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Articles 1 - 21 of 21
Full-Text Articles in Mechanical Engineering
Fundamental Understanding Of Interactions Among Flow, Turbulence, And Heat Transfer In Jet Impingement Cooling, Md. Jahed Hossain
Fundamental Understanding Of Interactions Among Flow, Turbulence, And Heat Transfer In Jet Impingement Cooling, Md. Jahed Hossain
Electronic Theses and Dissertations
The flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on three particular geometric configurations (a narrow wall, an array impingement configuration and a curved …
Shock Tube And Mid-Infrared Laser Absorption Measurements Of Ignition Delay Times And Species Time-Histories, Batikan Koroglu
Shock Tube And Mid-Infrared Laser Absorption Measurements Of Ignition Delay Times And Species Time-Histories, Batikan Koroglu
Electronic Theses and Dissertations
Energy consumption has increased dramatically as the world advances and becomes more industrialized. Over the next twenty five years, the U.S. Department of Energy expects the energy demand to increase by 29% with majority of the new energy coming from natural gas (methane). Another promising fuel source for power generation and transportation is the biofuels. The biofuel use in the US is shown to have increased substantially in the last decade. There are serious environmental concerns associated with greenhouse (e.g. carbon-dioxide) and toxic gas emissions (e.g. nitrogen oxides and aldehydes such as propanal) due to deriving energy from natural gas …
Investigation Of Real Gas Effects On Centrifugal Compressor Analytical Methods For Supercritical Co2 Power Cycles, Lauren Blanchette
Investigation Of Real Gas Effects On Centrifugal Compressor Analytical Methods For Supercritical Co2 Power Cycles, Lauren Blanchette
Electronic Theses and Dissertations
As supercritical carbon dioxide (sCO2) power cycles have shown potential to be the next generation power cycle, an immense amount of research has gone into developing this system. One of the setbacks facing development and optimization of this cycle is the unknown in current design and analysis methods ability to accurately model turbomachinery working with sCO2. Due to the desired inlet conditions to the compressor close proximity to the critical point, accurate design and analysis of this power cycle component is one of the main concerns. The present study provides aerodynamic analysis of a centrifugal compressor impeller blade with sCO2 …
Optimal Switch Timing For Piezoelectric-Based Semi-Active Vibration Reduction Techniques, Christopher Kelley
Optimal Switch Timing For Piezoelectric-Based Semi-Active Vibration Reduction Techniques, Christopher Kelley
Electronic Theses and Dissertations
Semi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every displacement extrema. Due to the complexity of analyzing a system with discrete switches, these control laws were developed based on intuition. The few analyses that attempt to determine an optimal switching law …
The Effect Of Vibrations On Cryogens Boil Off During Launch, Transfer And Transport, Erin Schlichenmaier
The Effect Of Vibrations On Cryogens Boil Off During Launch, Transfer And Transport, Erin Schlichenmaier
Electronic Theses and Dissertations
Boil-off of a cryogenic fluid which is caused by the temperature difference between the fluid and its environment is a phenomenon which has long been studied and is well understood. However, vibrational excitation of a cryogenic storage tank and the fluid inside it also play a role in the loss of cryogens. Mechanical energy applied to the system in the form of vibrational input is converted into thermal energy via viscous damping of the fluid. As a result, when a storage tank full of cryogenic fluids is vibrated, it boils off at an increased rate. A series of experiments were …
Transient Cfd Analysis Of Autorotation Using Hybrid Les And Adaptive Mesh Morphing Techniques, Patricia Coronado Domenge
Transient Cfd Analysis Of Autorotation Using Hybrid Les And Adaptive Mesh Morphing Techniques, Patricia Coronado Domenge
Electronic Theses and Dissertations
Large-Eddy Simulation (LES) based turbulence modeling is a developing area of research in Fluid-Structure Interaction (FSI). There is considerable scope for further scientific research in this field and this dissertation aims to extend it to the study of flow-induced motion. The emphasis of this work is on autorotation, an important category of flow-induced motion that is commonly seen in energy applications such as wind turbines and in aviation applications such as the autogyro. In contrast to existing works on FSI that typically assume prescribed motion of structures in a flow field, this research develops LES based FSI studies for large-scale …
Study On Anisotropic Plasticity And Fracture Of Lightweight Metal Sheets, Yueqian Jia
Study On Anisotropic Plasticity And Fracture Of Lightweight Metal Sheets, Yueqian Jia
Electronic Theses and Dissertations
How to reduce weight and increase fuel efficiency is a critical challenge in transportation industries. One way to resolve the problem is to adopting lightweight alloys (i.e. advanced high strength steel, aluminum alloys, or magnesium alloy) in structure designs and manufacturing. Fully understanding the mechanical properties of these materials is a key step. In order to fully characterize the plasticity and fracture of magnesium AZ31B-H24 sheets, a set of mechanical experiments (170 in total) were performed under both monotonic and non-proportional loading conditions, including monotonic uniaxial tension, notch tension, in-plane uniaxial compression, wide compression (or called biaxial compression), plane strain …
Characterization Of Slm-Manufactured Turbine Blade Microfeatures From Superalloy Powders, Brandon Ealy
Characterization Of Slm-Manufactured Turbine Blade Microfeatures From Superalloy Powders, Brandon Ealy
