Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 17 of 17
Full-Text Articles in Engineering
The Effect Of Laser Power And Scan Speed On Melt Pool Characteristics Of Pure Titanium And Ti-6al-4v Alloy For Selective Laser Melting, Chandrakanth Kusuma
The Effect Of Laser Power And Scan Speed On Melt Pool Characteristics Of Pure Titanium And Ti-6al-4v Alloy For Selective Laser Melting, Chandrakanth Kusuma
Browse all Theses and Dissertations
Selective Laser Melting (SLM) is an additive manufacturing (AM) technique that creates complex parts by selectively melting metal powder layer-by-layer. In SLM, the process parameters decide the quality of the fabricated component. In this study, single beads of commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy are melted on a substrate of the same material as powder using an in-house built SLM machine. Multiple combinations of laser power and scan speed are used for single bead fabrication while the laser beam diameter and powder layer thickness are kept constant. This experimental study investigates the influence of laser power, scan speed and …
Aircraft Thermal Management Using Liquefied Natural Gas, Sean Robert Nuzum
Aircraft Thermal Management Using Liquefied Natural Gas, Sean Robert Nuzum
Browse all Theses and Dissertations
Many technological advances are expected to increase the capabilities of the future aircraft, both civilian and military. These improvements come in many forms such as new wing or fuselage shapes to improve lift or decrease drag. Other improvements are internal. One of these areas is the inclusion of advanced electronic systems for various roles. These changes affect a wide range of aircraft systems including, but not limited to avionics, power generation and thermal management. While these modifications promise to increase aircraft capabilities such as its range, payload or other key performance parameters, there are some significant drawbacks. One drawback is …
Quantifying Amorphous Content Of Commercially Available Silicon Carbide Fibers, Ian Mark Wolford
Quantifying Amorphous Content Of Commercially Available Silicon Carbide Fibers, Ian Mark Wolford
Browse all Theses and Dissertations
SiC/SiC ceramic matrix composites (CMCs) with potential applications at =2700°F (1482°C) are of significant interest to the Air Force. The high temperature performance of SiC fibers used within these composites is greatly affected by the presence of amorphous SiOC and free carbon in the fibers. Therefore quantification of this non SiC material in commercially available SiC fibers is extremely important. In this work Hi Nicalon, Hi-Nicalon Type-S, Tyranno-SA3, Cef-NITE, and Sylramic SiC fibers were studied. Changes in mass, grain size, and amorphous content were measured as a function of processing temperature and time. The amorphous material in each fiber was …
An Adapted Approach To Process Mapping Across Alloy Systems And Additive Manufacturing Processes, Luke Charles Sheridan
An Adapted Approach To Process Mapping Across Alloy Systems And Additive Manufacturing Processes, Luke Charles Sheridan
Browse all Theses and Dissertations
The continually growing market for metal components fabricated using additive manufacturing (AM) processes has called for a greater understanding of the effects of process variables on the melt pool geometry and microstructure in manufactured components for various alloy systems. Process Mapping is a general approach that traces the influence of process parameters to thermal behavior and feature development during AM processing. Previous work has focused mainly on Ti-6Al-4V (Ti64), but this work uses novel mathematical derivations and adapted process mapping methodologies to construct new geometric, thermal, and microstructural process maps for Ti64 and two nickel superalloy material systems. This work …
Vehicle Level Transient Aircraft Thermal Management Modeling And Simulation, Adam Donovan
Vehicle Level Transient Aircraft Thermal Management Modeling And Simulation, Adam Donovan
Browse all Theses and Dissertations
Many advances in technology are expected to increase the capabilities of next generation aircraft, and these advances will increase the thermal load on the aircraft as well. In order to assess and account for these increased thermal loads, three studies were performed: a fuel pump trade study, a high energy pulsed system (HEPS) implementation study, and a legacy vehicle environmental control system (ECS) study. The fuel pump study addresses the effect of the implementation of a centrifugal fuel pump versus a variable displacement fuel pump. Traditionally, aircraft designers have used a centrifugal fuel pump over a piston based pump based …
Inlet Distortion Effects On The Unsteady Aerodynamics Of A Transonic Fan Stage, Daniel Oliver Reilly
Inlet Distortion Effects On The Unsteady Aerodynamics Of A Transonic Fan Stage, Daniel Oliver Reilly
Browse all Theses and Dissertations
