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

Basic question about local timestepping

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

Like Tree4Likes
  • 2 Post By flotus1
  • 2 Post By FMDenaro

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 20, 2020, 06:50
Default Basic question about local timestepping
  #1
Senior Member
 
Sayan Bhattacharjee
Join Date: Mar 2020
Posts: 495
Rep Power: 8
aerosayan is on a distinguished road
This maybe a basic question, but I don't know the answer to it.


I was reading a code that does local timestepping in each cell to allegedly accelerate the solution convergence of a steady compressible Euler solver.


As shown in the picture attached, we can see the logic being used to calculate the minimum timestep possible for a cell, then updating the cell values with an m-stage process.


I don't understand how this actually works, and how the solution make any physical sense.



Based on the code, we can see that each cell will be advanced to different points in time, since every cell will have a different timestep calculated for it.


How does the simulation work when each cell is at a different point in time?



Thanks
Attached Images
File Type: jpg local-timestep.jpg (54.8 KB, 12 views)

Last edited by aerosayan; December 20, 2020 at 06:52. Reason: clarfication of question
aerosayan is offline   Reply With Quote

Old   December 20, 2020, 07:00
Default
  #2
Super Moderator
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,427
Rep Power: 49
flotus1 has a spectacular aura aboutflotus1 has a spectacular aura about
Quote:
steady compressible Euler solver
The solution is only correct once the steady state is reached. I.e. the solution is fully converged.
sbaffini and aerosayan like this.
flotus1 is offline   Reply With Quote

Old   December 20, 2020, 07:13
Default
  #3
Senior Member
 
Sayan Bhattacharjee
Join Date: Mar 2020
Posts: 495
Rep Power: 8
aerosayan is on a distinguished road
Quote:
Originally Posted by flotus1 View Post
The solution is only correct once the steady state is reached. I.e. the solution is fully converged.

Okay, that seems correct. The simulations do work, and I've validated them before.


Thanks.
aerosayan is offline   Reply With Quote

Old   December 20, 2020, 09:19
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,887
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by aerosayan View Post
This maybe a basic question, but I don't know the answer to it.


I was reading a code that does local timestepping in each cell to allegedly accelerate the solution convergence of a steady compressible Euler solver.


As shown in the picture attached, we can see the logic being used to calculate the minimum timestep possible for a cell, then updating the cell values with an m-stage process.


I don't understand how this actually works, and how the solution make any physical sense.



Based on the code, we can see that each cell will be advanced to different points in time, since every cell will have a different timestep calculated for it.


How does the simulation work when each cell is at a different point in time?



Thanks

The key to understand the issue is to forget about a physical meaning of the time step and considering only that the equations have a residual that is driven to zero by using local parameters for accelerating the convergence.
aerosayan and aero_head like this.
FMDenaro is offline   Reply With Quote

Reply

Tags
local time stepping, timestep

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
AMI speed performance danny123 OpenFOAM 21 October 24, 2020 05:13
[blockMesh] BlockMeshmergePatchPairs hjasak OpenFOAM Meshing & Mesh Conversion 11 August 15, 2008 08:36
Convergence moving mesh lr103476 OpenFOAM Running, Solving & CFD 30 November 19, 2007 15:09
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 03:58
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07


All times are GMT -4. The time now is 23:09.