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Articles 1 - 23 of 23
Full-Text Articles in Engineering
Material Length Scales In Gradient-Dependent Plasticity/Damage And Size Effects: Theory And Computation, Rashid Kamel Abu Al-Rub
Material Length Scales In Gradient-Dependent Plasticity/Damage And Size Effects: Theory And Computation, Rashid Kamel Abu Al-Rub
LSU Doctoral Dissertations
Structural materials display a strong size-dependence when deformed non-uniformly into the inelastic range: smaller is stronger. This effect has important implications for an increasing number of applications in structural failure, electronics, functional coatings, composites, micro-electro-mechanical systems (MEMS), nanostructured materials, micro/nanometer fabrication technologies, etc. The mechanical behavior of these applications cannot be characterized by classical (local) continuum theories because they incorporate no ‘material length scales’ and consequently predict no size effects. On the other hand, it is still not possible to perform quantum and atomistic simulations on realistic time and structures. It is therefore necessary to develop a scale-dependent continuum theory …
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 …
Development Of Dynamic Travel Demand Models For Hurricane Evacuation, Haoqiang Fu
Development Of Dynamic Travel Demand Models For Hurricane Evacuation, Haoqiang Fu
LSU Doctoral Dissertations
Little attention has been given to estimating dynamic travel demand in transportation planning in the past. However, when factors influencing travel are changing significantly over time – such as with an approaching hurricane - dynamic demand and the resulting variation in traffic flow on the network become important. In this study, dynamic travel demand models for hurricane evacuation were developed with two methodologies: survival analysis and sequential choice model. Using survival analysis, the time before evacuation from a pending hurricane is modeled with those that do not evacuate considered as censored observations. A Cox proportional hazards regression model with time-dependent …
Numerical Simulation And Field Verification Of Inclined Piezocone Penetration Test In Cohesive Soils, Lei Wei
Numerical Simulation And Field Verification Of Inclined Piezocone Penetration Test In Cohesive Soils, Lei Wei
LSU Doctoral Dissertations
A large strain finite element analysis is performed to analyze the effect of soil anisotropy on the inclined piezocone penetration test in normally consolidated cohesive soils. The piezocone penetration is numerically simulated using the commercial finite element code ABAQUS. The saturated clay is modeled as a two-phase material and the effective stress principle is used to describe its behavior. A frictional contact interface utilizing Mohr-Coulomb's theory was chosen to represent interactions between the surface of the cone and the soil. The Anisotropic Modified Cam Clay Model (AMCCM) by Dafalias (1987) was chosen and implemented into ABAQUS through user subroutine UMAT. …
Optimization Of A Skewed Logistic Distribution With Respect To The Kolmogorov-Smirnov Test, James Charles Finney
Optimization Of A Skewed Logistic Distribution With Respect To The Kolmogorov-Smirnov Test, James Charles Finney
LSU Doctoral Dissertations
The four-parameter kappa distribution (Hosking 1994) was analyzed with respect to the various possible shapes of the probability density function. The general form for the cumulative distribution function when both h and k are non-zero is: F(x) = { 1 - h [ 1 - k ( x - ξ ) / α ]1/k }1/h. The parameters h and k work together to define the function's shape, ξ affects location, and α is the scale parameter. A method of selecting parameters to minimize the Kolmogorov-Smirnov test statistic, D, was developed. The technique was first described for the …
Chemical Production Complex Optimization, Pollution Reduction And Sustainable Development, Aimin Xu
Chemical Production Complex Optimization, Pollution Reduction And Sustainable Development, Aimin Xu
LSU Doctoral Dissertations
The objective of this research is to propose, develop and demonstrate chemical production complex optimization to determine the optimal configuration of chemical plants in a superstructure of possible plants. The Chemical Complex Analysis System is a new methodology that has been developed to determine the best configuration of plants in a chemical production complex based on the AIChE Total Cost Assessment (TCA) for economic, energy, environmental and sustainable costs. All new, energy-efficient, and environmentally acceptable plants using greenhouse gases that can produce potentially commercial products designed with HYSYS were integrated into the chemical complex using the System. The optimum configuration …
Modeling Event-Based Coupled Hydrologic And Mass Transport In Small Urban Watersheds, Yuhong Sheng
Modeling Event-Based Coupled Hydrologic And Mass Transport In Small Urban Watersheds, Yuhong Sheng
