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1. Bio-Inspired Propulsion: Towards Understanding the Role of Pectoral Fin Kinematics in Manta-like Swimming

   https://doi.org/10.3390/biomimetics7020045  

   Menzer, A. ; Gong, Y. ; Fish, F. ; Dong, H. ( June 2022 , Biomimetics)

   Gorb, S. (Ed.)

   Through computational fluid dynamics (CFD) simulations of a model manta ray body, the hydrodynamic role of manta-like bioinspired flapping is investigated. The manta ray model motion is reconstructed from synchronized high-resolution videos of manta ray swimming. Rotation angles of the model skeletal joints are altered to scale the pitching and bending, resulting in eight models with different pectoral fin pitching and bending ratios. Simulations are performed using an in-house developed immersed boundary method-based numerical solver. Pectoral fin pitching ratio (PR) is found to have significant implications in the thrust and efficiency of the manta model. This occurs due to more optimal vortex formation and shedding caused by the lower pitching ratio. Leading edge vortexes (LEVs) formed on the bottom of the fin, a characteristic of the higher PR cases, produced parasitic low pressure that hinders thrust force. Lowering the PR reduces the influence of this vortex while another LEV that forms on the top surface of the fin strengthens it. A moderately high bending ratio (BR) can slightly reduce power consumption. Finally, by combining a moderately high BR = 0.83 with PR = 0.67, further performance improvements can be made. This enhanced understanding of manta-inspired propulsive mechanics fills a gap in our understanding of the manta-like mobuliform locomotion. This motivates a new generation of manta-inspired robots that can mimic the high speed and efficiency of their biological counterpart.

    

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2. Bio-Inspired Propulsion: Towards Understanding the Role of Pectoral Fin Kinematics in Manta-like Swimming

   Alec Menzer, Yuchen Gong ( April 2022 , Biomimetics)

   MDPI (Ed.)

   Through computational fluid dynamics (CFD) simulations of a model manta ray body, the hydrodynamic role of manta-like bioinspired flapping is investigated. The manta ray model motion is reconstructed from synchronized high-resolution videos of manta ray swimming. Rotation angles of the model skeletal joints are altered to scale the pitching and bending, resulting in eight models with different pectoral fin pitching and bending ratios. Simulations are performed using an in-house developed immersed boundary method-based numerical solver. Pectoral fin pitching ratio (PR) is found to have significant implications in the thrust and efficiency of the manta model. This occurs due to more optimal vortex formation and shedding caused by the lower pitching ratio. Leading edge vortexes (LEVs) formed on the bottom of the fin, a characteristic of the higher PR cases, produced parasitic low pressure that hinders thrust force. Lowering the PR reduces the influence of this vortex while another LEV that forms on the top surface of the fin strengthens it. A moderately high bending ratio (BR) can slightly reduce power consumption. Finally, by combining a moderately high BR = 0.83 with PR = 0.67, further performance improvements can be made. This enhanced understanding of manta-inspired propulsive mechanics fills a gap in our understanding of the manta-like mobuliform locomotion. This motivates a new generation of manta-inspired robots that can mimic the high speed and efficiency of their biological counterpart 

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3. Modeling and Computation of Batoid Swimming Inspired Pitching Impact on Wake Structure and Hydrodynamic Performance

   Menzer, A. ; Li, C. ; Fish, F. ; Gong, Y. ; Dong, H. ( August 2022 , Fluids Engineering Division Summer Meeting)

   Through direction numerical simulation (DNS) of a model manta ray body, pectoral fin scaled pitching effect on hydrodynamic performance and wake is investigated. The manta ray model is derived from high-speed video of manta ray swimming with motion of the model prescribed to match the actual manta ray. Rotation angles of the model skeletal joints is altered to scale the pitching. This results in four manta ray models with different pectoral fin pitching ratios. The models are simulated using an in-house developed immersed boundary method-based numerical solver. Notable discrepancies in thrust production during the downstroke are observed, with the θ =1.0 case producing instantaneous thrust peak that is 19% higher than the θ =0.72 model. Cycle averaged thrust is highest for the θ =0.72 model case, however, which can be attributed to extended reverse thrust for the θ =1.0 model. Through analysis of the near-body wake structures produced during the downstroke, late leading-edge vortex (LEV) formation is discovered to be primarily responsible for the detrimental reverse thrust seen for the θR =1.0 model. Surface pressure contours confirm this finding. Meanwhile the upstroke possesses less pronounced force production. 

