Engineering Commons^™

Agile Manufacturing System Scheduling Using Genetic Algorithms And Simulated Annealing, Sherif Masoud

Archived Theses and Dissertations

Agile manufacturing is concerned with thriving in prevailing market conditions by quickly introducing new or modified products. This research deals with the scheduling of an agile manufacturing system (AMS), which performs both machining and assembly, with the objective of minimizing the makespan. The AMS allows the production of high varieties of modular products in small batches and at low costs. This problem is difficult to solve optimally and was solved in literature by heuristic algorithms. In the current research, four novel, genetic algorithms and simulated annealing-based, heuristics – General Genetic Algorithm, General Simulated Annealing, Heuristic Assisted Genetic Algorithm, and Heuristic …

Analysis Of The Cup Drawing Process And Optimization Of The Blank Holder Force, Hossam Gharib

Archived Theses and Dissertations

The process of deep drawing of a cylindrical cup is analyzed and optimized for the minimum punch force. An analytical model is developed for the cup drawing process by determining the variation of stresses and strains over the deforming sheet at any stage of deformation until a full cup is formed. The model uses finite difference approach and numerical analysis to solve for equilibrium, continuity, and plasticity equations. Then, optimization of the blank holder force (BHF) is carried out using the developed analytical model. Optimization is carried out using genetic algorithms to determine the optimum linear BHF scheme that minimizes …

Performance Of Self-Compacting Concrete, Mohamed Samir Rushdy

Archived Theses and Dissertations

Concrete compaction is one of the indispensable fundamentals of concrete manufacturing. However, thorough compaction cannot always be insured. This can be wholly or partially encountered in congested sections, out-of reach deep foundations and narrow or irregular precast components. On the other hand, typical vibrators were considered as contributor to health hazards to workers. Self-compacting concrete (SCC) is an emerging concrete where the cohesive yet flowable consistency of the concrete itself secures adequate placement with high level of homogeneity and little or no segregation. Such concrete is primarily achieved by incorporating admixtures that is referred to as viscosity modifying (VM) admixtures …

Adoption Of Iso 14001 By Construction Companies In Egypt, Dalia Abdel-Hamid Mahmoud Sakr

Archived Theses and Dissertations

No abstract provided.

Simulation Of Hot Electron And Quantum Effects In Algan/Gan Heterostructure Field Effect Transistors, N. Braga, R. Mickevicius, R. Gaska, H. Xu, M. S. Shur, M. Asif Khan, Grigory Simin, J. Yang

Faculty Publications

We report on simulations of electrical characteristics of AlGaN/(InGaN)/GaN heterostructurefield effect transistors with quantum and hot electroneffects taken into account. Polarization charges lead to quantum confinement of electrons in the channel and to the formation of two-dimensional electron gas. The electron quantization leads to the spread of the electronwave function into the barrier and bulk but does not have significant impact on dc electrical characteristics.Hot electrons play an important part in the charge transport by spilling over into the bulk GaN where they are captured by traps. This leads to negative differential conductivity, which is also observed experimentally. The simulation …

Bs News

Building Services Engineering

No abstract provided.

Least-Squares Finite-Element Lattice Boltzmann Method, Yusong Li, Eugene J. Leboeuf, P. K. Basu

Department of Civil and Environmental Engineering: Faculty Publications

A new numerical model of the lattice Boltzmann method utilizing least-squares finite element in space and Crank-Nicolson method in time is presented. The new method is able to solve problem domains that contain complex or irregular geometric boundaries by using finite-element method’s geometric flexibility and numerical stability, while employing efficient and accurate least-squares optimization. For the pure advection equation on a uniform mesh, the proposed method provides for fourth-order accuracy in space and second-order accuracy in time, with unconditional stability in the time domain. Accurate numerical results are presented through two-dimensional incompressible Poiseuille flow and Couette flow.

Utilizing Near-Field Measurements To Characterize Far-Field Radar Signatures, John R. Watkins

Theses and Dissertations

The increased need for stealth aircraft requires an on-site Far-Field (FF) Radar Cross-Section (RCS) measurement process. Conducting these measurements in on-site Near-Field (NF) monostatic facilities results in significant savings for manufacturers and acquisition programs. However, NF measurements are not directly extended to a FF RCS. Therefore, a large target Near-Field to Far-Field Transformation (NFFFT) is needed for RCS measurements. One approach requires an Inverse Synthetic Aperture Radar (ISAR) process to create accurate scattering maps. The focus of this work is the development of accurate NF scattering maps generated by a monostatic ISAR process. As a first look, the process is …

Afci Quarterly Input – Unlv April Through June, 2004, Harry Reid Center For Environmental Studies. Nuclear Science And Technology Division

Transmutation Research Program Reports (TRP)

Quarterly report highlighting research projects and objectives of the Transmutation Research Program at the Nuclear Science & Technology Division, Harry Reid Research Center.

