Numerical Simulation of Wave Loading on FPSO in Various Wave Conditions

Abstract

AbstractIn the design of Floating Production Storage and Offloading facilities (FPSO), it is important to predict the seakeeping parameters like FPSO motions. This paper focusses on the prediction of FPSO motions and wave impact loads in various irregular sea waves and proposes a Computational Fluid Dynamics (CFD) model. Accurate prediction of FPSO motions and wave impact loads requires the accurate prediction of wave kinematics. Waves generated by winds blowing over the water surface in real oceans are short-crested, so the dynamic responses of the moving structure will be very different in long crested and short-crested waves. In this paper, we have verified the pure propagation of oblique short-crested random waves in numerical wave tank with the analytical results, which serves as the basis of more complex analysis including ship hull interaction with waves.The proposed CFD model uses Multiphase Volume of Fluid Model (VOF) along with Six Degrees of Freedom Model (6DOF) to predict the hydrodynamic forces and the ship responses. Long crested and short-crested random waves are simulated in a numerical wave tank, where boundary conditions for free surface profiles and velocities are imposed at the velocity inlet boundary using Jonswap frequency spectrum and cosine-2s directional spreading function.Wave slamming loads and the structural responses depend on many factors, like sea state, FPSO speed, draft, wave heading angle, local structure etc. In this paper, we have analyzed the wave slamming on a moving FPSO for different sea states (unidirectional, multi directional with 45 deg and 90deg angular spread) and studied the resulting hydrodynamic forces and related structural interactions. Ship motions (heave, pitch and roll), vertical accelerations, pitch velocities, roll velocities and the wave impact pressures are compared among different sea states.