Engineering Commons^™

Computational Modeling Of Transient Processes During Run-In For Tribological Systems, Rob Morien

Theses and Dissertations

Understanding the frictional behavior of machine elements in mutual rolling or sliding contact is important for many engineering applications. When frictional sliding is initiated, the tribological system passes through several stages with each stage possessing its own unique frictional property. The initial transition process preceding stationary sliding is usually called “run-in”. During the run-in time interval, surface topographies of frictional contacts as well as lubricant distribution and surface tribofilms reorganize and adjust through asperity deformation and wear processes before reaching the steady state. This surface stability formed during run-in leads to an improvement in frictional performance during steady state operation, …

Advanced Self-Healing Polymer Composites For Wind Turbine Blades, Arun Kumar Koralagundi Matt

Theses and Dissertations

Wind energy is one of the prime sources of energy among the renewable sources of energy. Wind power has been one of the most promising sources of long-term, clean energy. Materials and design approach in commercial wind turbines have not seen a momentous change in the recent years. In this study, an intriguing bio-mimetic design approach is sought after, which is to heal damages as they arise in a composite material. Self-healing material systems in wind turbine blades have the potential to fulfill the requirement as an added safety mechanism to heal damages and prevent catastrophic failures. Effectively supplying healing …

Impact Location In An Isotropic Plate Without Training, Prasanna Rajbhandari

Theses and Dissertations

ABSTRACT

IMPACT LOCATION IN AN ISOTROPIC PLATE WITHOUT TRAINING

by

Prasanna Rajbhandari

The University of Wisconsin-Milwaukee, 2016

Under the Supervision of Professor Dr. Nathan Salowitz

Unexpected impacts are major concerns in the aerospace industry that can cause difficulty to detect damage. Techniques have been developed to determine the impact location using piezoelectric sensors. Most existing systems require training data to develop a database of known structural responses and properties that can be referenced for location of impacts. This data collection is time consuming and if an impact and corresponding sensor data is outside the range of training data, the system …

Application Of Reynolds Stress Model Using Direct Modeling And Actuator Disk Approaches For A Small-Scale Wind Turbine, Randall Scott Jackson

Theses and Dissertations

The Reynolds Stress Model (RSM) has been avoided for turbulence closure in CFD simulations of wind turbines, largely due to the computational expense and the high potential for numerical instability. The advantage of using RSM is having access to shear stresses that are not available from two-equation RANS-based closure models like k-e and k-w. Access to the shear stresses will aide in the understanding of how the blade design will affect the wake, particularly in the near-wake region. In this research, the RSM turbulence model has been successfully applied in simulating a three-bladed small-scale wind turbine through a direct-model approach …

Covert Contrast: The Acquisition Of Mandarin Tone 2 And Tone 3 In L2 Production And Perception, Liya Mar

Theses and Dissertations

This dissertation investigates the occurrence of an intermediate stage, termed a covert contrast, in the acquisition of Mandarin Tone 2 (T2) and Tone 3 (T3) by adult speakers of American English. A covert contrast is a statistically reliable distinction produced by language learners that is not perceived by native speakers of the target language (TL). In second language (L2) acquisition, whether a learner is judged as having acquired a TL phonemic contrast has largely depended on whether the contrast was perceived and transcribed by native speakers of the TL. However, categorical perception has shown that native listeners cannot perceive a …

Experimental And Numerical Characterization Of Scalable Cellulose Nano-Fiber Composite, Bamdad Barari Barari

Theses and Dissertations

Fiber-reinforced polymer composites have been used in recent years as an alternative to the conventional materials because of their low weight, high mechanical properties and low processing temperatures. Most polymer composites are traditionally made using reinforcing fibers such as carbon or glass fibers. However, there has been recent interest in making these reinforcing fibers from natural resources. The plant-derived cellulose nano-fibers (CNF) are a material with remarkable mechanical properties at the nano-scale that are much superior to the mechanical properties of the traditional natural fibers (such as jute, hemp, kenaf, etc) used in the natural-fiber based polymer composites. Because CNF …

A Study Of The Hydrostatic And Hydrodynamic Properties Of Aeoliscus Straigatus, Jeremy J. Keifenheim

Theses and Dissertations

Aeoliscus strigatus is a highly maneuverable fish found in the Indo-Pacific region. It boasts a unique head down posture and employs median paired fin propulsion to perform precise movements. The need for highly maneuverable underwater AUVs for exploration and testing drove the examination of the hydrostatics and hydrodynamics influencing Aeoliscus. To determine the stability of Aeoliscus the center of gravity and buoyancy were found. Center of gravity was experimentally located using the three plumb line method while center of buoyancy was located using two separate methods. The first method utilized the measured buoyant force, a rigidly mounted fish and a …

Coding Strategies For Cochlear Implants Under Adverse Environments, Qudsia Tahmina

Theses and Dissertations

Cochlear implants are electronic prosthetic devices that restores partial hearing in patients with severe to profound hearing loss. Although most coding strategies have significantly improved the perception of speech in quite listening conditions, there remains limitations on speech perception under adverse environments such as in background noise, reverberation and band-limited channels, and we propose strategies that improve the intelligibility of speech transmitted over the telephone networks, reverberated speech and speech in the presence of background noise. For telephone processed speech, we propose to examine the effects of adding low-frequency and high- frequency information to the band-limited telephone speech. Four listening …

Numerical And Experimental Studies Of Atomic Layer Deposition For Sustainability Improvement, Dongqing Pan

Theses and Dissertations

Atomic layer deposition (ALD) is an approved nano-scale thin films fabrication technique with remarkable uniformity and conformity in surface geometry. This dissertation presents numerical and experimental studies to investigate the transient physical and chemical ALD process in order to improve its sustainability performance in terms of throughput, wastes and emissions.

