On the Influence of Hull Girder Flexibility on the Wave

Numerical predictions and model test results of the wave induced bending moments in a 9,400 TEU post-Panamax container vessel are presented for two regular wave scenarios. Different numerical procedures have been applied: a linear and non-linear time-domain strip theory and a direct calculation (CFD) solving the Navier-Stokes equations with the free surface captured by a volume-of-fluid (VOF) method.

In all procedures the flexibility of the hull girder is modelled as a non-uniform Timoshenko beam. It is observed that the non-linear models agree well with the model tests and as there is no occurrence of severe slamming in the cases considered, the inexpensive non-linear strip theory is as accurate as the direct CFD calculation method.

In a comparison with the results using the rigid body assumption, the increase in the vertical bending moment (VBM) amidships due to the flexibility of the hull girder is found to be approximately 7% (peak-to-peak amplitude) in general. The non-linear responses, however, contain over-harmonic frequencies which may coincide with the natural frequency of the two-node vertical bending mode inducing resonance.

In that case the hull girder flexibility causes the responses to increase as much as 22% (peak-to-peak amplitude) in one of the present cases.