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Unsaturated Van Genuchten

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Old   August 12, 2014, 20:26
Exclamation Unsaturated Van Genuchten
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Victor Dobrochinski Barbosa
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Hello,

Imīm trying to model a simple model of unsaturated flow using the Van Genuchten model.

However, after setting all the inputs the prepricessor gives me de following error:

***************************************
** fatal error **
** capillary pressure curves not **
** properly defined **
***************************************

Any guess?

Thank you!
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Old   August 13, 2014, 17:49
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Victor Dobrochinski Barbosa
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These are my porous component inputs:

remark='!! Component 1 properties',
opor(1)=0.7,
oadrg(1)=6.38e-12,
obdrg(1)=0.55337,
ofcmn(1)=0.029,
ofcmx(1)=0.366,
iopcfd(1)=1,
iodfit(1)=3,
alphwobs(1)=3503.57,
xnwobs(1)=2.239,
xmwobs(1)=0.366,
itpobs(1)=0,
iaqsrb(1)=0,

Is there anything else I should enter?
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Old   August 14, 2014, 11:32
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Jeff Burnham
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If you have an older version, try adding the following namelist:

&pcap
fpcmx=0.12, remark=' capillarity parameters ',
pcmx=2.62e+4,
pexp=0.5,
/

These parameters are global and should not be used by the solver (since the component parameters you've provided over-write them), but in older versions of FLOW-3D the namelist might still be called and these placeholders will let you run the case better. Try it and let me know if it works. If not, the variable list you need to define for the Mualem drag model + van Genuchten model, and it looks like you might be missing the drying curve coefficients:

ALPHWOBS = wetting curve alpha coefficient in units of pressure
XNWOBS = van Genuchten wetting coefficient, fit from data
XMWOBS = 1 - 1/n = 1 - 1/XNWOBS

ALPHDOBS = drying curve alpha coefficient = ALPHWOBS or fit from data
XNDOBS = XNWOBS or fit from data
XMDOBS = 1 - 1/XNDOBS or fit from data

OPOR = Vpores/Vbulk = 1 - ρ_bulk/ρ_solids
OADRG = OPOR|g|/K_HC = OPOR μ/(k_IP ρ)
OBDRG = m = XMWOBS, or find from linear regression of the data


where

OPOR = volumetric porosity, in FLOW-3D (units of m^3 open/m^3 solid = dimensionless).
OADRG = drag coefficient 'a' of Mualem drag model, a function of saturated flow in the media (units of s^-1).
OBDRG = drag coefficient 'b' of Mualem drag model, a function of unsaturated capillary pressure in the media (dimensionless).
XMWOBS = van Genuchten model wetting coefficient 'n' (see User Manual for equations).
ρ_bulk = bulk density of the media (units of kg media/m^3 media, including solid and pores).
ρ_solids = micro density of the solid component used in the media (units of kg solids/m^3 solids).
|g| = magnitude of gravity (units of m^2/s).
K_HC = coefficient of saturated hydraulic conductivity in units of length (units of m/s),
k_IP = coefficient of saturated intrinisic permeability (units of m^2).
μ = fluid viscosity (units of kg/m/s).
ρ = fluid density (units of kg/m^3)
m = coefficient of Van Genuchten capillary pressure model (dimensionless)
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Old   August 14, 2014, 19:31
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Victor Dobrochinski Barbosa
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Thank you Mr. Burnham! It's running know!

However I'm not sure I understood which was the problem...

Could you explain me what these comands you told me to add are exactly doing?

Again, thank you!
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Old   August 14, 2014, 19:47
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Victor Dobrochinski Barbosa
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Should I paste these commands whenever I want to rerun?
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Old   August 14, 2014, 20:47
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Victor Dobrochinski Barbosa
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My prepin has only:

&PCAP
ivg=1,
/
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Old   August 15, 2014, 15:24
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Victor Dobrochinski Barbosa
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Iīm confused about how flow 3d defines the capillarity pressure.

For example, if I put a water level as initial condition, does it recognize the capillarity pressure on every point of the domain based on the water level?

And what if I want to put a capillarity pressure as boundary condition, to simulate a wetting condition, how do I do that?
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Old   August 15, 2014, 15:54
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There's an unsaturated porous media in the included examples: File > Add Example > Porous Medium Flow. That shows how to use pressure boundaries to make a wet boundary condition. As for the capillary pressure, it's computed in all cells in the porous component. It's based on the fluid fraction in the cell, the history of the cell (wetting or drying) and the capillary pressure curves you defined with the coefficients. Please refer to the User Manual for more detail.
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Old   August 17, 2014, 10:33
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Victor Dobrochinski Barbosa
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Thank you! You helped a lot!
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