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Wrong treatment of time derivatives in matrices (Jasak Presentation) |
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#1 |
Super Moderator
Tobias Holzmann
Join Date: Oct 2010
Location: Bad Wörishofen
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Dear community,
today I got an interesting presentation that was held last year Hrvoje Jasak with the title Pressure-Velocity Coupling in FOAM - Consistent Derivation for Steady and Transient Flow Solvers. Here it is described that the included time term in the matrices: Code:
fvVectorMatrix UEqn ( fvm::ddt(U) ... ) Can someone provide some information about that and does anyone know if this will be re-implemented in a correct and consistent way in future like Jasak suggested? However, there is one question left because based on the fact that the developers introduced the ddtCorr() function, they know that there is a problem (more or less), so why do they patch it instead of fix it. Maybe there is some special meaning of doing it in that way or there is no other possible way (but again, Jasak demonstrated it). In addition I want ask kindly if this ddtCorr is related to the Rhie Chow Interpolation because something is mentioned here: DdtPhiCorr However, here it is said that this stuff is consistent while Jasak mentioned in his presentation, that it is not consistent. In addition I will check out the paper that is mentioned in the above mentioned thread. Thanks in advance.
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Keep foaming, Tobias Holzmann |
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#2 |
Senior Member
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Dear Tobias,
I was at the presentation you are referring to and if I am not mistaking Jasak said the fix was already part of extend-4.0. That said, the technical details of the remainder of your question may need his attention as few of the OpenFOAM users grasp the exact and complete nature of the problem Jasak solved. Best Regards, -Louis |
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#3 |
Member
Michael Sukham
Join Date: Mar 2020
Location: India
Posts: 79
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I wish Dr. Jasak have written more on the presentation. I think the code snippets from foam extend 3.2 and 4.1 on this matter is same. I dont know whether the fix has been made because I am getting flux on moving meshes to be inconsistent.
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#4 |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
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There is an article on the subject: https://www.sciencedirect.com/scienc...45793018300495
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#5 |
Member
Michael Sukham
Join Date: Mar 2020
Location: India
Posts: 79
Rep Power: 6 ![]() |
Thank you Santiago!! I will go through the paper. I am working on HDPC shot sleeve partilaly filled with piston moving wall layer deletion. This will help me a lot
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#6 |
Member
Michael Sukham
Join Date: Mar 2020
Location: India
Posts: 79
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It has been updated in foam-extend 4.1 .
Code:
// Time-derivative matrix fvVectorMatrix ddtUEqn(fvm::ddt(U)); // Convection-diffusion matrix fvVectorMatrix HUEqn ( fvm::div(phi, U) - fvm::laplacian(nu, U) ); if (piso.momentumPredictor()) { solve(ddtUEqn + HUEqn == -fvc::grad(p)); } // Prepare clean 1/a_p without time derivative contribution volScalarField rAU = 1.0/HUEqn.A(); ![]() ![]() |
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