Mechanical Engineering Commons^™

Steps In The Development Of A Full Particle-In-Cell, Monte Carlo Simulation Of The Plasma In The Discharge Chamber Of An Ion Engine, Bryan James Penkal

Browse all Theses and Dissertations

The design and development of ion engines is a difficult and expensive process. In order to alleviate these costs and speed ion engine development, it is proposed to further develop a particle-in-cell (PIC), Monte-Carlo collision (MCC) model of an ion engine discharge chamber, which has previously been worked on by the Wright State Ion Engine Modeling Group. Performing detailed and accurate simulations of ion engines can lead to millions of dollars in savings in development costs.

In order to recognize these savings more work must be done on the present day models used to simulate ion engine performance. The work …

Bull's-Eye Structure With A Sub-Wavelength Circular Aperture, Masoud Zarepoor

Browse all Theses and Dissertations

This research focuses on improving the spatial resolution of terahertz (THz) imaging. Using a sub-wavelength aperture in a metal ground plane is the most common way to improve the spatial resolution, but a sub-wavelength aperture has low radiation transmission. To increase the radiation transmission of a sub-wavelength aperture, periodic circular grooves were put in the metal around the aperture. The sub-wavelength circular aperture and the periodic circular grooves around it are known as the bull's-eye structure. The bull's-eye structure shows high radiation transmission at its design frequency, and it also has sub-wavelength spatial resolution. This research designed the bull's-eye structure …

Structural-Acoustic Analysis And Optimization Of Embedded Exhaust-Washed Structures, Ryan N. Vogel

Browse all Theses and Dissertations

The configurations for high speed, low observable aircraft expose many critical areas on the structure to extreme environments of intense acoustic pressure loadings. When combined with primary structural and thermal loads, this effect can cause high cycle fatigue to aircraft skins and embedded exhaust system components. In past aircraft design methods, these vibro-acoustic loads have often been neglected based on their relatively small size compared to other thermal and structural loads and the difficulty in capturing their dynamic and frequency dependent responses. This approach is insufficient for effective advanced designs of complex aerospace structures, such as internal ducted exhaust systems …

Discussion Of Christine C. Shepard, Vera N. Agostini, Ben Gilmer, Tashya Allen, Jeff Stone, William Brooks And Michael W. Beck. Reply: Evaluating Alternative Future Sea-Level Rise Scenarios, Natural Hazards, 2012 Doi:10.1007/S11069-012-0160-2, A. Boretti

Mechanical and Aerospace Engineering Faculty Research & Creative Works

No abstract provided.

Hybrid Protocols For Maintaining Connectivity Of Multiagent Systems, Gerardo De La Torre, Tansel Yucelen, Eric N. Johnson

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This paper focuses on a new connectivity control architecture for networked multiagent systems based on hybrid protocols. Specifically, for a group of agents subject to Δ-disk proximity graphs, we consider the consensus problem while preserving connectedness with a priori given bounds on the control inputs. The bounds on the control inputs are shown not to depend on potential functions or system states. Instead, the bounds are user selected continuous functions. By using the proposed framework, we show that the maximum distance among neighboring agents decreases strictly, and hence the connectivity problem is solved while satisfying the consensus objective. © 2013 …

Analysis Of Laminated Anisotropic Plates And Shells Via A Modified Complementary Energy Principle Approach, Martin Claude Domfang

Dissertations (1934 -)

The present work is concerned with the finite element structural analysis of laminated anisotropic plates and shells. New elements based on a modified complementary energy principle are proposed to improve the analysis of such composite structures. Third order deformation plate and shell models incorporating a convergence parameter are developed to govern the general displacement field.

