Mechanical Engineering Commons^™

Integrated Experimental, Numerical, And Machine-Learning Framework For The Analysis Of Spray Dynamics In Diesel And Gasoline Direct-Injection (Gdi) Engines, Yassine El Marnissi

Theses and Dissertations

The regulation of diesel and gasoline direct injection (GDI) during cold starts has become subject to stricter numerical limits by both the Environmental Protection Agency (EPA) in the US and the European Commission (EC). For diesel engines, the EPA’s Clean Trucks Plan (Model Year 2027+) sets a certification NOₓ limit of 0.035 g/bhp-hr and an in-use fleet average limit of 0.050 g/bhp-hr, along with a PM limit of 0.005 g/bhp-hr, representing an 82.5% reduction in NOₓ compared to the former 0.2 g/bhp-hr standard. For gasoline engines, US standards regulate cold-start pollutants such as hydrocarbons (HC) ranging from 0.03 to 0.08 …

Investigation Of The Flow Field Morphology Of Film Cooling In Supersonic Flow, Umberto Sandri, Massimiliano Ferro, Alessio Picchi, Antonio Andreini, Bruno Facchini, Marc D. Polanka

Faculty Publications

Film cooling is widely implemented in highly thermally stressed gas turbine components. Its performance has been extensively investigated for several decades and many results are available in the literature. In conventional gas turbines, regions of supersonic flow are not prevalent and should generally be avoided. For this reason, results relative to film cooling in supersonic flow are limited. Nevertheless, a new interest related to Rotating Detonation Combustors (RDC) and supersonic turbines is growing. The implementation of those engine components in a gas turbine is likely to need film cooling for thermal protection. In this context, it becomes crucial to gain …

Dynamic Urban Air Mobility Systems Modeling And Simulation, Amer M. Ibrahim

Tennessee State University Alumni Theses and Dissertations

The use of electrical vertical takeoff and landing (eVTOL) aircraft to provide efficient, high-speed, on-demand air transportation within a metropolitan area is an increasingly popular topic, which is expected to bring fundamental changes to cities. The concept of Urban Air Mobility (UAM) has the potential to make meaningful door-to-door trip time savings compared with other transportation. The capability to manage many of these eVTOL aircraft safely in a congested urban area presents an unprecedented challenge in air traffic management. In order to enable safe and efficient autonomous on-demand free flight operations in UAM, a computational guidance algorithm with collision avoidance …

Influence Of Build Plate Location On Tensile Properties And Residual Stresses In Lpbf-Fabricated Stainless Steel 316 Components, Yareli Zelaya Pavón

Honors Program Theses and Research Projects

Additive manufacturing (AM), particularly Laser Powder Bed Fusion (LPBF), enables rapid production of complex metal components with minimal waste. Stainless Steel 316 (SS316) is widely used in engineering applications due to its corrosion resistance and mechanical reliability. This study investigates the influence of build plate location on tensile properties and residual stresses in LPBF-fabricated SS316. Twelve tensile specimens and nine unsupported bridge structures were fabricated at different build plate positions using a “machine model.” Tensile testing provided stress-strain data to evaluate peak stress, elastic modulus, and strain at break, while bridge curvature measurements quantified residual stress through warping. Results indicate …

Development And Validation Of 2nn-Meam Interatomic Potential For Sc And Al-Sc Alloys Thermodynamics Solidification And Intermetallic Ordering, Avik Mahata

Mechanical Engineering Faculty Publications

We present a second-nearest-neighbor Modified Embedded Atom Method (2NN–MEAM) potential for Scandium (Sc) and Aluminum-Scandium (Al–Sc) alloys that unifies cohesive, thermodynamic, and solidification behavior within a single transferable framework. The Sc component accurately reproduces cohesive energy, lattice constants, defect energetics, and the experimental melting point obtained from two-phase coexistence, demonstrating reliable description of both hcp and liquid phases. The Al–Sc binary interaction parameters were fitted using the L1₂–Al₃Sc reference and benchmarked against first-principles and calorimetric data. The potential reproduces the strong negative formation enthalpy of Al₃Sc (–0.45 eV atom⁻¹), correct relative stability …

Advancing Sustainable Co2 Mitigation: Experimental And Computational Analysis Of Thermal Carbon Chitosan Sorbent For Automotive Exhaust Capture, Dalia A. Ali Dr., Amir Ahmed Elgamal Eng., Rania Rushdy Moussa Dr.