LSU Doctoral Dissertations
To investigate the event-based coupled hydrologic and mass transport processes of particulate matter and their eventual fate in unit operations/processes, several methodologies were developed. Discrete rainfall-runoff events data were collected at two similar urban watersheds for model calibration and verification. A mathematically and physically-based criterion was proposed to differentiate rainfall-runoff events between either mass-limited or flow-limited. Statistical techniques of Logistic Regression and Discriminant Analysis were utilized to derive classification rules for event categories based on hydrologic data only. With watersheds assumed as either lumped systems or distributed systems, physically-based semi-empirical models were developed to simulate particulate mass delivery process during …
Numerical Methods For The Unsteady Incompressible Navier-Stokes Equations And Their Application To The Direct Numerical Simulation Of Turbulent Flows, Frank Herbert Muldoon
Numerical Methods For The Unsteady Incompressible Navier-Stokes 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 Navier-Stokes 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 one-third 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 and …
Ceria-Zirconia Oxide High Temperature Desulfurization Sorbent, Kwang Bok Yi
Ceria-Zirconia Oxide High Temperature Desulfurization Sorbent, Kwang Bok Yi
LSU Doctoral Dissertations
High temperature desulfurization of highly reducing coal-derived gases using ceria and ceria-zirconia sorbents is the primary object of this dissertation research. If H2S concentration is reduced to less than 1 ppmv the product gas may be used with fuel cells and downstream catalytic process. CeO2 is reduced to a non-stoichiometric oxide, which is superior to CeO2 in removing H2S. Moreover, ZrO2 addition to CeO2 to form a solid solution, Ce1-xZrxO2, increases the reducibility of CeO2. This should also result in improved desulfurization performance. Pure CeO2 and sorbents, both commercially available and prepared at LSU, were tested. XRD analysis indicated that …
Multifunctional Nanocomposite Co-Containing Diamondlike Carbon Thin Films, Fengli Wang
Multifunctional Nanocomposite Co-Containing Diamondlike Carbon Thin Films, Fengli Wang
LSU Doctoral Dissertations
Metal-containing, hydrogenated carbon films (Me-a-C:H) is a special class of nanocomposite films of particular interest since they can be multifunctional through the synergistic interaction of their individual components. Thus, nanocomposite thin films possess high potential in a wide field of engineering applications, especially in small scale devices. A series of multifunctional nanocomposite Co-a-C:H thin films have been synthesized by a hybrid chemical vapor deposition (CVD) and physical vapor deposition (PVD) process to uncover the relationship between synthesis, microstructure and properties. The effects of deposition parameters on the microstructural evolution and properties have been systematically studied. The results showed that the …
Numerical Modeling Of Strain Localization In Granular Materials Using Cosserat Theory Enhanced With Microfabric Properties, Mustafa Alsaleh
Numerical Modeling Of Strain Localization In Granular Materials Using Cosserat Theory Enhanced With Microfabric Properties, Mustafa Alsaleh
LSU Doctoral Dissertations
Finite element solution in the updated Lagrangian frame is used to investigate the strain localization phenomenon "shear bands" in granular materials. The micro-polar theory was used as the mathematical foundation for the continuum formulations. A laboratory testing results are used for verification and comparison with the numerical simulation. Silica sand and glass beads with different shape indices, size and surface roughness were tested under biaxial and triaxial loading conditions to investigate the physics of the problem. The shape non-uniformity and the irregular surface roughness of the grains were studied carefully to evaluate their effect on shear band characteristics. To this …
Small And Large Strain Monitoring Of Unsaturated Soil Behavior By Means Of Multiaxial Testing And Shear Wave Propagation, Oscar F. Porras Ortiz
Small And Large Strain Monitoring Of Unsaturated Soil Behavior By Means Of Multiaxial Testing And Shear Wave Propagation, Oscar F. Porras Ortiz
LSU Doctoral Dissertations
The deformation and strength behavior of dry and saturated soils is controlled by the effective stresses as defined by Terzaghi. However, Terzaghi’s definition of the effective stresses fails for unsaturated soils, as capillarity force influence is also important. The effects of capillarity forces in soil are evaluated by the concept of matrix suction. Several techniques are used to evaluate soil suction however their applications involve difficult calibrations and tedious methodology. Furthermore, suction is a microscopic property and it is influenced by interparticle soil attraction, which can change by sampling disturbance. This research program evaluates the effect of suction on stiffness …
