## Secrets of fish swimming

*Firstly, Vortex dynamics principles of direction control, speed control and energy saving of fish school are discussed in this lecture. A parallel Computational Fluid Dynamics(CFD) package for the two- and three-dimensional moving boundary problem is obtained, which combines the adaptive multi-grid finite volume method and the methods of immersed boundary and VOF (Volume of Fluid). With the CFD package, it is found that due to the interactions of vortices in the wakes, without proper control, a fish swims in a fish school with a given flapping rule can not keep the right position in the queue. In order to understand the secret of fish swimming, a new control strategy of fish motion is proposed for the first time, i.e., the locomotion speed is adjusted by the flapping frequency of the caudal, and the direction of swimming is controlled by the swinging of the head of a fish. The vortex dynamics principle of direction control is to generate vortices in favor of turning and preventing the harmful separation from the head. The vortex dynamics principle of speed control of fish school is that the merger of vortices with the same sign can speed up the fish. The vortex dynamics principle of energy saving of the swimming of a fish school is that when using the favorable vortical wake in front or by the side, the flapping frequency of the fish can be reduced up to 18.35%, therefore save energy. In addition, the new control strategy, which separates the speed control and direction control, is important in the construction of biomimetic robot fish, with which it will greatly simplify the control devices of biomimetic robot fish. Secondly, topology optimization method is applied to a caudal fin for the first time, which shows that with topology optimized caudal fin, a fish can swim easier, faster and more flexible. Key words: Self-propelled swimming;Control strategy of fish swimming; Direction control; Locomotion speed control; Topology optimization of a caudal fin.*

13/02/2019

Il seminario sarà tenuto dal Prof. Chui-Jie Wu della Dalian University of Technology.

Inizierà alle ore 12:00 e si terrà nella Sala Videoconferenze del DIMA

Professor Chuijie WU graduated at Jiangsu University on Jan. 1982, and as a senior visiting

scholar he worked at Department of Mechanical and Energy Engineering, University College, Cardiff, UK from 1996 to 1997; University of Tennessee Space Institute, USA from 1988 to 1989.; Department of Mechanical Engineering, Johns Hopkins University, USA in 2000; Department of Mathematics, Kennesaw State University, USA in 2012. He was directly promoted from Lecture to Professor in 1992. He was Professor of Department of Mechanics, Peking University from 1999 to 2003. He was the one of ten Chair professors at PLA University of Science and Technology from 2003 to 2008. As the Founding Dean, he found the School of Aeronautics and Astronautics, Dalian University of

Technology in 2008, and worked till now.

His research fields include Aerodynamics, vortex dynamics and flow control; Turbulence and nonlinear dynamics; Computational fluid dynamics; Environment fluid mechanics.