Cohesion of Large Groups of Self-Propelled Swimmers

Swimming animals gain several benefits when swimming together as a group. Crucially, the benefits of schooling can only be realized if the appropriate group structure is maintained. Using a three-dimensional far-field model of self-propelled swimmers, we examine whether passive hydrodynamic interactions alone can lead to the formation of cohesive groups of N swimmers. For N = 2, cohesive groups with several dynamical phases can form. For N > 2, subgroups of two form in some cases, while larger subgroups form in other cases. Initial misalignment of the swimmers leads them to diverge from each other when N = 2, but it can promote cohesion when N > 2.