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Full-Text Articles in Engineering
Simulations Of Diffusion Driven Phase Evolution In Heterogenous Solids, Subramanya Gautam Sadasiva
Simulations Of Diffusion Driven Phase Evolution In Heterogenous Solids, Subramanya Gautam Sadasiva
Open Access Dissertations
With reduction in size, ever greater operational demands are placed on electronics components at all levels of the device, starting from the transistor level to the level of the package and the solder interconnects. Concurrently, there has been a move to more complicated materials systems in order to meet health and environmental guidelines. These trends of reducing size, increasing loads have increased the necessity to understand the mechanisms of the failure. ^ As the length scales are reduced, it becomes increasingly important to consider interfacial and micro-structural effects that can be safely ignored at larger length scales owing to the …
Predicting Lubrication Performance Between The Slipper And Swashplate In Axial Piston Hydraulic Machines, Andrew T. Schenk
Predicting Lubrication Performance Between The Slipper And Swashplate In Axial Piston Hydraulic Machines, Andrew T. Schenk
Open Access Dissertations
Engineering of the sliding interfaces within swashplate type axial piston machines represents the most complex and difficult part of the design process. The sliding interfaces are subject to significant normal loads which must be supported while simultaneously preventing component wear to ensure long lasting operation. Proper lubrication design is essential to separate the solid bodies from each other, but the complexity of the physics involved makes this a difficult problem. This work focuses on lubrication and the resulting energy losses at the sliding interface between the slipper and swashplate. ^ To better understand the slipper lubrication performance, a numerical model …
Model-Based Powertrain Design And Control System Development For The Ideal All-Wheel Drive Electric Vehicle, Haotian Wu
Model-Based Powertrain Design And Control System Development For The Ideal All-Wheel Drive Electric Vehicle, Haotian Wu
Open Access Dissertations
The transfer case based all-wheel drive electric vehicle (TCAWDEV) and dual-axle AWDEV have been investigated to balance concerns about energy consumption, drivability and stability of vehicles. However, the mentioned powertrain architectures have the torque windup issue or the wheel skidding issue. The torque windup is an inherent issue of mechanical linked all-wheel drive systems. The hydraulic motor-based or the electric motor-based ideal all-wheel drive powertrain can provide feasible solutions to the mentioned issues. An ideal AWDEV (IAWDEV) powertrain architecture and its control schemes were proposed by this research; the architecture has four independent driving motors in powertrain. The IAWDEV gives …
Ultrashort Laser Pulse-Matter Interaction: Fundamentals And Early Stage Plasma Dynamics, Xin Zhao
Ultrashort Laser Pulse-Matter Interaction: Fundamentals And Early Stage Plasma Dynamics, Xin Zhao
Open Access Dissertations
Despite extensive studies for many years, the detailed mechanisms of ultrashort laser pulse (USLP)-matter interaction are still not fully understood and further fundamental investigation is required. This study seeks to provide an improved understanding of the USLP-material interaction by both theoretical and experimental investigations and to find ways to enhance laser energy coupling with different materials.^ A two-dimensional comprehensive hydrodynamic model for USLP ablation of metals and semiconductors is developed in this study. The model comprises a two-temperature model and a hydrodynamic model supplemented with a quotidian equation of state model, considering the relevant multiphysical phenomena during the laser-matter interaction. …
Coupled Fluid-Thermal Analysis Of Low-Pressure Sublimation And Condensation With Application To Freeze-Drying, Arnab Ganguly
Coupled Fluid-Thermal Analysis Of Low-Pressure Sublimation And Condensation With Application To Freeze-Drying, Arnab Ganguly
Open Access Dissertations
Freeze-drying is a low-pressure, low-temperature condensation pumping process widely used in the manufacture of bio-pharmaceuticals for removal of solvents by sublimation. The goal of the process is to provide a stable dosage form by removing the solvent in such a way that the sensitive molecular structure of the active substance is least disturbed. The vacuum environment presents unique challenges for understanding and controlling heat and mass transfer in the process. As a result, the design of equipment and associated processes has been largely empirical, slow and inefficient.^ A comprehensive simulation framework to predict both, process and equipment performance is critical …
Investigation Of Optical Near Field Using Near Field Scanning Optical Microscopy, Yan Li
Investigation Of Optical Near Field Using Near Field Scanning Optical Microscopy, Yan Li
Open Access Dissertations
Conventional optical imaging techniques have a fundamental resolution limit due to the diffraction limit of light. The advances of science and technology on the nanoscale demand a new tool for characterization. The Near Field Scanning Optical Microscopy (NSOM) has been developed to tackle certain aspects of this problem. The work presented here applies different types of NSOM to explore the near field distribution of metal plasmonic nanostructures.^ Ridge apertures with shapes like bowtie and C can be used to focus light into sub-diffraction limit spot with enhancement. This localization of the field near the exit of a bowtie aperture is …
