# Calculation of motion continuity error

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

 July 25, 2013, 04:41 Calculation of motion continuity error #1 Senior Member   Sasan Ghomi Join Date: Sep 2012 Location: Iran - Tehran Posts: 185 Rep Power: 6 Hi Dear Foamers, I am trying to understand calculating of motion continuity error. I think first line in below code is creating an object without any dimension and I don't understand the meaning of [d/dt ( Object ) ] . Also I couldn't understand what do meshPhi(U) do exactly . Code: volScalarField motionContErr = fvc::ddt(dimensionedScalar("1", dimless, 1.0), mesh) - fvc::div(fvc::meshPhi(U)); Can anybody help me for understanding this code? I appreciate any help from you. Thanks and best regards, Sasan.

 March 11, 2016, 15:24 #2 Senior Member   Dongyue Li Join Date: Jun 2012 Location: Torino, Italy Posts: 750 Rep Power: 9 Hi, This is for space conservative law equation, check it out in Peric: __________________ Im the translator of OpenFOAM User Guide Chinese Edition! But always newbie on CFD. http://dyfluid.com/en.html

 March 12, 2016, 17:15 #3 Member   Thomas Boucheres Join Date: May 2013 Posts: 41 Rep Power: 5 Hello, Sharonyue gives you good answer but maybe not so easy to understand if you are "new" to CFD discretization techniques If it is the case, maybe it is difficult to understand what means the time derivative of 1. Isn't it equalt to zero??? In fact, if you want to really understand the meshPhi(U) goal, you should read some courses on the topic "ALE technique" (for Arbitrary Lagrangian Eulerian) which allows the computation of flows on moving meshes. One difficulty in doing that is to respect a "hidden" conservation law which is called in the litterature the "GCL" (for Geometric Conservation Law). Roughly speaking, the time evolution of the mesh must be done in such a way that one respect a kind of compatibility condition( the so-called GCL) between the temporal evolution of the volume of a cell and the face flux resulting from the velocity associated with the mesh motion. This is precisely the meaning of the equation writtent by Sharonyue. sharonyue likes this.

 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 gschaider OpenFOAM 300 October 29, 2014 19:00 SteveGoat Fluent UDF and Scheme Programming 7 October 15, 2014 07:11 Yogini Fluent UDF and Scheme Programming 7 October 3, 2012 07:24 sen.1986 OpenFOAM 14 March 23, 2012 05:12 vaina74 OpenFOAM Installation 13 February 3, 2012 18:43

All times are GMT -4. The time now is 04:54.