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-   -   Another UDF question (http://www.cfd-online.com/Forums/fluent/30041-another-udf-question.html)

Christian July 17, 2002 08:06

Another UDF question
 
When I try to call "VaporizationLaw(p) in an otherwise working UDF, I get the message that *function "VaporizationLaw" not found*

Can anyone see what I should do?

Cheers Christian


Christian July 17, 2002 10:24

Re: Another UDF question
 
I have noticed that when I play around with the custom laws in droplet DPM, then the result changes.

Does anyone know why?

"play around with" means that I use the same laws as Fluent activates and in the same order. I just move them up and downwards in the custom law box and insert an "inactive" between some of the activated laws.

Cheers Christian

Lanre July 18, 2002 15:13

Re: Another UDF question
 
Unless you specify the "switching" between laws in your custom laws to match the default DPM switching, you'll obviously get different results.

Christian July 19, 2002 02:56

Re: Another UDF question
 
Hi Lanre Thanks for your reply.

You are saying that it is necessary with a switching law when I make a new law. Sounds just about right because I have noticed that my new law is not activated until "the other" laws that Fluent activates are finished, ie. In droplet DPM my law is not activated until the droplets are all evaporated.

Do you know how Fluent knows when to switch between the default droplet laws?

Do you know: When I try to call "VaporizationLaw(p) in an otherwise working UDF, I get the message that *function "VaporizationLaw" not found*

Maybe I could use this call in my new law instead of making a switch law?

Cheers Christian

Lanre July 21, 2002 13:08

Re: Another UDF question
 
The DPM model switches between laws in the sequence described in the Users Guide. The criteria for switching is based on the material properties of the DPM particle, e.g. when the vaporization temperature is reached, the vaporization law commences but only after the particle has gone through the heating law. You can request from Fluent the UDFs for the default DPM laws. The UDF Users Guide also has an example of UDF switching. Take a look there.

Christian July 22, 2002 02:51

Re: Another UDF question
 
Hi.

I am familiar with the switching example. But I was under the assumption that it was possible for the particle to "obey" more than one law at a time and that the criteria in all the laws were scanned for each calc.

I guess that what you say is that only one law can be active at a time and that this law is active until the criteria stated in it no longer is fulfilled.

Lanre July 22, 2002 12:50

Re: Another UDF question
 
That is correct...one law for one phenomena, e.g. boiling. Does your "particle" undergo several phenomological transformations simultaneously? I'd be interested to learn more.

Christian July 23, 2002 04:19

Re: Another UDF question
 
No. Not at present. But I am trying to understand how the UDF and particle laws work. I have testet several simple homemade laws to see the effects.

It is in that connection that I have observed that when the particle is in the, say boiling law, it remains there until the boiling stops. I.e. my law will first be activated after the boiling. I haven't read about this "restriction" in the manual and am therefore interested in knowing if there are other similar restrictions I should be aware of.


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