Importing results to initial conditions in a different simulation for convergence.

alexskerhut · May 5, 2016, 02:00

Hey!

I am defining a shear and temperature dependent viscosity as a user defined function in Fluent but the code diverges since the value of strain rate is used in denominator and at initial iterations the strain rate will be low which will lead to large fluctuations and hence divergence of the solution according to me.

I wish to run the simulation at constant viscosity for few iterations and then shift to the viscosity defined by UDF taking the final iterations value of constant viscosity simulations as initial conditions( mainly strain rate) for viscosity defined by UDF.

I hope this will solve my problem but I am not able to do that in fluent. Any help will be appreciated.

Thanks in advance!

LuckyTran · May 5, 2016, 17:39

No need to do anything fancy, this is straightforward.

Just run your simulation with the initial constant viscosity.

Then simply change the viscosity to the UDF. No need to export or import.

If you already have the simulation setup with the UDF-based viscosity, then simply change it to a constant viscosity in the material properties.

alexskerhut · May 6, 2016, 02:21

If I run the simulation with constant viscosity for say 50 iterations and when the solution is complete I just need to change the viscosity model and run again with required number of iterations. Is that what you want to say?

LuckyTran · May 6, 2016, 12:24

Yes.

You are free to change any number of settings and keep iterating.

alexskerhut · May 9, 2016, 09:32

Thanx a lot for the help. This solved my problem.

May 5, 2016, 02:00	Importing results to initial conditions in a different simulation for convergence.	#1
alexskerhut New Member Alex Skerhut Join Date: Mar 2016 Posts: 10 Rep Power: 10	Hey! I am defining a shear and temperature dependent viscosity as a user defined function in Fluent but the code diverges since the value of strain rate is used in denominator and at initial iterations the strain rate will be low which will lead to large fluctuations and hence divergence of the solution according to me. I wish to run the simulation at constant viscosity for few iterations and then shift to the viscosity defined by UDF taking the final iterations value of constant viscosity simulations as initial conditions( mainly strain rate) for viscosity defined by UDF. I hope this will solve my problem but I am not able to do that in fluent. Any help will be appreciated. Thanks in advance!

May 5, 2016, 17:39		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	No need to do anything fancy, this is straightforward. Just run your simulation with the initial constant viscosity. Then simply change the viscosity to the UDF. No need to export or import. If you already have the simulation setup with the UDF-based viscosity, then simply change it to a constant viscosity in the material properties. alexskerhut likes this.

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May 6, 2016, 02:21		#3
alexskerhut New Member Alex Skerhut Join Date: Mar 2016 Posts: 10 Rep Power: 10	If I run the simulation with constant viscosity for say 50 iterations and when the solution is complete I just need to change the viscosity model and run again with required number of iterations. Is that what you want to say?

May 6, 2016, 12:24		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	Yes. You are free to change any number of settings and keep iterating.

May 9, 2016, 09:32		#5
alexskerhut New Member Alex Skerhut Join Date: Mar 2016 Posts: 10 Rep Power: 10	Thanx a lot for the help. This solved my problem.