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Articles 2101 - 2130 of 3180

Full-Text Articles in Engineering

Cuinse2: Electronic Activities Of Grain Boundaries And Solar Cell Fabrication Studies, Mehmet Eray Erkan Jan 2012

Cuinse2: Electronic Activities Of Grain Boundaries And Solar Cell Fabrication Studies, Mehmet Eray Erkan

Material Science and Engineering Dissertations - Archive

This dissertation is composed of three studies related to chalcopyrite solar cells. The first study is on electronic activities of grain boundaries (GBs) in CuInSe2 (CIS). Despite being polycrystalline, chalcopyrite thin film solar cells have reached record power conversion efficiencies. This is against the classical understanding on the effect of GBs in semiconductor materials. Because GBs are expected to be recombination centers and barriers against the carrier flow, reducing the device efficiency. Therefore, a complete understanding on the electronic behavior of chalcopyrite GBs is missing. Moreover, the high efficiency chalcopyrite solar cells are grown with Na impurities which positively …

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Solution To Three Dimensional Incompressible Navier-Stokes Equations Using Finite Element Method, Shrinivas Ganesh Apte Jan 2012

Solution To Three Dimensional Incompressible Navier-Stokes Equations Using Finite Element Method, Shrinivas Ganesh Apte

Mechanical and Aerospace Engineering Theses - Archive

A primitive variable mixed order formulation of finite element method for solving three dimensional incompressible Navier-Stokes equations is presented. The method of weighted residuals is used to obtain the approximate solutions of linear and nonlinear partial differential equations. The physical domain is discretized by using unstructured tetrahedral elements. Unequal order interpolation functions are used for pressure & velocity variables while the temporal discretization is carried out by using an implicit time marching scheme based on finite differencing.One of the major difficulties arising during the finite element solution of the incompressible Navier-Stokes equations is the efficient factorization/preconditioning of the resulting indefinite …

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High Enthalpy Characterization Of The Uta Hypersonic Shock Tunnel, Raheem Temitope Bello Jan 2012

High Enthalpy Characterization Of The Uta Hypersonic Shock Tunnel, Raheem Temitope Bello

Mechanical and Aerospace Engineering Theses - Archive

In hypersonic wind tunnel testing, matching the flow enthalpy conditions for the hypersonic air-breathing corridor is of great importance in order to assure the validity of experimental results. The flow enthalpy of the UTA hypersonic shock tunnel is increased by a shock induced detonation driver. The detonation mixture consist of hydrogen and oxygen in stoichiometric quantities ( 2H2+O2 ? 2H2O). Experimental variations of pressure and the volume of the detonation section were performed to characterize the enthalpy limits, and overall performance of the UTA hypersonic shock tunnel. The UTA HST test section is designed for a nominal Mach number of …

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Wear And Tribofilm Formation With Zinc-Free Antiwear Additives, Pradip Sairam Pichumani Jan 2012

Wear And Tribofilm Formation With Zinc-Free Antiwear Additives, Pradip Sairam Pichumani

Material Science and Engineering Theses - Archive

Engine oil is used in all internal combustion engines to lubricate the moving parts & mitigate the wear due to friction. Along with the mentioned two functions, engine oil also serves to protect the engine from corrosion, clean debris, improves sealing and serves in thermal conductivity. Engine oil is either derived from petroleum derivatives or made synthetically. A number of additives are added to the engine oil (Base oil) to improve its performance and longevity. Antioxidants, pour point depressants, viscosity index improvers, antifoaming agents, corrosion inhibitors, etc are some of the additives that are added to improve the engine oil‘s …

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Experimental And Numerical Investigation Of Mass Transfer In Microreactors, Wei-Tsen Han Jan 2012

Experimental And Numerical Investigation Of Mass Transfer In Microreactors, Wei-Tsen Han

Mechanical and Aerospace Engineering Dissertations - Archive

In this work, two types of microreactors for reactions have been studied, which were involving multiple fluid phases: liquid-liquid (immiscible liquids) phase and gas-liquid phase. Investigation of mass transfer within reacting flows in microreactors has been carried out in these two multiphase systems. For the liquid-liquid phase, a microfluidic system was designed and fabricated to generate a slug flow pattern of immiscible liquids. This system was used to demonstrate the effect of the flow pattern on mass transfer and the effect on chemical reaction rate for a simple acid-base reaction. The reaction progression was tracked by measuring the pH along …

