557 - Fluid Mechanics of Collective Behaviour across Scales

Collective animal motions are observed in nature among birds (flocking), insects (bees, ants, etc), people (crowds), fish (schooling) and microorganisms (bacteria films). Collective behavior is believed to provide various advantages such as defense against predators, enhanced environment exploration or foraging. It is also likely that individuals benefit from school or flock dynamics through increased hydrodynamic or aerodynamic efficiency. The interaction of swarms with their environment as well as the relationship between the goals of the swarm and its members are the focus of investigations in disciplines ranging from Mathematics to Social Sciences. The concept of "swarm intelligence" is used to refer to complex self-organized patterns arising from local rules. The rules that determine the single individual behavior are based on a limited knowledge of the state of other agents and the environment and do not necessarily encode any centralized control. Global patterns emerge based on local information and may be unknown to single individuals. The understanding and identification of the fundamental rules that determine swarm behavior can be very valuable in the design of engineering devices with required swarming behavior such as robotic swarms.
In this workshop we will investigate collective behavior in flow environments, ranging from bacteria films to flocks of birds. We will discuss the merging collective patterns in these different systems and pose the question whether these patterns are the results of optimized physical interactions mediated by the environment, the result of learning processes, or both and to what extent is each component responsible for this behavior? We will distinguish distinct flow phenomena across scales, from the role of Stokes dynamics in low Reynolds number flows to fish schooling as water can mediate local and long range interactions due to the vortical structures developed by the swimmers. We will also investigate common themes that flow forces induce to such systems, such as the use of pressure signals to communicate between members of a collective.
Collective behavior has been investigated in the past in the context of Artifical Life through the use of agent based systems. A major deficiency so far of agent based simulations is the reduced physics involved in the models that prevents assessing the relative roles of behavioral and hydrodynamic traits. Today as a new set of experiments and field data is becoming available it is becoming essential to revisit these problems in a synergetic fashion, by acknoeldging uncertainties in the development of models and simulations, the gathering of data and the development of experiments. We hope that this workshop ill serve the role of enhancing the dialogue in the various communities that study collective phenomena and will elucidate the role of fluid mechanics in such processes.