Fast Dynamics of an Eel-Like Robot—Comparisons With Navier–Stokes Simulations
ABSTRACT This paper proposes a dynamic model of the swim of elongated fish suited to the online control of biomimetic eel-like robots. The approach can be considered as an extension of the original reactive ldquolarge elongated body theoryrdquo of Lighthill to the 3-D self-propulsion to which a resistive empirical model has been added. While all the mathematical fundamentals have been detailed by Boyer . (http://www.irccyn.ec-nantes.fr/hebergement/Publications/2007/3721.pdf, 2007), this paper essentially focuses on the numerical validation and calibration of the model and the study of swimming gaits. The proposed model is coupled to an algorithm allowing us to compute the motion of the fish head and the field of internal control torque from the knowledge of the imposed internal strain fields. Based on the Newton-Euler formalism of robot dynamics, this algorithm works faster than real time. As far as precision is concerned, many tests obtained with several planar and 3-D gaits are reported and compared (in the planar case) with a Navier-Stokes solver, which, until today have been devoted to the planar swim. The comparisons obtained are very encouraging since in all the cases we tested, the differences between our simplified and reference simulations do not exceed 10%.
Conference Paper: Control-oriented averaging of tail-actuated robotic fish dynamics[Show abstract] [Hide abstract]
ABSTRACT: Motivated by the need for efficient control design, in this paper we consider the averaging of dynamics for a tail-actuated robotic fish, based on an experimentally validated dynamic model that incorporates rigid body dynamics and Lighthill's large-amplitude elongated-body theory. We first show that classical averaging theory fails in this case because of the relatively large oscillatory input in the driving terms. On the other hand, while the first-order geometric averaging method for systems with highly oscillatory inputs is able to capture the original time-dependent dynamics, the resulting average model is overly complex for controller design. We propose a novel control-oriented, data-driven averaging approach for robotic fish dynamics, where a scaling function is introduced on top of the classical averaging method. We run extensive simulations for different combinations of tail-beat bias, amplitude, and frequency, and find that the scaling function is constant for the force equations and varies linearly with the tail-beat bias for the moment equation. The validity of the resulting average model has been confirmed in simulation results for open-loop dynamics with new sets of tail-beat parameters, and for closed-loop dynamics when proportional control of the tail-beat bias is used in target tracking.American Control Conference (ACC), 2013; 01/2013
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ABSTRACT: Several efforts have recently been made to relate the displacement of swimming three-link systems over strokes to geometric quantities of the strokes. In doing so, they provide powerful, intuitive representations of the bounds on a system's locomotion capabilities and the forms of its optimal strokes or gaits. While this approach has been successful for finding net rotations, noncommutativity concerns have prevented it from working for net translations. Our recent results on other locomoting systems have shown that the degree of this noncommutativity is dependent on the coordinates used to describe the problem and that it can be greatly mitigated by an optimal choice of coordinates. Here, we extend the benefits of this optimal-coordinate approach to the analysis of swimming at the extremes of low and high Reynolds numbers.IEEE Transactions on Robotics 06/2013; 29(3):615-624. · 2.65 Impact Factor
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ABSTRACT: A flexible cylindrical system unstable to flutter oscillations is analysed from the perspective of energy harvesting. In this work we analyse the non-linear reduced order model of a two-degree of freedom system of cylinders modelled with discrete stiffness and damping. The non-linear system of equations is solved in terms of cylinder deflection angles. We seek the flow speed range over which flutter oscillations are stable and correspondingly amenable to energy harvesting. Energy harvesters are modelled as viscous dashpots and the coefficients of damping are parametrised in order to determine combinations that harvest maximum power. We show that for harvesting the maximum possible energy the viscous dashpot should be placed away from the region driving the instability and for this model the optimal location is the fixed end. This result is robust to flow speed variation, action of viscous drag and to variations in cylinder geometry.Journal of Fluids and Structures 04/2012; · 2.23 Impact Factor