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NodalProjector: fix comments #1396

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Sep 23, 2020
Merged

NodalProjector: fix comments #1396

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c89cf29
NodalProjector: fix comments
mic84 Sep 22, 2020
7cfba95
NodalProjector: make comments clearer
mic84 Sep 22, 2020
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27 changes: 23 additions & 4 deletions Src/LinearSolvers/Projections/AMReX_NodalProjector.H
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Original file line number Diff line number Diff line change
Expand Up @@ -7,22 +7,41 @@
#include <AMReX_MLNodeLaplacian.H>
#include <AMReX_MLMG.H>

//
//
// *************************** DEFAULT MODE ***************************
//
// Solves
//
// div(sigma*grad(phi)) = div(vel) + S_nd + S_cc
//
// and performs the projection
//
// vel = vel - ( sigma / alpha ) * grad(phi)
// vel = vel - sigma * grad(phi)
//
// vel, sigma, alpha, and S_cc are cell-centered variables, while
// vel, sigma, and S_cc are cell-centered variables, while
// phi and S_nd are nodal-centered variables.
//
// *************************** CUSTOM MODE ***************************
//
// Solves
//
// div(sigma*grad(phi)) = rhs
//
// and performs the projection
//
// vel = vel - (sigma/alpha) * grad(phi)
//
// alpha is a cell-centered variable, while rhs is nodal-centered.
//
// In this mode, the user provides rhs and alpha
//
// By default alpha is assumed to be 1. Use setAlpha to change the default.
//
// The user can provide a custom RHS instead of letting NodalProjector to compute
// one. Use setCustomRHS to provide a custom RHS.
// Use setCustomRHS to provide a custom RHS, else "div(vel) + S_nd + S_cc"
// is used.
//
// Example: rhs = div(alpha*vel)
//
namespace amrex {

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6 changes: 3 additions & 3 deletions Src/LinearSolvers/Projections/AMReX_NodalProjector.cpp
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Expand Up @@ -241,7 +241,7 @@ NodalProjector::project ( Real a_rtol, Real a_atol )
// phi comes out already averaged-down and ready to be used by caller if needed
m_mlmg -> solve( GetVecOfPtrs(m_phi), GetVecOfConstPtrs(m_rhs), a_rtol, a_atol );

// Get fluxes -- fluxes = - (alpha/beta) * grad(phi)
// Get fluxes -- fluxes = - sigma * grad(phi)
m_mlmg -> getFluxes( GetVecOfPtrs(m_fluxes) );

// At this time, the fluxes are "correct" only on regions not covered by finer grids.
Expand All @@ -258,15 +258,15 @@ NodalProjector::project ( Real a_rtol, Real a_atol )
{
if (m_has_alpha)
{
// fluxes -> fluxes/alpha = -grad(phi)/beta
// fluxes -> fluxes/alpha = - ( sigma / alpha ) * grad(phi)
for (int n = 0; n < AMREX_SPACEDIM; ++n)
{
MultiFab::Divide( m_fluxes[lev], *m_alpha[lev], 0, n, 1, 0 );
}
}

//
// vel = vel + fluxes = vel - grad(phi) / beta
// vel = vel + fluxes = vel - ( sigma / alpha ) * grad(phi)
//
// Since we already averaged-down the velocity field and -grad(phi),
// we perform the projection by simply adding the two of them.
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