Development of computationally efficient nested hydrodynamic models
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Hydrodynamic numerical modelling of coastal zones typically requires a high level of horizontal spatial resolution to improve the realism of its solution, particularly in areas of complex bathymetry. These high resolution models result in high computational costs. One solution to this spatial resolution problem are nested models, which reduce computational needs by embedding a high resolution grid into a low resolution grid, that covers the entire model domain and the two grids interact with each other. A one-way nesting technique in the numerical model DIVAST was expanded by introducing two novel approaches to further reduce its computational effort and to in-crease the applicability and flexibility of the model. These features included the generation of irregular geometry boundaries and the transformation of the nested domain into a rotational coordinate system to allow the orientation of the model to be modified. A two-way nested modelling technique was developed to simulate tidal hydraulics in coastal zones. This technique enabled high resolution data in the nested domain to be transmitted to the low resolution domain. To the Author's knowledge this is the first two-way nested model that incorporates ghost cells that enables the formulation of the nested grid open boundaries as internal boundaries. Tidal turbine farms of different array configurations were incorporated into the two-way nested model, and possible changes in the tidal regime were identified with the use of the Linear Momentum Actuator Disc Theory. To the Author's knowledge this the first type of two-way nested modelling procedure that simulated the effects of tidal turbines. The model was extensively tested in a real coastal system. Results showed the two-way nested model can produce an accurate high resolution solution in areas of interest. and improve the realism of the solution in the low resolution coarse domain for a much lower computational effort than the standard single grid high resolution model. Applications of such a technique are applicable in sediment transport modelling, wave modelling, flood modelling and identifying possible environmental impacts of tidal turbine farms.