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

Explicit Duel Time Stepping

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

LinkBack Thread Tools Display Modes
Old   November 4, 2005, 09:25
Default Explicit Duel Time Stepping
Posts: n/a
I have implemented DTS in my code which is 3D multiblock structured. Explicit formulation. However testing out on simple cases, I found that the computational step i.e the psuedo time step/ no. of sub iterations has to be near the time step corrosponing to the smallest cell in the Grid. So essentialy for unsteady problems, DTS and global are eating out almost same computing time. Can anyone comment on it?


  Reply With Quote

Old   November 4, 2005, 11:28
Default Re: Explicit Duel Time Stepping
Posts: n/a
Dear Aditya,

The basic idea of introducing the DTS for unsteady problems is the fact that the problem becomes pseudo-steady, and hence convergence acceleration devices can be employed. Now in your case, the DTS is explicit, and you do not seem to use any convergence acceleration devices. And being explicit, you are bound by a stability criterion, and this is why you seem to get the computational time step closer to the time step corresponding to the smallest cell in the domain. You could have also run your test case without DTS in an explicit mode. You would end up in getting the same results. The fact that "DTS and global are eating out almost same computing time" is a conclusion, is a consequence of two factors- An explicit formulation bound by a stability criterion and the absence of convergence acceleration devices.

The possible remedies would include 1. Still explicit, but with convergence acceleration using multigrid, residual smoothing, enthalpy damping etc ... 2. Implicit, preferably matrix-free formulation with/without the aforementioned devices.

I work with implicit formulation, which does not have a stability bound, atleast in a linear sense, and use local time stepping in DTS. I have seen that for problems such as an oscillating airfoil problem in 2D, the use of implicit procedure speeds up drastically compared to an explicit procedure.

Hope this helps


  Reply With Quote

Old   November 7, 2005, 23:14
Default New Topics wanted
Posts: n/a
I am a PhD student of CFD. I want to do research on the current new things. Please help me to provide new topics in CFD.


  Reply With Quote


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
TimeVaryingMappedFixedValue irishdave OpenFOAM Running, Solving & CFD 29 May 3, 2017 08:59
Extrusion with OpenFoam problem No. Iterations 0 Lord Kelvin OpenFOAM Running, Solving & CFD 8 March 28, 2016 11:08
local time stepping in OF mecbe2002 OpenFOAM 2 May 19, 2010 03:52
Computational time sunnysun OpenFOAM Running, Solving & CFD 5 March 16, 2009 04:32
Convergence moving mesh lr103476 OpenFOAM Running, Solving & CFD 30 November 19, 2007 15:09

All times are GMT -4. The time now is 23:56.