ON THE MECHANICS OF SUBMERGED VERTICAL SLENDER STRUCTURES SUBJECTED TO VARYING AXIAL TENSION

This paper presents a mathematical basis for determining the structura l and hydroelastic behaviour of submerged vertical slender steel struc tures operating at low tension. These structures have significant bend ing stiffness combined with significant self-weight so that the axial force varies greatly from one end to the other and may even change sig n. Such structures form key components of drilling and production plat forms used for exploitation of hydrocarbons under the world's oceans. An understanding of their structural behaviour under reduced tension o ffers opportunities for cost reduction and further optimization, The b uckling behaviour at low tension is evaluated by retaining nonlinear c urvature terms and using an expansion in series to reduce the governin g equation to a set of linear ordinary differential equations, which a re then solved sequentially by employing Galerkin's technique. This ap proach is also extended to lateral oscillation of the structure when e xcited by forced horizontal oscillatory motions at the top end. The pa per uses these solution techniques to explore the behaviour at low ten sion of typical slender structures used in offshore developments.