A study on the hull girder under dynamic loading considering the effects of strain-rate dependency on material properties

  Objectives  The effects of such dynamic loading as whipping on the structural strength of a container ship has become an important subject in recent years. Given that, it is necessary to study the impact of such dynamic loading on the hull girder ultimate strength of the midship structure, in particular, to understand that of the strain-rate dependency of the material properties on its collapse behaviors.

  Methods  This paper takes the container ship as research object, establishes a half breadth model of midship section of a 3 100 TEU container ship. Commercial finite element analysis (FEA)software LS-DYNA is used to investigate the ultimate strength of hull girder subject to dynamic loads such as whipping. Considering the effect of the strain-rate dependency of the yield stress of the material, conventional Cowper-Symonds(CS) formula and improved CS models are employed to have dynamic analysis on the ultimate strength.

  Results  The results show that, the dynamic collapse load when such dynamic load as whipping is applied is about 7%-9% greater than quasi-static ultimate strength. Even when the time duration of applied dynamic loading is at the normal wave-induced loading level, the dynamic collapse load becomes about 4%-5% greater than quasi-static ultimate strength.

  Conclusions  when evaluating dynamic hull girder ultimate strength, there is no problem with using the conventional CS formula, however, to estimate residual deformation and residual strength using FEA, it might be necessary to use a proper material model.