In this thesis, we study the behaviour of Lovasz and Schrijver's lift-and-project operators N and N_0 while being applied recursively to the fractional stable set polytope of a graph. We focus on two related conjectures proposed by Liptak and Tuncel: the N-N_0 Conjecture and Rank Conjecture. First, we look at the algebraic derivation of new valid inequalities by the operators N and N_0. We then present algebraic characterizations of these valid inequalities. Tightly based on our algebraic characterizations, we give an alternate proof of a result of Lovasz and Schrijver, establishing the equivalence of N and N_0 operators on the fractional stable set polytope. Since the above mentioned conjectures involve also the recursive applications of N and N_0 operators, we also study the valid inequalities obtained by these lift-and-project operators after two applications. We show that the N-N_0 Conjecture is false, while the Rank Conjecture is true for all graphs with no more than 8 nodes.

The problem of liquid loading is common for all gas producing wells and should be identified and solved for efficient gas production. Production engineers and operators need to choose the best solution possible, one that is cost effective and also efficient in doing the job. The plunger lift operation is a cost-effective solution to this liquid loading problem and also is efficient in increasing the gas production. However, the current understanding of plunger lift operation has used field experience and some previous models that have restrictive assumptions which might not be applicable for all plunger lift installations. This research proposes a new plunger lift model that overcomes some of the limiting assumptions of earlier models by using additional data available in the form of pressure and temperature from new technology like smart plunger. The model is based on fundamental principles of mass conservation and pressure balance, and uses the smart plunger data as input. The implementation of the model is carried out in user-friendly and easily accessible software like Excel VBA (Visual Basic Applications). The model predicts the plunger velocity, plunger position and annulus liquid level during an upward travel of the plunger in an onshore gas well in East Texas. The results of model implementation in VBA show the importance of fluid properties for the model, apart from indicating that the model is optimized for the given set of input data. The model developed in this research considers only pressure drop due to gravitational effects, and thus provides a scope for improvement in modeling the plunger lift dynamics by adding frictional and acceleration components. This research also provides recommendations for future work that can be carried out on plunger lift modeling using smart plungers.

Aluminum nitride (AlN) thin films were deposited on Z-cut LiNbO3 substrates using the reactive RF magnetron sputtering in this thesis. By means of the analyses of XRD, SEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power of 165W and substrate temperature of 400¢J. The piezoelectric bi-layers structure of SAW devices was then fabricated. The interdigital transducers (IDTs) were fabricated on bi-layers structure. The AlN thin film thickness of piezoelectric bi-layers structure was varied in order to discuss its effects on SAW devices. From the experimental results, it reveals that the center frequency of SAW filters increases with the increased AlN thin films thickness. It means that the SAW velocity increases as the AlN thin films thickness increases. The effects of bi-layers structure on SAW devices can be discussed in detail by measuring the parameters of SAW devices like insertion loss (IL), electromechanical coupling coefficient (K2) and the temperature coefficient of delay (TCD).

Flow assurance is crucial in the oil industry since it guarantees the success and economic production of hydrocarbon fluid, especially in offshore and deep water oil fields. In fact, the ultimate goal of flow assurance is to maintain flow in the wellbore and pipelines as long as possible. One of the most common challenges in flow assurance is the buildup of solids, such as asphaltene and scale particles. These Solid particles can deposit in the wellbore, flowline, and riser and affect the wellbore performance by reducing the cross section of the pipeline, which eventually results in pipeline blockage. Hence, neglecting the importance of flow assurance problems and failure in thorough understanding of the fluid behavior in the production systems may result in plugged pipeline, production loss, flowline replacement, and early abandonments of the well. As a result, continuous evaluations are needed at the development stage and during the life of reservoirs to predict the potential, the extent, and the severity of the problem to plan for inhibition and remediation jobs. In fact, it is more preferable to prevent flow assurance problems through the designing and operating procedures rather than remediating the problems, which has higher risks of success and higher loss of revenue due to frequent well shut down. As a part of this research, we enhanced the capabilities of our in-house compositional wellbore simulator (UTWELL) to model various production and flow assurance scenarios. Initially, we developed and implemented a robust gas lift model into UTWELL to model artificial lift technique for reservoirs with low pressure. The developed model is able to model both steady state and transient flow along with blackoil and Equation-of-State compositional models. The improved version was successfully validated against a commercial simulator. Then, we applied our dynamic model to track the behavior of asphaltene during gas lift processes and evaluated the risk of asphaltene deposition. Several deposition mechanisms were incorporated to study the transportation, entrainment, and deposition of solid particles in the wellbore. The simulation results illustrated the effect of light gas injection on asphaltene deposition and well performance. Finally, a step by step algorithm is presented for coupling a geochemical package, IPhreeqc, with UTWELL. The developed model is able to model homogenous and heterogeneous, non-isothermal, non-isobaric aqueous phase reactions assuming local equilibrium or kinetic conditions. This tool was then utilized to model scale deposition in the wellbore for various scenarios. In addition, the results showed that integrating IPhreeqc has promise in terms of CPU time compared to the traditional approach of reading and writing the input and output files. / text

