Growth of Smaller Grain Attached on Larger One: Algorithm to Overcome   Unphysical Overlap between Grain
  As a smaller grain, which is attached on larger one, is growing, it pushes also the larger one and other grains in its surrounding. In a simulation of similar system, repulsive force such as contact force based on linear spring-dashpot model can not accommodate this situation when cell growing rate is faster than simulation time step, since it produces sudden large overlap between grains that makes unphysical result. An algorithm that preserves system linear momentum by introducing additional velocity induced by cell growth is presented in this work. It should be performed in an implicit step. The algorithm has successfully eliminated unphysical overlap. 
Acep Purqon, Sparisoma Viridi
cond-mat.soft