# hydrostatic pressure boundary problem

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 February 23, 2012, 02:02 hydrostatic pressure boundary problem #1 New Member   Join Date: Jan 2011 Posts: 10 Rep Power: 6 I am simulating a open channel flow with wave coundary condition. I set the out let bc as a hydrostatic BC, which is defined as p=rou*g*h (CFX expression as: waterDen*g*(waterD-y) where waterD is the water depth and the waterDen is the water density) but since the free surface in the channel is moving up and down, the water depth is changing according to the wave profile as a function of time. How can I define the waterD correctly and avoid back flow? Thanks!

 February 29, 2012, 21:57 #2 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 487 Rep Power: 10 I've never attempted this, so this might be stupid. Just a thought. Define an expression for instantaneous water height: Instantaneous Outlet Water Height = (areaAve(VolumeFractionWater)@Outlet) / (Total Outlet Height) You probably already have, but if not, look at the "flow over a hump" tutorial, it may help.

 March 2, 2012, 09:46 #3 Senior Member   Join Date: Jul 2011 Location: Berlin, Germany Posts: 120 Rep Power: 6 I would just replace your " waterDen*g*(waterD-y)" by the original formula rho*g*height in terms of CFX variables it would be "density*g*y" or whatever your height coordinate is. I hope someone will correct me if I am wrong. But to my knowledge writing it like this using the "density" variable would force CFX to use the density existing at the considered height...so you wouldn't have to mind about varying water levels...and having the same BC on the "air side" shouldn't cause any problem....

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