. DLP uses ultraviolet light to polymerize a slurry comprised of ceramic powder and photosensitive resin in layers to create solid parts. Printing parameters such as light intensity and exposure time are critical when producing these parts. Improper parameters can lead to over or under-curing, adversely impacting print quality and strength. Samples were printed at varying layer exposure times and then tested using ultrasonics to determine the degree of conversion. Additionally, ultrasonics were used as a non-destructive technique to obtain …

Additive Manufacturing Of Composites For Sensing And Harsh Environments Application, Md Sahid Hassan

Open Access Theses & Dissertations

Composite materials are made by combining two or more materials, such as fibers and resins to create a material system that has improved mechanical and physical properties compared to its individual components. The use of 3D printing technology in composite manufacturing allows for the creation of complex and custom shapes with precise control over the placement of the materials. This makes it possible to create composite parts with enhanced performance characteristics and reduced weight. The work presented in this dissertation lies in the design and development of highly flexible impact propagation sensor through material extrusion 3D printing technique. By using …

Development Of A Prototype Satellite-Tracking Telescope For Ground-Based Spectroscopy, Charles Smith

Graduate Theses and Dissertations

Spectroscopy is the practice of determining the chemical composition of a gas through analyzing the light that is filtered by the gas. Spectroscopy is commonly used by astronomers to deduce the atmospheric composition of planets. This process is done by initially measuring the spectrum of light from the star that the planet orbits, and then measuring it again once the planet is in between the observer and the star. The spectrum light that is filtered out is dependent on the chemical composition of the gas, and so this information can be used to determine the chemical composition of the atmosphere …

An Optimization Procedure To Design Nozzle Contours For Hypersonic Wind Tunnels, Omar Antonio Dominguez

Open Access Theses & Dissertations

Supersonic wind tunnels allow scientists and researchers to evaluate and analyze the behaviors of objects under real-life conditions when subjected to supersonic speeds. One of the main complexities when building a wind tunnel is the design of the convergent-divergent nozzle that is used to produce high-speed and high-quality flows. To achieve supersonic speeds, this nozzle adopts a specialized approach that incorporates the complexities of flow compressibility. The compressible effect is accurately evaluated using isentropic relations, allowing for precise determination of stagnation pressure and temperature, and static pressure and temperature relevant to the desired Mach number. Isentropic equations used to define …

Enhancing Damage Tolerance Of The Constituents Of Sandwich Composites, Zackery Nieto

Open Access Theses & Dissertations

Composite structures have become a lucrative material choice for researchers throughout various sectors such as green energy, arctic travel, and aerospace application due to their light weight, high-bending to stiffness ratio, and job tailorable applications through material selection. With the increasing demand for new and better composite technologies growing each year it is imperative to investigate new materials and analytical options to help the composite field as a whole grow. In this report various materials and statistical applications have been studied regarding the constituent materials in sandwich composites. For core materials an additive manufactured photoreactive resin has been characterized for …

Capabilities Of Sintered Silver As A High Temperature Packaging Material, Bakhtiyar Mohammad Nafis

Graduate Theses and Dissertations

With electrification progressing across many sectors including industry, automotive and aerospace, the power density requirements are changing. The increased power density results in higher and higher ambient temperatures that electronics are exposed to. The response has been to move towards wide bandgap (WBG) semiconductor devices that can withstand much greater temperatures and can operate at much higher voltages than silicon. Additionally, these WBG devices deliver low drain-source on resistance (RDS_on) capabilities, enabling high current power modules that increase power density even further. This also requires the packaging to evolve in order to withstand the new requirements. As a result, researchers …

Development And Biomechanical Analysis Toward A Mechanically Passive Wearable Shoulder Exoskeleton, Seyyed Morteza Asgari

Doctoral Dissertations

Shoulder disability is a prevalent health issue associated with various orthopedic and neurological conditions, like rotator cuff tear and peripheral nerve injury. Many individuals with shoulder disability experience mild to moderate impairment and struggle with elevating the shoulder or holding the arm against gravity. To address this clinical need, I have focused my research on developing wearable passive exoskeletons that provide continuous at-home movement assistance. Through a combination of experiments and computational tools, I aim to optimize the design of these exoskeletons.

