Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session L06: High Reynolds Number Swimming II |
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Chair: Patrick Musgrave, University of Florida Room: 133 |
Monday, November 21, 2022 8:00AM - 8:13AM |
L06.00001: Emulating a human walking gait in a double pendulum interacting with the incoming vortices Yahya Modarres-Sadeghi, Adrian Carleton, Umang Patel, Rishiraj Bose, Frank Sup We discuss a method to impose desired trajectories on a double pendulum placed in flow. In a long-term project, we are designing a robot to provide assistance to patients with walking disabilities by manipulating the flow of water in an underwater treadmill to enable the patients to follow a desired walking trajectory. In the present work, we show this concept using a double pendulum. A cylinder forced to rotate upstream the double pendulum controls the shedding frequency and strength of the vortices that interact with the double pendulum. These vortices then interact with a hydrofoil that is attached to the double pendulum and produce trajectories very similar to the human walking gait trajectories. |
Monday, November 21, 2022 8:13AM - 8:26AM |
L06.00002: Flow Structures Produced by Robotic Sea Lion Flippers of Varying Elasticity and Angular Velocity Ian W Moss, Aditya A Kulkarni, Megan C Leftwich Sea Lions generate thrust through a clap-like maneuver, abducting their fore flippers towards the chest region of their body. This motion incorporates a combination of both lift and drag based propulsion and can produce high propulsive efficiency. Furthermore, it is unique amongst other biological swimmers that rely mostly on body-caudal fin locomotion. To replicate a simplified model of this maneuver for planar particle image velocimetry (PIV) in a water channel, we developed a robotic sea lion flipper model using silicon mold and a 3D printed skeletal structure representing the elbow, wrist, and knuckle joints. Using a motor, the elbow joint is rotated at a constant angular velocity into a flat plate, representing the sea lion’s chest, while the wrist and knuckle joints remain passive. To decouple the effects of flexibility and angular velocity on the resulting flow structures of the clap, we now present three robotic flippers models made with different flexibilities. The flow structures and estimated thrust are compared to a baseline rigid sea lion flipper model to allow for us to determine the isolated, decoupled effects. |
Monday, November 21, 2022 8:26AM - 8:39AM |
L06.00003: Swimming at Higher Resonant Frequencies for Improved Thrust in Flexible Propulsors Patrick F Musgrave, Charlie M Tenney To swim at high speeds, biological swimmers (e.g. Tuna) oscillate their caudal fins at high frequencies, actively changing their body stiffness to efficiently amplify their tail-beat velocity. Similarly, a propulsor's higher resonant frequencies can be used to amplify tail-beat velocity. This study experimentally investigates flexible propulsors operating at their non-fundamental resonant frequencies (up to fifth natural frequency, ~50Hz). The flexible propulsors are thin aluminum beams in a clamped-free configuration in quiescent water excited by two pairs of antagonistic macro fiber composite (MFC) piezoelectric actuators. The maximum thrust of each propulsor occurs at the third or fourth resonance and corresponds with the frequency of maximum tail-beat velocity. The thrust coefficient (ratio of thrust to tail-beat velocity squared) decreases for increasing resonant frequency; this likely stems from the greater curvature in the propulsor deformation at higher mode shapes. Thus, higher resonant frequencies can produce greater thrust, but are less efficient at converting tail-beat velocity into thrust. Higher resonant frequencies could be useful as an acceleration method: temporarily gaining increased thrust but at lower efficiency, similar to acceleration in biological swimming. |
Monday, November 21, 2022 8:39AM - 8:52AM |
L06.00004: Autonomous navigation of simulated swimmers using deep reinforcement learning Aishwarya S Nair, Siddhartha Verma Enegy-efficiency in movement underwater is an important aspect of operation in autonomous underwater vehicles. In this work, we explore the feasibility of using hydrodynamic sensing for optimal underwater navigation. This study uses reinforcement learning coupled with 2-dimensional numerical simulations of self propelled swimmers. These artificial swimmers with mechanosensory inputs similar to the lateral line in biological fish are trained using deep reinforcement learning to optimally perform various actions such as obstacle avoidance and autonomous navigation towards a target. The swimmers trained in this manner can then be used to navigate more reliably in previously unmapped areas. By comparing the behavior exhibited by the swimmers in different flows such as uniform flow and Karman vortex fields, we analyze the different optimal strategies for navigation in each scenario. The results can then be used to develop control strategies for unmanned robots and underwater robotic swarms. |
Monday, November 21, 2022 8:52AM - 9:05AM |
L06.00005: Vortex sheet simulations of interacting flapping plates Monika Nitsche, Anand U Oza, Michael Siegel The motion of several plates in an inviscid and incompressible fluid is studied numerically, the general motivation being to understand the role of hydrodynamic interactions in mediating schooling and flocking behavior in animal collectives. The plates move vertically with a prescribed oscillatory motion and horizontally by their self-induced thrust forces. The trailing vorticity is simulated using a separated vortex sheet model. The simulations require a vortex shedding model, a model for the thrust forces, and a method to resolve the fluid motion near the plates. We discuss each aspect and apply the method to determine the dependence of the plate motion on the model parameters. |
Monday, November 21, 2022 9:05AM - 9:18AM |
