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August 3, 2012, 16:42 
Derivative of a scalar or a variable through UDF

#1 
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Fer Villa
Join Date: Apr 2012
Posts: 35
Rep Power: 5 
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  
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Ji Junjie
Join Date: Feb 2010
Location: Shanghai, China
Posts: 106
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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 
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Fer Villa
Join Date: Apr 2012
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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  
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Fer Villa
Join Date: Apr 2012
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Thank you very much again, your reply was very useful.
Quote:


February 3, 2015, 19:28 

#7 
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Join Date: Dec 2014
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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, 22:39 

#8 
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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. 

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