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Articles 7771 - 7800 of 11196
Full-Text Articles in Aerospace Engineering
Cfd Based Aerodynamic Modeling To Study Flight Dynamics Of A Flapping Wing Micro Air Vehicle, Alok Ashok Rege
Cfd Based Aerodynamic Modeling To Study Flight Dynamics Of A Flapping Wing Micro Air Vehicle, Alok Ashok Rege
Mechanical and Aerospace Engineering Theses - Archive
The demand for small unmanned air vehicles, commonly termed micro air vehicles or MAV's, is rapidly increasing. Driven by applications ranging from civil search-and-rescue missions to military surveillance missions, there is a rising level of interest and investment in better vehicle designs, and miniaturized components are enabling many rapid advances. The need to better understand fundamental aspects of flight for small vehicles has spawned a surge in high quality research in the area of micro air vehicles. These aircraft have a set of constraints which are, in many ways, considerably different from that of traditional aircraft and are often best …
Impact Of Louver Orientation On Air Flow Distribution And Thermal Management Of Data Centers, Kushal A. Aurangabadkar
Impact Of Louver Orientation On Air Flow Distribution And Thermal Management Of Data Centers, Kushal A. Aurangabadkar
Mechanical and Aerospace Engineering Theses - Archive
Nowadays with the increasing use of technology, Traditional data centers are being replaced by the highly efficient Containerized or Modular Data centers. The cooling systems and constructional cost employed for Traditional Data centers is more and inefficient. The research intricate, about 23% of the power is consumed by HVAC cooling units and which in turn leads to increase in operational costs. Hence in order to reduce the operational costs, free cooling with Air side economizer is incorporated, compared to other cooling systems. Airflow Distribution plays an important role in the Thermal management, if the airflow is less in quantity it …
Assessment Of The Mechanical Integrity Of Cu/Low-K Dielectric In A Flip Chip Package, Thiagarajan Raman
Assessment Of The Mechanical Integrity Of Cu/Low-K Dielectric In A Flip Chip Package, Thiagarajan Raman
Mechanical and Aerospace Engineering Theses - Archive
Miniaturization and more recently convergence have been driving the industry since the invention of the transistor and integrated circuit (IC). Though the gate delay has decreased with transistor scaling, the increase in the resistive capacitive (RC) interconnect delay due to shrinking interconnect dimensions has become a serious concern for the development of future-generation electronics. To reduce the delay due to resistance R, a major technology change was the replacement of Aluminum (Al) with Copper (Cu) interconnect layers in the BEoL (Back-end-of-line). Recently, some investigators have suggested using low-k dielectric (having dielectric constant less than 4) instead of SiO2 (k= 3.9) …
Numerical Study Of Sidewall Filling For Gas-Fed Pulse Detonation Engines, Wunnarat Rongrat
Numerical Study Of Sidewall Filling For Gas-Fed Pulse Detonation Engines, Wunnarat Rongrat
Mechanical and Aerospace Engineering Theses - Archive
Pulse detonation engines for aerospace propulsion are required to operate at 50-100 Hz meaning that each pulse is 10-20 ms long. Filling of the engine and the related purging process become dominant due to their long duration compared to ignition and detonation wave propagation. This study uses ANSYS FLUENT to investigate the filling of a 1 m long tube with an internal diameter of 100 mm. Six different configurations were investigated with an endwall port and various sidewall arrangements, including stagger and inclination. A stoichiometric mixture of gaseous octane and air at STP was used to ll the tube at …
Thermal Analysis Of High End Servers Based On Development Of Detail Model And Experiments, Shreyas Sampath
Thermal Analysis Of High End Servers Based On Development Of Detail Model And Experiments, Shreyas Sampath
Mechanical and Aerospace Engineering Theses - Archive
Thermal management of an efficient data center can be primarily dictated by efficient servers. Continued increase in power density and power dissipation of high end processors, thermal analysis and management has made it strategically important in the challenge of advanced thermal solutions. Present day CFD software provides powerful tools to create very accurate fluid and heat transfer solutions. Validation of a detailed model of a server in CFD corresponds to accurate flow and temperature models and these detailed server models are the foundational blocks for accurate data center thermal management solutions. In this research, an experimental study of the thermal …
