Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session A06: Locomotion: General |
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Chair: Cecilia Huertas-Cerdeira, University of Maryland College Park Room: Ballroom F |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A06.00001: Effect of substrate rigidity and temporal asymmetry on the force production of a bioinspired flexible paddle at intermediate Reynolds number Cong Hai Le, Margaret L Byron Flexibility is one of the key factors that enhances the performance and efficiency of animal swimming relative to rigid analogues. Often, flexible biological appendages (e.g. fins, legs, pleopods, cilia, flagella) protrude from a larger body wall or substrate; the proximity and relative geometry of this substrate can affect the flow generated by protruding appendages as they row or flap. However, previous work in both numerical and laboratory experiments has often assumed that biological propulsors are embedded in a rigid, flat surface, neglecting any hydrodynamic contribution due to the substrate's flexibility and curvature. To address this missing link, we attach a flexible paddle to a servomotor whose shaft is adjacent and parallel to a substrate that extends far beyond the edges of the paddle. Inspired by the paddle-like appendages (ctenes) of ctenophores, as well as the pleopods of crustaceans, we oscillate the paddle next to the substrate with glycerol as a working fluid, achieving Reynolds number on the order of 100. This oscillation ranges from highly temporally asymmetric (with a fast power stroke and a slow recovery stroke), to temporally symmetric (power stroke and recovery stroke are nearly identical in duration). Using Particle Image Velocimetry, we evaluate the velocity and pressure field of the generated flow to calculate the thrust and lift produced by the paddle under three different substrate conditions (rigid, flexible, and no substrate). In general, the presence of any substrate leads to a higher lift coefficient; thrust generation is dependent on both substrate condition and temporal asymmetry. These findings emphasize the importance of the potential contribution of substrate or body in biologically generated flows, as well as in bioinspired applications. |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A06.00002: Enhancing Metachronal Swimming Efficiency through Dynamic Substructure Oscillation Zhipeng Lou, Margaret L Byron, Chengyu Li Metachronal paddling is a swimming technique commonly used by various small invertebrates like ctenophores, gossamer worms, shrimp, and krill, especially in environments with low-to-intermediate Reynolds numbers. These creatures synchronize their appendages in a metachronal sequence to enhance propulsive efficiency through interactions between adjacent appendages. This efficiency gain can be enhanced by increasing the number of appendages, although there is a threshold beyond which no further efficiency can be gained. Drawing inspiration from gossamer worms, which combine body oscillations with metachronal appendage movements, we propose that oscillating the body or substructures can overcome these efficiency limits, improving swimming performance as additional appendages are incorporated. To investigate this hypothesis, we utilized a fluid-structure interaction solver that integrates an immersed boundary method-based computational fluid dynamics solver with a finite element method-based structural solver, through two-way coupling. We simulated passively deforming plates stroking in a metachronal order, with the rotation pivot fixed on either a stationary or a deformable substructure following a sinusoidal pattern. Preliminary findings indicate that a dynamic, waving substructure not only increases thrust during the power stroke but also reduces drag during the recovery stroke, compared to a stationary substructure. |
Sunday, November 24, 2024 8:26AM - 8:39AM |
A06.00003: Encoding spatiotemporally asymmetric motions in bioinspired magnetoactive propulsors enhances fluid pumping performance David J Peterman, Margaret L Byron Many organisms use the sequential beating of multiple propulsors to swim or pump fluids (i.e., metachronal coordination). Often, these propulsors have temporally and spatially asymmetric beating patterns. Increasing the relative duration of the power stroke vs. recovery stroke increases temporal asymmetry. Extending the propulsor during the power stroke (enhancing thrust), and collapsing it during the recovery stroke (reducing drag) increases spatial asymmetry. The parameter space of propulsor shape and kinematics is vast, yet we know little about how key changes in