In pursuit of this goal, I have designed, fabricated, and preliminarily evaluated a wearable, passive, cam-driven shoulder exoskeleton …

Deep Reinforcement Learning For The Design Of Structural Topologies, Nathan Brown

All Dissertations

Advances in machine learning algorithms and increased computational efficiencies have given engineers new capabilities and tools for engineering design. The presented work investigates using deep reinforcement learning (DRL), a subset of deep machine learning that teaches an agent to complete a task through accumulating experiences in an interactive environment, to design 2D structural topologies. Three unique structural topology design problems are investigated to validate DRL as a practical design automation tool to produce high-performing designs in structural topology domains.

The first design problem attempts to find a gradient-free alternative to solving the compliance minimization topology optimization problem. In the proposed …

Nonlinear Finite Element Model For Functionally Graded Porous Circular/Annular Micro-Plates Under Thermal And Mechanical Load, Enrique Nava Munoz

Masters Theses

A nonlinear finite element model for micro circular/annular plates under thermal and mechanical loading is developed using a third order shear deformation theory. In the kinematic assumptions, the change of plate thickness is allowed and no transverse shear strains are considered on the top and bottom surfaces. A power-law distribution is utilized to account for variations of two constituents through the thickness of the plate. Three different types of porosity distributions are considered. The strain gradient effect in micro scale structures is considered using the modified couple stress theory. The dynamic version of the principle of virtual displacements is used …

Husker Motorsports Active Drag Reduction System, Creighton Hughes, Evan Killian, Micah Busboom, Aj Johnson, Jude Steffen

Honors Theses

Formula SAE is a multifaceted competition that involves student teams designing and competing with an open-wheel style race car. There are 5 different dynamic events included in the competition. Each event requires a unique aerodynamic setup to have the best performance possible. This design project focuses on a drag reduction system (DRS) that will improve aerodynamic performance, resulting in faster lap times and increased competitiveness. Key features include a direct electronic actuation mechanism that will allow the rear wing to be adjusted during a race. The benefits of the DRS system, include increased speed, improved handling, and greater fuel efficiency …

Thermal Atomization On Superhydrophobic Surfaces Of Varying Temperature Jump Length, Eric D. Lee, Daniel Maynes, Julie Crockett, Brian D. Iverson

Faculty Publications

This paper presents an experimental study of drop impingement and thermal atomization on hydrophobic and superhydrophobic (SH) surfaces. Superhydrophobic surfaces having both microscale and nanoscale geometry are considered. Microscale SH surfaces are coated with a hydrophobic coating and exhibit micropillars and cavities which are classified using the surface solid fraction and center to center pitch. The solid fraction and pitch values explored in this study range from 0.05-1.0 and 8-60 μm respectively. Nanoscale textured surfaces are created by applying a blanket layer of carbon nanotubes. Both types of surfaces are further classified by a temperature jump length (λ …

Thermal Resistance Characterization Of High-Voltage Sic Power Module, Landon Lemmons

Mechanical Engineering Undergraduate Honors Theses

Researchers within the University of Arkansas Electrical Engineering Research Department have embarked on a project aimed at enhancing the thermal performance of high-voltage power modules. To aid in the progress of this project, the design, and development of a thermal tester device are needed. The primary objective of this device is to determine the various thermal properties of high-voltage power modules that the electrical engineering department has developed. Additionally, the project aims to facilitate electrical loading tests on power modules and provide researchers with the means to calibrate the power module in terms of thermal load. This project also possesses …

Development, Implementation, And Optimization Of A Modern, Subsonic/Supersonic Panel Method, Cory D. Goates

