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Articles 931 - 953 of 953
Full-Text Articles in Aerospace Engineering
Viscoplastic Finite-Element Simulation To Predict The Solder Joint Fatigue Life Of Different Flash Memory Die Stacking Architectures, Yong Je Lee
Mechanical and Aerospace Engineering Theses - Archive
This thesis focuses on the viscoplastic finite-element simulation to predict the solder joint fatigue life of different die stacking architectures for flash memory products. Four different stacked package architectures were evaluated as follows: pyramid, rotated, and spacer stacking, while interconnection (solder joint) was held constant. Number of dies for all four stacking configurations were varied from three, five and seven. To keep the package height constant, the die and die attach thickness were varied and the resulting effects on the stresses were investigated. A quarter and half symmetry model of stacked flash package are generated using ANSYS APDL script. 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 …
Modular Multi-Scale Assembly System For Mems Packaging, Rakesh Murthy
Modular Multi-Scale Assembly System For Mems Packaging, Rakesh Murthy
Mechanical and Aerospace Engineering Theses - Archive
A multi-scale robotic assembly problem is approached here with focus on mechanical design for precision positioning at the microscale. The assembly system is characterized in terms of accuracy/repeatability and calibration via experiments. The MEMS packaging requirements are studied from an assembly point of view. The tolerance budget of the assembly ranges from 4 microns to 300 microns. The system components include robots, microstages, end-effectors and fixtures that accomplish the assembly tasks. Task assignment amongst this hardware has been accomplished based on precision and dexterity availability. Various end-effectors and fixtures have been designed for use with off-the-shelf hardware (robots and microstages) …
Design And Analysis Of Multi-Functional Laparoscopic Tool, Vadakkapattu Candadai Venkat Raghavan
Design And Analysis Of Multi-Functional Laparoscopic Tool, Vadakkapattu Candadai Venkat Raghavan
Mechanical and Aerospace Engineering Theses - Archive
Laparoscopic tools have been developed over many years, but there is a need for a laparoscopic tool that can be used for multiple purposes without the need to be removed and reinserted in the body. This thesis discusses the design of such a multi-functional laparoscopic tool with the ability to independently actuate grasping and shearing mechanisms, and is modular enough to be easily adapted to robot assisted surgical techniques. The envisioned tool can be divided into three main sections - the surgeon interface, the transmission mechanism, and the end effector. The surgeon interface mainly consists of a handle and two …
Parametric Cycle Analysis For Pulse Detonation Engines, Haider Hekiri
Parametric Cycle Analysis For Pulse Detonation Engines, Haider Hekiri
Mechanical and Aerospace Engineering Theses - Archive
The performance of an ejector-driven pulse detonation engine (PDE) with an afterburner is analytically estimated. In the analysis, the PDE was modeled as a straight tube, closed at the front end and open at the other. A detonation wave starts to travel after it is ignited at the closed end, causing a Chapman-Jouguet detonation wave followed by a Taylor rarefaction to travel to the open end. At that point, rarefaction waves are reflected back to the closed end. The result is a high thrust due to both the primary and secondary flows of the ejector-driven PDE. A theoretical analysis is …
Airy Stress Function For Two Dimensional Inclusion Problems, Dharshini Rao Kavati
Airy Stress Function For Two Dimensional Inclusion Problems, Dharshini Rao Kavati
Mechanical and Aerospace Engineering Theses - Archive
This thesis addresses a problem of finding the elastic fields in a two-dimensional body containing an inhomogeneous inclusion using the Airy stress function which is determined so that the prescribed boundary condition at a far field and the continuity condition of the traction force and the displacement field at the interface are satisfied exactly. All the derivations and solving simultaneous equations are carried out using symbolic software.
