Modelling aspects for reduced stiffness in bulk carrier vessels

Abstract

Since the inception of merchant ships, bulk carriers have been used extensively for transporting cargo across oceans. With the passage of time, bulk carriers have been improvised to enhance both the cargo carrying capacity and safety of the cargo and crew. The target of this study is to address how stiffness reductions in the inner bottom plate and outer bottom plate affected the global redistribution of nominal stresses in double bottom of a bulk carrier vessel. The redistribution effect is then studied in relation to the buckling capacity of the double bottom. Two different principles of stiffness reductions are carried out. The first included reduced stiffness in the whole inner – and outer bottom plate in the centre tank and neighbouring tank. The second principle is to reduce stiffness in areas with compressive stresses only. A parametric study varying the degree of stiffness reductions and type of material coefficient is carried out for each principle. The results show that the reduced stiffness properties leads to significant nominal stress redistribution leading to reduced transverse stresses. This is most clearly seen for the thinnest outer bottom.