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-   -   Fatal overflow in linear solver error. Why? (http://www.cfd-online.com/Forums/cfx/22625-fatal-overflow-linear-solver-error-why.html)

zaidun May 30, 2006 05:31

Fatal overflow in linear solver error. Why?
 
| ERROR #004100018 has occurred in subroutine FINMES. | | Message: | | Fatal overflow in linear solver.

hi i run my analysis using k-epsilon turbulence model and after 9 iterations, above error ocuured. i mesh my model in Gambit and using boundary layer as follows;

-first layer thickness = 0.0001 m -expnasion factor = 1.2 -layer = 20 layer

can anybody give me an idea..


Glenn Horrocks May 30, 2006 18:20

Re: Fatal overflow in linear solver error. Why?
 
Hi,

Your simulation has diverged. Look in the documentation under obtaining convergence.

Glenn Horrocks

prayskyer June 1, 2006 00:31

Re: Fatal overflow in linear solver error. Why?
 
this problem happened again to me!Is there any BC not apprcieate for me???i set pressure for inlet,and pressure for outlet ,is it allowed???

Brendan June 9, 2006 09:12

Re: Fatal overflow in linear solver error. Why?
 
As a quick fix: Did you try adjusting your timestep from automatic to manual?

Divide the recommended auto time step by 10^3 and try it again.

Bdew8556 August 10, 2016 08:25

Great response Glenn,

Could you perhaps elaborate on what the physical timescale does?

I am aiming to run a steady flow simulation, what effect does it have in this case?

Cheers (Fellow Australian I see)

Brett

ghorrocks August 10, 2016 19:25

Hi Brett,

You certainly have dug up a thread from ancient history here. You are lucky that I am still around :) I have not seen the other people on this thread for 10 years....

Physical time scale is the rate at which CFX advances the numerical values in a steady state simulation. There are other ways of doing it used in other software such as under-relaxation, but CFX does it by a physical time scale. So a large time scale advances the values a large amount, a small time scale advances it a small amount. Large time scales can approach convergence quicker, but you can only go so fast before the numerics becomes unstable and the simulation diverges.

Note that the physical time scale in a steady state simulation is not the same as time step size in a transient simulation. A steady state simulation has many transient terms removed as they are zero for steady state, whereas a transient simulation includes all the transient terms.

Bdew8556 August 11, 2016 04:26

Thanks Glenn, Lucky indeed.

How does that related to the mesh density, ie the dx,dy,dz values? Is it the increment it adds on from the initial values at each cell?

Brett

ghorrocks August 11, 2016 05:59

Have a look at the CFX documentation and a CFD textbook for an answer to that question. The spatial discretisation is handled very differently to the time discretisation (for a transient simulation) or the convergence advancement procedure (for a steady state run). I will not describe the difference on the forum as it is far too complex. Hence see a textbook.


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