The Methodology And Analysis Of Computing The Ultimate Strength Of Hull And Damaged Hull

In the modern ship construction design research realm, people pay more and more attention to the ultimate strength of ship hull girders. This is because that the perfect construction design is closely neted the true strength store of the ship girders. However, in order to understand the actual strength store of ship hull girders, we must have a right assessment of the ultimate strength of ship hull girders. At the same time, The total losses of all ships during the years 1995-1996 are 367 in number (180 million in gross tonnage), grounding and collision accounts for total losses amounting to 33%, according to LR of Shipping' World Causalty Statistics, The perfectly evaluation of residual strength has an important function of guidance for succor or drag, so the study of the ultimate strength of damaged ships become more and more importance too.This thesis used along M.K.Rahman's curves of the standard relationship of the ship section element stress-strain . In the tensile zone, the stiffened panel is assumed ideal elasticity and plasticity, namely, in the elastic zone, the relationship of stress-strain obey Linear elastic law, and then in the plastic zone , the tensile elements are assumed to keep carrying the yield load. But in the compressive zone, three distinct zones in the whole range of element load-shortening behavior are considered: stable zone, no-load-shedding zone, load-shedding zone. A panel consists of a longitudinal stiffener with its attached plating is the primary element to bear the weight, the stiffened panel may have three collapse models under the load of ultimate moment: â‘ the panel will collapse due to stiffener flange compression; â‘¡the panel will collapse due to plate flange compression; â‘¢the panel will collapse due to stiffener and plate flange compression. With consideration of the asymmetry of cross section and the shift of ship if the ship damaged by the collision or grounding, choose the direction of total moment as the calculate coordinate, avoid the problem of inclined moment when confirm the neutral axis. In the way of progressivecollapse mechanism through incremented curvature, the neutral axis of cross section will not only moved up and down but also shift, so it must meet two equation condition: 1, the cross section is divided into two parts, tensile part and compressive part, the total moment F1, F2 in these two parts must be equal, namely, F1= F2;2, the lines between the center of these two parts must along the direction of total ultimate moment M. The total ultimate moment is the dot on the moment-curvature relationships which number of slope is zero or sign changed. And then use the residual strength index and sensitivity analysis to reflect the influence of different damaged position and extension by collision or grounding to hogging and sagging.Finally, on base of the above research contents, a program is developed in FORTRAN language by using this simplified method to analyse the ultimate strength of ship hull girders and damaged ships . In comparison with the results from some famous experts of International Ship & Offshore Structures Congress. This simplified method has engineering accuracy and can be used in the pre-phase of design. Lastly, this text take into account of the influence of axis power to the ultimate strength of full hull.