Design optimization of stiffening system for ocean thermal energy conversion (OTEC) cold water pipe (CWP)

Ocean thermal energy conversion (OTEC) uses heat from seawater to generate electrical energy by utilizing the temperature difference between the surface and deep ocean layer. Cold water pipe (CWP) attached to transport cold seawater over distances of up to 600 m to the plant is susceptible to failures caused by environmental loads. At this point, the CWP should be strengthened to prevent structural failure by inducing ring stiffeners along the pipe. To ensure its structural integrity, this study conducts a design optimization by investigating how the variation of ring stiffening system parameters such as height, thickness, distance between stiffeners, and shape of stiffeners influence the load-carrying capacity of the pipe using a Finite Element Analysis. Initially, the benchmarking procedure is done to ensure the reliability of the FEM modeling. After being verified, the modeling procedure is used for parametric study analyses. Results state that the higher and thicker stiffener ring increases the structural strength. In the case of the ring stiffener distance, as predicted, reducing the spacing between reinforcements is preferable to increasing the bending strength of CWP OTEC. Analyzing the variation of reinforcement height, thickness, and spacing, it was found that thickness had the most significant influence, followed by reinforcement height, and reinforcement spacing had the least. Additionally, changes in the shape of the reinforcement have minimal impact on the flexural strength of the structure when regions of identical moments of inertia exist.