Electronic Theses and Dissertations
The limits of gas turbine technology are heavily influenced by materials and manufacturing capabilities. Inconel remains the material of choice for most hot gas path (HGP) components in gas turbines, however recent increases in turbine inlet temperature (TIT) are associated with the development of advanced convective cooling methods and ceramic thermal barrier coatings. Increasing cycle efficiency and cycle specific work are the primary drivers for increasing TIT. Lately, incremental performance gains responsible for increasing the allowable TIT have been made mainly through innovations in cooling technology, specifically convective cooling schemes. An emerging manufacturing technology may further facilitate the increase of …
A Multi-Scale Approach To Study Solid Oxide Fuel Cells: From Mechanical Properties And Crystal Structure Of The Cell's Materials To The Development Of An Interactive And Interconnected Educational Tool, Amjad Aman
Electronic Theses and Dissertations
Solid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system performance, and studies related to reliability, robustness and durability. The goal of this dissertation is to further the understanding of the mechanical properties and crystal structure of materials used …
Catalytically Enhanced Heterogeneous Combustion Of Methane, Anthony Terracciano
Catalytically Enhanced Heterogeneous Combustion Of Methane, Anthony Terracciano
Electronic Theses and Dissertations
Heterogeneous combustion is an advanced internal combustion technique, which enables heat recuperation within the flame by utilizing a highly porous ceramic media as a regenerator. Heat released within the gas phase convectively transfers to the solid media. This heat within the solid media then travels towards the inlet, enabling reactant preheating. Such heat redistribution enables stable burning of both ultra-lean fuel/air mixtures, forming a more diffuse flame through the combustion chamber, and results in reduced pollutant formation. To further enhance heterogeneous combustion, the ceramic media can be coated with catalytically active materials, which facilitates surface based chemical reactions that could …
An Experimental Investigation Of Heat Transfer For Arrays Of Impingement Jets Onto The Featured Surfaces With Cylindrical And Elliptical Raised Surfaces, Marc A. Medina
Honors Undergraduate Theses
This study focuses on multi-jet impingement for gas turbine geometries in which the objective is to understand the influence of the roughness elements on a target surface to the heat transfer. Current work has proven that implementing roughness elements for multi-jet impingement target surfaces has increased heat transfer ranging anywhere from 10-30%. This study has chosen to investigate three different roughness elements, elliptical in cross-section, to compare to smooth surface geometries for multi-jet impingement. An experimental was taken for this study to extend the current knowledge of multi-jet impingement geometries and to further understand the heat transfer performance. A temperature …
Finite Element Simulation Of Single-Lap Shear Tests Utilizing The Cohesive Zone Approach, Wilson A. Perez
Finite Element Simulation Of Single-Lap Shear Tests Utilizing The Cohesive Zone Approach, Wilson A. Perez
Honors Undergraduate Theses
Many applications require adhesives with high strength to withstand the exhaustive loads encountered in regular operation. In aerospace applications, advanced adhesives are needed to bond metals, ceramics, and composites under shear loading. The lap shear test is the experiment of choice for evaluating shear strength capabilities of adhesives. Specifically during single-lap shear testing, two overlapping rectangular tabs bonded by a thin adhesive layer are subject to tension. Shear is imposed as a result. Debonding occurs when the shear strength of the adhesive is surpassed by the load applied by the testing mechanism. This research develops a finite element model (FEM) …
High Temperature Mechanics Of Aerospace Ceramic Composites Via Synchrotron Radiation, Albert Manero Ii
High Temperature Mechanics Of Aerospace Ceramic Composites Via Synchrotron Radiation, Albert Manero Ii
Electronic Theses and Dissertations
This research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine inlet temperatures exceeding 1100°C; and ii) ceramic matrix composites that have shown capability and promise for hypersonic applications beyond 1300°C. Understanding the mechanical and material properties of these materials as they evolve with temperature …
Dynamic Modeling Of Autorotation For Simultaneous Lift And Wind Energy Extraction, Sadaf Mackertich
Dynamic Modeling Of Autorotation For Simultaneous Lift And Wind Energy Extraction, Sadaf Mackertich
Electronic Theses and Dissertations
The goal of this thesis is to develop a multi-body dynamics model of autorotation with the objective of studying its application in energy harvesting. A rotor undergoing autorotation is termed an Autogyro. In the autorotation mode, the rotor is unpowered and its interaction with the wind causes an upward thrust force. The theory of an autorotating rotorcraft was originally studied for achieving safe flight at low speeds and later used for safe descent of helicopters under engine failure. The concept can potentially be used as a means to collect high-altitude wind energy. Autorotation is inherently a dynamic process and requires …
Non-Dispersive Infrared (Ndir) Gas Sensor Utilizing Light-Emitting-Diodes Suitable For Applications Demanding Low-Power And Lightweight Instruments, Kyle Thurmond
Electronic Theses and Dissertations
