Monitoring Residuals - Initial or Final?

BigPapi34 · November 3, 2014, 05:26

Hello,

Very quick question in relation to monitoring residuals of a transient simulation using a dynamic mesh, comparing with CFX.

When monitoring the residuals, should the 'Initial' (-f9) or 'Final' (-f13) be used? I would have thought it was the final however I have seen examples of people using the initial values.

Any thoughts or comments would be greatly appreciated.

RodriguezFatz · November 3, 2014, 05:31

I use the initial residuals. As I understand it, they are a measure of how good the "outer" iterations (i.e. the whole system of equations) are solved. If they are really small, that means, that all your equations are solved quite good.

Now, you take just each single of these equations and solve it. They all are solved idependently and if they are solved well, the final residual of each equation is low. But this doesn't mean, that the "ux" you solved for in "ux-equation" fits to the "ux" that is used in the solution of "uy-equation".

November 3, 2014, 05:26	Monitoring Residuals - Initial or Final?	#1
BigPapi34 New Member Join Date: Jan 2012 Posts: 22 Rep Power: 14	Hello, Very quick question in relation to monitoring residuals of a transient simulation using a dynamic mesh, comparing with CFX. When monitoring the residuals, should the 'Initial' (-f9) or 'Final' (-f13) be used? I would have thought it was the final however I have seen examples of people using the initial values. Any thoughts or comments would be greatly appreciated.

November 3, 2014, 05:31		#2
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26	I use the initial residuals. As I understand it, they are a measure of how good the "outer" iterations (i.e. the whole system of equations) are solved. If they are really small, that means, that all your equations are solved quite good. Now, you take just each single of these equations and solve it. They all are solved idependently and if they are solved well, the final residual of each equation is low. But this doesn't mean, that the "ux" you solved for in "ux-equation" fits to the "ux" that is used in the solution of "uy-equation". __________________ The skeleton ran out of shampoo in the shower. Last edited by RodriguezFatz; November 3, 2014 at 07:19.

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