The Numerical Solutions Solution Option tab in the Hydrodynamics Options form provides provides access to several of the numerical solutions schemes available in EFDC. The 2-Time Level and 3-Time Level solutions are primary, as shown in Figure 1. The standard case for Buoyancy Forcing is the Internal Pressure Gradient option. Other options can still be set in the EFDC.INP file if the user wants to make such a change, but they should understand the options and ensure the sub-models selected are correct if they make a change.
The solution schemes available with EFDC_GVC are Standardized (0), Ordered R/B Conjugate gradient (2), Reduced R/B Conjugate gradient (3), and Conjugate gradient for Wetting and Drying (9). The Internal Buoyancy forcing option must be specified.The 3 3-Time Level (3TL) or 2-Time Level (2TL) options allow the user to select the method to be used for numerical simulation. 2TL allows for domain decomposition, and therefore, applications that can use the MPI approach will benefit from this option. If using the EFDC_GVC model with GVC layering, the only Time Level solution available is the "3 Time Level"the 3TL. With the coming EEMS12, 3TL will be available for models with domain decomposition. However, the 3TL option can still be used effectively for certain lakes, and due to the self-correcting trapezoidal step approach used by the 3TL option, a much larger time step (delta T) can be used, which allows for much faster model simulation.
If using the 3TL option, the user must specify the momentum solution option Momentum Options (ISCDMA). Upwind Difference is the recommended momentum advection scheme. Central Difference and Experimental Upwind Difference (ISCDMA>2) are experimental, not fully tested, and not currently recommended to be used. The Trapezoidal Correction Scheme is typically set from 3 to 5, and 4 by default.
The 2TL solution is the most robust solution technique and supports domain decomposition. It is the recommended approach for the vast majority of modeling applications.
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Figure 1. Numerical Solutions Solution Option tab.