# help!

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 June 20, 2005, 11:23 help! #1 Teresa Guest   Posts: n/a Hi! I am implementing an udf, and I have an iterative equation in the "adjust" macro that I am extracting an enthalpy in every fluent iteration, with this enthalpy, my udf extracts a temperature that the udf passes by means of a macro define_profile as boundary condition and with this new temperature fluent extracts a new heat, and with this new heat a new enthalpy and a new temperature, and this way successively in every iteration of the same time-step. The problem is that on having been changing into every iteration the temperature, the heat that fluent gives at the every iteration is not good value, and the problem ends up by diverging. What I have thought is that inside the same one time-step, of for example 100 iterations, that fluent passes the temperature to define_profile as wall boundary condition every 10 iterations in order to in these 10 iterations the heat becomes stable, so that in these 10 iterations with the same temperature my iterative equation may converge and passes a value of heat trustworthier. Does someone know if it is possible to do? can I implement this in the adjust macro? I have thought also to use a newton-raphson to evaluate the heat in the adjust and that from certain iteration (inside the same one time-step) or certain condition of convergence that I impose to heat-flux, then to calculate the temperature and pass it like boundary-condition repeating the process. I would be grateful for all the ideas, or examples of udfs that could help me. thank you all (iīm sorry that my english is not very good, if somebody can help me and doesnīt understand something I will try to explain it better)

 June 21, 2005, 02:59 Re: help! #2 Luca Guest   Posts: n/a Hi Teresa! 1) just a silly question: why don't you extract directly temperature instead oh the enthalpy? 2) you can fix an under-relaxation factor to under-relax temperature for each iteration. 3) unfortunately adjust macro are run at each iteration. If you want it to be executed every 10 iterations you can include an "if" in the body of your function. You can check the iteration number (please look the UDF guide, there's a macro to access the iter number). Otherwise you can create a udf-on-demand function and launch itevety 10 iteration in the execute-command panel. Luca

 June 21, 2005, 06:01 Re: help! #3 Teresa Guest   Posts: n/a hi! thank you Luca for give me good ideas! I know that N_ITER macro passes de number of iterations but I donīt know how manipulate this in order to each 10 iteration of 100 iteration in a time-step do the operation that I want it to do, iteration of 1 time-step 1--------/ 2 / 3 / 4 / 5 //////////do a operation in the adjust 6 / 7 / 8 / 9 / 10-------/ 11--------/ 12 / 13 / 14 / 15 //////////do other operation in the adjust 16 / 17 / 18 / 19 / 20 -------/ etc. Thank you!!!!!

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