New Detonation Concepts For Propulsion And Power Generation, Eric Braun
New Detonation Concepts For Propulsion And Power Generation, Eric Braun
Mechanical and Aerospace Engineering Dissertations - Archive
A series of related analytical and experimental studies are focused on utilizing detonations for emerging propulsion and power generation devices. An understanding of the physical and thermodynamic processes for this unsteady thermodynamic cycle has taken over 100 years to develop. An overview of the thermodynamic processes and development history is provided.Thermodynamic cycle analysis of detonation-based systems has often been studied using surrogate models. A real gas model is used for a thermal efficiency prediction of a detonation wave based on the work and heat specified by process path diagrams and a control volume analysis. A combined first and second law …
Hygrothermally Stable Laminated Composites For Optimal Extension Twist Coupling In Closed Cell Configuration, Sean Muder
Hygrothermally Stable Laminated Composites For Optimal Extension Twist Coupling In Closed Cell Configuration, Sean Muder
Mechanical and Aerospace Engineering Theses - Archive
An optimization routine utilizing the sequential quadratic programming method is used to develop laminates that are hygrothermally stable in flat-strip configuration and are optimal for extension twist coupling in closed cell configuration. The performance of the laminates obtained from the optimization in terms of the level of extension twist coupling and hygrothermal stability are evaluated and compared to laminates from a previous routine. A parametric study is conducted to illustrate the relationships between the geometric dimensions of a representative closed cell section and the level of extension twist coupling. Results from the parametric study suggested a more practical optimization approach …
Design, Calibration And Testing Of A Force Balance For A Hypersonic Shock Tunnel, Pravin Vadassery
Design, Calibration And Testing Of A Force Balance For A Hypersonic Shock Tunnel, Pravin Vadassery
Mechanical and Aerospace Engineering Theses - Archive
The forces acting on a flight vehicle are critical for determining its performance. Of particular interest is the hypersonic regime. Force measurements are much more complex in hypersonic flows, where those speeds are simulated in shock tunnels. A force balance for such facilities contains sensitive gages that measure stress waves and ultimately determine the different components of force acting on the model. An external force balance was designed and fabricated for the UTA Hypersonic shock tunnel to measure drag at Mach 10. Static and dynamic calibrations were performed to find the transfer function of the system. Forces were recovered using …
Guidance And Control Of Unmanned Airships For Waypoint Navigation In The Presence Of Wind, Ghassan M. Atmeh
Guidance And Control Of Unmanned Airships For Waypoint Navigation In The Presence Of Wind, Ghassan M. Atmeh
Mechanical and Aerospace Engineering Theses - Archive
Airships are a specific class of Lighter-Than-Air (LTA) vehicles. These vehicles achieve lift mainly through buoyancy; the usually ellipsoidal shaped hull contains a lifting gas such as helium, which produces the required lift though air displacement. Due to this method of operation an airship has the ability to conduct low-power hover, which makes it ideal for applications requiring hovering over long periods of time such as surveillance, terrain mapping, meteorology and GPS. In such applications the conventional fixed wing unmanned aircraft is less suitable. The work presented in this thesis deals with designing a controller that is capable of navigating …
Heat Transfer Enhancement In A Rectangular Channel Using Vortex Generator In A Laminar Flow, Ninad C. Maniar
Heat Transfer Enhancement In A Rectangular Channel Using Vortex Generator In A Laminar Flow, Ninad C. Maniar
Mechanical and Aerospace Engineering Theses - Archive
Enhancement of heat transfer through various means has been an intense area of research for many years. There are numerous applications where high performance heat exchange is desired. The cooling of electronics, such as microprocessors, is one example. The recent rise in the studies of heat exchange enhancement techniques has also lead to efficient and compact heat exchangers. This research involves the numerical analysis of heat exchange enhancement in a rectangular channel using different types of longitudinal vortex generators (LVG) for a laminar flow. A computational fluid dynamics software package was used to compute the 3-D steady viscous flows with …
Cfd Analysis Of Direct Evaporative Cooling Zone Of Air-Side Economizer For Containerized Data Center, Niket Shah
