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Boundary condition confusion

Tue, 07/24/2007 - 9:00am — Learner
I'm new with the program, and relatively new to hydrodynamic modeling as a whole. Thus, this question should be very easy. While trying to model a situation, I need to select whether the boundary conditions of a branch are external head, external flow, or internal head. However, I have little clue as to what these mean and I can't find the answer anywhere. Could someone let me in on the secret?
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Hydrodynamics
Wed, 07/25/2007 - 4:36pm — Rob

External head condition is when the hydrodynamics of the upstream (US) or downstream (DS) end of a branch are controlled by a head condition such as fixed water level or a time series of water level data. An external flow condition is when the US or DS are set flows, such as a time series of flow data. An internal head is when the US or DS ends of the brnach are connected to another branch in the model and the internal (in the model predicted) head is used to pass water between the branches. I hope this helps. Cheers, Rob
Thu, 07/26/2007 - 9:01am — Learner

Thanks for the help rob. I have another questions regarding tributary temperature. I'm modeling a power plant on a lake, and thus the tributary flow (the power plant's cooling water outlet) is directly dependent on the inlet flow temperature. Is there any way to model this or is the tributary temperature file completely static? ED: If it turns out that there is no way to model this, is it possible to write some code which updates the trib flow temp file with every iteration, adjusting the temperature in relation to the inlet temperature? I'd assume I could do this pretty easily, unless CE-QUAL-W2 takes the file in once and then references back to it, as opposed to reading the value from the file every iteration. Thanks again.
Thu, 07/26/2007 - 11:36am — Rob

Does the power plant discharge (from cooling tower) go directly into the lake or does it go into a cooling pond and then pond dischages to the lake? This will help me inderstand what you mean by "inlet flow temperature". Is this inlet to the lake or the power plant. The tributary temperature file is static, but if you have a cooling pond and know the water temp out of the cooling tower into the pond but no temperature out of the pond then the pond itself could be modeled. You may need to break the description of your project more for me. The model reads in the input files as its simulating so as the model increments to a new time step it checks to see if it needs new informaiton from the input files. I hope this helps.
Fri, 07/27/2007 - 9:28am — Learner

Rob, Thanks again for the help so far. For reference, here is the google map of the location: http://maps.google.com/?ie=UTF8&ll=37.618413,-88.943295&spn=0.011643,0.026994&z=16&om=1 The powerplant is located on the Northwest corner of the Lake of Egypt. If you look on the map you'll notice a pier-structure jutting out ~1000' East-West into the lake in that corner. The power plant's cooling water is dumped directly into the lake (no cooling pond) on the North side of the pier at the furthest West point, and is pulled back into the power plant just South of the outlet, on the other side of the pier. This was done so the water must flow completely around the pier before it has a chance of being used again, thus allowing for a cooler water inlet. Is this clear?
Fri, 07/27/2007 - 10:54am — Rob

Thanks. That helps considerably. So what you could do is model the north side of the pier as one model segment and the south side of the pier as a separate segment. You will also want to make sure the pier influences the bathymetry of the two segments so they do not connect over this length. Another approach would to put in an internal weir. Either way you can have the cooling discharge into the lake as a tributary (static file, flow and temp) and the withdrawal out of the lake as a static flow file but the temperatures would be predicted by the W2 model. Keep in mind the temperature predictions are laterally averaged across the lake so if you need a more detailed temperature regime around the pier you may need to break the model up into several branches (1 br = north of pier West to East until the end of the pier, 2 br = South of pier West to East to the end of the pier, both connected to the main branch of the lake which would run from the South East to the North west). It looks like there are other "branches" that could be separated out for the lake as well. It all depends on how much detail you need. Also keep in mind the additional branches may add to computational cost - longer simulation run times. Hopefully this helps. Rob
Fri, 07/27/2007 - 11:01am — Learner

That's how I currently have the model setup, with 4 branches total modeling roughly the top half mile of the lake. My problem is that the outlet temperature of the cooling flow from the power plant is directly related to the inlet temperature, meaning it can't be drawn from a static file. How hard do you think it would be for someone with decent Fortran experience to code a little program which updates the "static" tributary temperature flow between iterations, drawing its data from CE-QUAL-W2's last iteration? Once again, if that's confusing just let me know.
Mon, 07/30/2007 - 9:06am — Rob

I think it would be relatively straight forward for someone to program the model to update the tribuatry temperature entering the lake dependent on the intake temperature but that assumes you know what the relationship is between the two and whether its dependent on the time of day. If you are interested in having our group look at this I will have Scott read this thread and then contact you off the forum. If you are interested in having our group look at this we can discuss it offline. Are you working for the US Corps of Eningeers?
Tue, 07/31/2007 - 8:02am — Learner

I'm actually acting as my company's guinea pig to see how hard it is to learn/use and its accuracy. The problem is, since I'm the guinea pig, no one else knows how to do it and thus I'm continually bouncing back to the user manual trying to work out my problems. As to the offer, thank you but I don't think we're at that phase yet. I've forfeited the power plant inlet/outlet for the moment and am just trying to work my way through the preprocessor to come up with a valid control file.
Fri, 08/03/2007 - 2:29pm — Rob

Understood