Subsea hole release boundary condition problems

dotapro · March 22, 2015, 04:36

Dear all, I'm trying to model methane gas released from a hole up to sea surface. My domain is 50mx50mx103m rectangular size while my hole size is 0.254 m diameter exactly in the middle of domain. Could someone help to verify my boundary conditions especially for sea outlet and sea surface as shown below:
Hole release: Inlet (3kg/s mass flow rate)
Sea water inlet: Inlet (1.5 m/s)
Sea bed: Wall
Sea water left & right sides: Symmetry
Sea water outlet: Outlet (0 Pa static pressure) or Opening (0 Pa) (Can anyone verify it?)(Should I change pressure to pgh instead of 0 Pa?)
Sea water surface: Outlet (0 Pa static pressure) or Opening (0 Pa) or Wall (Can anyone verify it?)

I know it is simple problem setup but I'm confused about it. Any help will be much appreciated.

ghorrocks · March 22, 2015, 04:51

You have not explained what you are trying to learn from the simulation, so cannot say what are suitable boundary conditions. But what you describe sounds OK for most applications.

If you activate buoyancy and use a buoyancy reference density equal to your water phase then the pressure boundaries will have the static head removed - so no need to include the rho*g*H bit.

dotapro · March 22, 2015, 05:05

I'm trying to measure the plume height and plume diameter on sea water surface. However, I'm getting overflow error from CFX which I want to make sure whether my boundary conditions are correct or wrong first before modifying my meshing? Again, is it better to use pressure outlet or opening in this case ?

ghorrocks · March 22, 2015, 05:19

That sounds like a complex simulation.

How can you model plume height on the surface when you are modelling the surface as a wall,opening or outlet?

dotapro · March 22, 2015, 05:37

Alright, I try to measure plume height (gas release from hole up to sea water surface if it has enough "energy" to reach topside) as well as plume diameter ( if gas pool can be formed on sea water surface if it has enough "energy" to reach topside). Plus, I hope no liquid will be leaving at sea water surface and only gas is allow to leave .

ghorrocks · March 22, 2015, 05:45

I have no experience in the sort of modelling you are talking about so I do not know what you define as the plume height or diameter. Can you show an image which shows what you are trying to measure?

March 22, 2015, 04:36	Subsea hole release boundary condition problems	#1
dotapro Member Join Date: Oct 2013 Location: Malaysia Posts: 39 Rep Power: 13	Dear all, I'm trying to model methane gas released from a hole up to sea surface. My domain is 50mx50mx103m rectangular size while my hole size is 0.254 m diameter exactly in the middle of domain. Could someone help to verify my boundary conditions especially for sea outlet and sea surface as shown below: Hole release: Inlet (3kg/s mass flow rate) Sea water inlet: Inlet (1.5 m/s) Sea bed: Wall Sea water left & right sides: Symmetry Sea water outlet: Outlet (0 Pa static pressure) or Opening (0 Pa) (Can anyone verify it?)(Should I change pressure to pgh instead of 0 Pa?) Sea water surface: Outlet (0 Pa static pressure) or Opening (0 Pa) or Wall (Can anyone verify it?) I know it is simple problem setup but I'm confused about it. Any help will be much appreciated.

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March 22, 2015, 04:51		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	You have not explained what you are trying to learn from the simulation, so cannot say what are suitable boundary conditions. But what you describe sounds OK for most applications. If you activate buoyancy and use a buoyancy reference density equal to your water phase then the pressure boundaries will have the static head removed - so no need to include the rhogH bit.

March 22, 2015, 05:05		#3
dotapro Member Join Date: Oct 2013 Location: Malaysia Posts: 39 Rep Power: 13	I'm trying to measure the plume height and plume diameter on sea water surface. However, I'm getting overflow error from CFX which I want to make sure whether my boundary conditions are correct or wrong first before modifying my meshing? Again, is it better to use pressure outlet or opening in this case ?

March 22, 2015, 05:19		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	That sounds like a complex simulation. How can you model plume height on the surface when you are modelling the surface as a wall,opening or outlet?

March 22, 2015, 05:37		#5
dotapro Member Join Date: Oct 2013 Location: Malaysia Posts: 39 Rep Power: 13	Alright, I try to measure plume height (gas release from hole up to sea water surface if it has enough "energy" to reach topside) as well as plume diameter ( if gas pool can be formed on sea water surface if it has enough "energy" to reach topside). Plus, I hope no liquid will be leaving at sea water surface and only gas is allow to leave .

March 22, 2015, 05:45		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	I have no experience in the sort of modelling you are talking about so I do not know what you define as the plume height or diameter. Can you show an image which shows what you are trying to measure?