# How does FLUENT process an UDF!!!!????

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 March 9, 2015, 06:03 #21 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 25 I don't know what you mean by "stopping". In what aspect is your current UDF not giving you what you want? I can not see the difference between what you want and what you get.

 March 9, 2015, 06:21 mass flux #22 Member   Baradwaj B S Join Date: Jan 2015 Posts: 75 Rep Power: 10 Hello pakk, PROBLEM : The problem is on devolatilization( or evaporation) of solid wood sphere. There is a sphere inside a cylindrical flow domain, through which hot air will be allowed to flow. This hot air evaporates the mixture of gases from the surface of the sphere. For this evaporation I am trying use an UDF. i.e, lets consider there is 1kg of water inside sphere. This gets evaporated to the flow domain continuously. for this I am using F_PROFILE (mass flow rate). After some seconds this 1kg of mass evaporates and the mass inside the sphere gets reduced. Once this mass becomes zero, there will not be any mass flow from the surface of the sphere. Since I cannot give 1 kg of mass directly in fluent, I am trying to consider a variable named "mass", which is what is in UDF. This "mass" I am reducing by some value (0.05 in this case). So after all the decrement this "mass" becomes zero. When this mass becomes zero, there should not be any mass flow rate from the surface of the sphere (F_PROFILE = 0.0. This I am trying to replicate in UDF (reducing mass to decrementing "mass in UDF) mass = mass - decrement. if(mass >0 && mass<=1) F_PROFILE(f,t,i) = -flwrt; else F_PROFILE(f,t,i) = 0.0; Hope you got the details clear. Thanks in advance, Bharadwaj B S

 March 9, 2015, 06:24 #23 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 25 I still can not see the difference between what you want and what you get. Mainly because you don't mention what you get. Why are you not happy with the UDF that you currently have?

 March 9, 2015, 06:39 Clarification #24 Member   Baradwaj B S Join Date: Jan 2015 Posts: 75 Rep Power: 10 Dear pakk, The mass decrement calculations should end for 3 iterations (i.e when mass = 1.0 once, 2nd iteration mass = mass - decrement (1.0-0.5) and mass = 0.5 - 0.5 (which is zero and gives false). (In this case the mass present inside the sphere is positive, i.e, it can still evaporate). For only first two values of "mass", F_PROFILE(f, t, i) should be equal to -flwrt; (i.e, 0.05). For further iterations the calculations will result in "mass < 0". and F_PROFILE(f,t,i) should be equal to 0.0. (condition when all the mass present inside the sphere gets evaporated totally). Now if you are clear, I think the conditions (mass <=1 && mass >0) are correct up to my knowledge. What would you suggest the condition should be for this problem? Thanks in advance, Bharadwaj B S

 March 9, 2015, 06:49 #25 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 25 You are asking me to help you change something in your UDF, but I don't know why anything should be changed. I don't know how to ask this more clear... You have a certain set of wishes, that you want the UDF to do. Let's call this set of wishes "A". If you use your UDF, it does things. Let's call these things "B". Is A equal to B? If so, be happy. If not, what is the difference?

March 9, 2015, 06:54
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 Originally Posted by pakk You are asking me to help you change something in your UDF, but I don't know why anything should be changed. I don't know how to ask this more clear... You have a certain set of wishes, that you want the UDF to do. Let's call this set of wishes "A". If you use your UDF, it does things. Let's call these things "B". Is A equal to B? If so, be happy. If not, what is the difference?
Dear pakk,

I dont know what is wrong with UDF. The UDF logically seems to be OKAY. But this is not giving me the proper results in FLUENT.

I am new to C programming. I could not find the problem with the previous UDF, so posted here.

March 9, 2015, 06:59
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 Originally Posted by Bharadwaj B S I dont know what is wrong with UDF. The UDF logically seems to be OKAY. But this is not giving me the proper results in FLUENT.
So you have tried it in Fluent, and you have observed the behavior of your UDF. But you want to keep that behavior secret from me? You can do that if you want, but in that case I can not help you, I'm afraid.

Or did you still not understand my question? I am asking you, already a few times: what does your UDF do? Every time, you answer what it SHOULD do, but that is not the question. If you can answer the question in your next post, I can help you, otherwise I give up.

 March 9, 2015, 07:00 Results #28 Member   Baradwaj B S Join Date: Jan 2015 Posts: 75 Rep Power: 10 Dear pakk, The results I want, When mass is greater than zero(mass>0.0) and less than or equal to one (mass <=1), the UDF should go inside the loop and provide some value to F_PROFILE(f,t,i). When the above conditioon is wrong ( obvioously when mass <0 or negative), compiler should assign F_PROFILE(f,t,i) to 0.0. First para gives me some mass flow rate. (if true) Second para gives me no mass flow rate. (i.e if first para is wrong). Thanks in advance, Bharadwaj B S

 March 9, 2015, 07:03 #29 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 25 And again you did not answer my question. I did not ask you what you WANT, or what the code SHOULD do, because I already know that. I asked you what you RECEIVED, what the code DID. I am sorry, but I am tired of asking the same simple question over and over, good luck with your problem.

 March 9, 2015, 07:10 Sorry #30 Member   Baradwaj B S Join Date: Jan 2015 Posts: 75 Rep Power: 10 Dear pakk, This UDF is giving all iterations some mass flow rate. (even after mass has become less than 0.0). I do not want FLUENT to give me mass flow rate after few iterations (i.e, 2 iterations in my case). But it is giving me that. QUESTION How to stop the mass flw rate after the calculations of mass has become 0.0.?? Thanks in advance, Bharadwaj B S

 March 9, 2015, 07:18 #31 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 25 This would have answered my question. Good luck with finding the solution.

 March 9, 2015, 07:32 Extremely sorry #32 Member   Baradwaj B S Join Date: Jan 2015 Posts: 75 Rep Power: 10 Dear pakk, I did not understand the question completely, my mind was stuck only explaining you what I want, instead I should have told you what is happening. It was completely a misunderstanding and nothing was intentional. Please help me on this programming, I am very much new to the C programming. I have learnt very less in this regard, throughout my graduation. Thanks in advance, Bharadwaj B S