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Experimental Identification Of Force Coefficients Of Hybrid Air Foil Bearings, Yu Ping Wang Jan 2012

Experimental Identification Of Force Coefficients Of Hybrid Air Foil Bearings, Yu Ping Wang

Mechanical and Aerospace Engineering Theses - Archive

Successful applications for air foil bearings in small to midsize turbo-machinery have been acknowledged. Air foil bearings do not require oil lubricant thus they are capable of operating under much higher temperature than oil-lubricated bearings and they entail less maintenance costs if well-designed. However, when rotor size increases beyond 100 mm in diameter, reliability becomes an issue due to comparable increase in rotor weight with respect to increase in load capacity of the bearing. Furthermore, dry rubbing during starts and stops also causes concerns due to typical slow acceleration and deceleration characteristics of large turbo-machinery. The concept of hybrid air …

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Experimental Feasibility Study Of Radial Injection Cooling Of Three-Pad Radial Air Foil Bearings, Suman K. Shrestha Jan 2012

Experimental Feasibility Study Of Radial Injection Cooling Of Three-Pad Radial Air Foil Bearings, Suman K. Shrestha

Mechanical and Aerospace Engineering Theses - Archive

Air foil bearings use ambient air as a lubricant allowing environment-friendly operation. When they are designed, installed, and operated properly, air foil bearings are very cost effective and reliable solution to oil-free turbomachinery. Because air is used as a lubricant, there are no mechanical contacts between the rotor and bearings and when the rotor is lifted off the bearing, near frictionless quiet operation is possible. However, due to the high speed operation, thermal management is one of the very important design factors to consider. Most widely accepted practice of the cooling method is axial cooling, which uses cooling air passing …

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Thermal Behavior Of Dielectric Materials During Rapid Heating, Daipayan Sarkar Jan 2012

Thermal Behavior Of Dielectric Materials During Rapid Heating, Daipayan Sarkar

Mechanical and Aerospace Engineering Theses - Archive

The objective of this research is to understand the temperature variation in dielectric materials of different geometry. The work is divided into three major segments. The Thermal Wave model has been taken into consideration as the classical Fourier law of heat conduction breaks down when a dielectric material of sub-micron geometry is heated rapidly. The first partof the work discusses primarily about the temperature distribution in a semi-infinite dielectric material, followed by the temperature profile in a finite body (plate) and finally mathematical formulation is presented for a two-layered body. The thermal wave equation is used because in dielectric materials …

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Mitigation Of Hot-Spots In High-End Microprocessors Using Bulk And Thin Film Thermoelectric Coolers, Agat Hirachan Jan 2012

Mitigation Of Hot-Spots In High-End Microprocessors Using Bulk And Thin Film Thermoelectric Coolers, Agat Hirachan

Mechanical and Aerospace Engineering Theses - Archive

Due to localized high heat fluxes, hot-spots are created in silicon chips. Cooling of the hot-spots is one of the major thermal challenges in today's integrated circuit (IC) industry. Many researches have been conducted to find ways to cool hot-spots using different techniques as uniform heating is highly desired. First part of the thesis focuses on cooling of hot-spot using conventional thermoelectric cooler (Melcor_CP1.0-31-05L.1) and a micro heat pipe. A chip package with conventional integrated heat spreader and heat sink was designed. Hot-spot was created at the center of the silicon die with background heat at rest of the area. …

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Dynamic Performance Of Offset-Preloaded Two Pad Foil Bearings, Shrikant Ashok Yadav Jan 2012

Dynamic Performance Of Offset-Preloaded Two Pad Foil Bearings, Shrikant Ashok Yadav

Mechanical and Aerospace Engineering Theses - Archive

Commercial application of the air foil bearing (AFB) in microturbomachinary have been acknowledged. Absence of external pressurizing and lubricating system makes them light and compact. Simple construction, low friction drag and reliability at high speed operations are few more advantages of the AFBs. With all these advantages AFB proves to be the suitable option for oil-free small turbomachinery which includes micro gas turbines with shaft power less than 1000hp. Micro gas turbine generators are typically two shaft configuration with power generation capacity less than 500KW. Although many micro gas turbines with AFBs have been developed, due to the proprietary nature …

