Mechanical Engineering Commons^™

Development Of An Advanced Stem Heating Model, Joshua L. Jones

Theses and Dissertations

A new one-dimensional heat conduction model for predicting stem heating during fires is presented. The model makes use of moisture and temperature dependent thermal properties for bark and wood. Also, the thermal aspects of the processes of bark swelling, desiccation, and devolatilization are treated in an approximate fashion. Simulation with a surface flux boundary condition requires that these phenomena be accounted for. Previous models have used temperature-time boundary conditions, which prevents them from being directly coupled to fire behavior models. This model uses a flux-time profile for its boundary condition, making it possible to eventually couple it to fire behavior …

Moving Screw Dislocations In Piezoelectric Bimaterials, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou

Department of Engineering Mechanics: Faculty Publications

An explicit solution for a moving screw dislocation in a piezoelectric bimaterial is given by means of complex variables. The electroelastic fields and forces acting on the moving dislocation are obtained in closed form. As special cases, solutions for a moving screw dislocation in a piezoelectric half-plane with a free or rigid surface are obtained explicitly.

Study Of Geometric Effects On Local Corrosion Rates For Lbe Loop, Chao Wu

UNLV Theses, Dissertations, Professional Papers, and Capstones

Corrosion is an extremely important issue in nuclear cooling system applications. Many scientific and engineering efforts have been contributed to the research of finding an ideal material, which has resistance to corrosive Lead Bismuth Eutectic (LBE). A Delta Loop was designed and constructed in Los Alamos National Lab (LANL) to obtain the experimental data. This loop is a multi-section closed system that differs in diameter from one part to another. As a result, an intensive study on the geometry effect is hence necessary and valuable. In this thesis, this problem was simulated by commercial software STAR-CD. Results provide a good …

Piezoelectric Sensor In The Application Of Rolling Bearing Health Monitoring, Yinyin Liu

Mechanical & Aerospace Engineering Theses & Dissertations

A condition-based monitoring concept for rolling element bearings in machinery utilizing a piezoelectric load sensor is investigated in this thesis. The radially polarized cylindrical piezoelectric sensor is modeled in its specific coordinates. The sensor registers the stress occurring in all directions around it. The sensor's behavior due to several typical loads is analyzed. Based on the induced stresses in the sensor, the sensor's output as an electric charge can be obtained using the method of integration.

Considering both the normal and tangential loads distributed on the rolling beating's roller-raceway contact surface, the dynamic stress distribution in the outer raceway was …

Analytical Model Of A Thermomechanical Hot Channel Coupled To A Friction Stir Welding Process, Saptarshi Mandal

Mechanical & Aerospace Engineering Theses & Dissertations

Although fusion welding techniques are well established, recent developments in solid state joining techniques have produced high quality welds in materials that are difficult to fusion weld. Friction Stir Welding (FSW) was developed in 1991 as a robust solid-state joining technique that uses a specially shaped rotating tool to generate heat and plasticize material around the tool. The tool then mixes plasticized material along the joint line to produce the weld. Over the last decade, FSW has become increasingly popular for welding aluminum. The combination of attractive properties of the weld and cost-efficiency has led researchers to investigate the feasibility …

Diode Laser Crystallization Of Hydrogenated Amorphous Silicon Thin Films For Solar Cell Applications, Brian A. Eaton

Mechanical & Aerospace Engineering Theses & Dissertations

The research objectives were to prove the crystallization of hydrogenated amorphous silicon (a-Si:H) thin films using a diode laser operating at an 805 nm wavelength and to provide morphology trends in laser crystallized samples. This work was primarily intended for solar cell applications.

One industry goal was to produce a high-efficiency and low-cost solar cell capable of competing economically with other energy sources at large scale in the world market. Excimer laser crystallization was one very promising technique. However, two important problems still hindered economic competition. This research addressed the problems associated with excimer laser crystallization by utilizing a diode …

Nonlinear Response And Fatigue Estimation Of Aerospace Curved Surface Panels To Acoustic And Thermal Loads, Adam Przekop

Mechanical & Aerospace Engineering Theses & Dissertations

This work presents a finite element modal formulation for large amplitude free vibration of arbitrary laminated composite shallow shells. The system equations of motion are formulated first in the physical structural-node degrees of freedom (DOF). Then, the system is transformed into general Duffing-type modal equations with modal amplitudes of coupled linear bending-inplane modes. The linear bending-inplane coupling is due to the shell curvature as well as unsymmetric lamination stacking. Multiple modes, inplane inertia, and the first-order transverse shear deformation for composites are considered in the formulation. A triangular shallow shell finite element is developed from an extension of the triangular …

Optimization-Based Architecture For Managing Complex Integrated Product Development Projects, Hisham Mohamed El-Sayed Abdelsalam

