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Articles 241 - 255 of 255
Full-Text Articles in Aerospace Engineering
On The Near Field Mean Flow Structure Of Transverse Jets Issuing Into A Supersonic Freestream, Dean Anthony Dickmann
On The Near Field Mean Flow Structure Of Transverse Jets Issuing Into A Supersonic Freestream, Dean Anthony Dickmann
Mechanical and Aerospace Engineering Dissertations - Archive
The near field mean flow structure of transverse jets issuing from a surface into supersonic crossflow is examined using numerical methods and separation topology. The Navier-Stokes solver Falcon, developed at Lockheed Martin, was used to simulate the interaction between the jet and freestream over a flat plate and a generic missile body. The near field flow structure included a l bow shock upstream of the jet interacting with the approaching boundary layer that forms a pair of horseshoe vortices while another l- structure closer to the jet formed a second pair of horseshoe vortices. As the jet was turned downstream …
Methodologies For Automated Microassembly, Mohammad A. Mayyas
Methodologies For Automated Microassembly, Mohammad A. Mayyas
Mechanical and Aerospace Engineering Dissertations - Archive
The development of micromachining technologies has provided wide applications in micro sensing and actuation. However, most of the demonstrated devices are selectively constructed by fabrication processes that are limited to complexity, configuration, dimension, and material variation. The monolithic fabrication has limitations and does not allow the inclusion of multiple components of incompatible processes. Therefore, the construction of 3D microstructures by heterogeneous microassembly is an alternate manufacturing route. In deterministic, monitored or controlled microassembly there has been considerable research in developing, analyzing and applying distributed algorithms for sensor and sensorless based assembly processes. Meso-scale teleoperated work-cells supported by Nano manipulators have …
Stress Distribution And Strength Prediction Of Composite Laminates With Multiple Holes, Brian Esp
Stress Distribution And Strength Prediction Of Composite Laminates With Multiple Holes, Brian Esp
Mechanical and Aerospace Engineering Dissertations - Archive
The major purpose of this study was to investigate failure of composite laminates with multiple unloaded holes in close proximity. The least square boundary collocation method for anisotropic materials was utilized to determine the state of stress. The approach utilized collocation on both the internal and external boundaries, making it relatively easy to implement. The method compared favorably to both published and finite element solutions. A failure prediction approach for an infinite, symmetric and balanced laminate, with two holes in close proximity was presented. The baseline material for consideration was IM7/977-3, a carbon fiber/epoxy lamina. The failure prediction method was …
An Analytical And Numerical Model For Design Of Non- Uniformly Powered Silicon Chips Based On Both Thermal And Device Clock Performance, Abhihit D. Kaisare
An Analytical And Numerical Model For Design Of Non- Uniformly Powered Silicon Chips Based On Both Thermal And Device Clock Performance, Abhihit D. Kaisare
Mechanical and Aerospace Engineering Dissertations - Archive
Silicon chips continue to grow in capabilities, complexity and performance. Silicon chips typically integrate functional components such as logic and level two (L2) cache memory in their architecture. This functional integration of logic and memory results in improved performance of the chip. However, the integration also introduces a layer of complexity in the thermal design and management of silicon chips. As a direct result of functional integration, the power map on a silicon chip is typically highly non-uniform and the assumption of a uniform heat flux across the chip surface has been shown to be invalid post Pentium II architecture. …
Context-Aware Inference System To Capture Design Rationale From Legacy Mcad, Ganeshram Ramji Iyer
Context-Aware Inference System To Capture Design Rationale From Legacy Mcad, Ganeshram Ramji Iyer
Mechanical and Aerospace Engineering Dissertations - Archive
There exist numerous design rationale systems that convert captured information into structured design rationale while providing rationale representation and retrieval. These systems woefully neglect the design rationale that is present in legacy CAD such as 2D drawings and 3D models. The dissertation addresses the issues that arise when dealing with the capture, representation and retrieval of design rationale from the 2D legacy CAD data, specifically the non-form related data (e.g. text and symbols). A definition for design rationale in the CAD domain is presented which forms the basis of the proposed approach. The approach uses a unique context-aware inference system …