An eight-node isoparametric quadrilateral element with two independent cross-sectional rotations and three normal displacements is utilized to describe the displacement field. The present modified complementary energy formulation incorporates a number of in-plane strain functions of various orders. The corresponding in-plane stresses for each lamina are …

Testing The Fuel Efficiency Of Tractors With Continuously Variable And Standard Geared Transmissions, Christopher N. Howard, Michael F. Kocher, Roger M. Hoy, Erin E. Blankenship

Department of Agricultural and Biological Systems Engineering: Faculty Publications

A John Deere 8295R IVT tractor with a continuously variable transmission (CVT) and a John Deere 8295R PowerShift (PST) tractor with a standard geared transmission (GT) were tested for fuel consumption at three different travel speeds with six different load levels applied per speed. The JD 8295R PST tractor was tested both at full throttle (FT) and shifted up two gears and throttled back (SUTB) to achieve the same travel speed as at full throttle. For each travel speed with each transmission mode, fuel consumption was determined to be linearly related to drawbar power. Linear regression analyses were performed, and …

Effects Of Initial Conditions On Rayleigh-Taylor Instability Using Elastic-Plastic Materials, Pamela Susan Roach

Masters Theses

"When an elastic-plastic solid is accelerated by a fluid of lower density, Rayleigh-Taylor instability (RTI) is observed, and the instability is mitigated by the material's mechanical strength, initial conditions, and the acceleration that drives the instability. Such instances of RTI are observed in supernovas, explosive welding, and inertial confinement fusion. In contrast to Newtonian fluids, experimental study of RTI in accelerated solids is traditionally hindered by difficulty to measure material properties and exceedingly small time scales. An understanding of the role initial conditions and material properties have on the growth of RTI will lead to better control of the instability. …

A Model Of Transient Heat Transfer In A Packed Bed Of Alumina Particles, Samira Shiri

Dissertations and Theses

The present study seeks to develop a robust system-scale heat transfer model for a sensible heat storage system. A novel mechanism to simulate axial dispersion and heat loss from the boundary of the sensible heat system to the environment is introduced. The most challenging topics to develop a robust heat transfer model are related to heat loss term, selecting the more reliable method to calculate heat transfer coefficient between fluid and solid, and investigating the effect of neglecting temperature dependency of materials properties. As the storage heat system has a vertical storage vessel, the dominant heat transfer mechanism from the …

Exploring The Interaction Of Two Self-Excited Energy Harvesters, Yi Han

Dissertations and Theses

No abstract provided.

Modeling, Numerical Analysis, And Predictions For The Detonation Of Multi-Component Energetic Solids, Michael Wayne Crochet

LSU Doctoral Dissertations

Metal powders are often used as an additive to conventional high explosives to enhance the post-detonation blast wave. Piston-impact simulations are commonly utilized to predict performance metrics such as detonation speed and strength, as well as assessing the impact and shock sensitivity of these materials. The system response is strongly influenced by the initial particle size distribution and material composition. Multiphase continuum models have been routinely applied at the macroscale to characterize the detonation of solid high explosives over engineering length scales. Current models lack a description of the physically permissible constitutive relations for mass transfer due to general chemical …

Polymer-Based Fluidic Devices Integrated With Perforated Micro- And Nanopore Membrane For Study Of Ionic And Dna Transport, Junseo Choi

LSU Doctoral Dissertations

This study aims to develop a process, allowing a low-cost and high-throughput fabrication technique to produce freestanding polymer membranes having perforated micro- and nanopores, and also to design 3D micro/nanofluidic devices with the membrane, enabling a study of ions and DNA transport through nanopores. Technically, we have designed and fabricated high quality silicon stamp. Then, they have been used as molds for modified nanoimprint lithography that takes advantages of a sacrificial layer to obtain freestanding polymer membrane. This technique allows easy fabrication of large area, fully released polymer membranes containing perforated micro- and sub-micropores. The membrane with perforated micropores has …

Analysis And Optimization Of Film Cooling Effectiveness, Hessam Babaee

LSU Doctoral Dissertations

In the first part, an optimization strategy is described that combines high-fidelity simu- lations with response surface construction, and is applied to pulsed film cooling for turbine blades. The response surface is constructed for the film cooling effectiveness as a function of duty cycle, in the range of DC between 0.05 and 1, and pulsation frequency St in the range of 0.2-2, using a pseudo-spectral projection method. The jet is fully modulated and the blowing ratio, when the jet is on, is 1.5 in all cases. Overall 73 direct numerical sim- ulations (DNS) using spectral element method were performed to …

