how can I make sure rhoSimplecFoam NEVER crashes?

mihaipruna · September 21, 2012, 17:10

Basically I want it to automatically cut off big numbers, replace divisions by 0 with something else, etc.
I tried relaxation factors and cellLimited gradients.
Is there a way to ensure you get a solution (even inaccurate) , always?

yhaomin2007 · December 25, 2012, 22:55

Hi, Mihai

Have you solved your problem, I think I have met the same problem like you.
I am running a simulation with a large area change, which makes the simulation very easy to crash.

Thank you

mihaipruna · December 27, 2012, 09:12

I had to streamline the geometry further. I was not able to get it to converge on my original model. WIth that, and residuals set to 10E-3, I was able to get it to converge. I had to set residuals this high because divergence occurred after a certain number of iterations. The residuals dropped to a certain level and then they started increasing (p mainly), and then the density would eventually reach either very large or small values, then it would crash.

So, in essence, I have not found a simple solution or a setting that would always ensure convergence just yet.

yhaomin2007 · December 27, 2012, 09:31

Is your flow a pressure driven flow or velocity driven flow? I think you can try time varying condition to get approach the condition you want. And I also suggest you try to decrease the relaxation factor to ensure stable.

mihaipruna · December 27, 2012, 11:10

I decided to go with pressure driven flow (total pressure).
In order to prevent my simulation from crashing right away , I had , for the inlet:

type totalPressure;
gamma 1.400000;
rho rho;
p0 uniform 29400.000000;
value uniform 26500.000000;

the 26500 was the static pressure and that was set to fixed at the outlet. I was not able to get the flow to a Mach number above 0.4 without it eventually crashing. Relaxation factors helped a bit.

So, again, it was a combination of factors and tweaks of residuals, relaxation factors, geometry and boundary conditions that yielded a converged solution.

September 21, 2012, 17:10	how can I make sure rhoSimplecFoam NEVER crashes?	#1
mihaipruna Senior Member Mihai Pruna Join Date: Apr 2010 Location: Boston Posts: 195 Rep Power: 16	Basically I want it to automatically cut off big numbers, replace divisions by 0 with something else, etc. I tried relaxation factors and cellLimited gradients. Is there a way to ensure you get a solution (even inaccurate) , always?

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December 25, 2012, 22:55		#2
yhaomin2007 Member Haomin Yuan Join Date: Jan 2012 Location: Madison, Wisconsin, USA Posts: 59 Rep Power: 14	Hi, Mihai Have you solved your problem, I think I have met the same problem like you. I am running a simulation with a large area change, which makes the simulation very easy to crash. Thank you

December 27, 2012, 09:12		#3
mihaipruna Senior Member Mihai Pruna Join Date: Apr 2010 Location: Boston Posts: 195 Rep Power: 16	I had to streamline the geometry further. I was not able to get it to converge on my original model. WIth that, and residuals set to 10E-3, I was able to get it to converge. I had to set residuals this high because divergence occurred after a certain number of iterations. The residuals dropped to a certain level and then they started increasing (p mainly), and then the density would eventually reach either very large or small values, then it would crash. So, in essence, I have not found a simple solution or a setting that would always ensure convergence just yet.

December 27, 2012, 09:31		#4
yhaomin2007 Member Haomin Yuan Join Date: Jan 2012 Location: Madison, Wisconsin, USA Posts: 59 Rep Power: 14	Is your flow a pressure driven flow or velocity driven flow? I think you can try time varying condition to get approach the condition you want. And I also suggest you try to decrease the relaxation factor to ensure stable.

December 27, 2012, 11:10		#5
mihaipruna Senior Member Mihai Pruna Join Date: Apr 2010 Location: Boston Posts: 195 Rep Power: 16	I decided to go with pressure driven flow (total pressure). In order to prevent my simulation from crashing right away , I had , for the inlet: type totalPressure; gamma 1.400000; rho rho; p0 uniform 29400.000000; value uniform 26500.000000; the 26500 was the static pressure and that was set to fixed at the outlet. I was not able to get the flow to a Mach number above 0.4 without it eventually crashing. Relaxation factors helped a bit. So, again, it was a combination of factors and tweaks of residuals, relaxation factors, geometry and boundary conditions that yielded a converged solution.