No description available.

Research efforts in this dissertation address aerodynamics and flight performance of flapping wing aircraft (ornithopters). Flapping wing aerodynamics was studied for various wing sizes, flapping frequencies, airspeeds, and angles of attack. Tested wings possessed both camber and dihedral. Experimental results were analyzed in the framework of momentum theory. Aerodynamic coefficients and Reynolds number are defined using a reference velocity as a vector sum of a freestream velocity and a stroke-averaged wingtip velocity. No abrupt stall was observed in flapping wings for the angle of attack up to vertical. If was found that in the presence of a freestream lift of a flapping wing in vertical position is higher than the propulsive thrust. Camber and dihedral increased both lift and thrust. Lift-curve slope, and maximum lift coefficient increased with Reynolds number. Performance model of an ornithopter was developed. Parametric studies of steady level flight of ornithopters with, and without a tail were performed. A model was proposed to account for wing-sizing effects during hover. Three micro ornithopter designs were presented. Ornithopter flight testing and data-logging was performed using a telemetry acquisition system, as well as motion capture technology. The ability of ornithopter for a sustained flight and a presence of passive aerodynamic stability were shown. Flight data were compared with performance simulations. Close agreement in terms of airspeed and flapping frequency was observed.

The purpose of this research is to numerically simulate, analyze, and visualize turbulent flow around rotating aerodynamic shaped 3-dimentional geometries using a custom-made software suite. The computational fluid dynamic program used for this research is called Numerical Wind Tunnel, NWT, which was developed by Dr. J. Militzer and his students over the last 15 years. In order to meet various simulation and prediction requirements of this research, the NWT was modified and improved by implementing many new features; in addition, many bugs have been fixed. Key features added to the NWT include improved boundary layer handling for Detached Eddy Simulation method, new implementations of Surrounding Cell Method and rewritten Lift and Drag Coefficients calculation algorithms, and new approaches to Mesh Refinement and Adaptation Criteria. The improved software is tested extensively by simulating turbulent flows around a rotating National Advisory Committee for Aeronautics (NACA) 0009 airfoil, and test results are compared with both experimental data and previous simulation data. The research was successful mainly because of the much-improved accuracy in predicting static lift and drag coefficients. Another achievement of this research is that the software also successfully predicted various events during an airfoil dynamic stall condition, which is a result of both accurate flow prediction and a NWT feature called Automatic Anisotropic Grid Adaptation.

No description available.

Crane lift path planning is time-consuming, prone to errors, and requires the practitioners to have exceptional visualization abilities, in particular, as the construction site is congested and dynamically changing. This research presents a methodology based on robotics motion planning to numerically solve the crane path planning problem. The proposed methodology integrates a database in order to automatically conduct 2D path planning for a crane lift operation, and accounts for the rotation of the lifted object during its movements. The proposed methodology has been implemented into a computer module, which provides a user-friendly interface to aid the practitioners to perform a collision-free path planning, and check the feasibility of the path at different stages of the project. Three examples are described in order to demonstrate the effectiveness of the proposed methodology and illustrate the essential features of the developed module. / Construction Engineering and Management

Thesis (M.S.)--Ohio University, November, 2004. / Title from PDF t.p. Includes bibliographical references (leaf 70).