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 February 2, 2011, 20:39 Startup Additional Variables #1 New Member   FM Join Date: Feb 2010 Posts: 14 Rep Power: 10 Hi I'm trying to simulate a problem which requires an Additional Variable "av". The domain's DENSITY is a function of this av: DENSITY = f (av). This av is a function of TEMPERATURE: av = f (TEMPERATURE). I give the initial temperature, but at the initialization of the run, appears an error: "Error processing expression 'Density'. The expression is invalid because: Dano is not available for use in this term" I think this is because I didn't find anywhere to put an inital value of the av. Where can I initialize the av? If I can't, what can I do? Thanks

 February 3, 2011, 15:44 #2 Senior Member   Join Date: Mar 2009 Location: Europe Posts: 168 Rep Power: 10 To be honest: i do not fully understand what you intend to do. There are different kinds of av. If you chose the option transport equation it is possible to initialize. The type algebraic equation should depend on other variables, so it is not required to initialize. __________________ - - - - - ------------------------------------------------------------------------ Please do not forget: I am not paid for answering your questions. Thousands of issues can cause a division by zero. Please do not capture a thread, with the argument: "I have the same issue ...."

 February 3, 2011, 19:49 #3 New Member   FM Join Date: Feb 2010 Posts: 14 Rep Power: 10 My av is an Algebraic Expression. Like I said: Density = f (av) and av = f (T). I think the problem is because the CFX initializes first its own variables (like Temperature, COndutivity, Density...); but my Density is a function of the av created, that is initialized olny after this primitive variables. I don't know if the problem is this... Can anyone help? Thanks

 February 4, 2011, 06:33 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,336 Rep Power: 110 I can't check this but I suspect you cannot made density a function of a additional variable. There are only limited variables you can make density a function of. You will have to specify density as a direct function of temperature.

March 28, 2011, 22:59
#5
New Member

eric
Join Date: Nov 2010
Posts: 16
Rep Power: 9
Quote:
 Originally Posted by ghorrocks I can't check this but I suspect you cannot made density a function of a additional variable. There are only limited variables you can make density a function of. You will have to specify density as a direct function of temperature.
Yeah, CFX11 Pre would show error information if additional variable is applied in density. In CFX12, although there is no any error or warning information in CFX pre, slover would be stopped because of the additional variable dependent density.

Glenn, do you think it is possible to solve this problem by using subroutine in CFX?

Actually I donot understand why CFX has such a limitation, is it because CFX can not initialize the density if additional variable is included?

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