Autonomous And Cooperative Multi-Uav Guidance In Adversarial Environment, Ugur Zengin
Autonomous And Cooperative Multi-Uav Guidance In Adversarial Environment, Ugur Zengin
Mechanical and Aerospace Engineering Dissertations - Archive
The research presented in this dissertation is aimed at developing rule-based autonomous and cooperative guidance strategies for UAVs to perform missions such as path planning, target tracking and rendezvous while reducing their risk/threat exposure level, and avoiding threats and/or obstacles by utilizing measurement information provided by sensors. First, a mathematical formulation is developed to represent the area of operation that contains various types of threats, obstacles, restricted areas, in a single framework. Once constructed, there will be no need to distinguish between adversaries as the framework already contains the information on what needs to be avoided and the level of …
Enhancement Of Pool Boiling Heat Transfer Using Thermally-Conductive Microporous Coating Techniques, Joo Han Kim
Enhancement Of Pool Boiling Heat Transfer Using Thermally-Conductive Microporous Coating Techniques, Joo Han Kim
Mechanical and Aerospace Engineering Dissertations - Archive
The present research is an experimental study of the enhancement of boiling heat transfer using microporous coating techniques. The current research is divided into four major phases. During the first phase, the effects of different metal particle sizes in the coating compound for thermally non-conductive microporous coating on pool boiling performance of refrigerants and water are investigated. The test surfaces, solid copper blocks with 1-cm² base, were tested at atmospheric pressure in saturated FC-72, R-123, and water. Results showed that the surface treatment by non-conductive microporous coating significantly enhanced both nucleate boiling and critical heat flux of all three refrigerants. …
Optimization Of The Tool Path In A Robotic Environment, Mukund Venkatachari Narasimhan
Optimization Of The Tool Path In A Robotic Environment, Mukund Venkatachari Narasimhan
Mechanical and Aerospace Engineering Dissertations - Archive
The rising costs and demand coupled with shrinking energy generating resources has triggered the need for optimum use of energy resources, minimizing the overhead costs and maximizing the profits. Robots have been long touted as a fit replacement of human labor force in manufacturing sectors. Slowly there is increased presence of robots in automobile and electronic industries. Typically they are used for welding, painting, ironing, assembly, pick and place, inspection, and testing. Mass production, fulfilling the ever increasing demand, can be accomplished by robots because of their precision, speed of operation and high endurance capabilities. This dissertation comprises of two …
Analysis And Optimal Design Of Beams Using Radial Basis Function, Yung-Kang Sun
Analysis And Optimal Design Of Beams Using Radial Basis Function, Yung-Kang Sun
Mechanical and Aerospace Engineering Dissertations - Archive
The application of Multiquadric Radial Basis Function (MQ RBF) in the analysis and optimal design of beams are addressed in this dissertation. For static analysis, a new Least Square Collocation (LSC) method is introduced. For buckling and vibration analysis, Rayleigh-Ritz analysis procedures are presented using MQ RBF basis function. Numerical results show that LSC can provide better results than the classical collocation method when the same number of collocation points are used. In vibration analysis, MQ RBF-based Rayleigh-Ritz can be used to calculate natural frequency accurately for several hundred modes. The important question of choosing shift parameters is discussed and …
Crashworthiness Design Optimization Using Surrogate Models, Cheng-Ho Tho
Crashworthiness Design Optimization Using Surrogate Models, Cheng-Ho Tho
Mechanical and Aerospace Engineering Dissertations - Archive
Despite the advances in computer technology, the enormous computational cost associated with the large-scale and complex nonlinear crashworthiness simulations renders it to be impractical to rely exclusively on computer simulations for crashworthiness design optimization. A preferable strategy is to employ the computational efficient surrogate model in lieu of the expensive simulations to facilitate the optimization process and design concept exploration. An added advantage of the surrogate models is that they tends to eliminate the high-frequency numerical noise which may hinder the performance of the direct gradient-based optimization technique by constructing smooth crash responses in the crashworthiness analysis. Even thought the …