The Role Of Microstructure On The Combustion And Impact Behavior Of Mechanically Activated Nickel/Aluminum Reactive Composites, Benjamin Aaron Mason
The Role Of Microstructure On The Combustion And Impact Behavior Of Mechanically Activated Nickel/Aluminum Reactive Composites, Benjamin Aaron Mason
Open Access Dissertations
Metal-based reactive composites are a class of materials that consist of at least one metals, such as Ni/Al, that have high-energy densities and can produce significant energy output during exothermic reaction after thermal or mechanical initiation. However, conventionally these materials typically have slow reaction rates and are difficult to ignite at typical micron particle size ranges limiting their application. Therefore, mechanical activation techniques have been used to create materials with high surface areas and smaller characteristic dimensions in order to increase combustion velocity and ignition sensitivity. Their combustion and mechanical impact behavior is being studied to develop the understanding needed …
Unsteady Flamelet Progress Variable Modeling Of Reacting Diesel Jets, Muhsin Mohammed Ameen
Unsteady Flamelet Progress Variable Modeling Of Reacting Diesel Jets, Muhsin Mohammed Ameen
Open Access Dissertations
Accurate modeling of turbulence/chemistry interactions in turbulent reacting diesel jets is critical to the development of predictive computational tools for diesel engines. The models should be able to predict the transient physical and chemical processes in the jets such as ignition and flame lift-off. In the first part of this work, an existing unsteady flamelet progress variable (UFPV) model is employed in Reynolds-averaged Navier-Stokes (RANS) simulations and large-eddy simulations (LES) to assess its accuracy. The RANS simulations predict that ignition occurs toward the leading tip of the jet, followed by ignition front propagation toward the stoichiometric surface, and flame propagation …
Droplet Behavior On Superhydrophobic Surfaces: Interfaces, Interactions, And Transport, Susmita Dash
Droplet Behavior On Superhydrophobic Surfaces: Interfaces, Interactions, And Transport, Susmita Dash
Open Access Dissertations
The primary objective of the present work is to study droplet dynamics on smooth hydrophobic and textured superhydrophobic surfaces, and to understand the dependence of interfacial interaction mechanisms on surface morphology. ^ A detailed understanding of the dynamics of droplet response to an applied electric field is essential for implementation of electrowetting techniques in various devices. In the first part of the thesis, a systematic study of the transient response in terms of contact angle and contact radius of a sessile droplet on a smooth hydrophobic surface under electrical actuation is presented. A scaling analysis predicts the response time of …
Thermal Efficiency And Emission Analysis Of Advanced Thermodynamic Strategies In A Multi-Cylinder Diesel Engine Utilizing Valve-Train Flexibility, Chuan Ding
Open Access Dissertations
Stringent emission regulations and a growing demand for fossil fuel drive the development of new technologies for internal combustion engines. Diesel engines are thermally efficient but require complex aftertreatment systems to reduce tailpipe emissions of unburned hydrocarbons (UHC), particulate matter (PM), and nitrogen oxides (NOx). These challenges require research into advanced thermodynamic strategies to improve thermal efficiency, control emission formation and manage exhaust temperature for downstream aftertreatment. The optimal performance for different on-road conditions is analyzed using a fully flexible valve-train on a modern diesel engine. The experimental investigation focuses on thermal management during idling and high-way cruise conditions. In …
Modeling The Dynamics And Stresses Of Elongated Particles In Vertical Axis Mixers, Xia Hua
Modeling The Dynamics And Stresses Of Elongated Particles In Vertical Axis Mixers, Xia Hua
Open Access Dissertations
Vertical axis mixers, such as high shear granulators and agitated filter dryers (AFDs), are commonly used in the processing of particulate materials. For example, AFDs are regularly used in the pharmaceutical industry to dry the wet active pharmaceutical ingredient (API) particles. During the drying process, an impeller blade agitates the bed to increase the drying rate and enhance drying uniformity. Unfortunately, the needle-shaped API particles tend to flow poorly, are frequently damaged, and can sometimes form undesirable agglomerates, causing manufacturing inefficiencies, flow stoppages, and unpredictable product quality. Therefore, it is important to gain an improved understanding of the system's particle …
Thermoelectric Waste Heat Recovery In Automobile Exhaust Systems: Topological Studies And Performance Analysis, Sumeet Kumar
Thermoelectric Waste Heat Recovery In Automobile Exhaust Systems: Topological Studies And Performance Analysis, Sumeet Kumar
Open Access Dissertations