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 …
Reliability Of Lead-Free Solder Under Cyclic Bending, Fahad Zahedi
Reliability Of Lead-Free Solder Under Cyclic Bending, Fahad Zahedi
Mechanical and Aerospace Engineering Theses - Archive
To characterize particular compositions of lead free solder, four point cyclic bending test was conducted to study the affects of accelerated stress testing on the package to board interconnects. Nine CTBGA packages with 0.5 mm ball pitch and 12 x 12 mm package size were reflowed on 8 layered PWB's using solder balls with lead free composition alloys and different PWB copper pad finishes. The boards were subjected to test conditions based on proposed standards by JEDEC. Strain gages were mounted at different locations on the test boards as well as on bare boards in order to observe the difference …
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 …
Failure Analysis Of Composite Laminates With A Hole By Using Finite Element Method, Moumita Roy
Failure Analysis Of Composite Laminates With A Hole By Using Finite Element Method, Moumita Roy
Mechanical and Aerospace Engineering Theses - Archive
Predicting the strength of a given laminate has been extensively studied. There have been several fracture models proposed but still the immense tests of composite laminates are still needed. Different material systems or lay-ups exhibit different failure modes and failure mechanisms. This thesis focuses in investigation of the failure mechanism of the [±?/02]s and [02/±?]s laminates with a hole. ANSYS finite element models with and without a crack in vicinity of hole were developed to investigate the effect of the stress distribution due to the presence of the angle ply crack. The stress concentrations were obtained. It is found that …
Structural Optimization Using Ansys And Regulated Multiquadric Response Surface Model, Ajaykumar Menon
Structural Optimization Using Ansys And Regulated Multiquadric Response Surface Model, Ajaykumar Menon
Mechanical and Aerospace Engineering Theses - Archive
The high computational expense of large non-linear and complex finite element analysis limits or often prohibits the use of conventional codes in engineering design and multidisciplinary optimization. Consequently alternate methods such as Design of experiments (DOE) and Response surface approximation are commonly used to minimize the computational cost of running such analysis and simulation. The basic approach of such methods is to construct a simplified mathematical approximation of the computationally expensive simulation and analysis code, which is then used in place of the original code to facilitate multidisciplinary optimization, design space exploration, reliability analysis etc. When such codes along with …
Investigation Of Pool Boiling Heat Transfer With Nanofluids, Gilberto Moreno
Investigation Of Pool Boiling Heat Transfer With Nanofluids, Gilberto Moreno
Mechanical and Aerospace Engineering Theses - Archive
This investigation conducts pool boiling experiments under saturated conditions (Tsat=60°C) using nanofluids as coolants. Four different nanofluids were tested including zinc oxide (ZnO)-water, aluminum oxide (Al2O3)-water, aluminum oxide (Al2O3)-water+ethylene glycol (ethylene glycol solution) and gold (Au)-water. At saturation (Tsat=60 °C), the pool boiling performance of Al2O3-water and ZnO-water nanofluids were similar. The maximum CHF enhancement as compared to predicted Zuber's [1] CHF evaluated at an equivalent saturation temperature is about 180% for Al2O3-water nanofluids and about 240% for ZnO-water nanofluids. In both cases, no degradation in the boiling heat transfer rate was observed for lower nanoparticle concentrations. The dispersion of …
The Thermal Characteristics Of Liquid-Heat-Spreader, Sang Muk Kwark
The Thermal Characteristics Of Liquid-Heat-Spreader, Sang Muk Kwark
Mechanical and Aerospace Engineering Theses - Archive
The present study is an experimental research of a liquid-heat-spreader (LHS) with saturated water at ~2.29 psia. A LHS, indirect liquid cooling module, was successfully fabricated using thin copper blocks and copper tubes using solder. Three types of LHS, Flat-type, L-type, and T-type, were developed for different orientations and were compared with solid metal blocks such as aluminum and copper. The Flat-type LHS, 100 (W) × 254 (L) × 3 (T) mm3, was designed for vertical orientation. It showed a remarkable thermal performance by dissipating heat flux of 119 W/cm2 with below 100? chip temperature at the typical condition. The …
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 …
Numerical Simulation Of Pulse Detonation Phenomena In A Parallel Environment, Prashaanth Ravindran
Numerical Simulation Of Pulse Detonation Phenomena In A Parallel Environment, Prashaanth Ravindran
Mechanical and Aerospace Engineering Theses - Archive
The objective of this work was to develop a parallel algorithm that would be used in the simulation of the detonation process in the chamber of a pulse detonation engine. The emphasis is laid on reducing computation time while maintaining the accuracy of the solution and subsequently developing a numerical solution to be in agreement with real-world physical characteristics of a detonation wave initiation, build-up and progression. The flow is assumed to be unsteady, inviscid and non heat conducting. To adhere to real time effects, the flow equations are coupled with finite rate chemistry and the vibrational energy equation are …
An Approximate Solution To Buckling Of Plates By The Galerkin Method, Yattender Rishi Dubey
An Approximate Solution To Buckling Of Plates By The Galerkin Method, Yattender Rishi Dubey
Mechanical and Aerospace Engineering Theses - Archive
