Mechanical Engineering Commons^™

Enhancement Of Single-Lap Joint Strength Under Tension Using Piezoelectric Actuation, Ryan Michael Meyer

LSU Master's Theses

Composite adhesively bonded joint structures have seen increased use over conventional riveted due to their ease of manufacturing and quality strength-to-weight ratios. However, adhesively bonded joints lack the rigidity and failure strength of riveted assemblies, due to high stress concentrations which develop in the adhesive layer, which makes them prone to undesirable deformation and failure. Piezoelectric materials feature the ability to produce mechanical strain when subjected to an applied voltage and vice-versa. Therefore, it is proposed to use piezoelectric actuators to transmit counterbalancing forces to increase the rigidity and strength of composite joints. Existing studies have been limited in that …

The Effect Of Anisotropic Surface Energy On The Stability Of Micro And Nano Wires, Ping Du

LSU Doctoral Dissertations

A liquid thread of radius R will break up into drops if the axial wavelength of the surface perturbation L > 2πR. If L < 2πR, the thread is stable and will remain intact. This is Rayleigh’s stability criterion based on a continuum model. We use molecular dynamics to simulate the evolution of Lennard-Jones liquid threads with equilibrium radius R = 2.3-6.6, where R has been non-dimensionalized by the distance at which the Lennard-Jones potential equals zero. We find that if R is fixed, the wavelength L is bounded by L_min and L_max. For L > L_max the thread always breaks up and stays as drops, and for L < L_min the thread remains intact. However, for L_min < L < L_max, the thread oscillates continuously among several shapes. The appearance of various shapes can be explained by the energy fluctuation of the system.

We also simulate the evolution of Lennard-Jones nanowires with equilibrium radius R = 1.57, 2.58, 3.59, and 4.60 by molecular dynamics. The wires …

Modeling And Simulation For Shape Memory Polymer Based Self-Healing Syntactic Foam, Wei Xu

LSU Doctoral Dissertations

Syntactic foams, renowned for their low density and high mechanical properties, are enjoying continuing growth in various civilian and military sectors. However, like laminated composites, foam cored structures are vulnerable to impact damages and suffering from inabilities in repairing macro-scale cracks. A self-healing mechanism for structural damage is genuinely desired. A recent development in self-healing structural damage is a two-step close then heal (CTH) scheme proposed by Li and Nettles [1] and elucidated by Li and Uppu [2], by mimicking the self-healing process of human skin. This concept has been further demonstrated in Nji and Li’s work [3] that a …

Macroinstability And Perturbation In Turbulent Stirred Tank Flows, Somnath Roy

LSU Doctoral Dissertations

Impeller stirred tank reactors (STRs) are commonly used in the chemical processing industries for a variety of mixing and blending technologies. In this research, a numerical study of flow and mixing inside turbulently agitated STRs are carried out. An immersed boundary method (IBM) is utilized to represent moving impeller geometries in the background of multi-block structured curvilinear fluid. The IBM This curvilinear-IBM methodology is further combined with the large eddy simulation (LES) technique to address the issue of modeling unsteady turbulent flows in the STR. Verification of the combined IBM-LES implementation strategy in curvilinear coordinates is done through comparisons with …

Near-Field Radiative Transfer: Thermal Radiation, Thermophotovoltaic Power Generation And Optical Characterization, Mathieu Francoeur

University of Kentucky Doctoral Dissertations

This dissertation focuses on near-field radiative transfer, which can be defined as the discipline concerned with energy transfer via electromagnetic waves at sub-wavelength distances. Three specific subjects related to this discipline are investigated, namely nearfield thermal radiation, nanoscale-gap thermophotovoltaic (nano-TPV) power generation and optical characterization. An algorithm for the solution of near-field thermal radiation problems in one-dimensional layered media is developed, and several tests are performed showing the accuracy, consistency and versatility of the procedure. The possibility of tuning near-field radiative heat transfer via thin films supporting surface phononpolaritons (SPhPs) in the infrared is afterwards investigated via the computation of …