Chemical Engineering

This study investigated the efficiency of thermal carbon chitosan (TCCS) sorbent for CO2 capture from vehicle exhaust emissions within a designed adsorption system. TCCS was synthesized and meticulously characterized using a series of analytical techniques, including Brunauer-Emmett-Teller (BET) surface area analysis, Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Ther- mogravimetric Analysis (TGA), Energy Dispersive X-ray Spectroscopy (EDX), and Differential Scanning Calo- rimetry (DSC). The TCCS adsorbent showed high thermal stability and a heating value (HHV) of 23.5 MJ/kg. Adsorption isotherm study demonstrated that the maximum capacity of CO2 adsorption is 0.084 kg.CO2/kg. TCCS, as well …

Tunable Phase-Change Metasurfaces Coupled With Mid-Infrared Molecular Vibrations, Haotian Tang, Liliana Stan, David A. Czaplewski, Xiaodong Yang, Jie Gao

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Chiral optical meta surfaces have emerged as a promising platform in coupling with molecular vibrational fingerprints through the enhanced light-matter interaction under different circularly polarized light illumination. This work reports the mode coupling between the mid-infrared phonon vibrations of polymethyl methacrylate (PMMA) molecules, and the thermally tunable chiral meta surfaces based on the phase-change material Ge₂Sb₂Te₅ (GST-225). Phase-change chiral meta surfaces with high circular dichroism (CD) in absorption and tunable plasmonic resonance in the frequency range of 48-56 THz are demonstrated, which covers the phonon vibrational frequency of PMMA molecules at 52 THz. The mode splitting features are observed in …

Advancing Radiation Shielding For Human Space Exploration, Bryan Trejo, Lea Scott, Eduardo Farfan

Symposium of Student Scholars

Beyond the safety of the Earth's magnetic field, out into the treacherous reaches of space, lies a harsh environment of radiation. This study examines radiation shielding strategies for crewed spacecraft operating in various environments, including Mars transit and deep space. Within these environments, ionizing radiation remains a critical challenge to long-duration, crewed space travel. Galactic Cosmic Rays (GCR), high-energy protons and heavy nuclei originating outside our solar system, as well as Solar Particle Events (SPE), highly energetic protons ejected continuously during the 11-year solar cycle, are all analyzed in their unique interactions with spacecraft material and biological tissues. Shielding to …

A Review Of Waste Heat Sources For District Heating, Olamide Opadokun, Yong Tao, Julian Lamb

Mechanical Engineering Faculty Publications

As the world's energy needs rise, carbon emissions and climate change become a bigger concern. Therefore, there is a growing need for cleaner energy sources as well as higher levels of energy efficiency. Building energy is of great interest to researchers and policymakers, as it accounts for about a third of global energy consumption, and this is projected to rise as more people gain access to higher incomes and improved amenities. For over a century, district energy systems have proved to be an efficient means of providing thermal energy to buildings, and developments in district heating have enabled the use …

Study On The Knock Resistance Offered By Thermally Stratifying Water Injections In A Single Cylinder Spark Ignition Engine, Aditya Datar

All Theses

Stochastic end-gas autoignition in SI engines, commonly called ‘knock’, limits attainable engine efficiencies. Multiple pathways to extend SI engine operation into knock-limited regions have been studied, including direct water injection (DWI). This study employs single-cylinder engine experiments and modeling to investigate the knock resistance offered by compression stroke water injections, which have shown to thermally stratify the cylinder in HCCI. In SI, thermally stratifying injections are expected to forcibly widen the cylinder temperature distribution by preferentially cooling the cylinder periphery. The end-gas is in the cylinder periphery; therefore, a cooler end-gas would result in longer ignition delays, thus providing knock …

Machine Learning-Enabled Safety-Critical Model Predictive Control For Uncertain Dynamical Systems, Hossein Nejatbakhsh Esfahani

All Dissertations

This dissertation explores the interactions between Model Predictive Control (MPC), Safety-critical Control, and Artificial Intelligence (AI)/Machine Learning (ML) methods, with a particular focus on Reinforcement Learning (RL) and Bayesian Optimization (BO). We then leverage AI/ML to address several challenges in the control design and safe operation of uncertain dynamical systems. In many applications, ranging from autonomous vehicles and robotics to energy systems and industrial processes, ensuring safety is as essential as satisfying control objectives. The use of Control Barrier Functions (CBFs) within the MPC framework recently has emerged as a powerful tool to guarantee safety by enforcing constraints in optimal …

