Origin of Propulsion: A synthetic view

How did the propulsion of small animals evolve into those of larger animals? We implement the concept that brain and mobility of animals evolved together (ASME JFE v131 031801-29 2009...IEEE JOE v33 563-578 2008... JEB v211 206-214 2008.). We follow a synthetic approach where hypothesis, experiments and animation are added or subtracted to the basic elements from known results (fluid dynamics video). In animals, the propulsion mechanism is simply the equality of elastohydrodynamic forces and drag. The controller is changed through optimization and the actuator is enlarged through imagination but within the structural constraints of the smaller animals. The nonlinear dynamics of inferiorolive neurons is taken to be fundamental in the phase synchronization of actuators in all animals. It is shown that the structural and kinematic building blocks of elastohydrodynamics have a higher degree of diversity in the cilium of paramecium and some are dropped or altered in an optimization process whereby the Reynolds number of the propulsors increases. In other words, the animal conceivably becomes larger and moves faster or increases agility as both the brain and actuators co-evolve as intrinsic and dormant structural and kinematic abilities come to the fore

Acoustic predation in a sailfish-flying fish cloak

Abstract When a sailfish circles to corral a school of flying fish in a vortex near the ocean surface, a tiny patch of arced surface waves confined to oppositely placed 70° sectors appears dispersing coherently, but why? It is modeled that, when the fish motions stop suddenly, the corralled school compacts, the tail shed propulsion vortices touch, break and radiate the pressure released from the centrifugal vortex rotation creating an acoustic monopole. The surface-wave patch is a section of the sphere of radiation. The oppositely placed curved bodies of the sailfish and the flying fish act as concave acoustic mirrors about the monopole creating a reverberating bell-shaped cloak in between which vibrates the ear bones and bladders of the flying fish disorienting them. A cup of water firmly struck on a table induces a similar vibration of a purely radial mode. The sailfish circles around the school at a depth where the wind induced underwater toroidal motion in the vertical plane becomes negligible such that the flying fish is unable to sense the tailwind direction above, limiting the ability to swim up and emerge in the right direction to glide. Experiments confirm that the flying fish tail rigidity is too low for a quick ballistic exit, which is not called for either

Linear Feedback Control of Boundary Layer Using Electromagnetic Microtiles

Thispaper presents a system-theory approach to control of a two-dimensionalturbulent flow of saltwater on a flat plate using Lorentzforces produced by microtiles of small magnets and electrodes. Beginningwith the two-dimensional Navier-Stokes equations of motion, a finite, dimensional,linear state variable, approximate model is obtained using Galerkin\u27s procedure.Based on this model, linear feedback control laws are obtainedto achieve stabilization of the perturbed flow to the baseflow. It is shown that spatially distributed longitudinal or surface-normalforces stabilize the flow perturbations. However, for lower wave numbers,longitudinal forces are more effective because surface-normal forces require largerelectrode voltages for the same response characteristics. Simulation results arepresented to show how stabilization is accomplished in the closed-loopsystem

Leading Edge Vortex in Flapping Fins

Insects and penguins flap their pectoral fins to produce forces. Flapping means simultaneous rolling and pitching oscillations with or without twist. Twisting is a differential pitching between the root and the tip of the fin, added to the normal pitching oscillation. The rolling and pitching oscillations are 90 deg apart. Flapping fins produce leading edge vortices which enhance lift forces and delay stall even at high angles of attack, and the mechanism is known as dynamic stall (ASME JFE v131 031801-29 2009...JEB v211 206-214 2008...IEEE JOE v33 59-68 2008.). In the fluid dynamics video we show dye-in-water flow visualization of the formation of the leading edge vortex (LEV) with and without twist. We also show the effects of increasing frequency of oscillation and roll angle on the LEV. In the absence of twist, the LEV is conically enlarging along span, with a spanwise flow away from the root. However, in the presence of twist, the LEV is more uniform along the span and this effect of twist becomes clearer as frequency of oscillation is increased; we explain that this is a result of the local and instantaneous angle of attack becoming more uniform along span due to twist