# The sum-up of forces on particles

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 August 15, 2013, 10:51 The sum-up of forces on particles #1 Member   Xiangyin Meng Join Date: Jun 2012 Location: London Posts: 70 Rep Power: 6 Hi, guys, I am using the solver 'icoUncoupledKinematicParcelFoam' to do some validations. My question is, to a particle, or a parcel, the force on it should be from both environmental field (like drag force) and collision. Now, I can find the programme for drag force, gravity force, etc, I can also find the programme for collision spring force as well. But, still can't find where they are added together for the particle or parcel. Really confused...

 August 15, 2013, 13:26 #2 Senior Member     Daniel P. Combest Join Date: Mar 2009 Location: St. Louis, USA Posts: 581 Rep Power: 20 Try looking at Code: `\$FOAM_SRC/lagrangian/intermediate/lnInclude/kinematicParcel.C` and look at the method calcVelocity. In there, you should see where the forces are collected to calculate the new parcel velocity in the lines Code: ``` const forceType& forces = td.cloud().forces(); // Momentum source due to particle forces const parcelType& p = static_cast(*this); const forceSuSp Fcp = forces.calcCoupled(p, dt, mass, Re, mu); const forceSuSp Fncp = forces.calcNonCoupled(p, dt, mass, Re, mu); const forceSuSp Feff = Fcp + Fncp; // New particle velocity //~~~~~~~~~~~~~~~~~~~~~~``` Good luck. __________________ Dan Find me on twitter @dancombest and LinkedIn

 August 15, 2013, 15:04 #3 Member   Xiangyin Meng Join Date: Jun 2012 Location: London Posts: 70 Rep Power: 6 Thank you very much! I found that and read it. By my understanding now, the velocity of parcel should be calculated twice, the one is in 'KinematicParcel.C' for particle forces, like drag force and gravity, while the other one is in 'CollidingParcel.C' for those forces due to collision. So, actually, the forces on the parcel are not collected altogether, but divided into two parts. Am I right? Thank you very much again!

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