Numerical Simulation Of Suspended Sediment Transport Caused By The Excavation Of Submarine Pipeline Laying In Oujiang River North Entrance

In the way of using dredger excavation to lay pipelines in the north entrance of Oujiang River, it will produce concentrated sediment which should spread into the surrounding and lead to the turbidity increase in the surrounding water by the action of tide and other dynamic factors. Meanwhile, the harmful material carried in sediment also can decline the water quality so as to damage the marine ecological environment. With the development of China's coastal economic construction, rapid increase of the maintenance engineering in ports and waterway construction, people increasingly pay more attention to the study of the environmental problems caused by the pipeline laying excavation.Numerical prediction is one of the effective means to simulate the suspended sediment transport and diffusion. It can save a lot of labor, material and financial resources compared with the actual measure. When using numerical simulation to predict sediment transport, you need to consider the suspended sediment transport and diffusion equation of discrete and related parameters in the model selection and generalization. Additional source term caused by the equation, namely the source intensity generalized treatment is the key point. It is closely related to the solution of diffusion equation and plays an important role on the precision of the prediction evaluation.In order to optimize the source intensity generalization and simulate the process of suspended sediment transport during underwater pipeline excavation in a project located in the north entrance of Oujiang River. The paper firstly set up the planar 2D tide and increment suspended sediment numerical model, and by the means of unstructured triangle mesh of finite element method to get the solution. The model was applied to put forward that the source intensity treatment adopts moving points approach, which is compared to the method of some typical fixed points along the excavation route. It discusses the effects brought by the moving points and the fixed points.Numerical model calculation reveals that source intensity, without considering the effects between two points either in the space or on the time continuity, is dealt by the fixed points. It is informed of the isoline independent distribution of the high concentrated suspended matter. The sandy water mostly spread into a small range like an oval-shaped section. While the source intensity dealt by the moving points, it takes combined effects of some proper points into consideration, reaching the ideal that the suspended concentration distribution influence on the whole work. Besides, excavation work is mainly influence the water quality by the long and narrow areas. The farther away from dredger, the better to slow down the speed of the sediments. It generally unfolded the effects to the water quality during the excavation and it is better than the method of fixed points.