Gas sensors that are low-power, light-weight, and rugged, while also remaining low-cost, have considerable appeal to areas from automotive to space flight. There are increasing demands for higher efficient vehicles with lower emissions in order meet regulations that are meant to mitigate or lessen the effects of climate change. An affordable, fast response sensor that can measure transient carbon monoxide (CO) and carbon dioxide (CO2) has broad application which can lead to more efficient, fuel flexible engines and regulations of harmful emissions. With compact, economical, low-power sensors that are able to continually monitor gases that are characteristic of burning materials, …
The Mechanical Response And Parametric Optimization Of Ankle-Foot Devices, Kevin Smith
The Mechanical Response And Parametric Optimization Of Ankle-Foot Devices, Kevin Smith
Electronic Theses and Dissertations
To improve the mobility of lower limb amputees, many modern prosthetic ankle-foot devices utilize a so called energy storing and return (ESAR) design. This allows for elastically stored energy to be returned to the gait cycle as forward propulsion. While ESAR type feet have been well accepted by the prosthetic community, the design and selection of a prosthetic device for a specific individual is often based on clinical feedback rather than engineering design. This is due to an incomplete understanding of the role of prosthetic design characteristics (e.g. stiffness, roll-over shape, etc.) have on the gait pattern of an individual. …
Heat Transfer And Pressure Measurements From Jet Array Impingement Onto A Large Radius Curved Surface, John Harrington
Heat Transfer And Pressure Measurements From Jet Array Impingement Onto A Large Radius Curved Surface, John Harrington
Electronic Theses and Dissertations
This study investigates the heat transfer and pressure drop characteristics of jet array impingement in two distinct parts. In the first part, the performance of a uniform array of jets on both a flat and a large radius curved target surface are compared. This comparison was done at average jet Reynolds number ranging from 55,000 to 125,000. In the second part, the characteristics of a non-uniform array of jets, more typical of geometries used in actual gas turbine combustors, are investigated, including the effects of the removal of downstream rows and the placement of rib features onto the target surface. …
Forced Convection Cooling Of Electric Motors Using Enhanced Surfaces, Mohammed Almaghrabi
Forced Convection Cooling Of Electric Motors Using Enhanced Surfaces, Mohammed Almaghrabi
Electronic Theses and Dissertations
Electric motors are extensively engaged in industrial and commercial applications such as electrical cars, energy-conversion systems, elevators, and actuators for aircrafts. Due to the significant internal heat generation, it is usually a challenge to design and manufacture high power density, high reliability, and low cost electric motors with superior performance. One of the efficient ways to dissipate the heat generated in the electrical motor is by using extended surfaces (i.e. heat sinks). These surfaces are extruded from the motor casing and air is forced though them by a cooling fan. This cooling approach is simple to be implemented and has …
Aeroelastic Investigation Of A Circumferentially Varying Tip Gap In An Axial Compressor Rotor, Ornan David Canon
Aeroelastic Investigation Of A Circumferentially Varying Tip Gap In An Axial Compressor Rotor, Ornan David Canon
Electronic Theses and Dissertations
The tip leakage flow in axial compressors is a significant factor in engine performance and a subject of investigation over the last several decades. Many studies have already shown that the vortices generated by this tip leakage can have a negative impact on the surrounding flow field and overall performance, and could potentially lead to excitations as well. This study examines the effect of these vortices on aeroelasticity. Specifically, it looks at the effect from a circumferentially varying tip gap, such as that produced by casing ovalization. For this project, the casing ovalization of an industrial gas turbine compressor was …
Structural Health Monitoring Of Composite Overwrapped Pressure Vessels, Luca Letizia
Structural Health Monitoring Of Composite Overwrapped Pressure Vessels, Luca Letizia
Honors Undergraduate Theses
This work is focusing to study the structural behavior of Composite Overwrapped Pressure Vessels (COPVs). These COPVs are found in many engineering applications. In the aerospace field, they are installed onto spaceships and aid the reorientation of the spacecraft in very far and airless, therefore frictionless, orbits to save energy and fuel. The intent of this research is to analyze the difference in performance of both perfectly intact and purposely damaged tanks. Understanding both the source and location of a structural fault will help NASA engineers predict the performance of COPVs subject to similar conditions, which could prevent failures of …
A Parametric Study Of Meso-Scale Patterns For Auxetic Mechanical Behavior Optimization, Matthew C. Schuler
A Parametric Study Of Meso-Scale Patterns For Auxetic Mechanical Behavior Optimization, Matthew C. Schuler
Honors Undergraduate Theses
This thesis focuses on the development, parameterization and optimization of a novel meso-scale pattern used to induce auxetic behavior, i.e., negative Poisson's ratio, at the bulk scale. Currently, the majority of auxetic structures are too porous to be utilized in conventional load-bearing applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new auxetic structures must be developed in order to confer superior thermo-mechanical responses to structures at high temperature. Additionally, patterns that take into account manufacturing limitations, while maintaining the properties characteristically attached to negative Poisson's Ratio materials, are ideal in order to utilize the potential …