Numerical Simulation Of Self-propelled Of "C"Type Swimming Fish Using The Immersed Boundary Method

Study on the mechanical mechanism of fish swimming has important significance for increasing needs of bionic technology. Therefore, the "C" type swimming fish (The fish bend its body into a "C" shape when swimming) as the research object, using immersed boundary method, a flexible model of freely self-propelled swimming fish that interact between internal forces, fish body movment, and fluid is established. The coupling relationship between the body movement produced by internal forces, the deformation movement caused by the fluid and the external fluid flow is numerical calculated. The mechanism of the self-propelled swimming is revealed by analysis of the hydrodynamic performance. The mainly result of this thesis is as follows:(1) Hybrid finite difference/finite element immersed boundary method (IBM) combined with traditional feedback force method is solved numerically with time and space discretization of computational fluid dynamics. When the continuous equations are discretized, hyper-elastic constitutive laws with finite element discretization of the flexible fish and an adaptive refined Cartesian grid with finite difference discretization of the fluid are used. Lagrangian and Eulerian variables are coupled by integral transforms with delta function kernels. Example of stationary cylinders in flow and fluid-induced vibration of a cantilever beam attached to a cylinder in flow is used to verify the feasibility of the feedback-forcing IBM and hybrid finite difference/finite element IBM.(2) The internal forces produced by the muscles and movement form are analysised theoretically. Based on the theoretical analysis, a flexible model of freely self-propelled swimming fish is established, and the fish is divided into three sections, namely, head, tail and tail fin.(3) The hydrodynamic performance of a single swimming fish is numerical simulated. The flow field characteristics and fish body movement characteristics of start, cruise and glide state of a swimming fish is analysised. The simulation results reveal the fluid dynamics mechanism of the conversion of "C" type and "S" type of fish body when self-propelled swimming.(4) The swimming fish models with different length of caudal fin, and with different elastic modulus of the tail and caudal fin, as well as with different energy produce by the muscles of fish are perspective simulated. The influence of key factors on swimming efficiency is shown by analysis of hydrodynamic performance.(5) Numerical investigation on swimming hydrodynamics of fish schooling is done. Usually, the fish will combine into a prismatic formation when swimming. Numerical results is shown that parallel formation of two swimming fishes can improve efficiency, also the the downstream fish of series formation of two swimming fishes affected by the anti-Karman vortex street will be passively swim to one side in order to obtain energy from the vortex field. It is concluded that the prismatic formation will increase the efficiency of fish schooling, which is the result of the fish themselves active control and the passive impact of external vortex field.