Investigation On Bottom Slamming Load For FPSO In Waves

The Boundary Element Method (BEM) is a popular method used to solve the bottom slamming caused by the entering of the two-dimensional wedge or three-dimensional cone into the initial still water with a constant velocity. Because of the limited research field and bad generosity of program, this method can not be applied in practical engineering widely.In this paper, a process which is easy to estimate the slamming load is proposed. The process has three steps. Firstly, the 3D BEM is applied to calculate the motions of the FPSO in frequency domain. Secondly the frequency-time transformation method is used to obtain the relative motions in time domain and get slamming occurrence time and its entry-water velocity. Finally, the two dimensional model established with the method of CFD(computational fluid dynamics) to directly calculate the distribution of the load and the vertical force on the FPSO section.The numerical results show that the FPSO which have the largest relative motions and relative velocity amplitudes, will more likely lead to occur slamming on the condition of blast loads and the incident wave angle of 135 degree. The max slamming loads is greatly related to the shape of the ship section. the half-breadth of the flat bottom is one of the most important factors for slamming loads coefficients, especially for full-formed ship of FPSO shape with large flat bottom. In this paper, a regression formula to estimate the slamming load coefficient is obtained, with the independent variable of the half breadth of the flat bottom, which is conveniently applied in the engineering practice.The method in this paper can be easily applied to estimate the slamming load magnitude with acceptable precision, and the results can be used for strength analysis of bottom frame.