Three-dimensional unstructured finite difference and volume model for barotropic coastal and estuarine circulation and application to Hurricane Ivan (2004) and Dennis (2005)

This study focuses on the development and application of three dimensional time-dependant, unstructured grid ocean, coastal, and estuarine numerical circulation model named UFDVM (Unstructured Finite Difference and Volume Model). UFDVM model was developed by combining finite difference and finite volume numerical schemes, taking advantage of the computational efficiency of the finite difference method (FDM), the exact conservation of finite volume method (FVM) and the flexibility of representing complex geometry with an orthogonal unstructured mesh system. The time-explicit Eulerian - Lagrangian Method (ELM) was used to discretize the non-linear advection term, thus removing the CFL condition for stability. To guarantee the conservation of mass, finite volume method was applied to the continuity equation. The propagation term was implemented by a semi-implicit numerical scheme, the so-called theta-method, for numerical stability. UFDVM exploited finite volume numerical scheme in horizontal diffusion term. Because the model used orthogonal unstructured computational grid, much flexibility to resolve complex coastal boundaries was allowed without any transformation of governing equations. The model has ability to treat wetting and drying of land. UFDVM was implemented Z-grid in vertical direction. The equilibrium turbulence model is used to determine the vertical eddy viscosity.;After successful comparisons with analytical solutions, UFDVM was applied to the Hurricane-induced storm surge simulations. Hurricane IVAN (2004) and DENNIS (2005) were simulated and compared between simulated results and real data. The model calculated storm surge elevation during the hurricane events using wind and atmospheric pressure fields produced by sophisticated wind models such as WINDGEN, NCEP WNA, NOAA HRD and Holland analytical wind models. Careful comparison with real measured data, combined WNA and HRD wind field with Holland atmospheric pressure produced best results for the simulations. Maximum inundation maps were produced for both hurricanes and compared with measured High Water Marks (HWM). Significant inundation occurred around Pensacola Bay, FL during Hurricane Ivan. The storm surge elevation of I-10 Bridge over Escambia Bay, FL was high enough to inundate the bridge.;A number of sensitivity simulations were performed to investigate storm surge level by various model inputs such as different types of simulated wind fields, with and without land reduction, air pressure, tides, bottom frictions, open boundary conditions, and different time step. Sensitivity tests revealed the wind fields and bottom frictions were the most important parameters to reproduce correct surge level and inundation compared to measured data. The land effects on the wind fields were tested. Wind fields with limited land reduction produced best results. Overall, the model UFDVM developed in this study simulated Hurricane IVAN and DENNIS efficiently and accurately.