Mechanical Engineering Commons^™

On The Nonlinear Tribological Jerk Dynamics At Sliding Interfaces, Divyeshkumar Patel

Theses and Dissertations

As the world desires the next industrial revolution, the potential threats that will undermine energy efficient innovations include detrimental frictional effects that exacerbate wear, hasten equipment breakdowns, and worsen heat dissipation. Capturing the inherently nonlinear manifestations of friction fundamentally has been difficult. A fundamental modeling scheme elucidating friction will bolster novel technologies synthesizing wear resistant materials and lubricants needed for sustainable energy efficiency.

Frictional dissipation at dynamical sliding interfaces has been studied for generations. Interfacial sliding frictional effects are prevalent in natural and artificial phenomena such as earthquake, hip and knee joints, and the moving parts of energy-producing and energy-consuming …

Evaluation And Forecast Of Energy Consumption In Different Sectors Of The United States Using Artificial Neural Networks, Arash Kialashaki

Theses and Dissertations

The United States is a country which consumes a vast amount of energy. In order to keep the development of the United States sustainable (diverse and productive over the time) energy planning should be carried out comprehensively and precisely. This dissertation presents a specific mathematical modeling approach towards energy demand modeling of the United States and forecast future energy demand. To generate more detailed and accurate results, this dissertation investigates the energy demand of each sector separately using the analysis of trend for unique set of independent parameters which affect the energy demand in that sector.

In solving a forecast …

Carbon Dioxide Photoreduction With Water Vapor By Titanium-Containing Magnesium-Aluminum Layered Double Hydroxides, Jinye Xu

Theses and Dissertations

Photocatalytic conversion of CO2 into value-added solar fuels is a promising approach to simultaneously address the greenhouse gas pollution and energy shortage issues. TiO2, the most widely studied photocatalyst, suffers from drawbacks like fast electron-hole recombination and limited CO2 adsorption. In this study, Ti-containing MgAl layered double hydroxides (MgAl/Ti-LDHs) were designed to provide high activity of CO2 photoreduction by dispersing Ti species over MgAl-LDHs which have been extensively investigated as CO2 adsorbent. This study was the first attempt to apply MgAl/Ti-LDHs for photoreduction of CO2 with water vapor.

MgAl/Ti-LDHs were prepared through coprecipitation (CP) method, the most common technique for …

Effect Of Junction Geometry On Monodispersed Microdroplet Generation In Microfluidic Aqueous Two-Phase Systems, Young Gyu Nam

Theses and Dissertations

Aqueous two-phase system (ATPS) consists of two immiscible water-based solutions of polymers, which can form phase partitioning. Dextran and polyethylene glycol I used in this thesis is the one of common components of aqueous two-phase system give a reliable and incompatible environment for purification of biomedical products and cellular macromolecules. Recently, ATPS have received increasing attention as a separation method in microfluidic device due to the advantages of biocompatibility, unlimited combination, and low interfacial tension. Hence, it became an important to discover researches related to ATPS microfluidic device.

Microdroplets produced in microfluidic device are a largely interesting phenomenon for various …

Novel Substrate-Bound Hybrid Nanomaterials For Anode Electrodes In Lithium-Ion Batteries, Haejune Kim

Theses and Dissertations

Li-ion batteries (LIBs) are commercially dominant in electrochemical energy storage devices. Their wide applications as power sources, from portable electronics to electric vehicles/hybrid electric vehicles, are mainly attributed to their superior energy density based on unit volume and unit weight over other battery systems. Growing demands for lighter, longer-lasting, and more powerful devices spur the development of new electrode materials, because the performance of LIBs is highly dependent on the characteristics of electrodes. The ideal candidate for anode materials of LIBs should have high lithium storage capability and stable structure after repeated charge/discharge cycles. Since its first commercialization by Sony …

Experimental, Numerical And Analytical Characterization Of Torsional Disk Coupling Systems, Alex B. Francis

Theses and Dissertations

Torsional couplings are used to transmit power between rotating components in various power systems while allowing for small amounts of misalignment that may otherwise lead to equipment failure. When selecting a proper coupling type and size, one has to consider three important conditions: (1) the maximum load applied to the coupling, (2) the maximum operation speed, and (3) the amount of misalignment allowable for normal operation. There are many types of flexible couplings that use various materials for the flexible element of the coupling. The design of the coupling and the materials used for the flexible portion will determine its …

A Study Of The Development Of An Analytical Wall Function For Large Eddy Simulation Of Turbulent Channel And Rectangular Duct Flow, Takahiko Hasegawa

Theses and Dissertations

This paper reports computational work of three-dimensional channel turbulent flow and rectangular duct flow with the Analytical Wall Function (AWF). The main purpose of this study is to establish and validate the new modeling of AWF for Large Eddy Simulation (LES-AWF). In order to compare the performance of the new modeling of LES-AWF, the conventional LES-AWF and Wall-resolved LES are applied. The new LES-AWF showed improvements of flow prediction in both of three-dimensional channel flow and rectangular duct flow, although the improvement in rectangular duct is relatively minor.

