# Problems in converging viscosity UDF dependent upon strain rate and temperature.

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 March 17, 2016, 07:33 Problems in converging viscosity UDF dependent upon strain rate and temperature. #1 New Member   Alex Skerhut Join Date: Mar 2016 Posts: 10 Rep Power: 2 Hi, I am interpreting a viscosity UDF which is dependent upon temperature and strain rate. The UDF interprets fine but does not lead to convergence and starts diverging from the very start and does not run even a single iteration. My UDF is as follows: #include DEFINE_PROPERTY(cell_viscosity,c,t) { double stress = 22.22e+06; double A = 8.86e+06; double energy = 145000; double R = 8.314; double n = 3.55; double mu_laminar,temp,strainrate,Z,D,E,F; temp= C_T(c,t); strainrate= C_STRAIN_RATE_MAG(c,t); Z= strainrate*exp(energy/(R*temp)); D= pow((Z/A),(1/n)); E= pow((Z/A),(2/n)); F= pow(E+1,0.5); mu_laminar= (stress*log(D+F))/(3*strainrate); return mu_laminar; } A similar viscosity model named carreau dependent upon strainrate and temperature converges fine but my udf does not even start iterating. It gives the error message #Divergence detected in AM solver: x-momentum - Increasing relaxation sweeps! Kindly help me in this my complete project depends upon the successful implementation of the viscosity UDF.

 March 17, 2016, 08:19 #2 Senior Member   Join Date: Nov 2013 Posts: 895 Rep Power: 12 Print the values to your screen. Code: ```Message("Z,D,E,F: %f,%f,%f,%f\n",Z,D,E,F); Message("Mu: %f\n",mu_laminar); return mu_laminar;``` (If I remember the syntax correctly, otherwise check the manual.) Then check if the values that are shown agree to what you want. If they don't, find out why not and fix your equations.

 Tags fluent - udf, udf and programming, udf compile, udf eror

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