Many animals in nature travel in groups either for protection, survival, or endurance. Among these, certain species do so under the burden of aero/hydrodynamic loads, which incites questions as to the significance of the multibody fluid-mediated interactions that are inherent to collective flying/swimming. Prime examples of such creatures are fish, which are commonly seen traveling in highly organized groups of large numbers. Indeed, over the years, there have been numerous attempts to examine hydrodynamic interactions among self-propelled fish-like swimmers. Though many have studied this phenomenon, their motivations have varied from understanding animal behavior to extracting universal fluid dynamical principles and transplanting them into engineering applications. The approaches utilized to carry out these investigations include theoretical and computational analyses, field observations, and experiments using various abstractions of biological fish. Here, we compile representative investigations focused on the collective hydrodynamics of fish-like swimmers. The selected body of works are reviewed in the context of their methodologies and findings, so as to draw parallels, contrast differences, and highlight open questions. Overall, the results of the surveyed studies provide foundational insights into the conditions (such as the relative positioning and synchronization between the members, as well as their swimming kinematics and speed) under which hydrodynamic interactions can lead to efficiency gains and/or group cohesion in two- and three-dimensional scenarios. They also shed some light on the mechanisms responsible for such energetic and stability enhancements in the context of wake-body, wake-wake, and body-body interactions.
Optimal fish array hydrodynamics in accelerating phalanx schools are investigated through a computational framework which combines high fidelity Computational Fluid Dynamics (CFD) simulations with a gradient free surrogate-based optimization algorithm. Critical parameters relevant to a phalanx fish school, such as midline kinematics, separation distance and phase synchronization, are investigated in light of efficient propulsion during an accelerating fish motion. Results show that the optimal midline kinematics in accelerating phalanx schools resemble those of accelerating solitary swimmers. The optimal separation distance in a phalanx school for thunniform biologically-inspired swimmers is shown to be around 2
- NSF-PAR ID:
- 10483335
- Publisher / Repository:
- IOP Science
- Date Published:
- Journal Name:
- Physica Scripta
- Volume:
- 98
- Issue:
- 3
- ISSN:
- 0031-8949
- Page Range / eLocation ID:
- 035010
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
null (Ed.)Abstract Swimming in schools has long been hypothesized to allow fish to save energy. Fish must exploit the energy from the wakes of their neighbors for maximum energy savings, a feat that requires them to both synchronize their tail movements and stay in certain positions relative to their neighbors. To maintain position in a school, we know that fish use multiple sensory systems, mainly their visual and flow sensing lateral line system. However, how fish synchronize their swimming movements in a school is still not well understood. Here we test the hypothesis that this synchronization may depend on functional differences in the two branches of the lateral line sensory system that detects water movements close to the fish’s body. The anterior branch, located on the head, encounters largely undisturbed free-stream flow, while the posterior branch, located on the trunk and tail, encounters flow that has been affected strongly by the tail movement. Thus, we hypothesize that the anterior branch may be more important for regulating position within the school, while the posterior branch may be more important for synchronizing tail movements. Our study examines functional differences in the anterior and posterior lateral line in the structure and tail synchronization of fish schools. We used a widely available aquarium fish that schools, the giant danio, Devario equipinnatus. Fish swam in a large circular tank where stereoscopic videos recordings were used to reconstruct the 3 D position of each individual within the school and to track tail kinematics to quantify synchronization. For one fish in each school, we ablated using cobalt chloride either the anterior region only, the posterior region only, or the entire lateral line system. We observed that ablating any region of the lateral line system causes fish to swim in a “box” or parallel swimming formation, which was different from the diamond formation observed in normal fish. Ablating only the anterior region did not substantially reduce tail beat synchronization but ablating only the posterior region caused fish to stop synchronizing their tail beats, largely because the tail beat frequency increased dramatically. Thus, the anterior and posterior lateral line system appear to have different behavioral functions in fish. Most importantly, we showed that the posterior lateral line system played a major role in determining tail beat synchrony in schooling fish. Without synchronization, swimming efficiency decreases, which can have an impact on the fitness of the individual fish and group.more » « less
-
more » « less
Abstract We report the effects of polymer size, concentration, and polymer fluid viscoelasticity on the propulsion kinematics of achiral microswimmers. Magnetically driven swimmer's step‐out frequency, orientation angle, and propulsion efficiency are shown to be dependent on fluid microstructure, viscosity, and viscoelasticity. Additionally, by exploring the swimming dynamics of two geometrically distinct achiral structures, we observe differences in propulsion efficiencies of swimmers. Results indicate that larger four‐bead swimmers are more efficiently propelled in fluids with significant elasticity in contrast to smaller 3‐bead swimmers, which are able to use shear thinning behavior for efficient propulsion. Insights gained from these investigations will assist the development of future microswimmer designs and control strategies targeting applications in complex fluids.
-
Some anguilliform swimmers such as eels and lampreys swim near the ground, which has been hypothesized to have hydrodynamic benefits. To investigate whether swimming near ground has hydrodynamics benefits, two large-eddy simulations of a self-propelled anguilliform swimmer are carried out—one swimming far away from the ground (free swimming) and the other near the ground, that is, midline at 0.07 of fish length (L) from the ground creating a gap of 0.04 L . Simulations are carried out under similar conditions with both fish starting from rest in a quiescent flow and reaching steady swimming (constant average speed). The numerical results show that both swimmers have similar speed, power consumption, efficiency, and wake structure during steady swimming. This indicates that swimming near the ground with a gap larger than 0.04 L does not improve the swimming performance of anguilliform swimmers when there is no incoming flow, that is, the interaction of the wake with the ground does not improve swimming performance. When there is incoming flow, however, swimming near the ground may help because the flow has lower velocities near the ground.more » « less
-
more » « less
The anterior body of many fishes is shaped like an airfoil turned on its side. With an oscillating angle to the swimming direction, such an airfoil experiences negative pressure due to both its shape and pitching movements. This negative pressure acts as thrust forces on the anterior body. Here, we apply a high-resolution, pressure-based approach to describe how two fishes, bluegill sunfish (
Lepomis macrochirus Rafinesque) and brook trout (Salvelinus fontinalis Mitchill), swimming in the carangiform mode, the most common fish swimming mode, generate thrust on their anterior bodies using leading-edge suction mechanics, much like an airfoil. These mechanics contrast with those previously reported in lampreys—anguilliform swimmers—which produce thrust with negative pressure but do so through undulatory mechanics. The thrust produced on the anterior bodies of these carangiform swimmers through negative pressure comprises 28% of the total thrust produced over the body and caudal fin, substantially decreasing the net drag on the anterior body. On the posterior region, subtle differences in body shape and kinematics allow trout to produce more thrust than bluegill, suggesting that they may swim more effectively. Despite the large phylogenetic distance between these species, and differences near the tail, the pressure profiles around the anterior body are similar. We suggest that such airfoil-like mechanics are highly efficient, because they require very little movement and therefore relatively little active muscular energy, and may be used by a wide range of fishes since many species have appropriately shaped bodies.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1402-4896/acb859
