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Published in Colin R. Gagg, Forensic Engineering, 2020
The subsequent inquiry into the failure of the Kurdistan did not establish a precise sequence of failure, which showed both brittle and ductile fracture. ‘The ship’s shell plates were found to have Charpy transition temperatures of between 5° and 20°C; the steel in contact with the sea water was close to or below its transition; and the steel in contact with the heated cargo was above its transition. Calculations of the thermal stresses in the ship resulting from the carriage of a warm cargo in a cold sea indicated that a high tensile stress level would have been present in the shell and bilge keel. It is thought that the stresses due to the impact of a wave on the bow, superimposed on the high thermal stress and the stresses due to the moderate wave bending moments, triggered the fracture of the Kurdistan’s bilge keel. The toughness of the shell plate was insufficient to arrest the propagating crack and complete failure ensued. The initiation of the fracture was due to the classic combination of poor weld metal toughness and high stresses in the presence of a defect.’[35–37]
Potential effect of 2nd generation intact stability criteria on future ship design process
Published in Pentti Kujala, Liangliang Lu, Marine Design XIII, 2018
Yaohua Zhou, Yanhong Hu, Gaofeng Zhang
In general, good designs for PR and PLS need to reserve sufficient transverse stability in wave, by keeping enough GM values or reducing the variations of GZ curves in wave for loading conditions. This usually means optimizing hull lines or setting upper limit for the height of gravity center (KG). On the contrary, setting lower limit for KG of ballast loading condition can lead to satisfaction of EA. Increasing roll damping coefficients will also be helpful in reducing the vulnerability of PR and EA, but it should be realized by passive measure such as modify the hull lines or enlarge the bilge keel. All these measures need more time spent on the optimization of hull lines and loading conditions. Since the design of hull lines needs to take a variety of influencing factors into account, this procedure will be more challenging and lead to more human resources consumption.
History and Overview
Published in T.L. Anderson, Fracture Mechanics, 2017
However, knowledge must be applied in order to be useful. Figure 1.1 shows an example of a Type 1 failure, where poor workmanship in a seemingly inconsequential structural detail caused a more recent fracture in a welded ship. In 1979, the Kurdistan oil tanker broke completely into two while sailing in the North Atlantic (Garwood, S.J., private communication, 1990). The combination of warm oil in the tanker with cold water in contact with the outer hull produced substantial thermal stresses. The fracture initiated from a bilge keel that was improperly welded. The weld failed to penetrate the structural detail, resulting in a severe stress concentration. Although the hull steel had adequate toughness to prevent fracture initiation, it failed to stop the propagating crack.
Operability analysis of traditional small fishing boats in Indonesia with different loading conditions
Published in Ships and Offshore Structures, 2023
Muhammad Iqbal, Momchil Terziev, Tahsin Tezdogan, Atilla Incecik
In this study, VERES, a plug-in of the ShipX software package was used to determine the ship RAOs. This method is based on the 2-D linear strip theory. The ship responses are assumed to vary linearly with incident wave amplitudes which are assumed to be small compared to the vessel dimensions. The wave steepness is also assumed to be small, so the waves are far from breaking. To determine the hydrodynamic forces, a potential theory is employed. The fluid is assumed as inviscid, irrotational, and incompressible. The viscous roll damping is determined from an empirical formula for roll motions. The components of this formula are frictional shear stress on the hull surface (Kato 1957), eddy damping (Ikeda et al. 1977), lift damping (Himeno 1981) and the bilge keel damping (Ikeda 1979). As the ship geometry considered in this study has no bilge keel, the latter component is not included.
Weakly nonlinear ship motion calculation and parametric rolling simulation based on the 3DTGF-HOBEM method
Published in Ships and Offshore Structures, 2021
Wen-jun Zhou, Ren-chuan Zhu, Xi Chen, Liang Hong
3-DOF:6-DOF:The freeroll decay curves in the non-zero speed case are displayed in Figure 13. Based on Himeno (1981), the roll damping can be assumed to have composed of skin friction damping, hull eddy shedding damping, lift force damping, bilge keel damping and free surface wave damping. The interactions between the five components are neglected. In this paper, the free surface wave damping is included in the roll damping coefficients as in free decay simulation the velocity has been considered. As only bare ship hull is considered, the bilge keel damping is zero. Furthermore, the lift force damping only takes a small portion in total damping at a low speed, which is also neglected. The skin friction damping and the eddy making damping are both related to fluid viscosity, which is also reflected in the coefficients.
On critical parameters of squall associated with the mooring design of a turret-moored FPSO
Published in Ships and Offshore Structures, 2018
Yu Cao, Xiaochuan Yu, Gong Xiang, Weidong Ruan, Ping Lu
The FPSO's loading condition will be provided as an input to the diffraction analysis. The additional damping due to bilge keel will also be calibrated in the simulation. Further, some inputs should be ready before doing mooring analysis, such as the mooring line properties, the environmental conditions, the wind and wave coefficients, etc. In fact, the mooring line properties need to be updated for more iteration cycles according to the design target and the criteria. It is always required to strike a balance between conservatism and cost efficiency of engineering design. The optimised design of turret mooring system is achieved by iterating the safety assessment. Here, the final parameters of the design model are given as follows: the anchoring system consists of nine lines arranged in three bundles, as shown in Figure 10. The angle between two adjacent bundles is 120° and the separation angle between two adjacent lines is 5°. Table 4 shows the theoretical mooring line composition.