Statistical Methods for Prediction of Characteristic Loads for Free Fall Lifeboats Based on CFD Screening Results

Computational Fluid Dynamics (CFD) has been used in a screening process to calculate characteristic loads for a Free Fall Lifeboat (FFLB) during impact and submergence. The link between various input, e.g. environmental conditions and host specific data, resulting structural loads and motion of the lifeboat is explored. The screening can be used together with host specific environmental conditions to find structural design loads and motion restrictions.Response based analysis have been developed for both short term and long term predictions. For the short term predictions a sea state given by (Hs, Tp) on the 100-year contour line is identified and a three hour irregular sea state is simulated. This time history of surface elevations is used for a large number of random lifeboat drops. From these random drops a distribution of wave height and corresponding wave steepness is derived which is then input to an interpolation in the database of CFD screening results. The resulting responses are fitted to a Weibull distribution and the 90% quantile in this short term load distribution is determined.The long term response analysis is further developed from the short term analysis. The short term distributions for each (Hs, Tp) are combined with the probability of occurrence of the sea state, and long term distributions are derived for the responses similar to the short term analysis.The screening results are used to identify critical load cases which are further investigated.Copyright © 2013 by ASME