L06.00006: Effects of the neuromechanical inputs on the swimming performance of an oblate jellyfish Alessandro Nitti, Michele Torre, Josef Kiendl, Alessandro Reali, Marco D. de Tullio The replication of the neuro-mechanical processes contributing to locomotion can advance the understanding of jellyfish biology and their environmental interactions. To this end, we propose a comprehensive simulation framework to deduce fundamental correlations between electrophysiological inputs and propulsive performance. The key simplifying assumption of axisymmetric field allows to work out a sophisticated model with a reasonable number of degrees of freedom. The monodomain model drives the diffusion of the electrophysiological excitation waves over the endothelial tissue, whereas a Hodgkin-Huxley neuron model addresses the reactive effects. Consequently, the electrical stimulus is translated into an active contraction of the subumbrellar muscle fibers whereas the outer part of the solid domain, which mimics the mesoglea, is modelled as a passive part, being responsible for the elastic recoil. Both activation parameters and material properties are tuned to match experimental observations from in-vivo experiments. The computational framework is completed by the axisymmetric Navier-Stokes solver, which, in conjunction with a direct-forcing immersed boundary treatment, incorporates the full excitation-contraction-locomotion scenario. |
Monday, November 21, 2022 9:18AM - 9:31AM |
L06.00007: Stable schooling arrangements of two and three swimmers Pedro C Ormonde, Amin Mivehchi, Keith W Moored We present data supporting the existence of two-swimmer schooling arrangements that are stable and arise spontaneously from hydrodynamic forces alone. Water channel experiments were performed with two NACA 0012, AR=3 hydrofoils where both swimmers are free to move in the horizontal plane. Stable arrangements deviate only slightly from a canonical, side-by-side formation for phase synchronies ranging from 160 to 200 degrees. The collective swimming speed is 15% higher than that of an isolated swimmer. These findings are also supported by 2D free-swimming simulations, PIV data and performance measurements. In a second experiment we then take these stable arrangements of two swimmers as a starting point for studies of larger schools. The two swimmers are positioned in a stable arrangement and fixed (translation not allowed in the plane). A third, fully unconstrained swimmer is then added downstream of the two fixed foils. The third swimmer is used to investigate larger schooling formations of fish-like swimmers. |
Monday, November 21, 2022 9:31AM - 9:44AM |
L06.00008: A Koopman operator-based approach to position sensing and estimation in unsteady flow Colin Rodwell, Kumar Sourav, Phanindra Tallapragada Position estimation using a time-series of pressure data from distributed sensors on a moving body in an unsteady flow field is a challenging problem that biological swimmers, such as fish, adeptly solve to enable effective station keeping, navigation, and swarming. Similar proprioceptive sensing is desired for bio-inspired artificial swimmers to enable similar behaviors. In flows with high Reynolds number and fluid-body interaction, the lack of a reduced model invalidates model-based estimation approaches, so data-driven time-series classification approaches must be used. In this work, we introduce a hybrid data-driven and model-driven approach, whereby pressure data is used to generate an approximation of the Koopman operator, which is the linear flow map that maps the observations (pressure data) one step forward in time with minimal error. The eigenvalues of that operator, sometimes known as the DMD modes, represent physical flow structures. We consider those modes as 'features' of the flow and use machine learning to perform estimation of the position based on these features, which results in higher estimation accuracy compared to applying machine learning directly to the time-series data. |
Monday, November 21, 2022 9:44AM - 9:57AM |
L06.00009: Experimental and Theoretical Study of the Roles of Body Flexibility in Undulatory Bioinspired Swimmers Brian Van Stratum, Jonathan Clark, Eric Barth, Kourosh Shoele Research has demonstrated that body flexibility is a determining parameter for oscillating objects in fluid flow. Understanding the role of body flexibility is crucial for many problems such as animal locomotion, robotics, and energy harvesting. In this study, we explore the impact of various parameters of swimmers with lateral undulation body motion on their swimming performance. In particular, the morphological parameters such as damping and stiffness and control policy parameters including effort and phasing are investigated. Here, the flow is modeled with Lighthill's elongated body model, and the structural dynamics are represented with a nonlinear large deformation viscoelastic beam model. We cross-compare the theoretical and computational results with corresponding results from towing tank experiments. A novel robot design used in these experiments is presented wherein the body stiffness is modified by changing the nominal fluid pressure, effectively developing antagonistic co-contraction of the silicone fluidic elastomeric actuators used along the body. |
Monday, November 21, 2022 9:57AM - 10:10AM Author not Attending |
L06.00010: Collective hydrodynamics of robotic fish Rohit S Pandhare, Mitchel L Timm, Hassan Masoud Many animals in nature travel in groups either for protection, survival, or endurance. Among these, fish do so under the burden of hydrodynamic loads, which incites questions as to the significance of the multi-body fluid-mediated interactions that facilitate collective swimming. We study such interactions in the idealized setting of a rotational array of robotic fish whose tails undergo a prescribed flapping motion, but whose swimming speed is determined as a natural result of the hydrodynamic effects. Specifically, we examine how the collective speed of the swimmers varies with the frequency and amplitude of their tail flapping, and with the phase difference between the tail motions of neighboring robots in the array. To visualize the flow field while the swimmers are in motion, we implement a camera system to track neutrally buoyant florescent seeding particles suspended in the water surrounding the fish. This three-dimensional particle tracking velocimetry technique allows us to capture the trajectory of the seeding particles and, thereby, derive the velocity and vorticity fields around the interacting fish. Applications that can directly benefit from the findings of our investigation include the design and control of robotic fish swarms. |
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