Engineering Commons^™

Enhancement Of Charge Transfer In Thermally-Expanded And Strain-Stabilized Tips-Pentacene Thin Films, Yang Li

Graduate College Dissertations and Theses

Two of the most critical experimentally accessible properties of small-molecule organic semiconductor materials are the charge carrier mobility, which probes charge transport, and the optical absorption spectrum which probes the energy levels of excited states. The impact of molecular packing on the optical and charge transport properties are often treated separately. However, these effects are actually linked at a fundamental level, and it is of interest to understand the interrelationship between them, as well as how they respond to strain and thermal expansion. In this thesis, we highlight the fundamental relationship between these two phenomena in 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene).

We present …

Numerical Simulations Of An Inductively Coupled Plasma Torch, Samuel Whitmore

Graduate College Dissertations and Theses

During entry into a planetary atmosphere, a blunt body (e.g. a spacecraft) traveling at hypersonic velocity creates a bow shock in front of it. In the highly energetic post shock environment, the body experiences heat transfer due to convective, chemical, and radiative processes. To protect the payload against this heating, a thermal protection system (TPS) is employed. Because a given propulsion system has a set amount of mass that it can launch to orbit, reducing the amount of mass used for TPS is desirable as this mass is freed up for mission-oriented payload. At the present, uncertainties in the flow …

Characterization Of The University Of Vermont Plasma Torch And Simulation Of Pyrolysis Gas And Plasma Interactions, Precious Jagun

Graduate College Dissertations and Theses

In previous studies done at the University of Vermont’s Inductively coupled Plasma (ICP) touch facility, the plasma conditions were always assumed to be in Local Thermodynamic Equilibrium(LTE) state. To improve the knowledge of the thermodynamic properties of the plasma conditions, in this study, experiments and analysis were conducted to determine whether or not the facility is indeed in LTE. LIF data was collected at 7mm off the exit of the quartz tube and compared with CEA simulations for the same plasma conditions. The facility was also better characterized by using LTE analyses of the absolute emission intensities to determine the …

Economic Efficiency And Carbon Emissions In Mes With Flexible Buildings, Zach Lawrence Hurwitz

Graduate College Dissertations and Theses

Multi-energy systems offer an opportunity to leverage energy conversion processes and temporary energy storage mechanisms to reduce costs and emissions during operation of campuses, cities, and buildings. With increasing options for flexibility in demand-side resources it is possible to meet demand without sacrificing comfort and convenience of MES occupants.

This Thesis develops a multi-period, linear optimization model of an MES with flexible buildings that captures nonlinearities in the efficiency of energy conversion processes. The flexible buildings are parametrized, in part, based on historical data from a college campus in Vermont, USA. The idea of the MES model is to investigate …

Utilizing Machine Learning For Respiratory Rate Detection Via Radar Sensor, Anwar Elhadad

Graduate College Dissertations and Theses

In this research, we investigate a data processing method to capture the respiratory rate of a person by utilizing a doppler radar to monitor their body movement during respiration. We utilize a machine learning algorithm with a radar sensor to capture the chest movement of a person while breathing and determine the respiratory rate according to that movement. We are using a Random Forest classifier to distinguish between different classes of pulses. After that, the algorithm constructs a sinusoidal signal representing the breathing rate of the sample. By applying this technique, we can detect the breathing rate accurately for different …

Exciton Coherence In 1d Phthalocyanine Based Organic Crystalline Thin Films, Kimngan Burrill

Graduate College Dissertations and Theses

Quantum coherence plays a vital role in the excitonic properties of organic semiconductors. Several theoretical and experimental studies have shown an unprecedented role of coherence in charge transfer and transport processes, which in turn can improve the performance of electronic devices. Specifically, an enhancement of exciton coherence size can result in fast energy transport and efficient charge separation. The ability to tailor the design and performance of organic electronics based on exciton coherence effects represents the possibility of ultrafast electronic applications in communication and information technology.

