# Which procedure to solve Ueqn without momentum predictor.

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 July 2, 2013, 21:04 Which procedure to solve Ueqn without momentum predictor. #1 Senior Member   Dongyue Li Join Date: Jun 2012 Location: Torino, Italy Posts: 675 Rep Power: 8 Hi, This is icoFoam's code,: Code: ```fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U) - fvm::laplacian(nu, U) ); solve(UEqn == -fvc::grad(p));//this term is only executed when the momentumPredictor flag is set to true // --- PISO loop for (int corr=0; corr

 July 2, 2013, 23:37 #2 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 418 Rep Power: 14 Hi, in the PISO method, U is predicted and then corrected in the pressure-velocity coupling loop, so that, if you don't predict the velocity, the velocity used to start the coupling loop is a derivative of the velocity in the last time step as is done in interFoam and other solvers. In the code you've cited the matrix for the momentum equation is assembled so that you have the A and H methods available for the use in the PISO loop, the line: HbyA = rAU*UEqn.H(); calculates a first approximation for U using the H operator applied to the velocity of the last-timestep or which was predicted when you solved the UEqn (if you did it) and the A operator. If you need it, please check the definition of these operators in chapter 2.7 of my Ph.D. thesis https://drive.google.com/file/d/0B2l...it?usp=sharing and Jasak's Ph.D. and other's thesis. Regards. Tushar@cfd and sharonyue like this. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Post-doctoral Fellow Research Center for Computational Mechanics (CIMEC) - CONICET/FICH-UNL T.E.: 54-342-4511594 Ext. 1005 Güemes 3450 - (3000) Santa Fe Santa Fe - Argentina http://www.cimec.org.ar Last edited by wyldckat; April 1, 2014 at 15:01. Reason: rectified link according to request

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