This paper describes how the design of a catenary riser can be formulated as an optimization problem by using riser costs as the criteria function, design requirements in terms of maximum allowable stress and buckling capacity as constraints, and riser dimensions as free variables. The theory has been implemented in a computer program that can generate an optimized riser design 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 to minimize a nonlinear function subjected to general constraints. A case study where design parameters and requirements have been varied is also presented. The importance of buckling versus allowable equivalent stress as the most critical constraint has been investigated for varying water depth. The Conclusion of this work is that optimization is a useful tool for riser design, and that the proposed strategy for selection of design variables and constraints will enable an engineer to identify designs with minimum costs in an efficient way.

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