The University of Nevada, Las Vegas supports the AFCI through research and development of technologies for economic and environmentally sound refinement of spent nuclear fuel. The UNLV program has four components: infrastructure, international collaboration, student-based research, and management and program support.

Inside Unlv, Holly Ivy De Vore, Caryn Key, Carol C. Harter, Richard Morgan

Inside UNLV

No abstract provided.

An Assessment Of Modern Methods For Rotor Track And Balance, Michael J. Renzi

Theses and Dissertations

One routine maintenance item facing the helicopter industry today is the issue of rotor track and balance (RT&B). While the task of reducing vibrations is often overlooked as simply an unimportant maintenance concern, what should not be overlooked is the extensive amount of time and money committed by maintenance to smoothing an aircraft. If there were a way to make the process of rotor track and balance more efficient it would be a huge boost to the helicopter industry in both time and money. The first steps towards research into new and improved methods is to evaluate what is currently …

Cold Flow Testing Of A Modified Subscale Model Exhaust System For A Space Based Laser, David B. Jarrett

Theses and Dissertations

The aim of this research was a continued study of gas-dynamic phenomena that occurred in a set of stacked nozzles as reported by Captains Ian Bautista in 2003 and Scott Bergren in 2002. The arrangement of the stacked nozzles was a modified version of a 1/5th scale-model of one quadrant of the conceptual Space Based Laser Integrated Flight Experiment (SBL IFX) gas dynamic laser. Rather than cylindrical rings of nozzles, the stacked nozzles were flat and able to be rotated about a vector normal to the nozzle exits. This set of stacked flat nozzles was installed on a blow-down/vacuum wind …

Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen

Theses and Dissertations

The fretting fatigue behavior of the shot-peened titanium alloy, Ti-6Al-4V, was investigated under a corrosive environment of synthetic seawater. Fretting fatigue tests were performed over a wide stress range to determine the effect of seawater at high and low cycle fatigue regimes. The results from this study showed: (1) seawater significantly reduces the fretting fatigue life of shot-peened Ti-6Al-4V at both high and low cycle fatigue relative to its counterpart in ambient laboratory conditions, (2) shot peening increases the fretting fatigue life of Ti-6Al-4V when tested under dry and seawater conditions relative to its counterpart of unpeened Ti-6Al-4V, (3) surface …

Synchronous Motor Phase Control By Vector Addition Of Induced Winding Voltages, Daniel J. Simon, Dennis L. Feucht

Electrical and Computer Engineering Faculty Publications

We propose a simple low-cost approach to the winding-sensed control of three-phase synchronous permanent-magnet motors. Our approach results from a straightforward but elegant application of vector-based motor theory. The method therefore does not depend on the differential equations that describe the motor dynamics, and it does not depend on the particular motor parameters. The single method we derive applies to both wye- and delta-configured motors. We vectorially sum the voltage waveforms at the motor terminals in a certain way and use their zero crossings to produce a correctly phased six-step switch sequence. We discuss the implementation for both wye- and …

Time Series Classification Using Gaussian Mixture Models Of Reconstructed Phase Spaces, Richard J. Povinelli, Michael T. Johnson, Andrew C. Lindgren, Jinjin Ye

Electrical and Computer Engineering Faculty Research and Publications

A new signal classification approach is presented that is based upon modeling the dynamics of a system as they are captured in a reconstructed phase space. The modeling is done using full covariance Gaussian mixture models of time domain signatures, in contrast with current and previous work in signal classification that is typically focused on either linear systems analysis using frequency content or simple nonlinear machine learning models such as artificial neural networks. The proposed approach has strong theoretical foundations based on dynamical systems and topological theorems, resulting in a signal reconstruction, which is asymptotically guaranteed to be a complete …

Correlation And Covariance Of Satellite Scatterometer Measurements, David G. Long, Peter K. Yoho

Faculty Publications

Capable scatterometer designs have been developed that seek improved resolution through the use of higher pulse sampling rates. The high sampling rates bring the traditional scatterometry assumption of measurement independence into question. This paper uses fundamental scattering theory to derive general expressions for correlation and covariance between scatterometer measurements and provides practical analysis using current and future instruments as examples. The paper derives expressions for the measurement variance parameter Kp when measurement correlation due to Rayleigh fading effects is present and relates Kp to the statistics of multiple pulse measurements. A function of the transmit signal modulation and receive processing, …

Optimization Studies Of Thermal Bimorph Cantilevers, Electrostatic Torsion Actuators And Variable Capacitors, Wuyong Peng

Dissertations

In this dissertation, theoretical analyses and optimization studies are given for three kinds of MEMS devices: thermal bimorph cantilevers, electrostatic torsion actuators, and variable capacitors. Calculation, simulation, and experimental data are used to confirm the device behavior and demonstrate the application of the design approaches.