these properties can alter the flows produced. |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A06.00004: Numerical exploration of the role of appendage flexibility in drag-based rowing at intermediate Reynolds numbers Mohammadreza Zharfa, Margaret L Byron Ctenophores, a phylum of gelatinous marine zooplankton, employ millimeter-scale flexible appendages (ctenes) composed of bundled cilia (hair-like oscillating structures) to generate flow by beating sequentially in rows (i.e., metachronal coordination, a strategy used by many aquatic invertebrates). They are the largest animals that employ cilia for locomotion, making them an ideal subject for studying the hydrodynamic scaling of ciliary flows from low to intermediate Reynolds numbers. Here, we focus on investigating the fluid-structure interaction (FSI) of these flexible appendages by implementing a freely available two-dimensional solver (IB2D) that uses the immersed boundary method (IBM). We simulate a single appendage and compare different cases of varying rigidity by hybridizing prescribed kinematics (as measured in freely swimming ctenophores) with two-way coupling (in which the appendage interacts freely with the surrounding fluid). We prescribe the kinematics from the root of the appendage to a fixed point, leaving the remainder of the appendage free. We then explore the effects of changing the flexibility-rigidness ratio (from fully prescribed to fully flexible) on the generated drag and thrust forces during the power and recovery strokes. Our results provide insight into both fundamental biology via key functional behaviors such as swimming as well as the potential role of flexibility in future bioinspired technology development. |
Sunday, November 24, 2024 8:52AM - 9:05AM |
A06.00005: Impact of swimming frequency on robotically-controlled jellyfish swimming dynamics Noa Yoder, John O. Dabiri The fluid dynamics of jellyfish motion are of particular interest for engineers looking to address the energy demands of underwater propulsion due to their extremely low cost of transport compared to other swimming organisms. Previous work developed a method of externally stimulating Aurelia aurita jellyfish with a microcontroller that sends electrical impulses through electrodes embedded in the bell muscle. Our study explores the impact of the frequency of the bell muscle contractions on jellyfish propulsion by recording downward swimming in a 2.1m vertical tank. The jellyfish were equipped with positively-buoyant microcontrollers that varied stimulation frequency, and quantitative flow visualization was used to measure the wake dynamics. Models of jellyfish swimming in existing literature suggest that swimmers could be capable of varying their swimming speed by varying contraction frequency. Here, our results found that at low frequencies the contractions did not generate enough thrust for the jellyfish to act against the buoyancy of the controller, while at high frequencies the jellyfish muscles were not capable of contracting quickly enough to keep up with every impulse. However, for an intermediate range of frequencies jellyfish swimming speeds were found to be insensitive to the frequency of bell contraction. These results were compared with newly-developed models incorporating co-flow effect on vortex rings to seek an explanation for the observed insensitivity |
Sunday, November 24, 2024 9:05AM - 9:18AM |
A06.00006: A vibration driven slender elastic swimmer Prashanth Chivkula, Phanindra Tallapragada In recent times, there has been a surge of interest in bio-inspired approaches to underwater locomotion. Birds and fish are known to flap their wings or tails in patterns to move the fluid around their bodies to generate motion. To replicate such a fluid-structure coupling researchers have considered using heaving flexible panels to determine specific traits for optimal performance. As a result, some favorable conditions such as fluid-structure resonance, modulus of elasticity, flexibility, etc. have been identified to improve efficiency of underwater locomotion. This has led to the design of aquatic robots with appendages that are passively actuated with an internal rotor. |
Sunday, November 24, 2024 9:18AM - 9:31AM |
