Optimal design of two-dimensional riser fairings for vortex-induced vibration suppression based on genetic algorithm

Vortex-induced vibration (VIV) manifests its destructiveness on marine risers in deep-water oil and gas development. Many types of riser fairings are employed in the practical applications of ocean engineering due to their effectiveness in suppressing VIV. However, few reports have been found on the optimal design of the fairing profile. In this study, we conduct shape optimization by integrating computational fluid dynamics and genetic algorithm at a low Reynolds number. The fairing profile is parameterized by B\'ezier curves with control points adopted as design variables, and lift coefficient is selected as the objective function to obtain optimal fairing. The optimal solution shows that the water-drop-shaped fairing presents a high performance in the condition of two degrees of freedom (DOFs), whereas the caudal fin-like-shaped fairing has good stability in 3-DOF condition. Optimization results indicate that the water-drop-shaped fairing suppresses amplitude up to 99% and reduces drag coefficient by almost 51% at Ur=5.0 for the 2-DOF condition. For the 3-DOF condition, the formation of two symmetric vorticities with opposite directions generated at the bilateral of the optimal fairing leads to fairing stability in flow.