Material Parameters of Porous Domain as Variable?

mapeth · December 13, 2014, 11:15

Hello everybody,

I'm working on a flow problem in a porous domain for a while. The domain is a thick walled cylinder with a pressure gradient from the inside to the outside. It consists of a silica matrix partially filled with ice. At a certain pressure the ice starts melting, where the actual flow simulation begins. The melting is implemented by sources.

Now about my problem(s). As the ice melts, the porosity and permeability of the domain changes in reality. This is where I struggle. I can't make the porosity and permeability dependent on the amount of molten ice. Actually I can't make it dependent on anything! Whether Ansys ignores the change or gives me an error like: "MoltenFraction" is not available at this point. The "MoltenFraction" variable is achieved by this workaround: http://www.edr.no/blogg/ansys_blogge...rations_in_cfx

A friend told me, that I can't make all material parameters variable over the duration of the simulation run. Is this true? And where can I read what I can change and what not?

Has anybody an idea how to get the material parameters variable over simulation run?
Thanks alot for any help!

Regards
Matthias

ghorrocks · December 14, 2014, 01:57

Your friend is correct, not all parameters can be made variable. If the parameter can be varied you just assign a variable to it and it will work. But if it cannot be made variable it will give an error message.

I am not sure whether porosity can be made a variable. If not then you are stuck - it cannot be made a variable. You will have to find another way of modelling your melting (or move to a different CFD code). Note CFX does not have a built in melting model so you are going to have to develop a suitable model for this yourself.

mapeth · December 14, 2014, 13:17

Uhm! That's really bad. All other options of CFX are too complex

But thanks for confirming my concern. Maybe I'll have to use something like Flac3D.
But is there some kind of list of parameters that stay the same? Its just because I could make a CEL for time dependent porosity without errors, but the porosity stayed the same over time! In the documentation I did not find any hints what is updated every loop and what is not. Just imagine you build all of your nice expressions and some of them are just ignored...

ghorrocks · December 14, 2014, 17:25

From a quick look at FLAC3D it is a very different piece of software with a very specific focus. If FLAC3D has the physics you need then it probably is a better choice.

I do not know how to get a list of variables which must be constant. But your expressions won't be ignored as you suggest - it will give an error message if you define something which must be constant as a variable.

mapeth · December 15, 2014, 09:28

Yes, Flac3D is especially built for geotechnical applications. I have worked with it on a previous university. However, they don't have the licenses here. Now, where I can't make CFX go geotechnical, I think I have to organize something.
Thanks again for your time ghorrocks.

December 13, 2014, 11:15	Material Parameters of Porous Domain as Variable?	#1
mapeth New Member Matthias T. Join Date: Dec 2014 Posts: 5 Rep Power: 12	Hello everybody, I'm working on a flow problem in a porous domain for a while. The domain is a thick walled cylinder with a pressure gradient from the inside to the outside. It consists of a silica matrix partially filled with ice. At a certain pressure the ice starts melting, where the actual flow simulation begins. The melting is implemented by sources. Now about my problem(s). As the ice melts, the porosity and permeability of the domain changes in reality. This is where I struggle. I can't make the porosity and permeability dependent on the amount of molten ice. Actually I can't make it dependent on anything! Whether Ansys ignores the change or gives me an error like: "MoltenFraction" is not available at this point. The "MoltenFraction" variable is achieved by this workaround: http://www.edr.no/blogg/ansys_blogge...rations_in_cfx A friend told me, that I can't make all material parameters variable over the duration of the simulation run. Is this true? And where can I read what I can change and what not? Has anybody an idea how to get the material parameters variable over simulation run? Thanks alot for any help! Regards Matthias

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December 14, 2014, 01:57		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Your friend is correct, not all parameters can be made variable. If the parameter can be varied you just assign a variable to it and it will work. But if it cannot be made variable it will give an error message. I am not sure whether porosity can be made a variable. If not then you are stuck - it cannot be made a variable. You will have to find another way of modelling your melting (or move to a different CFD code). Note CFX does not have a built in melting model so you are going to have to develop a suitable model for this yourself.

December 14, 2014, 13:17		#3
mapeth New Member Matthias T. Join Date: Dec 2014 Posts: 5 Rep Power: 12	Uhm! That's really bad. All other options of CFX are too complex But thanks for confirming my concern. Maybe I'll have to use something like Flac3D. But is there some kind of list of parameters that stay the same? Its just because I could make a CEL for time dependent porosity without errors, but the porosity stayed the same over time! In the documentation I did not find any hints what is updated every loop and what is not. Just imagine you build all of your nice expressions and some of them are just ignored...

December 14, 2014, 17:25		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	From a quick look at FLAC3D it is a very different piece of software with a very specific focus. If FLAC3D has the physics you need then it probably is a better choice. I do not know how to get a list of variables which must be constant. But your expressions won't be ignored as you suggest - it will give an error message if you define something which must be constant as a variable.

December 15, 2014, 09:28		#5
mapeth New Member Matthias T. Join Date: Dec 2014 Posts: 5 Rep Power: 12	Yes, Flac3D is especially built for geotechnical applications. I have worked with it on a previous university. However, they don't have the licenses here. Now, where I can't make CFX go geotechnical, I think I have to organize something. Thanks again for your time ghorrocks.