| In the northern part of our country, the aquaculture areas are mainly concentrated in the coastal areas of Liaoning province, which is the most representative of the aquaculture area in Liaoning province. Zhuanghe sea is located on the coast of Liaodong Peninsula, east to Dalian Dandong, west to Dalian, which is a typical open sea. The tide of Zhuanghe coastal water is irregular semidiurnal tide, where M2 is the main component, the properties of tidal current is reciprocating flow. At present, the water body of the Zhuanghe sea is facing many problems: on the one hand, there are too many pollutants discharged from estuary and near shore, which restricts the development of mariculture; on the other hand, a part of artificial feeding casting is for biological growth, the remaining part enters into the aquaculture water, while the excretion of biological organisms in the form of ammonia and phosphate is released into the water, accumulated at the bottom of the breeding area, resulting in the pollution of the breeding area. The discharge and deposition of pollutants in aquaculture area can cause eutrophication of water body and the deterioration of water quality, which can also lead to imbalance, disorder and even complete collapse of aquaculture ecosystem. As far as the present, the water exchange capacity of the aquaculture area has not been fully studied, so the study of the sea water exchange capacity has important practical significance.In this paper, the mathematical model of the depth averaged two-dimensional implicit hydrodynamic model is developed. The model is based on the unstructured quadtree rectangular grid, the finite volume method is used to discrete the control equations. Fluxes at cell faces are determined using the Rhie and Chow’s momentum interpolation method to avoid spurious checkerboard oscillations. The SIMPLEC method is derived for water level correction equations, the discretized algebraic equations are solved iteratively using the GMRES method with ILUT preconditioning for speeding the computation.Based on the hydrodynamic model, the model of contaminant transport and diffusion is established by Lagrange particle tracking method. The model is used to simulate the hydrodynamic process in Bohai sea, the results show that the model can well simulate the hydrodynamic forces in the coastal area. The full implicit scheme is used in this numerical example, and its time step is up to 1800 s, the results indicate that the time step of the implicit scheme is not dependent on the condition of CLF. In order to verify the Lagrangian particle tracking module, oil film transport path and diffusion of ideal harbor square are calculated under the combined action of wind and current, the simulated results of the dynamic transport and diffusion process are almost same with that of Tkalich. Further application of Lagrange particle trajectory is carried out to simulate the movement of pollutants of aquaculture waters in Zhuanghe.The three-dimensional ECOMSED flow model is used coupled with the conservative Lagrangian particle tracking module in this paper. The hydrodynamic model of this model is an approximate model of the original equation of three-dimensional oblique compression, which is based on static pressure and Boussinesqhypothesis. The free sea surface and the horizontal grid adopt the curvilinear-orthogonal coordinate system, the sigma coordinate is used in vertical direction. Spatial variable configures apply Arakawa-C format; the 2.5 order turbulence closure model is used to calculate the vertical mixing and diffusion coefficient, the horizontal turbulent viscosity and diffusion coefficient are calculated based on Smagorinsky parameterization method. Explicit format is used in the horizontal direction, vertical direction by using the implicit format. Firstly the three-dimensional ECOMSED model is used to simulate the wind-driven flowof Sailimu Lakel, the flow is consistent with the overall meet the requirements of calculation, the desired effect can be obtained.It can be also used to simulate the hydrodynamic changes of the North Yellow Sea Zhuanghe aquaculture area. By comparing the simulation results of the water level, velocity and flow direction of the two measurement point, the ideal results can be obtained and the reliability of the model can be verified. At the same time, the trajectory and migration of the conservative particles in the region are calculated and analyzed. The research results show that the residual current directions of spring and neap tides are basically the same, the tide residual current of flood tide is significantly greater than that of the neap tide, there is a tide residual current from the northeast to the southwest in the nearshore water, a tide residual currentfrom the southwest to the northeast for outside sea. There is a big difference of particle trajectories at different locations around the small Changshan Islands and Rock Island, indicating that the water exchange capacity varies from region to region. In culture area, trajectory of the particles is whole to eastward, and the smaller part is transported to the southwest, which is consistent with the distribution of the residual current. |
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