Optimization of bulk carrier hull design through CAD modelling and FEM structural analysis - a case study

Recording of frequent structural damage to the hull of bulk carriers (some of it serious) motivates the need to use the concept of computer-based rational design through advanced analysis methods. The aim of this paper was to optimize - through structural and dimensional modeling - the mid ship section of the 165,000 dwt bulk carriers, under the effect of general combined stresses (longitudinal-vertical bending, transverse-vertical bending and longitudinal torsion) also considering specific local stresses. Using computer-aided design (CAD) and finite element methods (FEM), an operational calculation tool was provided. Considering the ship fully loaded (draft T) with light ore, the midship section main frame was analyzed, in the framing system changing area (from the vertical shell panels transverse ones to the hopper tank area longitudinal ones) concluding that the highest Von Mises stresses appear here (the maximum calculated value being 14,910 daN/cm2).Considering ship as a beam, maximum bending moment (3293 MNm) and largest ship beam deformation (25.99 mm) have been noted for the ship loaded with heavy ore (draft 0.8T); the maximum shear force (790 MN) was obtained for the ship in ballast (draft 0.45 T). Given the size and weight of the ship, those values are within the acceptable limits prescribed by classification societies. The validation of the research has been done by checking compliance with the rules of class society (corrections were applied for 12 sections, selecting 8 representative load cases). It was found that the bending moments do not exceed the maximal values, while critical situations are recorded for the shear forces for 4 of the selected load cases (consequently, the shear forces were subjected to reduction, to be within the acceptable values).