Nanotube Film-Enhanced 3-D Photoanode For Application In Microsystems Technology, Fareed Dawan

LSU Doctoral Dissertations

Surface area plays an important factor in the energy conversion performance of solar cells. It has also emerged as a critical factor in the evolution of high-performance micro-electro-mechanical systems (MEMS) and multifunctional microstructures most of which will benefit from integrated on-chip solar power. Presented here is the hierarchical fabrication and characterization of TiO2 nanotubes on non-planar 3-dimensional microstructures for enhanced performance of the photoanode in dye-sensitized solar cells (DSSCs). The objective is to increase photoanode performance within a 1 cm2 lateral footprint area by increasing the vertical surface area through the formation of TiO2 nanotubes on 3-D microstructures. In the …

Steady And Unsteady Thermo-Strucural Simulation Of Thermally Actuated Micro- And Nano-Structures, Elham Maghsoudi

LSU Doctoral Dissertations

This dissertation provides a thermo-structural simulation for nano-scale and micro-scale structures with pinned and fixed boundary conditions which are either thermally positioned, buckled, or actuated. The study begins with simulating a pinned-pinned beam in micro-scale and nano-scale. The steady state thermo-structural equation is solved numerically using an implicit Finite Difference method implemented in Matlab to obtain the thermal positioning response, which is the thermally steady state center displacement, by adding a constant, time-independent heat flux to the structure. The results show the steady state thermal displacement of the system is a function of the geometry, pressure, material properties, and constant …

Investigations Of The Effects Of Flame Configuration On The Combustion Of Laminar Diffusion Flame, Li Lu

LSU Doctoral Dissertations

Motivation and objective to study double inverse diffusion flame is introduced, followed by the literature survey on soot formation in inverse diffusion flame (IDF), application of the unique structure of double inverse diffusion flame (DIDF), radiation effects on DIDF, factors that affect the formation of nitric oxide and effects of elevated pressure on diffusion flames. Numerical method is validated by the result of flame height for IDF, which is consistent with result from previous research. In present work, two DIDF burner configurations with different size are used to conduct the simulation. Ethylene is used as the fuel. For each of …

3d Integration Of Micro- And Nanostructures Into Bio-Analytical Devices, Bahador Farshchian

LSU Doctoral Dissertations

This study aims to develop a process which allows 3D integration of micro and nanostructures in microchannels. A fabrication process was established for the large area integration of hierarchical micro and nanostructures in microchannels. This novel process, which is called 3D molding, takes advantage of an intermediate thin flexible stamp such as PDMS from soft lithography and a hard mold such as brass from hot embossing process. However, the use of a thin intermediate polydimethylsiloxane (PDMS) stamp inevitably causes dimensional changes in the 3D molded channel, with respect to those in the brass mold protrusion and the intermediate PDMS stamp …

Developing Defect-Tolerant Demolding Process In Nanoimprint Lithography, Alborz Amirsadeghi

LSU Doctoral Dissertations

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we first investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist containing a base (either tripropyleneglycol diacrylate with shorter chain length or polypropyleneglycol diacrylate with longer chain length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine after imprinting the UV resist on a silicon stamp. In general, the shorter monomer shows a larger demolding force. Decreasing the cross-linking …

Thermal Cycling And Thermal Radiation Performances Of Novel Thermal Barrier Coatings, Li Wang

LSU Doctoral Dissertations

Thermal barrier coatings (TBCs) play an important role in protecting the superalloy components from the hot gas stream in gas-turbine engines. Driven by the higher inlet temperature of modern gas turbine engines for higher efficiency and less harmful gas emission, exploration of TBC new materials and thermal radiation effects of TBCs have attracted more attentions recently. In this study, thermochemical compatibility of Gd2Zr2O7 (GZ) and yttria-stabilized-zirconia (YSZ) at 1300 ºC was investigated. Single, double and three ceramic-layered GZ based TBCs were prepared and their thermal cycling properties were performed under different thermal conditions. Thermochemical compatibility investigation showed that YSZ tended …