Characterization Of Carbon-Fiber Reinforced Polyetherimide Thermoplastic Composites Using Mechanical And Ultrasonic Methods, Mohannad A. Alhaidri

Theses and Dissertations

Continuous fiber-reinforced thermoplastics (CFRT) have the potential for being a mass-produced material for high-performance applications. The primary challenge of using CFRT is achieving fiber wet-out due to the high viscosity of thermoplastics. This results in higher temperatures and pressures required for processing the composites. Co-mingling thermoplastic fibers with a reinforcing fiber, potentially, can enable better wetting by reducing the distance the matrix needs to flow. This could result in shorter cycle times and better consolidation at lower temperatures and pressures. In this study, a polyetherimide (PEI) fiber was comingled with carbon fibers (CF). The resultant fibers were woven into fabrics …

Effect Of Processing Parameters And Matrix Shrinkage On Porosity Formation During Synthesis Of Metal Matrix Composites With Dual-Scale Fiber Reinforcements Using Pressure Infiltration Process, Reihaneh Etemadi

Theses and Dissertations

This is first such study on porosity formation phenomena observed in dual-scale fiber preforms during the synthesis of metal matrix composites (MMCs) using the gas-based pressure infiltration process (gas PIP). In this thesis, different mechanisms of porosity formation during pressure infiltration of Al-Si alloys into Nextel's 3D woven ceramic-fabric reinforcements (a dual-porosity or dual-scale porous medium) are studied. The effect of processing conditions in terms of the infiltration temperature and pressure on porosity content of the ceramic fabric infiltrated by the alloys through the gas PIP is investigated. Relative density (RD), defined as the ratio of the actual MMC density …

Wetting, Superhydrophobicity, And Icephobicity In Biomimetic Composite Materials, Vahid Hejazi

Theses and Dissertations

Recent developments in nano- and bio-technology require new materials. Among these new classes of materials which have emerged in the recent years are biomimetic materials, which mimic structure and properties of materials found in living nature. There are a large number of biological objects including bacteria, animals and plants with properties of interest for engineers. Among these properties is the ability of the lotus leaf and other natural materials to repel water, which has inspired researchers to prepare similar surfaces. The Lotus effect involving roughness-induced superhydrophobicity is a way to design nonwetting, self-cleaning, omniphobic, icephobic, and antifouling surfaces. The range …

Improved Wind Turbine Control Strategies For Maximizing Power Output And Minimizing Power Flicker, Quan Chen

Theses and Dissertations

For reducing the cost of energy (COE) for wind power, controls techniques are important for enhancing energy yield, reducing structural load and improving power quality. This thesis presents the control strategies studies for wind turbine both from the perspectives of both maximizing power output and reducing power flicker and structural load,

First, a self-optimizing robust control scheme is developed with the objective of maximizing the power output of a variable speed wind turbine with doubly-fed induction generator (DFIG) operated in Region 2. Wind power generation can be divided into two stages: conversion from aerodynamic power to rotor (mechanical) power and …

Modeling Of Instabilities And Self-Organization At The Frictional Interface, Vahid Mortazavi

Theses and Dissertations

The field of friction-induced self-organization and its practical importance remains unknown territory to many tribologists. Friction is usually thought of as irreversible dissipation of energy and deterioration; however, under certain conditions, friction can lead to the formation of new structures at the interface, including in-situ tribofilms and various patterns at the interface.

This thesis studies self-organization and instabilities at the frictional interface, including the instability due to the temperature-dependency of the coefficient of friction, the transient process of frictional running-in, frictional Turing systems, the stick-and-slip phenomenon, and, finally, contact angle (CA) hysteresis as an example of solid-liquid friction and dissipation. …

Damage Detection Of Mixed-Mode Cracks In Large Truss Structures Using Wavelet Transform, Hussain Altammar

Theses and Dissertations

The use of dynamic response in damage identification has been gaining considerable attention over the last two decades. The aim of these methods is to detect the presence of a defect or a crack in components or structures. This study focuses on using modal properties for the damage detection of mixed-mode cracks in truss structures. The behavior of a mixed-mode crack is simulated by developing a macroscopic model that is integrated with the finite element model of a truss structure. The modal properties obtained from the model of the damaged structure are found to be comparable to the results of …

Development Of Novel Passive Control Techniques For More Uniform Temperature At Combustor Exit And Hybrid Les/Rans Modeling, Alka Gupta

Theses and Dissertations

Gas turbines have become an important, widespread, and reliable device in the field of power generation. For any gas turbine system, the combustor is an integral part responsible for the combustion of the fuel. A number of studies have shown that the flow field exiting a combustor is highly non-uniform in pressure, velocity and, most importantly, temperature. Hot streaks amongst other non-uniformities cause varying thermal stresses on turbine blades and put pressure on the blade materials. In particular, these non-uniformities can have detrimental effects on the performance of the engine and cause a reduction in the expected life of critical …

Reactor Scale Simulation Of Atomic Layer Deposition, Mohammad Reza Shaeri

Theses and Dissertations

In order to modify the characteristics of an atomic layer deposition (ALD) process, a numerical model to simulate a general ALD process in a reactor scale is presented. Simulations are described by deposition of Al₂O₃ from trimethylaluminum and ozone as the metal and oxygen sources, respectively, and inert argon as the purge gas, inside viscous flow reactors. The simulations are performed for a fixed operating pressure of 10 Torr (1330 Pa) and two substrate temperatures at 250 °C and 300 °C. The flow inside the reactor is a continuum; therefore, the Navier-Stokes, energy and species transport equations …