Hydrodynamic Verification on the Motion Characteristics of FPSO Based on the Full Scale Measurement Data Features of Current and Wind

FPSO is subjected to complex sea loads during its service life. Series of coupled hydrodynamic analysis in time domain for FPSO and its mooring system have been conducted within the recent ten years. Among these analyses, the coefficients of wind force and current force for FPSO hull were calculated by the empirical formulae mostly. It is known that these coefficients are of great importance in the motion predictions of the FPSO in the analysis. The verification of the feasibility of these formulae is necessary. In this paper, the feasibility and the accuracy of these empirical formulae are verified through the comparison between the results of hydrodynamic analysis and those of full scale measurement data. A full scale measurement project sponsored by CNOOC for Nanhai Fenjin, an FPSO operating in South China Sea, has been carrying out by Shanghai Jiao Tong University since Oct 2007. Large amount of valuable data of the six-degree motions for the FPSO has been obtained. To do the comparison, a typical serious sea state is selected out to be the objective course. In the course, the response spectrums for heave, roll and pitch motions are calculated based on the measurement data. Besides, a series of coupled hydrodynamic analysis for the FPSO are conducted, using the code DeepC. The response spectrums of the motions for heave, roll and pitch in the same sea state are also obtained through the spectrum analysis. Using these motion spectrums, comparisons between the results of hydrodynamic analysis and those of full scale measurement are fulfilled. With the comparisons, the feasibility of the empirical formulae of the coefficients for wind force and current force are verified. The correction coefficients are added to the empirical formulae and new hydrodynamic analysis based on the new formulae are conducted. It is shown that the new analysis results are in good agreement with those of the full scale measurement, which validated the practicability and feasibility of the modified formulae on the motion prediction of FPSO.