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Open Access A method to improve instationary force error estimates for undulatory swimmers

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Our aim is to improve the analysis of the force dynamics common to experimental investigations of oscillatory locomotion in underwater research. This paper proposes a new method for instationary force error modelling and correction, calibrating on a passive body at laboratory scale. The calibration function is applied to instantaneous force estimates during undulatory swimming under turbulent flow conditions. The main advantage of this method is automated phase shift correction. This study uses a force plate to directly obtain the instantaneous streamwise and lateral forces on a passive and actuated fish robot under turbulent flow conditions. Force estimates are simultaneously obtained using the momentum deficit method, coupled for the passive case using a linear transfer function. The resulting instantaneous error model is evaluated in three turbulent flow experiments, during which the robot is actuated to mimic a swimming fish. Mean, median and modulo general linear transfer functions are evaluated to determine the best performing general function. Actuated instantaneous force estimate errors are reduced by 64%–93% in the streamwise and 75%–91% in the transverse directions. It was found that all three transfer functions had similar performance, considering the instationary force estimates during actuation. The modulo function performed best for the passive case.
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Document Type: Research Article

Publication date: March 1, 2016

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