On the shape of Superbubbles evolving in the Galactic Plane
  The galactic supershells are cavities in the interstellar medium. These shells can be explained by introducing the concept of superbubbles, the theoretical result of multiple supernova. The superbubbles can be analytically described if the ambient medium has a constant density both in the so-called bursting phase and in the subsequent adiabatic expansion. In order to solve the expansion of superbubbles in the ISM, which is a non-homogeneous medium, a numerical technique is used that divides the sphere into many sectors. By varying the time of the bursting phenomenon and the time over which the phenomenon is followed, elliptical and hour-glass shapes or vertical walls can be obtained. Application of the developed theory/code to the super-shell associated with GW~46.4+5 and with GSH 238 allows us to say that the suggested physical parameters are consistent with our theory. The map of the expanding superbubble's velocity can be tentatively traced by generating random points on the expanding surface. The structure of the galactic plane as a result of the evolution of many super-bubbles was simulated by adopting the percolation theory in order to generate new OB associations. 
Lorenzo Zaninetti