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A process-based 3-D hydrodynamic model is established to simulate the rip current structures under irregular bathymetry. The depth-varying wave-induced residual momentum, the surface rollers, the turbulent mixing and the wave-current interactions are considered. Experimental datasets are used to validate the model, and it is shown that the model can effectively describe the 3-D structures of the rip currents in both normal and oblique wave incident cases. The flow patterns of the rip currents see various characteristics for different incident wave directions. In the normal incident case, pairs of counter-rotating primary circulation cells are formed, and an offshore rip flow occurs in the embayment troughs. The peak seaward velocities occur at the top of the bed boundary layer, and the undertow is incorporated in addition to the rip currents. In the oblique incident case, the longshore currents are dominant, which result in a meandering flow along the depth contour, and the undertow is weaker compared to that in the normal incident condition.

A three-dimensional (3-D) numerical model is established to investigate the tidal current motion characteristics around the harbor entrance. Computational approaches consist of the finite difference method, time-splitting technique, C-grid, and a high-order turbulence closure model. The Ocean General Circulation Model (OGCM) inundation scheme is incorporated in the model. An engineering application, Lianyungang Harbor, China, is used as a real-life case. The model is validated by showing that the simulated results agree well with the field data. In the approach channel, the tidal current shows a deflection effect especially in the bottom layer. As for Lianyungang Harbor, a jet flow forms at the tip of the northern breakwater, which drives a circulation flow at the inner side of the harbor entrance. In the vertical, the flow is significantly stratified at the entrance section within the channel, where the flow direction varies between layers and the speed distribution is quite uniform. These 3-D features become less evident to the offshore. Additionally, the sensitivity analysis shows that the flow deflection is related to the channel depth. Simulation results also imply that the siltation rate at the entrance section of the approach channel tends to be more uniform by the 3-D flow motion feature, and could be more significant with the increase of the channel depth.