The influence of fluid transported inside a riser/pipe on the riser/pipe behavior is investigated. The riser/pipe considered is extensible, flexible and experiencing large displacements. The present work is an extension of the previous study by the authors of the effect of axial deformation on natural frequencies of marine cables (paper presented at ISOPE-97). The two-dimensional model used in that study is modified by adding the virtual work done by the inertia force of transported fluid mass. Equations of motion of the system are obtained and numerical examples are given to demonstrate this influence for the case of steady transporting state.
The influence of internal flow on the dynamic behavior and stability of pipes has been studied extensively for more than three decades. The research work related to vibration of straight and curved pipes can be found, for example, in Housner (1952), Paidoussis (1970), Doll and Mote (1976), and Escobar and Ting (1986). Literature review on this subject can be found in the book by Blevins (1990). The influence of the same aspects on the marine risers has been studied by many researchers in recent years, however the investigation is limited to the simple cases. Reviews of these studies are briefly mentioned herein. Irani et al (1987) presented the dynamic analysis of risers with internal steady flow and nutation dampers in three dimensions using finite element method. The results indicated that the internal flow reduced the stiffness of marine risers, and provided a negative damping mechanism. Patel and Seyed (1989) studied the internal slug flow induced vibration of flexible risers. They concluded that the effect of slug flow was significant for moderate to large water depths or in the large pressure area, and the slug flow caused additional source of cyclic fatigue loading.
