潮汐条件下浑水异重流形成机制及模拟方法研究

Under proper conditions, turbid density current can appear along silty-muddy estuaries and coasts under tidal and wave action. Moreover, sediment deposition of port and waterway engineering, etc. caused by turbid density current cannot be ignored. This study is proposed to carry out research on the formation mechanism and simulation methods of turbid density current under tidal action by use of such means as data analysis, theoretical derivation, flume experiment and generalized physical model test, etc. First, the generating conditions and influence factors of turbid density current under tidal action are analyzed via flume experiment. Second, based on basic theories such as fluid mechanics, mechanics of sediment movement and similarity theory, the similarity criterion for the simulation of turbid density current along estuary and coast areas is studied by taking into full consideration the formation mechanism of density current and movement characteristics of cohesive sediments. Then, on basis of the existing data, the study is intended to set up the mathematic model of turbid density current movement characteristics, deal with key issues and put forward the calculation mode of turbid density current deposition. Last, via the generalized physical model test, simulation methods of turbid density current as proposed are verified, and the spatial and temporal distribution characteristics of turbid density current deposition under different conditions are also discussed. Anticipated results can clarify the basic movement law of turbid density current under tidal action, thus providing a scientific basis for port and waterway development and desilting of river channels downstream tidal sluice gates.

在潮汐和波浪作用下的淤泥质河口海岸，合适条件下也能产生浑水异重流，而且浑水异重流造成的港口航道、挡潮闸等工程的泥沙淤积不容忽视。本项研究拟采用资料分析、理论研究、水槽实验等研究手段，研究潮汐条件下浑水异重流的形成机制和模拟方法。首先，通过水槽实验和理论分析，对潮汐条件下浑水异重流的形成机制和影响因素进行研究；再次，依据流体力学、泥沙运动力学及相似理论等基础理论，并充分考虑浑水异重流的形成机制、显著特征和黏性泥沙的运动特性，构建能够反映浑水异重流运动特征的数学模型，解决其中的关键技术问题，提出浑水异重流淤积的计算模式。最后，通过典型港口航道及闸下异重流淤积的模拟，对所提出的浑水异重流模拟方法进行验证，并探讨不同条件下浑水异重流淤积的时空分布特征。预期成果可阐明潮汐条件下浑水异重流运动的基本规律，为港口航道开发和闸下河道防淤减淤提供科学依据。

在对以往异重流形成条件及模拟技术研究回顾和总结的基础上，分析了潮汐条件下异重流存在的可能性及模拟技术上存在的的困难和问题。对河口区挡潮闸和港口进行了现场调查和测量，获得了丰富的现场实测资料。在长水槽中进行了潮汐条件下异重流形成条件的实验研究，并建立了相对应的数学模型模型研究，最后以福建木兰溪建闸和浙江灵江建闸为例进行了物理模型试验和数学模型计算研究。得到以下主要结论如下：.（1）在合适的条件下，潮汐作用水域能够产生异重流，并形成异重流输沙。现场实测资料表明，河口挡潮闸近区和港池尾部在最高潮位前2-3小时内，由于水深较大，动力较弱，含沙量垂线分布发生变化，泥沙向底层聚集，局部区域形成了含沙量浓度差，进而形成异重流，至落潮初期2小时后，落潮流速增大，异重流逐渐消失。整个过程呈现出明渠输沙和异重流输沙交互过渡的的特征。.（2）现场实测和水槽实验资料表明，潮汐条件下异重流发生的临界条件及影响因素和恒定流明显的不同，异重流修正Fr数要小于恒定流条件下异重流发生的临界Fr数，约为0.5左右。闸下渠底比降或者港池地形并不起主要作用，异重流产生和维持条件取决于外部潮流动力的强弱和含沙量的大小。.（3）考虑含沙量密度差造成的浮力影响，建立了三维异重流数学模型。考虑异重流形成条件及运动特征，提出了潮汐条件下异重流模拟应该遵循的相似理论。通过潮汐河口建闸物理模型试验和数学模型模拟的实例研究，表明考虑密度差影响所建立的异重流数学模型和考虑异重流模拟相似准则的物理模型可以较好的模拟出潮汐条件下异重流的产生和造成的泥沙淤积。