foam-extend4.1-coherent-io/applications/solvers/multiphase/settlingFoam/UEqn.H

// Solve the Momentum equation

fvVectorMatrix UEqn
(
    fvm::ddt(rho, U)
  + fvm::div(phi, U)
  + fvc::div
    (
        (Alpha/(scalar(1.001) - Alpha))*(sqr(rhoc)/rho)*Vdj*Vdj,
        "div(phiVdj,Vdj)"
    )
  - fvm::laplacian(mu, U, "laplacian(muEff,U)")
);

if (pimple.momentumPredictor())
{
    solve
    (
        UEqn
     ==
        fvc::reconstruct
        (
            (
              - ghf*fvc::snGrad(rho)
              - fvc::snGrad(p)
            )*mesh.magSf()
        )
    );
}