Coefficient loop iteration

vortex69 · May 20, 2016, 14:54

In CFX solver control , there are two options namely "Max. Coeff. Loops" and "Min. Coeff. Loops". What is meant by COEFFICIENT LOOPS here ?

Far · May 20, 2016, 15:24

outer loops for your simulation. no of iterations for that time step

vortex69 · May 20, 2016, 15:31

thank you, but what do u mean by "outer loops for your simulation"

vortex69 · May 20, 2016, 15:32

Quote:

Originally Posted by vortex69

In CFX solver control , there are two options namely "Max. Coeff. Loops" and "Min. Coeff. Loops". What is meant by COEFFICIENT LOOPS here ?

thank you, but what do u mean by "outer loops for your simulation"?

ghorrocks · May 21, 2016, 07:10

In a transient simulation you typically do 3-5 iterations per time step. These iterations are called coefficient loops as the equations are linearised for each iteration, so the non-linear part of the Navier Stokes equation is introduced by updating the linear coefficients.

vortex69 · May 21, 2016, 10:59

Quote:

Originally Posted by ghorrocks

In a transient simulation you typically do 3-5 iterations per time step. These iterations are called coefficient loops as the equations are linearised for each iteration, so the non-linear part of the Navier Stokes equation is introduced by updating the linear coefficients.

thank you very much, could you please shortly explain what do u mean by "non-linear part of the Navier Stokes equation is introduced by updating the linear coefficients" ? ( I really need to know that and I would appreciate it if u help me )

ghorrocks · May 22, 2016, 07:25

The convection term in the Navier Stokes equations (https://en.wikipedia.org/wiki/Navier...okes_equations) is non linear as it has the velocity multiplied by the gradient of velocity. You can't solve this with a linear equation solver. So you linearise it by assuming the non-linear component is constant thereby making the equations linear and solveable by linear solvers. But to account for the non-linearity you then re-calculate the constant you use to model the non-linear component and repeat the process.

May 20, 2016, 14:54	Coefficient loop iteration	#1
vortex69 New Member Ali Join Date: Apr 2016 Location: Germany Posts: 26 Rep Power: 10	In CFX solver control , there are two options namely "Max. Coeff. Loops" and "Min. Coeff. Loops". What is meant by COEFFICIENT LOOPS here ?

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May 20, 2016, 15:24		#2
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	outer loops for your simulation. no of iterations for that time step

May 20, 2016, 15:31		#3
vortex69 New Member Ali Join Date: Apr 2016 Location: Germany Posts: 26 Rep Power: 10	thank you, but what do u mean by "outer loops for your simulation"

May 21, 2016, 07:10		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	In a transient simulation you typically do 3-5 iterations per time step. These iterations are called coefficient loops as the equations are linearised for each iteration, so the non-linear part of the Navier Stokes equation is introduced by updating the linear coefficients.

May 22, 2016, 07:25		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	The convection term in the Navier Stokes equations (https://en.wikipedia.org/wiki/Navier...okes_equations) is non linear as it has the velocity multiplied by the gradient of velocity. You can't solve this with a linear equation solver. So you linearise it by assuming the non-linear component is constant thereby making the equations linear and solveable by linear solvers. But to account for the non-linearity you then re-calculate the constant you use to model the non-linear component and repeat the process.