Sean D. Peterson

Energy harvesting from base excitation of ionic polymer metal composites in fluid environments

In this paper, we analytically and experimentally study the energy harvesting capability of submerged ionic polymer metal composites?(IPMCs). We consider base excitation of an IPMC strip that is shunted with an electric impedance and immersed in a fluid environment. We develop a modeling framework to predict the energy scavenged from the IPMC vibration as a function of the excitation frequency range, the constitutive and geometric properties of the IPMC, and the electric shunting load. The mechanical vibration of the IPMC strip is modeled through Kirchhoff?Love plate theory. The effect of the encompassing fluid on the IPMC vibration is described by using a linearized solution of the Navier?Stokes equations, that is traditionally considered in modeling atomic force microscope cantilevers. The dynamic chemo-electric response of the IPMC is described through the Poisson?Nernst?Planck model, in which the effect of mechanical deformations of the backbone polymer is accounted for. We present a closed-form solution for the current flowing through the IPMC strip as a function of the voltage across its electrodes and its deformation. We use modal analysis to establish a handleable expression for the power harvested from the vibrating IPMC and to optimize the shunting impedance for maximum energy harvesting. We validate theoretical findings through experiments conducted on IPMC strips vibrating in aqueous environments.

Evolution of jets emanating from short holes into crossflow

The evolution of a short injection-hole jet issuing into a crossflow at low blowing ratios is presented. Particle image velocimetry (PIV) is used to determine structural features of the jet/crossflow interaction throughout its development from within the jet supply channel (which feeds the holes), through the injection hole, and into the crossflow. The effect of supply channel feed orientations, i.e. counter to, or in the same direction as the crossflow is emphasized. Feed orientation profoundly affects such jet characteristics as trajectory and lateral spreading, as well as its structural features. Fluid within the high-speed supply channel exhibits swirling motions similar to the flow induced by a pair of counter-rotating vortices. The sense of rotation of the swirling fluid depends upon the orientation of the supply channel flow with respect to the crossflow, and in turn impacts the in-hole velocity fields. In the coflow supply channel geometry (channel flow is in the same direction as the free stream), a pair of vortices exists within the hole with the same sense of rotation as the primary jet counter-rotating vortex pair (CRVP)

A Particle Image Velocimetry Study of Vibrating Ionic Polymer Metal Composites in Aqueous Environments

Low power consumption and activation voltage combined with high flexibility and minimal weight make ionic polymer metal composites (IPMCs) well-suited for miniaturized underwater propulsion systems. In the present study, we investigate the flow field generated by an IPMC strip vibrating in a quiescent aqueous environment using planar particle image velocimetry. We use the time-averaged flow field to compute the momentum transfer to the fluid and estimate the mean thrust generated by the vibrating actuator. We find that the mean thrust produced by the vibrating IPMC increases with the Reynolds number, defined by the maximum tip speed and IPMC width, and is only marginally affected by the relative vibration amplitude. The results of this study can guide the optimization of IPMC-based propulsion systems for miniature biomimetic robotic swimmers.

Hydrodynamics of underwater propulsors based on ionic polymer?metal composites: a numerical study

Ionic polymer–metal composite (IPMC) actuators have shown promise as miniature underwater propulsors due to their high flexibility, reduced weight, and low activation voltage and power consumption. In this paper, we analyze the hydrodynamics of a vibrating IPMC actuator in an aqueous environment in order to develop a comprehensive understanding of thrust generation mechanisms of IPMC actuators. More specifically, we numerically analyze the flow of a viscous fluid generated by a cantilever IPMC actuator vibrating along its fundamental mode shape. We compute the thrust produced by the actuator as a function of its frequency of oscillation and maximum tip displacement. We show that thrust generation of vibrating IPMC actuators is highly correlated with vortex shedding. We find that vorticity production is prominent at the IPMC tip and increases as the oscillation frequency increases. We analyze the lateral force and the moment exerted by the IPMC on the surrounding fluid. Further, we study the power transferred by the vibrating IPMC to the encompassing fluid. We validate our numerical findings through available particle image velocimetry experiments.

Energy exchange between a vortex ring and an ionic polymer metal composite

In this letter, we study the transient response of a cantilevered ionic polymer metal composite impacted by a self-propagating vortex ring in an otherwise quiescent fluid. Experiments are performed using time-resolved particle image velocimetry to elucidate the flow physics during the vortex ring propagation and subsequent interaction with the cantilever. Images from these experiments are analyzed to extract the vibration of the structure, which is used to estimate the energy transferred from the vortex ring. A small fraction of this energy is further transduced into an electrical signal by the chemoelectromechanical behavior of the ionic polymer metal composite.

Energy harvesting from the tail beating of a carangiform swimmer using ionic polymer-metal composites.

