Research On Fast-start Mechanism Of The Bionic Robot-fish Aid GMM

The application and manufacture of robots are noticed specially in many fields with the development of science. The bionic robot-fish is an important one of the robots since it can swim in the small tube and is not affected by the circumstance, for example, toxic or polluted liquid. Therefore, it is important to research bionic robot-fishes.In this paper, the alloy sheet is simulated as the framework of the fishtail, the giant magnetostrictive material (GMM), which is stuck on the sheet, as the muscle of the fish and the external magnetic field as the nerve to control the swing of the fishtail. By analyzing fast-start of fishes bionically, a mechanics model and new analytical method are presented. By discussing and predigesting the model, dynamic equations, boundary conditions and initial conditions are obtained for swimming of robot-fish. Firstly, consider a simple model, or linear model. Using the method of separation of variables, the problem is divided into two sorts of equations, which are expressed by two functions of spatial coordinate and time respectively. One of them is transformed to the problem of eigenvalues and eigenvectors, and the other is reduced to the problem of the ordinary differential equation of the second order about time. By aiding the adjoint symplectic orthonormal relations between eigenvectors (or vibration modes) and the superposition principle, the expression of analytic solution is obtained. Secondly, the nonlinear model is discussed, in which the large deformation and nonlinear damp are considered. By adopting eigensolutions, nonlinear dynamic equations and the method of small parameter expansions, the recursive formulas are obtained, so that a numerical method for nonlinear problem is derived. By numerical computation and analysis, the fast-start mechanism of the bionic robot-fish is revealed. Besides, effects of material constants, geometrical parameters and circumstance factors for bionic fish starting are researched. The results show that the average propulsion of the robot-fish is not monotone increased with the frequency of the external magnetic fields. But there is an optimal frequency of the fields, in other words, the average propulsion is the strongest at the frequency of system. Thus, the mode of the optimal starting is devised. In numerical results, it is discovered that the optimal mode for the starting is the fast-transition which is from the lower order mode to the higher order mode so that the robot-fish can swim quick from the static state. The results show still that the start velocity of the bionic fish can be controlled by adjusting the frequency and intensity of the external magnetic fields. It should be point that the contrail of the fish is not a beeline and there is an angle between the initial state and the transient state of fish body. The angle depends on the intensity of the external magnetic fields. Numerical results agree with start-modes of fishes. The method and results provide theoretical foundation and applied basis for designing bionic robot-fish.