Numerical tidal current modeling using fine boundary-fitted grids for tidal flats

Fine grids with small spacing in; boundary-fitted coordinates are normally used to treat the computation of fluid dynamics for estuarine areas and tid al flats. However, the adoption of Cartesian components of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a dif ficulty in solving implicitly the transformed momentum equations, and also complicate the wet-dry point judgement used for flood areas. To solve this problem, equations in terms of generalized contravariant velocity vectors i n curvilinear coordinates are derived in the present study, by virtue of wh ich, an Alternative-Direction-Implicit numerical scheme in non-orthogonal g rids would then be easily obtained, and wet-dry point judgement would as we ll be largely simplified. A comparison is made between the explicit scheme and implicit scheme, showing that the present model is accurate and numeric ally stable for computations of fluid dynamics for estuarine areas and tida l flats.