| Northern bank of Hangzhou bay, no matter whose marine, river or highway transportation, is quite favorable. The shoreline which is suitable for building harbors is long because of the existence of the deep channel. It is essential for the current and further development of economy of northern bank of Hangzhou bay to grasp northern deep channel conditions and erosion situation. However, the shipping erosion and deposition conditions in deep channel all depend on the hydrodynamic condition and the transportation-of sediment. So it should be vitally important to study the flow structure in the deep channel of northern shore in Hangzhou Bay by three-dimensional flow mathematical model.On the basis of research status of Hangzhou bay, this article established a two-dimensional flow model of Hangzhou Bay and a nested three-dimensional deep channel flow model. The flow domain was divided respectively by unstructured triangular grid and the three-dimensional vertical layered dynamic grid, and the governing equations were discrete and solved by the finite volume method. After measurement of flow rate and tidal data of Hangzhou Bay, it showed that the model parameter selection is reasonable, and it can ensure accuracy.This article extracted the required boundary conditions of the three-dimensional deep channel flow model from the numerical simulation of two-dimensional flow in Hangzhou Bay and calculated the three-dimensional flow field within the deep channel water domain. Comparing with the two-dimensional measured data, the result was better. And then, the flow characteristics of the three-dimensional deep channel were analyzed, it showed that:on the planar, the maximum vertical velocity reached 2.94 m/s in the surface layer of the Zhapu deep channel, the average maximum vertical velocity of flow and ebb was 1.83m/s and 1.34m/s, the average velocity in the bottom layer was 50% of the velocity in surface layer, and intermediate layer and bottom layer were tended to the same. On the section of flow field and the profile of the flow velocity was 0.16 m/s faster in the flat area than the bed surface of the deep channel. In the deep channel area, the velocity near the center would be faster than both two sides. As the topography fluctuated, both the flow velocity and flow direction changed apparently, so the turbulence intensity got stronger and it resulted in eddy easily.It first simulated the flow structure change in deep channel after the Hangzhou Bay Bridge Project, the results showed that:on the planar, the flow velocity changed greatly near the pier, the velocity in front of and behind the pier reduced and increased near the pier. The main influent of pier on the flow velocity was in the first 70m and the last 200m. The current velocity gradient on the section of Zhapu reduced after the project, accompanying with the turbulence intensity became weaken, and then followed by the insufficient of scouring dynamics on the seabed. In the neighborhood of the bridge pier, horseshoe vortex would result in local scour besides the pier for the increase of flow velocity besides the pier and the reduce of flow velocity in front of and behind pier. On the profile, the upstream water level lifted and downstream surface dropped because of the resistance resulted from the pier, for the downstream reach from bridge pier to Zhapu, the water level lifted 2-7cm, the flow velocity 2Km away from the front pier decreased about 0.3m/s and meanwhile decreased 0.1m/s-0.15m/s in the deep channel of Zhapu 8Km away from pier. In the upstream, water dropped 2-5cm, the longitudinal velocity is almost zero and transverse velocity is about 0.4m/s behind the pier. The flow velocity 2Km away from the behind pier decreased about 0.1 m/s, and which showed the impact on downstream flow velocity was greater than upstream. Overall, the impact of Hangzhou Bay Bridge can slow the flow velocity of deep channel.The study above has significance reference value on deep channel maintenance of the north shore of Hangzhou bay. |
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