Abstract: In this paper, a three-dimensional hydrodynamic model of Sanmen Bay is constructed. Different mesh scales are set up after comparing and analyzing the calculation results with the measured data, and the tidal current characteristics of three sections and four typical points are analyzed. The results show that: when the study water is a bay with many harbor branches and complex topography, the relative deviation of the numerical simulation value will increase with the mesh scale. When the mesh scale increases to a certain value, the relative deviation will stabilize due to the accumulation of multiple errors. The topography is a key factor affecting the calculation of tidal currents. The tidal range and current velocity values in the inter-tidal waters with drastic topographic changes and small water depths are relatively large, while in the flat areas with large water depths, they are almost unaffected by the mesh scale. The current direction has a low sensitivity to the mesh scale and has no obvious relationship with the mesh scale. The horizontal vortex viscosity coefficient is positively correlated with the mesh area and the mesh area has a greater effect on the current velocity deformation rate S_ij at the larger places. Comprehensive analysis shows that, in the calculation of tidal currents, it is necessary to encrypt the mesh in the shore with complicated topography, inter-tidal zone with small water depth and islands, and to determine the appropriate mesh scale by considering the factors of calculation time, stable convergence of the model calculation and the accuracy of the calculated values, so as to make the calculation results meet the requirements of accuracy.

Key words: three-dimensional hydrodynamic model, mesh scale, tidal wave characteristics, numerical simulation