# Boundary conditions problem

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 May 25, 2014, 09:23 Boundary conditions problem #1 New Member   Pieter-Jan Join Date: May 2014 Posts: 9 Rep Power: 4 Hey guys! I'm making a model in Flow 3D, about the final stages of placing a GBS on the seafloor (1.5m above seabed till 0m above seabed). The total height of my model is 2 m sand + 1,5m water height + GBS. The z=0 line is at the surface of the sand. I have some problems with my boundary conditions, and with my initial state. t this moment, the initial state does NOT contain water, how can I fix this? I have a circular mesh, with the following boundary conditions: - zmin (z=-2m) wall - zmax (z=4m) pressure (equal to 50m water depth) - xmin pressure (fluid fraction = 1, fluid elevation = 50, no specified pressure) - xmax = same as xmin - ymin = same as xmin - ymax = same as xmin My initial conditions are: - pressure: hydrostatic - fluid initialization: fluid elevation = 0 Can anyone please help me? I tried the manual, but I find it quite confusing Thanx!

May 25, 2014, 21:49
#2
New Member

Sugonghak PC Bang
Join Date: Feb 2014
Posts: 18
Rep Power: 4
Quote:
 Originally Posted by pj6620 Hey guys! I'm making a model in Flow 3D, about the final stages of placing a GBS on the seafloor (1.5m above seabed till 0m above seabed). The total height of my model is 2 m sand + 1,5m water height + GBS. The z=0 line is at the surface of the sand. I have some problems with my boundary conditions, and with my initial state. t this moment, the initial state does NOT contain water, how can I fix this? I have a circular mesh, with the following boundary conditions: - zmin (z=-2m) wall - zmax (z=4m) pressure (equal to 50m water depth) - xmin pressure (fluid fraction = 1, fluid elevation = 50, no specified pressure) - xmax = same as xmin - ymin = same as xmin - ymax = same as xmin My initial conditions are: - pressure: hydrostatic - fluid initialization: fluid elevation = 0 Can anyone please help me? I tried the manual, but I find it quite confusing Thanx!
Add fluid at initial stage (t=0)

 May 26, 2014, 01:41 #3 New Member   Pieter-Jan Join Date: May 2014 Posts: 9 Rep Power: 4 Thanx for your reply, but how do i do that?

May 26, 2014, 04:06
#4
New Member

Sugonghak PC Bang
Join Date: Feb 2014
Posts: 18
Rep Power: 4
Please check as per attached.
Attached Images
 initial.jpg (30.2 KB, 37 views) fluid.png (19.0 KB, 32 views)

May 26, 2014, 04:09
#5
New Member

Sugonghak PC Bang
Join Date: Feb 2014
Posts: 18
Rep Power: 4
Quote:
 Originally Posted by pj6620 Thanx for your reply, but how do i do that?
I supposed you have added the fluid region right? but how can you not seen any water? hmm...

 May 26, 2014, 04:51 #6 New Member   Pieter-Jan Join Date: May 2014 Posts: 9 Rep Power: 4 Thanx for your reply! When I FAVOR my model, I get fluid now! But, I still think there is a problem with my Boundary conditions, since my solver gets the following error: pressure iteration diverging - restarting cycle with smaller time-step size excessive pressure convergence failures Or is this due to something different? (I changed my ymin and ymax to S, since I found in the manual: Axisymmetric calculations without swirl (azimuthal flow) call for symmetry-plane boundary conditions on the Y Min and Y Max boundaries.)

May 26, 2014, 20:35
#7
New Member

Sugonghak PC Bang
Join Date: Feb 2014
Posts: 18
Rep Power: 4
Quote:
 Originally Posted by pj6620 Thanx for your reply! When I FAVOR my model, I get fluid now! But, I still think there is a problem with my Boundary conditions, since my solver gets the following error: pressure iteration diverging - restarting cycle with smaller time-step size excessive pressure convergence failures Or is this due to something different? (I changed my ymin and ymax to S, since I found in the manual: Axisymmetric calculations without swirl (azimuthal flow) call for symmetry-plane boundary conditions on the Y Min and Y Max boundaries.)
Then, set a smaller time-step. LOL

 June 2, 2014, 03:42 #9 New Member   Pieter-Jan Join Date: May 2014 Posts: 9 Rep Power: 4 Thanx for your detailed info Jeff! Unfortunately, that didn't work either, so I made a Cartesian mesh. The solver works, but I have another problem now (erosion related), I'll make a new thread for that, since it has nothing to do with this problem.

June 4, 2014, 05:15
Inform
#10
New Member

Zohaib
Join Date: Jun 2014
Posts: 2
Rep Power: 0
Hello Mr:

change your boundaries conditions like x min = specfice pressure have fluid fraction is 1 & fluid height = your required height,
X max = outflow, y min, y max, z min = wall & last z max = specified pressure haveing fluid fraction is zero. then run the model.
Quote:
 Originally Posted by pj6620 Hey guys! I'm making a model in Flow 3D, about the final stages of placing a GBS on the seafloor (1.5m above seabed till 0m above seabed). The total height of my model is 2 m sand + 1,5m water height + GBS. The z=0 line is at the surface of the sand. I have some problems with my boundary conditions, and with my initial state. t this moment, the initial state does NOT contain water, how can I fix this? I have a circular mesh, with the following boundary conditions: - zmin (z=-2m) wall - zmax (z=4m) pressure (equal to 50m water depth) - xmin pressure (fluid fraction = 1, fluid elevation = 50, no specified pressure) - xmax = same as xmin - ymin = same as xmin - ymax = same as xmin My initial conditions are: - pressure: hydrostatic - fluid initialization: fluid elevation = 0 Can anyone please help me? I tried the manual, but I find it quite confusing Thanx!

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