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Articles 121  134 of 134
FullText Articles in Mechanical Engineering
Intrinsic Stress And High Temperature Properties Of MetalContanining Hydrogenated Amorphous Carbon Coatings, Bo Shi
LSU Doctoral Dissertations
A detailed examination of the intrinsic stress development and mechanical properties of titaniumcontaining hydrogenated amorphous carbon (TiC:H) and WC:H coatings, deposited in an inductively coupled plasma (ICP) assisted hybrid chemical/physical vapor deposition (CVD/PVD) environment was carried out. Intrinsic stresses within those coatings were found to be compressive and dependent on compositions. The intrinsic compression within TiC:H was further shown to be significantly influenced by the energy of ionic species bombarding the substrate during growth. The results suggested that ion bombardment played a significant role in intrinsic stress generation within TiC:H, and was likely to ...
On The Stability Of Rotor Bearing Systems Based On Hopf Bifurcation Theory, Jianke Wang
On The Stability Of Rotor Bearing Systems Based On Hopf Bifurcation Theory, Jianke Wang
LSU Doctoral Dissertations
This research is aimed to establish instability criteria for a rotorbearing system which consists of a rotor supported by two fluidfilm journal bearings. The static and dynamic characteristics of rotorbearing systems with consideration of turbulent effects are evaluated by applying the Hopf bifurcation theory (HBT) to the equations of motion. A method is developed for predicting the stability envelope of rotorbearing systems using HBT. Results are compared with published literature obtained using a trialanderror method. A method based on HBT is presented for predicting the occurrence of a hysteresis phenomenon, which is observed in experimental results dealing with the instability ...
Effects Of Strong Surface Energy Anisotropy On Stationary And Migrating GrainBoundary Grooves, Donghong Min
Effects Of Strong Surface Energy Anisotropy On Stationary And Migrating GrainBoundary Grooves, Donghong Min
LSU Doctoral Dissertations
Grainboundary migration controls grain growth and is important in materials processing and synthesis. When a grain boundary ends at a free surface, a groove will develop at the tip to reduce the combined surface and grainboundary energies. This groove may hinder the grain boundary movement and its effect needs to be understood. Previous studies have solved the groove profile for stationary or migrating grain boundaries by assuming small groove slopes with isotropic surface free energy. This work extends the analysis to finite slopes with isotropic or anisotropic surface free energy.
We first study migrating grainboundary grooves with isotropic surface energy ...
Nonlinear Control And Its Application To Active TiltingPad Bearings, Zhijun Cai
Nonlinear Control And Its Application To Active TiltingPad Bearings, Zhijun Cai
LSU Doctoral Dissertations
The drawbacks of active magnetic bearings are arousing interest in the adaptation of mechanical bearings for active use. A promising mechanical bearing candidate for active operation is the tiltingpad bearing. In this research, we introduce an active tiltingpad bearing with linear actuators that translate each pad. The use of feedback in determining the actuator forces allows for the automatic, continuous adjustment of the pad position during the machine operation. In this work, we develop the dynamic model of the active bearing system such that the actuator forces are the control inputs. The hydrodynamic force is modeled as a spring/damperlike ...
Structural Integrity And Fatigue Crack Propagation Life Assessment Of Welded And WeldRepaired Structures, Mohammad Shah Alam
Structural Integrity And Fatigue Crack Propagation Life Assessment Of Welded And WeldRepaired Structures, Mohammad Shah Alam
LSU Doctoral Dissertations
Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is assessed and necessary precaution is taken appropriately. Structural integrity includes tasks in many areas, such as structural analysis, failure analysis, nondestructive testing, corrosion, fatigue and creep analysis, metallurgy and materials, fracture mechanics, fatigue life assessment, welding metallurgy, development of repairing ...
Fabrication Of High Aspect Ratio Vibrating Cylinder Microgyroscope Structures By Use Of The Liga Process, Yohannes Mamo Desta
Fabrication Of High Aspect Ratio Vibrating Cylinder Microgyroscope Structures By Use Of The Liga Process, Yohannes Mamo Desta
LSU Doctoral Dissertations
Inertial grade microgyroscopes are of great importance to improve and augment inertial navigation systems based on GPS for industrial, automotive, and military applications. The efforts by various research groups worldwide to develop inertial grade microgyroscopes have not been successful to date. In 1994, the Department of Mechanical Engineering at Louisiana State University and SatCon Technology Corporation (Boston, Massachusetts) proposed a series of shock tolerant micromachined vibrating cylinder rate gyroscopes with aspect ratios of up to 250:1 to meet the needs of inertial navigation systems based on existing conventional vibrating cylinder gyroscopes. Each microgyroscope consisted of a tall thin shell ...
Turbine Blade Tip Cooling And Heat Transfer, Hasan Nasir
Turbine Blade Tip Cooling And Heat Transfer, Hasan Nasir
LSU Doctoral Dissertations
Turbine blade tip leakage flow from blade pressure side to suction side over the tip surface increases the thermal loading to the blade tip, leading to a high local temperature and thus, is considered one of the primary sources of blade failure. Leakage flow can be reduced by using a recessed or squealer tip blade or by cooling the blade tip to incorporate film cooling. The performance of different recessed tip geometries were investigated and compared with plane tip performance. A transient liquid crystal technique was employed to measure detailed heat transfer coefficient distributions. Coolant injection from holes located on ...