The objective of this thesis is the excitonic coherence studies of 1D crystalline thin …

A State Estimation Framework For Fatigue Monitoring And Prognosis Of Minimally Instrumented Structural And Biomechanical Systems, Benjamin Leblanc

Graduate College Dissertations and Theses

Fatigue damage is the continuous degradation of a material, primarily due to the formation of microcracks and resulting from the repeated application of stress cycles. Traditionally a fatigue analysis was performed during the structural design stage of a machine or structure; however, more recently there has been increased interest in the monitoring and prognosis of fatigue damage in existing and operating structures. In monitoring, the structure already exists and its mechanical properties can be estimated by processing sensor measurements and non-destructive testing. The traditional approach to fatigue monitoring is to carry out a visual inspection, find macroscopic cracks and then …

The Incidence Of Inverter Incidents: Understanding And Quantifying Contributions To Risk In Systems With Large Amounts Of Inverter-Based Resources, Caroline Rose Popiel

Graduate College Dissertations and Theses

Renewable energy is an important and growing percentage of the total power supply. Additionally, non-wires alternatives, which are meant to substitute for the construction of more transmission lines, are increasing in quantity as the demand for electrical power increases. Many non-wires alternatives take the form of renewable energy resources and batteries, and are distributed over short distances through neighborhoods and communities. Inverters are used to connect these DC resources to the AC grid.

However, there is growing industry concern that the disconnect function that is inherent to interconnection standards for inverter-based resources has the potential to result in a cascading …

Using Dielectric Characterization To Study Transport And Thermal Properties Of Gas/Supercritical Fluid Embedded Polymer Solution, Xiangxiao Yao

Graduate College Dissertations and Theses

Gas/supercritical fluid (SCF) and polymer mixtures are applied broadly in industry, such as rigid and light foam products for aircraft use, foamed cushion in chairs or shoes, and gas separation membranes for capturing methane from landfill gas. To understand the gas transport properties and polymer thermal properties of the mixture, we detected the dielectric properties of the mixture at two conditions and developed a novel self-designed system for high temperature and high pressure measurement.

The transport properties of physical blowing agents in polymers is viewed as a critical parameter controlling the final foam product’s foam density, cell density, and cell …

Subsurface Sensing With Shakers And Inspection Vehicles, Jonathan Robert Burton

Graduate College Dissertations and Theses

This research furthers the capability and understanding of subsurface sensing techniques. Proper inspection of small culverts can prevent roadway failures, major traffic disturbances and save tens of thousands of dollars on costly repairs. The Vermont Agency of Transportation (VTrans) has adopted a policy requiring all culverts to be inspected every 5 years, resulting in around 9,600 small culverts needing to be inspected annually. Having the proper equipment available to efficiently and effectively inspect small culverts at an affordable price is crucial for road infrastructure maintenance. In this thesis, an inspection vehicle is optimized for efficient and effective small culvert inspection. …

The Iteration Domain Reference Governor, A Constraint Management Scheme For Batch Processes, Aidan Ridner Laracy

Graduate College Dissertations and Theses

In this work, a novel combination of Reference Governors (RG) and Iterative Learning Control (ILC) to address the issue of simultaneous learning and constraint management in systems that perform a task repeatedly is proposed. The proposed control strategy leverages the measured output from the previous iterations to improve tracking, while guaranteeing constraint satisfaction during the learning process.

To achieve this, the plant is modeled by a linear system with uncertainties. An RG solution based on a robust Maximal Admissible Set (MAS) is proposed that endows the ILC algorithm with constraint management capabilities. The proposed method is applied to the Scalar …

Reference Governors: From Theory To Practice, Joycer Osorio

Graduate College Dissertations and Theses

Control systems that are subject to constraints due to physical limitations, hardware

protection, or safety considerations have led to challenging control problems that have

piqued the interest of control practitioners and theoreticians for many decades. In

general, the design of constraint management schemes must meet several stringent

requirements, for example: low computational burden, performance, recovery mechanisms

from infeasibility conditions, robustness, and formulation simplicity. These

requirements have been particularly difficult to meet for the following three classes

of systems: stochastic systems, linear systems driven by unmodeled disturbances,

and nonlinear systems. Hence, in this work, we develop three constraint management

schemes, based …

Enabling Innovation In The Energy System Transition, Bonnie Wylie Pratt

Graduate College Dissertations and Theses

Innovation in the electric sector has the potential to drive job growth, decrease environmental impacts, reduce rate payer costs, and increase reliability and resiliency. However, the traditional electric system was built to deliver a controlled flow of energy from a centralized location with maximum reliability and minimum cost. As both customer expectations and generation technologies change, new avenues for grid innovation are being explored. Residential customers, commercial and industrial clients, and electric utilities must all find a way to balance goals for decarbonization and social justice with maintaining a least cost, reliable power grid. Grounded in Geel’s energy system transition …

