On the dynamics of relativistic multi-layer spherical shell systems
  The relativistic time evolution of multi-layer spherically symmetric shell systems---consisting of infinitely thin shells separated by vacuum regions---is examined. Whenever two shells collide the evolution is continued with the assumption that the collision is totally transparent. The time evolution of various multi-layer shell systems---comprised by large number of shells thereby mimicking the behavior of a thick shell making it possible to study the formation of acoustic singularities---is analyzed numerically and compared in certain cases to the corresponding Newtonian time evolution. The analytic setup is chosen such that the developed code is capable of following the evolution even inside the black hole region. This, in particular, allowed us to investigate the mass inflation phenomenon in the chosen framework. 
Merse E.Gaspar and Istvan Racz
gr-qc