Mechanical & Aerospace Engineering Theses & Dissertations

By the mid-1990's, the importance of early introduction of new products to both market share and profitability became fully understood. Thus, reducing product time-to-market became an essential requirement for continuous competition. Integrated Product Development (IPD) is a holistic approach that helps to overcome problems that arise in a complex product development project. IPD emphasis is to provide a framework for an effective planning and managing of engineering projects. Coupled with the fact that about 70% of the life cycle cost of a product is committed at early design phases, the motivation for developing and implementing more effective methodologies for managing …

A Self-Retracting Fully Compliant Bistable Micromechanism, Nathan D. Masters, Larry L. Howell

Faculty Publications

A new class of fully compliant bistable mechanisms with the added benefit of integrated self-retraction has been developed (hereafter identified as Self-Retracting Fully compliant Bistable Mechanism or SRFBM). A technique using tensural pivots to manage compressive loading in compliant mechanisms is introduced and implemented in the SRFBM. The elimination of traditional kinematic joints and their associated clearance allows a total displacement between stable positions of 8.5 m, and the mechanism size is less than 300 m square when using 2.0 m minimum line widths. Maximum actuation force is approximately 500 N. The SRFBM's small linear displacement and reasonable actuation force …

The Displacement Of The Thermally Grown Oxide In Thermal Barrier Systems Upon Temperature Cycling, Anette M. Karlsson, J. W. Hutchinson, A. G. Evans

Mechanical Engineering Faculty Publications

Models that characterize the displacement instability of the thermally grown oxide (TGO) found in some thermal barrier systems are reviewed, consolidated and extended. It is demonstrated that the simulations are only consistent with the observations whenever the bond coat and TGO both undergo plastic deformation. The TGO yields at the peak temperature, during growth, while the bond coat yields on thermal cycling. The trends oppose. Namely, the TGO displacement is diminished by increasing the high temperature strength of the bond coat, but is increased upon increasing the TGO strength. The model rationalizes certain experimental trends, particularly the decrease in durability …

Identification Of Macro- And Micro-Compliant Mechanism Configurations Resulting In Bistable Behavior, Brian D. Jensen

Theses and Dissertations

The purpose of this research is to identify the configurations of several mechanism classes which result in bistable behavior. Bistable mechanisms have use in many applications, such as switches, clasps, closures, hinges, and so on. A powerful method for the design of such mechanisms would allow the realization of working designs much more easily than has been possible in the past. A method for the design of bistable mechanisms is especially needed for micro-electro-mechanical systems (MEMS) because fabrication and material constraints often prevent the use of simple, well-known bistable mechanism configurations. In addition, this knowledge allows designers to take advantage …

A Self-Retracting Fully-Compliant Bistable Micromechanism, Nathan D. Masters

Theses and Dissertations

The purpose of this research is to present a class of Self-Retracting Fully-compliant Bistable Micromechanisms (SRFBM). Fully-compliant mechanisms are needed to overcome the inherent limitations of microfabricated pin joints, especially in bistable mechanisms. The elimination of the clearances associated with pin joints will allow more efficient bistable mechanisms with smaller travel. Small travel, in a linear path facilitates integration with efficient on-chip actuators. Tensural pivots are developed and used to deal with the compressive loading to which the mechanism is subject. SRFBM are modeled using the Pseudo-Rigid-Body Model and finite element analysis. Suitable configurations of the SRFBM concept have been …

Jun 2003, Tractor Museum

Lester F. Larsen Tractor Museum: Planning and Development Documents

Rehabilitation of Behlen Building Test Car Location Inside Insulation

Development Of In-Plane Compliant Bistable Microrelays, Troy Alan Gomm

Theses and Dissertations

Bistable microrelays have many possible applications and have the potential to reduce the size, weight, power consumption, and cost of products in which they are used. This research outlines the current state of microrelays, presents three new compliant bistable micromechanisms, and characterizes their performance as microrelays. The characterization includes a treatment of a new force-tester, a preliminary contact resistance study, contact-force measurements, switching time measurements, insertion loss, AC isolation, breakdown voltage, and DC isolation. This document also includes recommendations for further research.

Renewable Energy Limits, Florida Solar Energy Center, Ross Mccluney

FSEC Energy Research Center®

"The more we get out of the world the less we leave, and in the long run we shall have to pay our debts at a time that may be very inconvenient for our own survival." - Norbert Wiener

Introduction: The world's energy and environmental crises are inextricably linked. The processes of extracting, processing, and burning fossil fuels generates copious pollution of air, water, and land. Fossil-fuel-derived energy lies at the heart of other environmental problems. Fossil energy powers the bulldozers clearing rainforests. It runs the tractors and other farm equipment of industrial agriculture, compacting and mineralizing soils thus increasing …

Interfacial Edge Crack Between Two Bonded Dissimilar Orthotropic Strips Under Antiplane Point Loading, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou

Department of Engineering Mechanics: Faculty Publications

A closed-form solution is obtained for the interfacial edge crack between two bonded dissimilar orthotropic strips loaded by antiplane point loading in form of screw dislocation or line force. Conformal mapping and existing dislocation solutions are utilized for constructing the fundamental solution of the problem. The stress intensity factor (SIF) and the energy release rate(ERR) are obtained explicitly.