Knee Articular Cartilage Material Properties Estimation Through Fea, Eduardo Enrique Valdez

Graduate College Dissertations and Theses

Osteoarthritis (OA) is a debilitating disease that leads to disability and loss of quality of life. Post-traumatic osteoarthritis (PTOA) is a version of OA that develops after acute injury to the knee. PTOA is of particular interest because the disease can manifest earlier in life compared to primary OA. Several studies have shown that changes in the mechanical properties of soft tissues in the knee (articulating cartilage and menisci) are associated with worsening OA grades. Changes to the tissue mechanical properties must be considered to generate realistic computational models of individuals who have suffered traumatic injuries to the knee. Therefore, …

The Utilization Of Software Defined Radios For Adaptive, Phased Array Antenna Systems, Evan Fennelly

Graduate College Dissertations and Theses

The increased use of internet of things (IoT) devices will result in them being deployed

in a wide variety of environments and therefore warrant antenna systems that can be

adapted to improve link performance. Flexible communication technologies allow for

increased throughput, reliability, and improved efficiency in wireless channels. This

can be accomplished by implementing phased array antennas, among others. Phased

arrays create a beam that can be steered electronically, but are expensive to implement

given the many phase precise hardware components that need to be adjustable. A

software defined radio approach to beamforming can reduce this complexity for each

array …

Reference Governors For Time-Varying Systems And Constraints, Collin Freiheit

Graduate College Dissertations and Theses

Control systems are often subject to constraints imposed by physical limitations or safety considerations, and require means of constraint management to ensure the stability and safety of the system. For real-time implementation, constraint management schemes must not carry a heavy computational burden; however many of the current solutions are computationally unattractive, especially those with robust formulations. Thus, the design of constraint management schemes with low computational loads is an important and practical problem for control engineers. Reference Governor (RG) is an efficient constraint management scheme that is attractive for real-time implementation due to its low computational complexity and ease of …

Microwave Assisted Heating Of A Ferromagnetically-Doped Propellant For Small Satellites: An Efficacy Study, Thomas Joseph Heffernan

Graduate College Dissertations and Theses

In the interest of mitigating high launch costs, small satellites are often chosen as secondary payloads during launch operations. Their lower mission importance dictates stringent restrictions on the propulsion systems which can be implemented as they cannot contain combustible or toxic agents; a common solution to this prob- lem is implementation of micronozzles with cold-gas propellants in order to generate thrust. The present research explores the efficacy of leveraging microwave-assisted decomposition of a ’green’ chemical blowing agent, namely Azodicarbonamide, as a propellant for use in a microthruster. The thermal evolution of a heterogeneous ferromagnetic-doped propellant is analyzed numerically using COMSOL …

Open Source Quantitative Stress Prediction Leveraging Wearable Sensing And Machine Learning Methods, Blake Hewgill

Graduate College Dissertations and Theses

The ability to monitor physiological parameters in an individual is paramount for the evaluation of physical health and the detection of many ailments. Wearable technologies are being introduced on a widening scale to address the absence of low-cost and non-invasive health monitoring as compared to medical grade equipment and technologies. By leveraging wearable technologies to supplement or replace traditional gold-standard measurement techniques, the research community can develop a deeper multifaceted understanding of the relationship between specific physiological parameters and particular health conditions. One particular research area in which wearable technologies are beginning to see application is the quantification of physical …

A Software Defined Radio Interrogator For Passive Harmonic Transponders, Timothy Fennell Laracy

Graduate College Dissertations and Theses

Passive wireless sensors provide an opportunity for long term monitoring of remote environments. Since these devices are not battery powered, they can be deployed for an indefinite amount of time. Such devices are energized by an interrogation signal that enables them to transmit information via a return signal. Some systems (e.g., RFID) utilize the same frequency for interrogation and the return, which causes unwanted interference, particularly in cluttered environments. This work considers an interrogation system for a different class of passive devices, i.e., passive harmonic transponders. Specifically, results are presented for a single-board software defined radio (SDR) interrogation system which …

Experimental And Computational Studies Of Heat Transfer In Flexible Two-Dimensional Woven Fiber Ceramic Materials, Rodrigo Penide Fernandez

