The present paper deals with the method of optimum design of laminated composite structures using the finite element method (FEM) and the genetic algorithm (GA) for single-material as well as hybrid laminates. Eight-noded layered elements have been used for 3-D finite element analysis. Weight and cost optimization of Graphite-epoxy/Kevlar-epoxy hybrid composite plate subjected to Tsai-Hill criteria-based design constraint have been carried out. Fiber orientation and material in each lamina, as well as the number of lamina in the laminate have been used as design variables. A multi-objective approach has been used to achieve the optimum design of a laminate for combined weighted cost and weight minimization. The results obtained from the integrated module show that GA with FEM can lead to a global optimal solution for both single as well as multiple objective functions.

Subsea rigid jumpers which are used to connect flowlines and risers to other subsea structures are inherently susceptible to vibration because they must be flexible enough to accommodate translation of the flowline, installation tolerances and settlement of pipeline end terminations (PLETs.) In locations where there are bottom currents, the jumpers can be subjected to vortex induced vibrations. When internal flow rates are high, they are susceptible to flow induced vibration, and they may also be excited by slugging. In some cases, the design constraints force the designs to be 3 dimensional and employ strategies to enhance damping. This paper describes a methodology for assessing subsea jumpers for vibration induced fatigue. The method employs a combination of transient dynamic, harmonic and modal finite element analysis with the VIV tool SHEAR7. The methodology is able to show generally improved VIV fatigue lives compared to more traditional methods based on DNV-RP-F105 because of the ability to define current loading over the jumper length and to assess the effects of strakes and coulomb damping. Further, the methodology is also capable of assessing the effect of tuned vibration dampers which are sometimes used to suppress FIV.

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