While running temperature model in HEC-RAS, my model went unstable due to advection diffusion calculation instability. HEC-RAS uses QUICKEST-ULTIMATE scheme for water quality modelling. Can anyone shed any light regarding this problem? Also what algorithm HEC-RAS follows for solving advection diffusion equation in temperature model?
Dear Nushrat
Usually software models get unstable solution which embarrasses the researcher.
Pleases I advice you to solve the heat transfer partial differential equation numerically and then write a simple program in FORTRAN language to simulate your results. If it is difficult, I can help you.
best regards
Almost the unstablity of such models are the relation between the values of dispersivities and grids size and the velocity values. In other words the convective pi term value compared with the dispersion pi term value. The dispersion term value => the convection term
Dear Nushrat
If u use DEM raster image u must increase the resolution to (e.g. 5*5m2) or less . This is to prevent the reverse slope. And if u didn’t has such image , u must modify the slopes or the elevations of the flow field to prevent reversing flow.On the other hand, the grid size must be suiable to prevent numerical dispersion.
Dear Nushrat Yeasmin
Most instabilities in mathematical model solution is the boundary conditions of the model domain.
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