CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

general question

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 16, 1998, 20:24
Default general question
  #1
jay
Guest
 
Posts: n/a
In the event of a simulation, what is one to make of the fact that the residuals oscillate wildly for the first few iterations, and then settle down and fall nicely. Aside from the explanations of why this happens, is a soln from such trend to be trusted as being...good/trustable or..."can't trust it, need to re-do until you obtain a decent trend from the beginning." Your thoughts people?
  Reply With Quote

Old   December 17, 1998, 14:09
Default Re: general question
  #2
John C. Chien
Guest
 
Posts: n/a
When you say " residuals oscillate wildly ...", I think you are talking about getting steady-state solutions using iterative methods. Let's reverse the process, say, you now have the steady-state solution ( regardless how you define it ), then the (n-1)th solution will be considered as a non-steady-state solution. This (n-1)th solution is not going to create any oscillation for you. So , the reason why you are getting oscillating residuals is mainly because the initial guess is a " wild guess ". The right way to do is to study the problem and come up with a good initial algebraic or analytical flow field. I have used this approach since early 70's, and the advantage is "fast convergency". This is an area where the reward is high. This requires knowledge and experience about the fluid dynamic part of the problem, that is why CFD is not equal to CFD code or just running CFD code. The difference can be several minuites instead of several days of computing time.
  Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to solver coupled transport equations chris1980 OpenFOAM Running, Solving & CFD 8 October 29, 2019 08:15
General question what fluid properties do you use harly OpenFOAM Running, Solving & CFD 0 November 18, 2008 16:38
A general C question niklas OpenFOAM 1 September 8, 2008 12:38
Poisson Solver question Suresh Main CFD Forum 3 August 12, 2005 05:37
question K.L.Huang Siemens 1 March 29, 2000 05:57


All times are GMT -4. The time now is 03:40.