Non-linear Effect on Wave-Induced Loads in Vehicles Carrier for Hull Design

Abstract

The structural rules of classification societies typically specify various loads corresponding to the sea states which are expected to be encountered by a ship throughout her service life. Consideration of these loads, particularly those for the most severe sea states expected to be encountered, and their impact on hull design are important factors in ensuring ship structural safety. This paper summarizes research carried out by the authors using tank tests and numerical calculations into non-linear phenomena and the level of non-linear effect on loads with the same period as the encounter wave period. Although it is well known that various phenomena, from the change of the wetted surface to breaking waves, are included within the term of non-linear phenomena, the authors focused on those non-linear phenomena resulting from the changes of the geometrical areas on hull surfaces subject to sea water pressure, i.e. the change of the wetted surface, which are expected to be dominant with respect to the non-linearity acting on the loads. In order to investigate behavior of this pressure in detail, hydrodynamic pressure was measured at over 300 points on the hull surface using FBG sensors, the latest optical fiber sensor, and the non-linear phenomena were investigated with respect to not only ship motions and hull girder bending moments, but also with respect to various pressures acting upon the entire hull surface. In addition, the level of the non-linear effect under irregular waves with high wave heights was investigated based upon numerical calculations because the structural rules assume the similar wave conditions.