# Some basic doubts on solvers

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 February 27, 2011, 18:46 Some basic doubts on solvers #1 Member   Join Date: Nov 2010 Posts: 33 Rep Power: 7 Sponsored Links I have some basic doubts in the working of interFoam/dambreak case: 1. What difference does it make case if the following changes are made in controlDict: Start time: 0 end time : 1 Changed to start time: 0 end time: 0.25 I understand that it reduces the simulation time, but what happens to the quality/correctness of the results? 2. What equation is interFoam/dambreak actually solving? From the code in pEqn.H: Code: ```{ volScalarField rUA = 1.0/UEqn.A(); surfaceScalarField rUAf = fvc::interpolate(rUA); U = rUA*UEqn.H(); surfaceScalarField phiU ( "phiU", (fvc::interpolate(U) & mesh.Sf()) + fvc::ddtPhiCorr(rUA, rho, U, phi) ); adjustPhi(phiU, U, p); phi = phiU + ( fvc::interpolate(interface.sigmaK())*fvc::snGrad(alpha1)*mesh.magSf() + fvc::interpolate(rho)*(g & mesh.Sf()) )*rUAf; for(int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++) { fvScalarMatrix pEqn ( fvm::laplacian(rUAf, p) == fvc::div(phi) ); pEqn.setReference(pRefCell, pRefValue); if (corr == nCorr-1 && nonOrth == nNonOrthCorr) { pEqn.solve(mesh.solver(p.name() + "Final")); } else { pEqn.solve(mesh.solver(p.name())); } if (nonOrth == nNonOrthCorr) { phi -= pEqn.flux(); } } U += rUA*fvc::reconstruct((phi - phiU)/rUAf); U.correctBoundaryConditions(); }``` How do you interpret the mathematical version of equation being solved? 3. How does solving of some equation narrows down to PCG solver which solves the equation of the form Ax=b? Thanks.

February 28, 2011, 08:46
#2
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Santiago Marquez Damian
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Quote:
 Originally Posted by pkr I have some basic doubts in the working of interFoam/dambreak case: 1. What difference does it make case if the following changes are made in controlDict: Start time: 0 end time : 1 Changed to start time: 0 end time: 0.25 I understand that it reduces the simulation time, but what happens to the quality/correctness of the results?
I should be the same with the only difference of total simulation time.

Quote:
 2. What equation is interFoam/dambreak actually solving? From the code in pEqn.H: Code: ```{ volScalarField rUA = 1.0/UEqn.A(); surfaceScalarField rUAf = fvc::interpolate(rUA); U = rUA*UEqn.H(); surfaceScalarField phiU ( "phiU", (fvc::interpolate(U) & mesh.Sf()) + fvc::ddtPhiCorr(rUA, rho, U, phi) ); adjustPhi(phiU, U, p); phi = phiU + ( fvc::interpolate(interface.sigmaK())*fvc::snGrad(alpha1)*mesh.magSf() + fvc::interpolate(rho)*(g & mesh.Sf()) )*rUAf; for(int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++) { fvScalarMatrix pEqn ( fvm::laplacian(rUAf, p) == fvc::div(phi) ); pEqn.setReference(pRefCell, pRefValue); if (corr == nCorr-1 && nonOrth == nNonOrthCorr) { pEqn.solve(mesh.solver(p.name() + "Final")); } else { pEqn.solve(mesh.solver(p.name())); } if (nonOrth == nNonOrthCorr) { phi -= pEqn.flux(); } } U += rUA*fvc::reconstruct((phi - phiU)/rUAf); U.correctBoundaryConditions(); }``` How do you interpret the mathematical version of equation being solved?
Check Edin Berberovic's paper "Drop impact onto a liquid..."

Quote:
 3. How does solving of some equation narrows down to PCG solver which solves the equation of the form Ax=b? Thanks.
I can't understand the phrase at all, but type of solvers are selected in fvSolution dictionary. This dictionary tells to .solve() method which solver have to be used.

Regards.
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