Generalization of waving-plate theory to multiple interacting swimmers

Abstract

Early research in aerodynamics and biological propulsion was dramatically advanced by the analytical solutions of Theodorsen, von Kármán, Wu and others. While these classical solutions apply only to isolated swimmers, the flow interactions between multiple swimmers are relevant to many practical applications, including the schooling and flocking of animal collectives. In this work, we derive a class of solutions that describe the hydrodynamic interactions between an arbitrary number of swimmers in a two-dimensional inviscid fluid. Our approach is rooted in multiply-connected complex analysis and exploits several recent results. Specifically, the transcendental (Schottky-Klein) prime function serves as the basic building block to construct the appropriate conformal maps and leading-edge-suction functions, which allows us to solve the modified Schwarz problem that arises. As such, our solutions generalize classical thin aerofoil theory, specifically Wu's waving-plate analysis, to the case of multiple swimmers. For the case of a pair of interacting swimmers, we develop an efficient numerical implementation that allows rapid computations of the forces on each swimmer. We investigate flow-mediated equilibria and find excellent agreement between our new solutions and previously reported experimental results. Our solutions recover and unify disparate results in the literature, thereby opening the door for future studies into the interactions between multiple swimmers.

Stability of schooling patterns of a fish pair swimming against a flow

“…Experiments and numerical simulations of self-propelled flapping wings and plates (Becker, Masoud, Newbolt, Shelley, & Ristroph, 2015;Newbolt, Zhang, & Ristroph, 2019;Ramananarivo, Fang, Oza, Zhang, & Ristroph, 2016) indicate that orderly formations in schools may emerge simply through flow interactions, and that hydrodynamic mechanisms may be enough to support a group's collective motion. These, along with other studies (Baddoo, Moore, Oza, & Crowdy, 2021;Kurt et al, 2021;Lin et al, 2019), have investigated the stability of spatial configurations of such schooling systems via experimental measurements and/or numerical predictions of hydrodynamic forces. Kurt et al (2021) and Peng et al (2018) have shown propensity for a stable side-by-side configuration in pitching airfoils and plates, while Newbolt et al (2019) and Lin et al (2019) provide evidence of stable configurations in two hydrofoils swimming in tandem.…”