Meaning of non-physical points ...

deeps · December 27, 2013, 02:56

Hi All,

I had few queries regarding SU2 terminology.

1. Several times I encounter this msg: The solution contains n non-physical points. What does this refer to ?

2. How are the residuals defined? Lets say the value at some iteration for variable 1 is -3.4567. What does it indicate? Does it mean log_10 (Var1_i iter/ Var1_ i-1 iter)?

3. Has anyone tried using 2 level Multigrid? How to decide optimal child/parent ratio for a given grid?

Would appreciate your response.
Thanks,
Deepanshu.

fpalacios · January 11, 2014, 23:05

Non-physical points means that after the solution update the density is negative.
Su2 computed the L2 norm of the residual and plots the Log10 of the value. In other words a value of -12 means that the residual is 10^-12.
To set the optimal parameters of the MG is an art. when you have convergence issues do not forget to reduce:
% Damping factor for the residual restriction
MG_DAMP_RESTRICTION= ____
%
% Damping factor for the correction prolongation
MG_DAMP_PROLONGATION= ____

Best Regards,
Francisco

deeps · January 13, 2014, 01:20

Dear Francisco,

Thank you for your inputs.

Deepanshu.

momo_sjx · January 14, 2014, 18:51

Set Multigrid=0, the non-physical points can be removed.
It works sometimes for me.

deeps · January 29, 2014, 02:04

Thanks Sean for your inputs.

December 27, 2013, 02:56	Meaning of non-physical points ...	#1
deeps New Member Join Date: Nov 2009 Posts: 19 Rep Power: 17	Hi All, I had few queries regarding SU2 terminology. 1. Several times I encounter this msg: The solution contains n non-physical points. What does this refer to ? 2. How are the residuals defined? Lets say the value at some iteration for variable 1 is -3.4567. What does it indicate? Does it mean log_10 (Var1_i iter/ Var1_ i-1 iter)? 3. Has anyone tried using 2 level Multigrid? How to decide optimal child/parent ratio for a given grid? Would appreciate your response. Thanks, Deepanshu.

January 11, 2014, 23:05		#2
fpalacios Super Moderator Francisco Palacios Join Date: Jan 2013 Location: Long Beach, CA Posts: 404 Rep Power: 15	Non-physical points means that after the solution update the density is negative. Su2 computed the L2 norm of the residual and plots the Log10 of the value. In other words a value of -12 means that the residual is 10^-12. To set the optimal parameters of the MG is an art. when you have convergence issues do not forget to reduce: % Damping factor for the residual restriction MG_DAMP_RESTRICTION= ____ % % Damping factor for the correction prolongation MG_DAMP_PROLONGATION= ____ Best Regards, Francisco akun646 likes this.

January 13, 2014, 01:20	Meaning of non-physical points ...	#3
deeps New Member Join Date: Nov 2009 Posts: 19 Rep Power: 17	Dear Francisco, Thank you for your inputs. Deepanshu.

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January 14, 2014, 18:51		#4
momo_sjx Member Sean (J.X.) Shi Join Date: May 2012 Location: US Posts: 34 Rep Power: 14	Set Multigrid=0, the non-physical points can be removed. It works sometimes for me.

January 29, 2014, 02:04		#5
deeps New Member Join Date: Nov 2009 Posts: 19 Rep Power: 17	Thanks Sean for your inputs.