The demand for improved fuel efficiency in automobiles has placed an emphasis on exhaust system waste heat recovery as a 40% of the fuel's chemical energy is lost to the environment in modern spark ignition engines. To advance fuel economy, researchers are currently evaluating technologies to exploit exhaust stream thermal power using thermoelectric generators (TEGs) that operate using the Seebeck effect. Thermoelectric generators have the potential to recover some of this waste energy in the exhaust stream potentially improving fuel economy by as much as 5%. ^ Attempts are made to maximize the electrical power generation by optimizing the thermoelectric …
Structure-Functionality Relationship Of Collagen Scaffolds For Tissue Engineering, Seungman Park
Structure-Functionality Relationship Of Collagen Scaffolds For Tissue Engineering, Seungman Park
Open Access Dissertations
Tissue engineering is a promising technology that enables scientists to create artificial organs or replace damaged tissues using animal cells and other components. For successful tissue regeneration, many factors should be taken into account, however, three components are most crucial: cell, scaffold, and soluble factor(s). In order to check the functionality after regeneration of desired tissues, various approaches have been attempted, depending on the physical, biological, and chemical properties of the tissues. Recently, the importance of the extracellular matrix (ECM) microstructure is being considered to be important in this regard. The ECM is closely associated with various functional properties of …
Effects Of Flow Orientation On Condensation In Tubes, Il Chung Park
Effects Of Flow Orientation On Condensation In Tubes, Il Chung Park
Open Access Dissertations
This study explores the interfacial and heat transfer characteristics of annular condensation of FC-72 in vertical downflow, vertical upflow and horizontal flow as well as the effects of channel orientation on flow condensation. Two separate condensation test modules are employed, one for high-speed video imaging of the film interface and the second for heat transfer measurements. Condensation in both test modules is achieved by rejecting the heat to a counterflow of cooling water. The heat transfer measurements are obtained along the inner wall of an 11.89-mm i.d. and 1,259.84-mm long stainless steel tube. ^ For vertical downflow, the film at …
Non-Intrusive Two-Phase Flow Regime Identification And Transport Characterization In Microchannels Subject To Uniform And Non-Uniform Heat Input, Susan N. Ritchey
Non-Intrusive Two-Phase Flow Regime Identification And Transport Characterization In Microchannels Subject To Uniform And Non-Uniform Heat Input, Susan N. Ritchey
Open Access Dissertations
Direct integration of compact microchannel heat sinks is an attractive thermal management solution for the dissipation of high heat fluxes, specifically under boiling conditions that provide high rates of heat transfer at a uniform heat sink temperature. Under two-phase flow conditions, the heat transfer and pressure drop are a function of the local flow regime. Development of sensors that detect local void fraction and flow regimes may enable better understanding of the fundamental flow phenomena. ^ The void fraction in air-water two-phase adiabatic flow in a microchannel is measured in this work using a custom-designed impedance-based sensor with electrodes on …
Understanding Preferred Leg Stiffness And Layered Control Strategies For Locomotion, Zhuohua H. Shen
Understanding Preferred Leg Stiffness And Layered Control Strategies For Locomotion, Zhuohua H. Shen
Open Access Dissertations
Despite advancement in the field of robotics, current legged robots still cannot achieve the kind of locomotion stability animals and humans have. In order to develop legged robots with greater stability, we need to better understand general locomotion dynamics and control principles. Here we demonstrate that a mathematical modeling approach could greatly enable the discovery and understanding of general locomotion principles. ^ It is found that animal leg stiffness when scaled by its weight and leg length falls in a narrow region between 7 and 27. Rarely in biology does such a universal preference exist. It is not known completely …
Algebraic Level Sets For Cad/Cae Integration And Moving Boundary Problems, Kritika Upreti
Algebraic Level Sets For Cad/Cae Integration And Moving Boundary Problems, Kritika Upreti
Open Access Dissertations
Boundary representation (B-rep) of CAD models obtained from solid modeling kernels are commonly used in design, and analysis applications outside the CAD systems. Boolean operations between interacting B-rep CAD models as well as analysis of such multi-body systems are fundamental operations on B-rep geometries in CAD/CAE applications. However, the boundary representation of B-rep solids is, in general, not a suitable representation for analysis operations which lead to CAD/CAE integration challenges due to the need for conversion from B-rep to volumetric approximations. The major challenges include intermediate mesh generation step, capturing CAD features and associated behavior exactly and recurring point containment …
Coal Gasification For Fuel Synthesis: Multiphysics Modeling And New Concepts, Jian Xu
Coal Gasification For Fuel Synthesis: Multiphysics Modeling And New Concepts, Jian Xu
Open Access Dissertations