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Dynamic Mode Decomposition Of Detonation Waves, Rahul Kumar Jan 2012

Dynamic Mode Decomposition Of Detonation Waves, Rahul Kumar

Mechanical and Aerospace Engineering Theses - Archive

Dynamic mode decomposition is applied to study the self-excited fluctuations supported by transversely unstable detonations. The focus of this study is on the effect of forcing on the limit cycle solutions. Using DMD, only the most coherent modes are analyzed. The most coherent modes in this case are the fundamental and the fourth harmonic. The analysis is based on the coherency of the self-excited detonation modes due to turbulence. Analysis reveals coherency is significantly affected with a turbulent Mach number greater than 0.3 and also the regions downstream of the shock are more affected by turbulence than the region just …

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Trajectory Generation And Constrained Control Of Quadrotors, Carlos Alberto Tule Jan 2012

Trajectory Generation And Constrained Control Of Quadrotors, Carlos Alberto Tule

Mechanical and Aerospace Engineering Theses - Archive

Unmanned Aerial Systems, although still in early development, are expected to grow in both the military and civil sectors. As part of the UAV sector, the quadrotor helicopter platform has been receiving a lot of interest from various academic and research institutions because of their simplistic design and low cost to manufacture, yet remaining a challenging platform to control. Four different controllers were derived for the trajectory generation and constrained control of a quadrotor platform. The rst approach involves the linear version of the Model Predictive Control (MPC) algorithm to solve the state constrained optimization problem. The second approach uses …

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Stress Analysis In Curved Composite Due To Thermal Loading, Jared Cornelius Polk Jan 2012

Stress Analysis In Curved Composite Due To Thermal Loading, Jared Cornelius Polk

Mechanical and Aerospace Engineering Theses - Archive

Many structures in aircraft, cars, trucks, ships, machines, tools, bridges, and buildings, consist of curved sections. These sections vary from straight line segments that have curvature at either one or both ends, segments with compound curvatures, segments with two mutually perpendicular curvatures or Gaussian curvatures, and segments with a simple curvature. With the advancements made in multi-purpose composites over the past 60 years, composites slowly but steadily have been appearing in these various vehicles, compound structures, and buildings. These composite sections provide added benefits over isotropic, polymeric, and ceramic materials by generally having a higher specific strength, higher specific stiffnesses, …

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Using Gpu-Based Computing To Accelerate Finite Element Problems, Jacob Watt Jan 2012

Using Gpu-Based Computing To Accelerate Finite Element Problems, Jacob Watt

Mechanical and Aerospace Engineering Theses - Archive

Historically Graphics Processing Units (GPU) have been used for offloading graphical visualization and made popular in use for video games, but with the development of NVIDIA's CUDA architecture and programing language there has been an increase in the use of GPUs in general purpose (GPGPU) programing. Problems involving large systems of linear equations, such as the Finite Element Analysis (FEA), can benefit greatly from the parallel computing capabilities of GPUs. In my thesis I will solve Poisson's equation and discuss the advantages and disadvantages of the massively parallel environment of GPUs. I will show that on a unstructured grid that …

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Determination Of Factors To Improve Effectiveness Of Triangulation Members For A Formula Sae Race Car Frame, Vikram Nair Jan 2012

Determination Of Factors To Improve Effectiveness Of Triangulation Members For A Formula Sae Race Car Frame, Vikram Nair

Mechanical and Aerospace Engineering Theses - Archive

This thesis suggests which factors have significant effect on the torsional and flexural stiffness of a space frame without contributing excessively to its weight. These factors are used as design variables to display the interaction plots generated by performing a Design of Experiments (DOE) using the Hyperstudy tool in Hyperworks by Altair®. The DOE will also provide a mathematical model which can help predict the responses by varying several factors in the design. The node - element models are created in ANSYS classic and are analyzed for various load cases that are representative of the loads on a formula SAE …

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Characterization Of Uta Hypersonic Shock Tunnel, Derek Glenn Leamon Jan 2012

Characterization Of Uta Hypersonic Shock Tunnel, Derek Glenn Leamon

Mechanical and Aerospace Engineering Theses - Archive

Characterization of a hypersonic shock tunnel was performed under low enthalpy conditions. A rake was designed and fabricated to measure pitot pressure and heat flux at three axial locations in the test section. Pitot pressures at three locations provided an indication of the inviscid core. Thin film RTD sensors with a fast response time were fabricated to measure the heat flux under these low enthalpy conditions. The Cook-Felderman algorithm was used to estimate the heat flux from the temperature history. Results for the first millisecond of test time showed a probe tip surface temperature increase of 15-20 K and a …

