Developing a risk-based methodology for addressing green water in FPSO designs
As part of an international JIP, Bureau Veritas explores how to use the results of scale model tests and CFD to enhance safety in FPSO designs.
Recent FPSO projects in moderate to severe environmental conditions, such as the waters in the North Sea and around Brazil, have raised concerns among operators about the risks associated with green water. Greenwater occurs in severe weather conditions, when waves and motions can become so large that water flows onto the ship’s deck, potentially damaging safety-critical elements of the unit.
Due to its complexity, current methods for managing this hydrodynamic phenomenon rely on the performance of tests using scale models. Developments made in Computational Fluid Dynamics (CFD) have enabled operators to add this as a complementary tool to model tests, since CFD can capture small geometric details of topsides that cannot be reproduced in a model. In addition, once validated, CFD computations can accelerate the evaluation of different design solutions. While the procedures to perform a deterministic assessment of green water load through model tests or CFD are reasonably defined and continuously improved, there remain important questions about the identification of critical conditions and the practical application of results to structural design.
Working alongside major oil and gas players, including designers, operators, shipyards and research institutes, Bureau Veritas has initiated an FPSO Greenwater Joint Industrial Project (JIP) to develop a risk-based methodology for addressing the risks of green water on FPSOs. Currently, whenever green water is a concern, great effort is put into tests and CFD, but operators remain unsure how to use the results. And green water loading can sometimes still occur, even in conditions that were never identified as critical. This JIP seeks to address those problems, optimizing the use of green water assessments and integrating green water controls in the formal safety assessments of FPSOs.