Additional variable

Luigi · July 20, 2012, 09:07

I should run simulations in which the kinematic diffusivity is a function of the additional variable itself. In particular, the concentration of a solute is the additional variable, of which I have to solve the transport equation, and its diffusivity is a function of the concentration itself. The Solver reports this error message:
Error processing expression 'Kinematic Diffusivity'.
The expression is invalid because:
Concentration is not available for use in this term

Error processing expression: Kinematic Diffusivity = D.

Does it mean that is impossible to set the kinematic diffusivity as a function of the additional variable??
If not, how can I avoid this error?
If so, is there any chance to solve the problem?

Felggv · July 20, 2012, 15:07

Hi there,

I had the same message but with a different variable.

I wanted to calculate Temperature using the Mass Fraction, but in CFX, the mass fraction of a component cannot be used to calculate temperature in the default configurations of the CFX.

What I was told to do was to add this variable to the "default" by modifying the RULES file in CFX>etc folder, and I was properly warned by people here that mf was not set as default for a good reason, so if that's your solution for the problem, you should backup this file and monitor the results.

Here's the topic where they've helped me: http://www.cfd-online.com/Forums/cfx...ple-solve.html

There's another way to solve the problem by adding a line of CCL command instead of modifying the RULES, it's post #15 there.

I'm not sure, but I think you don't have to create another variable since concentration is already there. If your problem is like mine, you should just enable it to use for you purpose.

Sorry for the long text

ghorrocks · July 20, 2012, 19:16

You can work around this by editting the rules file (see Felipe's link for this) but be aware that it is not supported by default because something is missing - it might not work at all, it might be completely wrong or it might give incorrect results in a very specific setup. What I am trying to say is it is not supported and you have to do your own checks to make sure it is working correctly.

Luigi · July 22, 2012, 15:46

Thanks for your help,

but where can I find the RULES file??

Felggv · July 22, 2012, 17:35

It should be here:

C:\Program Files\ANSYS Inc\v130\CFX\etc

Luigi · July 23, 2012, 07:45

Thank you,
I have modified the RULES file and the simulation run, but this message appears:
Invalid entries in Dependency List for Kinematic Diffusivity have been found. Please ensure entries are defined in the VARIABLES file

I think that it is not a problem.

Anyway, thanks a lot! Now I can carry out my simulations!!

Felggv · July 23, 2012, 10:28

Luigi,

As some guys have warned me here, check out the results to see if they're not absurd because of the modification.

Hope it works well

Luigi · July 23, 2012, 10:52

As I can see from preliminary results, it semms to work well!

NewToAnsys · March 26, 2019, 15:29

In such a case, where one of the material properties of the domain is dependent on another variable (which has been added to the dependency list of the property in the RULES file), an analysis that normally could be run at steady state would have to be transient right? Since the material property of the domain is changing, at least initially?

ghorrocks · March 26, 2019, 17:51

As discussed on the other thread - no, changing material properties does not mean you need a transient simulation.

July 22, 2012, 15:46	Where is the RULES file?	#4
Luigi New Member Luigi Gurreri Join Date: Jul 2012 Posts: 18 Rep Power: 14	Thanks for your help, but where can I find the RULES file??

July 23, 2012, 07:45	Simulation is running	#6
Luigi New Member Luigi Gurreri Join Date: Jul 2012 Posts: 18 Rep Power: 14	Thank you, I have modified the RULES file and the simulation run, but this message appears: Invalid entries in Dependency List for Kinematic Diffusivity have been found. Please ensure entries are defined in the VARIABLES file I think that it is not a problem. Anyway, thanks a lot! Now I can carry out my simulations!!

March 26, 2019, 17:51		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	As discussed on the other thread - no, changing material properties does not mean you need a transient simulation. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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July 20, 2012, 09:07	Additional variable	#1
Luigi New Member Luigi Gurreri Join Date: Jul 2012 Posts: 18 Rep Power: 14	I should run simulations in which the kinematic diffusivity is a function of the additional variable itself. In particular, the concentration of a solute is the additional variable, of which I have to solve the transport equation, and its diffusivity is a function of the concentration itself. The Solver reports this error message: Error processing expression 'Kinematic Diffusivity'. The expression is invalid because: Concentration is not available for use in this term Error processing expression: Kinematic Diffusivity = D. Does it mean that is impossible to set the kinematic diffusivity as a function of the additional variable?? If not, how can I avoid this error? If so, is there any chance to solve the problem?

July 20, 2012, 15:07		#2
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	Hi there, I had the same message but with a different variable. I wanted to calculate Temperature using the Mass Fraction, but in CFX, the mass fraction of a component cannot be used to calculate temperature in the default configurations of the CFX. What I was told to do was to add this variable to the "default" by modifying the RULES file in CFX>etc folder, and I was properly warned by people here that mf was not set as default for a good reason, so if that's your solution for the problem, you should backup this file and monitor the results. Here's the topic where they've helped me: http://www.cfd-online.com/Forums/cfx...ple-solve.html There's another way to solve the problem by adding a line of CCL command instead of modifying the RULES, it's post #15 there. I'm not sure, but I think you don't have to create another variable since concentration is already there. If your problem is like mine, you should just enable it to use for you purpose. Sorry for the long text

July 20, 2012, 19:16		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	You can work around this by editting the rules file (see Felipe's link for this) but be aware that it is not supported by default because something is missing - it might not work at all, it might be completely wrong or it might give incorrect results in a very specific setup. What I am trying to say is it is not supported and you have to do your own checks to make sure it is working correctly.

July 22, 2012, 17:35		#5
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	It should be here: C:\Program Files\ANSYS Inc\v130\CFX\etc

July 23, 2012, 10:28		#7
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	Luigi, As some guys have warned me here, check out the results to see if they're not absurd because of the modification. Hope it works well

July 23, 2012, 10:52		#8
Luigi New Member Luigi Gurreri Join Date: Jul 2012 Posts: 18 Rep Power: 14	As I can see from preliminary results, it semms to work well!

March 26, 2019, 15:29		#9
NewToAnsys New Member Join Date: Oct 2018 Posts: 17 Rep Power: 8	In such a case, where one of the material properties of the domain is dependent on another variable (which has been added to the dependency list of the property in the RULES file), an analysis that normally could be run at steady state would have to be transient right? Since the material property of the domain is changing, at least initially?