Hydrodynamic limits from the self-organized kinetic system for body attitude coordination

The self-organized kinetic system for body attitude coordination (SOKB) was recently derived by Degond et al. (Math. Models Methods Appl. Sci. 27(6), 1005-1049, 2017). This system describe a new collective motion for multi-agents dynamics, where each agent is described by its position and body attitude: agents travel at a constant speed in a given direction and their body can rotate round it adopting different configurations (representing by rotation matrix in $\mathrm{SO(3)}$). In this paper, we study the hydrodynamic limit of the scaled SOKB system with the constant intensity of coordination by employing the Generalized Collision Invariants (GCI)-based Hilbert expansion approach. The limit is the self-organized hydrodynamic model for body attitude coordination (SOHB). In spherical coordinates, the SOHB system is singular. To avoid this coordinate singularity, we transfer SOHB system into a non-singular form by stereographic projection. This work provides the first analytically rigorous justification of the modeling and asymptotic analysis in Degond et al. (Math. Models Methods Appl. Sci. 27(6), 1005-1049, 2017).