Reconfiguration of elastic blades in oscillatory flow

Leclercq, Tristan; Langre, Emmanuel de

doi:10.1017/jfm.2017.910

Cited by 53 publications

(52 citation statements)

References 43 publications

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“…In this work, we only considered swimmers with a moderate length of the caudal fin, but it would be very engaging to tackle the effects of the deformation modes of long and flexible tails. [45][46][47]…”

Section: A Thrust Analysismentioning

confidence: 99%

Study of the thrust–drag balance with a swimming robotic fish

et al. 2018

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A robotic fish is used to test the validity of a simplification made in the context of fish locomotion. With this artificial aquatic swimmer, we verify that the momentum equation results from a simple balance between a thrust and a drag that can be treated independently in the small amplitude regime. The thrust produced by the flexible robot is proportional to A 2 f 2 , where A and f are the respective tailbeat amplitude and oscillation frequency, irrespective of whether or not f coincides with the resonant frequency of the fish. The drag is proportional to U 2 0 , where U 0 is the swimming velocity. These three physical quantities set the value of the Strouhal number in this regime. For larger amplitudes, we found that the drag coefficient is not constant but increases quadratically with the fin amplitude. As a consequence, the achieved locomotion velocity decreases, or the Strouhal number increases, as a function of the fin amplitude.

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Section: A Thrust Analysismentioning

confidence: 99%

Study of the thrust–drag balance with a swimming robotic fish

et al. 2018

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“…Their classification means that the shape of stem is independent of the magnitude of the oscillatory motion ( ). In addition to , Leclercq & De Langre (2018) found the non-dimensional parameters and . It is easy to realize that .…”

Section: Resultsmentioning

confidence: 97%

“…Leclercq & De Langre (2018) adopted another set of non-dimensional parameters: as the length scale and as the time scale; is the natural period of the submerged stem, where is the added mass of the submerged stem for a unit added mass coefficient. Leclercq & De Langre (2018) found that the product of the natural period and cyclic wave frequency describes the transition from ‘static’ regime to their ‘convective’ and ‘modal’ regimes for . They also defined a fourth regime named the ‘large-amplitude regime, static reconfiguration with fast reversal’ for .…”

Section: Resultsmentioning

confidence: 99%

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Experimental investigation of the wave-induced motion of and force distribution along a flexible stem

et al. 2019

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The work presents an experimental investigation into the motion of and hydrodynamic forces along a single flexible stem in regular waves. The experiment covers a large range in relevant non-dimensional parameters: the drag-to-stiffness ratio $CaL\in [0.003,3.8]$, the inertia-to-stiffness ratio $CaL/KC\in [4\times 10^{-5},14.8]$, the Keulegan–Carpenter number $KC\in [3.8,145]$ and the Reynolds number $Re\in [230,2900]$. The two first parameters relate to the response of the stem in waves and thus account for material properties, while the two last parameters are relevant for hydrodynamic forces on the stem. The displacement of the stem was captured with a digital video camera and the displacement along the stem was captured for every 2.5 mm at 25 Hz. This unique laboratory data set allowed for the following analyses: (i) Determination of the relevant non-dimensional parameter to predict the stem motion and shape. (ii) A direct comparison between the measured force for mimics of two lengths (0.15 m and 0.30 m) illustrating the force reduction potential for flexible mimics. (iii) Direct evaluation of the average force coefficients $C_{D}$ (drag) and $C_{M}$ (inertia) for the flexible stems. (iv) The distributed external hydrodynamic loading and the internal shear forces were estimated from the laboratory experiments. The distribution of the shear force helped to understand the breakage mechanisms of flexible stems. (v) A linkage between phase lags and internal shear forces was suggested. The data set is considered valuable as validation material for numerical models of stem motion in waves.

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“…The blade motion due to flexibility reduces the relative velocity between flow and vegetation as well as the frontal area, resulting in a reduced drag that decreases velocity attenuation and wave attenuation in the vegetation meadow (Abdolahpour et al, 2018;Bouma et al, 2005;Houser et al, 2015;Mullarney & Henderson, 2010;Paul et al, 2012;Riffe et al, 2011;Rupprecht et al, 2017;Zeller et al, 2014). Numerical models have been developed to solve a force balance equation for the vegetation motion, considering gravity, buoyancy, structural damping, bending stiffness as restoring forces, as well as drag and inertia as driving forces (Ikeda et al, 2001;Leclercq & de Langre, 2018;Luhar & Nepf, 2016;Zeller et al, 2014;Zhu & Chen, 2015).…”

Section: Introductionmentioning

confidence: 99%

Mechanisms for the Asymmetric Motion of Submerged Aquatic Vegetation in Waves: A Consistent‐Mass Cable Model

et al. 2020

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Submerged aquatic vegetation (SAV) provides primary products for the food web, as well as shelter and nursery for many juvenile species. SAV can also attenuate waves, stabilize the seabed, and improve water quality. These environmental services are influenced by the dynamic motion of SAV. In this paper, a consistent‐mass cable model was developed to investigate flow interaction with a flexible vegetation blade. Compared with previous vegetation models, the cable model showed improvements in simulating blade motions in waves with and without currents, especially for “second‐normal‐mode‐like” blade motion. Wave asymmetry would cause blade motion to be asymmetric. However, asymmetric blade motion may also occur in symmetric waves. Results indicate that the asymmetric blade motion in symmetric waves is induced by two major mechanisms: (i) the spatial asymmetry of the encountered wave orbital velocities (wave motion relative to blade) due to blade displacements and (ii) the asymmetric action on the blade by vertical wave orbital velocities. Consequently, the blade motion is asymmetric even underneath symmetric waves unless (i) blade length ( l) is much smaller than the wavelength ( lfalse/L≪1), (ii) blade length is much smaller than the water depth ( lfalse/h≪1) in finite water depth waves, or (iii) water depth is much smaller than the wavelength ( hfalse/L≪1). Peak asymmetric blade motion occurs as lfalse/L increases to a critical value. The peak asymmetry increases with wave height and blade length but decreases with increasing blade flexural rigidity. Blade motion characteristics play an important role in wave‐vegetation interaction, wave‐driven currents, wave‐attenuation capacity, breakage of vegetation and ecosystem services.

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Reconfiguration of elastic blades in oscillatory flow

Cited by 53 publications

References 43 publications

Study of the thrust–drag balance with a swimming robotic fish

Study of the thrust–drag balance with a swimming robotic fish

Experimental investigation of the wave-induced motion of and force distribution along a flexible stem

Mechanisms for the Asymmetric Motion of Submerged Aquatic Vegetation in Waves: A Consistent‐Mass Cable Model

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