
[Sponsors] 
Derivative of a scalar or a variable through UDF 

LinkBack  Thread Tools  Search this Thread  Display Modes 
August 3, 2012, 16:42 
Derivative of a scalar or a variable through UDF

#1 
Member
Fer Villa
Join Date: Apr 2012
Posts: 35
Rep Power: 13 
Hi,
I need help!!! I need calculate of derivative of a scalar, in my case, the derivative of the volume fraction. Anyone knows how I can calculate this derivative through UDF??? because I only know the macros for the derivative of the velocity (C_DUDX(c,t), C_DUDY(c,t), C_DUDZ(c,t),...). is there a way to calculate the derivative of a scalar or a variable other than velocity? Thanks!!! 

August 6, 2012, 01:41 

#3  
Senior Member
Join Date: Feb 2010
Posts: 164
Rep Power: 16 
As Amir said, store the volume fraction into a UDSI and do not solve the equation of this UDSI. Then achieve the derivative by C_UDSI_G.
Use the following code to get the volume fraction. Material *mix_mat = mixture_material(Get_Domain(1)); Material *spe_mat = NULL; real all_mass_fracts[MAX_SPE_EQNS]; real all_mole_fracts[MAX_SPE_EQNS]; int i = 1; mixture_species_loop(mix_mat, spe_mat, i) { all_mass_fracts[i] = C_YI(c,t,i); } Mole_Fraction(mix_mat, all_mass_fracts, all_mole_fracts); After this, the mole fractions of all species can be found in the array "all_mole_fracts". Quote:


August 6, 2012, 09:07 

#4 
Member
Fer Villa
Join Date: Apr 2012
Posts: 35
Rep Power: 13 
Thank you very much for their replies.
I don't understand how store the volume fraction in a UDS without solving this UDS. I have to create a UDS through the graphical interface? Can you please explain more. Thanks!!! Last edited by fevi84; August 6, 2012 at 09:38. 

August 6, 2012, 13:20 

#6  
Member
Fer Villa
Join Date: Apr 2012
Posts: 35
Rep Power: 13 
Thank you very much again, your reply was very useful.
Quote:


February 3, 2015, 18:28 

#7 
Member
Join Date: Dec 2014
Posts: 38
Rep Power: 10 
Hello,
Could one of you tell me difference between gradient and derivative in fluent. I used code: fprintf(fp2, "DWDZ %f ", C_DWDZ(c, t)); fprintf(fp2, "CWG %lf \n", C_W_G(c, t)[2]); but the values are different. 

February 3, 2015, 21:39 

#8 
Member
Join Date: Dec 2014
Posts: 38
Rep Power: 10 
Dear colleagues,
I don't know why in previous version of a code, fluent plotted wrong values but after I add: fprintf(fp2, "DWDZ %f ", C_DWDZ(c, t)); fprintf(fp2, "CWG[0] %lf \n", C_W_G(c, t)[0]); fprintf(fp2, "CWG[1] %lf \n", C_W_G(c, t)[1]); fprintf(fp2, "CWG[2] %lf \n", C_W_G(c, t)[2]); fluent plotted the same values for derivative of a velocity and for C_W_G(c, t)[2], I cannot see difference between this and previous one, but it works and the results are the same so it means that gradient and derivative are the same. 

Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
UDF derivative  libia87  Fluent UDF and Scheme Programming  0  March 30, 2012 04:14 
can i get pressure derivative in UDF?  ruirui389  Fluent UDF and Scheme Programming  4  April 8, 2011 04:12 
UDF  accessing face variable problem  argeus  FLUENT  2  February 9, 2011 04:08 
UDF extern variable  mean time moment coefficient  enry  Fluent UDF and Scheme Programming  0  November 14, 2009 06:56 
Env variable not set  gruber2  OpenFOAM Installation  5  December 30, 2005 04:27 