A Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Predicting Hydrodynamic Coefficients of Risers: Part II – Staggered Buoyancy Module and Straked Riser

Abstract

Hydrodynamic force coefficients are important parameters in the design and assessment of marine risers. The hydrodynamic coefficients are widely used for assessing marine riser responses due to floater motion excitation and vortex-induced vibrations (VIV). Traditionally, the hydrodynamic coefficients have been obtained from physical model tests on short rigid riser sections. Recently, the offshore industry has started to use Computational Fluid Dynamics (CFD) analysis for predicting the hydrodynamic coefficients, due to the recent advancement of CFD software and high-performance computing capabilities. However, a reliable CFD modeling practice is required for CFD analysis to be a more widely accepted prediction tool in the industry. A joint industry effort has been initiated for developing and verifying a reliable CFD modeling practice through a working group of the Reproducible Offshore CFD JIP. Within the working group, a CFD modeling practice document was written based on existing practices already validated with model test data and verified by blind validations with three CFD practitioners. The first year work focused on a bare riser with circular cross-section and has been published in OMAE 2021. This paper presents the working group’s second-year verification activities for a staggered buoyancy module and a straked riser. The verification work covers three numerical test problems: 1) stationary riser in steady current, 2) riser under forced-oscillation in calm water, 3) riser under forced-oscillation in steady current. In the stationary riser simulation, drag coefficient and lift coefficient from verifiers are compared. In the forced-oscillation simulation in calm water, the fully-submerged riser section oscillates with a sinusoidal motion, and damping and added-mass coefficients are compared. In the forced-oscillation simulation in steady current, where the riser oscillates in either inline or perpendicular direction to the steady current, lift coefficient and added mass coefficient are compared. By following the modeling practice, the CFD predictions are consistent with each other and close to the model test data for the majority of the test cases.