ULTIMATE TORSIONAL STRENGTH ANALYSIS OF CONTAINER SHIP ALICE MATHAI Associate Professor, Dept. of Civil Engineering, M A College of Engineering Kothamangalam 686666, Kerala, India alice_mathai@rediffmail.com GEORGE JOHN P. Professor, Dept. of Electrical Electronics Engineering, M A College of Engineering Kothamangalam686666, Kerala ,India gjpmace@rediff.com MATHEW JOSE JIN M Tech Student, Dept. of Civil Engineering, M A College of Engineering Kothamangalam, Kerala, India mathewjosejin@gmail.com Abstract: Container ships with wide hatch openings are thin walled open sections and have low torsional stiffness. Hence response arising from torsional loads is significant and subsequently the torsional analysis of container ship is necessary. Using the ANSYS software, the progressive collapse behaviour of a typical container vessel under torsion was analysed. The effect of torsional moment on the ultimate strength of ship hull subjected to design vertical shear force was also determined. Full hull between the bulkheads was modeled with fully restrained warping displacement at the unloaded end. When pure torsion is applied, the hull corner regions are typically the most highly stressed areas, which may collapse. Thus, scantlings of the hull corner region should be sufficient for ship hulls with large deck openings. The ultimate strength based safety factor under pure torsion for the vessel, is 4.5, which is reduced by 30% when subjected to design vertical shear force also. Keywords: Torsion; container ship; finite element. 1. Introduction Container shipping in global scale has revolutionized the field of Naval Architecture and Marine Engineering by rapid economic progress and fast transshipment. When a ship is sailing at sea, it is subjected to various load patterns with many magnitudes which cause deformation of its structure, as well as stresses. The first design step is to assume exact loads acting on the structure concerned, in order to estimate the structural strength in a reasonable way and consequently to develop the design [Yasuhisa et al., (2009)]. Container ship structures are characterized by large hatch openings [Tuper E.C., (1996). The effects of torsional load component on the ship hull structure are not considered during the design stage and the moments induced thereby were not defined in the shipping manuals. It is thus of importance to better understand the torsional strength characteristics of ships with large hatch openings. The primary aim is to investigate the ultimate strength characteristics of ship hulls with large hatch openings under torsion. Axial (warping) stresses as well as shear stresses are normally developed for thin-walled beams with open cross sections subjected to torsion. The calculation of these stresses and the study of the distribution and magnitude of warping and shear stresses for a typical container vessel hull cross section under torsion are done. Torsion is caused by forces which do not pass through the shear centre axis of a ship hull cross section. Torsional moments acting on a ship hull may generally be divided into two components, namely static (i.e., still water) torsion and dynamic (i.e., wave induced) torsion. 2. Loads causing torsion Stillwater torsion is due to non-symmetrical cargo loading over port and starboard with the vessel as a whole remaining upright. In a seaway, wave induced torsion is caused by non-symmetrical distribution of hydrostatic and hydrodynamic forces over port and starboard (fig.1). Mass acceleration forces resulting from the ship’s motion also contribute to dynamic torsional moments. Finally, there may also be some torsional (vibratory) contribution arising from propeller shaft torque variations, vertical free forces from the propellers in twin screw vessels, and perhaps free horizontal forces in the engine. For practical purposes, dynamic torsion is dominant because cargo is usually evenly loaded over port and starboard. Alice Mathai et al. / International Journal of Engineering Science and Technology (IJEST) ISSN : 0975-5462 Vol. 5 No.03 March 2013 512