# BC problem: modelling ground as a porous material

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March 17, 2012, 14:25
BC problem: modelling ground as a porous material
#1
New Member

CH. Lee
Join Date: May 2010
Location: Seoul, Republic of Korea
Posts: 5
Rep Power: 9
Hi,
As shown in the attached figure, ground and well is modeled (axisymmetric) as a porous material using laminar flow, energy equation and some UDF for the porous resistances. There is only one phase (water).
Because of ground water flow from the outside boundary, I choose the pressure inlet BC for the outside and bottom boundary (upper boundary is modeled as a wall).
: 1 velocity inlet, 1 outlet at well surface. porosity = 1 in the well, porosity < 1 in the ground.

Q1: To model the hydrostatic pressure due to the gravity, I checked the gravity box and specified operating density (=0). In that case, I can see a pressure distribution with depth direction. However, if I use 998.2 kg/m3 as the operating density, can I get pressure head through the analysis? Because, in this case, pressure = 0 at the whole domain from the result.
[gradient of groundwater flow is calculated in the total head difference in the aspect of groundwater. total head = potential head (due to the gravity, location) + pressure head + dynamic head (in most cases, = 0) ]

Q2: For the outside and bottom boundary, I used a gauge pressure = 0 at boundaries. Is that reasonable?
I can see many reverse flow faces in this case at the pressure inlet boundary with operating density = 998.2 kg/m3.
Also, I've tried to give a reverse pressure to the boundary for the equal pressure in the ground using simple UDF ( (height - location) * 998.2 * 9.81 ). This is for the equal pressure at the boundary to model pressure head.
How can I model the pressure which is only due to the pressure head not static pressure? Any suggestions?

Thanks
Attached Images
 Fig.png (12.6 KB, 22 views)

Last edited by cryfreer; March 17, 2012 at 19:58. Reason: correcting

 March 17, 2012, 19:54 #2 New Member   CH. Lee Join Date: May 2010 Location: Seoul, Republic of Korea Posts: 5 Rep Power: 9 Problem solved using UDF, Thanks Last edited by cryfreer; March 18, 2012 at 05:22.

March 19, 2012, 02:14
#3
New Member

Abdul Halim
Join Date: Mar 2012
Posts: 5
Rep Power: 7
Quote:
 Originally Posted by cryfreer Hi, As shown in the attached figure, ground and well is modeled (axisymmetric) as a porous material using laminar flow, energy equation and some UDF for the porous resistances. There is only one phase (water). Because of ground water flow from the outside boundary, I choose the pressure inlet BC for the outside and bottom boundary (upper boundary is modeled as a wall). : 1 velocity inlet, 1 outlet at well surface. porosity = 1 in the well, porosity < 1 in the ground. Q1: To model the hydrostatic pressure due to the gravity, I checked the gravity box and specified operating density (=0). In that case, I can see a pressure distribution with depth direction. However, if I use 998.2 kg/m3 as the operating density, can I get pressure head through the analysis? Because, in this case, pressure = 0 at the whole domain from the result. [gradient of groundwater flow is calculated in the total head difference in the aspect of groundwater. total head = potential head (due to the gravity, location) + pressure head + dynamic head (in most cases, = 0) ] Q2: For the outside and bottom boundary, I used a gauge pressure = 0 at boundaries. Is that reasonable? I can see many reverse flow faces in this case at the pressure inlet boundary with operating density = 998.2 kg/m3. Also, I've tried to give a reverse pressure to the boundary for the equal pressure in the ground using simple UDF ( (height - location) * 998.2 * 9.81 ). This is for the equal pressure at the boundary to model pressure head. How can I model the pressure which is only due to the pressure head not static pressure? Any suggestions? Thanks
excuse me sir, I'm also working in porous media, but I can't definite it. May be can you help me? my email is abdulhalim060189@yahoo.co.id

 Tags boundary condition, porous media

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