FDPSO is a multifunction floating platform, which has the combined function of drilling, production, storage and offloading oil. The moonpool is necessary for drilling operation and the moonpool size effect will play a role on the hydrodynamic performance of FDPSO. A study of the moonpool size effect on such performance of FDPSO hull is presented in this paper, making use of numerical analysis and model tests techniques. The code WADAM is used for the hydrodynamic performance analysis. A model test aiming to validate the accuracy of the numerical analysis results was conducted in the Ocean Engineering basin in the State Key Laboratory of Ocean Engineering in the Shanghai Jiao Tong University. The model test included decaying test and white noise test. The decaying tests are performed in still water for heave, roll and pitch. White noise tests were carried out to obtain the RAO of FDPSO, with the wave incoming direction of 180° and 135°. The numerical results show a good agreement with the model test results, indicating a reliable model. The “piston” motion of the water inside the moonpool is significant, affecting the hydrodynamic performance of the FDPSO. The effect of moonpool size on the hydrodynamic performance of the FDPSO is analyzed through a numerical method. The relationship between the piston natural frequency of the water column inside the moonpool and its diameter and draft, are studied. An empirical formula of the “piston” natural frequency is proposed, and its validity is assessed.

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