Oil Tanker Structure Node Design Improvement Based On CSR Fatigue Life Requirement

The Common Structural Rules have been developed in response to a consistent and Persistent call from industry for an increased standard of structural safety, which have been entered into force since 1st April, 2006. The rules for double hull oil tankers were jointly developed by Lloyd's Register(LR), American Bureau of Shipping(ABS) and Det Norske Veritas(DNV). The new rules have introduced now the most forward design idea, widely has used the newest achievements in scientific research, in which fatigue life appraisal is the unified standard of fatigue analysis. Therefore, fatigue life appraisal research is of importance.Based on CSR criteria and the fatigue strength theory, the paper makes a thorough study on the fatigue assessment method in the new standard and checks the fatigue strength of typical joints in the tanker structures. The accumulated fatigue damage is calculated according to S-N curve and Miner linear cumulative damage theory; and the long-term distribution of the structural stress range is assumed the composition of Weibull force ranges. This method mainly includes the calculation of wave-induced loads and the range of each stress component, the composition of stress range and the analysis of fatigue accumulating damage.The object of this research is the 26000t Double hull oil tank, whose fatigue life appraisal is analyzed by nominal stress method. By analysis and arrangement on the factors and positions of the fatigue crack from all kinds of ships, the key joints of the side shell, the ship bottom and their connection are analyzed and designed, and the joint design is optimized to reduce the high stress and improve the stress concentration, so that anti-fatigue performance of the hull will be better. Also, the joint form are improved and compared based on calculation analysis. The best sizes in different regions are given out respectively in considering design code for the purpose of saving materials, and the joint form of soft toe and back soft bracket plate have positive significance of anti-fatigue performance.Finally, based on the summary of this research, some valuable conclusions and suggestions to design and research are put forward. The prospects of research direction and working contents are also discussed.