Detailed CFD Simulations of Green Water Flow on FPSO Deck

Oil production in ultra-deep waters places some new challenges for floating units. As an FPSO is one of most common types of production units adopted by Petrobras, its behavior in extreme conditions has to be fully tested and verified. During extreme sea storms, ship type floating structures may be subjected to water on deck events (green water). In order to allow a detailed structural analysis, Computational Fluid Dynamics (CFD) techniques may be used to investigate detailed loads due to water on deck propagation, especially in beam sea conditions, which are not traditionally covered by maritime rules. Based on model test results, water ingress and water on deck propagation are simulated through CFD analysis. The methodology adopted consists of two different approaches: (i) The influence of a riser balcony lateral extent is analyzed based on a 2D wave propagation model and; (ii) the complex flow behavior through topside equipment is discussed by using a 3D simulation of a restricted deck area, including some strategies for impact protection. The results of the simulations allow investigation of the complex flow behavior depending on the riser balcony extent and topside configuration, as well as the resulting loads on critical structures. For a side hull balcony, its protective effect against wave run-up in beam waves is only effective with a lateral extent of 8m. By performing water on deck simulations, the benefits of "V" type protections are quantified leading to 20% loading reduction when compared to flat plates. The simulations reveal CFD as a very powerful tool to assess detailed transient pressure distributions for optimized structural design.