Development Of An Unstructured Grid Two-dimensional Estuary And Ocean Numerical Model

Numerical simulation plays an important role in scientific research, engineering application, and disaster forecast. Ocean numerical models, as the tool of simulating hydrodynamics of rivers, seas, and oceans on computers, are being well developed. Traditional ocean models usually use rectangular structured grid, which has limited capability of local refinement and coastline fitting, and is hard to fit complex coastlines and project structures in estuaries, bays, and islands. Unstructured grid can be refined at arbitrary local area and fit any coastline, which avoids the flaw of structured grid. Most of the distinguished unstructured grid ocean models in the world now are developed abroad. Domestic models which achieved the international advances are lacked. So there is need to develop an unstructured grid estuary and ocean numerical model with complete proprietary intellectual property rights, which could be further improved to achieve the international advances.In this thesis, an unstructured grid two-dimensional estuary and ocean numerical model is developed. The model uses triangular grid and finite-volume method. It solves elevation at centroid of grid cell, and solves velocities of x- and y- direction at mid-point of grid side. Such architecture needs no horizontal coordinate conversion, which is simple, efficient, and easy to conserve, while it's convenient to address the moving tidal flat. The model uses vertically-integrated two-dimensional control equation set. Continuity equation, momentum equation, and salinity equation are solved by using finite-volume method to guarantee conservation. A control volume of triangular cell is used in solving continuity equation and salinity equation. A rhombic control volume is used to solve momentum, while TVD scheme is used in treating velocity advection to enhance stability. Two methods of solving barotropic force are designed. The first method interpolates elevation first and then solves barotropic in rhombic control volume. The second method constructs 4 control volumes whose vertices are elevation points, calculating elevation gradients by using control-volume, and then averages the elevation gradients. Solving baroclinic is similar to solving barotropic. In solving salinity advection, according to Darwish and Moukalled's experience of constructing TVD advection scheme under unstructured grid, and Li's analysis and improvement to it, a method of calculating upwind r value is designed for the unstructured grid of the model, and TVD advection is constructed based on this r value. Predictor-corrector temporal method is used in the model to promote accuracy of hydrodynamics. A moving tidal flat boundary is included in the model.By an ideal circular lake experiment, the second method of solving barotropic force is proved to be more accurate. The simulated result is highly close to analytic solution. The TVD scheme for salinity advection is tested by an ideal reversing current numerical experiment. Results show that it eliminates numerical dispersion while reduces numerical diffusion. The Superbee limiter would produce artificial sharp gradient. So the Monotonic limiter and Minimode limiter are recommended. The model's hydrodynamics is validated in the Huangpu River, and elevation results are consistent with observed data.The model is calibrated and validated in Changjiang Estuary. Different Manning's coefficients are taken at different areas of the model domain. By simulating the current in Changjiang Estuary in August 2007, the model result is calibrated by comparing with observed elevation, current velocity, and current direction. By simulating the current and salinity in late 2004 and early 2005, the model result is validated by comparing with observed current velocity, current direction, and salinity. The calibration results are good in general. In validation, the current velocity and current direction results are close, but salinity differences are slightly big, which is because three-dimensional saltwater wedge can't be made in a two-dimensional model, and salinity variation is related to initial condition.Though various experiments, calibration, and validation, the conclusion could be drawn that in this model, the calculating method of barotropic force and salinity advection scheme are highly accurate, and the model is applicable in the simulation of estuarine and short sea areas.