All Graduate Theses and Dissertations, Fall 2023 to Present

In the early stages of aircraft design, engineers consider many different design concepts, examining the trade-offs between different component arrangements and sizes, thrust and power requirements, etc. Because so many different designs are considered, it is best in the early stages of design to use simulation tools that are fast; accuracy is secondary. A common simulation tool for early design and analysis is the panel method. Panel methods were first developed in the 1950s and 1960s with the advent of modern computers. Despite being reasonably accurate and very fast, their development was abandoned in the late 1980s in favor of …

Enhanced Biofouling Properties Of Polyethersulfone Membranes Using Multi-Functional Thermo-Responsive Polymers For Ultra-Filtration Applications, Homa Ghasemi

Theses and Dissertations

The accumulation and growth of microorganisms on a membrane surface, known as membrane biofouling, has been a significant issue in the effective use of membrane technology for water and wastewater treatment. To overcome these challenges, this study aimed to modify the surface of a polyethersulfone (PES) membrane through the use of a multi-functionalized thermo-responsive polymer. The primary objectives of chemical treatment on membrane surfaces are to enhance surface hydrophilicity and provide anti-bacterial/biocidal properties.To evaluate the effectiveness of these modifications, the performance of the modified membranes was tested for their ability to resist biofouling through filtration of bovine serum albumin (BSA), …

Model Of Surface Waves On A Viscoelastic Material In A Cylindrical Container With Edge Constraints, Phillip Wilson

All Theses

A theoretical model is developed for the resonant frequencies and mode shapes of pinned edge surface waves on a viscoelastic fluid contained in a finite depth cylindrical container. A boundary integral approach is used to map the governing equations to the domain boundary. The surface waves obey an eigenvalue operator equation that depends on four dimensionless parameters: the cylinder aspect ratio, the Bond number, the Ohnesorge number, and the elastocapillary number. A solution is constructed using a Rayleigh-Ritz variational procedure over a constrained function space, which is able to effectively incorporate the pinned edge boundary condition. Mode shapes are defined …

Design Space Visualization And Exploration For Many Goal Problems Under Uncertainity, Niharika Balaji

Theses and Dissertations

ABSTRACT

Designing a complex engineered system is challenging due to many conflicting goals, uncertainties, and multiple interactions. Traditional optimization approaches often yield single-point solutions, which may not be suitable for early design stages due to their susceptibility to changes in conditions and uncertainties. To address this challenge, a satisficing approach is employed. This approach enables designers to effectively navigate the design space and identify satisficing solutions that balance conflicting goals in the face of uncertainties and changes in conditions. From a systems design perspective, we view design as an iterative process that involves making informed decisions based on available information …

Underwater Image Enhancement: A Pipeline For Underwater Computer Visions, Humberto Lebron Rivera

Theses and Dissertations

Ocean exploration has surged in popularity and significance in recent years, including diverse areas like maritime archeology, underwater resources, and submerged structure inspection. The activities mentioned above heavily depend on vision and imagery, a challenge in the unpredictable marine world. This thesis presents a conditional generative adversarial network model for image-to-image translation problems. We designed and trained the model with the end goal of enhancing underwater images. Five metrics were employed for validation to quantify our model’s resulting enhanced images. By doing so, we aim to establish a pipeline that can leverage aerial computer vision algorithms for marine applications.

Our …

Deep Learning And Generative Ai Approaches For Automated Diagnosis And Personalized Treatment: Bridging Machine Learning, Medicine, And Biomechanics In Predicting Tissue Mechanics And Biomaterial Properties., Yasin Shokrollahi

Theses and Dissertations

Machine learning, particularly deep neural networks, has demonstrated significant potential in predicting high-dimensional tasks across various domains. This work encompasses a detailed review of Generative AI in healthcare and three studies integrating machine learning with finite element analysis for predicting biomechanical behaviors and properties. Initially, we provide a comprehensive overview of Generative AI applications in healthcare, focusing on Transformers and Denoising Diffusion models and suggesting potential research avenues to address existing challenges.

