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Thesis (Ph. D.)--University of Washington.

Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Bibliography: leaves 239-252.

MT 2018

A well-known feature of first-order phase transitions is that fixed boundary conditions can strongly influence finite-size corrections, modifying the leading corrections for an L3 lattice in 3d from order 1/L3 under periodic boundary conditions to 1/L. A rather similar effect, albeit of completely different origin, occurs when the system possesses an exponential low-temperature phase degeneracy of the form 23L which causes for periodic boundary conditions a leading correction of order 1/L2 in 3d. We discuss a 3d plaquette Hamiltonian (“gonihedric”) Ising model, which displays such a degeneracy and manifests the modified scaling behaviour. We also investigate an apparent discrepancy between the fixed and periodic boundary condition latent heats for the model when extrapolating to the thermodynamic limit.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 60-61). Also available via the Internet.

Thesis (M.S.)--Florida State University, 2003. / Advisor: Dr. Farrukh S. Alvi, Florida State University, FAMU-FSU College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (Aug. 27, 2004). Includes bibliographical references.

A numerical model has been developed for investigating boundary layer transition control for a three-dimensional flat plate boundary layer. Control of a periodically forced boundary layer in an incompressible fluid is studied using surface heating techniques. The spatially evolving boundary layer is simulated. The Navier-Stokes and energy equations are integrated using a fully implicit finite difference/spectral method. The Navier-Stokes equations are in vorticity-velocity form and are coupled with the energy equation through the viscosity dependence on temperature. Both passive and active methods of control by surface heating are investigated. In passive methods of control, wall heating is employed to alter the stability characteristics of the mean flow. Both uniform and nonuniform surface temperature distributions are studied. In the active control investigations, temperature perturbations are introduced locally along finite heater strips to directly attenuate the instability waves in the flow. A feedback control loop is employed in which a downstream sensor is used to monitor wall shear stress fluctuations. Passive control of small amplitude two-dimensional Tollmien-Schlichting waves and three-dimensional oblique waves are numerically simulated with both uniform and nonuniform passive heating applied. Strong reductions in both amplitude levels and amplification rates are achieved. Active control of small amplitude two-dimensional and three-dimensional disturbances is also numerically simulated. With proper phase control, in phase reinforcement and out of phase attenuation is demonstrated. A receptivity study is performed to study how localized temperature perturbations are generated into Tollmien-Schlichting waves. It is shown that narrow heater strips are more receptive in that they maximize the amplitude level of the disturbances in the flow. It is also found that the local temperature fluctuations cause mainly a strong normal gradient in spanwise vorticity. Control of the early stages of the nonlinear breakdown process is also investigated. Uniform passive control is applied to both the fundamental and sub-harmonic routes to turbulence. A strong reduction in amplitude levels and growth rates results. In particular, the three-dimensional growth rates are significantly reduced below the uncontrolled levels. Active control of the fundamental breakdown process is also numerically simulated. Control is achieved using either a two-dimensional or three-dimensional control input.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 70-74). Also available via the Internet.

Thesis (Ph. D.)--Stanford University, 1978. / "Printed in 2003 by digital xerographic process on acid-free paper"--P. after T.p. Includes abstract (p. iv). Includes bibliographical references (p. 213-217). Also issued in print.