Cfd Analysis Of Direct Evaporative Cooling Zone Of Air-Side Economizer For Containerized Data Center, Niket Shah
Mechanical and Aerospace Engineering Theses - Archive
Conventional data centers are extremely large buildings that have complex power distribution and cooling systems. These traditional brick and mortar data centers employ relatively expensive cooling systems and are inefficient. It has in turn led to an increase in construction and operational costs. Jonathan Koomey, Ph.D. of Lawrence Berkeley National Laboratory estimated that worldwide data center power consumption was 152.5 Billion kWh in 2005. In 2007, the US EPA estimated that servers and data centers, “consumed about 61 billion kilowatt-hours (kWh) in 2006 (1.5 percent of total U.S. electricity consumption) for a total electricity cost of about $4.5 billion. These …
Surface Measurements And Predictions Of Full-Coverage Film Cooling, Gregory Natsui
Surface Measurements And Predictions Of Full-Coverage Film Cooling, Gregory Natsui
Electronic Theses and Dissertations
Full-coverage film cooling is investigated both experimentally and numerically. First, surface measurements local of adiabatic film cooling effectiveness and heat transfer augmentation for four different arrays are described. Reported next is a comparison between two very common turbulence models, Realizable k-ε and SST k-ω, and their ability to predict local film cooling effectiveness throughout a full-coverage array. The objective of the experimental study is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for four surfaces cooled by large, both in hole count and in non-dimensional spacing, arrays of film cooling holes. The four arrays are of …
Agglomeration, Evaporation And Morphological Changes In Droplets With Nanosilica And Nanoalumina Suspensions In An Acoustic Field, Erick Tijerino
Agglomeration, Evaporation And Morphological Changes In Droplets With Nanosilica And Nanoalumina Suspensions In An Acoustic Field, Erick Tijerino
Electronic Theses and Dissertations
Acoustic levitation permits the study of droplet dynamics without the effects of surface interactions present in other techniques such as pendant droplet methods. Despite the complexities of the interactions of the acoustic field with the suspended droplet, acoustic levitation provides distinct advantages of controlling morphology of droplets with nanosuspensions post precipitation. Droplet morphology is controlled by vaporization, deformation and agglomeration of nanoparticles, and therefore their respective timescales are important to control the final shape. The balance of forces acting on the droplet, such as the acoustic pressure and surface tension, determine the geometry of the levitated droplet. Thus, the morphology …
Investigation Of Instabilities Affecting Detonations: Improving The Resolution Using Block-Structured Adaptive Mesh Refinement, Prashaanth Ravindran
Investigation Of Instabilities Affecting Detonations: Improving The Resolution Using Block-Structured Adaptive Mesh Refinement, Prashaanth Ravindran
Mechanical and Aerospace Engineering Dissertations - Archive
The unstable nature of detonation waves is a result of the critical relationship between the hydrodynamic shock and the chemical reactions sustaining the shock. A perturbative analysis of the critical point is quite challenging due to the multiple spatio-temporal scales involved along with the non-linear nature of the shock-reaction mechanism. The author's research attempts to provide detailed resolution of the instabilities at the shock front. Another key aspect of the present research is to develop an understanding of the causality between the non-linear dynamics of the front and the eventual breakdown of the sub-structures. An accurate numerical simulation of detonation …
Thrust Vector Control Of An Upper-Stage Rocket With Multiple Propellant Slosh Modes, Mahmut Reyhanoglu, Jaime Rubio Hervas
Thrust Vector Control Of An Upper-Stage Rocket With Multiple Propellant Slosh Modes, Mahmut Reyhanoglu, Jaime Rubio Hervas
Physical Sciences - Daytona Beach
“The thrust vector control problem for an upper-stage rocket with propellant slosh dynamics is considered. The control inputs are defined by the gimbal deflection angle of a main engine and a pitching moment about the center of mass of the spacecraft. The rocket acceleration due to the main engine thrust is assumed to be large enough so that surface tension forces do not significantly affect the propellant motion during main engine burns. A multi-mass-spring model of the sloshing fuel is introduced to represent the prominent sloshing modes. A nonlinear feedback controller is designed to control the translational velocity vector and …
