Dynamics of a fluid-conveying pipe composed of two different materials

Abstract

The dynamics of fluid-conveying cantilevered pipe consisting of two segments made of different materials is studied, focusing on the effects induced by different length ratios between the two segments. Two kinds of hybrid pipes are considered: one is made of steel and aluminum and the other is made of aluminum and epoxy. The complex frequency of the four lowest modes of the hybrid system is calculated in two representative cases for successively increasing values of the flow velocity to demonstrate how transition from stability to instability takes place. Compared with a uniform pipe conveying fluid, it is found that the hybrid pipe is capable of displaying more complex and sometimes unexpected dynamical behaviors. The numerical results show that in such a hybrid pipe system, an instability–restabilization–instability sequence would occur as the flow velocity is successively increasing. When the length ratio between the two segments is successively increased, the lowest order of unstable modes may frequently shift from one to another. It is also demonstrated that with increasing flow velocity, the flutter instability first occurring in the fourth mode is possible and a certain unstable mode may suddenly regain stability, which has not been reported before. Furthermore, when the segment made of softer material is placed at the clamped end, the system is much easier to lose stability. Some of these new results observed in the hybrid pipe system are also expected to be helpful in controlling the dynamical behaviors of fluid-conveying pipes.