ABSTRACT

An analysis method for the global structural strength of the cylindrical FPSO is established. The hydrodynamic model is developed by AQWA. The characteristic parameters suitable for cylindrical FPSO are proposed and the wave loads under different design wave parameters are obtained. The loads, including lightship weight, pressure of tanks, wave loads, are applied to the FE model. The result shows that the stress concentration is easy to occur at the bottom of the main hull, radial bulkhead, ring bulkhead and shell of hull, where the local reinforcing stiffener can be arranged to reduce the stress. More attention should be paid during the construction of welding and the frequency of inspection on these areas should be increased under the offshore operating condition.

INTRODUCTION

FPSO (Floating Production Storage and Offloading) is mainly composed of two parts, including the topsides and the main hull. The role of the topsides is to process the mixture of oil, gas and water received from the riser. The role of the hull is to store oil. The concept of FPSO has been widely recognized by major oil companies. After decades of exploration, experts in the field of offshore oil and gas have designed and developed different types of FPSO, which can be divided into two categories: ship-type FPSO and cylindrical FPSO.

The turret-type single-point mooring requires large investment and high maintenance costs (Vijayalaksmi et al., 2012). Cylindrical FPSO, as a newly developed offshore structure, has received extensive attention by researchers. Compared with ship-type FPSO, the cylindrical FPSO is arranged symmetrically and the hull is isotropic in all directions generally, which has no vane effect. Thus, the stability of cylindrical FPSO is better and make it more suitable for complex wave conditions (Wang et al., 2011). In addition, the multi-point mooring system is adopted by cylindrical FPSO instead of single point mooring system, which is better in cost. The characteristics of the cylindrical FPSO of the Sevan Marine series are summarized (Wu, 2012). AQWA is used to study the hydrodynamic response of cylindrical and ship-type offshore platforms under extreme conditions based on the South China Sea (Wang, 2013), The results of which show that the cylindrical drilling and storage platforms have better motion response and anti-overturning ability. The numerical calculation method is introduced to analyze the motion response and wave load characteristics of cylindrical platforms (Zhang et al., 2014), and the Morison formula is used to calculate the wave loads of the platforms.

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