Capillary Imbibition Of Shear-Thinning Xanthan Gum Solutions, Aimee Sayster

All Theses

Capillary rise in confined geometries plays a critical role in numerous natural and industrial processes. While classical models such as the Lucas–Washburn equation accurately describe the dynamics of Newtonian fluids, they fail to capture the complex behavior of shear-thinning, non- Newtonian fluids whose viscosity varies with shear rate. This research investigates the capillary rise dynamics of shear-thinning xanthan gum polymer solutions in capillary tubes. The rheological behavior of each fluid is characterized using the Ellis model, which accounts for shear-thinning effects through three key parameters: zero-shear viscosity μ0, characteristic shear stress τ1/2 and viscosity index α. Experimental data was collected …

Computational Fluid Dynamics Based Optimization Method Applied To Hydrokinetic Turbine Devices, Stuart Glenn Fletcher

Graduate Theses and Dissertations

This thesis presents a computational investigation of optimal kinematic operating parameters governing various hydrokinetic turbines (HKT) systems for the use of power generation within river and tidal environments. Two separate studies are performed. The first study investigates optimal cycle parameters for simple and complex kinematic modes governing the motion of oscillating foil energy harvesters (OFEH). An iterative gradient-ascent optimization method is used to search for local efficiency optima based on an initial set of kinematic parameters. To search the operational space for up to eight degrees of freedom (DOF), a maximin space filling condition was implemented to efficiently compute initial …

Optimal Control Of Human Exercise Using An Individualized Physiological Three-Tank Model And Dynamic Programming, Asal Lotfi

All Theses

This thesis develops a physiologically inspired three-tank model of human bioenergetics to describe and optimize fatigue and recovery during exercise. The aerobic, phosphagen, and glycogen systems are modeled as coupled reservoirs whose states constrain instantaneous power output. Building on this representation, dynamic programming is used to compute pacing strategies that respect physiological limits while maximizing task-specific goals such as peak power or total work over a fixed duration, enabling individualized, goal-driven exercise prescriptions. The three-tank dynamics are formulated in continuous time and then discretized under a zero-order-hold assumption for simulation and optimal control. Model parameters are linked to standard field …

Dynamic Modeling And Simulation Of A Power Generation Steam Rankine Cycle For A Fluoride Salt-Cooled High-Temperature Reactor Nuclear Power Plant, William R. Ton

Master's Theses

Nuclear Fluoride Salt-Cooled High-Temperature Reactors (FHRs) have the potential to greatly improve nuclear technology in terms of safety and cost. By combining molten salt coolant technology from the Molten Salt Reactor (MSR) and TRISO fuel technology from the Very High Temperature Gas Reactor (VHTR), FHRs may operate at significantly lower pressures than Light Water Reactors (LWRs) and with a more robust fuel source that is excellent at containing fission products. However, as no FHR has been built, there are still many design questions to address. This thesis uses transient computer modeling and simulation to investigate how an FHR could potentially …

Study Of Fatigue Endurance Of Alsi10mg Post Heat Treatments And Subsequently Aged At Service Temperature, Luis Alfredo Barrera

Open Access Theses & Dissertations

Laser Powder Bed Fusion (LBPF) AlSi10Mg is used in the aerospace and automotive industries for its refined microstructure and ductility compared to cast alloys. However, LPBF processes can inherently lead to defects that may act as fatigue crack initiators, such as lack of fusion, balling, and keyhole porosity. This work focuses on the analysis of high-cycle fatigue (HCF) endurance of AlSi10Mg under expected service conditions. For this study, AlSi10Mg specimens were printed on an EOS M290 LPBF system and heat-treated by stress relief (SR1), Hot Isostatic Pressing (HIP), and Hot Isostatic Pressing + T6 (HIP+T6), as per ASTM 3318. Specimens …

Powder Degradation Analysis In Reused Pure Tungsten For Electron Beam Melting (Ebm), Hernan Valenzuela

Open Access Theses & Dissertations

Additive manufacturing (AM) enables unparalleled design freedom and geometric complexity, driving its adoption in aerospace and medical fields. A major advantage of metal powder AM technologies, such as Electron Beam Melting (EBM), is its ability to reuse unused metal powder, reducing material waste and costs. However, reusing powder repeatedly alters its properties, affecting the final product. Despite its significance, research on powder degradation remains limited, primarily focusing on alloys like Ti-6Al-4V. This thesis investigates the degradation of pure tungsten powder reused over multiple Electron Beam Melting (EBM) cycles. A literature review revealed general powder-reuse mechanisms across additive manufacturing (AM) technologies …

Enhancing Tribological Performance Of Graphite Coatings Through Spray Deposition And Adhesion-Promoting Polydopamine Underlayers, Adedoyin Ayomide Abe