Design And Operating Strategies For Bioreactors Treating Dynamically Varying Concentrations Of Gas-Phase Volatile Organic Compounds (Vocs), Congna Li
LSU Doctoral Dissertations
The dynamically varying concentrations of volatile organic compounds (VOCs) in most waste gas streams present a challenge in design and operation of biofilters treating such off-gases. Studies described in this dissertation were directed toward development and experimental testing of two design modifications/operating strategies that have the potential to improve biofilter performance during unsteady-state loadings. In the first design modification studied, activated carbon was incorporated into biofilter packing media and a novel periodic operating strategy, Sequencing Batch Biofilter (SBB) operation, was tested under “normal” and various “shock” loading conditions treating methyl ethyl ketone contaminated air. Results demonstrate how the operational flexibility …
Morphological Evolution And Instabilities Of Solid Thin Films And Wires, Wanxi Kan
Morphological Evolution And Instabilities Of Solid Thin Films And Wires, Wanxi Kan
LSU Doctoral Dissertations
This dissertation can be divided into four parts. In part I (Chapter 2), the diffusion controlled growth of multiple compound phases is studied with the nonlinear Kirkendall effect included. This part analyzes the growth of N compound phases. The method of finding intrinsic diffusion coefficients from only the positions of interfaces is found for two layers. In addition, the asymptotic analysis valid for small concentration gradients is applied to the “multi-foil” method of measuring intrinsic diffusion coefficients and yields an analytic solution for the displacement curve. A bounded solid film on a substrate can breakup from the edge into islands …
Electrodeposition Of Feconicu Quaternary System, Qiang Huang
Electrodeposition Of Feconicu Quaternary System, Qiang Huang
LSU Doctoral Dissertations
Electrodeposition is a cost-effective method to produce thin film materials, which have been used widely in the microelectronic industry, and is advantageous to fabricate metal deposits into recessed and curved areas. In this dissertation, FeCoNiCu quaternary alloy system was investigated, both experimentally and theoretically, for fabrication of multilayers, grating structures, and nanowires. Multilayer structures are composed of alternating ferromagnetic and nonmagnetic nanometric layers, and are of interest due to the giant magnetoresistance (GMR) property it possesses, a change in electric resistance in the presence of an external magnetic field. In addition, the compositional modulation, or the composition contrast, in multilayer …
Synthesis, Structure, And Tribological Behavior Of Nanocomposite Dlc Based Thin Films, Varshni Singh
Synthesis, Structure, And Tribological Behavior Of Nanocomposite Dlc Based Thin Films, Varshni Singh
LSU Doctoral Dissertations
Diamond-like carbon (DLC) films possess a combination of attractive properties and have been largely employed to modify the tribological behavior of materials. Nanocomposite, metal-containing DLC films are the new generation of these coatings providing tremendous potential to modify and tailor their properties expanding their applications in the field of nanotechnology. The present study investigates nanoscale effects on the tribological behavior of composite nanostructured DLC-based films and functional coatings. Three aspects were studied: (i) effect of Cr interlayer on a functionally gradient substrate; (ii) nanoparticulate Cr-containing DLC (Cr-DLC) films; and (iii) nanocomposite multilayered Cr/DLC coatings. Intensified plasma assisted nitriding produced a …
Dynamic Performance Of Bridges And Vehicles Under Strong Wind, Suren Chen
Dynamic Performance Of Bridges And Vehicles Under Strong Wind, Suren Chen
LSU Doctoral Dissertations
The record of span length for flexible bridges has been broken with the development of modern materials and construction techniques. With the increase of bridge span, the dynamic response of the bridge becomes more significant under external wind action and traffic loads. The present research targets specifically on dynamic performance of bridges as well as the transportation under strong wind. The dissertation studied the coupled vibration features of bridges under strong wind. The current research proposed the modal coupling assessment technique for bridges. A closed-form spectral solution and a practical methodology are provided to predict coupled multimode vibration without actually …
Replication Of Metal-Based High-Aspect Microscale Structures By High Temperature Micromolding, Dongmei Cao
Replication Of Metal-Based High-Aspect 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 three-dimensional 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 …
Modeling The Hydrologic And Particulate Loadings From Paved Urban Surfaces, Chad Michael Cristina
