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Gravity effect

Posted Apr 19, 2012, 2:03 p.m. EDT Computational Fluid Dynamics (CFD) Version 5.0 13 Replies

Jiri Beranek
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Hi,

Sorry for my newbie question. I'm trying to simulate 2D two-phase flow in porous media. I'm wondering whether COMSOL considers gravity effect when applying Two-Phase Darcy's Law physics.

Thank you,
Jiri
13 Replies Last Post Oct 22, 2015, 8:24 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 19, 2012, 4:17 p.m. EDT
Hi

I'm not by my WS and I'm not using Darcy flow regularly, so I do not know for sure, but if it's possible it must come as a domain boundary load that you must add with a variable of the type "whatever_physics_tag".rho*g_const in the direction that is desired on your model.
As by default COMSOL does certainly not include a "turned on" gravity component, there i no way for COMOSL to know in which direction to apply any load, this is left to the users to define

--
Good luck
Ivar
Hi I'm not by my WS and I'm not using Darcy flow regularly, so I do not know for sure, but if it's possible it must come as a domain boundary load that you must add with a variable of the type "whatever_physics_tag".rho*g_const in the direction that is desired on your model. As by default COMSOL does certainly not include a "turned on" gravity component, there i no way for COMOSL to know in which direction to apply any load, this is left to the users to define -- Good luck Ivar
Jiri Beranek
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Posted: 1 decade ago Apr 22, 2012, 1:21 p.m. EDT
Hi Ivar

Thank you for your quick reply.

There are two physics related to Darcy's law within Porous Media and Subsurface Flow: Darcy's Law (DL) and Two-Phase Darcy's Law (TPDL). The first one has the gravity component that can be literally turned on. Unfortunately, I cannot find anything related to gravity component within TPDL physics. I also noted that DL equations contain a gravity constant while TPDL equations not.

Thank you
Jiri
Hi Ivar Thank you for your quick reply. There are two physics related to Darcy's law within Porous Media and Subsurface Flow: Darcy's Law (DL) and Two-Phase Darcy's Law (TPDL). The first one has the gravity component that can be literally turned on. Unfortunately, I cannot find anything related to gravity component within TPDL physics. I also noted that DL equations contain a gravity constant while TPDL equations not. Thank you Jiri
Sumitava De
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Posted: 1 decade ago Aug 22, 2012, 10:50 a.m. EDT
Hi

I have to include coriolis force and centrifugal force in Darcy's Law. I cannot figure out how to do that. please help. The author mentioned he knows how to include gravity in single phase . if would be helpful if he can tell how he does that.

Thanks

Hi I have to include coriolis force and centrifugal force in Darcy's Law. I cannot figure out how to do that. please help. The author mentioned he knows how to include gravity in single phase . if would be helpful if he can tell how he does that. Thanks
Jinfu Xiao
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Posted: 1 decade ago Aug 22, 2012, 12:25 p.m. EDT
For the structure interface, the gravity is defined in "body force"
For fluid interface, the gravity can be defined in"volume force"
For the structure interface, the gravity is defined in "body force" For fluid interface, the gravity can be defined in"volume force"
Marios Karaoulis
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Posted: 1 decade ago Sep 21, 2012, 1:46 p.m. EDT
I am a little bit confused. Are gravitational effects implemented?
I am a little bit confused. Are gravitational effects implemented?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 21, 2012, 2:32 p.m. EDT
Hi

gravity fores act on the domain as Body or "volume" forces, defined such as "material.rho*g_const" in [N/m^3] along the direction wanted (and g_const is COMSOL's internal name for 9.81[m/s^2] see the doc).

A centrifugal force can be applied the same way but you should then define a cylindrical coordinate frame and use a material.rho*sys2.r*omega^2 where omega is the rotation in as 2*pi*freq[1/s]

material.rho is the density of the active materials, it's a new synonyme to solid.rho or ht.rho ... generic for all physics, check the 4.3 doc


--
Good luck
Ivar
Hi gravity fores act on the domain as Body or "volume" forces, defined such as "material.rho*g_const" in [N/m^3] along the direction wanted (and g_const is COMSOL's internal name for 9.81[m/s^2] see the doc). A centrifugal force can be applied the same way but you should then define a cylindrical coordinate frame and use a material.rho*sys2.r*omega^2 where omega is the rotation in as 2*pi*freq[1/s] material.rho is the density of the active materials, it's a new synonyme to solid.rho or ht.rho ... generic for all physics, check the 4.3 doc -- Good luck Ivar
Marios Karaoulis
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Posted: 1 decade ago Sep 24, 2012, 3:54 p.m. EDT
Thanks Ivar,

I don't see a way to define body or volume forces in this module. All that is included is values for saturation and fluid/matrix properties.

