Modelling of Wave-Structure Interaction of a Cylinder in Irregular Sea Waves with Vessel Motions Using Coupled Transient CFD and Diffraction Methodology

Abstract

Abstract This paper is a continuation of previous paper (OMAE2014-23225) where a parametric study was performed for wave- structure interaction on a hollow cylinder in regular sea waves without vessel motions, and the effect of waves and current on the motion of the cylinder and the associated forces using a high fidelity methodology (OMAE2013-11569) to couple CFD with diffraction analysis. This approach was demonstrated for predicting the motions and loads of subsea equipment and structures during offshore operations. Instead of relying on simplified equations or empirical formulations to calculate and estimate the hydrodynamics coefficients, or using steady-state CFD simulation on a stationary equipment and structure to predict drag and added masses on submerged structures in traditional approaches, this methodology couples the transient CFD with diffraction analysis. In this paper, we extend the solution to include wave-structure interaction in irregular sea waves and vessel motions. Irregular waves are modelled using a JONSWAP wave spectrum. Simulations are performed to investigate effect of significant wave height, peak wave frequency (time period) of irregular sea waves, and vessel motions on the motion of a hollow cylinder in irregular sea waves. The results are compared with the traditional approach in current practice. The time domain diffraction simulation is coupled with multiphase CFD simulation of subsea equipment and structures in waves. A transient CFD model with rigid body motion for the equipment and structure calculates added masses, forces and moments on the equipment and structure for diffraction analysis, while diffraction analysis calculates linear and angular velocities for CFD simulation. The results provide better understanding of structure motion and associated forces in waves using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations, or by using steady - state CFD analyses in traditional decoupled approaches. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in waves during offshore operations.