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non newtonian viscosity problem

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Old   June 27, 2012, 07:21
Default non newtonian viscosity problem
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Dr. Moloy Kumar Banerjee
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Dear all,
I am simulating the problem of blood flow through an artery in 2D considering laminar flow. For this I am using the Walburn and Scneck model to define the blood viscosity using the equation:
mu_lam=K*(strain)^(n-1), where K=14.67*10^(-3) and n=0.7755. In order to define the viscosity I am using the following UDF:
#include "udf.h"
DEFINE_PROPERTY(cell_viscosity_power_law,c,t)
{
double mu_lam;
double strain;
double muinf = 14.67e-3;
double n = .7755;
strain = pow(C_DUDX(c, t),2)+ pow(C_DVDY(c, t),2)+
2*pow(C_DUDY(c, t)+ C_DVDX(c, t),2)+
2*pow(C_DUDZ(c, t),2)+
2*pow(C_DVDZ(c, t),2);
strain = pow(strain, 0.5);
strain =fabs(strain);
mu_lam=muinf*pow(strain,n-1);
return mu_lam;
}
But, once I try to solve it the solver gives the error: Divergence detected in the AMG solver.
Please help me....
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Old   July 3, 2012, 16:47
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Casey
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You should repost this in the UDF section of the forum. You will likely get more help.
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Old   July 3, 2012, 16:48
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I think it is because when Strain = 0, you will be dividing by zero. Try adding an if statment in there that says if strain is below some value than mu_lam = some large value... or make stain = pow(C_DU...) + 1x10^(-12),
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Old   July 4, 2012, 02:51
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Dr. Moloy Kumar Banerjee
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Thanks for the reply. It works properly.
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Old   July 5, 2012, 15:47
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no problem.
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