Thesis (MScIng)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (M.C.E.)--University of Delaware, 2009. / Principal faculty advisors: Jamie H. MacMahan and James T. Kirby, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Although turbulence near the ocean surface is of great significance to the air-sea exchange of heat, gas and momentum it is a poorly understood phenomenon especially at high wind speeds when vertical transfer processes tend to be greatest. This work evaluates ocean surface turbulence at high sea states by exploiting heat as a naturally occurring passive tracer. To this end, a freely drifting instrument with a mechanically driven temperature profiler, fixed depth thermistors and conductivity cells was used to monitor the fine scale temperature structure and breaking wave activity. These open ocean measurements form the basis for a comprehensive account of the near surface turbulence field. Temperature profiles reveal a rich fine structure which, when combined with independent air-sea heat flux measurements reveal the presence of a surface layer of wave enhanced turbulence, modulated by subsurface advection associated with Langmuir circulation. The concept of wave enhanced turbulence, previously based on observations in fetch limited environments, is here extended to open ocean storm conditions. Generation of turbulence depends on the scale and frequency of breaking events. Our observations, which span a wide range of conditions from a coastal strait to the open ocean, show that wind speed or wave age are inadequate predictors of the occurrence frequency of wave breaking, motivating a scaling based on energy input. The decay of turbulence following wave breaking proceeds more rapidly than for isotropic turbulence, permitting generation of a thermal boundary layer a few centimetres thick, which accounts for brief temperature fluctuations observed beneath breaking waves. Advection due to Langmuir circulation also leaves its signature on the near surface temperature field. Both advection and enhanced diffusion are reconciled in a two-dimensional model of the upper ocean boundary layer, providing a framework for studying Langmuir circulation and upper ocean turbulence in terms of the measured temperature structure. The depth integrated dissipation derived from a model analysis of the data closely matches the energy input into the wave field, identifying breaking waves as the major source of turbulent kinetic energy. / Graduate