Graduate College Dissertations and Theses

Flexible thermal protection materials made from two-dimensional woven ceramics fibers are of significant interest for hypersonic inflatable aerodynamic decelerators being developed by NASA for future missions on Mars and other planets. A key component of the thermal shield is a heat-resistant outer ceramic fabric that must withstand harsh aero-thermal atmospheric entry conditions. However, a predictive understanding of heat conduction processes in complex woven-fiber ceramic materials under deformation is currently lacking. This dissertation presents a combined experimental and computational study of thermal conductivity in alumina-based Nextel-440 and silicon carbide Hi-Nicalon 5-harness-satin woven fabrics, using the hot-disk transient plane source method and …

Understanding Grain Boundary And Stress Concentration Effects On Strengthening Mechanisms In Nanotwinned Metals, Qiongjiali Fang

Graduate College Dissertations and Theses

The superior strength and large tensile plasticity of nanotwinned (nt) face-centered-cubic metals have been explained by different twin size-dependent dislocation mechanisms and their inherent strengthening/softening effects. Grain boundary (GB) plasticity generally induces softening in nanocrystalline metals; however, our current understanding of the role of GBs in plasticity of nt metals remains limited. Contradicting reports exist in literature on how twin size influences stress concentration at GB – twin boundary (TB) intersections, which facilitates dislocation nucleation. In this thesis, molecular dynamics (MD) simulations and finite element analysis (FEA) were used to study the effects of GB plasticity and stress concentrations, on …

Three-Phase Hybrid Model Of Bacterial Biofilm Growth, Xing Jin

Graduate College Dissertations and Theses

Bacterial biofilms play a critical role in environmental processes, water treatment, human health, and food processing. They exhibit highly complex dynamics due to the interactions between the bacteria and the extracellular polymeric substance (EPS), water, nutrients, and minerals that make up the biofilm. In the current dissertation, a hybrid computational model was proposed for simulation of biofilm growth processes using a multiphase continuum for the transport of water and EPS, as well as nutrient diffusion, and discrete phase particles for simulation of bacterial cells and their interactions. Mass and momentum conservations of each phase and bacterial motion, rotation, growth, division, …

Optimization Of Mixing Efficiency In Low Reynolds Unlike Doublet Injectors By Incorporating Swirl, Samuel Braggins Ligon

Graduate College Dissertations and Theses

One of the largest issues concerning industrial cube satellite manufacturing is the development of propulsion systems at extremely small scales. Bipropellant cube satellite propulsion systems face challenges associated with the mixing of two fluids which operate in low Reynolds number environments. Low Reynolds, or laminar, fluid flow is unique to cube satellite injection systems because of their unprecedented small scale. This work is intended to both test the validity of a proposed cube satellite injection system, and to test the accuracy of numerical method approaches to solving the problem of laminar flow mixing in such devices. The proposed injector is …

Electric Grid Decarbonization Pathways: Landscape Impacts, Policy Interactions, And The Need For Cooperation, Austin Wesley Thomas

Graduate College Dissertations and Theses

Climate change has motivated governments around the world to ratify aggressive greenhouse gas emissions reduction targets. Meeting these targets will require improved energy efficiency, behavior changes, and energy system decarbonization. Many climate change and energy policy targets imply the deployment of large amounts of low carbon, renewable energy resources like wind turbines and solar photovoltaic (PV) panels but do not specify how these resources will be sited on the landscape. The relationships between weather conditions, terrain, land cover, existing electric grid infrastructure, and electricity consumers will govern how these wind and solar PV infrastructure configurations develop and how quickly they …

Software Defined Radio Based Frequency Modulated Continuous Wave Ground Penetrating Radar, Patrick Fiske

Graduate College Dissertations and Theses

Frequency modulated continuous wave (FMCW) radar allows for a wide range of research applications. One primary use of this technology and what is explored in this thesis, is imaging in the form of ground penetrating radar. To generate proper results, spectral wide-band reconstruction has been developed to overcome hardware limitations allowing for high resolution radar. Requiring complex reconstruction algorithms, the proposed method benefits greatly in terms of performance and implementation compared to other radar systems.

This thesis develops a wideband linearly frequency modulated radar leveraging a software-defined radio (SDR). The modular system is capable of a tunable wideband bandwidth up …