Subsequently, we addressed soccer-related ocular injuries by combining finite element analysis and machine learning to predict retinal mechanics following a soccer ball hit rapidly. The prediction errors are …

Extremum Seeking Control Algorithms For Extremely High Frequency Antenna System Pointing, Scott Shore

Mechanical Engineering ETDs

The research examines the application of extremum seeking control (ESC) algorithms to ground station antenna pointing for extremely high frequency (EHF) communication systems. ESC algorithms search for local maxima or minima by locating where an objective function gradient goes to zero. With wireless communication expanding into higher frequencies, the ground station pointing requirement is increasing. ESC presents a method which utilizes available equipment and information to perform ground station pointing. Additionally, ESC algorithms do not rely on assumptions or approximations needed for other techniques. The dissertation demonstrates ESC algorithm feasibility for the ground station pointing problem, benchmarks the ESC algorithms …

Physics-Based Machine Learning Methods For Control And Sensing In Fish-Like Robots, Colin Rodwell

All Dissertations

Underwater robots are important for the construction and maintenance of underwater infrastructure, underwater resource extraction, and defense. However, they currently fall far behind biological swimmers such as fish in agility, efficiency, and sensing capabilities. As a result, mimicking the capabilities of biological swimmers has become an area of significant research interest. In this work, we focus specifically on improving the control and sensing capabilities of fish-like robots.

Our control work focuses on using the Chaplygin sleigh, a two-dimensional nonholonomic system which has been used to model fish-like swimming, as part of a curriculum to train a reinforcement learning agent to …

Improving Sizing Resolution Of Particle Impactors In The Nanoparticle Range, Shivuday Kala

All Dissertations

The application of particle size measurement extends across many fields: air quality measurement, pharmaceutical studies, paint and coating production, and nanoparticle formulation to name a few. Therefore, accurate measurement of nanoparticles is critical to aerosol science. While devices currently exist that can size and count nanoparticles such as electrical mobility spectrometers, dynamic light scattering devices, and small angle X-ray scattering devices, their high costs, complex operation, and lack of outdoor usability, restrict their use in practical applications. Among the devices that can size aerosols down to the nanoscale, cascade impactors stand out because of their robustness, relatively simple design, low …

Experimental Analysis Of Nonlinear Wave Propagation In Bistable Mechanical Metamaterials With A Defect, Samuel R. Harre

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Mechanical metamaterials built up of compliant units can support the propagation of linear and nonlinear waves. A popular architecture consists of a one-dimensional chain of bistable elements connected by linear springs. This type of chain can support nonlinear transition waves that switch each element from one stable state to the other as they propagate along the chain. One way to manipulate the propagation of such waves is via introduction of a local inhomogeneity, i.e., a defect in the otherwise periodic chain. Recent analytical and numerical work has shown that based on its initial velocity, a transition wave may be reflected, …

An Icfd Fluid Model Used In A Mash Tl-6 Vehicle Model, Md Zunayed Habib

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

The objective of this thesis was to develop an ICFD finite element model of a partially filled deformable container suitable for impact scenarios. This model will be later incorporated into the existing TL-6 vehicle model, which is a tractor-tank trailer vehicle model. Previous finite element fluid models for the TL-6 vehicle used an elastic fluid model, which could not predict the fluid behavior correctly.

A study was conducted on the ICFD modeling and an improved ICFD model has been developed using the LS-DYNA, a finite element analysis software. Different properties and parameters of the fluid and the container were adopted …

Characterization Of Interlayer Laser Shock Peening During Fused Filament Fabrication Of Polylactic Acid (Pla), Fabien Denise

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

The field of additive manufacturing (AM) has gained a significant amount of popularity due to the increasing need for more sustainable manufacturing techniques and the adaptive development of complex product geometries. The problem is that AM parts routinely exhibit flaws or weaknesses that affect functionality or performance. Over the years, surface treatments have been developed to compensate certain flaws or weaknesses in manufactured products. Combining surface treatments with the modularity of additive manufacturing could lead to more adaptable and creative improvements of product functions in the future. The current work evaluates the feasibility of pursuing a new research axis in …

