This paper presents the effect of axial extensibility on threedimensional behavior of the tensioned pipes/risers. The large strain model formulation is developed by variational approach based on the elastica theory and the work-energy principle. The finite element method is used to find the nonlinear static configuration and large static strain. The natural frequencies and mode shapes are calculated by using the assumed-modes finite element method. The pipes/risers perform tensioned beam behavior when the bending stiffness dominates, and the stability of the pipes/risers reduces as the axial extensibility increases. On the contrary, the pipes/risers perform the tensioned cable behavior when the axial stiffness dominates, and the stability of the pipes/risers increases as the axial extensibility increases.
The tensioned pipes/risers have been applied in various fields of engineering industry. From the literature, several research works such as Skop and Clark (1972), Fang and Lyon (1996), Lee and Mote (1997), Öz and Boyaci (2000), Öz (2001), and Öz and Evrensel (2002) have employed the small displacement theory to study the tensioned pipes behaviors. The previous investigations could predict precisely the linear behavior of the tensioned pipes, which are encountered in applications of the pipelines for conveying gas, oil, water, dangerous liquids in chemical plant, and cooling water in nuclear power plant. In offshore applications, the tensioned pipes/risers are used as a linkage between the well bore and the floating vessel. Because of extreme ocean environments, the tensioned pipes/risers applied in deep water are usually experiencing the large displacement and large deformation. Consequently, the linear behavior with small deformation which was reported in previous works may be no longer valid. This paper is motivated to investigate the behavior of three-dimensional tensioned pipes/risers with large displacement and large deformation.