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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.

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.

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

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.

To determine the effect of body shape on the response of underwater vehicles to surface waves in shallow water, the wave radiation hydrodynamic forces are evaluated for a family of (i) prolate spheroidal hull forms and (ii) cylindrical bodies with hemispherical nose and conical tail sections by systematically varying the geometric parameters but keeping displacement constant. The added-mass and wave damping coefficients are determined using a frequency-domain, simple-source based boundary integral method. Results are obtained for a range of wave frequencies and depths of vehicle submergence all for a fixed water depth of 10 m. With the wave exciting force and moment determined using the Froude-Krylov theory, the response transfer functions for heave and pitch are then determined. The heave and pitch response spectra in actual littoral seas are then determined with the sea state modeled using TMA spectral relations. Results show that vehicle slenderness is a key factor affecting the hydrodynamic coefficients and response. The results show two characteristics that increase the radiation hydrodynamic forces corresponding to heave and pitch motions: namely, vehicle length and further-away from mid-vehicle location of the body shoulder. The opposite is true for the oscillatory surge motion. By utilizing these observed characteristics, one can design the lines for maximum radiation forces and consequently minimum hull response for the critical modes of rigid-body motion in given waters and vehicle missions. In the studies carried out in the thesis, a hull with a long parallel middle body with hemispherical nose and conical tail sections has better heave and pitch response characteristics compared prolate spheroid geometry of same volume. The methodology developed herein, which is computationally efficient, can be used to determine optimal hull geometry for minimal passive vehicle response in a given sea. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

This study is performed in tandem with numerous experiments performed by the U.S. Navy to characterize the ocean environment in the South Florida region. The research performed in this study includes signal processing steps for isolating ocean phenomena, such as internal waves, in the magnetic field. Raw magnetometer signals, one on shore and one underwater, are processed and removed of common distortions. They are then run through a series of filtering techniques, including frequency domain cancellation (FDC). The results of the filtered magnetic residual are compared to similarly processed Acoustic Doppler Current Profiler (ADCP) data to correlate whether a magnetic signature is caused by ocean phenomena. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection