Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H5: Biofluids: Swimming |
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Chair: Leif Ristroph, Courant Institute Room: 3008 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H5.00001: Optimal Swimming with a Burst-and-Coast Behaviour Emre Akoz, Keith Moored Swimming animals are typically assumed to be continuously adding power to the fluid throughout a period of motion. On the other hand, animals have been observed using a non-continuously powered motion described as a burst-and-coast or burst-and-glide behavior. When animals use a non-continuously powered motion it is estimated that their cost of transport is reduced by as much as 45{\%}. However, there are competing mechanisms in the literature that lead to this conclusion. The present study aims to identify the underlying mechanism of burst-and-coast energy savings and to quantify the scaling of optimal motions. A two-dimensional boundary element method approach is used to quantify the performance and wake structure of a free-swimming pitching panel operating with a burst-and-coast behavior. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H5.00002: Stability may not compromise Maneuverability in Aquatic Periodic Locomotion Eva Kanso, Fangxu Jing Most aquatic vertebrates swim by lateral flapping of their bodies and caudal fins. While much effort has been devoted to understanding the flapping kinematics and its influence on the swimming efficiency, little is known about the stability (or lack of) of periodic swimming. It is believed that stability limits maneuverability and body designs/flapping motions that are adapted for stable swimming are not suitable for high maneuverability and vice versa. Here, we consider an idealized model of a planar elliptic body undergoing prescribed periodic heaving and pitching in a perfect fluid. We show that periodic locomotion depends on several parameters including the aspect ratio of the body and the amplitude and phase of the prescribed flapping. We then study the stability of periodic locomotion using Floquet theory. We find that interesting trends of switching between stable and unstable motions emerge and evolve as we continuously vary the parameter values. This suggests that, when it comes to live organisms, maneuverability and stability need not be thought of as disjoint properties, rather the organism may manipulate its motion in favor of one or the other depending on the task at hand. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H5.00003: Stereoscopic Particle Image Velocimetry Used to Study the Wake Patterns of an Ideal Anguilliform Swimming Motion Brandon Taravella, J. Baker Potts, Matthew Stegmeir The University of New Orleans recently acquired a self-contained stereoscopic particle image velocimetry system for use in their 125 ft long towing tank. This system is being used to study the wake flow behind an anguilliform swimming robot that swims with an ideal motion that is theorized not to produce any trailing vortices. The presentation will describe the particulars of the SPIV system along with details of installation of the SPIV system within the towing tank. The calibration routine will be discussed in detail and results of the free-flow runs will be discussed. Preliminary results from the anguilliform swimming motion will also be presented. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H5.00004: The hydrodynamics and kinematics of sea lion swimming Megan C. Leftwich, Chen Friedman A highly interactive, non-research, female sea lion was used for studying its thrust production mechanisms at the Smithsonian National Zoo in Washington, DC. Videography was used for flipper kinematics extraction by tracing the flipper center line and studying the flipper shape throughout the thrust phase. Acceleration from rest was studied with respect to flipper angular rate and flipper shape by digitizing the videos using 10 points spanning root to tip. Resulting functions reveal spanwise camber of up to 32\%, with instantaneous angular rates as high as 20 rad/sec, generating thrust values in the range of $150$-$680$~N. The sea lion flipper was scanned using several 3D scanning techniques to generate a 3D model which will be used to reproduce a scaled robotic flipper for testing in a controlled laboratory setting. Techniques included two highly accurate structured light based 3D scanner, an image based software, capable of generating 3D meshes, and a kinect based scanner. A silicone mold of the flipper was also created for reference and comparison. The 3D models are used to extract several section airfoils which aid in both modeling the flipper computationally and designing foreflipper based robotic platforms. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H5.00005: A Study of Kinematics Modeling and the Computational Optimization of the Human Underwater Undulatory Kick by Comparison of Swimmers and Body Orientations Xiaoran Zhu, Geng Liu, Yan Ren, Haibo Dong Underwater Undulatory Swimming (UUS), better known as the underwater dolphin kick, is the most important technique in competitive swimming. Faster than three of the four strokes in swimming, UUS is permitted in the 15m after dives and turns. In this study, we compared the UUS of a college-level swimmer and a younger swimmer. 3D human models were built and reconstructed using stereo-videos for identifying key components of undulatory kick kinematics with respect to strongly flexing joints. A gradient-based optimizer and an immersed boundary method based CFD solver was then used to study the hydrodynamic performance of each swimmer. Optimal settings of current kinematic models will help us to understand the efficiency of the observed undulatory kick mechanisms and further improvements of the human UUS strategy. