Determination and Mitigation of Hydrodynamic Loads in an Open FPSO Turret by Model Tests

Abstract

When transiting to and from the field, disconnectable FPSOs have an open moonpool inside the turret where the buoy is normally situated. Inside the turret are a number of internal components designed to interface with the buoy. These components represent a large capital investment and are critical to FPSO operation. During adverse weather conditions, there is a potential for large hydrodynamic loads on these components due to wave action and the vessel’s seakeeping response. Deriving realistic design values for this equipment can be challenging due to the complex nature of the fluid dynamics inside the turret. This paper describes a unique model test campaign undertaken for a cyclonic region FPSO. It details the findings of using a highly detailed turret model to verify hydrodynamic design loads. Results about the turret’s natural modes are discussed. Correlation between the hydrodynamic loads inside the turret with the vessel’s seakeeping response is also investigated. The influence of draft and forward speed with respect to the hydrodynamic loading is presented. Based on observations made during the test campaign, the worst loading case is likely to occur during the initial transit to site. A possible mitigation method was investigated in the form of a temporary cover plate, effectively closing off the moonpool.