Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session G23: Biological Fluid Dynamics: Locomotion Swimming - Bio-inspired Propulsion |
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Chair: Keith Moored, Lehigh University Room: Georgia World Congress Center B311 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G23.00001: Scaling Laws of Bio-Inspired Propulsion Keith W Moored, Fatma Ayancik, Qiang Zhong, Daniel Quinn Aquatic animals oscillate their fins in combined heaving and pitching motions in order to swim fast and efficiently. To date there still are not accurate scaling laws to describe the physics of swimming. Here we focus on pitch-dominated swimmers and we develop scaling laws to predict the thrust and power of both two and three-dimensional propulsors pitching about their leading edge. Additionally, extensive two- and three-dimensional potential flow simulations as well as experiments show excellent collapse of the data for the thrust and power by using the developed scaling terms. The scaling laws are further extended to the cost of transport (CoT). These scaling relations offer the first mechanistic rationale for the scaling of swimming energetics observed in biology. Specifically, the CoT is shown to scale predominately with the added mass power. This suggests that the CoT of organisms using unsteady propulsion will scale with their mass as CoT ~ m-1/3, which is indeed consistent with existing biological data. Finally, these scaling relations offer a framework that can be extended to combined heaving and pitching motions and intermittent swimming. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G23.00002: Flow-mediated formations of a robotic school Joel W Newbolt, Jun Zhang, Leif Ristroph Motivated by schools of fish and flocks of birds, we perform experiments on a “robotic school” consisting of many flapping hydrofoils swimming in tandem. These foils have a prescribed heaving motion but are free in the swimming direction; the fluid forces on each foil determine its swimming speed and spacing relative to its neighbors. Previous results have shown that the reverse von Kármán wake generated by a heaving hydrofoil can provide stable positions to a second hydrofoil heaving in the wake (Ramananarivo et al. at NYU). New results for groups of more than two hydrofoils show that all trailing foils experience stable positions in the wake of their upstream neighbors. Force measurements confirm that the strength of these interactions weakens only slightly for each successive foil, thus the dominant interaction is that between each foil and the wake generated by its nearest upstream neighbor. We also find that allowing periodic interactions between the wake of the last foil and the body of the first foil can cause boosts in speed that are passed between successive foils. We reproduce these results using a simple wake-follower interaction model that can be extrapolated to predict the dynamics of larger groups. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G23.00003: Wake characteristics of a bio-inspired propulsor behind a streamlined body Seth A. Brooks, Melissa A Green A stationary streamlined tuna-like body was added upstream of a pitching trapezoidal panel to investigate how the wake of a whole fish model may differ from an isolated caudal fin model. Stereo particle image velocimetry was conducted in multiple planes along the lower half span of the panel, both with and without the upstream body. The data was phase-averaged, mirrored about the midspan plane, and interpolated into a volume. The Strouhal number was 0.37 and the Reynolds number was 17000 (with body) and 2300 (panel only). In both cases, the wake deformation exhibited transverse expansion and spanwise compression. Spanwise vortex cores lost coherence at the midspan at similar streamwise locations in both cases. For these reasons, the effects of a body’s boundary layer did not alter the main structure of the wake; however, several small-scale structures only appeared in the wake without the model body. Future experiments will involve actuation of the posterior half of the body in addition to the model caudal fin. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G23.00004: Evolutionary optimization of the flexibility and gait for a self-propelled bio-inspired propulsor Fatma Ayancik, Keith W Moored Many animals propel themselves through the water with sinusoidal, continuous gaits while some others adopt an intermittent and/or a non-sinusoidal gait. Additionally, animal propulsors can range in their flexibility from highly flexible to very stiff. Here, we examine the interplay between the flexibility of a propulsor and its gait. To probe this interplay, an evolutionary algorithm coupled with a two-dimensional boundary element method numerical framework is used to solve the multi-objective optimization problem where both the non-dimensional speed and range of a self-propelled swimmer are maximized. The hydrofoil is forced in a periodic pitching motion about its leading edge where the shape and the intermittency of the gait are varied by using Jacobi elliptic functions and burst-and-coast swimming, respectively. A lumped flexibility model in the form of a torsional spring is located at the mid-chord to model chordwise flexibility in the hydrofoil where the non-dimensional flexibility is altered by varying the spring stiffness. The results are presented in a novel performance map, which examines the interplay between the efficiency, the swimming speed, and the range of swimmer. The associated wake dynamics are also discussed. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G23.00005: On the high-performance swimming of a tuna-inspired underwater vehicle Part I: Design and performance study Joseph Zhu, Carl White, Dylan Wainwright, Valentina Di Santo, George Lauder, Hilary Bart-Smith Comprehensive comparative studies between bio-inspired robots and their biological counterparts are largely absent. In this study, we developed a thunniform robotic platform to study essential components of thunniform locomotion: tail beat frequency and amplitude; swimming speed; caudal fin pitch angle and flexibility; morphology; and midline kinematics. The platform achieved a maximum tail beat frequency and swimming speed of 15 Hz and 4.0 BL/s, respectively. High-speed video captured the swimming mechanics of the platform from the ventral view at 1000 frames/s. Midline kinematics extracted from these videos were analyzed and compared against corresponding biological data. In addition, the platform’s power consumption and static thrust were rigorously measured at various tail beat frequencies, indicating the high efficiency of the platform. