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Old   December 9, 2013, 11:16
Exclamation urgent problem : fluid height
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ouni firas
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Dear experts :

I am trying to simulate a flow through a labyrinth weir. I put a condition to limit the left limit Xmin specific pressur (fluid height = 5.34 m) for X max It was puted as an overflow, Ymin Ymax & & Zmin Were puted as a Wall, Zmax WAS puted as symmetry , the initial condition for the fluid height was 5.34m. after completing the simulation OF RESULTS are shown in figures, the problem is that the height of the fluid does not remain constant, but for the example Weir height the fluid remains constant. i want to know how to have an initial height of fluid constant for all time
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Old   December 9, 2013, 11:47
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It sounds like you set it up right, just like the Example simulation (Flow Over a Weir). Did you make an initial fluid region for fluid at t = 0? You should do that as well to speed up the time to steady state. After you do that, check your boundary conditions again and make sure they're what you described, because they sound correct. Good luck.
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Old   December 9, 2013, 11:55
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Dear Jeff Burnham

I did not understand the initial fluid for fluid region at year t = 0. I have a condition that limits Xmin I put as specific pressur (Fluid height = 5.34m) and I created a fluid Region with ZLow = 0 and Zhight = 5.34m. i did not Understand the initial fluid for fluid Region at year t = 0.

Thanks greatly
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Old   December 9, 2013, 12:00
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An initial fluid region is the same. It is fluid location at t = 0. Check that you have Gravity physics active, and that gz is negative (pointing downward), e.g. gz = -9.81 (if you're using SI units).
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Old   December 9, 2013, 12:32
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yes i use the SI and gz = -9.81 . for the Xmax wich is puted as Outflow, can it cause a problem? In the exemple (Weir) I found this remark in the '' &bcdata'' : pbctyp=1.0, remark='specified boundary p=0.0 is stagnation pressure' AND fbct(1,5)=0., remark='no fluid below bottom boundary', . do you think that they have any influence in this problem

thank you greatly .
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Old   December 9, 2013, 13:26
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Outflow boundaries are only correct when Froude number Fr > 1 (supercritical flow) at the boundary. If flow is subcritical (Fr <= 1), then Outflow will drain out the flow, so use a pressure-type boundary instead, with stagnation option checked and specified fluid elevation.
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Old   December 9, 2013, 18:17
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thank you greatly

Mr Burnham do you think that the lenght of the chanel influence in the initial condition because this problem appear just with the channel wich has 100m as a lenght ?
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