Fuel synthesis through gasification of carbonaceous materials (e.g. coal and biomass) has the potential to provide a solution to the increasing demand for energy and liquid transportation fuels. To theoretically understand the complex physical and chemical processes in a gasifier and to identify the most influential parameters for syngas production, we first developed a multi-physics and multi-scale model to simulate the gasification processes in a well-stirred reactor. This model is the first of its kind and considers detailed gas-phase chemistry, particle-phase reactions, moisture drying, devolatilization, porous structure evolution, convective and radiative heat transfer, as well as full coupling between the …
Development Of Methodologies For Evaluating Performance Of Fault Detection And Diagnostics Protocols Applied To Unitary Air-Conditioning Equipment, David P. Yuill
Open Access Dissertations
This thesis describes the development of standardized methodologies and methods for evaluating the performance of fault detection and diagnostics (FDD) protocols that are intended for air-cooled vapor compression unitary air-conditioners. Although there are currently many FDD protocols available commercially and there are jurisdictions in which the building codes require FDD, there is currently no standardized method to determine how effective the FDD might be at detecting and diagnosing faults.^ An FDD evaluation method is proposed, in which the evaluator passes data from a large number of scenarios to a candidate FDD protocol, and collects the responses from each scenario. The …
Novel Energy Efficient Electrohydraulic Steer-By-Wire Technology, Naseem Daher
Novel Energy Efficient Electrohydraulic Steer-By-Wire Technology, Naseem Daher
Open Access Dissertations
Improving energy efficiency, productivity, safety, and comfort of mobile machines is of utmost priority to original equipment manufacturers, suppliers, and consumers given the escalating fuel prices and increased awareness to the environment and workplace hazards. A major breakthrough in the realm of high power motion control is pump displacement controlled (DC) actuation, which does away with hydraulic valves for motion control and uses a variable displacement pump as both a flow source and final control element, thus eliminating throttling losses associated with hydraulic control valves. This work deals with researching and implementing DC technology for realizing the steering function of …
Investigation Of The Influence Of Gravitational Body Force Effects On Critical Heat Flux For Flow Boiling With Subcooled And Two-Phase Inlet, Christopher Alan Konishi
Investigation Of The Influence Of Gravitational Body Force Effects On Critical Heat Flux For Flow Boiling With Subcooled And Two-Phase Inlet, Christopher Alan Konishi
Open Access Dissertations
Space agencies worldwide are being confronted with the challenges of more distant manned space missions, which will demand greater energy efficiency and reduced weight and volume. One method being considered to reduce the weight and volume is to replace present single-phase Thermal Control Systems (TCSs) with ones that rely on flow boiling and condensation. This transition will require a thorough understanding of the influence of reduced gravity on flow boiling and condensation, and the development of predictive tools for both. The primary purpose of the present study is to investigate the impact gravitational body force effects have on flow boiling …
High Fidelity Simulations Of Electrokinetic Phenomena In Microfluidic Devices, Qian Li
High Fidelity Simulations Of Electrokinetic Phenomena In Microfluidic Devices, Qian Li
Open Access Dissertations
Electroosmotic flow with electrokinetic effects is the primary method of fluid handling in micro-total analysis systems. Under external applied electric fields, electrokinetic micro-devices allow for innovative functionality in a wide range of microfluidic applications including sample injection, separation, rapid micromixing, and miniaturized chemical and biochemical analysis and detection. This dissertation focuses on simulations of two electrokinetic phenomena, isotachophoresis (ITP) and electrokinetic instability (EKI). A set of coupled governing equations including the incompressible Naiver-Stokes equations, Nernst-Planck transport equations and a charge conservation equation are solved in the simulation. A multiblock in-house solver based on high-order finite difference schemes is developed to …
Fundamental Design Principles Of Novel Mems Based "Landau" Switches, Sensors, And Actuators : Role Of Electrode Geometry And Operation Regime, Ankit Jain
Open Access Dissertations
Microelectromechanical systems (MEMS) are considered as potential candidates for "More-Moore" and "More-than-Moore" applications due to their versatile use as sensors, switches, and actuators. Examples include accelerometers for sensing, RF-MEMS capacitive switches in communication, suspended-gate (SG) FETs in computation, and deformable mirrors in optics. In spite of the wide range of applications of MEMS in diverse fields, one of the major challenges for MEMS is their instability. Instability divides the operation into stable and unstable regimes and poses fundamental challenges for several applications. For example: Tuning range of deformable mirrors is fundamentally limited by pull-in instability, RF-MEMS capacitive switches suffer from …