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Showing content with the highest reputation on 03/17/2011 in all areas

  1. Hi! I have a beginners question about the wetting/drying in RMA2. I am about to model a planned artificial lake here in northern Finland and did generate the mesh for the planned area. To examine the mesh quality I withdrew water from the mesh (single material) with BQ card to empty (and later fill) the lake. All worked fine during the withdrawal and the water elevation decreased at the rate calculated by BQ discharge and surface area information. However, as I try to fill the lake by changing the BQT value to positive, the solution sooner or later diverges. I have tried different values for diffusion (direct assignment and Peclet), roughness coefficient (direct and automatic assignment), DE card depth limits etc. without success. To see if the divergence had something to do with bottom topography, I created a simple geometry with parabolic depth distribution. The same problem however applies to this geometry as well. During the rewetting, the solution diverges. Sometimes I manage to run the simulation through but the water level does not rise as it should. At the perimeter of the wet area the grid cells simply switch back and forth between wet and dry and the water elevation remains much the same. The simplified model is 10x10 km (some 6.2 by 6.2 miles) and has maximum depth of 10 m (30 ft) at the centre. The elements are quadrilateral 25x25 ( 400 metre grid spacing, tried also with refined grid of 200 m spacing). I calculate first 300 hours with BQT value of -8.8E-6 and from 300 to 600 hours with +8.8E-6. At 300 hours the water elevation has dropped from the initial +0.5 m to -8.9 m but only rises by approximately one meter (to -7.8m) by the end of the simulation. I would be grateful if you had time to help me with this problem and tell which factors I should consider. It must be something simple I'm missing here. I am ready to send the necessary files of the simplified problem when needed. Yours, Heimo
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