Discussion Groups

Simulation CFD

Reply
Member
clayton.scelzi
Posts: 4
Registered: ‎08-07-2011

Flat lines detected in Convergence Monitor - Auto Stop.

316 Views, 4 Replies
03-20-2013 11:15 AM

I am trying to simulate airflow through a duct and out grilles. When i run the simulation it ends pretty quickly and reads Flat lines detected in Convergence Monitor - Auto Stop. in the message window. There is no flow through the duct or out the grilles? What does Flat lines detected in Convergence Monitor - Auto Stop. mean and how would i fix it?

Please use plain text.
Distinguished Contributor
Cnoj
Posts: 106
Registered: ‎11-26-2008

Re: Flat lines detected in Convergence Monitor - Auto Stop.

03-20-2013 02:30 PM in reply to: clayton.scelzi

The flat lines message means your simulation completed successfully:

http://wikihelp.autodesk.com/Simulation_CFD/enu/2013/Help/0407-Learning407/0687-Self-Pac687/0704-Cha...

 

Sounds like you have not set up the flow correctly.

 

Please use plain text.
Member
clayton.scelzi
Posts: 4
Registered: ‎08-07-2011

Re: Flat lines detected in Convergence Monitor - Auto Stop.

03-21-2013 05:24 AM in reply to: clayton.scelzi
I have an air mass in my room and also I have multiple air masses inside my ductwork in a series that connects to the outside. I have a volumetric flow rate set at the inlet which pulls from outside the room geometry.i have then smaller air masses which connect to the outside and have a pressure of 0 set to those. Do I need to have anymore boundary conditions set where the multiple air masses connect?
Please use plain text.
*Expert Elite*
OmkarJ
Posts: 440
Registered: ‎10-02-2012

Re: Flat lines detected in Convergence Monitor - Auto Stop.

03-21-2013 07:14 AM in reply to: clayton.scelzi

A picture would be helpful here. As long as different regions of your geometry are connected and have same material, there is no other boundary condition needed. 

 

The message your reported is actually an indication that SimCFD thinks the average value plots have flattened. If you are not happy with the current convergence, you can always adjust the setting of Solve >> Solution Control >> Automatic Convergence Assessment as tight, or even unclick it and stop the iterations when you see the lines flatten.

 

OJ

Please use plain text.
Distinguished Contributor
ilyas
Posts: 141
Registered: ‎06-13-2012

Re: Flat lines detected in Convergence Monitor - Auto Stop.

03-24-2013 07:13 PM in reply to: clayton.scelzi

Hi, you don't need to do anything between the interface of two like fluid materials. Sim CFD would treat it as one fluid domain.

I once imported a duct model from revit and ran an analysis. My duct was modelled along with the AC. I applied a volume flow rate at the inlet duct surface but forgot to suppress my solid AC. Hence, the inlet became a wall and there was no flow and the solver stops immediately after a few iterations. Could this be your case?

Please use plain text.