Digital Commons Network^™

A Distributed Surrogate Methodology For Inverse Most Probable Point Searches In Reliability Based Design Optimization, James Davidson

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Surrogate models are commonly used in place of prohibitively expensive computational models to drive iterative procedures necessary for engineering design and analysis such as global optimization. Additionally, surrogate modeling has been applied to reliability based design optimization which constrains designs to those which provide a satisfactory reliability against failure considering system parameter uncertainties. Through surrogate modeling the analysis time is significantly reduced when the total number of evaluated samples upon which the final model is built is less than the number which would have otherwise been required using the expensive model directly with the analysis algorithm. Too few samples will …

Surface Treatments To Tailor The Wettability Of Carbon Nanotube Arrays, Lvmeng He

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Carbon nanotubes (CNTs) have gained great attention due to their excellent mechanical, electrical, and thermal properties. Carbon nanotube (CNT) arrays attached to solid substrates resemble a nano-carpet and have potentials in a variety of devices. In this study, the focus is to investigate the surface modification approaches of CNT carpets on flat (compressed) graphite. Wettability, or permeation of a liquid such as water into the CNT strands, may play very significant roles in many applications where a CNT-coated device may be used in aqueous environment. Short-term microwave plasma treatments were used in this project to functionalize CNT carpets for wettability. …

High Temperature Transient Creep Analysis Of Metals, Sara Mirmasoudi

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The ability to design vehicles capable of reaching hypersonic speeds has become a necessity to satisfy industry requirements, hence requiring the need for better understanding of creep behavior of materials. Although the steady state creep of metals has been analyzed rigorously, there is little known about transient creep of many metals. Understanding transient creep behavior of metals is crucial in analysis and design of short term hypersonic flight applications. Hence, a transient creep analysis of 304SS, Al7075-T6, Al2024-T6, Inconel 625, Inconel 718, and Rene N4 is carried out focusing on the microstructural behavior of these metals undergoing high temperature operating …

Deposition And Characterization Of Ceramic Thin Films And A New Experimental Approach To Evaluate The Mechanical Integrity Of Film/Substrate Interfacial Layers, Yang Mu

LSU Doctoral Dissertations

Due to their corrosion resistance, high temperature stability, high strength, and high hardness, refractory ceramic thin films and coatings have been utilized for surface engineering of mechanical components and mechanical fabrication tools. Adhesion between ceramic thin films and coatings and the substrate is of critical concern for performance and life time of coated systems. In this dissertation, a custom designed and constructed ultra-high-vacuum (UHV) vapor phase deposition system was used for the preparation of ceramic thin films through low-pressure high-density plasma assisted physical vapor deposition (PVD) methods. Deposited thin films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), …

On The Thermally Induced Failure Of Rolling Element Bearings, Jafar Takabi

LSU Doctoral Dissertations

This dissertation is devoted to the investigation of thermally induced seizure of rolling element bearings. A comprehensive thermal model of the rolling element bearings is developed which can predict the operating temperature of the bearing components in a wide range of operating conditions. The validity of this thermal model is verified by comparing the simulation results with a set of experiments. The results of simulations reveal that the rotational speed, oil viscosity and cooling rate of the housing have a significant influence on the operating temperature of the rolling bearings. To provide detailed information about all of the contact forces …

Molecular Dynamics Simulation Study Of Single Dna Nucleotides Transport Through Nanoslits, Kai Xia

LSU Doctoral Dissertations

There is potential for flight time based DNA sequencing involving disassembly into individual nucleotides which would pass through a nanochannel with 2 or more detectors. Molecular dynamics simulation of electrophoretic motion of single DNA nucleotides through 3 nm wide hydrophobic slits was performed. Electric field strength (E) varied from 0.0 to 0.6 V/nm. Slit walls were smooth or had a roughness similar to nucleotide size. Multiple nucleotide-wall adsorptions occurred. The electric field did not influence the nucleotide adsorption and desorption mechanism for E ¡Ü 0.1 V/nm, but influenced nucleotide orientation relative to the field direction. The nucleotide-wall interactions differed due …

Challenges Towards Structural Integrity And Performance Improvement Of Welded Structures, Mohammad Washim Dewan