Modeling, Fabrication, And Optimization Of Niobium Cavities: Phase Ii Final Report, Robert A. Schill Jr., Mohamed Trabia, William Culbreth

Transmutation Sciences Materials (TRP)

Niobium cavities are important parts of the integrated NC/SC high-power linacs. Over the years, researchers in several countries have tested various cavity shapes. They concluded that elliptically shaped cells are the most appropriate shape for superconducting cavities. The need for very clean surfaces lead to the use of a buffered chemical polishing produce for surface cleaning to get good performance of the cavities. The second phase has resulted in an experimental setup of a fluid flow experiment with experimentation to be completed in the third year. Some of these results were presented at American Nuclear Society, Student Conference April 2-5, …

Design Of Predictive Controllers By Dynamic Programming And Neural Networks, Chen-Wen Yen, Mark L. Nagurka

Mechanical Engineering Faculty Research and Publications

This paper proposes a method for the design of predictive controllers for nonlinear systems. The method consists of two phases, a solution phase and a learning phase. In the solution phase, dynamic programming is applied to obtain a closed-loop control law. In the learning phase, neural networks are used to simulate the control law. This phase overcomes the "curse of dimensionality" problem that has often hindered the implementation of control laws generated by dynamic programming. Experimental results demonstrate the effectiveness of the method

Robust Pi Controller Design Satisfying Gain And Phase Margin Constraints, Mark L. Nagurka, O. Yaniv

Mechanical Engineering Faculty Research and Publications

This paper presents a control design algorithm for determining PI-type controllers satisfying specifications on gain margin, phase margin, and an upper bound on the (complementary) sensitivity for a finite set of plants. Important properties of the algorithm are: (i) it can be applied to plants of any order including plants with delay, unstable plants, and plants given by measured data, (ii) it is efficient and fast, and as such can be used in near real-time to determine controller parameters (for on-line modification of the plant model including its uncertainty and/or the specifications), (iii) it can be used to identify the …

Optically Transparent, Scratch-Resistant, Diamond-Like Carbon Coatings, Xiao-Ming He, Deok-Hyung Lee, Michael A. Nastasi, Kevin C. Walter, Michel G. Tuszewski

Department of Mechanical and Materials Engineering: Faculty Publications

A plasma-based method for the deposition of diamond-like carbon (DLC) coatings is described. The process uses a radio-frequency inductively coupled discharge to generate a plasma at relatively low gas pressures. The deposition process is environmentally friendly and scaleble to large areas, and components that have geometrically complicated surfaces can be processed. The method has been used to deposit abherent 100-400 nm thick DLC coatings on metals, glass, and polymers. These coatings are between three and four times harder than steel and are therefore scratch resistant, and transparent to visible light. Boron and silicon doping of the DLC coatings have produced …

Method For Producing Fluorinated Damond-Like Carbon Films, Marko J. Hakovirta, Michael Nastasi, Deok-Hyung Lee, Xiao-Ming He

Department of Mechanical and Materials Engineering: Faculty Publications

Fluorinated, diamond-like carbon (F-DLC) films are produced by a pulsed, glow-discharge plasma immersion ion processing procedure. The pulsed, glow-discharge plasma was generated at a pressure of 1 Pa from an acetylene (CH) and hexafluoroethane (CF) gas mixture, and the fluorinated, diamond-like carbon films were deposited on silicon <100>Substrates. The film hardness and wear resistance were found to be strongly dependent on the fluorine content incorporated into the coatings. The hardness of the F-DLC films was found to decrease considerably when the fluorine content in the coatings reached about 20%. The contact angle of water on the F-DLC coatings was found …

Paper On Measurement Of The Nanomechanical Properties Of Thin Films Using Afam Receives Recognition, Donna Hurley, Joseph A. Turner, Paul Rice, Joshua Wiehn

Department of Engineering Mechanics: Faculty Publications

NIST researchers are developing atomic force acoustic microscopy (AFAM) methods to quantitatively determine the elastic properties of thin films. The AFAM technique measures the frequencies of an atomic force microscope (AFM) cantilever’s first two flexural resonances while in contact with a material. The indentation modulus, M, of an unknown or test material can then be obtained by comparing the resonant spectra of the test material to those of a reference material. To examine metrology issues for this emerging technique, AFAM results have been compared with those obtained by other methods, such as instrumented indentation. The results show that better agreement …