All boundary conditions are related with flux.

Also when I expand the "Equation", I see
u=-k/m grap (P),
while it should be u=-k/m grap (P+rho*g*grad(D)).

Thanks Ivar, I don't see a way to define body or volume forces in this module. All that is included is values for saturation and fluid/matrix properties. All boundary conditions are related with flux. Also when I expand the "Equation", I see u=-k/m grap (P), while it should be u=-k/m grap (P+rho*g*grad(D)).
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 25, 2012, 10:41 a.m. EDT
Hi

you are right, no volume/body force here as in pure DL & TPDL you only solve for pressure, (I'm not often in these physics so I missed that one ;)

But you have it in FP, sh/could you use this one ?

--
Good luck
Ivar
Hi you are right, no volume/body force here as in pure DL & TPDL you only solve for pressure, (I'm not often in these physics so I missed that one ;) But you have it in FP, sh/could you use this one ? -- Good luck Ivar
Sumitava De
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Posted: 1 decade ago Mar 7, 2013, 7:00 p.m. EST
But if we use FP module , then by neglecting inertial term , we can only get down from modified NS equation to Brinkman equation. We can never get to Darcys law as the viscous term will still be there
But if we use FP module , then by neglecting inertial term , we can only get down from modified NS equation to Brinkman equation. We can never get to Darcys law as the viscous term will still be there
GuRu@BFI
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Posted: 10 years ago Mar 4, 2015, 11:34 a.m. EST
I have the same problem.
I want to use Darcy model but there is no volume force option!
Is it possible to add the volume force as weak contribution?
If yes, then how? Can you give the weak contribution expression.

Thanks in advance.
I have the same problem. I want to use Darcy model but there is no volume force option! Is it possible to add the volume force as weak contribution? If yes, then how? Can you give the weak contribution expression. Thanks in advance.
GuRu@BFI
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Posted: 10 years ago Mar 6, 2015, 6:18 a.m. EST
Thanks for the post. I noticed a typing mistake in the equation.
u=-k/m grad(P), when the gravity turned off.
u=-k/m (grad(P)+rho*g). when the gravity turned on (g is gravity vector). This should be manually edited in the equation view...


Thanks Ivar,

I don't see a way to define body or volume forces in this module. All that is included is values for saturation and fluid/matrix properties.

All boundary conditions are related with flux.

Also when I expand the "Equation", I see
u=-k/m grap (P),
while it should be u=-k/m grap (P+rho*g*grad(D)).


Thanks for the post. I noticed a typing mistake in the equation. u=-k/m grad(P), when the gravity turned off. u=-k/m (grad(P)+rho*g). when the gravity turned on (g is gravity vector). This should be manually edited in the equation view... [QUOTE] Thanks Ivar, I don't see a way to define body or volume forces in this module. All that is included is values for saturation and fluid/matrix properties. All boundary conditions are related with flux. Also when I expand the "Equation", I see u=-k/m grap (P), while it should be u=-k/m grap (P+rho*g*grad(D)). [/QUOTE]
Prem Gandhi
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Posted: 10 years ago Apr 15, 2015, 3:12 p.m. EDT
I would like to know how to manually edit the equations because I am not able to find any option to edit the equation. Your help is appreciated.


Thanks for the post. I noticed a typing mistake in the equation.
u=-k/m grad(P), when the gravity turned off.
u=-k/m (grad(P)+rho*g). when the gravity turned on (g is gravity vector). This should be manually edited in the equation view...


Thanks Ivar,

I don't see a way to define body or volume forces in this module. All that is included is values for saturation and fluid/matrix properties.

All boundary conditions are related with flux.

Also when I expand the "Equation", I see
u=-k/m grap (P),
while it should be u=-k/m grap (P+rho*g*grad(D)).



I would like to know how to manually edit the equations because I am not able to find any option to edit the equation. Your help is appreciated. [QUOTE] Thanks for the post. I noticed a typing mistake in the equation. u=-k/m grad(P), when the gravity turned off. u=-k/m (grad(P)+rho*g). when the gravity turned on (g is gravity vector). This should be manually edited in the equation view... [QUOTE] Thanks Ivar, I don't see a way to define body or volume forces in this module. All that is included is values for saturation and fluid/matrix properties. All boundary conditions are related with flux. Also when I expand the "Equation", I see u=-k/m grap (P), while it should be u=-k/m grap (P+rho*g*grad(D)). [/QUOTE] [/QUOTE]
Riz
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Posted: 9 years ago Oct 22, 2015, 8:24 a.m. EDT
Did you find how to apply Body force in Darcy's law

--
Zarghaam
Did you find how to apply Body force in Darcy's law -- Zarghaam

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