# BC Problems/Confusions

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 February 18, 2005, 05:11 BC Problems/Confusions #1 Shazlan Guest   Posts: n/a Hi all, I need to analyze a toiletbowl. The problem is in setting the boundary regions. The inlets, where the water is flushed into the bowl, is okay - at least, that's what I think. The outlet is located just after the siphon. The problem is on how to indicate the open area (where our butt is). I was thinking of using pressure BC, since it is subjected to atmospheric pressure and temperature, but pressure and outlet BC cannot co-exist. How do I 'tell' star-cd that the area, which consist of atmospheric air? or in other words, how do I go about approching this problem. I am assuming that toiletbowl is quite common that everybody knows the general geometry and concepts on how it works. Your help is highly appreciated!

 February 19, 2005, 13:04 Re: BC Problems/Confusions #2 Ted Crilly Guest   Posts: n/a as far as i can remember i'm sure pressure and outlet can co-exist in the same model/domain, the outlet has to be fixed, ie. 1.5 kg/s not split (0.5) etc, so choose a fixed outlet with the flowrate that you know and specify it, then use pressure boundary with pressure details / atmospheric etc it should work fine, just make sure not to use split option of outlet ted crilly

 February 21, 2005, 04:35 Re: BC Problems/Confusions #3 Shazlan Guest   Posts: n/a Thanks for your comment. However, the flow rate at the outlet is not fixed and not known a priori - it is hope to know the value from the analysis. How else can I incorporate the atmospheric details in my analysis? Please advice.

 February 22, 2005, 03:52 Re: BC Problems/Confusions #4 Ted Crilly Guest   Posts: n/a hi , i would have thought the volume/mass of water is fixed, for example if your toilet has a 15Litre cistern, and it flushing in 15 seconds etc. This could be setup as a fixed outlet boundary @ 1 litre/second. You other alternative i believe would be to use multiple pressure boundaries, if your flows are not fixed, you would need accurate pressures though to predict the flows correctly etc -ted crilly

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