Optimization of Hydrodynamic Coefficients for VIV Prediction

Abstract

Vortices generated when flow pass offshore slender structures may cause structural vibrations due to fluid-structure interaction, termed vortex-induced vibrations (VIV). VIV can cause severe accumulated fatigue damage, which need to be considered in the structure design. To capture the non-linearities of different riser systems and time varying flow, time domain models are better alternatives than frequency domain models to predict VIV. The input hydrodynamic parameters of time domain models are semi-empirical. However, versatile databases of hydrodynamic parameters are not well established, due to the large variations of the flow conditions, riser systems, and corresponding sub-structures. An optimization procedure could be implemented as an alternative to conventional experimental methods for establishing adaptive hydrodynamic parameter databases capable of accurately handling changes in the underlying structure of the system or flow regime. Literatures on application of optimization algorithms for various offshore engineering problems have been reviewed. VIV represents a constrained non-linear programming problem, where the sequential quadratic programming (SQP) algorithm – NLPQLP has been applied in this study. This paper proposes an optimization procedure of input hydrodynamic parameters for the time domain VIV solver - VIVANA-TD [21], for VIV prediction of various riser systems. A workflow integrating optimization and time domain VIV simulation has been established in the software work bench SIMA. By investigating the VIV prediction of typical laboratory model tests with optimized parameters, the feasibility of optimization using sequential quadratic non-linear programming algorithm - NLPQLP has been demonstrated.