Computationed Investigation On Bottom Slamming Load For FPSO

The Boundary Element Method (BEM) of Two-dimensional wedge or three-dimensional blunt falling on to calm water at a constant velocity is used as a popular method for bottom slamming. This method can't reflect ship's real motion when the environmental factors of the FPSO's installation site are taken into account. To overcome this limititation, Dai Yangshan calculates hull bottom slamming loads and bending moments in the time domain by combining the strip theory, which is used to predict ship motion, with the empirical formula for bottom slamming proposed by Ochi. Wang Ge introduces a direct calculation method, which is based on three-dimensional motion theory and the slamming theory and considers the environmental factors, to analysis the FPSO's bow against wave impact loads by a series of engineering software.A direct calculation approach for FPSO's bottom slamming prediction is proposed in this paper. The new approach uses three-dimensional Green function method to predict ship motions relative to waves and the empirical formula proposed by Ochi to calculat wave slamming pressure. The Vertical relative motion spectral is transformed to time signals by frequency-time transformation method, to predict the bottom slamming occurrence and the load magnitude in time history.The method in this paper can be easily applied to estimate the slamming load magnitude and the occurrence frequency with acceptable precision, and the results can be used for fatigue analysis of bottom planes.