In this paper, a class of isolation systems with rigid limiters has been considered. For this class of systems, some general discrete-time models described by means of some impact Poincaré maps have been established. Two examples: a simple isolation system of one-stage and a real isolation system of two-stages have been investigated. The calculated results show that those models can reveal complex nonlinear behaviors. And even a small random perturbation may change the dynamical character of the system.
KeywordsIsolation systems with rigid limiters · Impact Poincaré map · Vibro-impact systems
IntroductionIsolation systems with stops, (Fig. 1) are usually used in real engineering in order to safeguard equipment and to restrict the vibrating amplitudes of systems. The limiters can be divided into rigid, elastic and plastic ones. When the isolation systems are constructed with rigid limiters, in mechanics, they belong to a class of non-smooth systems, i.e. the vibro-impact systems, which are driven in some way and which also undergo intermittent or a continuous sequence of contacts with motion limiting constraints [1,2]. There are many references on this topic [3][4][5][6][7][8][9][10][11][12][13][14][15] . However, it is very difficult to investigate those systems. The main difficulty is that the dynamics of such systems are not continuous, but rather of intermittent type. A general way to characterize the behavior of impacting systems is to study the discrete-time system associated to the overall dynamics.More precisely, if between the impacts the systems hold smoothness properties, by integrating the smooth vector field and incorporating the impact conditions, a so-called impact Poincaré map for this system may be theoretically derived [16]. If the system is subject to an in-finiteness of impacts and if the derived map is explicitly calculable, one can obtain a discrete-time system, which is easily simulated by iterations. Unfortunately, to obtain the closed solution of equation at free-flight phase is difficult, even for very simple systems, so it may be impossible to obtain the impact Poincaré map.In this paper, a class of vibro-impact systems, i.e. isolation systems with rigid limiters for marine engine, is considered. Due to small angular velocity, this class of systems can be restricted using the following assumptions: (1) during the free-flight time, the equation of motion for those systems is smooth, and there are only some small nonlinear terms in the equation. Because of the weak nonlinearity of the equation, one can use the perturbation method to obtain an approximated solution in closed form, so that some approximated impact Poincaré maps can be derived; (2) the motion of those systems can be divided into two periods: during shock and after shock. Due to large shock action, during shock the external excitations can be neglected. The external excitations after shock are here assumed as deterministic and random cases.