| dc.description.abstract | This thesis presents work studying water waves propagating atop background shear currents. A growing body of research, to which this thesis contributes, indicates that accounting for the effects of shear currents are important for accurate modeling of wave phenomena, as commonly occurring sheared currents especially near coastlines can have a notable effect on wave propagation. The present work further develops methods for modeling wave-shear current interactions and demonstrates some of the distinct differences in commonly observed wave patterns due to the presence of shear. A combination of experimental, numerical, and theoretical methods are used. In particular, a new, unique laboratory setup was developed and used to make experimental observations of wave phenomena atop strong shear currents where the waves travel in a broad range of directions relative to the current, a useful scale model of the ocean.
Key accomplishments and results include the development of a new inversion method for reconstructing the current depth-profile from analysis of a measured wave spectrum, with importance to the field of remote sensing of currents. The method is easy to implement and was demonstrated to improve the accuracy of the estimation of shear currents compared to existing state-of-the-art methods, validated based on data collected in the laboratory. Measuring the wave spectrum via radar or optical-based detection and using an inversion method to deduce the currents is a popular technique for mapping currents over a much larger spatial scale than what is practical with in situ point measurements, and the method developed here has the potential to improve the detail of the depth-profile of remotely-sensed flows.
In addition, the first experimental observations were made of the effects of shear on ship wakes and ring wave patterns, confirming theoretical predictions. In the case of ship waves, the wavelength of the transverse waves following the ship was observed to vary notably for upstream versus downstream motion at the same speed relative to the water surface, while the wake became rotated and skewed for the case of ship motion perpendicular to the flow. For ring waves, asymmetries in the wave pattern were observed, due to the shear-induced anisotropy in wave dispersion. For both cases, experimental results agreed qualitatively with theoretical predictions.
A framework was developed for modeling the wave patterns produced by a general moving surface pressure distribution, a model of a surface impinging body such as a ship, in the presence of shear currents of arbitrary depth-dependence. The technique was applied to modeling the wave resistance of realistic ships traveling atop shear currents measured at the mouth of the Columbia River, predicting up to a 3x difference in the wave resistance depending on the direction of motion relative to the surface.
Lastly, a commonly-used method for approximating the wave dispersion relation in the presence of arbitrary shear currents (the piecewise linear approximation) was further developed and applied to modeling wave problems atop shear currents such as the Doppler resonance phenomenon for a moving and oscillating source at the surface. | nb_NO |