A computational study was conducted to understand the influence of aircraft inlet distortion flow on the unsteady aerodynamic loading of a gas turbine fan stage. A single stage, transonic fan design with no inlet guide vanes was modeled with a commercial, computational fluid dynamics solver, STAR-CCM+, using the harmonic balance technique. The baseline inlet boundary condition applied to the model is consistent with that of a homeomorphic variant of the M2129 S-duct, and exhibited stagnation pressure distortion and a swirl pattern. The baseline inlet flow was decomposed and parameterized into a set of inlet boundary conditions which were individually applied …
Thermoelectric Transport And Energy Conversion Using Novel 2d Materials, Luke J. Wirth
Thermoelectric Transport And Energy Conversion Using Novel 2d Materials, Luke J. Wirth
Browse all Theses and Dissertations
Nanomaterials hold great promise for applications in thermal management and thermoelectric power generation. Defects in these are important as they are generally inevitably introduced during fabrication or intentionally engineered to control the properties of the nanomaterials. Here, we investigate how phonon-contributed thermal conductance in narrow graphene, boron nitride (BN), and silicene nanoribbons (NRs), responds to the presence of a vacancy defect and the corresponding geometric distortion, from first principles using the non-equilibrium Green's function method. Analyses are made of the geometries, phonon conductance coefficients, and local densities of states (LDOS) of pristine and defected nanoribbons. It is found that hydrogen …
The Design And Experimental Investigation Of Novel Double-Blade Wind Turbine Models Inspired By Houck's Concept, Laura E. Carpenter
The Design And Experimental Investigation Of Novel Double-Blade Wind Turbine Models Inspired By Houck's Concept, Laura E. Carpenter
Browse all Theses and Dissertations
Energy can be captured from wind turbines efficiently today. However there's always room for improvement up to the Betz's limit of 59.3% efficiency. A novel wind turbine blade was designed with double blade rotor inspired by Houck's concept in an attempt to improve the efficiency of the horizontal axis wind turbine. Scaled wind turbine models with a diameter of 150 mm were designed in SolidWorks adjusting the parameters of stagger, gap, and decalage. The general design comprises of two modern blades attached by a curved flow guide at the tip. Fourteen blade models were designed and tested to obtain power, …
Elucidating The Role Of Microstructure, Texture, And Microtexture On The Dwell Fatigue Response Of Ti-6al-4v, Alec Mitchell Blankenship
Elucidating The Role Of Microstructure, Texture, And Microtexture On The Dwell Fatigue Response Of Ti-6al-4v, Alec Mitchell Blankenship
Browse all Theses and Dissertations
Ambient temperature dwell sensitivity is known to be deleterious to the fatigue response of near-alpha titanium alloys. Dwell fatigue refers to the presence of a sustained hold at peak stress as opposed to the continuous variation of normal cyclic fatigue loading. This reduction in failure life-times from dwell loading is attributed to early crack nucleation and faster crack propagation. The degradation is the result of plastic anisotropy on the microstructural scale along with tendency of titanium alloys to creep at low temperatures at stresses well below the 0.2% offset yield strength. Despite being the most widely used titanium alloy, Ti-6Al-4V …
Computer Modeling Of A Solar Thermal System For Space Heating, Dhananjay D. Deshpande
Computer Modeling Of A Solar Thermal System For Space Heating, Dhananjay D. Deshpande
Browse all Theses and Dissertations
Most applications of flat plate, low-temperature solar thermal panels are for water heating, such as producing domestic hot water or raising the temperature of swimming pools. This is reasonable given that the large masses of water present in these systems inherently provide built-in thermal energy storage so that a separate energy storage tank does not have to be purchased. For a space heating system, extra thermal energy storage generally has to be purchased and is a detriment to the economics of these systems. Despite the economic drawbacks of solar thermal space heating, this thesis focuses on the size of thermal …
Transient Analysis Of A Solid Oxide Fuel Cell/ Gas Turbine Hybrid System For Distributed Electric Propulsion, Venkata Adithya Chakravarthula
Transient Analysis Of A Solid Oxide Fuel Cell/ Gas Turbine Hybrid System For Distributed Electric Propulsion, Venkata Adithya Chakravarthula
Browse all Theses and Dissertations
Gas turbine technology for aerospace applications are approaching limits in efficiency gains as increases in efficiency today occurs in very small increments. One limitation in conventional gas turbine technology is the combustion process, which destroys most of the exergy in the cycle. To address this limitation in a traditional Brayton power cycle, a hybrid system which is integrated with Solid Oxide Fuel Cell (SOFC) and gas turbine is developed. Hybrid systems involving fuel cells have better efficiencies than conventional power generation systems. Power generation systems with improved performance from low fuel utilizations and low maintenance costs are possible. The combination …
Development Of Analytical Equations For Optimum Tilt Of Two-Axis And Single-Axis Rotating Solar Panels For Clear-Atmosphere Condition, Gaurav Subhash Gugale
