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July 1, 2009, 10:44 
pond depth

#1 
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Johannes Gérson Janzen
Join Date: Jul 2009
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Dear friends,
I have no experience with CFX. I need to simulate the hydrodynamics of stabilization ponds. I am encountering difficulties in defining the water depth in the pond. At the beginning of the simulation the pond must already have some depth of water. How do I do that? Thanks 

July 2, 2009, 03:31 

#3 
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Ali Torbaty
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Location: Sydney, Australia
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you should make some expressions to define volume of water and volume of air through initialisation.
1 define an expression for initial water level, say: InitWatLevel = 2[m] 2 make a step function defining water volume: WatVol = step((InitWatLevel  z)/1[m]) 3 make a step function defining air volume: AirVol = 1  WatVol 4 use WatVol and AirVol expressions in Domain/Initialisation to define volume fraction of each fluid good luck ps. check Tutorial 7: Free Surface Flow Over a Bump 

July 3, 2009, 12:21 

#5 
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The height of the pond should be controlled by outlet weir. Try to find the outlet weir elevation and do a simple math.


July 6, 2009, 16:13 
+ pond depth

#6 
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Johannes Gérson Janzen
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Thanks for the reply.
The pond consists of one inlet pipe and one outlet pipe. The output may be in a position below the inlet. As inlet condition, I'm defining the normal speed. In the pond the conditions are similar as in the manual: h = 2 [m] initialVOFAir step = ((z  h) / 1 [m]) initialVOFWater = 1  initialVOFAir initialP = 998 [kg m ^ 3] * g * (hz) * initialVOFWater As outlet condition, we adopted the normal speed (which equals the speed of entry). What is the error that is being committed? 

July 6, 2009, 16:38 

#7 
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George
Join Date: Mar 2009
Location: Birmingham, UK
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you tell us ...
btw the equation initialVOFAir = step((z  h) / 1 [m]) you forgot to define the air pressure in the pressure initialisation PS if you have multiphase leave one phase volume fraction initialisation as automatic.
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July 7, 2009, 11:02 

#8  
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Quote:
For designing optimization purpose, you may also consider a worst case scenario water level and use it as your modeling base 

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