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

Mengyue Chen, Xiuquan Liu+2 more|arXiv (Cornell University)|Jan 11, 2018

Fluid Dynamics and Vibration Analysis45 references3 citations

TL;DR

This study presents a genetic algorithm-based shape optimization of two-dimensional riser fairings to suppress vortex-induced vibrations (VIV) at low Reynolds numbers. By parameterizing fairing profiles with Bézier curves and minimizing lift coefficient as the objective, the optimal water-drop-shaped fairing reduces VIV amplitude by up to 99% and drag by 51% in 2-DOF conditions, while a caudal fin-like shape ensures stability in 3-DOF flow environments.

ABSTRACT

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 Bézier 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.

Motivation & Objective

• To address the lack of systematic optimal design methods for riser fairings in marine engineering.
• To suppress vortex-induced vibrations (VIV) in deepwater risers, which can lead to structural fatigue and failure.
• To develop a shape optimization framework integrating computational fluid dynamics (CFD) and genetic algorithms for fairing profile design.
• To identify optimal fairing geometries that minimize lift coefficient and enhance stability under varying degrees of freedom (DOFs).

Proposed method

• Parameterized fairing profiles using Bézier curves with control points as design variables.
• Employed computational fluid dynamics (CFD) to simulate fluid-structure interaction and compute lift coefficients.
• Applied a non-dominated sorting genetic algorithm (NSGA-II) to search for optimal fairing shapes.
• Optimized for two conditions: two degrees of freedom (2-DOF) and three degrees of freedom (3-DOF) of motion.
• Used lift coefficient as the primary objective function to minimize vortex-induced forces.
• Conducted simulations at a low Reynolds number (Ur = 5.0) to evaluate performance under controlled flow conditions.

Experimental results

Research questions

• RQ1 What fairing profile geometry minimizes vortex-induced lift forces on marine risers in 2-DOF motion?
• RQ2 How does the optimal fairing shape differ in stability and performance under 3-DOF motion compared to 2-DOF?
• RQ3 Can a Bézier curve-based parameterization effectively represent and optimize fairing profiles for VIV suppression?
• RQ4 What flow structures (e.g., vortices) are associated with stable fairing performance in 3-DOF conditions?
• RQ5 To what extent can the genetic algorithm-driven optimization reduce VIV amplitude and drag coefficient?

Key findings

• The water-drop-shaped fairing achieved a maximum reduction of 99% in vortex-induced vibration amplitude under 2-DOF conditions at Ur = 5.0.
• The drag coefficient was reduced by approximately 51% for the optimal water-drop-shaped fairing in the 2-DOF configuration.
• In 3-DOF conditions, the optimal caudal fin-like fairing exhibited enhanced stability due to the formation of two symmetric counter-rotating vortices on either side.
• The symmetric vortex structures generated by the 3-DOF optimal fairing contributed to balanced lift forces and reduced dynamic response.
• The genetic algorithm successfully identified superior fairing geometries that outperformed conventional shapes in both amplitude suppression and drag reduction.
• The integration of CFD with genetic algorithm enabled efficient exploration of complex design spaces for fairing optimization.