Geochemical Evaluation Of High Sulfate Levels In Ponca Creek, Northeastern Nebraska, Jon C. Atkinson
Geochemical Evaluation Of High Sulfate Levels In Ponca Creek, Northeastern Nebraska, Jon C. Atkinson
United States Air Force: Publications
Most surface water and shallow groundwater occurring in northeastern Nebraska are of the calcium bicarbonate type, with minor concentrations (e.g., 10–200 mg/L) of sulfate (SO4). Examination of historical water quality data (major cations and anions) for Ponca Creek, a predominantly ephemeral streamin northeastern Nebraska, revealed that SO4 concentrations ranged from about 110 to almost 1000mg/L and contribute to a calcium sulfate hydrochemical facies. Consequently, most SO4 concentrations were above the U.S. Environmental Protection Agency secondary maximum contaminant level in drinking water of 250 mg/L. Sulfate concentrations for the same period for a nearby stream, Verdigre Creek, …
Evaluation Of Niobium As Candidate Electrode Material For Dc High Voltage Photoelectron Guns, Mahzad Bastaninejad, Md. Abdulla Mohamed, Abdelmageed Elmustafa, P. Adderley, J. Clark, S. Covert, J. Hansknecht, C. Hernandez-Garcia, M. Poelker, R. Mammei, K. Surles-Law, P. Williams
Evaluation Of Niobium As Candidate Electrode Material For Dc High Voltage Photoelectron Guns, Mahzad Bastaninejad, Md. Abdulla Mohamed, Abdelmageed Elmustafa, P. Adderley, J. Clark, S. Covert, J. Hansknecht, C. Hernandez-Garcia, M. Poelker, R. Mammei, K. Surles-Law, P. Williams
Mechanical & Aerospace Engineering Faculty Publications
The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. A total of eight electrodes were evaluated: two 304 stainless steel electrodes polished to mirrorlike finish with diamond grit and six niobium electrodes (two single-crystal, two large-grain, and two fine-grain) that were chemically polished using a buffered-chemical acid solution. Upon the first application of high voltage, the best large-grain and single-crystal niobium electrodes performed better than the best stainless steel electrodes, exhibiting less field emission at comparable voltage and field strength. In all cases, field emission …
Design And Development Of Ionic Liquid Dual-Mode Spacecraft Propellants, Steven P. Berg
Design And Development Of Ionic Liquid Dual-Mode Spacecraft Propellants, Steven P. Berg
Masters Theses
"Energetic ionic liquids capable of dual-mode chemical monopropellant or bipropellant and electric electrospray rocket propulsion are investigated. Following an extensive literature review, ionic liquids [Bmim][dca], [Bmim][NO₃], and [Emim][EtSO₄] are selected for study since their physical properties align well with the current state-of-the-art in chemical and electrospray propellants. Simulations show that these liquids will not be useful for monopropellant propulsion due to the prediction of solid carbon formation in the exhaust and performance 13-23% below that of hydrazine. Considering these ionic liquids as a fuel component in a binary monopropellant mixture with hydroxyl ammonium nitrate shows 1-4% improved specific impulse over …
Numerical Investigation Of Second-Law Characteristics Of Ramjet Throttling, Jonathan Albert Sheldon
Numerical Investigation Of Second-Law Characteristics Of Ramjet Throttling, Jonathan Albert Sheldon
Masters Theses
"A numerical study of a generic axisymmetric ramjet operating at conditions corresponding to flight Mach 3.0 and a standard altitude of 10 km is presented. The study includes both modeling of steady-state flowfields in the ramjet as well as transient throttling maneuvers in which the throttle is decreased or increased from maximum or minimum throttle positions. The results presented here focus on entropy generation and performance characteristics. Combustion-generated exothermic heat release is modeled using simple volumetric energy addition to the flow within a defined heat release zone. The study utilizes two levels of wall boundary modeling, corresponding respectively to inviscid …
Analysis Of Optimal Control Derivations For Aerial Defense, Andrew John Friedrichs
Analysis Of Optimal Control Derivations For Aerial Defense, Andrew John Friedrichs
Masters Theses
"Optimal control will be used to derive four guidance laws for the purpose of defending an aircraft from incoming missiles. The dynamics of the defending missile, and the overall engagement are used in these derivations. They are evaluated first in two degrees of freedom, then in six degrees. The guidance objective is to move a defending missile between the aircraft and the attacker. Optimal control is used to derive different commanded accelerations. Utilizing small changes in the cost functions, four applications will be derived. Triangle Guidance is used for inspiration, and initially a direct approach is attempted. In the course …
