Thesis (M. S.)--Florida State University, 2006. / Advisor: James J. O'Brien, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed June 12, 2006). Document formatted into pages; contains ix, 36 pages. Includes bibliographical references.

Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2006. / Narayanan Komerath, Committee Chair ; Lakshmi Sankar, Committee Member ; JVR Prasad, Committee Member ; Mark Costello, Committee Member ; A. Terrence Conlisk Jr., Committee Member.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 63-65).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 185-191).

No description available.

The breakdown of vertically propagating planetary waves in the stratosphere is investigated using an ultra-high horizontal resolution Contour Dynamics with Surgery model. In the model, planetary waves are forced at the tropopause and propagate upwards through the stratosphere and into an absorbing sponge (the first of its kind for such a model). In the context of wave breaking, two aspects of the system are questioned, namely, (1) what is the sensitivity to upper-boundary conditions? and (2) given perfect upper-boundary conditions what controls wave breaking? (1) In a Boussinesq environment. wave breaking is compared using: (a) a rigid upper-boundary condition (as in previous work) and (b) an absorbing sponge (preventing spurious reflections). In (a) both local (to the forcing) and remote breaking is evidenced for weak forcing while only local breaking is observed for sufficiently strong forcing. In (b) remote breaking is absent and local breaking, which occurs for sufficiently strong forcing, has quite a different character to that seen in (a). Compressibility effects are also investigated. (2) A quasi-linear theory is developed which predicts wave breaking if the zonal mean flow decelerates by more than one-half of its initial value (via positive group-velocity/zonal-mean-flow feedbacks). This so-called “one-half” rule for planetary wave breaking is confirmed through fully-nonlinear simulations. Numerical simulations detail the precise sequence of events leading up to and after wave breaking. / Graduate

Aerodynamically bluff elastic structures such as suspension bridges and industrial smokestacks have been observed to vibrate violently in the presence of a low speed wind. Although a number of theories such as Den Hartog's quasi-steady instability criterion and the vortex resonance theory have been proposed to explain the phenomenon, the problem is still not completely solved nor yet fully understood. The purpose of this research was to dynamically test a number of two-dimensional cylinders of simple cross-section and to observe whether or not the results correlated with either of the two theories mentioned above. Necessary aerodynamic coefficients were obtained by the graphical integration of measured surface pressure distributions. Tests were performed on models mounted elastically with six degrees of freedom. Generally only one of two modes of vibration was excited at a given airspeed. Dynamic response curves are presented for several lightly damped cylinders. For cylinders with rectangular cross-section of length/width (b/h/ greater than 0.75, vibration occurred at any airspeed above a certain minimum which depended on the structural damping (galloping). Cylinders with b/h less than 0.683 were found to vibrate over a limited range of airspeeds which always included the critical velocity for resonance with the periodic formation of vortices in the wakes. Using quasi-steady theory, it was found that the D-section and rectangles with b/h less than 0.683 have zero aerodynamic damping to large relative angles of attack, due to the symmetry of the wake pressures at angles of attack greater than zero. Because of this the D-section is subject to galloping only when given a substantial initial amplitude. Vortex resonance was observed for all the cylinders tested with two exceptions; the reversed D-section and the D-section with the flat face initially at an angle of attack greater than 40°, both of which appear to be completely stable. Measurements of the frequency of vortex formation for stationary cylinders gave Strouhal numbers which showed only slight variation over the speed range used in the tests, However, a strong variation with b/h was noted for the rectangles 1.0 < b/h < 3.0. During vibration of any kind, the frequency of vortex formation was controlled at the frequency of vibration which in all cases was a natural frequency of the system being tested. An energy balance based on quasi-steady theory and neglecting structural damping yields velocity-amplitude curves which give good agreement with the experimental data for the galloping D-section and the square section at various initial angles of attack. The test results indicate that the steady state aerodynamic coefficients provide a useful approximation to the dynamic values; they also indicate that any theory which will completely predict the behaviour of such systems must include the effects of both negative aerodynamic damping and vortex resonance. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

While endeavouring to produce macroscopic vortex rings in liquid helium by a drop method, a general study of the formation of vortex rings when a liquid drop falls into a stationary bath of the same liquid was made. Preliminary investigations were made using room temperature liquids with a wide range of surface tensions, densities and viscosities. A cryostat was designed to study vortex ring formation in liquid nitrogen, liquid helium I, and liquid helium II. A numerical method, involving vorticity and Stokes stream function as parameters, for the solution of non-steady, rotational, viscous flows is outlined. Experimental results confirm the reported existence of optimum dropping heights from which the drop develops into a superior vortex ring. These optimum heights are analysed, by a photographic study, in terms of the liquid drop oscillation. It is found that optimum vortex rings are formed, if the drop is spherical at the moment of contact with the bath, and is changing from an oblate spheroid to a prolate spheroid. Vortex rings were detected in liquid nitrogen but not in liquid helium. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A literature survey was undertaken to collect information on multiple pump-sump design, the problems involved and solutions offered by various authors. This led to a study of the vortex forming mechanisms and a detailed examination of their significance to the design of a particular multiple pump-sump. An 'in-line' sump layout was selected because it was considered that such an arrangement may give the smallest sump volume, which often proves the cheapest. Though this layout is known to give rise to severe vortex formations, a better understanding of the vortex forming mechanisms might permit the development of a satisfactorily operating 'in-line' sump. Hot film anemometry techniques were used to monitor the turbulence levels within the sump and provide an index of the condition of the flow entering the bellmouth intakes. Considerable practical difficulties were experienced in making the anemometer probe function reliably. Because of the inherent inaccuracy of any unidirectional sensor within a fluid, the normal turbulence intensity parameter [formula omitted] was replaced by measurements of the main stream velocity fluctuations (dU), which offered a better representation of the comparative state of the flows within the sump. It was found that the introduction of various flow guides about the bellmouth intakes to physically suppress eddy shedding from the adjacent upstream pumps, significantly improved the sump performance. The tapering of the sump by varying the angle between the channel walls to reduce the deceleration of the flow along the channel, also added to the flow stability. It was concluded that the present study indicated the feasibility of constructing a workable 'in-line' sump configuration, and that further investigations encorporatlng direct pump efficiency tests in conjunction with turbulence measurements would be worth while. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The classical theory of rectilinear vortex motion has been generalized to include vortices in thin fluids of varying depth on curved surfaces. The equations of motion are examined to lowest order in a perturbation expansion in which the depth of fluid is considered small in comparison with the principal radii of curvature of the surface. Existence of a generalized vortex streamfunction is proved and used to generate conservation laws. A number of simple vortex systems are described. In particular, criteria for the stability of rings of vortices on surfaces of revolution are found. In contradistinction to the result of von Karman, double rings (vortex streets) in both staggered and symmetric configurations may be stable. The effects of finite core size are examined. Departures from radial symmetry in core vorticity distributions are shown to introduce small wobbles in the vortex motion. The case of an elliptical core is treated in detail. Applications of the theory to atmospheric cyclones and superfluid vortices are discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate