PREDICTION OF ULTIMATE GLOBAL BEHAVIOUR OF BULK CARRIERS UNDER DOUBLE BOTTOM BENDING

Abstract eng:
It has been generally accepted that the ultimate longitudinal strength of ships is well characterized by the strength of representative longitudinally stiffened panels, which are composed of plate panels, longitudinal stiffeners and transverse frames. For panels in compression, the basic load case usually consists of simultaneously applied (a) longitudinal compression arising from the vertical bending moment, (b) transverse compression arising from the in-plane pressure loading and (c) local bending arising from the lateral pressure. However, simplified methods to determine the ultimate hull girder strength are applicable to well (longitudinally) stiffened hulls when under vertical global bending, but are not applicable for e.g. bulk carriers when significant double bottom bending may also occur due to Alternate Hold loading (AHL). The hull girder capacity should, therefore, be evaluated with due account of lateral and transverse loads for a large extent of the hull. The conventional Smith type method and other simplified methods cannot account for the effect of double bottom bending. Therefore, ISUM methods or computationally demanding nonlinear finite element methods need to be considered. It should be noted that FE analysis based on a limited extent of the hull girder may not predict the true ultimate hull girder strength. Hence to ensure that results of FE analyses are not affected by boundary conditions, the model needs to be sufficiently long. In this paper the ultimate strength of a (1/2+1+1/2) hold tank model of a bulk carrier under AHL conditions was studied with the nonlinear finite element method. The stress redistribution due to double bottom bending was analysed in view of different AHL conditions.

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