Mechanical Engineering Commons^™

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 …

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 …

Measurement Of Continuum Breakdown Using A Disc Spin-Down Experiment In Low Pressure Air, Tathagata Acharya

LSU Doctoral Dissertations

As flow becomes rarefied, a quantity called as the tangential momentum accommodation coefficient (TMAC) becomes important because it is a measure of the momentum transport from a gas molecule to a surface. Very few experimental measurements of continuum breakdown in boundary layer flows exist. All experimental measurements of the TMAC in macro-scale boundary layer flows have been done in the continuum slip and the transition flow regimes. Moreover the experimental apparatus used by previous researchers cannot accommodate for materials that are planar by nature such as those used in the field of aerospace and microfabrication. The objectives of this research …

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 …

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 …

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 …

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 …

Numerical Evaluation And Analysis Of The Adhesion Phenomena In Thermal Barrier Coating Systems Through Bio-Mimicking Plasma Process, Naser Imran Hossain

LSU Master's Theses

Thermal Barrier Coatings or TBCs when abbreviated are an imperative part of the thermal protection system of expensive equipment and machinery in the automobile and aeronautics industry. They provide protection to expensive alloy materials upto a temperature of 2700° C without expensive metallurgical additions. Unfortunately, the problem of coating adhesion has plagued the TBC field for years, leading to catastrophic failures in critical TBC systems. Efforts to chemically improve bond strength has not been entirely successful, so the only other efficient way to do this would be some kind of mechanical interlocking that occurs at micro/nano scales. This research work …

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 …

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 …

Comparison Of In Vivo Human Knee Joint Kinematics Using Axodes, Jacob Hipps

LSU Master's Theses

The human knee is of particular interest because of its importance in mobility. Pain and stability can be directly related to the motion, or kinematics, of the knee. Many studies have been conducted to quantify human knee kinematics, both in vitro and in vivo. One of the inherent issues with in vivo, skin mounted measurement systems is that they do not account for soft tissue artifact. Compensation for soft tissue artifact has been a difficult challenge for skin mounted tracking systems and has not yet been achieved. Therefore, bone mounted skeletal pins were chosen as the method of gathering kinematic …

Electric Field Influence On The Combustion Of Fuel Droplets, Solomon Benghan

LSU Master's Theses

Improving the combustion efficiency of fuels in combustion devices has become imperative in the face of the diminishing rate of the discovery of new energy sources and an ever increasing demand for energy. While there are other ways of improving combustion efficiency, this study investigated the effect of electric field on the combustion of fuel droplets. In order to model the physics of the problem, a mass transfer evaporation model, heat transfer evaporation model and a simple burning droplet model were considered and their result compared to existing result from literature. A burning rate constant of 1.380mm2/s, 14.910mm2/s and 0.612mm2/s …

Dynamic Characterization Of Vocal Fold Virbrations, Zhenyi Wei

LSU Doctoral Dissertations

An emerging trend among voice specialists is the use of quantitative protocols for the diagnosis and treatment of voice disorders. Vocal fold vibrations are directly related to voice quality. This research is devoted to providing an objective means of characterizing these vibrations. Our goal is to develop a dynamic model of vocal fold vibration, and map the parameter space of the model to a class of voice disorders; thus, furthering the assessment and diagnosis of voice disorder in clinical settings.

To this end, this dissertation introduces a new seven-mass biomechanical model for the vibration of vocal folds. The model is …

Advanced Ceramics And Composites Based On Rice Hulls, Peigen Zhang

LSU Doctoral Dissertations

As a by-product of the agricultural industry, rice hulls are available at large volume across the world. The disposal of the rice hulls itself is a big problem for the rice millers where the rice paddies are peeled off and rice hulls are produced. There have been many disposal methods developed, but the true value of the rice hulls would be more appreciated when they are employed to produce high value-added advanced ceramics. In this dissertation, advanced ceramics, such as AlN nanowires, SiC whiskers, mullite and SiC/Al2O3 nano-sized composites, were developed and studied based on the rice hulls. The SiC …

Novel Surface Modifications And New Nanostructured Titania Synthesis For High-Performance Lithium-Ion Batteries And Solar Cells, Dongsheng Guan

LSU Doctoral Dissertations

With the rapid development of electronic devices, electrical vehicles and space aerocrafts, rechargeable lithium-ion batteries (LIBs) have attract numerous interests due to high energy and power density, long lifespan and low self discharge. Spinel LiMn2O4 is a promising cathode material for novel LIBs thanks to high working potential, easy synthesis and low cost, but its severe capacity drop mostly due to inevitable reactions with electrolytes is a drawback. In the dissertation, ultrathin and highly-conformal Al2O3 coatings are grown on the surface of micro-sized and nanosized LiMn2O4 with atomic layer deposition. Thickness of Al2O3 ALD coatings can be precisely controlled by …