Development Of Analytical Equations For Optimum Tilt Of Two-Axis And Single-Axis Rotating Solar Panels For Clear-Atmosphere Condition, Gaurav Subhash Gugale
Browse all Theses and Dissertations
Solar Energy is a renewable energy source which is used widely in recent times. Photovoltaic panels collect the sun’s energy and convert it to electricity. Photovoltaic panels are being widely used in both domestic applications, commercial applications, and small-scale power generation applications. Photovoltaic panels are easy to install, they generate most of their power when electrical demands peak, prices of photovoltaic panels are dropping rapidly, photovoltaic panels require low maintenance, their operating costs are minimal, and they are highly suitable for remote applications. The amount of electricity produced by photovoltaic panels depends on the amount of sunlight the panel captures. …
On The Experimental Evaluation Of Loss Production And Reduction In A Highly Loaded Low Pressure Turbine Cascade, Philip Steven Bear
On The Experimental Evaluation Of Loss Production And Reduction In A Highly Loaded Low Pressure Turbine Cascade, Philip Steven Bear
Browse all Theses and Dissertations
Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with …
The Effects Of Micro-Dimple Texture On The Friction And Thermal Behavior Of A Point Contact, Utsav Kamleshbhai Parmar
The Effects Of Micro-Dimple Texture On The Friction And Thermal Behavior Of A Point Contact, Utsav Kamleshbhai Parmar
Browse all Theses and Dissertations
This study investigates the effects of the micro-dimple texture on the friction and surface temperature performances of a ball-on-disk contact, operating under the speed and load ranges that cover typical gearing applications. Circular shaped micro-dimple arrays with different dimple center distances and dimple depths are implemented on the ball surface to quantify the impacts of these two parameters on the friction coefficient and the maximum ball surface temperature. In addition, the contacts of three surface texture combinations, namely micro-dimpled and polished ball surface versus polished disk surface, polished ball surface versus polished disk surface and ground ball surface versus ground …
Hybrid Particle Image Velocimetry With The Combination Of Cross-Correlation And Optical Flow Method, Mark Bradley Johnson
Hybrid Particle Image Velocimetry With The Combination Of Cross-Correlation And Optical Flow Method, Mark Bradley Johnson
Browse all Theses and Dissertations
Particle Image Velocimetry (PIV) has been of relevant discussions lately as the equipment used to obtain temporally and spatially resolved flow fields have advanced rapidly. Despite these advancements, the accuracy of evaluating these images have yet to exceed expectations. Current techniques typically utilize one method, either correlation based (frequently) or optical flow (non-frequently), and both are vulnerable to specific conditions incorporated in the PIV images. Only through the combination of two methods, cross correlation and optical flow, can a technique benefit from the strengths of each method while concealing the flaws each individual method contains. The Hybrid Particle Image Velocimetry …
Locally Optimized Covariance Kriging For Non-Stationary System Responses, Daniel Lee Clark Jr.
Locally Optimized Covariance Kriging For Non-Stationary System Responses, Daniel Lee Clark Jr.
Browse all Theses and Dissertations
In this thesis, the Locally-Optimized Covariance (LOC) Kriging method is developed. This method represents a flexible surrogate modeling approach for approximating a non-stationary Kriging covariance structures for deterministic responses. The non-stationary covariance structure is approximated by aggregating multiple stationary localities. The aforementioned localities are determined to be statistically significant utilizing the Non-Stationary Identification Test. This methodology is applied to various demonstration problems including simple one and two-dimensional analytical cases, a deterministic fatigue and creep life model, and a five-dimensional fluid-structural interaction problem. The practical significance of LOC-Kriging is discussed in detail and is directly compared to stationary Kriging considering computational …
Feasibility Of Attaining Fully Equiaxed Microstructure Through Process Variable Control For Additive Manufacturing Of Ti-6al-4v, Sarah Louise Kuntz
Feasibility Of Attaining Fully Equiaxed Microstructure Through Process Variable Control For Additive Manufacturing Of Ti-6al-4v, Sarah Louise Kuntz
Browse all Theses and Dissertations
One of the greatest challenges in additive manufacturing is fabricating titanium structures with consistent and desirable microstructure. To date, fully columnar deposits have been achieved through direct control of process variables. However, the introduction of external factors appears necessary to achieve fully equiaxed grain morphology using existing commercial processes. This work introduces and employs an analytic model to relate process variables to solidification thermal conditions and expected beta grain morphology at the surface of and at the deepest point in the melt pool. The latter is required in order to ensure the deposited microstructure is maintained even after the deposition …