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G23.00006: On the high-performance swimming of a tuna-inspired underwater vehicle Part II: Computational analysis Huy Tran, Martha Christino, Junshi Wang, Carl White, Joseph Zhu, George Lauder, Hilary Bart-Smith, Haibo Dong High-fidelity flow simulations are used to examine the key hydrodynamic features and thrust performance of the tuna-inspired underwater vehicle (TunaBot) swimming at a constant forward velocity. The numerical modeling approach employs a sharp-interface immersed-boundary-method (IBM)-based incompressible flow solver with adaptive mesh refinement (AMR) method. The three-dimensional, time-dependent kinematics of the body-fin system of the TunaBot is obtained via a stereo-videographic technique. The computational model is then directly reconstructed based on the experimental data with remarkably high accuracy. The primary objectives of the computational effort are to quantify the thrust performance of the TunaBot at different Reynolds number as well as to establish the mechanisms responsible for thrust production. Simulations show that the bending angle and bending rate of the TunaBot’s caudal peduncle play important roles in thrust producing. A distinct system of connected vortices produced by the TunaBot is also examined in detail for understanding the thrust producing mechanism. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G23.00007: Hydrodynamic and Maneuvering Control of an Underwater Vessel with Undulating-Fin Propulsion Mohammad Irfan Uddin, Oscar M Curet Undulating-fin propulsion, consisting of an elongated membrane to generate multi-directional thrust, can enhance the mobility and station keeping capabilities of an underwater vessel. Fish with this propulsion mechanism are able to maneuver in multiple directions, including forward, backward, rapid reverse, upward, forward-lateral and steady positioning. However, lack of adequate platform to explore the potential has restrained the use of the undulating fin propulsion for underwater vessels. In this work, we study the hydrodynamics and turning control of a robotic vessel equipped with a single undulating fin running along the length of the robot. We present hydrodynamic characterization and maneuvering control scheme to predict forces, torques and motion. As a first approach, we focus on control of horizontal maneuvering, comprising of surge, sway and yaw motion. |
Monday, November 19, 2018 12:06PM - 12:19PM |
G23.00008: Evolutionary Optimization of Soft Swimming Robots Andrew Hess, Tong Gao Engineering a soft robotic swimmer presents a unique challenge due to the inherently large numbers of degrees of freedom associated with their design. We present a method of developing optimal designs for soft swimmers powered by artificial muscle. To do so, the U-NSGA-III multi-objective optimization method is coupled with a FD/DLM FSI method simulating robotic fish actuated by an artificial muscle model. Since U-NSGA-III is a multi-objective method it in effect produces a map of potentially optimal solutions. This information can then be employed in the design of robotic swimmers as well as the research of swimming methods. We successfully evolve multiple, unique swimmers that are biomimetic in nature from an initial set of randomly selected design parameters, in essence reproducing a small piece of natural evolution. |
Monday, November 19, 2018 12:19PM - 12:32PM |
G23.00009: The Flow Structures Generated by a Robotic Sea Lion Foreflipper Elijah S Kashi, Aditya Kulkarni, Alexis Amechi, Rahi Patel, Megan Leftwich The sea lion produces thrust by clapping its large foreflippers into its abdomen. As this is significantly different from typical BCF modes of swimming, it is expected that the resulting flow structures will not resemble a reverse von Kármán street. We have conducted flow visualization experiments on a robotic flipper in a static test facility, replicating an animal accelerating from rest. The geometry of the robotic foreflipper is derived from laser scans of a foreflipper of an adult female California sea lion. Dye flow visualizations have produced qualitative data on flow structure formation during sea lion locomotion. Experiments include various flipper clap speeds, flipper locations and dye injection sites. We are gathering quantitative data through particle image velocimetry (PIV) experimentation, eventually comparing this data to live sea lion propulsive capabilities. Using results from the completed dye visualizations, we will be able to determine high priority areas in the wake where we will focus our PIV efforts. Data gathered through PIV will provide greater insight into the mechanics behind sea lion propulsion, moving the project one step closer to its ultimate goal of biological mimicry of a highly developed and efficient underwater propulsion system. |
Monday, November 19, 2018 12:32PM - 12:45PM |
G23.00010: Controlled Buckling Modes in a Slender Column used to Passively Recreate Backwards Travelling Wave in Biomimetic Robotic Fish Capable of Generating Fast-Starts Todd Currier, Yahya Modarres-Sadeghi An experimental study is conducted on a robotic fish designed to emulate the fast-startle response observed in live fishes. The caudal fin, dorsal and anal fin are modeled based on the northern pike and are 3D printed in a single part using mixed materials, rigid plastic to represent bone structures and rubber for the connective tissues. The robotic model is actuated using pressurized pistons. A total of two pistons are supplied through lightweight high-capacity service lines. The source of pressure is carbon dioxide with a 4.82 MPa peak operating pressure resulting in a body response that can cycle a C-start maneuver in milliseconds. The buckling modes of a slender column in compression are used to produce organic movements in the body with only two sources of actuation. The buckling of the beam interacting with the fluid results in a backwards travelling wave in the body of the robotic fish passively that is kinematically similar to the live fish. Two column lengths are tested for performance as well as control parameters (pressure magnitude, solenoid engagement duration, and time between solenoid engagements). The prototype design is deployed in a swift moving river to validate overall performance and the ability to perform fast-starts in the field. |
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