Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G19: Bio: Flapping and Swimming I |
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Chair: Tyler Van Buren, Princeton University Room: D136 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G19.00001: Effect of trailing edge shape on the wake and propulsive performance of pitching panels Tyler Van Buren, Daniel Floryan, Daniel Brunner, Utku Senturk, Alexander Smits We present the effects of the trailing edge shape on the wake and propulsive performance of a pitching panel with an aspect ratio of 1. The trailing edges are symmetric chevron shapes with convex and concave orientations of varying degree. Concave trailing edges delay the natural vortex bending and compression of the wake, and the streamwise velocity field contains a single jet-like structure. Conversely, convex trailing edges promote wake compression and produce a wake split into four jets. Deviation from the square trailing edge mostly reduces the thrust and efficiency. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G19.00002: Experimental study of surface pattern effects on the propulsive performance and wake of a bio-inspired pitching panel Justin King, Rajeev Kumar, Melissa Green Force measurements and stereoscopic particle image velocimetry (PIV) were used to characterize the propulsive performance and wake structure of rigid, bio-inspired trapezoidal pitching panels. In the literature, it has been demonstrated that quantities such as thrust coefficient and propulsive efficiency are affected by changes in the surface characteristics of a pitching panel or foil. More specifically, the variation of surface pattern produces significant changes in wake structure and dynamics, especially in the distribution of vorticity in the wake. Force measurements and PIV data were collected for multiple surface patterns chosen to mimic fish surface morphology over a Strouhal number range of 0.17 to 0.56. Performance quantities are compared with the three-dimensional vortex wake structure for both the patterned and smooth panels to determine the nature and magnitude of surface pattern effects in terms of thrust produced, drag reduced, and wake vortices reshaped and reorganized. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G19.00003: Momentum distribution in the wake of a bio-inspired trapezoidal pitching panel. Rajeev Kumar, Justin King, Melissa Green A trapezoidal pitching panel that models a fish caudal fin was used to study the distribution of streamwise momentum in its wake. The three-dimensional phase-averaged velocity fields were captured using stereoscopic PIV at Strouhal numbers (St) ranging from 0.17 to 0.56. The pitching trapezoidal panel wake consists of chains of interacting vortex rings that induce significant three-dimensional flows. With increasing Strouhal number, this wake structure induces flow with increasing non-dimensional downstream momentum, which is consistent with greater non-dimensional thrust production at higher St shown previously in the literature. Also at higher St, these chains of vortex rings split and diverge in the transverse direction, giving rise to a pair of downstream jets. At the highest St, a region of downstream momentum lower than the freestream is observed along the centerline between the jet pair. This loss of momentum surplus may be related to a previously described decline in propulsive efficiency at higher St. The momentum distribution is also studied in the time-averaged velocity fields to show how the average momentum is distributed over the same range of St. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G19.00004: A computational investigation of heaving flexible panels in a fluid Alexander Hoover, Ricardo Cortez, Lisa Fauci, Eric Tytell We present a 3-dimensional computational model of a flexible panel with heave oscillations at the leading edge. Our approach uses direct numerical simulations of the fully coupled fluid-structure interaction system within an immersed boundary framework. The effective flexibility of the panel is varied over a range of heaving frequencies and bending rigidities, with the resulting force measurements recorded. We find good agreement with recent experimental results, confirming that resonant peaks of the trailing edge amplitude correspond to localized boosts in thrust. We then use the model to explore the relationship between the thrust recorded from a tethered, heaving panel and the forward swimming speed of an untethered, heaving panel. The deflections of the panels are further examined with beam mode analysis from the Euler-Bernoulli beam equation. Spanwise variations of the panel dimensions are also considered. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G19.00005: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 9:05AM - 9:18AM |
