Turbulent flows induced by the interaction of continuous internal waves and a sloping bottom
| Autor: | Je-Cheng Kuo, 郭哲成 |
|---|---|
| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 Internal waves occur in the interface between two layers of fluids with density stratification. In order to better understand the characteristics of continuous internal waves, a series of experiments were conducted in a laboratory tank. The upper and lower layers are fresh water of 15 cm thick and salt water of 30 cm thick, respectively. The periods of internal waves are 2.5, 5.5 and 6.6 sec. A micro-ADV is used to measure velocity profiles. Wave profiles at the density interface and the free surface are monitored respectively by an ultrasonic and capacitance wave gauges. Our results indicate that particle velocities (u and w) above and below the density interface have opposite directions. The speed is peaked near the density interface and it becomes weaker further away from the interface. Empirical Mode Decomposition is used to remove noise from the observed particle velocities, and the period is consistent with those derived from the interface elevations. The observed particle velocities also compare favorably with the theoretical results. When internal waves propagate without the interference of a sloping bottom, the turbulence induced is rather insignificant. The turbulence is more significant only near the density interface. With the existence of a sloping bottom, the internal waves gradually shoal and deform, the crest becomes sharp and steep, finally the waves become unstable, break and overturn. In this study the effect of bottom slope and the steepness of internal waves on the reflectivity of incoming waves are investigated. The reflectivity is smaller with gentler slope, and it increases and reaches a constant value with steeper slopes. The observed energy dissipation rateεis higher near the slope. Three methods were used to estimate the energy dissipation rate and shear stress; namely, the inertial dissipation, the TKE and auto-correlation method. Theε estimated from the auto-correlation method is larger than that from the other two methods, but their trend is similar. The energy dissipation rate is found to increase with a gentler sloping bottom. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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