The fluid mechanics employed by aquatic animals in their escape or attack maneuvers, what we call survival hydrodynamics, are fascinating because the recorded performance in animals is truly impressive. Such performance forces us to pose some basic questions on the underlying flow mechanisms that are not yet in use in engineered vehicles. A closely related issue is the ability of animals to sense the flow velocity and pressure field around them in order to detect and discriminate threats in environments where vision or other sensing is of limited or no use. We review work on animal flow sensing and actuation as a source of inspiration and as a way to formulate a number of basic problems and investigate the flow mechanisms that enable animals to perform these remarkable maneuvers. We also describe some intriguing mechanisms of actuation and sensing.

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This paper studies the effects of geometrical features on harbor seal whiskers on its force reduction ability. Each feature in the seal whisker is sequentially stripped from the original whisker shape. Four whisker-like geometries are created from such methodology. 3D simulations of flow around the structures are performed and the resulting forces on the structures are non-dimensionalized. The lift and drag coefficients of these structures are compared to the real whisker case. The undulations on minor and major axes are found to be necessary in reducing the lift forces. Existence of only one of the undulations fails to weaken the flow and break the vortex tubes and braids in the wake. The offset angle between leading edge and trailing edge are found to have slight effects on the lift and drag coefficients. The reduction in drag coefficient is found to be dependent on the existence of undulations in minor axis. The force responses of whisker-like geometries with undulations on one of their axes are found to be periodic. When the force response on whisker-like geometries with both undulations are found to be chaotic. Vortex shedding frequency of the structure is observed to decrease considerably when no offset angle is introduced into the geometry. This may result in longer lifespan of the structure.@en

In this paper, inline and transverse forces on elliptical cylinder immersed in the wake of circular cylinder are carefully evaluated. The effects of variations on characteristic dimension, inline and transverse position of the elliptical cylinder are determined through numerical simulations at Re =1300 based on the diameter of circular cylinder. The results indicate minute effects due to variation on inline positioning. However, variations on transverse positioning and characteristic dimension have profound effects on the amplitude of lift coefficient as well as frequency peaks in Power Spectral Density (PSD). 1:1 frequency lock-in is observed for all simulation cases.

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