A Study Of The Integration Of An Inlet Noise Radiation Code With The Aircraft Noise Prediction Program, Devin Kyle Boyle
A Study Of The Integration Of An Inlet Noise Radiation Code With The Aircraft Noise Prediction Program, Devin Kyle Boyle
Masters Theses
"A numerical method has been developed in order to study the effect of turbofan inlet acoustic treatment on the resulting cumulative noise heard by observers on the ground. The approach to creating the tool was to combine the capabilities of the NASA-developed Aircraft Noise Prediction Program (ANOPP) with the fan noise propagation and radiation code developed at Missouri University of Science and Technology. ANOPP can be used to predict the noise metrics resulting from a typical commercial aircraft with turbofan engines on several different flight profiles, including takeoff, approach/landing and a steady (constant altitude/airspeed) flyover. These capabilities are valuable for …
Studies Of Inductive Plasmas And Their Application To Theta-Pinch Devices Via Numerical Modeling, Warner C. Meeks
Studies Of Inductive Plasmas And Their Application To Theta-Pinch Devices Via Numerical Modeling, Warner C. Meeks
Masters Theses
"First, a globally-averaged RF plasma model is used to investigate exit conditions immediately following a RF pre-ionization stage. Analysis shows that reducing pulse duration from 10⁻⁶ to 10⁻⁷ seconds increases peak ion energy fraction by 17% (from 16 to 33%) and doubles final conductivity. Pulse waveforms are square in nature, and ion energy fraction is defined in this work as the percentage of total input energy entrained in ions. Increasing total energy deposition from 5 to 160 mJ increases ion energy fraction from 33% to 58% at a 200 ns pulse duration. This increase is not linear however, showing instead …
Gray Gas Analysis Of Radiative Preheating Effects On Shock Induced Combustion, Pratibha Raghunandan
Gray Gas Analysis Of Radiative Preheating Effects On Shock Induced Combustion, Pratibha Raghunandan
Masters Theses
"The use of detonations in combustors has been receiving increased attention in recent times. The presence of shock waves in such combustors invariably poses the existence of two domains that present different physics for the flow processes. The variation of upstream temperature due to radiative heating by the products of combustion was given particular attention in the present study. The modeling of heat transfer across a normal shock wave of negligible thickness was done by considering the reactants and the products of combustion to be in radiative equilibrium with each other. The quantification of emissivity of the products of combustion …
Development Of Detailed Computational Flow Model Of High End Server And Validation Using Experimental Methods, Vijayalayan Pandiyan
Development Of Detailed Computational Flow Model Of High End Server And Validation Using Experimental Methods, Vijayalayan Pandiyan
Mechanical and Aerospace Engineering Theses - Archive
The continued development of the microprocessor has led to significant increase in high frequency interconnects and power dissipation. High power devices are pushing the limits of air cooling in data center environments. Data center power consumption continues to grow at a rapid pace. In light of this increasing trend in power consumption, computer systems researchers, application designers, power and cooling engineers, and governmental bodies have all launched research efforts to improve data center energy efficiency [1]. Rack servers tend to be the main perpetrators of wasting energy and represent the largest portion of the IT energy load in a typical …
Experimental/Computational Analysis Of Active Cooling Of Stacked Device Using Multidimensional Configured Thermoelectric Modules, Vaidehi Bharat Patel
Experimental/Computational Analysis Of Active Cooling Of Stacked Device Using Multidimensional Configured Thermoelectric Modules, Vaidehi Bharat Patel
Mechanical and Aerospace Engineering Theses - Archive
Stacked devices are currently used widely because of their smaller footprint and corresponding ability to accommodate heterogeneous devices such as memory and logic and enable a silicon efficiency greater than 100%. This configuration will results in thermal management challenges due to the torturous heat dissipation path. In addition, the non-uniformity in chip power distribution results in an increased spreading resistance as well as temperature gradient at the device level that can degrade performance and reliability. In this study the Thermoelectric Modules were configured in a multidimensional form surrounding a three dimensional cold core. The corresponding Computational Fluid Dynamics model is …