For thermal bimorph cantilevers, an analytical model is presented which allows theoretical analysis and quantitative optimization of the performance based on material properties and device dimensions. Bimorph cantilevers are divided into two categories for deflection optimization: either the total thickness is constant, or the cantilever has one constant and one variable layer thickness. The optimum …

Mechanisms Of Layer-Transfer Related To Silicon-On-Insulator Structures, Bo Chen

Dissertations

The objective of this dissertation was to study the mechanisms that affect an efficient hydrogenation process in silicon and to validate a hypothesis concerning the hydrogenation mechanism of pre-implanted silicon wafers under hydrogen-plasma processing. These studies are related to a general process. A trapping layer for hydrogen was introduced by ion beam implantation into the silicon wafer. Next, this wafer was hydrogenated using a hydrogen plasma. It was hypothesized that the trapping layer acts as a getterer for the hydrogen diffusing into the silicon wafer. It was found that a large amount of hydrogen could be absorbed in the trapping …

Performance Evaluation Of Communication Systems With Transmit Diversity, Chunjun Gao

Dissertations

Transmit diversity is a key technique to combat fading with multiple transmit antennae for next-generation wireless communication systems. Space-time block code (STBC) is a main component of this technique. This dissertation consists of four parts: the first three discuss performance evaluation of STBCs in various circumstances, the fourth outlines a novel differential scheme with full transmit diversity.

In the first part, closed-form expressions for the bit error rate (BER) are derived for STBC based on Alamouti's scheme and utilizing M-ary phase shift keying (MPSK) modulation. The analysis is carried out for a slow, flat Rayleigh fading channel with coherent detection …

The Design Of Adjustable Spherical Mechanisms Using Plane-To-Sphere And Sphere-To-Plane Projections, Wen-Tzong Lee

Dissertations

The spherical mechanism is a particular type of spatial mechanism. Due to the orientation of its joint axes and the curvature of its links, the workspaces of spherical mechanisms (whether line segments, closed loops or area regions) are spherical in curvature. This characteristic of spherical mechanisms makes them quite effective and practical in motion path and function generation applications requiring spherical rigid body kinematics.

Although there are design methods available for spherical mechanisms, most of these methods do not consider the design of a single adjustable spherical mechanism. With an adjustable spherical mechanism, the user could for example, relocate the …

Development Of Dynamic Recursive Models For Freeway Travel Time Predictions, Xiaobo Liu

Dissertations

Traffic congestion has been a major problem in metropolitan areas, which is caused by either insufficient roadway capacity or unforesceable incidents. In order to promote the efficiency of the existing roadway networks and mitigate the impact of traffic congestion, the development of a sound prediction model for travel times is desirable.

A comprehensive literature review about existing prediction models was conducted by investigating the advantages, disadvantages, and limitations of each model. Based on the features and properties of previous models, the base models including exponential smoothing model (ESM), moving average model (MAM), and Kalman filtering model (KFM) are developed to …

Multi-Rate Access Schemes And Successive Interference Cancellation For Wireless Multimedia Mc-Cdma Communications, Mizhou Tan

Dissertations

To catch up with the fast changes of the information challenges, providing multimedia services has become a very important requirement for future wireless communications. A proper system, capable of supporting multi-rate transmissions as well as handling high quality of service (QoS) requirements in hostile wireless communication environments, should be sought. Multi-carrier CDMA (MC-CDMA), a combination of multi-carrier modulation (MCM) and direct-sequence CDMA (DS-CDMA), appears to be one of the most elegant solutions. In this dissertation, four multi-rate access schemes, termed uncoded fixed spreading length (UFSL), coded fixed spreading length (CFSL), multi-code fixed spreading length (MFSL) and variable spreading length (VSL), …

Boron And Phosphorous Implantation Into (100) Germanium : Modeling And Investigation Of Dopant Annealing Behavior, Yong Seok Suh

Dissertations

Germanium is increasingly being considered at this time for future silicon compatible optoelectronic and complementary metal oxide semiconductor (CMOS) device application. Germanium implantation will be a critical process for future device fabrication. However, critical properties like Pearson parameters and dopant activation temperatures are not well established. In this study, boron and phosphorus were implanted into (100) germanium with energies ranging from 20 to 320 keV and doses of 5 x 10¹³ to 5 x 10¹⁶ cm^-2. The behavior of the boron and phosphorus before and after annealing for 3 hours at 400, 600 or 800°C in …

