博士 / 國立成功大學 / 水利及海洋工程學系碩博士班 / 97 / A 2-D numerical model was developed to simulate wave breaking and Bragg scattering of water waves. The model solves the Reynolds averaged Navier-Stokes (RANS) equations coupled with the k-ε turbulence closure model. To track free surface configurations, the VOF/PLIC is employed. Before applying the present model to the simulation of flow fields under wave breaking and resonant Bragg reflection, it is necessary to confirm the validity of the model. Based on comparisons between numerical and experimental results for the water elevations and the velocity components, the present RANS model is demonstrated to provide the satisfactory performance.
At the post-breaking stage on a composite sloping bottom, i.e. the barred or stepped beach profile, the energy dissipation may be followed by another occurrence of wave breaking if the local water depth increases or keeps constant. The numerical results show that the vorticity and the turbulent flow induced by breaking immediately dissipate during the stage of the decline of energy dissipation. These results are quite different from the previous study for wave breaking on a uniformly sloping bottom. It is interesting to note that the horizontal velocity in the stable wave front reaches 60 to 70 % of the local wave celerity. The analysis of turbulent budget also reveals that the turbulence advection dominates the turbulence transport mechanism at the stage of the decline of energy dissipation, while the turbulence production ceases. Since the model neglects the air entrainment, it is only applied to the simulation of spilling breaker.
For the simulation of flow field when waves propagate on a serial of artificial bars, the numerical result demonstrates that the amplitude of water elevation at the downstream of the serial bars for the near-resonant case is only half of that for non-resonant case. The simulated flow field under Bragg reflection appears to like the flow under the partial standing waves, unlike the flow of a progressive wave. Note that the antinodes are shown to be located in front of the leading bars and each interval between two bars, while the nodes are located above the leeside of bars. Therefore, the local flow field around each bar forms an independently closed circulation, and also results in a different mechanism of vortex generation and dissipation. It is also found that the calculated vortex intensity at the last bar is only one third of that at the leading bar for the near-resonant case. The stability of the artificial bars under the wave-structure interaction is also investigated with the simulated results.
| Identifer | oai:union.ndltd.org:TW/097NCKU5083012 |
| Date | January 2009 |
| Creators | Chin-Yen Tsai, 蔡金晏 |
| Contributors | Tai-Wen Hsu, 許泰文 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 159 |
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