local time-step

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

 December 22, 2004, 09:37 local time-step #1 ZondeR Guest   Posts: n/a Sponsored Links Hi everybody, I have just discovered the "local time-step", that is using a time-step varying in space, and I have some questions about it, it would be nice if some of you could help me. .Does it have something to do with "fractional step"? .Will a result of a local time-step computation be just like the one of a steady state computation? .Are there some tricks or things I should care about when using this option? like special care for convergence or so. .Do you have any comment about it? Thanks

 December 22, 2004, 17:57 Re: local time-step #3 ZondeR Guest   Posts: n/a Thank you very much! by fractional step, I was refering to a previous message in this forum :"Annie , Wed, 15 Dec 2004, 1:58 a.m." I guess I just have to find that bok from Hirsch now.

 December 23, 2004, 11:24 Re: local time-step #4 Biga Guest   Posts: n/a Yes! I strongly recommend reading Hirsch... =) About fractional step, I really got it wrong. It doesn't have nothing to do with what I said. It's all about how to integrate incompressible flows in time, which have decoupled momentum and pressure equations. Here is an article on that subject I've just googled: http://anziamj.austms.org.au/V45/CTAC2003/Armf/Armf.pdf Regards, Biga

 December 23, 2004, 20:10 Re: local time-step #5 noName Guest   Posts: n/a When people use the words Fractional Step, most often, they are refering to the fact that different terms of the governing equation are treated separately. This is what I understand from the literature, please correct me if I am wrong. E.g. ADI (for parabolic equations) is the simplest form of fractional stepping -- take a half step in X ignoring any evolution in Y and then take another half step in Y ignoring any evolution in X. Do this without losing consistency, and do it implicitly, giving the required stability. E.g. Often (e.g. in spectral methods) people integrate the convective term in a half step and the remaining (pressure, viscous) terms in another half step. E.g. Some others use a multi-step, Adams-type, method and alternately evaluate different terms using previous data.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post pUl| FLUENT 31 August 21, 2015 04:46 msrinath80 OpenFOAM Running, Solving & CFD 18 March 3, 2015 06:36 sandisk FLUENT 0 July 18, 2011 02:57 lr103476 OpenFOAM Running, Solving & CFD 30 November 19, 2007 15:09 skabilan OpenFOAM Running, Solving & CFD 12 September 17, 2007 17:48