Fabrication And Characterization Of A Polymeric Nanofluidic Device For Dna Analysis, Jiahao Wu

LSU Doctoral Dissertations

The growing needs for cheaper and faster sequencing of long biopolymers such as DNA and RNA have prompted the development of new technologies. Among the novel techniques for analyzing these biopolymers, an approach using nanochannel based fluidic devices is attractive because it is a label-free, amplification-free, single-molecule method that can be scaled for high-throughput analysis. Despite recent demonstrations of nanochannel based fluidic devices for analyzing physical properties of such biopolymers, most of the devices have been fabricated in inorganic materials such as silicon, silicon nitride and glass using expensive high end nanofabrication techniques such as focused ion beam and electron …

Effect Of Surface Roughness On The Efficiency Of Self-Healing Polymers, Ifeanyi Janarus Okoro

LSU Master's Theses

A shape memory polymer (SMP) is a smart material capable of maintaining two distinct shapes depending on its temperature. A SMP is soft at temperatures above its glass transition temperature but hard below it. When copolyester thermoplastic additives are dispersed in a SMP, it becomes a SMP-based particulate composite capable of self-healing at both the molecular level and the structural level. This makes it very desirable for industrial applications. Upon damage to the composite, the surfaces at the damage interface have to come into contact for efficient healing; the shape memory effect, coupled with a confined recovery (healing) process, ensures …

Development Of A Laboratory Scale Reactor Facility To Generate Hydrogen Rich Syngas Via Thermochemical Energy Conversion, Mandeep Sharma

LSU Master's Theses

The thesis provides data needed for development of a conical spouted bed (CSB) reactor for the purpose of producing hydrogen rich synthesis gas (syngas). The syngas has potential to utilize energy more efficiently, eliminate pollutant emissions and significantly cut emissions of greenhouse gases. The development of CSB reactor system involves three phases. The first phase investigates the hydrodynamic behavior of a small, laboratory scale, conical spouted bed (CSB) by considering the effect of specific system parameters (stagnated bed height, particle size and inlet diameter) on minimum spouting velocity (ums)o, stable operating pressure drop (∆Pms) and maximum pressure drop (∆PM). Experimental …

Mechanistic Analysis And Reduced Order Modeling Of Forced Film Cooling Flows, Guillaume Francois Bidan

LSU Doctoral Dissertations

Abstract Unforced and forced film cooling jets are investigated in view to develop a reduced order model of the velocity and temperature fields. First, a vertical jet in cross-flow, a configuration well documented at high blowing ratios, is investigated at low blowing ratios using experimental visualizations and large eddy simulations. The unforced study reveals that dominant structures at low blowing ratio can be significantly different from the ones formed at high blowing ratio and describes their evolution and transition as the blowing ratio is changed. The forced jet investigations extend the results of past numerical studies in terms of starting …

Micro & Nano Scale Mechanical Testing And Assembly With Applications To Metal Based Microsystems, Ke Chen

LSU Doctoral Dissertations

Metal-based high-aspect-ratio microscale structures (HARMS) are fundamental building blocks for functional metallic micro devices. This dissertation focuses on addressing several problems in fabrication and assembly of metal based microchannel devices. First, the materials’ responses to mechanical deformation at micro & nano scales, namely the mechanical “size effect”, have been explored by molding single crystal Al with long rectangular diamond punches and long wedge shaped indenters. It is noticed that the contact pressure of rectangular punches pressed into single crystal Al strongly depends on the punch width, while that of long wedge shaped indenters depends on the included wedge angle. We …

Topology And Shape Optimization Of Hydrodynamically–Lubricated Bearings For Enhanced Load-Carrying Capacity, Mohammad Fesanghary

