Initialization problem in open channel flow simulation

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April 11, 2015, 08:18
Initialization problem in open channel flow simulation
#1
Senior Member

Sangwoo Kim
Join Date: Jul 2014
Location: Seoul, South Korea
Posts: 112
Rep Power: 7
Hi all.

I'm analyzing a propeller in a tank. I attached simple schematic figure.

Behind the propeller is a pipe, so air will be sucked because of a negative pressure there and rise to the surface.

I made a field function for a hydrostatic pressure distribution
--> hydro distribution = (\$\$Position[1]<=1)?{\$\$DensityofWater}*9.81*(1-\$\$Position[1]):0 (i.e. reference altitude is y=1.0m and gravity acts along -y direction)

Problem is that I can not initialize the hydrostatic pressure. star-ccm+ gave me an error.
"Unable to compute field function a hydrostatic pressure on "region", Please check that function is defined here"

If I don't initialize the pressure, then hydrostatic pressure distribution should be calculated in solver and it will take too long, and it didn't even converge.

I'm using MRF and multiphase - VOF.

Attached Images
 figure.jpg (31.7 KB, 38 views)
__________________
Best regards

 April 13, 2015, 16:35 #2 Senior Member   Matt Join Date: Aug 2014 Posts: 797 Rep Power: 12 I have have seen it do something similar resulting from poorly defined region names that had extra '.' separators in the region name. So if I had a region named 'Region' and a boundary named 'Boundary One' I named it as 'Region.Boundary.One' So it was looking for a region boundary named Boundary not Boundary.One. It doesn't appear that this is your problem though. I will say that it looks like maybe your DensityofWater field function maybe defined or called wrong. Perhaps I am mistaken, but I thought that a double \$\$ is for a vector, not a scalar. Also, have you tried expert initialization (grid sequencing)? That has cut (literally) days off my analyses in the past. It isn't always appropriate, but when it works it works well.