Effects Of Simultaneous Co2 Addition To The Fuel And Oxidizer Streams On Soot Formation In Co-Flow Diffusion Ethylene Flame, Yu Yang, Shu Zheng, Yuzhen He, Hao Liu, Ran Sui, Qiang Lu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Soot formation in a co-flow diffusion ethylene flame with the addition of CO₂ to the fuel (the CO₂-F), oxidizer (the CO₂-O), and fuel/oxidizer (the CO₂-F/O) streams was numerically and experimentally investigated in this study. The effects of different CO₂ addition ways on soot inception, soot condensation, H-abstraction-C₂H₂-addition (HACA) and oxidation by O₂/OH processes, were quantitatively analyzed by introducing the integrated reaction rates over the whole computational domain. The simulated and experimental results showed that the CO₂-F/O was the most effective in inhibiting soot formation …

The Role Of Atomic Layer Deposited Coatings On Lithium-Ion Transport: A Comprehensive Study, Yufang He, Hiep Pham, Xinhua Liang, Jonghyun Park

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Use of Ultrathin Film Coatings Prepared through Atomic Layer Deposition (ALD) Has Become Widespread for Improving Lithium-Ion Diffusivity of Active Particles, Which Plays a Crucial Role in Determining the Rate Capability of Lithium-Ion Batteries (LIBs). in This Study, the Impact of ALD Coating Thickness on Ionic Diffusivity in CeO2-Coated LiMn2O4 (LMO) Cathode Particles is Comprehensively Investigated through First-Principles Calculations by Focusing on the Trade-Offs between the Physical Properties of the Film and its Impact on the Diffusivity of Ions. Our Findings Indicate that Several Physical Factors Affect the Diffusivity of the Coating, Including the Crystal-Amorphous Structure that Depends on …

Quantifying The Effect Of Stable Stratification On Low-Reynolds Number Flow Past A Horizontal Cylinder, Holland Kartchner

All Graduate Theses and Dissertations, Fall 2023 to Present

In this research, we study the behavior of flow around a cylinder in the presence of stable stratification, which refers to variations in density throughout the fluid. This phenomenon is observed in natural and industrial settings. We use computer simulations to analyze how stratification affects the flow patterns created by the cylinder. Specifically, we investigate situations where the stratification is perpendicular to the flow direction, and the wake exhibits two-dimensional characteristics. We use spectral-element method based computational fluids dynamics to simulate the phenomena. During the simulations, we vary two important parameters: the Densimetric Froude Number (Fr) and the …

Estimated Aerodynamic Forces And Moments And Optimal Orientation Of The V-Bat Airframe During Vertical Landing In Gusty Conditions, Parker C. Carter

All Graduate Theses and Dissertations, Fall 2023 to Present

Ship based Unmanned Air Systems (UAS) are an important tool used by the United States Navy for situational awareness and short-range operations. Naval UAS are used to provide real-time intelligence, surveillance, reconnaissance, and target-acquisition while being low cost, mission flexible, and safe. Unfortunately UAS suffer disadvantages with respect to adverse environmental conditions caused by the air being displaced by the ship. The accumulation of one or more adverse conditions is known as airwake. To counteract the effects of airwake, the objectives of this work are to first evaluate the effect of forces and moments during the vertical landing phase of …

Viscosity Of Adsorbent Slurries For Washcoating Applications, Nitish Chauhan

Theses and Dissertations

The viscosity of adsorbent slurries is pivotal in understanding their rheological behavior, yet, the research on adsorbent slurry viscosity has been limited. This study addresses this gap by analyzing porous and non-porous solutes' behavior in solvents and then applying it to the washcoating adsorbents on ceramic substrates. By examining MIL-101 (Cr), glass beads, silica nanoparticles, and Titania, the study aims to comprehend the viscosity variations of each solute in the solvents, water and ethanol. A key observation from this study was the significant role of wetting in determining viscosity, as initial results found that MIL-101 (Cr) exhibited the highest viscosity …

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 …