Study On Structural Lightweight Design Of Oil Tankers

In April 2006,the Common Structural Rules (CSR) was implemented by the International Association of Classification Societies (IACS) in order to unify the difference and the security level of ship structure rules between Classification Societies. CSR was divided into two parts, CSR for Double Hull Oil Tankers and CSR for Bulk Carriers, which were compiled by different IACS members, and the technical route and technical background are different in the aspect of common questions. In order to solve the incongruity of the two parts, Harmonised Common Structural Rules for Oil Tankers and Bulk Carriers (HCSR) was compiled by IACS, added Goal Based Standard (GBS) requirements. Consequently, the standard of HCSR is higher, and the contents of HCSR are more comprehensive than CSR.Due to the publishment of HCSR, the weight of ship will increase due to the changed rule requirements and analysis criteria. According to this issue, the Very Large Crude Carrier(VLCC) that meets CSR standard having a deadweight capacity of about 308,000 tons is chosen as the example of Double Hull Oil Tanker. Based on HCSR, the lightweighting researches were conducted, and main contents were as follows:(1) According to the direct strength anslysis of HCSR, yielding strength and buckling strength were checked seperately based on cargo hold finite element analysis carried out for VLCC. Based on the analysis results, the influence on structural weight of Oil Tankers is analysed.(2) Based on rule calculation of HCSR, the mathematical model of midship section structure optimization and design was established, using the minimum section area as the object, meeting the constraint condition of hull girder strength, hull local scantling and slenderness requirements. The midship section optimization and design were carried out by three optimization algorithms, Multi-Island Genetic Algorithm, Simulated Annealing and Particle Swarm Optimization.(3) Based on direct strength anslysis, the optimization and design of cargo hold finite element model, built by Patran, were carried out by the general optimization software Isight,integrating MSC. Patran/Nastran. The mathematical model of whole cargo hold structure optimization was established, using the minimum weight of middle cargo hold as the object,meanwhile meeting the constraint condition of yielding strength and buckling strength in direct calculation.(4) Exploratory study on how the stress homogenization can influence the ship weight was carried out, but the corresponding relation between the stress homogenization and the ship weight were not given out and it is necessary to be researched in future work.