The rigorous descriptions of linear and nonlinear guided wave theory are given together with a geometrical description that helps in the understanding of the physical phenomena taking place. The nonlinear waveguide discussed in this dissertation is composed of a linear thin film and substrate with a cladding material whose refractive index varies with the intensity of the light. Experimentally, this was accomplished, by placing an oriented liquid crystal (highly nonlinear but extremely slow) on top of a thin film glass waveguide. When the liquid crystal used was K15, light-induced mode cutoff was observed. The TE(,0) mode became leaky as the guided wave power was increased. This was a consequence of the light-induced increase in refractive index due to thermal effects. This behaviour was studied as a function of temperature. Light by light modulation was also accomplished with this setup. The theory of the linear and nonlinear prism coupler and the first experimental investigations on the nonlinear prism coupler are given. The nonlinear prism coupler used was obtained by depositing a small amount of MBBA liquid crystal in the gap beween the input coupling prism and the thin film. The basic properties of the nonlinear prism coupler were demonstrated experimentally and the results obtained were verified to have their origin in the temperature component of the nonlinear index of refraction. Good qualitative agreement between the theory developed and experiments were obtained. Bistability and switching in a thin film waveguide with a K18 liquid crystal cladding has been demonstrated for the first time. These experiments made use of the interesting phenomena associated with the nematic to isotropic phase transition. Such behaviour was satisfactorily explained by the intense light scattering associated with the critical opalescence that accompanies such a phase transition in a liquid crystal. Both the TE(,0) and the TM(,0) modes were found to exhibit such behaviour.

To establish the credibility of surface wave measurements from two phased-array WERA HF (High Frequency) radars, SEACOOS (SouthEast Atlantic Coastal Ocean Observing System) funded the Mini-Waves experiment from March to May, 2005. For this study, the surface wave parameter (significant wave height) and directional wave spectrum obtained from two WERA radars were compared with those obtained from two Tri-Axys buoys during the same period. The Wyatt (1990) method was used to obtain the directional wave spectra, and significant wave heights were obtained by integrating the directional wave spectra over all directions and the selected frequency band. The SWAN (Simulating WAve Nearshore) directional wave model was used to evaluate the comparison results between WERA radars and buoys. There was a good agreement between WERA radars and Tri-Axys buoys when the echo-Doppler spectrum had a high 2nd-order SNR (signal-to-noise) ratio. The measurements didn?t agree in low sea states when the echo-Doppler spectrum had a lower SNR. Also, strong horizontal current shear caused by Florida Current (FC) had an effect on wave propagation direction. To improve the quality of WERA radar wave measurements, a longer sampling interval (10-minute interval) and procedures to remove the effect of RFI are needed.

Wave-induced circulation in general coastal environments is simulated by coupling two widely-used finite-element models, namely, a refraction-diffraction-reflection model based on the elliptic mild-slope equation, and a two-dimensional (depth-averaged) shelf-scale circulation model. Such models yield wave-induced current-fields and set-up/down. This involves exploration of some numerical and practical issues, for example, the selection of appropriate boundary condition and grid resolution, numerical errors owing to higher-order derivatives, etc. Computations of the wave forcing from the elliptic wave model, and the wave-induced quantities from the circulation model, are validated with theoretical and published results. The coupled system is then used to simulate the wave-induced circulation in the domains where structures (e.g. breakwater, jetty, etc.) and bathymetric features (e.g. shoal, etc.) are present. In practice, usually an approximate form of the wave-induced forcing is used. This has certain limitations in some application, which have been poorly studied so far. Therefore, here we consider two alternative approaches. The performance of these wave forcing formulations is examined in the regions where the effects of wave reflection, diffraction and focusing are significant. It is observed that the “generalized approach” provides satisfactory results in most situations, provided a grid resolution of L/10 or more is achievable for the wave model domain. The widely-used simplified approach may produce a chaotic pattern of set-up/down and current field in the regions where the wave field is not purely progressive. The third approach ignores the effect of wave diffraction and reflection, and primarily simulates the effect of energy dissipation. Differences up to 25 percent are observed between the modeled current fields obtained with the generalized and the simplified approach. The results suggest that the generalized approach can be used with little practical difficulty and greater reliability.