Graduate Theses and Dissertations

Graphite is a widely studied solid lubricant valued for its low friction and layered structure. However, its application as a durable coating remains constrained by poor adhesion to metal substrates and limited wear resistance under sliding. This dissertation presents a systematic approach to overcoming these limitations by integrating deposition process optimization with surface chemistry modification to develop scalable, high-performance graphite coatings. Unlike many prior studies that focus on polished or idealized surfaces, this work targets steel substrates with elevated roughness levels (Sa ≥ 1 μm), aligning with conditions found in practical engineering components. The first phase of research begins by …

Small Laser-Textured Dimples For Improved Tribological Performance Of Cocrmo In Artificial Hip Joints, William Basore Bennett

Graduate Theses and Dissertations

Total hip replacement is a highly successful surgical intervention that restores mobility and improves quality of life for patients with severe joint degeneration. However, the long-term durability of artificial hip joints remains limited by tribological challenges, particularly wear-related failures that can lead to osteolysis and revision surgeries. In metal-on-polyethylene bearing systems, reducing friction and wear at the interface between cobalt–chromium–molybdenum (CCM) femoral heads and ultra-high molecular weight polyethylene (UHMWPE) liners is critical to extending implant lifespan. Laser surface texturing has emerged as a promising technique to improve tribological performance by introducing micro-dimples that enhance lubricant retention and reduce asperity contact. …

Multi-Criteria Decision-Making For Sustainable Design: Stakeholder Prioritization And Methodological Comparison In Solar And E-Bike Applications, Swagath Madhu Gowda

All Theses

This thesis focuses on using Multi-Criteria Decision-Making (MCDM) methods to support sustainable product design by addressing the trade-offs between environmental, economic, and social goals. The research is presented through two studies that demonstrate how both subjective and objective decision-making approaches can guide sustainability evaluations.

The first study applies the Analytic Hierarchy Process (AHP) to assess residential solar panels by incorporating stakeholder perspectives from sustainability experts, end users, and industry professionals. Using Life Cycle Sustainability Assessment (LCSA) data, this study identifies how different stakeholder groups prioritize sustainability criteria and applies Aggregation of Individual Priorities (AIP) to combine their judgments. A one-at-a-time …

Locomotion And Balance Control In A Biped Robot With Continuum Legs And A Kangaroo-Inspired Tail, Gavin A. Platt

All Theses

This thesis work presents the design, testing, and validation of a continuum-legged biped robot equipped with a kangaroo inspired tail for enhanced stability and adaptability. Unlike traditional rigid link robots, this one expands on soft-legged robots and utilizes tendon-driven continuum robots to mimic octopus and kangaroo behavior for locomotion. The robot uses a hierarchical hybrid control framework to implement walking, obstacle avoidance, vaulting, and push recovery behaviors. To test the performance of the robot four sets of experiments were conducted to validate these systems and evaluate how they performed. The results demonstrate stable walking with rhythmic tail load transfer, effective …

Comparison Of Ti-6al-4v Powder And Bulk Specimen Properties Across Manufacturers In Laser Powder-Blown Ded, Alejandro Javier Hernandez

Open Access Theses & Dissertations

The investigation and comparison of 4 different Ti64 powder feedstocks from 3 different manufacturers was done to determine if the quality of the powder had a profound effect on the properties of the bulk specimens despite using the same processing parameters. The characteristics of the powder observed are the atomization process used, particle size distribution, flowability, and its density. The Ti64 printing parameters for directed energy deposition that were kept consistent were the feed rate, scanning speed, and laser power. Coupons with varying build angles (0-30°) were printed to measure the impact of overhangs on bulk specimen properties (ultimate tensile …

Exploratory Diver Geotechnical Equipment (Edge), Angel Villicana, Merrick Zellers, Erik Heuchert, Lucas Heuchert

Mechanical Engineering

The goal of this report is to showcase how our final Core Sampler design and prototype address the needs of Navy Divers. Geotechnical equipment for Navy divers has not been updated since the early to mid-1980s, resulting in imprecise and outdated sampling methods. The primary purpose of this project is to enhance, modernize, and redesign a tool to collect a minimally disturbed core sample of the seabed for geotechnical evaluation. This report presents the full development of our project from concept to verification and final outcomes. It begins with the statement of disclaimer, followed by a four-panel executive summary and …

Particle Migration In Non-Newtonian Fluid Flows Through Curved Microchannels, Sanskruti Ramesh Raut

All Dissertations

Innovations in microfabrication over the past three decades have enabled the development of microfluidic devices with intricate channel geometry. Microfluidic platforms offer controlled manipulation of fluids and particles by leveraging the internally induced and/or externally imposed force field(s). The demand for compact microchannel geometry has turned the attention toward curved microchannels with significantly reduced footprints. However, most of the previous studies in curved microchannels have been limited to particle migration in Newtonian fluids. The influence of fluid rheology has remained largely unexplored.

