长江口水文、泥沙过程与圆桩冲刷的数值模拟

IOCAS-IR > 海洋环流与波动重点实验室

	长江口水文、泥沙过程与圆桩冲刷的数值模拟
其他题名	Three-dimensional numerical simulation of flow, sediment transport and scour around a pier in the Yangtze River estuary
	赵恩宝
学位类型	博士
	2008-06-12
学位授予单位	中国科学院海洋研究所
学位授予地点	海洋研究所
关键词	长江口悬沙 Ecomsed 欧拉二相流水动力泥沙输运
摘要	本文主要利用ECOMSED模式对长江口及邻近海域的水文、泥沙过程进行三维数值模拟，并结合实测资料分析其水动力、泥沙输运、底床冲淤等特征；然后利用欧拉二相流模型模拟小尺度条件下长江口底床上圆桩周围的水流和泥沙冲刷、输运规律。通过资料分析和ECOMSED数值模拟结果比较，我们得出：长江口口门内为非正规半日潮流区，潮流运动形式多为往复流，落潮流占优。落潮流速大于涨潮流速，流速垂向分布从表层到底层递减。悬沙浓度与流速关系密切，一般来说，流速越大，悬沙浓度越高；一个潮周期过程中会出现两次、三次或四次泥沙再悬浮，分别是涨急、落急、涨转落、落转涨时刻；盐水楔结构对粘性与非粘性悬沙浓度的分布起决定性作用，转流时泥沙再悬浮主要是由于这时会出现盐水楔，并形成垂向环流，使床面大量未被固结的泥沙再悬浮，形成峰值。悬浮泥沙垂向分布可分为垂线型，斜线型，抛物线型和L型。流场和底床冲淤变化与水深关系密切：深水区，流速较大，底床冲淤变化也较大。其中，受径流影响区表现为淤积，受潮流影响区表现为冲刷；浅水区基本表现为淤积。从模式运行结果和实测资料比较可以看出，该模型可以较好的模拟长江口水流、悬浮泥沙分布与变化；能够再现在径流入海口处，盐水楔结构及其诱生的垂向环流从形成到发展，又到消失的完整过程；也能够展示底床的冲淤变化。对于我们模拟长江口背景流场，了解该区域内水动力变化、悬浮泥沙输运、底床冲淤等有重要意义。在欧拉二相流模型对长江口底床上圆桩周围的水流和局部冲刷数值模拟过程中，我们不仅考虑水流和泥沙之间的作用，还引入泥沙颗粒之间的相互影响。模拟结果较合理的展示了圆桩周围的流场类型和底床冲刷变化：在圆桩前方，流速减小并形成垂向涡旋，从而产生局部冲刷；在圆桩两侧，水流加速，挟带上游泥沙向下输送，并在内侧堆积；而在圆桩后面，存在流速分离区。在该分离区内流速很小，并且当流速较大时，会产生回流，形成两个对称的漩涡。流速越大，圆桩前由垂向涡旋引起的局部冲刷就越明显；而当底床泥沙粒径变小时，泥沙临界起动流速变小，底床也更容易被冲刷。悬浮泥沙浓度分布受流场的影响，并且当粒径小而流速大时，能悬浮到更高的深度。
其他摘要	In this paper, we use the ECOMSED model to simulate the flow and sediment transport in the Yangtze River estuary and the adjacent area. At meantime, we fully analyze and discuss the survey data. The following conclusions are obtained throughout the work: it is non-formal shallow semidiurnal tide in the estuary. The ebb tide is much stronger than the flood tide, and the velocities decrease along the depth. The distribution of suspended sediment concentration is associated with the velocity. The concentration becomes higher when the velocity increases. The sediment can be resuspended four times during one tidal period at most. Two times happen at the maximum velocity time of ebb tide and flood tide separately, and the other two happen during the current turning periods. There will be a saline-water intrusion front during the current turning period, and this is the cause of the sediment re-suspension. The vertical distribution of suspended sediment concentration can be divided into four patterns: beeline, diagonal line, parabola and L-shaped. The flow pattern and bed change are associated with the water depth. The velocity is bigger and the bed change higher where the water is deep. The sediment deposits at the riverine current area and suspends at the tidal current. The sediment generally deposits at shallow water. Comparing the simulate results with the survey data, we conclude that the model can simulate the flow pattern, sediment transportation, salinity distribution and bed change properly. It is of great significance to us to understand the Yangtze River estuary. A three dimension Eulerian two-phase numerical model for the simulation of flow pattern and local scour around a pier is presented, too. Both flow-particle and particle-particle interactions are considered in the model. The results show that the velocity field and local scour around the pier is reasonable. In front of the pier, the velocity decreases and forms a vortex which induces the scour hole. At both sides of the pier, the velocities accelerate, and laminated load is accumulated nearby. Behind the pier, there is a separation zone with two symmetrical eddies when the inflow velocity is about 1.1 m/s. In this separation zone, velocity magnitude is the least, and local scour around the pier is the weakest, even deposit happens for a long run. The scour hole around the pier is more evident at higher velocity because of the vortex formed in front of the pier. The bed is easier to scour when the grain size is small, because the critical stress of bed is small. The sediment concentration is associated with velocity, and the sediment could be suspended to a higher layer when the grain size is small and the velocity is high.
页数	90
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1347
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	赵恩宝. 长江口水文、泥沙过程与圆桩冲刷的数值模拟[D]. 海洋研究所. 中国科学院海洋研究所,2008.

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