error

svdingare · October 3, 2009, 14:33

Pl let me know why we get following error?
Error: divergence detected in AMG solver: temperature
Error Object: ()
B.R.Sunil

Bak_Flow · October 5, 2009, 10:52

Dear Sunil,

this looks like a fluent error!

What the code is telling you is that at the non-linear (or outer iteration) you are on the Algebraic MultiGrid diverged. This means that you gave it a matrix that it could not reduce the residuals on.

There are only 2 ways to solve these problems:

1. Give it an easier (or reasonable) problem to solve
2. Work harder at solving it

It is useful in fluent to look at the behavior before this happend....what were the temperature residulas doing? What did the solution look like?

In approach 1 above what you can usually do is decrease the under-relaxations, drop to a first order method, solve a simpler problem...maybe you have made density a complicated function of temp, make a better mesh, make the initial guess closer to a solution, relax the problem by marching it as a transient to steady state, etc.

If you are close to have a problem you can solve then you can work on 2.....this is usually the case when you have something that is basically working but diverges occasionally......so just to get it throught the "tough spots" you give the AMG some tweaks....maybe a few more sweeps or a tighter tollerance, etc.

I hope this is of help.....please let us know how you make out.

Regards,

Bak_Flow

svdingare · October 5, 2009, 11:04

Dear bak_flow,
Thank you very much.
b.r.
sunil

October 3, 2009, 14:33	error	#1
svdingare New Member svdingare Join Date: Oct 2009 Posts: 4 Rep Power: 17	Pl let me know why we get following error? Error: divergence detected in AMG solver: temperature Error Object: () B.R.Sunil

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October 5, 2009, 10:52		#2
Bak_Flow New Member Join Date: Jun 2009 Posts: 8 Rep Power: 17	Dear Sunil, this looks like a fluent error! What the code is telling you is that at the non-linear (or outer iteration) you are on the Algebraic MultiGrid diverged. This means that you gave it a matrix that it could not reduce the residuals on. There are only 2 ways to solve these problems: 1. Give it an easier (or reasonable) problem to solve 2. Work harder at solving it It is useful in fluent to look at the behavior before this happend....what were the temperature residulas doing? What did the solution look like? In approach 1 above what you can usually do is decrease the under-relaxations, drop to a first order method, solve a simpler problem...maybe you have made density a complicated function of temp, make a better mesh, make the initial guess closer to a solution, relax the problem by marching it as a transient to steady state, etc. If you are close to have a problem you can solve then you can work on 2.....this is usually the case when you have something that is basically working but diverges occasionally......so just to get it throught the "tough spots" you give the AMG some tweaks....maybe a few more sweeps or a tighter tollerance, etc. I hope this is of help.....please let us know how you make out. Regards, Bak_Flow

October 5, 2009, 11:04		#3
svdingare New Member svdingare Join Date: Oct 2009 Posts: 4 Rep Power: 17	Dear bak_flow, Thank you very much. b.r. sunil