Flow sensing and feedback control for maintaining school cohesion in uncoordinated flapping swimmers

Fish often swim in schools. Flow interactions are thought to be beneficial for schooling. Recent work shows that flow interactions cause a pair of free inline swimmers, flapping at the same frequency, to passively stabilize at discrete locations relative to each other and that these passively stable formations are energetically beneficial. However, the stability of these formations is sensitive to finite mismatch in flapping frequencies. Here, we propose a local flow sensing model and feedback controller that stabilize a pair of frequency-uncoordinated swimmers into a cohesive formation. Our findings bear relevance to understanding fish collective behavior and for designing bio-inspired underwater robotics.