Modeling The Hydrologic And Particulate Loadings From Paved Urban Surfaces, Chad Michael Cristina
LSU Doctoral Dissertations
This dissertation details the results of recent investigations concerning non-colloidal particulate matter found in urban rainfall-runoff and urban snowmelt. Three forms of the power law model (PLM) were used to model particle number density. It was found that significant model error could be introduced into PLMs when the median diameter particle was used to estimate the number of particles per interval, but the SSE of continuous PLMs could be significantly reduced through the use of correction factors when the sieve interval was large (P<0.05). Additionally, a multiple PLM analysis may be more appropriate than a single PLM analysis when changes in particle population occur within a single gradation. PLMs were also used to model the relationship between cumulative granulometric mass and cumulative particulate-bound metal mass. The use of such calibrated PLMs provided considerable cost reduction when compared to conventional direct measurements of particulate-bound metal mass. A first flush analysis indicated that only events with average volumetric flow rates approaching 1 L/min/m of drainage width exhibit a rapid depletion of particulate matter consistent with the concentration-based definition of the first flush. An analysis of particle separation mechanisms indicated that 90% of these particles, by mass, could be removed from the discharge with detention times of 30 min and 120 min for snowmelt and rainfall-runoff, respectively, in a typical roadside drainage system. It was also found that the kinematic wave model could accurately model significant aspects of rainfall-runoff events in traffic-impacted watersheds provided that abstractions were incorporated into the modeling process. For this watershed the source of abstraction was attributable to vehicular traffic. For high-intensity events with more than 10 vehicles per runoff volume (VPV) the runoff coefficient varied between 0.6 and 0.9 while for low-intensity events with fewer than 10 VPV the coefficient ranged between 0.2 and 0.4.
Modeling The Effects Of Rainfall Intensity And Deep Chiseling On Infiltration And Runoff Within Drainmod For Alluvial Soils, Daniel Nyabiba Moriasi
Modeling The Effects Of Rainfall Intensity And Deep Chiseling On Infiltration And Runoff Within Drainmod For Alluvial Soils, Daniel Nyabiba Moriasi
LSU Doctoral Dissertations
Accurate hydrologic models are needed to aid engineers and researchers design, install and evaluate efficient and cost-effective agricultural water management systems to reduce risks associated with food production, and to reduce soil erosion and water pollution. One model used for the alluvial soils of Louisiana is DRAINMOD. This model does not accurately predict infiltration and runoff for the crusting-prone alluvial soils of Louisiana. The main goal of this study was to modify the current DRAINMOD model to incorporate the effects of rainfall intensity and deep chiseling to improve its estimation of infiltration and surface runoff. The second goal was to …
Processing, Microstructure And Mechanical Behavior Of Nanocomposite Multilayers, Zuqiang Qi
Processing, Microstructure And Mechanical Behavior Of Nanocomposite Multilayers, Zuqiang Qi
LSU Doctoral Dissertations
Nanoscale multilayer coatings have high potential for numerous engineering applications because they can exhibit enhanced properties due to nanoscale effects and combine different properties from individual components. At present, scale effects on the mechanical behavior of multilayers are not well understood. Three multilayer nanocomposite systems, namely Al/Al2O3, Ti/TiN, and Cr/a-C, have been synthesized by using a dual-gun e-beam physical vapor deposition, to investigate the effect of layer thickness, the nature of components and their microstructures on the mechanical behavior. The deposited Al and Ti nanolayers were found to have polycrystalline fcc and hcp structure, respectively, the Cr and TiN layers …
Design And Fabrication Of Electromagnetic Micro-Relays Using The Uv-Liga Technique, John Dalton Williams
Design And Fabrication Of Electromagnetic Micro-Relays Using The Uv-Liga Technique, John Dalton Williams
LSU Doctoral Dissertations
This dissertation reports a research effort to microfabricate an electromagnetic relay for power applications using a multilayer UV-LIGA process. A mechanically wrapped coil was used and very simple design for the magnetic circuit was adopted to increase the design flexibility and performances. The broad material selection and the capability of making high aspect ratio microstructures of the UV-LIGA make the technology best suited for fabricating microelectromechanical power relays. Fabrication of the device required significant advances in the optical lithography of SU-8 negative photoresist. Research proved that aspect-ratios up to 40:1 in isolated open field structures of thickness between 1 and …