Construction of an obstacle in the center of a cometary particle bed made up of 140 000 polydisperse spheres consisting of a porous dust-ice mixture with a volume ratio of 2:1, and exposure to a particle wind. Top row: construction of the particle bed. (a) Loose filling of a horizontal layer at the bottom of the simulation domain with non-contacting randomly positioned and sized (chosen from eight discrete sizes) spherical particles. (b) Removal of particles in the center region and insertion of an obstacle built of wall elements. (c) Compaction of the particle layer to the bulk mass density and porosity of comet 67P and removal of particles above the given layer thickness. Bottom row: (d–f) several stages after the introduction of the particle wind. Particles from the granular atmosphere are removed for better representation. The color bar is adapted to the changing overall level of the particle bed.