The mathematical model for stability analysis of flexible marine pipes conveying fluid is developed via vectorial formulation in the natural coordinate. The remarkable features in the present model involve high extensibility due to large axial strain, cross-sectional change due to Poisson effect, and fluid-pipe interactions due to internal flow. The parameters dominating stability of the pipe are found to be density of pipe material, external and internal variable fluid static pressures, top tension, Poisson's ratio, slenderness ratio, structural inclination, drag coefficients, current velocity, and internal flow velocity. Due to the space limitation, only a discussion concerning the top tension, the pipe's weight, and the internal flow velocity is presented.
The marine pipe stated herein is considered as the pipe experiencing large displacements under offshore environment, where its exact configurations and nonlinear behavior are determined and studied based on the elastica theory. Application of the marine pipe can be found extensively in deep-ocean mining industry such as deployment of marine risers, flexible pipes, and hoses. Even though those structures are absolutely pertinent to the marine pipes, so far most buckling analyses of them have not been treated based on the elastica theory. Examples of the related research work are found in Huang and Dareing (1967, 1968), Bemitsas (1980), Bernitsas and Kokkinis (1983a, 1983b, 1984), Vaz and Patel (1995). They studied buckling of drilled string, marine risers, and submerged slender tubular columns based on the linear small displacement theory. Although the linear theory can yield the bifurcation criteria, but it gives no information about post-buckling behavior and post-buckling stability of the structures, which are indispensable for nonlinear system operation control. Furthermore, the linear theory cannot govern the effect of large deflection imperfection of the marine pipes induced by lateral action of static current.
