Different geometry of confining shocks. In 2D (periodic in y-direction, infinite in z-direction), the confining shocks resemble corrugated sheets (left panel). In 3D (periodic in y- and z-direction) they evoke the idea of cardboard egg wrappings (right panel). Both simulations have M_u = 21.7. Color coded is density (log10(ρ); particles/cm³ in 2D; g/cm³ in 3D) and, right panel only, the driving efficiency f_eff at the shock surface.