Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J07: Biofluids: High Re Locomotion II |
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Chair: Pankaj Rohilla, Georgia Institute of Technology Room: 103A |
Sunday, November 19, 2023 4:35PM - 4:48PM |
J07.00001: Group cohesion in the presence of three-dimensional hydrodynamic interactions Mohamed Niged Mabrouk, Daniel Floryan Swimming in groups can confer several benefits, including defence against predators, enhanced foraging success, and increased hydrodynamic efficiency. Our understanding of collective animal motion has traditionally been driven by models based on phenomenological behavioural rules, but more recent work has highlighted the critical importance of hydrodynamic interactions among a group of swimmers. To study how hydrodynamic interactions affect group cohesion, we develop a three-dimensional, inviscid, far-field model of a swimmer, a superposition of which forms a group of swimmers. In a group of two model swimmers, we observe several dynamical phases, including following, divergence, collision, and oscillation. In larger groups, more complex dynamics arise. Our results illustrate when groups can passively and stably form through hydrodynamic interactions alone, and when other action is needed to maintain cohesion. |
Sunday, November 19, 2023 4:48PM - 5:01PM |
J07.00002: Stability and energetics of schooling fish: insights from direct numerical simulations Athanasios Giannenas, Jung-Hee Seo, Rajat Mittal Since the early 1970's it has been hypothesized that fish gain considerable hydrodynamic benefits by swimming in schools. Studies have shown that schooling fish can, in certain formations, obtain higher swimming efficiencies compared to their isolated counterparts. However, many of the beneficial formations predicted by studies may be unstable and fish may have to expend additional energy in order to maintain their position within the group. Thus, schooling formations may arise from a compromise between energy savings and stability. In the current study, we employ 3D direct numerical simulations (DNS) coupled with body-dynamics to explore the stability and energetics of freely-swimming fish in various schooling formations. The model allows for multiple degrees-of-freedom in the motion of the fish and the simulations provide insights into the stability of various schooling formations. |
Sunday, November 19, 2023 5:01PM - 5:14PM |
J07.00003: Three-dimensional hydrodynamic interactions inside a robotic fish school Subhra Shankha Koley, Edwin Rajeev, James C Liao Inspired by experiments with schooling shiners (Notemigonus crysoleucas), we fabricated a robotic, 4-fish school consisting of a flexible polymer having a refractive index similar to water, enabling unobstructed optical access and facilitating flow visualization inside a fish school. Each robotic fish has been actuated independently at a tailbeat frequency of 4-7 Hz to mimic live fish, over a range of Re (O[10^5]). We altered the tailbeat phase differences between neighboring fish and characterized the hydrodynamic interactions by measuring the flow field using time-resolved stereo Particle Image Velocimetry (PIV). Two different two-dimensional schooling configurations have been tested to assess the influence of different flow phenomena resulting from 1) a diamond arrangement, where inline swimming is aided by a strong channeling effect, and 2) a formation with two in-line fish rows placed side-by-side, which accentuates the inline swimming effect. Preliminary results suggest that out-of-plane flow generated from our two-dimensional schooling arrangement can be substantial, up to 25% of the freestream velocity. Our novel experimental approach allows, for the first time, the characterization of the hydrodynamics inside a school using actual fish-like 3D models at environmentally relevant high Re, which might be challenging to simulate using Computational Fluid Dynamics (CFD). Our work is poised to contribute valuable insights and inspire innovative arrangements for underwater vehicles. |
Sunday, November 19, 2023 5:14PM - 5:27PM |
J07.00004: Performance Benefits for Frequency and Amplitude Control of Inline Swimmers Benjamin Kramer, Amin Mivehchi, Keith W Moored Numerous studies of fish schooling have observed thrust and efficiency benefits for a leader-follower in-line formation when a fixed relative spacing is maintained and an optimal phase synchronization is chosen. Here, we present new simulations considering the hydrodynamic effects of two different approaches of controlling the thrust and, therefore, relative spacing between leader-follower pitching foils: frequency and amplitude control. Although both approaches can control the thrust by varying the frequency/amplitude of the follower, the performance benefits received by the follower foil can differ due to alterations in vortex-body interactions. Frequency control leads to mismatched frequencies resulting in a constantly changing phasing between an impinging vortex and the follower’s motion leading to low performance benefits. Amplitude control preserves frequency matching between the leader and follower and the ability to tune the phase difference between the swimmers. It will be shown that since amplitude control is able to maintain a constant, favorable phase angle the follower can take advantage of the leader’s wake and experience greater performance benefits compared to frequency control. These findings aid in the design of formation control schemes of schooling bio-robots that derive hydrodynamic benefits from schooling interactions. |
