Transient Dynamics Of Repeated Impact Of Flexible-bar Structures

Flexible bar-like structure is a kind of common applied structure in engineering. The theoretical and numerical studies on the repeated impacts between flexible bars are much difficult due to the complicated transient structural responses and variable topological structures in impact and separation processes.The present dissertation uses the full-continous body model and applies the methods of the expansion of transient wave functions in a series of Eigenfunctions (wave modes) in elasticity to solve the repeated impact problems of the four flexible-bar structures. The main researches are shown as foliowings:(1) By the use of the expansion of transient wave modes, the transient responses during impact and separation processes are derived. The completely theoretical solutions are obtained to consider the travellings of impact-induced transient waves, so as to implement correct numerical simulations.(2) Based on the theoretical solutions, the impact force can be calculated by the transient interior force between the impact-contact surfaces of the temporary combined structure. An approach called "transient interior force method" is presented to calculate reasonably the repeated impact forces for flexible structures.(3) The numerical investigations for the four flexible-bar structures show the transient interior force method can be convergent for the time step length and the truncation of wave modes.(4) By the use of the expansion of transient wave modes and the ransient interior force method, the method to solve the repeated impact problems of flexible bar structures is built. The repeted impact problems of the four flexible bar structures are solved. They are a free fly bar impact against a fixed bar, a forced moving bar impact against a fixed bar, a forced moving bar impact against a fixed bar by considering dampings and a forced moving bar impact against a fixed bar with variable sections.(5) The propagations of the impact-induced transient waves and second impact zones are investigated by the present method and the characteristics method. (6) The repeated impact problem of a forced moving bar impact against a fixed bar is investigated by the present method. The numerical results show that the present method can capature the secondary impact processes with small impact impulses usually havimg a short time interval and a small impact force.(7) The repeated impact problem of a forced moving bar impact against a fixed bar by considering damping is investigated by the present method. The damping effects on short term and long term dynamical responses are studied numerically.(8) The repeated impact problem of a forced moving bar impact against a fixed bar with variable sections is investigated by the present method. The effects of the variation of the section area on short term and long term dynamical responses are studied numerically.