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Computational Study Of Heat Transfer Enhancement For A Dimpled Surface In A Channel, Abhijit Paranjape Jan 2012

Computational Study Of Heat Transfer Enhancement For A Dimpled Surface In A Channel, Abhijit Paranjape

Mechanical and Aerospace Engineering Theses - Archive

Heat transfer augmentation techniques have gained great importance in different engineering applications to deal with thermal management issues. In this work, a numerical investigation was carried out to see the effects of spherical dimple arrays on heat transfer characteristics in a channel. These effects were observed for dimples on the bottom wall of the channel for laminar airflows. The effects of a 21×7 staggered array and a 19×4 inline array on the bottom wall were investigated using a 3D steady viscous computational fluid dynamics package with an unstructured grid. The heat transfer characteristics were studied as a function of the …

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Spur Gear Analysis Using Mathcad, Jaydeep K. Panchal Jan 2012

Spur Gear Analysis Using Mathcad, Jaydeep K. Panchal

Mechanical and Aerospace Engineering Theses - Archive

In gear manufacturing applications, it is required to calculate surface stress and bending stress with minimum error. This thesis represents engineering calculation of bending and surface compression of external teethed involute spur gear. One may change the input values to calculate the engineering data for gears. The freedom of changing input values gives the capability to program to calculate for factor, Y; and the bending geometry factor, J to analyze spur gear geometry. Here the engineering gear calculation has been done by developing program in Mathcad software. The program is designed to calculate surface and bending stress data by input …

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Torsional Analysis Of A Composite I-Beam, Vishal Mukesh Smita Sanghavi Jan 2012

Torsional Analysis Of A Composite I-Beam, Vishal Mukesh Smita Sanghavi

Mechanical and Aerospace Engineering Theses - Archive

A simple methodology for analysis of thin walled composite I-Beam subjected to free torsion and restrained torsion is developed. Classical Lamination Theory is extended from the laminate level to the structural level for analysis purpose.The developed expressions for shear center, equivalent torsional rigidity and equivalent warping rigidity for a composite mono-symmetric I-Beam depends on the material properties, ply stacking sequence, fiber orientation and geometryThe results from the proposed theory gives better agreement with the ANSYSTM results than the traditional smeared property approach.

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Control Of A Teleoperating Robotic Arm Subject To Time Delays, Pankaj Prakash Sarda Jan 2012

Control Of A Teleoperating Robotic Arm Subject To Time Delays, Pankaj Prakash Sarda

Mechanical and Aerospace Engineering Theses - Archive

Robotics in Minimally Invasive Surgeries (MIS) can be explored to its full potential if there is complete transparency between the surgeon and the virtual environment. In the setup, haptic device which conveys force from the surgeon to the surgery site and vice verse acts as the master station and robotic arm at the surgery site acts as the slave robot. In surgeries carried out remotely, time delays in the communication channels can cause commanded velocity/force to overshoot before the surgeon can even pull out during a task causing temporary or permanent damage during the surgery. Since the physical capability of …

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Study Of The Surface Roughness Evolution In Fatigued 316l Stainless Steel, Ye Wang Jan 2012

Study Of The Surface Roughness Evolution In Fatigued 316l Stainless Steel, Ye Wang

Mechanical and Aerospace Engineering Theses - Archive

Fatigue is a critical design consideration in many aerospace structures. As improvements are sought in overall performance, maintenance requirements, and total service life of modern aircrafts, the demands for fatigue control techniques, such as material design for fatigue resistance, reliable fatigue life prediction, and continuous material damage monitoring, have increased. The most common practices to ensure fatigue safety include: fracture mechanics based fatigue life prediction, periodic non-destructive inspections, and material processing control. Reasonable successes have been achieved by applying these three techniques to ensure the safe operation of aerospace structures. It is worth mentioning that most of the present fatigue …

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New Developments In Cognitive Optimization, Parvati Aruna Kandala Jan 2012

