[hhuchenyh]

Hello everyone：
I am a new OpenFOAM user with few experience in C++ coding. And I want to add some extra forces in Sollidparticle at lagrange particle tracking.I tried my best to understand the code in SolidParticle.c but I still have some questions.They are as follows:
As stated in essay,The Lagrangian equations are the following:
(dU_)/dt=(Uc-U_)*Dc+(1-ρc/ρp )*g
And the U_ expression in codes are as follows(Line 82 in soildParticle.C version ：OpenFOAMv7):
U_ = (U_ + dt*(Dc*Uc + (1.0 - rhoc/rhop)*td.g()))/(1.0 + dt*Dc);
I thought it would be the following expression:
U_=U_+[(Uc-U_)*Dc+(1-ρc/ρp )*g]*dt
I hope you can help me. Thank you very much.

[hhuchenyh]

Sorry,I know the meaning of this expression now.The expression is just an implicit Euler method to solve the U_.