[Mohammadmz]

Hi all,

I’m running an interFoam VOF simulation of laser melting with ultrasonic vibration applied as a coded momentum source. The setup works fine in the liquid metal region, but near the gas phase, the velocity blows up to e+9 – e+11 m/s, causing divergence immediately.

Solver: interFoam
VOF field: alpha.metal
Forcing: volumetric ultrasonic force applied in molten region.
loop:
forAll(C, cellI)
{
scalar y = C[cellI].y();


if (T[cellI] > 1673 && alpha[cellI] >= 0.8 && y >= 0.001 && y <= 0.004)
{
// ---- Smooth activation (tanh-type ramp) ----
scalar Tmid = 0.5 * (1673.0 + 1723.0); // midpoint
scalar dT = 0.25 * (1723.0 - 1673.0); // smoothness range

scalar Tfac = 0.5 * (1.0 + tanh((T[cellI] - Tmid)/dT)); // smooth 0→1


scalar weight = Tfac;

// Optional cutoff for negligible weight
if (weight < 1e-3) continue;


// if (weight <= smallValue) continue; // skip negligible contributions

// Local volumetric force (N/m3)

scalar alphaWeight = 0.5 * (1.0 + tanh((alpha[cellI] - 0.95)/0.02));
//scalar rhoRatio = rho0 / (rho1 + smallValue);
scalar fMix = (alphaWeight * Fmetal_t) + ((1.0 - alphaWeight) * Fgas_t);
scalar fLocal = fMix * weight ;
// scalar rhoLocal = (alpha[cellI]*Fmetal) + ((1.0-alpha[cellI])*Fgas);
vector fPerVol = vector(0,fLocal, 0);

// Convert to total force per cell (N)
vector fCell = fPerVol ;

// Add to equation source (eqn.source expects total force per cell)
eqn.source()[cellI] += fCell;

totalAppliedForce += fCell;
appliedCellCount += 1.0;
count++;
}
}

// -------------------- Info output -------------------- //
Info << "Ultrasonic Force at t = " << t << " s"
<< " : base fVol = " << fVol << " [N/m3]"
<< ", applied to " << count << " cells"
<< ", totalAppliedForce = " << totalAppliedForce << " N"
<< endl;

Any insight or suggestions to avoid unphysical velocities in the argon gas region would be greatly appreciated.

Thanks!