Fix surface/local demonstration of triangulated surfaces for granular models

This animation illustrates the fix surface/local command in the GRANSURF package, which supports modeling more complex surfaces as it is possible with the fix wall/gran/region command. The geometries of the casing of the feeder and the screw are read from STL format files. The LAMMPS dump image command supports visualizing those surfaces either as a wireframe mesh or with triangles. The polydisperse particles that are dumped into the feeder are color coded by their diameter.