CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

conditions for unsteady problems

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 7, 2009, 02:42
Unhappy conditions for unsteady problems
  #1
New Member
 
Join Date: Nov 2009
Posts: 4
Rep Power: 7
dvdromnu is on a distinguished road
Hi,
I am solving unsteady state convective diffusion scalar equation using finite volume method(explicitly).
My problem is:
For steady state problem the solution converges at some time step and we get results. That means steady state problem is independent of initial conditions.
For unsteady state problem I am printing the values of scalar at a particular time step.
So My question is, for unsteady problem what initial conditions I have to take..?
means if I run unsteady problem for long time as in case of steady problem I am getting the same result of Steady state problem.

So, how I have to solve unsteady problem. What initial conditions I should take. What is the difference between unsteady state and steady state solutions
dvdromnu is offline   Reply With Quote

Old   November 7, 2009, 15:02
Default
  #2
Senior Member
 
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,890
Rep Power: 25
alberto will become famous soon enoughalberto will become famous soon enough
If the problem admits a steady state solution, the unsteady solution procedure should lead to the same solution, if it is run long enough.
__________________
Alberto

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image.
GeekoCFD 32bit - The 32bit edition of GeekoCFD.
GeekoCFD text mode - A smaller version of GeekoCFD, text-mode only, with only OpenFOAM. Available in a variety of virtual formats.
alberto is offline   Reply With Quote

Old   November 8, 2009, 01:45
Smile
  #3
New Member
 
Join Date: Nov 2009
Posts: 4
Rep Power: 7
dvdromnu is on a distinguished road
Thank You................
dvdromnu is offline   Reply With Quote

Old   November 8, 2009, 02:52
Default
  #4
Senior Member
 
Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,890
Rep Power: 25
alberto will become famous soon enoughalberto will become famous soon enough
Quote:
Originally Posted by dvdromnu View Post
Thank You................
I'm sorry for the very vague answer. If you want more details, you should provide some more information about your problem.

Best,
__________________
Alberto

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image.
GeekoCFD 32bit - The 32bit edition of GeekoCFD.
GeekoCFD text mode - A smaller version of GeekoCFD, text-mode only, with only OpenFOAM. Available in a variety of virtual formats.
alberto is offline   Reply With Quote

Old   November 9, 2009, 01:49
Default solution profile
  #5
New Member
 
Join Date: Nov 2009
Posts: 4
Rep Power: 7
dvdromnu is on a distinguished road
Actually I want to know whether there is any difference in solution procedure of unsteady state and steady state scalar convective diffusion equation.

Also I want to know if we solve scalar equation with diffusion term only(without convection term) we will get one solution. Now, if we solve the same including convection term, we get another solution. So, adding convection term changes the solution profile( with only diffusion term) or it shifts the solution profile..?
dvdromnu is offline   Reply With Quote

Old   November 9, 2009, 03:15
Default
  #6
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 646
Rep Power: 10
dmoroian is on a distinguished road
Hello .... dvdromnu (actually it would be nice to have a name here),
If the equations you're solving admit a solution, and if that solution is unique, then it doesn't matter what initial conditions you start with (as long as they are physical or representative for your equations).
If you're interested in the steady state solution, then again it doesn't matter what approach you use (steady/unsteady).
If the convection/diffusion equation has the same steady state solution as the diffusion only equation, then you will not see any "profile shift".
The only difference would be in the choice of the solver, and the amount of computational time requested (shorter for steady state and longer for unsteady).

I hope this was useful,
Dragos
dmoroian is offline   Reply With Quote

Reply

Tags
initial conditions, unsteady

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
Boundary conditions Cmesh high AOA pcasto OpenFOAM Running, Solving & CFD 3 February 5, 2009 07:04
Outlet conditions in BuoyantFoam jont OpenFOAM Running, Solving & CFD 2 October 15, 2007 08:55
Problems considering boundary conditions Morten Andersen CFX 1 January 18, 2007 10:04
Problems turbFoam harwin OpenFOAM Pre-Processing 6 December 7, 2006 06:36
compressible boundary conditions vivian Main CFD Forum 8 April 24, 2006 07:23


All times are GMT -4. The time now is 03:19.