A06.00007: Tunable fin stiffness patterns for improved performance in fish-inspired unmanned underwater vehicles Cecilia Huertas-Cerdeira, Shirah Abrishamian, John Gallo, Lena Johnson Nature’s swimmers show unparalleled efficiency and agility, and the ability to replicate their mechanics will result in significant improvements to the performance of unmanned underwater vehicles. The propulsive appendages of biological swimmers possess complex mechanical properties. Here, the stiffness patterns of fish caudal (rear) fins and their effect on propulsive performance are of interest. Fish are capable of actively changing the stiffness of their fins via antagonistic muscle actuation. This allows them to adapt the overall fin stiffness to swimming speed but also to tune the stiffness pattern of the fin to manipulate its flow-induced deformation and resulting flow mechanics. |
Sunday, November 24, 2024 9:31AM - 9:44AM |
A06.00008: Shape matters in near-ground oscillatory and undulatory swimming Leo Liu, Yuanhang Zhu, Zihao Huang, Haibo Dong, Daniel B Quinn Previously we presented a robotic platform for studying the thrust and efficiency of a flexible fin while varying ground distance, frequency, and fin wavenumber (oscillatory vs. undulatory). We found that the fin experiences a lateral suction force that increases with Strouhal number, but decreases with wavenumber and ground proximity. Thrust generation and power consumption follow the same trend and are not susceptible to ground effects. In this study, we test how different fin shape contributes to performance, when coupled with ground distance, frequency, and fin wavenumber. We measure the force response and power consumption on a rectangular (control), triangular (manta ray), and elliptical (bluespotted ribbontail ray) fin. Consistent with previous studies, we observe that ground effect has strong influence on the lateral suction force; it is most prominent when operating with the rectangular fin at low wavenumber, low ground distance, and high Strouhal number. Thrust generation and power consumption are not as heavily influenced by the ground than lift. Finally, we measure the three-dimensional wake structures using multi-layer stereo PIV to explain the observed performance differences and simulate 3D undulatory fins to better understand the lateral suction force. This study advances our understanding of fin shapes in oscillatory and undulatory swimming, offering valuable insights into stingray locomotion and the design of bio-inspired robotic systems. |
Sunday, November 24, 2024 9:44AM - 9:57AM |
A06.00009: Effect of Reynolds number on hydrodynamics of undulating elastic propulsors with tapered thickness Andrew C Lenart, Christopher Jawetz, Alexander Alexeev Thickness tapering leads to enhanced hydrodynamic performance of oscillating elastic propulsors by drastically increasing the hydrodynamic thrust and efficiency compared to elastic propulsors with uniform thickness. Thickness tapering leads to the acoustic black hole effect at the propulsor trailing edge that minimizes the wave reflection and promotes the development of the traveling waves propagating along the propulsor length. We use fluid-structure interaction computational modeling to explore the hydrodynamic mechanism leading to the enhanced hydrodynamics of tapered propulsors. In particular, we probe the effects Reynolds number and viscosity on the emerging flow patterns, hydrodynamic forces, and especially how the performance gains of propulsor thickness tapering can either be assisted or hindered. Our simulations provide useful guidelines for designing efficient bio-mimetic robotic swimmers. |
Sunday, November 24, 2024 9:57AM - 10:10AM |
A06.00010: Computational flow analysis towards understanding the hydrodynamics in a body flexible tuna-like swimming platform John Michael Kelly, Genevie Forrer, Joe Zhu, Hilary Bart-Smith, Haibo Dong The Tunabot Flex is a high-performance Tuna-like swimming robot. Numerical simulations are employed to understand the hydrodynamics in the platform, understand the impact of body flexibility, compare to real tuna swimming, and explore design improvements to mimic a real tuna and optimize performance more closely. In this research, high-speed videos of the Tunabot Flex swimming are taken during semi-tethered experiments during forward swimming at varying speeds/frequencies. The motion is then reconstructed digitally by matching frame-by-frame the position of the real platform in the videos with a 3D model. The modeled swimmer is then simulated using an immersed boundary method based direct numerical flow solver. The simulations are used to uncover hydrodynamics and performance in the platform. Comparisons are made with similar simulations of biological tuna swimming and rigid-body versions of the platform. Modeling changes to kinematics, morphology, and frequency of the swimmer are made virtually, enhancing the understanding of the physics and limitations of the platform, as well as inform future design changes in the robot. |
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