To be specific, in this dissertation, the transient process of ALD is studied extensively through both numerical and experimental approaches to find the influential factors on the two main critical sustainability issues: low throughput and negative environmental impacts. Different numerical schemes are developed and studied for ALD process simulations. In …

Effects Of Surface Topography And Vibrations On Wetting: Superhydrophobicity, Icephobicity And Corrosion Resistance, Rahul Ramachandran

Theses and Dissertations

Concrete and metallic materials are widely used in construction and water industry. The interaction of both these materials with water and ice (or snow) produces undesirable results and is therefore of interest. Water that gets absorbed into the pores of dry concrete expands on freezing and can lead to crack formation. Also, the ice accretion on concrete surfaces such as roadways can have disastrous consequence. Metallic components used in the water industry undergo corrosion due to contact with aqueous corrosive solutions. Therefore, it is desirable to make concrete water/ice-repellent, and to make metallic surfaces corrosion-resistant.

Recent advances in micro/nanotechnology have …

Numerical And Experimental Study Of Liquid Breakup Process In Solid Rocket Motor Nozzle, Yi-Hsin Yen

Theses and Dissertations

Rocket propulsion is an important travel method for space exploration and national defense, rockets needs to be able to withstand wide range of operation environment and also stable and precise enough to carry sophisticated payload into orbit, those engineering requirement makes rocket becomes one of the state of the art industry. The rocket family have been classified into two major group of liquid and solid rocket based on the fuel phase of liquid or solid state. The solid rocket has the advantages of simple working mechanism, less maintenance and preparing procedure and higher storage safety, those characters of solid rocket …

Modeling The Feasibility Of Corn Stover Combustion As A Heat Source At Corn Ethanol Plants, Sulekha Tamvada

Theses and Dissertations

Alternative energy sources are of prime interest for most of the nations across the world. Rising fuel prices and depleting petroleum reserves are of serious national and global concern. Bio-fuels if proved feasible for larger scale implementation could become the ideal breakthrough in easing the extensive dependence on fossil fuels and retaining the current engine technology of fossil fuels. Current methods of producing bio-fuels rely heavily on the consumption of non-renewable energy in the production process. Therefore, it is desirable to find renewable alternatives to these non-renewable energy sources.

Although bio-mass based fuels have been tested and proven to be …

Multi-Level Optimal Design Using Game Theory With Model Updating By Low Discrepancy Sampling, Yanchen Xu

Theses and Dissertations

The Design of Experiment (DOE) based response surface methodology (RSM) is a commonly used technique for solving optimization problems. The traditional DOE method has some shortcomings when used to update the RSM model. This thesis aims to develop a new DOE technique to solve the model updating problems in design optimization. Toward this end, a new DOE based RSM method is proposed to solve this problem by using low-discrepancy sequence method to generate the additional data points needed to update the model to replace the traditional factor and level based DOE method.

Tested on a couple of numerical example problems, …

Inverse Approaches For Recovery Of Distributed Loads, Aleysha Kobiske

Theses and Dissertations

Inverse load recovery is a well-researched topic which involves determining an unknown force acting on a structure from the induced strain. The methodology used to determine an unknown loading imposed on a structure begins with a finite element model of the structure. Unit loads are applied at each known load location and the strain data is collected from the model. The strain data collected from the structure during operation or from simulation is compared to the strain produced from the unit loads. The result is an estimate of the imposed load.

In order to obtain the best results possible for …

Dynamic Moving Load Identification Using Optimal Sensor Placement And Model Reduction, Paul Augustine

Theses and Dissertations

A structure in service can be subjected to static, dynamic or moving loads. Several situations in practice involve estimation of moving loads which induce vibrations in the structure on which they are applied. An accurate estimation of these loads will ensure product quality and reliability of the final design, and mitigate the cost of structural health monitoring systems. The moving nature of dynamic loads increases the computational difficulty of the problem. One of the types of Inverse Problems involves estimation of the applied load from measured structural response such as strain or accelerations.

Measuring response at a limited number of …

Performance Optimization And Statistical Analysis Of Basic Immune Simulator (Bis) Using The Flame Gpu Environment, Shailesh Tamrakar

Theses and Dissertations

Agent-based models (ABMs) are increasingly being used to study population dynamics in complex systems such as the human immune system. Previously, Folcik et al. developed a Basic Immune Simulator (BIS) and implemented it using the RePast ABM simulation framework. However, frameworks such as RePast are designed to execute serially on CPUs and therefore cannot efficiently handle large simulations. In this thesis, we developed a parallel implementation of immune simulator using FLAME GPU, a parallel ABM simulation framework designed to execute of Graphics Processing Units(GPUs). The parallel implementation was tested against the original RePast implementation for accuracy by running a simulation …

Investigation Of Distributed Model Predictive Control For Economic Load Shifting In Building Hvac Systems, Peter Kinsella

Theses and Dissertations

One of the major challenges that building owners and operators face is maintaining a low cost of operation. In certain markets within the U.S., electrical cost varies throughout the day; it is higher during times of peak demand. This leaves the customer the incentive to cut back electrical use during peak demand periods. Since 40% of the peak electrical demand is due to the operation of the building HVAC system alone, the opportunity exists for shifting the building cooling load to off-peak hours. This can be done by pre-cooling the space, thereby using the building mass as a sort of …

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 …