LSU Doctoral Dissertations

Welding is a fabrication process that joint materials, is extensively utilized in almost every field of metal constructions. Heterogeneity in mechanical properties, metallurgical and geometrical defects, post-weld residual stresses and distortion due to non-linear welding processes are prime concerns for performance reduction and failures of welded structures. Consequently, structural integrity analysis and performance improvement of weld joints are important issues that must be considered for structural safety and durability under loading. In this study, an extensive experimental program and analysis were undertaken on the challenges towards structural integrity analysis and performance improvement of different welded joints. Two widely used welding …

On The Role Of Surface Roughness In Elastohydrodynamic Lubrication Of Tribological Components, Mohammad Masjedi

LSU Doctoral Dissertations

The present dissertation investigates the effect of surface roughness in the elastohydrodynamic lubrication (EHL). Since many essential components of the machinery such as gears, rolling element bearings, cam-followers, and heavily loaded journal bearings operate under the mixed EHL condition, and given the fact that nearly all engineering surfaces are rough to some extent, there is a need for an extensive research which can realistically quantify the effect of the surface roughness in such applications. We thus seek to develop an applied engineering approach for the treatment of the mixed EHL for prediction of the performance of machinery. Both line-contact and …

Numerical Studies Of Liquid-Liquid Segmented Flows In Square Microchannels Using A Front-Tracking Algorithm, Eamonn Daire Walker

LSU Doctoral Dissertations

Liquid-liquid segmented flows in a square microchannel are investigated numerically using a hybrid front-tracking/front-capturing method. The code is found to be well-adapted to a large range of flow parameters, but droplet flows are limited by poor accuracy at Laplace number above 100 – 1000 and plug flows are limited by the code’s current inability to adequately model the flow in thin films at low capillary numbers. A Schwarz-Aitken acceleration technique is investigated as a means to reduce computation time, but is found not to be advantageous compared to the parallel multigrid formulation of the code. Numerical simulations are divided into …

Experimental Study Of A Cascade Of Low Pressure Turbine Blades With Upstream Periodic Stator Wakes, Carlos Rene Gonzalez Rodriguez

LSU Master's Theses

The objective of this study is to experimentally study film cooling flows. A closed-loop wind tunnel with a four passage linear cascade of US Air Force Research Laboratory (AFRL) ultra-high-lift L1A low pressure turbine (LPT) blades and upstream wake generator is used in conjunction with Particle Image Velocimetry (PIV) flow visualization technique to study turbulent film cooling flows due to the interaction between vanes and blades. Further post-processing in the form of Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) modal analyses is performed to determine the relevant modes that characterize the coherent structures in the flow. An image …

A Comparative Assessment Of Ergonomic Risk Factors In University Personnel Using Rula And Reba Aiming To Study The Cause And Effect Relationship, Nabila Chowdhury

LSU Master's Theses

The aim of this research was to conduct an ergonomic assessment of working postures and the design of computer workstations of the employees in Louisiana State University. The purpose of the study was threefold- (1) to determine the major ergonomic issues in university employees while working on computer workstations, (2) to compare the two ergonomic assessment tools (RULA and REBA) to see how similarly or differently they assess the risks present in the same working condition and (3) to develop a model that correlates between working condition, work posture and computer workstation design with their effects on musculoskeletal system. This …

Offshore Turbine Arrays: Numerical Modeling And Experimental Validation, Thomas Kroll, William Hall, Ian Gagnon

Honors Theses and Capstones

The interaction between wind turbines in a large wind farm needs to be better understood to reduce array losses and improve energy production. A numerical test bed for an array of offshore wind turbines was developed in the open-source computational fluid dynamics (CFD) framework OpenFOAM. It provides a computational tool which can be used in combination with physical model turbine array studies in the Flow Physics Facility (FPF) at UNH as well as other test facilities.

Turbines were modeled as actuator disks with turbulence sources to reduce computational cost. Both k-ϵ and k-ω SST turbulence models were utilized to capture …

Increasing Efficiency Of Thermal Desalination, Jarrod A. Edwards, Mackinzie Washington, Chan Jung, Ben Garrison

Chancellor’s Honors Program Projects

No abstract provided.

