CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

A Peculiar Convergence Issue

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Display Modes
Old   February 18, 2013, 15:16
Default A Peculiar Convergence Issue
New Member
Join Date: Apr 2010
Posts: 12
Rep Power: 9
pano is on a distinguished road
Hi people,

I have a question regarding convergence.

I use a CFD software which is very specialised on Marine applications. It is not actually a fully RANSE approach, it is rather based on Rankine source panel method, i.e. on potential flow theory for the free surface and it is coupled with boundary layer analysis for the viscous force components.
The problem has as follows:
If the convergrence criteria are left at their default values, my cases do not converge.
I notice that the criterion that fails is the free surface elevation (waveheight residual if you like). And so, I raise it by 100% (just to experiment) and as soon as it converges, I manually call the software to execute one more iteration. Then I notice that the result after this iteration are different to the results of the same iteration with original setup.
Then, I keep asking for more and more iterations (one at a time of course) to be completed only to find out that the waveheight residual is actually decreasing even beyond the original criterion value (with the original setup it would increase and eventually totally diverge).
Why does the software miss these solutions with the original setup and happens fo find them with the manual iterations? Where would you turn your attention to? Would you alter the relaxation factors to make it "search better"? Do sou suspect another source of error?
The worrying bit is that the results do change quite substantially during those final manual iterations and so this has to be addressed properly.

Thanks for your time.

pano is offline   Reply With Quote


cfd, convergence, marine, residual

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Continuity convergence issue on a 3d wing Nick R FLUENT 18 February 4, 2015 12:21
[ICEM] issue occur after extrude 2D airfoil mesh and convergence problem in CFX shiyun ANSYS Meshing & Geometry 4 May 9, 2012 19:55
Force can not converge colopolo CFX 13 October 4, 2011 22:03
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
Convergence issue Jake FLUENT 3 June 30, 2005 04:12

All times are GMT -4. The time now is 18:44.