Replication Of MetalBased HighAspect Microscale Structures By High Temperature Micromolding, Dongmei Cao
Replication Of MetalBased HighAspect Microscale Structures By High Temperature Micromolding, Dongmei Cao
LSU Doctoral Dissertations
In microsystem technology a large range of materials will be available only after the necessary microfabrication technologies have been developed or adapted. More than a decade ago, the existing microfabrication technologies were restricted to structuring and shaping techniques producing threedimensional microstructures out of silicon, mostly unfilled plastics or a few pure metals or binary alloys. However, the choice of materials for microcomponents is determined by the function and conditions of use of microsystems. Some microdevices can only work well when made of specific metal components. To meet this need, several microfabrication techniques have been developed, such as second electroforming of ...
Numerical Methods For The Unsteady Incompressible NavierStokes Equations And Their Application To The Direct Numerical Simulation Of Turbulent Flows, Frank Herbert Muldoon
Numerical Methods For The Unsteady Incompressible NavierStokes Equations And Their Application To The Direct Numerical Simulation Of Turbulent Flows, Frank Herbert Muldoon
LSU Doctoral Dissertations
Two new methods for the efficient parallel computation of the unsteady incompressible NavierStokes equations are presented. Such efficient methods are desired for large scale parallel computations of unsteady turbulent flows such as Direct Numerical Simulations (DNS). The performance of the new methods has a distinct advantage over the artificial compressibility method, in that the methods exhibit robust convergence for a variety of flow problems without extensive need for tuning computational parameters. These methods and others have been implemented in a computer program designed for massively parallel computer architectures, written by the author and used to obtain all results in this ...
The Spectral Conforming Model And Its Applications, Jaeho Shim
The Spectral Conforming Model And Its Applications, Jaeho Shim
LSU Doctoral Dissertations
It has been observed that finite element or finite difference model of order can approximate with fair accuracy less than onethird of the eigenvalues of the underlying continuous system corresponding to the low spectrum. The new discrete model, namely the spectral conforming model, is developed to predict the eigenvalues of continuous systems in both the low and high spectra. The spectral conforming models are developed using an inverse vibration method. The classical vibration problem is the direct method. In the direct approach, the characteristic behaviors of the system, i.e. frequency response, natural frequency, and steady state response are analyzed ...
Advanced Turbulence Modeling For Industrial Flows, Raymond Michael Jones
Advanced Turbulence Modeling For Industrial Flows, Raymond Michael Jones
LSU Doctoral Dissertations
This dissertation deals with the development of an improved twoequation turbulence model and its application to various flows. Six different conventional turbulence models were initially tested for predicting the flow inside of an unbaffled stirred tank reactor (STR), and the results are compared with experimental LDV data. Each of the models use low Reynolds number corrections. Results indicate that the radial velocity component in the impeller discharge region is overpredicted by each of the models. The tangential velocity component in the impeller discharge region is predicted well by the models, but is underpredicted near the shaft. The low Reynolds number ...
The Transcendental Eigenvalue Problem And Its Application In System Identification, Kumar Vikram Singh
The Transcendental Eigenvalue Problem And Its Application In System Identification, Kumar Vikram Singh
LSU Doctoral Dissertations
An accurate mathematical model is needed to solve direct and inverse problems related to engineering analysis and design. Inverse problems of identifying the physical parameters of a nonuniform continuous system based on the spectral data are still unsolved. Traditional methods, for the system identification purpose, describe the continuous structure by a certain discrete model. In dynamic analysis, finite element or finite difference approximation methods are frequently used and they lead to an algebraic eigenvalue problem. The characteristic equation associated with the algebraic eigenvalue problem is a polynomial. Whereas, the spectral characteristic of a continuous system is represented by certain transcendental ...
Manufacturing And Analysis Of A Liga Heat Exchanger For The Surface Of A Tube: A Cooling Simulation Of The Leading Edge Region Of A Turbine Blade, Christophe Marques
Manufacturing And Analysis Of A Liga Heat Exchanger For The Surface Of A Tube: A Cooling Simulation Of The Leading Edge Region Of A Turbine Blade, Christophe Marques
LSU Doctoral Dissertations
Fabricating nickel micro heat exchangers directly on planar or nonplanar metal surfaces has been demonstrated using the LIGA micromachining process. These heat exchangers can effectively control the temperature of surfaces in high heat flux applications. Of particular interest is the temperature control of gas turbine engine components. The locations in the gas turbine engine where improved, efficient cooling is required includes gas turbine blades, stator vanes, the turbine disk, and the combustor liner. In this dissertation, the primary application of interest is the use of such heat exchangers to cool airfoils such as turbine blades. In the first part of ...
Large Eddy Simulations Of Complex Turbulent Flows, Mayank Tyagi
Large Eddy Simulations Of Complex Turbulent Flows, Mayank Tyagi
LSU Doctoral Dissertations
In this dissertation a solution methodology for complex turbulent flows of industrial interests is developed using a combination of Large Eddy Simulation (LES) and Immersed Boundary Method (IBM) concepts. LES is an intermediate approach to turbulence simulation in which the onus of modeling of “universal” small scales is appropriately transferred to the resolution of “problemdependent” large scales or eddies. IBM combines the efficiency inherent in using a fixed Cartesian grid to compute the fluid motion, along with the ease of tracking the immersed boundary at a set of moving Lagrangian points. Numerical code developed for this dissertation solves unsteady, filtered ...