void applyBCs(scalarField& P) const
{
// Apply the Neumann boundary condition that grad(P) dot surface = 0
int xN = P.ubound(firstDim);
int yN = P.ubound(secondDim);
int zN = P.ubound(thirdDim);
Range all = Range::all();
// lower x
P(0,all,all) = P(2,all,all);
P(1,all,all) = P(2,all,all);
// upper x
P(xN,all,all) = P(xN-2,all,all);
P(xN-1,all,all) = P(xN-2,all,all);
// lower y
P(all,0,all) = P(all,2,all);
P(all,1,all) = P(all,2,all);
// upper y
P(all,yN,all) = P(all,yN-2,all);
P(all,yN-1,all) = P(all,yN-2,all);
// lower z
P(all,all,0) = P(all,all,2) - 2*gravityPressureGradient_;
P(all,all,1) = P(all,all,2) - gravityPressureGradient_;
// upper z
P(all,all,zN) = P(all,all,zN-2) + 2*gravityPressureGradient_;
P(all,all,zN-1) = P(all,all,zN-2) + gravityPressureGradient_;
}