New Developments In Cognitive Optimization, Parvati Aruna Kandala

Mechanical and Aerospace Engineering Theses - Archive

This work presents an approach to solve function optimization problems using cognitive optimization. A cognitive search algorithm which is developed mimics human cognition in structure and characteristics. This algorithm is developed based on the key aspects of a cognitive system, namely, the use of prior knowledge, communication, and self-organization. The processes have the knowledge of how to solve the optimization problems from traditional techniques such as bracketing, gradient search and interval-halving methods. This search algorithm shows that, by passing messages, the processes communicate, share information, and self-organize around the solution. A mat lab program is coded to perform the tests …

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Transient Analysis Of A Pulsed Detonation Combustor Using The Numerical Propulsion System Simulation, Anthony Scott Hasler Jan 2012

Transient Analysis Of A Pulsed Detonation Combustor Using The Numerical Propulsion System Simulation, Anthony Scott Hasler

Mechanical and Aerospace Engineering Theses - Archive

The performance of a hybrid mixed flow turbofan (with detonation tubes installed in the bypass duct) is investigated in this study and compared with a baseline model of a mixed flow turbofan with a standard combustion chamber as a duct burner. Previous studies have shown that pulsed detonation combustors have the potential to be more efficient than standard combustors, but they also present new challenges that must be overcome before they can be utilized. The Numerical Propulsion System Simulation (NPSS) will be used to perform the analysis with a pulsed detonation combustor model based on a numerical simulation done by …

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Analytical Method For Analyzing C-Channel Stiffener Made Of Laminate Composite, Tattchapong Kumton Jan 2012

Analytical Method For Analyzing C-Channel Stiffener Made Of Laminate Composite, Tattchapong Kumton

Mechanical and Aerospace Engineering Theses - Archive

Composite materials play the important role in the aviation industry. Conventional materials such as aluminum were replaced by composite material on the main structures. The objective of this study focuses on development of analytical method to analyze the laminated composite structure with C-channel cross-section. A lamination theory base closed-form solution was developed to analysis ply stresses on the C-channel cross-section. The developed method contains the effects of coupling due to unsymmetrical of both laminate and structural configuration levels. The present method also included the expression of the sectional properties such as centroid, axial and bending stiffnesses of cross-section. The results …

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Particle Advection Using The Lattice-Boltzmann Method, Matthew Carroll Jan 2012

Particle Advection Using The Lattice-Boltzmann Method, Matthew Carroll

Mechanical and Aerospace Engineering Theses - Archive

Lattice-Boltzmann Method (LBM) CFD analysis can be helpful in analysing fluid flow through porous media and complex geometries that may be difficult to simulate using traditional CFD methods. In this thesis, the technical details of lattice Botlzmann particle advection are presented. The lattice Botlzmann equations are explained as well as a method for introducing a particle in a fluid flow and advecting the particle using viscous, pressure, and gravitational forces. A method is developed to advect a particle through a computational lattice mesh using pressure forces, gravitational forces, as well as LBM-specific viscous force equations. The capability of the particle …

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Stress Concentrations Around A Square Cutout In A Composite Plate, Colin Cannon Jan 2012

Stress Concentrations Around A Square Cutout In A Composite Plate, Colin Cannon

Mechanical and Aerospace Engineering Theses - Archive

Composite structure in the aircraft industry has been in development for well over half a century and yet the understanding of the effects of a square cutout is generally limited to quasi-isotropic laminates. Currently, the closed-form solution to calculate the stresses around a cutout is limited to symmetric anisotropic laminates with limitations on the cutout shapes. Finite Element Analysis, using MSC PATRAN and NASTRAN, was performed on 2D composite laminates containing square cutouts with rounded corners. The laminate stacking sequence was varied from symmetrical and balanced to unsymmetrical and unbalanced and the square cutouts each had different radii at the …

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Cfd Based Aerodynamic Modeling To Study Flight Dynamics Of A Flapping Wing Micro Air Vehicle, Alok Ashok Rege Jan 2012

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 …

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Impact Of Louver Orientation On Air Flow Distribution And Thermal Management Of Data Centers, Kushal A. Aurangabadkar Jan 2012

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 …

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Assessment Of The Mechanical Integrity Of Cu/Low-K Dielectric In A Flip Chip Package, Thiagarajan Raman Jan 2012

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) …

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Numerical Study Of Sidewall Filling For Gas-Fed Pulse Detonation Engines, Wunnarat Rongrat Jan 2012

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 …

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