[Kanarya]

Hi Ignacio,
I think, you have some problem with your code…
If you do not mind, you can send me the code and I can check it.
kah.recep@gmail.com
best regards,

[jipaz]

Hi Kanarya:

I applied the modifications to the code you recommended to me, but I'm still getting the same error messages:

Updating solution at time level N... done.
iter continuity u-aire u-solidos v-aire v-solidos gt-solidos k epsilon vf-solidos time/iter
# Divergence detected in AMG solver: mp-x-momentum -> Decreasing coarsening group size!
# Divergence detected in AMG solver: mp-x-momentum -> Increasing relaxation sweeps!
# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!

Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vof-1
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vof-1
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vof-1
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Divergence detected in AMG solver: epsilon
Divergence detected in AMG solver: vof-1# Divergence detected in AMG solver: pressure correction -> Increasing relaxation sweeps!

Primitive Error at Node 0: floating point exception

Primitive Error at Node 1: floating point exception

Primitive Error at Node 2: floating point exception

Primitive Error at Node 3: floating point exception

Error: floating point exception
Error Object: #f

I'm using a non-uniform grid in radial direction, and thinking that this could be a problem, I returned to a radial uniform grid, but I got the same error messages for the uniform grid case.

Then I changed the UDF drag model to modified Syamlal-O'Brien as wrttien in the Fluent UDF manual example and the case start and continue running properly without any error messages, so I'm sure the problem is the EMMS UDF drag model.

Any help is very welcome

Regards,

Ignacio

[jipaz]

Dear all, finally I found what is the problem. According many papers the initial conditions for riser simulations are setting as Vg=0.0, Vs=0.0, so when the run starts, the Reynold number becomes 0.0, and Cd becomes no-definded, and then the run crashes.

In fact my EMMS UDF drag function commented by Kanarya, including some minor modifications done by myself is working properly.

Now I defined initial Vg as 1e-6, and the case is able to start doing 2 iterations, now my problem is flow reversal detected in pressure outlet, but I think i'm walking in the right direction.

Regards,

Ignacio

[jipaz]

Dear all:

Finally I found the problem, my EMMS drag model code was not correct, be careful about writing the code properly, and be careful about the if's and else if's statements.

Thanks again Kanarya.

Good luck doing CFD simulations.

Regards,

Ignacio

[Kant]

Can You tell me how to solve the non-linear equations in variables a & Usc?

[SOURAV GANGULI]

Can anyone tell me the operating condition to run emms drag model?

[Rakhim]

Originally Posted by Kanarya

Hi,
you should compile it.
I think, to send my code to you is not good idea for you!
you should just modify the code from Syamlal-O'Brien drag which is included in the Udf examples.
I think you do not have much experiance with UDF.
I suggest you to get familiar with it and then you will see that it is not so difficult to implement it.
If you have the code and it is not working you can ask some specific questions and I will try to help you!

Best!

Hi Kanarya,

I have pretty much similar problem. When I incorporate udf (I modified Symlal model which is provided in the fluent manual), divergence problem occured. My udf (attached below) is modifying drag coefficient between 2 phases in multiphase flow. Could you please have a look?

#include "udf.h"

#define diamrbc 5.5e-6


DEFINE_EXCHANGE_PROPERTY(custom_drag, cell, mix_thread, s_col, f_col)
{
Thread *thread_p, *thread_rbc;
real u_vel_p, u_vel_rbc, v_vel_p, v_vel_rbc, w_vel_p, w_vel_rbc, abs_vrbc,
rho_rbc, mu_p, reyrbc,
cd_rbc;


/* find the threads for the plasma (primary) */
/* and rbc (secondary phases) */
thread_p = THREAD_SUB_THREAD(mix_thread, s_col);/* plasma*/
thread_rbc = THREAD_SUB_THREAD(mix_thread, f_col);/* rbc*/

/* find phase velocities and properties*/
u_vel_p = C_U(cell, thread_p);
v_vel_p = C_V(cell, thread_p);
w_vel_p = C_W(cell, thread_p);
u_vel_rbc = C_U(cell, thread_rbc);
v_vel_rbc = C_V(cell, thread_rbc);
w_vel_rbc = C_W(cell, thread_rbc);
rho_rbc = C_R(cell, thread_rbc);
mu_p = C_MU_L(cell, thread_p);

/*compute velocity*/
abs_vrbc = sqrt(pow(u_vel_p - u_vel_rbc, 2) + pow(v_vel_p - v_vel_rbc, 2) + pow(w_vel_p - w_vel_rbc, 2));


/*compute Reynolds number*/
reyrbc = rho_rbc*abs_vrbc*diamrbc / mu_p;




/*compute drag and return drag coeff, k_g_s*/
cd_rbc = 5.847e-05*pow(reyrbc, 2) - 0.02132*reyrbc + 1.904;


return cd_rbc;
}