In two experimental operations in deep water off the west coast of British Columbia, temperature and velocity microstructure have been recorded with a spatial resolution of 2 millimeters or better, from the thermocline down to a depth of 330 meters. Some measurements have been taken along horizontal paths at discrete depths, and, by superimposing a cycling vertical velocity on the constant forward motion, others have been taken along "saw—tooth" paths, revealing some new features of the fine structure of the ocean and the occurrence of turbulence below the thermocline. On one occasion sea-water conductivity was also measured, enabling the computation of density and examination of the occurrence and characteristics of the microstructure in relation to the density structure. Power spectra of velocity fluctuations have been computed and energy dissipation rates obtained. Estimates are made of mean energy dissipation as a function of depth and total dissipation throughout the ocean volume. The velocity spectra are compared with existing ideas of Kolmogoroff's universal spectral function for isotropic turbulence and discrepancies at high wavenumbers are attributed, at least in part, to the effect of buoyancy forces resulting from small scale density fluctuations. A new empirical version of the universal function is derived from what is considered to be the best ocean turbulence data available. Vertical transport of heat is calculated for a number of samples, from microscale measurements of temperature gradient and mean vertical gradient. A mean eddy coefficient of thermal diffusivity is estimated for the region. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Supervisor: Professor Robert W. Stewart The process by which the wind makes sea waves grow is not well-understood, partly because of the lack of adequate observational information on the normal pressures which transfer energy to the waves. The principal object of this experiment has been to provide some of the missing data. A system for making simultaneous measurements of normal pressure and wave height was developed and tested in the laboratory and in the field. The system consisted of a disc-shaped buoy 23 cm in diameter (in which was embedded the pressure sensor) which rode up and down on a vertical rod, which was the wave sensor. Careful attention was paid to rejecting so-called "dynamic" pressures associated with the distortion of the air flow by the buoy. The results from the experiment are presented as power and cross-spectra of the pressure and wave signals. Spectra of Energy (E) and Momentum (τω) fluxes to the waves, and of ζ, the fractional energy increase of the waves per radian, are also presented. Wave power spectra are found to be normal for the site; the pressure power spectra consist of a "basic" spectrum similar to that observed over land, on which is superimposed a wave-induced "hump". The phase angle between the waves and the pressure at the frequency of the peak of the wave spectrum is found to be shifted from -180° (pressures high over wave troughs) by amounts which exceed the theoretical predictions of Miles (1957) by an average of 20 ± 5° over a wide range of conditions. The Ė and τω spectra are found to be sharply peaked at or above the frequency of the peak of the wave spectrum. The integrated energy fluxes Ē show large scatter, indicating that the wave generation process varies considerably in time (and space). The integrated momentum fluxes τω to the waves show no significant difference from total fluxes from air to water computed assuming a constant drag coefficient of 1.2 x 10⁻³; it appears that about 80% of the total drag of the water on the wind is caused by the wave generation process. The ζ spectra exceed the predictions of Miles' (1957) theory by factors of 5 to 8, indicating that his "inviscid laminar" model is not adequate to explain observed rates of wave growth. The present results fall close to an empirical curve suggested by Snyder and Cox (1966) except at high frequencies, where they are considerably lower. A dimensionless plot of ζ versus the ratio of wind speed to wave speed is presented; the observed data is fitted by the simple relation [formula omitted], where [formula omitted]is the ratio of the densities of air and water, U₂ is the mean wind speed at a height of two meters, and c is the phase velocity of the waves. This formula is only considered applicable for U₅/c < 6, where U₅ is the mean wind speed at 5 meters height. Also presented are the results of a dry-land comparison of the buoy pressure sensor with two other pressure sensors; besides indicating that the buoy sensor was adequate, this comparison produced some interesting preliminary information on the vertical and horizontal structure of the turbulent pressure field in the atmospheric boundary layer. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Observed properties of the internal wave groups which occur in the southern Strait of Georgia are summarized, with particular emphasis on those properties which must be explained by any theory of generation. Current measurements within Boundary Pass are described. These measurements suggest a generation mechanism in the form of impulsive disturbances to the stratified water mass within the Strait, caused by the abrupt changes in current speed which are observed to characterize the tidal flow close to both turns of the tide. Such a mechanism is shown to explain the most important observed properties: origin in space near the mouths of the passes between the Gulf Islands, origin in time near both turns of the tide, uni-directional propagation into the Strait, and origin of a varying number of groups on one turn of the tide. The form of wave groups which result from the initial-value problem for a stratified fluid is examined. A linear model is shown to result in wave groups which are of the same general form as the groups observed in the Strait, but much less compact, indicating the necessity of some effect to counteract dispersion. Since observed waves are of distinctly finite amplitude, nonlinear effects were included and time-dependent theory developed for "long-short" waves in a thin-layer system, characteristic of the southern Strait. For a restricted class of initial conditions, solutions are obtained by a comparison technique, using known solutions of the Korteweg-deVries equation. This class of solutions suggests that the general initial-value problem results, for large x and t, in a number of "solitons", individual solitary waves of the thin-layer system. Surface effects associated with the internal waves in the Strait are described, and the reflectivity changes examined in some detail. The usual explanation of the effect of shallow internal waves on the surface wave field is in terms of wave damping by a surface organic film which is periodically expanded and contracted by internal wave-induced motions. It is shown that, under certain conditions, the effect may equally well, be-due to periodic changes in-surface wave amplitude and vector wave number caused-by radiation stress effects induced by the presence of internal waves. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The effects of wave directionality on the loads and motions of long structures is investigated in this thesis. A numerical method based on Green's theorem is developed to compute the exciting forces and hydrodynamic coefficients due to the interaction of a regular oblique wave train with an infinitely long, semi-immersed floating cylinder of arbitrary shape. Comparisons are made with previous results obtained using other solution techniques. The results obtained from the solution of the oblique wave diffraction problem are used to determine the transfer functions and response amplitude operators for a structure of finite length and hence the loads and amplitudes of motion of the structure in short-crested seas. The wave loads and body motions in short-crested seas are compared to corresponding results for long-crested seas. This is expressed as a directionally averaged, frequency dependent reduction factor for the wave loads and a response ratio for the body motions. Numerical results are presented for the force reduction factor and response ratio of a long floating box subject to a directional wave spectrum with a cosine power type energy spreading function. Applications of the results of the present procedure include such long structures as floating bridges and breakwaters. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1972. / Microfiche copy available in Archives and Science / Vita. / Bibliography: leaves 123-126. / Ph.D.

No description available.

ter have most of their energy held in the region of the water column near to the surface. Tsunamis are extremely long waves with long periods that can range from five minutes to several hours. Due to their very long wavelengths, tsunamis travel at the shallow water wave celerity which is equal to the square root of the gravitational acceleration times the water depth. The speed of a tsunami in the open ocean can reach in excess of 500 miles per hour. Tsunamis are also characterized by low wave height when moving through oceanic depths and are often hard to recognize when seen out in the deep ocean. As tsunamis approach the coastal region, they are affected by the rapid decrease in water depth. / US Navy (USN) author.