Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Meteorology. / Vita. / Bibliography: leaves 169-174. / Ph.D.

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A phase-space asymptotic approach to wave propagation in homogeneous dispersive media is discussed which has several advantages by comparison to conventional techniques, such as the stationary phase method, ordinary ray tracing, etc. This approach, which is based on the wave-kinetic theory, ^7/8 is used to examine in detail three types of one-dimensional canonic dispersive media: cubic, quintic and sinusoidal. The analysis is also carried out using standard Fourier techniques for comparison purposes. Lastly, a link is made between the wave-kinetic method and integrals appearing in catastrophe theory. ^10/11 / M.S.

The method of multiple scales is used to analyze the nonlinear effects of the gas motion as well as the acoustic lining material on the propagation and attenuation of sound in two-dimensional and circular ducts of uniform cross sections in the absence of mean flow. The ducts are lined with a point-reacting acoustic material consisting of a porous sheet or of a perforated plate followed by honey-comb cavities and backed by the impervious walls of the ducts. The effect of the acoustic material is included either by characterizing the material by a semi-empirical nonlinear impedance or by coupling the waves in the duct with those in the liner. Analytical expressions are obtained for the absorption coefficient in terms of the sound frequency, the physical properties of the porous sheet or the perforated plate, and the geometrical parameters of the flow configuration. The results show that the nonlinearity flattens and broadens the absorption vs. sound frequency curve, irrespective of the geometrical dimensions or the porous material acoustic properties, in agreement with the experimental observations. The effect of the gas nonlinearity increases with increasing sound frequency, whereas the effect of the material non- linearity decreases with increasing sound frequency. Moreover, the sharper the resonant tuning is the narrower the adverse frequency bandwidth is. / Ph. D.

The purpose of this thesis is to investigate the properties and wave velocities for an axially symmetric medium. The investigation consists of four parts. In the first part, the physical properties of the medium are defined. Then the stress-strain relations for the case under consideration are obtained from the general case. This is done by imposing the condition of symmetry on the strain energy function. Next the measurable constants are round in terms or the natural constants. This is done by applying simple extensions and shears to the material. After the measurable constants are determined in terms or the natural constants, then the relationship is inverted and the natural constants are found in terms or the measurable constants. Some elastic constants are then determined for an arbitrary direction, as it is not likely that the stresses will always be imposed along an axis of symmetry. Following this major part, the equations of motion for a vibrating medium are determined in terms or the natural constants by substituting the stress-strain relations. This is very straightforward, but must be done. The final step is made by finding the velocities of propagation of the waves by using the equations of motion. This is done by assuming a solution and substituting into the equations of motion. From these equations, a cubic equation defining the three principal velocities arises. The solution of this cubic equation is the culmination of this investigation. / M.S.

The long time behavior of antisymmetric as well as symmetric waves on a two-dimensional liquid sheet is studied, the effects of the surrounding fluid being taken into account. The non-linear Schrödinger equation governing the wave motion is derived by the method of multiple scales. Modulatory stability, wave-wave interaction and non-linear stability are studied and a possible mechanism accounting for the disintegration of the sheet is found. / M.S.

Thesis (M.S.)--Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.

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A the'.is submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in the fulfillment of the requirements of the Degree of Magister Scientae. June 1992 / Aspects of the brown alga Pict~'ppt;eris lQ..n..qifolia at. Palm Beach, Natal, were investigated wi\'-;.hspecial reference to the effect of wave expozu~e~ A description of the species is giv~n and the nomencluture discussed. D~strib1i.ltion of n. ).or~gifolia was det~rmimad from literature and herbarium speof.mens . various r(\~:~thodosf measuring wave exposure were assessed and review~~d. At'!;:.emptswere made to quantify sand abrasion and deposition in tihe scudy si.tes. Morphological and structural aspect;s of the cha LLus were found to vary considerably with season and wave exposure" Light and scanning electron microscopy studie.s indicated the relatjvely complex cell organisation of this brown alga. The prolific regeneration from various thallus sections of .Q. longifolia indicate that regenerat.ion is an important survival strate 'JY following damage. Sexual reproduction and tetrasporogenesis were investigated. Sex.ual reproduction was not prolific in the field, however, tetraspores were abundant and are believed to be particul~rly importcmt in high wave exposure areas. 11. _j.Q.ngi;f'clige,x_periences a range of environmental conditions and responds to these with morphological, structural and reproductive &daptations.

Standard GPS receivers are unable to provide the rate or precision required when used on a small vessel such as an Unmanned Surface Vehicles (USVs). To overcome this, the thesis presents a low cost high rate motion measurement system for an USV with underwater and oceanographic purposes. The work integrates an Inertial Measurement Unit (IMU), a GPS receiver, a flux-gate compass, a tilt sensor and develops a software package, using real time data fusion methods, for an USV to aid in the navigation and control as well as controlling an onboard Acoustic Doppler Current Profiler (ADCP).While ADCPs non-intrusively measure water flow, they suffer from the inability to discriminate between motions in the water column and self-motion. Thus, the vessel motion contamination needs to be removed to analyze the data and the system developed in this thesis provides the motion measurements and processing to accomplish this task. / by Chrystel Gelin. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.