In this paper, we study energy harvesting from the beating of a biomimetic fish tail using ionic polymer-metal composites. The design of the biomimetic tail is based on carangiform swimmers and is specifically inspired by the morphology of the heterocercal tail of thresher sharks. The tail is constituted of a soft silicone matrix molded in the form of the heterocercal tail and reinforced by a steel beam of rectangular cross section. We propose a modeling framework for the underwater vibration of the biomimetic tail, wherein the tail is assimilated to a cantilever beam with rectangular cross section and heterogeneous physical properties. We focus on base excitation in the form of a superimposed rotation about a fixed axis and we consider the regime of moderately large-amplitude vibrations. In this context, the effect of the encompassing fluid is described through a hydrodynamic function, which accounts for inertial, viscous and convective phenomena. The model is validated through experiments in which the base excitation is systematically varied and the motion of selected points on the biomimetic tail tracked in time. The feasibility of harvesting energy from an ionic polymer-metal composite attached to the vibrating structure is experimentally and theoretically assessed. The response of the transducer is described using a black-box model, where the voltage output is controlled by the rate of change of the mean curvature. Experiments are performed to elucidate the impact of the shunting resistance, the frequency of the base excitation and the placement of the ionic polymer-metal composite on energy harvesting from the considered biomimetic tail.

Non-Uniform Flow Behavior in a Parallel Plate Flow Chamber Alters Endothelial Cell Responses

Arterial flow characteristics determine vessel health by modulating vascular endothelial cells. One system used to study these interactions is the parallel plate flow chamber. The present in vitro study quantified the uniformity of fluid flow across a parallel plate flow chamber and characterized plate-location dependent endothelial cell gene expression. More specifically, shear stress varied by as much as 11% across the chamber area, which caused non-uniform ecNOS (p < 0.05) and COX-2 (p < 0.05) mRNA expression across the plate area. Results herein suggest that chamber variations may result during construction or assembly, which ultimately affect flow-sensitive cell responses (including mRNA expression). Therefore, these limitations should be considered when reporting endothelial cell responses to fluid flow using parallel plate flow chambers.

Three-dimensional particle tracking using micro-particle image velocimetry hardware

A method for tracking the three-dimensional position and computing the three velocity components of a micro-particle using information encoded in the ring structure of the particle image is introduced. The proposed technique can be employed in most existing micro-particle image velocimetry systems without any additional hardware and details of the optical train are not required. The technique utilizes a set of calibration images of a particle at various known distances from the focal plane (in the out-of-plane direction) in order to create a calibration curve. The calibration curve, which relates the radius of the outermost ring to the distance of the particle from focus is used to deduce the out-of-plane location of particles in experimental images. From successive images the particles velocity is computed. The in-plane particle velocity is deduced from traditional particle tracking methods.

Temporally-resolved hydrodynamics in the vicinity of a vibrating ionic polymer metal composite

In this paper, we study the hydrodynamics induced by an ionic polymer metal composite (IPMC) cantilever vibrating in a quiescent fluid. Time-resolved particle image velocimetry is used to measure the velocity field in the vicinity of the vibrating IPMC strip and a control volume analysis is utilized to estimate the thrust production per unit IPMC width. The governing fluid dynamics dimensionless parameters are varied parametrically to ascertain the influence of the Reynolds number, the peak tip displacement to IPMC length ratio, and the IPMC aspect ratio. It is found that the Reynolds number is the dominant parameter in determining the thrust produced by the IPMC, while the relative tip displacement and aspect ratio play secondary roles. An increase in the relative tip displacement has a minimal effect on the produced thrust, while an increase in the aspect ratio results in a mild decrease in thrust production. It is further found that estimating the thrust from the mean velocity field significantly under...

The influence of inlet velocity profile and secondary flow on pulsatile flow in a model artery with stenosis

(Received 30 May 2007 and in revised form 3 July 2008) The results of an experimental investigation to determine the influence of two physiologically relevant inlet conditions on the flow physics downstream of an idealized stenosis are presented. The two inlet conditions are an asymmetric mean inlet velocity profile and an asymmetric mean inlet velocity profile plus secondary flow, as found downstream of a bend. The stenosis is modelled as an axisymmetric 75 % area reduction occlusion with a length-to-diameter ratio of 2. The flow was forced by a 10-harmonic carotid artery-inspired waveform with mean, maximum and minimum Reynolds numbers of 364, 1424 and 24, respectively, and a Womersley number of 4.6. Laser Doppler velocimetry and particle image velocimetry were used to characterize the spatial and temporal evolution of a baseline case (no disturbances) as well as the two physiologically relevant inlet conditions. The asymmetric inlet velocity profile was found to reduce the region of influence of the stenosis by forcing the stenotic jet towards the tube wall via an induced non-uniform radial pressure gradient, similar to the Coanda effect. Curvature-induced secondary flow was found to play a minor role in the near-stenosis region. Vortex ring formation was relatively unaffected by the mean velocity gradient and secondary flow. Evidence of remnants of the starting vortex ring was observed far downstream in all cases.