Numerical Study On Capillarity- Dominant Free Surface And Interfacial Flows, Zhaoyuan Wang
Numerical Study On Capillarity- Dominant Free Surface And Interfacial Flows, Zhaoyuan Wang
Mechanical and Aerospace Engineering Dissertations - Archive
The continuum surface force (CSF) method has been extensively employed in the volume-of-fluid (VOF), level set (LS) and front tracking methods to model surface tension forces. Its ability is limited for the surface tension dominant free surface and interfacial flows due to the existence of spurious currents. These currents may lead to disastrous interface instabilities and failure of grid convergence, which are present in all the previous versions of the CSF algorithm. In this study, a coupled level set and volume-of-fluid method (CLSVOF) is employed for interface tracking, which offers more accurate computations of the curvature and the normal vector …
Numerical Study Of Chemically Reacting Viscous Flow Relevant To Pulsed Detonation Engines, Tae-Hyeong Yi
Numerical Study Of Chemically Reacting Viscous Flow Relevant To Pulsed Detonation Engines, Tae-Hyeong Yi
Mechanical and Aerospace Engineering Dissertations - Archive
A computational fluid dynamics code for two-dimensional, multi-species, laminar Navier-Stokes equations is developed to simulate a recently proposed engine concept for a pulsed detonation based propulsion system and to investigate the feasibility of the engine of the concept.The governing equations that include transport phenomena such as viscosity, thermal conduction and diffusion are coupled with chemical reactions. The gas is assumed to be thermally perfect and in chemically non-equilibrium. The stiffness due to coupling the fluid dynamics and the chemical kinetics is properly taken care of by using a time-operator splitting method and a variable coefficient ordinary differential equation solver. A …
Arc-Heated Gas Flow Experiments For Hypersonic Propulsion Applications, Christopher Matthew Roseberry
Arc-Heated Gas Flow Experiments For Hypersonic Propulsion Applications, Christopher Matthew Roseberry
Mechanical and Aerospace Engineering Dissertations - Archive
Although hydrogen is an attractive fuel for a hypersonic air-breathing vehicle in terms of reaction rate, flame temperature, and energy content per unit mass, the substantial tank volume required to store hydrogen imposes a drag penalty to performance that tends to offset these advantages. An alternative approach is to carry a hydrocarbon fuel and convert it on-board into a hydrogen-rich gas mixture to be injected into the engine combustors. To investigate this approach, the UTA Arc-Heated Wind Tunnel facility was modified to run on methane rather than the normally used nitrogen. Previously, this facility was extensively developed for the purpose …
Experimental Characterization Of Femtosecond Laser Micromachining For Silicon Mold Fabrication And Hot Embossing For Polymer Microreplication, Sunil Ranganath Belligundu
Experimental Characterization Of Femtosecond Laser Micromachining For Silicon Mold Fabrication And Hot Embossing For Polymer Microreplication, Sunil Ranganath Belligundu
Mechanical and Aerospace Engineering Dissertations - Archive
Hot embossing is a fabrication technique employed for replicating microfeatures on a polymer surface that was primarily developed to fabricate MEMS devices for microfluidic applications. This manuscript deals with characterization of the femtosecond laser micromachining (FLM) and hot embossing (HEMM) processes for master mold fabrication on silicon and polymer replication respectively. Given the required size of the features to be fabricated or replicated, process parameters for FLM can be determined using the derived empirical equations, process parameters for the HEMM process can be established using the characteristic plots. A novel two-stage embossing process is developed and introduced that employs polymer …
An Experimental Investigation Of Ionization Of Supersonic Air By A Corona Discharge, Udyavar S. Satyanand
An Experimental Investigation Of Ionization Of Supersonic Air By A Corona Discharge, Udyavar S. Satyanand
Mechanical and Aerospace Engineering Dissertations - Archive
A technique is developed to ionize supersonic air flow in a shock tube by a weak corona discharge. The driven section of the tube is open to the atmosphere. The shock propagates in the driven section at about 1 km/s by means of an area contraction near the downstream end of the driven section. Air is ionized by a unipolar corona discharge device comprising of a sharp-edged wedge as a high-field electrode inserted in a 41.25 mm (2 in.) ID tube that forms a low-field electrode. The device requires less than 0.5 W. A ring probe, downstream of the corona …