This thesis presents a semi-analytical method to solve the governing differential equation of plates using the Galerkin method. Symbolic algebra software is extensively used to perform necessary calculations. In this thesis, the lateral deflection of a plate is expressed in a series of polynomials each of which satisfies the given homogeneous boundary conditions. The coefficients of these polynomials are found out by the Galerkin method. Symbolic algebra software works best while handling necessary algebra to generate admissible polynomials and build required matrices for solving for the coefficients.This thesis demonstrates the calculation of the lateral load for different plates under different …
Spreading, Solidification And Remelting Behavior Of Liquid Metal Droplets Sequentially Impinging Onto A Metal Substrate, Lister Manohar Pinto
Spreading, Solidification And Remelting Behavior Of Liquid Metal Droplets Sequentially Impinging Onto A Metal Substrate, Lister Manohar Pinto
Mechanical and Aerospace Engineering Theses - Archive
The fluid dynamics and simultaneous solidification of two successive molten metal droplets impacting a flat substrate is investigated numerically. The primary objective is to investigate the effects of initial droplet and substrate temperature, and the latent heat of substrate material, on the spreading, solidification and remelting of molten tin droplets impacting a substrate of the same material. A robust fluid-flow solver that is capable of modeling rapidly deforming free surfaces involving a moving phase-change boundary is employed in the study. The Navier-Stokes equations are solved using a finite volume formulation. A two-step projection method is used to solve for incompressible …
Design Optimization And Synthesis Of Manipulators Based On Various Manipulation Indices, Sandipak Bagchi
Design Optimization And Synthesis Of Manipulators Based On Various Manipulation Indices, Sandipak Bagchi
Mechanical and Aerospace Engineering Theses - Archive
Design optimization of serial manipulators involves striking a balance between an appropriate joint angle and exact link lengths. The optimization technique used in this thesis uses a unique algorithm that optimizes the joint angle through an Inverse Kinematics program. The synthesis problem involves setting up an accurate design length so as to reach a set of given target points inside the workspace without any singularity. The optimization process based on task specification focuses on the maximization of manipulability index, the objective function subjected to link length and joint angle constraints. The results obtained were plotted and animated to visualize the …
Polymer Tube Embedded In-Plane Micropump: Design, Analysis And Fabrication, Ashutosh Kole
Polymer Tube Embedded In-Plane Micropump: Design, Analysis And Fabrication, Ashutosh Kole
Mechanical and Aerospace Engineering Theses - Archive
This thesis presents the design, analysis, and fabrication of a novel polymer tube embedded in-plane micropump. The key component of the proposed micropump is a Parylene polymer tube that is embedded into the trench of a silicon die. Advantages of embedding a Parylene polymer tube are biocompatibility and leakage free environments. The issue of leakage of fluid presented in [1] is eliminated by inserting the polymer tube. The tube itself acts as a diaphragm, which transfers the force and motion of thermal actuators to fluid. The structural analysis and the fabrication of the Parylene tube along with the coupled-field multiphysics …
Study Of Blast Wave Impact On Concrete, Ajit Geevarghese John
Study Of Blast Wave Impact On Concrete, Ajit Geevarghese John
Mechanical and Aerospace Engineering Theses - Archive
The past decade has brought an upsurge of terrorist attacks throughout the world. A common form of attack is bombings employed against a civilian structure. These bombs lead to blast waves resulting from high explosive bursts in air, causing severe structural damage to buildings that often collapse before evacuation is possible. These blast waves subject the buildings to repeated dynamic loading in the form of reflecting shock waves which then finally lead to their destruction. Many studies have been carried out to understand the static loading of these structures. The current study is to protect existing buildings from an explosion. …
Research For Dynamic Seal Friction Modeling In Linear Motion Hydraulic Piston Applications, Brian Edward Suisse
Research For Dynamic Seal Friction Modeling In Linear Motion Hydraulic Piston Applications, Brian Edward Suisse
Mechanical and Aerospace Engineering Theses - Archive
This paper presents a unique physics-based analytic model for dynamic seal friction in hydraulic actuators as a function of cylinder pressure, seal material, piston rod dimensions, piston rod seal gland dimensions, and other influencing factors. Results from a series of friction tests are presented. Finite element analysis of an installed seal is used to predict contact stress between the seal and the gland, providing a normal force against the sealing surface. This information is used to determine coefficients of friction within the test specimen. From the analysis, a pressure-sensitive model is generated. The friction model is overlaid on the test …
Investigation Of Minimum Response For Damage Assessment, Jeffrey Kirk
Investigation Of Minimum Response For Damage Assessment, Jeffrey Kirk
Mechanical and Aerospace Engineering Theses - Archive
Assessment of structural damage based on changes in vibratory response characteristics has been researched for many years, with much attention directed toward the use of modal parameters. Modal responses contribute to form points of local minima in the frequency response of a system. The frequency and amplitude values corresponding to these points of minimum response can be analytically determined, experimentally measured, and shown to exhibit sensitivity to damage. This work was performed to investigate the possible contribution that explicitly targeted minimum response information could provide in a damage detection process. A simple 6-DOF discrete spring-mass system was used to conduct …