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Vhanmane S.,Research and Rule Development Division | Bhattacharya B.,Indian Institute of Technology Kharagpur
Journal of Offshore Mechanics and Arctic Engineering | Year: 2011

The ultimate strength of a ship's hull depends on its material and geometric properties, some or all of which may be random in nature. In addition, initial imperfections in the form of initial deflection and residual welding stresses in plating between stiffeners can significantly affect the hull ultimate strength. In this paper, the effect of randomness in yield strength and in the initial imperfections on ultimate hull girder strength is determined. Different levels of statistical dependence between yield strength and initial imperfection of stiffeners and plating between stiffeners have been considered. The methodology is applied on a bulk carrier and a VLCC tanker. © 2011 American Society of Mechanical Engineers. Source

Vhanmane S.C.,Research and Rule Development Division | Patra P.K.,Research and Rule Development Division
11th International Symposium on Practical Design of Ships and Other Floating Structures, PRADS 2010 | Year: 2010

Ultimate strength is one of the most fundamental limit states related to stiffness and strength of ship hull girder. The growing concern regarding safety of ships and the uncertain nature of load-strength variables makes reliability assessment of ships very important. The simplest outcome of all assessment is the code formula for quick checking of safety of structure involving the use of partial safety factors. The hull girder reliability depends on limit state function, stochastic description of the variables and the method of reliability computation. In this paper, the various aspects which can alter the calculation of hull girder reliability index are assessed in the context of ultimate limit state (ULS) function. Candidate structures taken in this study are: a bulk carrier and a VLCC tanker. The results reveal that there is a large scatter of reliability index values with varying limit state models of ultimate strength. The observations of this study also brought target reliability index and derivation of partial safety factors based on target reliability index into discussion. It highlights the need for a common limit state equation, models for load-strength evaluation and reliability method to be adopted while assessing the reliability index. © 2010 COPPE/UFRJ. Source

Doshi K.,Research and Rule Development Division | Vhanmane S.,Research and Rule Development Division
Ocean Engineering | Year: 2013

Present ship building rules follow SN curve approach to evaluate the fatigue damage at identified locations while use of fracture mechanics approach is yet to receive due attention. In the present work, a methodology of evaluation of fatigue life of the longitudinal stiffener and transverse web frame connection using fracture mechanics has been demonstrated. Since, various factors such as the crack dimensions, the crack growth law parameters and the applied loads are random in nature; they have been accounted for considering their randomness. Numerical results obtained with the present method for fatigue life of an oil tanker are compared with those based on IACS Common structural rules and a good agreement is observed between them. The present method may find useful application to risk based inspection of ship structures. © 2013 Elsevier Ltd. Source

Choudhary G.K.,Research and Rule Development Division | Doshi K.M.,Research and Rule Development Division
Ocean Engineering | Year: 2015

The Common Structural Rules for Oil Tankers (OT) and Bulk carriers (BC) of IACS mandate the computation of shear flow in hull girders. Such computation involves determinate as well as indeterminate shear flow evaluation due to the multi-celled nature of the OT and BC transverse sections. This necessitates formulation of an algorithm for automatic detection of closed cells within a ship section as well as for automatic determination of positions of virtual slits for computation of indeterminate shear flows. It is also common practice to neglect the effect of longitudinal stiffeners when evaluating the shear flow in cross sections or to consider such effect using a gross approach. In the current work, the computation of shear flow in practical ship transverse sections has been performed. For this purpose an algorithm and subsequent program was developed to automate shear flow calculations which is applicable to any ship type. The results of the program were validated against benchmark examples as well as finite element results. Case studies were performed on VLCC and BC midship sections. The results also prove that consideration of longitudinal stiffeners does not significantly affect the magnitude of the shear stresses developed in the ship plating. © 2015 Elsevier Ltd. All rights reserved. Source

Kurinjivelan P.,Research and Rule Development Division | Kumar R.,Research and Rule Development Division | Samanta A.,Research and Rule Development Division
11th International Symposium on Practical Design of Ships and Other Floating Structures, PRADS 2010 | Year: 2010

SN curves are generally prepared for a unidirectional stress state. But, in practice the welded joints are subjected to combined normal and shear stresses. Therefore, it is essential to provide guideline on how to calculate fatigue life when combined normal and shear stresses are present. In the present paper a new approach based on the resultant of normal and shear stress is proposed for proportional loading conditions. The resultant of the normal and shear stress is taken as reference stress and the effect of angle of inclination of the resultant stress with the normal to the weld toe is taken care by a correction factor. The corrected resultant stress can be used with the SN curve for normal direction. The present method is compared with the experimental data from the available literature (Kim and Yamada, 2005) and with other existing methods. It is observed that the mean interaction curve of present method has better agreement with the experimental data. © 2010 COPPE/UFRJ. Source

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