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 fevi84 August 3, 2012 16:42

Derivative of a scalar or a variable through UDF

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!!!

 Amir August 5, 2012 11:29

Hi,

You can store it in a UDS and retrieve its derivation.

Bests,

 gearboy August 6, 2012 01:41

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:
 Originally Posted by fevi84 (Post 375311) 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!!!

 fevi84 August 6, 2012 09:07

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?

Thanks!!!

 gearboy August 6, 2012 10:40

1 Attachment(s)
Attachment 15027

As to the usage, see chapter "Example UDF that Utilizes UDM and UDS Variables" in Fluent 6.3 UDF pdf manual(page 3-43).

Quote:
 Originally Posted by fevi84 (Post 375602) 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!!!

 fevi84 August 6, 2012 13:20

Quote:
 Originally Posted by gearboy (Post 375614) Attachment 15027 As to the usage, see chapter "Example UDF that Utilizes UDM and UDS Variables" in Fluent 6.3 UDF pdf manual(page 3-43).

 Harry321 February 3, 2015 19:28

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.

 Harry321 February 3, 2015 22:39

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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