Tremendous interest to the study of guided waves in pipe inspection in the oil, chemical, and power generating industries has peaked during the last decade. Since the advantages are inspecting long lengths of pipe quickly and without removing insulation. Recent researches in defects inspection are determined by reflection coefficients from the cracks. However, the purpose of this thesis is to excite at a single probe position and to receive the signals of guided waves with the form of loops. For the variations of wave profiles of guided wave, this thesis aimed at the largest energy distribution of wave profiles to proceed with the researches of mode conversion phenomena caused by defects. This thesis utilizes the partial loading source, and excites the non-axisymmetric and axisymmetric guided waves individually along the carbon steel pipes with circumferential defects and without defects to contrast and analyze. According to the change of wave profiles, we can find the variables that change wave profiles for different guided waves modes include propagating distance and frequency, and these cause that the circumferential energy distribution will change. For the non-axisymmetric guided waves in this thesis are non-dispersive, and its variations of phase velocity and group velocity are small, so the variations of wave profiles are also small. Moreover we study the mode conversion phenomena caused by defects from its position which the circumferential energy is largest. It also investigates new modes from mode conversion phenomena produced by defects more completely. Finally, we can predict the types and the number of new modes from mode conversion phenomena by phase velocity dispersion curve, and compare with the experiments well.

Surface gravity waves and internal waves are two of the most common natural phenomena in the ocean. While oceanographers believe that internal waves have greater influence over the surface waves, if is not clear to what extent that the former have affected the latter. As an internal wave propagating in the ocean, short period flow could be induced on the free surface layer. Moreover, as internal waves propagating over a submarine ridge, internal breaking accompanying by large vortex may have occurred, which may also affect the properties of the surface waves. To prove the relationship between them, basic mathematical equations have been derived, but had never been proven in the laboratory experiments or field observations. In this thesis, the results of a series of laboratory experiments conducted at the National Sun Yen-sen University are employed to study the waveform evolution and change to the physical parameters of the surface waves, resulting from the generation of internal waves induced on a stratified fluid, as both propagate together above a plane bottom or across single ridge. These experiments were carried out in a stratified two-layer fresh/brine water system (upper layer with fresh water density 996 kg / m3; bottom layer brine water with 1030 kg / m3) in a steel framed wave tank of 12m long with cross-section of 0.7 m high by 0.5 m wide. A plunging-type wave maker was used to produce the designated surface waves, from which the internal waves were induced at the interface. Based on the experimental results in the fluid system with uniform density, wave height and period of the surface wave were first calibrated. It was found that the amplitude of a surface wave decreased first due to the breaking of the internal wave on the apex of a submerged ridge and then increased due to wave regeneration at the back of the ridge, when the surface wave propagated over single ridge. Beyond the ridge, the peak period with maximum energy associated with the transmitted wave remained almost the same with that of the incident waves. In a stratified fluid system, wave height of the surface waves and internal waves did not suffer much change but the peak period of a surface wave increased as an internal wave just across the apex of the obstacle, under a condition referred to as weaken interaction between the waves and the obstacle. For the intense wave breaking condition at the interface, wave height of the internal waves decreased and the period of surface waves or internal waves shortened. However, wave height of the surface wave above the apex of the obstacle increased due to the intense wave breaking. The results obtained from the present laboratory experiments on the interaction between a surface wave and the induced internal wave could benefit others interested in surface and internal wave interaction for practical applications in oceanography or numerical modeling.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

