CFD Online Discussion Forums - viscosity udf don't use correct temperature and strain rate

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viscosity udf don't use correct temperature and strain rate

hello. im use udf for calculate strain rate and temperature dependent viscosity. but viscosity udf don't use correct temperature and strain rate. how to solve this problem? this is my udf

Code:

# include <udf.h>

int counter=0;

DEFINE_PROPERTY(U_Visc,c,t)

{

real Temp;

real Visc;

real str;

real stress;

real asinh_input;

real asinh_output;

real b;

real Z;

real  A;

real alfa;

real blfa;

real n ;

real  Q;

real  R;/* Specific gas constant */

real  strlimit;

real Visc_limit;

real viscmin;

 A = 2.095E11 ;/* Material constant 304 ss*/

 blfa =  3.233E5;

 alfa= 0.0000050867;

 n = 1.812;

 Q = 74640;

 R = 8.314;

 Visc_limit = 2.E5;





Temp = C_T(c,t); /*0.7Tm*/

begin_c_loop(c, t)

{

 str = C_STRAIN_RATE_MAG(c,t);

b=exp(Q/(R*Temp));

Z = str*b;

asinh_input = pow(Z/A,1./n);

asinh_output = log(asinh_input + sqrt(asinh_input * asinh_input + 1));

stress = (1. /alfa)*asinh_output;

Visc = stress/(3. *str);

if ( (Visc > Visc_limit) || (str == 0) )

{

    Visc = Visc_limit;

}



if ( (Visc < 0) )

{

    Visc = 0;

}

C_UDMI(c,t,0)=stress;

C_UDMI(c,t,1)=Visc;

C_UDMI(c,t,2)=str;

C_UDMI(c,t,3)=Temp;

C_UDMI(c,t,4)=Z;

C_UDMI(c,t,5)=asinh_input;

C_UDMI(c,t,6)=asinh_output;

C_UDMI(c,t,7)=b;



if(counter<=20)

{

counter++;CX_Message("Strain= %E(1/s) Viscosity =%E PaS\n", str, Visc);

/* CX_Message("Strain*1e6= %E\n", str*1e6); */

}



return Visc;

end_c_loop(c, t)

}



}

and this is themprature diagram in udm
thank you
best regards
Rezvani

Temp = C_T(c,t); /*0.7Tm*/
begin_c_loop(c, t)

Switch these two lines.

thank you .still udm s are wrong. how to fix udm?

try this code

Code:

# include <udf.h>

int counter=0;

DEFINE_PROPERTY(U_Visc,c,t)

{

real Temp;

real Visc;

real str;

real stress;

real asinh_input;

real asinh_output;

real b;

real Z;

real  A;

real alfa;

real blfa;

real n ;

real  Q;

real  R;/* Specific gas constant */

real  strlimit;

real Visc_limit;

real viscmin;

 A = 2.095E11 ;/* Material constant 304 ss*/

 blfa =  3.233E5;

 alfa= 0.0000050867;

 n = 1.812;

 Q = 74640;

 R = 8.314;

 Visc_limit = 2.E5;



Temp = C_T(c,t); /*0.7Tm*/

str = C_STRAIN_RATE_MAG(c,t);

b=exp(Q/(R*Temp));

Z = str*b;

asinh_input = pow(Z/A,1./n);

asinh_output = log(asinh_input + sqrt(asinh_input * asinh_input + 1));

stress = (1. /alfa)*asinh_output;

Visc = stress/(3. *str);

if ( (Visc > Visc_limit) || (str == 0) )

{

    Visc = Visc_limit;

}



if ( (Visc < 0) )

{

    Visc = 0;

}

C_UDMI(c,t,0)=stress;

C_UDMI(c,t,1)=Visc;

C_UDMI(c,t,2)=str;

C_UDMI(c,t,3)=Temp;

C_UDMI(c,t,4)=Z;

C_UDMI(c,t,5)=asinh_input;

C_UDMI(c,t,6)=asinh_output;

C_UDMI(c,t,7)=b;



if(counter<=20)

{

counter++;

Message0("Strain= %E(1/s) Viscosity =%E PaS\n", str, Visc);

/* Message0("Strain*1e6= %E\n", str*1e6); */

}



return Visc;

}

hello. if dont use begin_c_loop(c, t) fluent show this error

Code:

     4  1.0000e+00  4.1831e-02  1.6884e-02  1.7000e-02  3.5638e-04  0:22:44   46

        Stabilizing temperature to enhance linear solver robustness.

 temperature limited to 1.000000e+00 in 4967024 cells on zone 4 in domain 1

  temperature limited to 5.000000e+03 in 19391 cells on zone 4 in domain 1

 

 Artificial walls on 82 faces (0.7% area) of pressure-outlet 9 to prevent fluid from flowing into the boundary.

     5  1.0000e+00  3.9380e-02  2.1037e-02  2.0857e-02  1.6664e-03  0:27:24   45





Error at Node 1: floating point exceptiEon

rror at Node 0: floating point exception

        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.

        Stabilizing pressure correction using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: pressure correction        Stabilizing temperature to enhance linear solver robustness.

        Stabilizing temperature using GMRES to enhance linear solver robustness.



Divergence detected in AMG solver: temperature

 Artificial walls on 5428 faces (46.2% area) of pressure-outlet 9 to prevent fluid from flowing into the boundary.



Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: temperature

Error at host: floating point exception



===============Message from the Cortex Process================================



Compute processes interrupted. Processing can be resumed.



==============================================================================

how to prevent this error?
thank you

Check those UDMs that you used. Plot them, see which one is not what you expect.

Quote:

Originally Posted by pakk (Post 804653)

Check those UDMs that you used. Plot them, see which one is not what you expect.

Hello. viscosity works well. and it match with temperature and ... .
but udm s(temperature, stress,... ) are wrong.
if i use begin_c_loop(c, t) udm s are wrong. if i dont use begin_c_loop(c, t) then give error!!
thank you.
best regards.

If temperature and stress are wrong, focus on that.
You don't give me much to work with, so I can't help more.

begin_c_loop(c, t) is already included in DEFINE_PROPERTY macro

you don't need to make additional loop over cell

from your log I can see the error comes out on 4th iteration. look at domain on 3th iteration, check udms distribution, analyse all variable you have applied to model:
temperature, stresses so on

Quote:

Hello. viscosity works well. and it match with temperature and ... .

if viscosity works well. and it match with temperature it means UDF works well.
in that case simulation doesn't work cause of viscosity values you've applied