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Results at Junctions

Tue, 11/11/2008 - 7:41pm — Michael
I am modelling a lake which has a main spine and four connecting fingers. I would have expected that the results at the downstream end of a finger (where it connects to the main spine) would be very similar to the results in the main spine of the lake at that junction. But the results (for the density of a generic constituent) are quite different. This occurs at the downstream end of all four fingers. Why aren't the results on either side of each "junction" siimilar?
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Hydrodynamics
Wed, 11/12/2008 - 10:33am — chris

Michael, It's hard to say without knowing more about the system and your model. One possibility is that the residence time of the arms could be much longer than the main stem, with the majority of the flow passing through the main stem and the branches are back-waters. If you haven't already done so, it would be a good idea to turn on the internal mass, energy, and volume balances (turn on VBC, EBC, and MBC in the control file). The output for the balances are written to the snapshot file output, so you'd have to turn on that output option also. This will let you know if the model is conserving mass and energy. chris
Wed, 11/12/2008 - 6:12pm — Michael

Hi Chris The % errors are all extremely small (E-10). The main spine of the lake is about 1 kilometre long, whereas the fingers are about 100-400 metres. The length of my segments are not very long - only 20-50 metres. The results at consecutive segments in the main spine are "similar", showing a gradual change in concentration as you move up the lake. The results at consecutvie segments within the fingers also show a gradual change in concentration. It is only at the junctions where a large difference occurs, between the finger and the lake. There is no inflow at the usptream end of any of the fingers or the main spine. The only inflow is a tidal variation at the dowsntream end of the main lake.
Thu, 11/13/2008 - 4:10pm — chris

Michael, How different are the concentrations in the fingers compared to the main stem? Are the concentrations in the fingers near the initial condition values? If you want, you can send me your model (bergerc@cecs.pdx.edu) and I can take a quick look and make sure your model is working ok. Just send me the input files. chris