In this paper we study the two dimensional motion of three linked rigid bodies moving through a fluid. The bodies change their orientation relative to each other in a way which mimics the swimming of fish. In contrast to previous simulations the bodies are connected by an elastic skin. The skin responds to the movement of the bodies and the pressure of the fluid and alters the flow around the bodies. In particular it prevents fluid moving between them. The system of bodies and skin is similar in appearance to a swimming leech or tadpole depending on the relative size of the bodies. We simulate the system using SPH, with three types of particles: liquid particles, boundary force particles determining the surface of the rigid bodies, and skin particles defining the elastic skin. The latter interact with each other, and with the boundary force particles to which they are anchored, by linear spring forces. The boundary force particles and the skin particles interact with the fluid particles by pair forces which are similar to the forces used in the Immersed Boundary method. The algorithm is based on a Lagrangian, and the equations of motion conserve linear momentum exactly and angular momentum very accurately. We compare the motion of rigid bodies with and without skin keeping the total mass of the bodies plus skin fixed. When the ellipses are identical, and the forward gait is used, the bodies swim ~13% faster when they are connected by skin, and they require less energy. When the ellipses have different sizes, with the front ellipse largest, they travel ~39% faster and use less energy. The algorithm is simple and robust and can be applied to bodies of arbitrary shape and in domains which include free surfaces and stratified fluids.
A numerical simulation method of fish adaption behavior based on deep reinforcement learning and fluid-structure coupling-realization of some lateral line functions
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）
How do trout regulate patterns of muscle contraction to optimize propulsive efficiency during steady swimming
The College of River and Ocean Engineering, Chongqing Jiaotong University,Chongqing, 400016, China（重庆交通大学河流海洋工程学院）；State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, 610065, China（四川大学水利与山区河流工程重点实验室）；Chongqing Deepflow Intelligent Computing Technology Co., Ltd, Chongqing, 401122, China（重庆深流智能计算技术有限公司）