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H5.00006: On the efficient swimming of a ray-inspired underwater vehicle Part I: Experimental study on swimming optimization of control and fin structure Jianzhong Zhu, Mervyn Lopez, Ventress Williams, Theophilus Aluko, Haibo Dong, Hilary Bart-Smith Batoid fish such as manta and cownose rays are among the most agile and energy efficient swimming creatures. These capabilities arise from flapping and bending their dorsally flattened pectoral fins. To assess this contribution, this study focuses on the study of a bio-inspired underwater vehicle---the MantaBot---where biological design criteria are applied. The MantaBot consists of two parts: a rigid body rendered from a CT scanning image of a cownose ray and two flexible fins driven by tensegrity actuators. The experiments were conducted in a water tank where the MantaBot was attached to a rail for rectilinear swimming. Three stereo-videos were taken and digitized to measure the 3D kinematics. Results showed that the fins conduct deformations in both spanwise and chordwise directions during steady swimming. Optimal operation conditions were determined for fastest swimming by surveying a wide range of parameters. Contributions of thrust generation and amplitude hindrance of various portions of the fin volume were examined. Additionally, fin tip structure, material and bending properties were studied for optimal swimming. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H5.00007: The effect of flexibility on ribbon-fin-based propulsion Hanlin Liu, Bevan Taylor, Evan Latshaw, Oscar Curet Ribbon-fin-based propulsion has the potential to improve the maneuverability of underwater vehicles navigating in complex environments. In this type of propulsion a series of rays are used to send traveling waves along an elongated fin. The use of flexible rays could further enhance the propulsive efficiency of undulating ribbon fins. In this work, we characterize the mechanical behavior and performance of a robotic undulating ribbon fin with different ray flexibilities. We tested the physical model in a water tunnel. In a series of experiments we measure the propulsive force, power consumption and swimming speed of the robotic fin for different ray flexural stiffness, wave frequencies and flow conditions. We found that an increase in flexibility decreases both thrust production and power consumption. Flexible rays could improve or worsen the propulsive performance compared to a rigid counterpart depending on the actuation parameters. We present the result concerning the different performance between rigid and flexible fins. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H5.00008: On the efficient swimming of a ray-inspired underwater vehicle. Part II: Computational analysis of fin hydrodynamics Geng Liu, Yan Ren, Jianzhou Zhu, Hilary Bart-Smith, Haibo Dong High-fidelity numerical simulations are being used to examine the key hydrodynamic features and thrust performance of the fin of a manta ray-inspired underwater vehicle (MantaBot) which is moving at a constant forward velocity. The numerical modeling approach employs a parallelized DNS immersed boundary solver for low-Reynolds number flows past highly deformable bodies such as fish pectoral fins and insect wings. The three-dimensional, time-dependent fin kinematics is obtained via a stereo-videographic technique. The primary objectives of the CFD effort are to quantify the thrust performance of the MantaBot fin with different bending stiffness as well as to establish the mechanisms responsible for thrust production. Simulations show that the bending angle and bending rate of the fin play important roles in thrust producing. A distinct system of connected vortices produced by the deformable fins is also examined in detail for understanding the thrust producing mechanisms. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H5.00009: A fish-like robot : Mechanics of swimming due to constraints Phanindra Tallapragada, Rijan Malla It is well known that due to reasons of symmetry, a body with one degree of actuation cannot swim in an ideal fluid. However certain velocity constraints arising in fluid-body interactions, such as the Kutta condition classically applied at the trailing cusp of a Joukowski hydrofoil break this symmetry through vortex shedding. Thus Joukowski foils that vary shape periodically can be shown to be able to swim through vortex shedding. In general it can be shown that vortex shedding due to the Kutta condition is equivalent to nonintegrable constraints arising in the mechanics of finite-dimensional mechanical systems. This equivalence allows hydrodynamic problems involving vortex shedding, especially those pertaining to swimming and related phenomena to be framed in the context of geometric mechanics on manifolds. This formal equivalence also allows the design of bio inspired robots that swim not due to shape change but due to internal moving masses and rotors. Such robots lacking articulated joints are easy to design, build and control. We present such a fish-like robot that swims due to the rotation of internal rotors. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H5.00010: Fast Computation of Fully Resolved Neuromechanically Simulated Locomotion Namu Patel, Neelesh A. Patankar In fish, caudally propagating waves of neural activity produce muscle bending moments. These moments, coupled with forces due to the body's elastic properties and forces due to fluid-body interactions, determine the deformation kinematics for swimming. Fully resolved simulations of neurally-activated swimming can be used to decode activation patterns underlying observed behaviors in a swimming animal. These computations are expensive; the time stepping requirement is onerous due to the canonically used explicit coupling between the elastic body and the fluid. To overcome this barrier, we use our prior result that deformation kinematics closely follow the preferred kinematics due to muscle activation when a swimmer has a sufficiently stiff body. Thus, we can impose the preferred deformation kinematics directly on the body immersed in the fluid. In this way, the need to solve the elastic equations is eliminated. Here, we couple physiochemical and physiomechanical equations to a constraint-based self-propulsion formulation. With this method, we demonstrate how different behaviors, such as turning, emerge from varying the neural signal. [Preview Abstract] |
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