Safety Life Assessment of Thick High Tensile Steel Plates onLarge Container Ships

In this paper， the underwater vibration and sound radiation of perforated plates are discussed employing the finite element method and the indirect boundary element method. Firstly， the inherent frequency of perforated plates is calculated both in air and water. It is seen that the frequency of perforated plates in air is lower than that for non-perforated ones： as the opening area increases， most of the inherent frequencies decrease. However， in water， the inherent frequency of perforated plates is higher than that of non-perforated ones， sFatigue is one of the main damage modes of ships and ocean engineering structures. The application of high tensile steel makes the fatigue problem in ship hulls even more severe. For large container ships whose decks are constructed with thick high tensile steel plates， it is essential to study the safety life assessment of those parts with welding defects. In this paper， the fatigue loading spectrum is generated from a long-term distribution which obeys the two-parameter Weibull distribution， and the unique crack growth rate model is adopted to predict the crack size at a certain given time. By combining the predicted crack size， the calculation of stress intensity factor， and the reference stress in Failure Assessment Diagram （FAD）， a procedure to estimate the safety life of a cracked thick high tensile steel plate is presented. The corresponding problem in a container ship is then investigated via a calculation program. Finally， the influences of the fatigue loading spectrum on damage tolerance and fatigue life are analyzed. Results indicate that both the length of the fatigue load repetition period as well as the shape parameter of Weibull distribution greatly affect the fatigue safety life.