Engineering Commons^™

Stability Analysis Of The Rotary Drill-String, Liangming Pan

Doctoral Dissertations

Oil and natural gas are major energy sources for modern society. A rotary drilling system is the best known technology to extract them from underground. The vibration and stability of drilling systems have been studied for decades to improve drilling efficiency and protect expensive down-hole components. It is well known that severe drill-string vibrations are caused by many different loads: axial loads such as the hook load and the self-weight of the drill-string, end torques applied by the surface motor and restrained at the bit, the inertial load caused by whirling, the fluid drag force, and the contact force between …

The Role Of Channel-Land Architecture, Diffusion Media Transport Properties, And Aging Effects On Water Transport And Storage In Polymer Electrolyte Fuel Cells, Jacob Michael Lamanna

Doctoral Dissertations

Thermally driven transport of water vapor in polymer electrolyte fuel cells, also known as the heat-pipe effect or phase-change-induced flow, can transport several times the generated amount of water given enough temperature differentials. Understanding this transport process is necessary to properly engineer the water balance in the fuel cell to ensure high performance and long operational life. Channel-land architecture, diffusion media heat and mass transport properties, and operational age can all have an influence on thermally driven flow. High resolution neutron imaging was used to determine the steady-state water accumulation in various cell configurations to understand the influence of these …

Kinesthetic Haptics Sensing And Discovery With Bilateral Teleoperation Systems, Tian Qiu

Doctoral Dissertations

In the mechanical engineering field of robotics, bilateral teleoperation is a classic but still increasing research topic. In bilateral teleoperation, a human operator moves the master manipulator, and a slave manipulator is controlled to follow the motion of the master in a remote, potentially hostile environment. This dissertation focuses on kinesthetic perception analysis in teleoperation systems. Design of the controllers of the systems is studied as the influential factor of this issue. The controllers that can provide different force tracking capability are compared using the same experimental protocol. A 6 DOF teleoperation system is configured as the system testbed. An …

Modeling, Analysis, And Control Of A Mobile Robot For In Vivo Fluoroscopy Of Human Joints During Natural Movements, Matthew A. Young

Doctoral Dissertations

In this dissertation, the modeling, analysis and control of a multi-degree of freedom (mdof) robotic fluoroscope was investigated. A prototype robotic fluoroscope exists, and consists of a 3 dof mobile platform with two 2 dof Cartesian manipulators mounted symmetrically on opposite sides of the platform. One Cartesian manipulator positions the x-ray generator and the other Cartesian manipulator positions the x-ray imaging device. The robotic fluoroscope is used to x-ray skeletal joints of interest of human subjects performing natural movement activities. In order to collect the data, the Cartesian manipulators must keep the x-ray generation and imaging devices accurately aligned while …

Strain-Based Design Methodology Of Large Diameter Grade X80 Linepipe, Mark D. Lower

Doctoral Dissertations

Continuous growth in energy demand is driving oil and natural gas production to areas that are often located far from major markets where the terrain is prone to earthquakes, landslides, and other types of ground motion. Transmission pipelines that cross this type of terrain can experience large longitudinal strains and plastic circumferential elongation as the pipeline experiences alignment changes resulting from differential ground movement. Such displacements can potentially impact pipeline safety by adversely affecting structural capacity and leak tight integrity of the linepipe steel.

Planning for new long-distance transmission pipelines usually involves consideration of higher strength linepipe steels because their …

Transport Resistance In Polymer Electrolyte Fuel Cells, Jon Patrick Owejan

Doctoral Dissertations

Fuel cells offer the potential for high efficiency energy conversion with only water and heat as significant products of the electrochemical reaction. For a cost-competitive product, fuel cell researchers are exploring the limits of the Pt catalyst loading in parallel with performance and durability trade-offs. A significant portion of the performance loss in low-cost PEMFCs is associated with the partial pressure of oxygen (for an air cathode) at the Pt surface. This dissertation explores the main components of oxygen transport resistance which are associated with diffusion through partially saturated porous media and the ionomer coating in the catalyst layer.

Under …

A Study Of Indentation Cracking In Brittle Materials Using Cohesive Zone Finite Elements, Kurt E. Johanns

Doctoral Dissertations

Cohesive zone finite element simulations of pyramidal indentation cracking in brittle materials have been carried out in order to: (1) critically examine indentation cracking models that relate fracture toughness to indentation data; (2) determine the underlying physical mechanisms of indentation crack growth from a continuum view and their relationship to material properties; (3) explore the influence of indenter geometry on crack extension; and (4) provide a platform from which future simulations can add more complex material behavior as well as guidance for experimental measurements of fracture toughness. Standard fracture toughness geometries in addition to simplified indentation geometries were simulated in …

Thermal Hydraulic Characteristics Of Fuel Defects In Plate Type Nuclear Research Reactors, Isaac Thomas Bodey

Doctoral Dissertations

Turbulent flow coupled with heat transfer is investigated for a High Flux Isotope Reactor (HFIR) fuel plate. The Reynolds Averaged Navier-Stokes Models are used for fluid dynamics and the transfer of heat from a thermal nuclear fuel plate using the Multi-physics code COMSOL. Simulation outcomes are compared with experimental data from the Advanced Neutron Source Reactor Thermal Hydraulic Test Loop. The computational results for the High Flux Isotope Reactor core system provide a more physically accurate simulation of this system by modeling the turbulent flow field in conjunction with the diffusion of thermal energy within the solid and fluid phases …