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

Help on EXPERT

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 17, 2001, 17:13
Default Help on EXPERT
  #1
Tim
Guest
 
Posts: n/a
Hi,

I am new to CFD and PHOENICS and I am trying to simulate natural convection around a series of cylinders. I have been having trouble with convergence so I have tried using EXPERT. I have gotten expert to work with EXPERT=T, NOWIPE=T, and by LOAD(030) into the Q1 file (note that in POLIS it says LOAD(30), which does not work...). However, for some of my simulations that I did get convergence for, using EXPERT resulted in an increase in time and number of iterations before convergence occurred. Is this something that occurrs from time to time? Secondly, I have no information on expsol, expdtf, inres, etc... Where can I find information on this? I perused through the polis but found nothing on these. If I turn expsol to true, what does it do? What does it adjust?

Thank you for any insight on these questions, Tim
  Reply With Quote

Old   July 19, 2001, 05:30
Default Re: Help on EXPERT
  #2
Mike Malin
Guest
 
Posts: n/a
EXPERT has fell into disuse at CHAM as a dynamic relaxation device, largely because it has been superceded by SARAH (Self-Adjusting Relaxation AlgoritHm).

SARAH is documented on-line at the following web address:

http://www.cham.co.uk/phoenics/d_pol...nc_s.htm#sarah

SARAH can be set in the VR Editor or in the Q1 input file by means of the PIL Command SARAH=0.001, for example. Typical values of SARAH range from 0.00001 to 0.1, depending on the application. Like EXPERT it does not always lead to improvement.
  Reply With Quote

Old   August 9, 2001, 16:31
Default Re: Help on EXPERT
  #3
Tim
Guest
 
Posts: n/a
Thanks Mike, really appreciate the input. Is there any way of determining what a suitable value for SARAH would be or is it simply trial and error? Also, will the initial values used for the false time step relaxation factors affect convergence is using SARAH?

Thanks, Tim
  Reply With Quote

Old   August 13, 2001, 10:02
Default Re: Help on EXPERT
  #4
Mike Malin
Guest
 
Posts: n/a
The optimim value of SARAH depends on the application, but typically I start with 1.e-3 and if PHOENICS diverges or oscillates, I then use the graphical interrupt facility to lower SARAH to 1.e-4 or even 1.e-5 if need be. If PHOENICS doesn't recover, I can then start again with the lower SARAH value.

I don't believe that the initial DTFALS values should have an effect, but I have not experimented with them, so I cannot be sure without trying.

  Reply With Quote

Old   August 15, 2001, 10:50
Default Re: Help on EXPERT
  #5
Tim
Guest
 
Posts: n/a
Thanks again Mike!

I have tried using SARAH starting with 1e-3 and I found that it was too large and changed it in flight. Found out that a SARAH value of 1e-5 is what is needed.

Thanks again, Tim
  Reply With Quote

Old   August 21, 2001, 14:15
Default Re: Help on EXPERT
  #6
PattiMichelle
Guest
 
Posts: n/a
Isn't that funny? I thought that EXPERT was newer than SARAH. I got the impression from the documentation that SARAH was much older. I guess they need a little more updating. Patti
  Reply With Quote

Reply

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
expert parameter sometimes1900 CFX 3 October 27, 2008 12:41
To who are expert Tony FLUENT 1 February 24, 2007 15:26
Combustion expert? HP FLUENT 2 August 16, 2004 03:55
Expert Opinion Rooh-ul-Amin Khuram CD-adapco 14 July 15, 2000 19:43
FSI/FIV Expert Needed Dmitry Paramonov Main CFD Forum 2 July 31, 1999 12:48


All times are GMT -4. The time now is 16:06.