Sunday, November 19, 2023 5:27PM - 5:40PM |
J07.00005: Self-Organization pattern of multi-swimmers in a side-by-side configuration Amin Mivehchi, Keith W Moored
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Sunday, November 19, 2023 5:40PM - 5:53PM |
J07.00006: Performance of schooling tuna-like robotic swimmers Pedro C Ormonde, Matthew Stasolla, Joe Zhu, Hilary Bart-Smith, Keith W Moored A robotic platform is developed to study the performance of schooling fish. A tuna-like robot with sinusoidal pitching motion of its tail is connected to a dual air-bearing platform. The hydrodynamic performance of the robotic fish is measured in water channel experiments using a six-axis torque and force sensor. Two fish-like robots are positioned at different canonical schooling arrangements: In-line and side-to-side. One swimmer is constrained while the second is freely swimming, being supported by air bearings. The effects of swimming close to a neighbor (schooling) are compared to swimming in isolation as well as to literature results for schooling self-propelled hydrofoils. The performance and stability of the minimal school is investigated. |
Sunday, November 19, 2023 5:53PM - 6:06PM |
J07.00007: Enhancing Collective Efficiency of a Pair In-line Pitching Hydrofoils in a Stable Formation Seyedali Seyedmirzaei Sarraf, Benjamin Kramer, Amin Mivehchi, Keith W Moored Schooling fish exhibit remarkable efficiency as they swim together, dynamically adjusting their movements relative to one another. Recent research has demonstrated that passive hydrodynamic forces can create 1D and 2D stable arrangements for a pair of swimmers, leading to speed and efficiency benefits regulated by hydrodynamic interactions. However, in an in-line configuration, the highest efficiency position is not necessarily at the 1D stable location for swimmers. We postulate that stable formations can be tailored to coincide with high efficiency zones by controlling the amplitude ratio of leader and follower. To investigate this further, our study focuses on purely pitching in-line hydrofoils with matched and mismatched amplitudes between the leader and the follower hydrofoil. We employ direct force measurements and particle image velocimetry to analyze the efficiency benefits and 1D stability criterion. Additionally, we extend our research to consider different upstream velocities and in-phase and out-of-phase pitching synchronizations at multiple spacings, providing a comprehensive understanding of the hydrodynamic interactions and efficiency enhancement potential. |
Sunday, November 19, 2023 6:06PM - 6:19PM |
J07.00008: Development of a platform of Tunabots to study hydrodynamics in fish schooling Joe Zhu, Yuanhang Zhu, John M Kelly, Daniel Quinn, Keith W Moored, Haibo Dong, Hilary Bart-Smith The study of coordinated fish swimming, specifically observed in fish schools, has captivated interest across multiple disciplines, from biology to robotics. Investigating the underlying mechanisms of this behavior holds great potential for advancing bio-inspired robotic systems and gaining deeper insights into animal behavior. In this research, we introduce a novel platform consisting of multiple traverses and Tunabots, designed to explore coordinated fish swimming. The Tunabots interact in real-time, enabling the examination of emergent behaviors arising from hydrodynamic interactions. The interactions and swimming behaviors were quantified, recorded, and later compared with a comprehensive numerical study. This platform serves as a valuable tool to delve into diverse aspects of fish schooling and related phenomena. |
Sunday, November 19, 2023 6:19PM - 6:32PM |
J07.00009: Hydrodynamic interactions between high-frequency pitching propulsors Yuanhang Zhu, Daniel Quinn High-performance swimmers such as tuna often operate at high frequencies, yet experimental studies of pitching hydrofoils are often conducted at low frequencies. What results is a gap between the complex biological system and its low-order representation. In this experimental study, we use high-frequency pitching hydrofoils to achieve high Reynolds numbers while maintaining biologically relevant Strouhal numbers. We investigate the hydrodynamic interactions between high-frequency pitching propulsors and show that these interactions are dictated by the kinematics and spacing of neighboring swimmers. We find that equilibrium constellations of the schooling swimmers can be manipulated by changing the pitching frequency. We use multi-layer stereo PIV to capture three-dimensional flow structures within these constellations to further understand their formation mechanism. Understanding the schooling mechanism at high frequencies can provide insights into the design and control of future high-speed multi-agent bio-inspired robotic platforms. |
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