3-D Numerical Simulation Of Reactive Extrusion And Its Application To Polymerization Of Ε-Caprolactone In Co-Rotating Twin-Screw Extruders, Linjie Zhu

Dissertations

A 3-D numerical simulation model was proposed to predict the polymerization of ε-caprolactone in fully-filled conveying elements and kneading blocks of co-rotating twin-screw extruders, in which the kinetics equation for polymerization is coupled with continuity equation, momentum equation, and energy equation. With the 3-D model, parametric studies have been carried out to investigate the effects of screw configurations, screw diameter, operational conditions, values of heat from reaction, initiator concentration, and heat transfer conditions at barrel surface upon the polymerization progress. Two simulation models for the polymerization in the partially-filled channels were developed based on the conveying mechanisms of the reaction …

Providing Guaranteed Qos In The Hose-Modeled Vpn, Dong Wei

Dissertations

With the development of the Internet, Internet service providers (ISPs) are required to offer revenue-generating and value-added services instead of only providing bandwidth and access services. Virtual Private Network (VPN) is one of the most important value-added services for ISPs.

The "classical" VPN service is provided by implementing layer 2 technologies, either Frame Relay (FR) or Asynchronous Transfer Mode (ATM). With FR or ATM, virtual circuits are created before data delivery. Since the bandwidth and buffers are reserved, the QoS requirements can be naturally guaranteed. In the past few years, layer 3 VPN technologies are widely deployed due to the …

Phase Noise Effects On Ofdm : Analysis And Mitigation, Songping Wu

Dissertations

Orthogonal frequency division multiplexing (OFDM) is a promising technique which has high spectrum efficiency and the robustness against channel frequency selectivity. One drawback of OFDM is its sensitivity to phase noise. It has been shown that even small phase noise leads to significant performance loss of OFDM. Therefore, phase noise effects on OFDM systems need to be analyzed and methods be provided to its mitigation.

Motivated by what have been proposed in the literature, the exact signal to interference plus noise ratio (SINR) is derived in this dissertation for arbitrary phase noise levels. In a multiple access environment with multiple …

Enhancing Qos Provisioning And Granularity In Next Generation Internet, Jie Yang

Dissertations

Next Generation IP technology has the potential to prevail, both in the access and in the core networks, as we are moving towards a multi-service, multimedia and high-speed networking environment. Many new applications, including the multimedia applications, have been developed and deployed, and demand Quality of Service (QoS) support from the Internet, in addition to the current best effort service. Therefore, QoS provisioning techniques in the Internet to guarantee some specific QoS parameters are more a requirement than a desire. Due to the large amount of data flows and bandwidth demand, as well as the various QoS requirements, scalability and …

Statistical Anomaly Denial Of Service And Reconnaissance Intrusion Detection, Zheng Zhang

Dissertations

This dissertation presents the architecture, methods and results of the Hierarchical Intrusion Detection Engine (HIDE) and the Reconnaissance Intrusion Detection System (RIDS); the former is denial-of-service (DoS) attack detector while the latter is a scan and probe (P&S) reconnaissance detector; both are statistical anomaly systems.

The HIDE is a packet-oriented, observation-window using, hierarchical, multi-tier, anomaly based network intrusion detection system, which monitors several network traffic parameters simultaneously, constructs a 64-bin probability density function (PDF) for each, statistically compares it to a reference PDF of normal behavior using a similarity metric, then combines the results into an anomaly status vector that …

Mobile Agent Based Distributed Network Management : Modeling, Methodologies And Applications, Jian Ye

Dissertations

The explosive growth of the Internet and the continued dramatic increase for all wireless services are fueling the demand for increased capacity, data rates, support of multimedia services, and support for different Quality of Services (QoS) requirements for different classes of services. Furthermore future communication networks will be strongly characterized by heterogeneity. In order to meet the objectives of instant adaptability to the users' requirements and of interoperability and seamless operation within the heterogeneous networking environments, flexibility in terms of network and resource management will be a key design issue. The new emerging technology of mobile agent (MA) has arisen …

Ad Hoc Network Security And Modeling With Stochastic Petri Nets, Congzhe Zhang

Dissertations

Advances in wireless technology and portable computing along with demands for high user mobility have provided a major promotion toward the development of ad hoc networks. These networks feature dynamic topology, self-organization, limited bandwidth and battery power of a node. Unlike the existing commercial wireless systems and fixed infrastructure networks, they do not rely on specialized routers for path discovery and traffic routing. Security is an important issue in such networks. Typically, mobile nodes are significantly more susceptible to physical attacks than their wired counterparts.

This research intends to investigate the ad hoc network routing security by proposing a performance …