Results 1  10
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17
2012 Energy harvesting efficiency of piezoelectric flags in axial flows
 J. Fluid Mech
"... flags in axial flows ..."
Effects of Body Elasticity on Stability of Underwater Locomotion
, 2014
"... We examine the stability of the “coast ” motion of fish, that is to say, the motion of a neutrally buoyant fish at constant speed in a straight line. The forces and moments acting on the fish body are thus perfectly balanced. The fish motion is said to be unstable if a perturbation in the conditions ..."
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We examine the stability of the “coast ” motion of fish, that is to say, the motion of a neutrally buoyant fish at constant speed in a straight line. The forces and moments acting on the fish body are thus perfectly balanced. The fish motion is said to be unstable if a perturbation in the conditions surrounding the fish results in forces and moments that tend to increase the perturbation and it is stable if these emerging forces tend to reduce the perturbation and return the fish to its original state. Stability may be achieved actively or passively. Active stabilization requires neurological control that activates musculoskeletal components to compensate for the external perturbations acting against stability. Passive stabilization on the other hand requires no energy input by the fish and is dependent upon the fish morphology, i.e. geometry and elastic properties. In this paper, we use a deformable body consisting of an articulated body equipped with torsional springs at its hinge joints and submerged in an unbounded perfect fluid as a simple model to study passive stability as a function of the body geometry and spring stiffness. We show that for given body dimensions, the spring elasticity, when properly chosen, leads to passive stabilization of the (otherwise unstable) coast motion. 1
Unraveling Flow Patterns through Nonlinear
 Manifold Learning. PLoS ONE. 2014 03; 9(3):e91131. Available from: http://dx.doi.org/10.1371%2Fjournal.pone.0091131
"... From climatology to biofluidics, the characterization of complex flows relies on computationally expensive kinematic and kinetic measurements. In addition, such big data are difficult to handle in real time, thereby hampering advancements in the area of flow control and distributed sensing. Here, we ..."
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From climatology to biofluidics, the characterization of complex flows relies on computationally expensive kinematic and kinetic measurements. In addition, such big data are difficult to handle in real time, thereby hampering advancements in the area of flow control and distributed sensing. Here, we propose a novel framework for unsupervised characterization of flow patterns through nonlinear manifold learning. Specifically, we apply the isometric feature mapping (Isomap) to experimental video data of the wake past a circular cylinder from steady to turbulent flows. Without direct velocity measurements, we show that manifold topology is intrinsically related to flow regime and that Isomap global coordinates can unravel salient flow features.
ENERGY HARVESTING FROM AXIAL FLOW INDUCED INSTABILITIES IN SLENDER STRUCTURES
"... In this work we examine the prospects for harvesting energy from flutter instabilities of a slender, flexible cylinder in an axial flow stream. We couple the fluidsolid model and include energy harvesting as curvature based damping. In the first instance we model the reduced order system comprisi ..."
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In this work we examine the prospects for harvesting energy from flutter instabilities of a slender, flexible cylinder in an axial flow stream. We couple the fluidsolid model and include energy harvesting as curvature based damping. In the first instance we model the reduced order system comprising of an articulated rigid cylinder pair with discrete springs and dampers and demonstrate the scope for harvesting energy from flutter instabilities. Extending the study to a continuously varying system confirms the scope for energy harvesting. The numerical models are employed to find the optimal damping distributions and we see that the two configurations give very different results. We examine the subtle differences between the two apparently canonical configurations that lead to these differing optimals.
Falling, flapping, flying, swimming,...:
, 2009
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Route de Saclay
"... The present work investigates the possibility to produce electrical energy from the flutter oscillations of a flexible plate placed in an axial flow and covered with piezoelectric patches that convert bending and stretching of the plate’s surface into electric charge displacement. A fullycoupled n ..."
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The present work investigates the possibility to produce electrical energy from the flutter oscillations of a flexible plate placed in an axial flow and covered with piezoelectric patches that convert bending and stretching of the plate’s surface into electric charge displacement. A fullycoupled nonlinear model for the dynamics of the fluidsolidelectric system is presented and used to determine the influence of the different system parameters on the stability, nonlinear dynamics and energy harvesting efficiency of the system. In particular, the role of the tuning between the fluidsolid and electrical systems is investigated as well as the impact of the flow velocity and fluidsolid mass ratio.
Under consideration for publication in J. Fluid Mech. 1 The origin of hysteresis in the flag instability
"... (Received?; revised?; accepted?. To be entered by editorial office) The flapping flag instability occurs when a flexible cantilevered plate is immersed in a uniform airflow. To this day, the nonlinear aspects of this aeroelastic instability are largely unknown. In particular, experiments in the lit ..."
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(Received?; revised?; accepted?. To be entered by editorial office) The flapping flag instability occurs when a flexible cantilevered plate is immersed in a uniform airflow. To this day, the nonlinear aspects of this aeroelastic instability are largely unknown. In particular, experiments in the literature all report a large hysteresis loop, while the bifurcation in numerical simulations is either supercritical or subcritical with a small hysteresis loop. In this paper, this discrepancy is addressed. First weakly nonlinear stability analyses are conducted in the slenderbody and twodimensional limits, and second new experiments are performed with flat and curved plates. The discrepancy is attributed to inevitable planeity defects of the plates in the experiments. 1.
Linear stability analysis of coupled parallel flexible plates in an axial flow
"... We study here the linear stability of N identical flexible plates with clampedfree boundary conditions forced by a uniform parallel flow. Flow viscosity and elastic damping are neglected, and the flow around the plates is assumed potential. The shedding of vorticity from the plates ’ trailing edge ..."
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We study here the linear stability of N identical flexible plates with clampedfree boundary conditions forced by a uniform parallel flow. Flow viscosity and elastic damping are neglected, and the flow around the plates is assumed potential. The shedding of vorticity from the plates ’ trailing edges is accounted for by introducing a forcefree wake behind each plate. A Galerkin method is used to compute the eigenmodes of the system. We are interested in the effects of the number of plates and their relative distance on the stability property of the state of rest, as well as in the nature and structure of the coupled states. Detailed results are presented for the cases N = 2,
DOI 10.1007/s0016200901176 ORIGINAL ARTICLE
"... Falling cards and flapping flags: understanding fluid–solid interactions using an unsteady point vortex model ..."
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Falling cards and flapping flags: understanding fluid–solid interactions using an unsteady point vortex model