Methods For Determining Grease Service Levels In An Ah-64d Intermediate Gearbox Using On-Board Sensors, Travis Steven Edwards

Theses and Dissertations

The intermediate gearbox (IGB) on the AH-64D was chosen as the subject for this study based on the persistent grease leaks that require grounding aircraft. The aircraft is not currently equipped with a method of detecting grease loss during flight, so techniques for analyzing the usefulness of old metrics and possible new techniques can be tested. The main objective of this study is to use the aircraft’s on-board sensors to develop a method of determining the lubrication level of the IGB. Currently, the most reliable method for detecting a fault on the aircraft is through the use of vibration-based condition …

Predictive Methods For End Of Life Prognosis In Composites, Vamsee Vadlamudi

Theses and Dissertations

The long-term properties of continuous fiber reinforced composite materials are increasingly important as applications in airplanes, cars, and other safety critical structures are growing rapidly. The mechanical, electrical, and thermal properties of composite materials are altered by the initiation and accumulation of discrete fracture events whose distribution and eventual interaction defines the limits of design, such as strength and life. There is a correlation that exists between the long term behavior of those materials under combined mechanical, thermal, and electrical fields, and the functional properties and characteristics of the composite materials that requires a fundamental understanding of the material state …

Self-Assembly Kinetics Of Microscale Components: A Parametric Evaluation, Jose Miguel Carballo

USF Tampa Graduate Theses and Dissertations

The goal of the present work is to develop, and evaluate a parametric model of a basic microscale Self-Assembly (SA) interaction that provides scaling predictions of process rates as a function of key process variables. At the microscale, assembly by “grasp and release” is generally challenging. Recent research efforts have proposed adapting nanoscale self-assembly (SA) processes to the microscale. SA offers the potential for reduced equipment cost and increased throughput by harnessing attractive forces (most commonly, capillary) to spontaneously assemble components. However, there are challenges for implementing microscale SA as a commercial process. The existing lack of design tools prevents …

A Numerical And Experimental Investigation Of Flow Induced Noise In Hydraulic Counterbalance Valves, Mutasim Mohamed Elsheikh

USF Tampa Graduate Theses and Dissertations

The main objective of this study is to explore the complex fluid flow phenomena that result in the generation of a high frequency noise in counterbalance valves through an experimental and numerical investigation of the flow. Once the influence of the different components involved in noise generation is established, a secondary objective is the introduction of design modifications that eliminate the undesired effect without altering the operation envelope or the performance of the valve.

A hydraulic test bench was used to carry out an experimental investigation of the noise generation process. A computer based data acquisition system was used to …

Use Of Anaerobic Adhesive For Prevailing Torque Locking Feature On Threaded Product, Alan Hernandez

USF Tampa Graduate Theses and Dissertations

The purpose of this research is to determine if anaerobic adhesive can be used as a prevailing torque locking feature. Maintaining preload in critical joints is the usual standard that anaerobic adhesives are held to in aerospace and other industry. To test if anaerobic adhesive can be used as a prevailing torque locking feature a test procedure was developed and implemented to measure the removal torque of threaded fasteners after an allotted cure time. In total, 191 threaded fasteners of different material and coatings were tested in the unseated and seated states with various strengths and varieties of anaerobic adhesive. …

Experimental Investigation Of Encapsulated Phase Change Materials For Thermal Energy Storage, Tanvir E. Alam

USF Tampa Graduate Theses and Dissertations

Thermal energy storage (TES) is one of the most attractive and cost effective solutions to the intermittent generation systems like solar, wind and other renewable sources, compared to alternatives. It creates a bridge between the power supply and demand during peak hours or at times of emergency to ensure the continuous supply of energy. Among all the TES systems, latent heat thermal energy storage (LHTES) draws lots of interests as it has high energy density and can store or retrieve energy isothermally. Two major technical challenges associated with the LHTES are low thermal conductivity of the phase change materials (PCMs), …

Color Removal From Pulp Mill Effluent Using Coal Ash Produced From Georgia Power Coal Combustion Plants, Christopher B. Willett

Electronic Theses and Dissertations

Two environmental concerns currently face Georgia: coal fly ash (CFA) waste from coal power plants, and the effluent generated by pulp mills. Pulp mill effluent discolors surface waters into which it is discharged, and has been proven to negatively impact the dissolved oxygen and carbon necessary for aquatic life. The proposed solution is a cost-effective adsorption treatment using an inexpensive but abundantly available waste material: CFA. CFA possesses beneficial properties that allow it to effectively remove contaminants, and is available at significantly reduced cost. The primary research objective was to define treatment parameters that would result in the maximum removal …

Computational Fluid Dynamics Modeling Of The Effects Of Water Injection In A Diesel Engine, Rabun Z. Wallace