Qualitative And Statistical Analysis Of The Florida Photovoltaic Rebate Program, Florida Solar Energy Center, Jennifer Szaro

FSEC Energy Research Center®

The Florida Photovoltaic (PV) Rebate Program, which began in March of 1999, has led to the installation of 52 utility interactive PV systems in seven electric utility service territories. The Program offered $4 per installed DC Watt to Florida electric consumers who installed grid-connected photovoltaic equipment in accordance with a series of quality control requirements developed and administered by the Florida Solar Energy Center. All rebated installations are currently being monitored in an effort to collect statistically significant reliability, performance and cost data on grid-connected PV systems. Funding for this program was provided through a one-time grant from the Florida …

Investigation Of The Iced Flowfield Characteristics Related To The Stall Margin Instrumentation Used In Icing Conditions, Erik Pederson

Dissertations

The purpose of this dissertation is to investigate the relationship between the flowfield surrounding an iced airfoil and the stall margin instrumentation developed for use in icing conditions. The stall margin system indicates to the pilot the change in available lift due to ice accretions on the leading edge of an airfoil. This system displays the change in the form of a normalized lift coefficient. Four pressure ports are chosen to specifically maintain a constant calibration curve, for pressure versus normalized lift coefficient, regardless of ice shape. This allows these pressures to be used to determine the change in maximum …

Cooperative Path Planning For Timing Critical Missions, Timothy W. Mclain, Randal W. Beard

Faculty Publications

This paper presents a cooperative path planning approach for teams of vehicles operating under timing constraints. A cooperative control approach based on coordination variables and coordination functions is introduced and applied to cooperative timing problems. Three types of timing constraints are considered: simultaneous arrival, tight sequencing, and loose sequencing. Simulation results demonstrating the approach are presented.

Theoretical And Experimental Studies Of The Field-Induced Phenomena In Flowing Suspensions, Nikolai Markarian

Dissertations

The present work describes results of experimental and theoretical studies of the behavior of dilute suspensions subject to high gradient AC electric fields. When a spatially non-uniform electric field is applied to a suspension, in which the particles and the suspending fluid have different dielectric permittivities andlor conductivities, the particles migrate towards the regions of high or low electric field strengths depending on the sign of their polarization. This phenomenon, referred to as dielectrophoresis, has found numerous applications for the control and manipulation of the particle motions.

Presented in Chapter 3 are the results of studying the field -induced motion …

Experimental Study Of Ignition Of Mechanical Alloy And Pure Metal Powders, Ruslan Mudryy

Theses

Mechanical alloys of Al Mg, AI Zr, Al Ti, Al Li, Al C, Al Mg H, B Mg, B Al, and B Ti were produced and tested for possible applications as high energy density additives to fuels, propellants, explosives, and incendiaries. These new materials are metastable, supersaturated, nanocrystalline solid solutions that include a base metal as a solvent and another component (metal or gas, e.g. hydrogen) as a solute. Phase changes occurring in such materials during ignition and combustion are expected to significantly affect both ignition and bum rates. This experimental program focused on the characterization of ignition kinetics of …

Direct Simulation Of Electrorheological Suspensions Subjected To Pressure Driven Flow And Spatially Non-Uniform Electric Field, Arun Thankamony John Kadaksham

Theses

A numerical method based on the distributed Lagrange Multiplier method is developed for direct simulation of electrorheological (ER) suspensions subjected to pressure driven flows and spatially non-uniform electric fields. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method and the point-dipole approximation is used to model the electrostatic forces acting on the polarized particles. Simulations show that the particles move to the regions of high electric field when the value of β, the Clausius-Mossotti factor is positive and they move to the regions of low electric field when the value of …

Analysis Of Random Packing Of Uniform Spheres Using The Monte Carlo Simulation Method, Sai S. Tulluri

Theses

The study of random packing of spheres has had a long history. It particularly interests many researchers because randomly packed hard spheres exhibit some features of the properties of simple liquid, e.g. the packing density and the radial distribution. Many researchers have studied random packing both experimentally and also by using computer simulation.

Monte Carlo simulation method was used to generate random loose packing of hard spheres. Packing characteristics like packing density, radial distribution function, co-ordination, angular distribution and fabric tensor have been computed for this packing system.

The packing density for a system of 8000 particles with a diameter …

Addition Of A Chain-Cell Search Method And A Van Der Waals Force Model To A Particle Dynamics Code, Michael J. Sweetman

Theses

This project studies the implementation of a computational time saving technique and adds an additional force model into a discrete element method simulation code. Both aspects of the project are focused on increasing the versatility of an existing particle dynamics code by increasing the execution speed and available force models for simulation.

The first portion of the project consisted of adding a function to the collision detection mechanism to hash the particles into a spatial grid. This hashing function allows a search for near neighbor particles to be restricted to the space immediately adjacent to the particle of interest, thereby …