G19.00006: Adjoint-based optimization of fish swimming gaits Daniel Floryan, Clarence W. Rowley, Alexander J. Smits We study a simplified model of fish swimming, namely a flat plate periodically pitching about its leading edge. Using gradient-based optimization, we seek periodic gaits that are optimal in regards to a particular objective (e.g. maximal thrust). The two-dimensional immersed boundary projection method is used to investigate the flow states, and its adjoint formulation is used to efficiently calculate the gradient of the objective function needed for optimization. The adjoint method also provides sensitivity information, which may be used to elucidate the physics responsible for optimality. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G19.00007: Nonstandard Gaits in Unsteady Hydrodynamics Michael Fairchild, Clarence Rowley Marine biology has long inspired the design and engineering of underwater vehicles. The literature examining the kinematics and dynamics of fishes, ranging from undulatory anguilliform swimmers to oscillatory ostraciiform ones, is vast. Past numerical studies of these organisms have principally focused on gaits characterized by sinusoidal pitching and heaving motions. It is conceivable that more sophisticated gaits could perform better in some respects, for example as measured by thrust generation or by cost of transport. This work uses an unsteady boundary-element method to numerically investigate the hydrodynamics and propulsive efficiency of high-Reynolds-number swimmers whose gaits are encoded by Fourier series or by Jacobi elliptic functions. Numerical results are presented with an emphasis on identifying particular wake structures and modes of motion that are associated with optimal swimming. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G19.00008: Phototactic guidance of a tissue-engineered soft-robotic ray. Sung-Jin Park, Mattia Gazzola, Kyung Soo Park, Shirley Park, Valentina Di Santo, Karl Deisseroth, George V. Lauder, L. Mahadevan, Kevin Kit Parker Inspired by the relatively simple morphological blueprint provided by batoid fish such as stingrays and skates, we created a biohybrid system that enables an artificial animal, a tissue-engineered ray - to swim and phototactically follow a light cue. By patterning dissociated rat cardiomyocytes on an elastomeric body enclosing a microfabricated gold skeleton, we replicated fish morphology at 1/10 scale and captured basic fin deflection patterns of batoid fish. Optogenetics allows for phototactic guidance, steering, and turning maneuvers. Optical stimulation induced sequential muscle activation via serpentine-patterned muscle circuits, leading to coordinated undulatory swimming. The speed and direction of the ray was controlled by modulating light frequency and by independently eliciting right and left fins, allowing the biohybrid machine to maneuver through an obstacle course. [Preview Abstract] |
Monday, November 21, 2016 9:44AM - 9:57AM |
G19.00009: Outsourcing neural active control to passive composite mechanics: a tissue engineered cyborg ray. Mattia Gazzola, Sung Jin Park, Kyung Soo Park, Shirley Park, Valentina Di Santo, Karl Deisseroth, George V. Lauder, L. Mahadevan, Kevin Kit Parker Translating the blueprint that stingrays and skates provide, we create a cyborg swimming ray capable of orchestrating adaptive maneuvering and phototactic navigation. The impossibility of replicating the neural system of batoids fish is bypassed by outsourcing algorithmic functionalities to the body composite mechanics, hence casting the active control problem into a design, passive one. We present a first step in engineering multilevel "brain-body-flow" systems that couple sensory information to motor coordination and movement, leading to behavior. This work paves the way for the development of autonomous and adaptive artificial creatures able to process multiple sensory inputs and produce complex behaviors in distributed systems and may represent a path toward soft-robotic ``embodied cognition''. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G19.00010: Stiffness Modulation of Rayed Fins by Curvature Khoi Nguyen, Ning Yu, Madhusudhan Venkadesan, Mahesh Bandi, Shreyas Mandre Fishes with rayed fins comprise over 99\% of all extant fish species. Multifunctional use of fins, from propulsion to station holding, requires substantial modulation of stiffness. We propose that fishes stiffen the fin by curving it transverse to its length. This effect is similar to stiffening a dollar bill by curling it because of curvature-induced coupling of out-of-plane bending with in-plane stretching. Unlike a piece of paper, rayed fins are a composite of rays and membranes. We model this as parallel elastic beams (rays) with springy interconnections (membranes). Our analysis shows that the key parameters stiffening the fin are the ray anisotropy to bending, the misalignment of principal bending directions of adjacent rays, and the membrane elasticity. The composite fin stiffens when the principal bending directions of adjacent rays are misaligned due to fin curvature, which necessarily causes the membrane to stretch. Unlike a homogenous thin sheet, composite rayed structures are able to mimic curvature-induced stiffening by using misaligned rays even if the fin appears geometrically flat. Preliminary radiographic evidence from the rays of fish fins supports such a mechanism. [Preview Abstract] |
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