Low-Order Modeling Of Micro-Flier Impact With Thin Stationary Energetic Targets, Mark B. Fry

LSU Master's Theses

The impact of high-speed (500-1500 m/s), laser driven micro-fliers with thin energetic targets (10-100 &# 956;m) is being examined to characterize impact-induced heating and combustion of these materials. Aluminum fliers are propelled by a laser into a thin metallic target plate having a layer of energetic material deposited on its backside. Mass spectrometry is performed in vacuo on the energetic side to interrogate the shock-induced chemistry of the energetic material. It is important to ignite and possibly detonate the energetic material without perforation of the target plate avoiding contamination of the vacuum chamber. To guide development of these experiments, a …

Combinatorial Multi-Level Mold Inserts Using Micro Machining And X-Ray Lithography, Oblesh Jinka

LSU Master's Theses

The present technology advancement in biomedical, micro-electro-mechanical systems (MEMS) engineering, bio-MEMS, healthcare, etc. is driving the need to fabricate devices with multi-level, high aspect ratio and complex microstructures, which in turn requires high quality mold inserts with all these features. The present thesis is concentrated in fabricating a multi-level mold insert with complex quasi 3 dimensional micro structures with dimensions down to 10µm and aspect ratios greater than 30 using a process combination of micro milling with X-ray lithography. Therefore, in this study the main focus was to fabricate a high quality mold insert template, which can be electroplated to …

The Effect Of Elevated Water Content On Ethanol Combustion, Baine Bernard Breaux

LSU Master's Theses

Ethanol is currently being considered as a potential alternative to traditional fuels. However, the fuel offers a low return in terms of energy output per dollar invested when compared to fossil fuels. More than 1/3 of the cost associated with bio-ethanol production is devoted to distillation and water removal. This study seeks to validate the use of hydrous ethanol as a practical fuel to be used in lieu of fossil fuels or anhydrous ethanol. Success would reduce the production cost associated with ethanol fuel. Hydrous ethanol was burned in a swirl-stabilized combustor, air is introduced at a constant flow rate …

Flow Distribution And Heat Transfer Coefficients Inside Gas Holes Discharging, Amirhossein Eshtiaghi

LSU Master's Theses

Fluid flow and heat transfer coefficient associated with flow inside short holes (L/D=1) discharging orthogonally into a crossflow was investigated experimentally and numerically for (Re) ̅ ranging from 0.5×105 to 2×105, and blowing ratio ranging from 1.3 to 3.2. The basic configuration studied consists of a feed tube with five orthogonally located gas holes. Four different hole configurations were studied. The transient heat transfer study employs an IR-camera to determine the local heat transfer coefficient inside each hole. Velocity measurements and numerical flow simulation were used to better understand the measured heat transfer distribution inside the hole. The Nusselt number …

Characterizing Impact Induced Hot-Spot Morphology In Granular Solid Explosive, John Gilbert

LSU Master's Theses

Deformation induced ignition of heterogeneous solid explosives is believed to originate at hot-spots within the material which are local regions of elevated temperature resulting from dissipative mechanisms such as plastic deformation and inter-particle friction. Inert meso-scale modeling of these materials can principally account for hot-spot formation enabling the characterization of hot-spot size and temperature distributions which are important for ignition but are di_x000E_cult to experimentally resolve. The focus of this study is to characterize hot-spot morphology, as well as the distribution of hot-spots, behind quasi-steady compaction waves computed from predicted temperature fields resulting from numerical simulations of rigid planar piston …

Towards The Development Of Biotin Carboxylase Driven Robotic Nanoswimmers, Rachel Yates

LSU Master's Theses

The objective of this research is to take the first step towards demonstrating the use of the enzyme biotin carboxylase (BC) as a biomolecular motor. BC is a homodimeric protein involved in fatty biosynthesis in all organisms. The conjecture is that BC can convert chemical energy into useful mechanical work via its conformation change, which acts as a fin or flexible oar producing nonreciprocal motion. To this end, we fabricate a proof-of-concept biomolecular machine driven by BC molecules, viz., a robotic nanoswimmer. This machine consists of a Janus-type nanosize silica particle, where one hemisphere is coated with an intermediate layer …

Programming And Healing Temperature Effects On The Efficiency Of Confined Self-Healing Polymers, Yves Quentin Yougoubare

LSU Master's Theses

Shape memory polymers are smart materials capable of fixing a temporary shape and returning to their initial shape in response to an external stimulus. Since the discovery and acknowledgment of their importance in 1960s, shape memory polymers have been the subject of tremendous and continuous attention. In a previous study conducted on a biomimetic shape memory polymer (SMP), the ability of a self-healing composite to heal, and to repair and restore structural-length scale damage using a close-then-heal (CTH) self-healing mechanism was examined and validated. The present study is purposed with investigation of the effects on healing efficiencies of the variation …