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4. A new propulsion enhancement mechanism in metachronal rowing at intermediate Reynolds numbers

   https://doi.org/10.1017/jfm.2023.739  

   Lionetti, Seth ; Lou, Zhipeng ; Herrera-Amaya, Adrian ; Byron, Margaret L. ; Li, Chengyu ( November 2023 , Journal of Fluid Mechanics)

   Metachronal rowing is a biological propulsion mechanism employed by many swimming invertebrates (e.g. copepods, ctenophores, krill and shrimp). Animals that swim using this mechanism feature rows of appendages that oscillate in a coordinated wave. In this study, we used observations of a swimming ctenophore (comb jelly) to examine the hydrodynamic performance and vortex dynamics associated with metachronal rowing. We first reconstructed the beating kinematics of ctenophore appendages based on a high-speed video of a metachronally coordinated row. Following the reconstruction, two numerical models were developed and simulated using an in-house immersed-boundary-method-based computational fluid dynamics solver. The two models included the original geometry (16 appendages in a row) and a sparse geometry (8 appendages, formed by removing every other appendage along the row). We found that appendage tip vortex interactions contribute to hydrodynamic performance via a vortex-weakening mechanism. Through this mechanism, appendage tip vortices are significantly weakened during the drag-producing recovery stroke. As a result, the swimming ctenophore produces less overall drag, and its thrust-to-power ratio is significantly improved (up to 55.0 % compared with the sparse model). Our parametric study indicated that such a propulsion enhancement mechanism is less effective at higher Reynolds numbers. Simulations were also used to investigate the effects of substrate curvature on the unsteady hydrodynamics. Our results illustrated that, compared with a flat substrate, arranging appendages on a curved substrate can boost the overall thrust generation by up to 29.5 %. These findings provide new insights into the fluid dynamic principles of propulsion enhancement underlying metachronal rowing.

    

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5. Regulation of the swimming kinematics of lampreys Petromyzon marinus across changes in viscosity

   https://doi.org/10.1242/jeb.245457  

   Tytell, Eric D. ; Cooper, Lauren O. ; Lin, Yuexia Luna ; Reis, Pedro M. ( April 2023 , Journal of Experimental Biology)

   The bodies of most swimming fishes are very flexible and deform due to both external fluid dynamic forces and internal musculoskeletal forces. If fluid forces change, the body motion will also change unless the fish senses the change and alters its muscle activity to compensate. Lampreys and other fishes have mechanosensory cells in their spinal cords that allow them to sense how their body is bending. We hypothesized that lampreys (Petromyzon marinus) actively regulate body curvature to maintaina fairly constant swimming waveform even as swimming speed and fluid dynamic forces change. To test this hypothesis, we measured the steady swimming kinematics of lampreys swimming in normal water, and water in which the viscosity was increased by 10 or 20 times by adding methylcellulose. Increasing the viscosity over this range increases the drag coefficient, potentially increasing fluid forces up to 40%. Previous computational results suggested that if lampreys did not compensate for these forces, the swimming speed would drop by about 52%, the amplitude would drop by 39%, and posterior body curvature would increase by about 31% , while tail beat frequency would remain the same. Five juvenile sea lampreys were filmed swimming through still water, and midlines were digitized using standard techniques. Although swimming speed dropped by 44% from 1× to 10× viscosity, amplitude only decreased by 4% , and curvature increased by 7%, a much smaller change than the amount we estimated if there was no compensation. To examine the waveform overall, we performed a complex orthogonal decomposition and found that the first mode of the swimming waveform (the primary swimming pattern) did not change substantially, even at 20× viscosity. Thus, it appears that lampreys are compensating, at least partially, for the changes in viscosity, which in turn suggests that sensory feedback is involved in regulating the body waveform.

    

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