To understand the function of the cardiovascular system, the propagation of waves in arteries has to be investigated, since they carry information which can be used for the prevention and diagnosis of cardiovascular diseases. The main goal of this thesis is to improve the understanding of wave propagation in central and peripheral arteries studying the local hemodynamics of the ascending aorta, the carotid artery and the femoral artery by analysing human, animal and in vitro data. Also, another aim is to introduce a technique for non-invasive determination of the local arterial distensibility, the wave speed, and wave intensities. Arterial hemodynamics is here studied using wave intensity analysis, a time domain technique based on pressure and velocity measurements that is derived from the 1D theory of wave propagation in elastic tubes. Also, variations of this technique were used, such as (i) the non-invasive wave intensity analysis that relies on diameter and velocity measurements and (ii) the reservoir-wave approach in which pressure is considered the sum of a pressure due to the elastic properties of the arteries and a pressure due to the travelling wave. To identify the correct analysis to describe the wave propagation in the ascending aorta using pressure and velocity measurements, the hemodynamics of the canine ascending aorta was studied invasively using the traditional wave intensity (or waveonly) analysis and the reservoir-wave approach in both control condition and during total aorta occlusions in order to provide clear reflection sites. The models produced a remarkably similar wave intensity curves, although the intensity magnitudes were different. The reservoir-wave model always yielded lower values for all hemodynamic parameters studied. Both models led to the conclusion that distal occlusions have little or no effect on hemodynamics in the ascending aorta. Since the ascending aorta is not an accessible vessel its examination in clinical routine is challenging. More superficial arteries, such as carotid, radial, brachial and femoral arteries, might be easier to examine, in particular using ultrasound equipment that is normally available in the clinic. These considerations led to the second study of this thesis that is the introduction of a new technique for the non-invasive determination of arterial distensibility, local wave speed and wave intensities to study arterial hemodynamics in humans. The technique relies only on diameter and velocity measurements that can be obtained using ultrasound. In particular, the technique was used for the first time to study the hemodynamic of the carotid and femoral arteries in a large population of healthy humans to investigate the changes with age and gender. The carotid artery was more affected by the aging process than the femoral artery, even in healthy subjects. Local wave speed, distensibility and hemodynamic wave intensity parameters (except the reflection index) had strong correlations with age at the carotid artery. The mechanical properties and hemodynamic parameters of the femoral artery were not significantly age-dependent, but local wave speed, distensibility and forward wave intensity were significantly gender-dependent. The findings of the first and second studies contributed to the design of the third study. The carotid artery is an elastic artery relatively close to the heart and thus the hemodynamics of this vessel is related to left ventricular function. For this reason, the carotid hemodynamics of the same healthy population was investigated for the first time using the reservoir-wave approach. Pressure and velocity measurements were separated into their reservoir and excess components and the effects of age and gender on these parameters were studied. It was found that in the carotid artery reservoir and excess components are strongly affected by the ageing process. From the above studies some questions about the hemodynamics of central arteries remained unsolved. For this reason it was decided to carry out in vitro experiments in a mock circulatory system to investigate the effects of variation of compliance and stroke volume on the reservoir and excess pressure components of the ascending aorta. This allows for the study of different physiological and pathological conditions, such as age, hypertension, atherosclerosis and ventricular dysfunction in relation to vascular compliance and stroke volume. The reservoir and excess components of the measured pressure wave were both significantly related to aortic compliance and stroke volume, but the reservoir pressure had a stronger relationship with aortic compliance compared with the excess pressure and its magnitude increased more significantly when the aorta became stiffer. Wave speeds, calculated using measured and excess pressures, followed the same pattern, but the one calculated using excess pressure was smaller than the other. Wave speed was strongly related to aortic compliance, but not to the change of stroke volume. In conclusion, the use of the wave-only and the reservoir-wave models led to different values of wave speed and intensities that can be explained considering the anatomy of the arterial system. Notably, elastic and muscular arteries are differently affected by age and gender. The hemodynamics of the carotid artery are strongly related to age also in healthy subjects. Pressure and flow velocity in the carotid artery can be separated into their reservoir and excess components. The new non-invasive technique based on diameter and velocity measurements could be relevant in clinical practice as a screening tool.

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