Optimal Actuation In Active Vibration Control Using Pole-Placement, Carla Ann Guzzardo

LSU Doctoral Dissertations

The purpose of this study was to find and demonstrate a method of optimal actuation in a mechanical system to control its vibration response. The overall aim is to develop an active vibration control method with a minimum control effort, allowing the smallest actuators and lowest control input. Mechanical systems were approximated by discrete masses connected with springs and dampers. Both numerical and analytical methods were used to determine the optimum force selection vector, or input vector, to accomplish the pole placement, finding the optimal location of actuators and their relative gain so that the control effort is minimized. The …

Turbine Blade Internal Cooling: Trailing Edge, Coolant-Passage Entry, Bend Effect And Improvement In Thermal Performance, Krishnendu Saha

LSU Doctoral Dissertations

Efficient cooling of gas turbine blade is imperative for safe operation of the gas turbine engine at high temperatures. In the present work, two converging lattice structures suitable for trailing edge applications are tested and their performance is compared with a conventional pin-fin configuration. Another constant cross section lattice structure is tested to see the cooling efficiency of lattice channels with different number of sub-channels. Converging lattice structures show higher heat transfer enhancement and comparable or higher thermal performance than traditional pin-fin cooling used in gas turbine trailing edge. The highest pressure drop incurred in a multi-pass channel is at …

Energetic Nanoparticles As Fuel Additives For Enhanced Performance In Propulsion Systems, Srinibas Karmakar

LSU Doctoral Dissertations

Biofuels are currently being explored as a carbon-neutral fuel alternative to petroleum-based fuels. However, biofuels such as ethanol has lower energy density (~27MJ/kg) relative to petroleum fuels (~ 45 MJ/kg). Adding high-energy density particles (such as boron with heating value of ~ 58.5 MJ/kg) to biofuels can generate fuel slurry with higher energy density than the base fuel, and represents a potential strategy toward making biofuels more viable. However, the combustion of boron is inhibited (specifically, the ignition is delayed) by the initial presence of an oxide layer, and its high evaporation and boiling temperatures. The present study investigates the …

Stability Problems In Constrained Pendulum Systems And Time-Delayed Systems, Prashanth Ramachandran

LSU Doctoral Dissertations

In this dissertation, we study the boundary of stability of a class of linear mechanical systems as a function of a parameter. We consider two different systems under this class: a constrained double pendulum connected by a rigid rod and a state-feedback-controlled mechanical system with time delay. In the first system, the destabilizing parameter is the distance between the supports of the two pendulums. In the second system, the destabilizing parameter is the time delay. In the constrained double pendulum system, linear perturbation analysis is used to determine the natural frequency of the system. Our analysis reveals a zone of …

Numerical And Experimental Evaluation Of Preheated Premixed Flames At Lean And Rich Conditions, Joseph Edward Gibson

LSU Master's Theses

Preheating a combustible mixture enhances the laminar burning flux characteristic m_ad with high reaction firing rates. As a result, the flammable zone as defined by inlet conditions of equivalence ratio and temperature is expanded beyond that available at standard ambient conditions; however, fundamental questions in these combustion regimes have not been addressed. In this thesis, preheated lean and rich combustion of methane/air mixtures is studied numerically and experimentally to catalog and confirm expected trends in these regimes. Numerical simulations were completed using both GRI-Mech 3.0 and San Diego mechanisms in the combustion code Cantera. An adiabatic simulation data set …

Modeling Of Dynamics Of Gyroscopic Systems, Siddharth Sharma

LSU Master's Theses

The amplitude of vibrations of a rotating system operating near or at its critical speed grows without bound. This poses a serious problem for the rotating machinery industry from the perspective of design, maintenance, vibration troubleshooting and stability of the rotating equipments.

In this thesis, we wish to develop an exact method of analysis for the system of a mass-less symmetrical shaft rotating in symmetrical bearings (SSSB) with finite displacement at bearing end. The method so developed is expected to be extended to the SSSB model of a shaft having mass. The stability analysis is performed for both the systems. …

Bucky Gel Actuator For Morphing Applications, Ali Kadkhoda Ghamsari

LSU Doctoral Dissertations

Since the demonstration of Bucky Gel Actuator (BGA) in 2005, a great deal of effort has been exerted to develop novel applications for electro-active morphing materials. Three-layered bimorph nanocomposite has become an excellent candidate for morphing applications since it can be easily fabricated, operated in air, and driven with few volts. There has been limited published study on the mechanical properties of BGA. In this study, the effect of three parameters: layer thickness, carbon nanotube type, and weight fraction of components, on the mechanical properties was investigated. Samples were characterized via nano-indentation and DMA. It was found that BGA composed …