Electronic Theses and Dissertations

Water injection has been used in internal combustion engines for many years. It has been used to cool combustion temperatures, reduce emissions, and in some instances clean carbon buildup from the cylinder. Research has shown that the water to fuel mass ratio is most effective between 20-30%, so the upper and lower limit were used for simulations in Converge CFD. To validate the CFD model, a case without water injection was compared to experimental data from Sandia National Laboratory. The predicted in-cylinder pressure and heat release rate showed good agreement with the experimental data. Cases were run with the injection …

Networked Heterogeneous Systems In A Ros-Enabled Cloud Environment, Christopher Reid

Electronic Theses and Dissertations

It is important in the development of cloud robotics that the challenges presented by transferring computational loads to networked resources are properly addressed. The challenges include network latency, data integrity, security, and privacy. The objective of the present work is to investigate the issues of latency and data integrity in a representative cloud robotics environment. The present work involves setting up a cloud robotics network in an open-source Robot Operating System (ROS) framework and carrying out investigations on the levels of latency and reduction in data integrity as utilization of the network increases. In this study, a virtual datacenter has …

Physics And Applications Of A Pdms Based Centrifugal Microfluidic System, Ziliang Cai

LSU Doctoral Dissertations

The objective of this research work is to develop a centrifugal microfluidic system for general purposes based on microfabrication technologies including SU-8 photolithography, polydimethylsiloxane (PDMS) casting. The main contribution of this research is to integrate a flyball governor system into the polymer based centrifugal microfluidic platform. A series of function units are developed based on this unique mechanism. In the first part, three pinch valve systems were designed and tested. The first one is based on the magnetic force and the second one is on the basis of spring force and the last one is a membrane valve. All valving …

On An Effective Submodeling Procedure For Stresses Determined With Finite Element Analysis, Ajay Ashok Kardak

LSU Doctoral Dissertations

Submodeling can enable stress analysts using finite elements to focus analysis on a subregion containing the stress concentration of interest, with consequent computational savings. Such benefits are only truly realized if the boundary conditions on the edges of the subregion that were originally contained within the global region are sufficiently accurate. These boundary conditions are drawn from initial global finite element analysis (FEA), and consequently themselves have errors that in turn lead to errors in the stresses sought. When these last boundary-condition errors are controlled, and the discretization errors incurred by the FEA of ensuing submodels are also controlled, submodeling …

Healing-On-Demand Polymer Composites Based On Shape Memory Polyurethane Fibers And Polymeric Artificial Muscles, Pengfei Zhang

LSU Doctoral Dissertations

In this dissertation, the healing-on-demand polymer composites based on shape memory polyurethane fibers and artificial muscles are investigated, for understanding and developing a novel healing-on-demand composite so that it would be used for industrial applications that could heal structural-length scale damage and leaking autonomously, repeatedly, efficiently, timely, and molecularly. Firstly, the structural relaxation behavior of shape memory polyurethane (SMPU) fiber was studied by theoretical analysis and experimental test. Then, a self-healing composite based on cold-drawn short SMPU fiber was prepared and tested for evaluating its crack-healing performance. After that, polymer artificial muscle based healing-on-demand composite was developed and characterized. Based …

Modeling Two-Phase Flow And Heat Transfer In Polygonal Microchannels, Sai Sashankh Rao

LSU Doctoral Dissertations

Microfluidics is a burgeoning research area with applications ranging from microfluidic cooling to biomolecule synthesis. Here we study two problems to gain an improved understanding of two-phase flow and heat transfer in microfluidic devices. We also study a third problem on boundary layer flow out of theoretical interest. In the first problem, we study the heat and mass transfer in polygonal micro heat pipes under small imposed temperature differences. A micro heat pipe, used in electronics cooling, consists of a closed polygonal microchannel filled with a wetting liquid and a long vapor bubble. We model the evaporation, fluid flow, and …

Study Of Active Vibration Control Using The Method Of Receptances, Amit Maha

LSU Doctoral Dissertations

Using the Method of Receptance, it is possible in general to assign 2_x0002_ poles (i.e. n conjugate pairs) of an axially vibrating rod of variable cross section by sensing the state at _x0002_ points along the rod. Using the sensor data, closed loop feedback control gains can be calculated by solving a simple set of linear equations. The feedback gains can be applied to generate the required control force using an actuator. This partial pole assignment can be done without continuous or discrete analytical modeling. Therefore, the physical parameters such as the rigidity, the density, and the variable cross-sectional area …