Optimization of catenary risers

This paper describes how the design of a catenary riser can be formulated a s an optimization problem by ruing riser costs as the criteria function, de sign requirements in terms of maximum allowable stress and buckling capacit y as constraints, and riser dimensions as free variables. The theory has be en implemented in a computer program that can generate an optimized riser d esign for given design parameters such as water depth, diameter, pressure, and platform excursions. The developed software consists of a conventional program for two-dimensional riser analysis and a set of standard routines t o minimize a nonlinear function subjected to general constraints. A case st udy where design parameters and requirements have been varied is also prese nted The importance of buckling versus allowable equivalent stress as the m ost critical constraint has been investigated for varying water depth. The conclusion of this work is that optimization is a useful tool for riser des ign, and that the proposed strategy for selection of design variables and c onstraints will enable an engineer to identify designs with minimum costs i n art efficient way.