Large Scale Finite Element Analysis Using Gpu Parallel Computing, Ashkan Akbariyeh
Large Scale Finite Element Analysis Using Gpu Parallel Computing, Ashkan Akbariyeh
Mechanical and Aerospace Engineering Theses - Archive
In the past years, graphic processing units have become a new abundant parallelcomputing resource on personal computers. In this work parallel computation ofa typical case in nite element analysis for solids has been practiced. The solutionof 3-D linear elastic static problems with 3 degree of freedom is fully implementedutilizing the current GPU technology. Discretization of the problem has been donefor two cases of: Tetrahedral and Hexahedral elements. Acceleration of the solutionhas been realized using SIMT parallel algorithms. Sparse matrix storage formats aswell as matrix-vector operations are investigated for optimum hardware utilization.preconditioned conjugate gradient method has been fully implemented on the …
Protection Of Humanity’S Cultural And Historic Heritage In Space, Justin St. P. Walsh
Protection Of Humanity’S Cultural And Historic Heritage In Space, Justin St. P. Walsh
Art Faculty Articles and Research
While the international community has acted forcefully since World War II to protect sites and objects of cultural or historic significance on Earth, little attention has been paid to the same kinds of sites and objects in space. There are important ethical and scholarly reasons for wanting to preserve sites and in situ objects in off-Earth contexts from destruction or commercial exploitation. Innovative space research equipment, such as spacecraft, satellites, and space stations, and the locations of historic missions, such as Tranquility Base, therefore deserve formal international recognition and protection. Appropriate models for developing a comprehensive protective scheme can be …
Thermal Stability Characteristics Of Fisher-Tropsch And Hydroprocessed Alternative Aviation Fuels In A Fixed Bed Reactor, Sergio Quintero
Thermal Stability Characteristics Of Fisher-Tropsch And Hydroprocessed Alternative Aviation Fuels In A Fixed Bed Reactor, Sergio Quintero
Electronic Theses and Dissertations
Growing prices, limited supply, and public concern about greenhouse gases associated with crude-derived jet fuels have led to development of renewable alternatives which must be compatible with the worldwide civilian and military aviation infrastructure, which were designed for operation with Jet-A/JP-8. Any alternative fuel should not have negative effects on the aircraft engines and fuel systems, especially from a thermal stability perspective, since any adverse effect of the physical properties, and chemical composition, including existence of trace elements, of those fuels may only be revealed after extensive operation, resulting in higher life-cycle maintenance and operation costs. This study considered four …
A Filter-Forcing Turbulence Model For Large Eddy Simulation Incorporating The Compressible "Poor Man's" Navier--Stokes Equations, Joshua Strodtbeck
A Filter-Forcing Turbulence Model For Large Eddy Simulation Incorporating The Compressible "Poor Man's" Navier--Stokes Equations, Joshua Strodtbeck
Theses and Dissertations--Mechanical and Aerospace Engineering
A new approach to large-eddy simulation (LES) based on the use of explicit spatial filtering combined with backscatter forcing is presented. The forcing uses a discrete dynamical system (DDS) called the compressible ``poor man's'' Navier--Stokes (CPMNS) equations. This DDS is derived from the governing equations and is shown to exhibit good spectral and dynamical properties for use in a turbulence model. An overview and critique of existing turbulence theory and turbulence models is given. A comprehensive theoretical case is presented arguing that traditional LES equations contain unresolved scales in terms generally thought to be resolved, and that this can only …
Design And Flight Testing Of A Warping Wing For Autonomous Flight Control, Edward Brady Doepke
Design And Flight Testing Of A Warping Wing For Autonomous Flight Control, Edward Brady Doepke
Theses and Dissertations--Mechanical and Aerospace Engineering
Inflatable-wing Unmanned Aerial Vehicles (UAVs) have the ability to be packed in a fraction of their deployed volume. This makes them ideal for many deployable UAV designs, but inflatable wings can be flexible and don’t have conventional control surfaces. This thesis will investigate the use of wing warping as a means of autonomous control for inflatable wings. Due to complexities associated with manufacturing inflatable structures a new method of rapid prototyping deformable wings is used in place of inflatables to decrease cost and design-cycle time. A UAV testbed was developed and integrated with the warping wings and flown in a …