In the first part of this dissertation, we present a systematic experimental study on the influences of fluid …

Universal Systems Simulation Via Constraint Hypergraphs With Applications To Digital Twins, John Morris

All Dissertations

The characterization of systems encompasses a variety of modeling frameworks designed to capture specific behaviors and components of various system domains. Whatever the framework, the core elements of a system representation are the information of the system and a description of how that information is related. The relations in deterministic systems are functions, which, when composed to form executable processes, can be used to simulate system data. A declarative modeling framework is one that encodes mechanisms for preparing these simulations within the model structure, allowing an external agent to form the execution processes required for a given context. To date, …

Scalable Carbon-Based Electrodes For Hole-Transport Layer-Free Perovskite Solar Cells., Sharmin Akter

Electronic Theses and Dissertations

Perovskite solar cells (PSCs) have rapidly reached certified single-junction efficiencies near 26%, but deployment is still limited by operational instability, scale-up challenges, and the cost and complexity of typical device stacks. This dissertation explores a simpler, scalable approach: HTL-free PSCs using low-cost, chemically robust carbon (e.g., carbon black) counter electrodes compatible with low-temperature, solution processing. This work demonstrates how carbon-ink formulation, scalable deposition (blade vs. slot-die), and work-function-tuning additives control film quality, interfacial energetics, and device performance. Carbon inks were developed for both coating methods by systematically varying carbon-to-binder ratio, polymer chemistry, and solvent system. Among the binders screened, ethyl …

In-Field Tractor Operational Load Profile Generation In Support Of Advanced Tractor Testing In Mixedmode Power, Andrew Donesky

Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–

This dissertation addresses the need to better characterize real-world tractor power requirements across drawbar, power take-off (PTO), and hydraulic modes to support more representative tractor testing. Conventional testing protocols, such as OECD Code 2, emphasize steady-state performance under controlled high-load conditions, which do not reflect the mixed and dynamic demands of modern field operations. To address this gap, a Tractor Instrumentation System (TIS) was developed, validated, and deployed to collect high-resolution, mixed-mode power data during planting, anhydrous ammonia application, and grain cart operations. The TIS integrates physical sensors, including custom load pins, hydraulic pressure/flow sensors, and a redesigned PTO torque …

Residential Hvac Installation Faults: Field Prevalence, Drivers, And Energy Impacts, Seyed Ali Rooholghodos

Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–

Faults in residential comfort systems can have detrimental effects on the performance of the system, reducing the energy efficiency, affecting indoor comfort, and shortening equipment lifespan. Many of the faults occur at installation. However, there has not previously been a systematic and nationally representative study to indicate the prevalence of the faults, meaning the distribution of faults by fault type and fault intensity. Understanding true fault prevalence is essential to be able to identify derivers, and to assess the incremental electricity consumption of the new installation systems.

This study presents on-site data from 341 new central cooling systems—air conditioners and …

Large-Scale Experimental Study On The Impact Of Air Cleaning & Ventilation On Indoor Air Quality And Student Illness-Related Absenteeism, Daud Nosham

Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–

This large-scale randomized experimental field study investigated the effect of portable air purifiers (PAPs) on classroom’s air quality and student’s illness related absenteeism. PAPs were installed in 317 classrooms from various school districts located in Eastern Nebraska. The classrooms were randomly assigned into four conditions: three treatment conditions (T1, T2 & T3) and one control condition (device without any filter). T1 was equipped with HEPA filters, T2 added Activated Carbon (AC) layer to HEPA, and T3 further integrated Germicidal Ultraviolet (GUV) alongside HEPA and AC filters. The measured variables were carbon dioxide (CO2), fine particles (PN2.5) and coarse particles (PNcoarse), …

Experimental Characterization Of An Additively Manufactured Porous Gyroid Air-Cooled Heat Sink, Grant S. Resler

Mechanical Engineering Undergraduate Honors Theses

This paper presents the development of a ducted test facility designed to evaluate heat sinks efficiency at varying air velocities. This enables the evaluation of both heat transfer and pressure drop performance. These metrics are essential to the overall efficiency of heat sinks and help identify the optimal air velocity to achieve the desired thermal performance. A standard plate fin heat sink was used as a control for comparison to a novel heat sink. The specialized heat sink geometry was generated using nTop, a generative design software focused on additive manufacturing. This design was fabricated via Direct Metal Laser Sintering …