Slamming Induced Whipping Computations on a Large Database of Container Ships

Full scale campaigns and model tests have shown an important high frequency contributions to extreme vertical bending moments, coming from the global ship vibrations induced by non-linear slamming impacts, the so-called whipping phenomenon. Numerical models including fully-coupled hydro-elastic response and non-linear hydrodynamic loads (both wave loads and impulsive slamming loads) have been developed in the last decade, which show good agreement with models tests, at least in head waves where the extreme vertical bending moments are likely to be reached. At the same time, methodologies have been developed to compute the design bending moment including whipping, corresponding to a 25-year return period. These methodologies range from the most simple regular design wave approach, to the more developed multiple design sea states approach. In the context of on-going discussions at the IACS, it was decided to perform such slamming induced whipping computations on a large database of post-Panamax container ship models, to assess the range of design bending moment increase due to this phenomenon. The database used in this paper consists in 17 ships, represented either by Timoshenko beam models or by three dimensional full length finite element models. The results indicate that the increase of wave bending moment due to the slamming induced whipping ranges from 15% to 40%. The influence of the full hydro-elastic coupling is assessed. Some key points of the methodologies used to get the design bending moment corresponding to a 25-year return period are also analyzed: inaccuracy due to the use of regular or irregular design waves, and bias due to filtering. A simple relation is found between the whipping coefficient and the block coefficient.