The thrust benefits of lateral configurations of two-dimensional undulating fish-like bodies are investigated using high-fidelity numerical simulation. The solution of the Navier--Stokes equations is carried out with a viscous vortex particle method. Configurations of tethered pairs of fish arranged side by side are studied by varying the lateral separation distance and relative phase difference. It is shown that, in mirroring symmetry, the fish in the pair augment each other's thrust even at relatively large separations (up to ten body lengths). At small distances, this augmentation is primarily brought about by a peristaltic pumping in the gap between the fish, whereas at larger distances, the thrust is affected by subtle changes in the vortex shedding at the tail due to interactions with the other fish. In cases without symmetric undulation, one fish always draws more benefit from the interaction than the other. Finally, lateral configurations with three fish are studied with mirroring symmetry between neighboring fish. Whereas the center fish draws a net thrust benefit, this comes at the expense of a net drag on the outer two fish. Each adjacent pair in this arrangement is slightly affected by the presence of the third fish.
Fish swimming style and schooling behaviour are two important aspects of underwater locomotion. How swimming style affects fish schooling is investigated by a representative problem setup consisting of two tethered NACA0012 hydrofoils undulating in a free stream flow at various wavelengths $ λ^* = 0.8 - 8 $, front-back distance $ D = 0,\ 0.25,\ 0.5,\ 0.75 $, phase difference $ ϕ/π= 0,\ 0.5,\ 1,\ 1.5 $, and lateral gap distance $ G = 0.25,\ 0.3,\ 0.35 $ with fixed Reynolds number $ Re = 5000 $, Strouhal number $ St = 0.4 $, and maximum amplitude $ A_{max} = 0.1 $. In total, 336 cases were simul…
One of the most highly debated questions in the field of animal swarming and social behaviour, is the collective random patterns and chaotic behaviour formed by some animal species, in particular if there is a danger. Is such a behaviour beneficial or unfavourable for survival? Here we report on one of the most remarkable forms of animal swarming and social behaviour - fish schooling - from a hydrodynamic point of view. We found that some fish species do not have preferred orientation and they swarm in a random pattern mode, despite the excess of energy consumed. Our analyses, which includes c…
Traveling waves in a continuum model of schooling swimmers
New Jersey Institute of Technology（新泽理工学院）；University of Southern California（南加州大学）；Courant Institute of Mathematical Sciences（库朗数学科学研究所）；Flatiron Institute（平顿研究所）
Optimum control strategies for maximum thrust production in underwater undulatory swimming
Laboratoire de Tribologie et Dynamique des Systemes, École Centrale de Lyon（里昂中央理工学院）；Université Côte d’Azur, CNRS, INPHYNI（蔚蓝海岸大学）；Departamento de Física Fundamental, Universidad Nacional de Educación a Distancia（西班牙国立远程教育大学）；Université Côte d’Azur, CNRS, I3S（蔚蓝海岸大学）；IUF, Paris（法国高等研究学院）
We establish through numerical simulation conditions for optimal undulatory propulsion for a single fish, and for a pair of hydrodynamically interacting fish, accounting for linear and angular recoil. We first employ systematic 2D simulations to identify conditions for minimal propulsive power of a self-propelled fish, and continue with targeted 3D simulations for a danio-like fish. We find that the Strouhal number, phase angle between heave and pitch at the trailing edge, and angle of attack are principal parameters. Angular recoil has significant impact on efficiency, while optimized body be…
The wavelength of undulatory kinematics of fish is an important parameter to determine their hydrodynamic performance. This study focuses on numerical examination of this feature by reconstructing the real physiological model and kinematics of steadily swimmning Jack Fish. We perform three-dimensional numerical simulations for flows over these models composed of the trunk, and dorsal, anal, and caudal fins. Moreover, we prescribe the carangiform-like motion for its undulation for a range of wavelengths. Undulation with larger wavelengths improves the hydrodynamic performance of the carangiform…
Department of Mechanical Engineering, Penn State University（宾夕法尼亚州立大学机械工程系）
In this work we developed a mathematical model and a simulation platform for a fish-inspired robotic template, namely Magnetic, Modular, Undulatory Robotics ($μ$Bots). Through this platform, we systematically explored the effects of design and fluid parameters on the swimming performance via reinforcement learning. The mathematical model was composed of two interacting subsystems, the robot dynamics and the hydrodynamics, and the hydrodynamic model consisted of reactive components (added-mass and pressure forces) and resistive components (drag and friction forces), which were then nondimension…
