Hydrodynamic Coefficient Maps for Riser Interference Analysis

Abstract

Riser wake interference analysis is conducted based on analytical / semi-empirical models such as Blevins’ and Huse’s models. These models are used for modeling the reduction in particle flow velocity due to the presence of a cylindrical object upstream in the flow path. However, these models are often too conservative and accurate only for circular cylinders. Many top tensioned risers (TTRs) use vortex induced vibration (VIV) suppression devices such as strakes or fairings. There is a need for alternate methods to obtain drag and lift coefficient datasets for circular cylinders with strakes and fairings. Two such approaches are to obtain data from Computational Fluid Dynamics (CFD) simulations or from experimental large-scale model test data. Interpolation and/or extrapolation methods are needed to obtain additional data points for global riser finite element analysis. This paper presents a methodology to obtain hydrodynamic coefficients for TTRs with VIV suppression devices. The proposed methodology uses a combination of empirical formulas based on Blevins’ model and numerical interpolation techniques along with experimental tow tank test data and CFD analysis. The resulting data is then input as user-defined drag/lift coefficients into a global riser finite element analysis to obtain a more realistic riser system response.