Nonparametric Estimation Of Derivatives With Applications, Benjamin Hall

University of Kentucky Doctoral Dissertations

We review several nonparametric regression techniques and discuss their various strengths and weaknesses with an emphasis on derivative estimation and confidence band creation. We develop a generalized C(p) criterion for tuning parameter selection when interest lies in estimating one or more derivatives and the estimator is both linear in the observed responses and self-consistent. We propose a method for constructing simultaneous confidence bands for the mean response and one or more derivatives, where simultaneous now refers both to values of the covariate and to all derivatives under consideration. In addition we generalize the simultaneous confidence bands to account for heteroscedastic …

Elastohydrodynamic Analysis Of Spur Gears Using Load-Sharing Concept: Running-In And Steady-State, Saleh Akbarzadeh

LSU Doctoral Dissertations

Gears are widely used in industry and hence their performance is of vital importance. Under the typical operating conditions of gears, the lubricant layer formed between the teeth of the pinion and the gear cannot completely separate the surfaces and contact of asperities of the pinion and gear occurs. This case is usually referred to as mixed lubrication problem. In this research the load-sharing concept has been employed to predict the performance of the pinion-gear system. The load-sharing concept is an efficient method to solve the mixed lubrication problem and is capable to predict the thickness of the lubricant film, …

Experimental And Analytical Study Of The Surface Texturing Enhanced Lubrication Elements, Yifan Qiu

LSU Doctoral Dissertations

Surface texturing is a method that modifies the frictional surface of a nominally flat tribocomponent by shallow patterns. It is found that with added patterns to the surface of a mechanical face seal or thrust bearing, their tribological performance improves, i.e. both friction and wear rate decrease. The current research concentrates on the analysis of hydrodynamic effect responsible for the performance enhancement of the spiral groove patterns and dimples on mechanical seal-like structures and the experimental evaluation of the tribological behavior of these structures. Surface textures considered are: dimple texture and spiral groove pattern. In the research on the dimple …

Analysis Of Wake Vortices Of A Medium Range Twin-Propeller Military Cargo Aircraft Using Statistically Designed Experiments, Burhan Sahin

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental study was initiated to analyze the trajectories of the streamwise vortices behind the wing tip and flap of a medium range and propeller driven twin-engine military cargo aircraft. The model used for the experimental study was a generic, high wing and half model of a propeller driven aircraft and mounted within Old Dominion University's Low Speed Wind Tunnel where the wind tunnel flow speed was set to constant value of 9 m/sec. The main purpose of the study was to reach regression models for the motion and vorticity strength of both vortices under varying factors such as angle …

Study Of Microstructure Effect On The Thermal Properties Of Yttria-Stabilized-Zirconia Thermal Barrier Coatings Made By Atmospheric Plasma Spray And Pressing Machine, Monica Bohorquez De Silva

LSU Doctoral Dissertations

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve a higher working temperature and thus lead to better efficiency. Yttria-Stabilized-Zirconia (YSZ), a material with low thermal conductivity, is commonly used as the top coat layer to provide the thermal barrier effect. In this dissertation the thermo-physical properties of a variety of TBCs samples made out of different fabrication techniques were investigated and compared. The first set of samples was fabricated using a pressing machine device to fabricate 0.5 inch diameter disk shaped YSZ-Al2O3 samples. The YSZ-Al2O3 powder mixture was made of 0, 1, 2, 3, 4 and …

Model-Based Nonlinear Control Of Active Tilting-Pad Bearings, An Wu

LSU Doctoral Dissertations

A promising mechanical bearing candidate for active operation is the tilting-pad bearing. The proposed active tilting-pad bearing has linear actuators that radially translate each pad. The use of feedback control in determining the actuator forces allows for the automatic, continuous adjustment of the pad position during the operation of the rotating machine. In the first part of the dissertation, we develop a nonlinear dynamic model of the active bearing system. The hydrodynamic force produced by the fluid film is modeled as a nonlinear, squeeze-film damper plus repellent spring. A model-based nonlinear controller is then designed to exponentially regulate the rotor …