Preliminary Design of Composite Catenary Risers Using Optimization Techniques

Abstract

The use of steel risers for deepwater application is not always feasible, due to its high weight. Fiber reinforced composite materials offer an interesting alternative due to its several advantages, such as high specific strength and stiffness, high corrosion resistance, low thermal conductivity, good structural damping, and high fatigue resistance. Thus, the use of composite risers is an interesting alternative to deepwater oil fields. The design of composite risers requires the consideration of different load conditions and lamination schemes. Therefore, the design of a composite riser joint is more complex than conventional risers since strength and stiffness of these components depend on the number of layers and the thickness and orientation of each layer. This work presents a methodology for design of Composite Catenary Risers (CCR) based on the procedure used for design of conventional risers. An optimization technique is applied to the preliminary design of composite riser joints in order to minimize the cost of joint, assumed proportional to the volume of material. The design variables are the thickness and orientation of each layer. Strength and stability constraints are considered in the optimization model. Simple and efficient expressions, based on the Classical Lamination Theory, are used for stress computation and stability analysis. Multiple load cases are included. The proposed methodology is applied to the preliminary design of CCRs with different water depths, liner materials, and failure criteria.