|July 25, 2013, 04:41||
Calculation of motion continuity error
Join Date: Sep 2012
Location: Iran - Tehran
Posts: 185Rep Power: 5
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 .
volScalarField motionContErr = fvc::ddt(dimensionedScalar("1", dimless, 1.0), mesh) - fvc::div(fvc::meshPhi(U));
I appreciate any help from you.
Thanks and best regards,
|March 11, 2016, 15:24||
Join Date: Jun 2012
Location: Torino, Italy
Posts: 742Rep Power: 9
Im the translator of OpenFOAM User Guide Chinese Edition! But always newbie on CFD.
|March 12, 2016, 17:15||
Join Date: May 2013
Posts: 37Rep Power: 5
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.
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