LSU Doctoral Dissertations

Bearings are basic and essential components of nearly all machinery. They must be designed to work under different loads, speeds, and environments. Of all the performance parameters, load-carrying capacity (LCC) is often the most crucial design constraint. The objective of this research is to investigate different design methodologies that significantly improve the LCC of liquid-lubricated bearings. This goal can be achieved by either altering the surface texture or the bearing geometrical configuration. The methodology used here is based on mathematical topological/shape optimization algorithms. These methods can effectively improve the design performance while avoiding time-consuming trial-and-error design techniques. The first category …

Graph Rigidity-Based Formation Control Of Planar Multi-Agent Systems, Xiaoyu Cai

LSU Doctoral Dissertations

A multi-agent system is a network of interacting "agents" that collectively perform a complex task. This dissertation is concerned with the decentralized formation control of multi-agent systems moving in the plane. The formation problem is defined as designing control inputs for the agents so that they form and maintain a pre-defined, planar geometric shape. The focus is on three related problems with increasing level of complexity: formation acquisition, formation maneuvering, and target interception. Three different "dynamic" models, also with increasing level of complexity, are considered for the motion of the agents: the single-integrator model, the double-integrator model, and the full …

Modeling And Simulation Of Surface Profile Forming Process Of Microlenses And Their Application In Optical Interconnection Devices, Zhengyu Miao

LSU Doctoral Dissertations

Free space micro-optical systems require to integrate microlens array, micromirrors, optical waveguides, beam splitter, etc. on a single substrate. Out-of-plane microlens array fabricated by direct lithography provides pre-alignment during mask fabrication stage and has the advantage of mass manufacturing at low cost. However, this technology requires precise control of the surface profile of microlenses, which is a major technical challenge. The quality control of the surface profile of microlenses limits their applications. In this dissertation, the surface forming process of the out-of-plane microlenses in UV-lithography fabrication was modeled and simulated using a simplified cellular automata model. The microlens array was …

Multiscale Analysis Of Contact In Smooth And Rough Surfaces: Contact Characteristics And Tribo-Damage, Ali Beheshti

LSU Doctoral Dissertations

This dissertation is comprised of two major interrelated foci. The first focus is to investigate the effect of surface roughness on the behavior of dry contacting bodies through both deterministic and statistical approaches. In the current research, different statistical micro-contact models are employed together with the bulk deformation of the bounding solids to predict the characteristics of the dry rough line-contact and elliptical point-contact including the apparent pressure profile, contact dimensions and real area of contact. Further, based on the results of numerical simulations, useful relationships are provided for the contact characteristics. In addition, a robust approach for the deterministic …

Characterization And Verification Of A Closed Loop Wind Tunnel With A Linear Cascade And Upstream Wake Generator, Christopher Foreman

LSU Master's Theses

A closed loop wind tunnel designed to study film cooling was completed in May 2011 along with a removable wake generating device. The test section featured a three blade, four passage linear cascade utilizing the Air Force Office of Scientific Research L1A low pressure turbine blade. The wake generator is unique because its blades are flat plates with round leading and trailing edges instead of circular rods. In this report, the test section of the wind tunnel is characterized and validated through velocity and pressure measurements in the test section. Hot-wire surveys were used to characterize the velocity and turbulence …

Modeling The Structural-Thermal-Electrical Coupling In An Electrostatically Actuated Mems Switch And Its Impact On The Switch Stability, Hassen M. Ouakad, Mohammad I. Younis

Mechanical Engineering Faculty Scholarship

Modeling and analysis for the static behavior and collapse instabilities of a MEMS cantilever switch subjected to both electrical and thermal loadings are presented. The thermal loading forces can be as a result of a huge amount of switching contact of the microswitch. The model considers the microbeam as a continuous medium and the electric force as a nonlinear function of displacement and accounts for its fringing-field effect. The electric force is assumed to be distributed over specific lengths underneath the microbeam. A boundary-value solver is used to study the collapse instability, which brings the microbeam from its unstuck configuration …