Structural Optimization of Mid-ship Section of Double Hull Tanker Considering Lifecycle Holistic Risk

Recently, structural design of a ship considering various risks in the lifecycle of the ship has become more and more important. In the committee IV.1 (Design Principle and Criteria) of the International Ship and Offshore Structural Congress (ISSC), it is discussed that sustainability of ships and marine structures should be evaluated when the structure is constructed based on assessment of "holistic risk" which includes assessment of safety, environment, social responsibility and etc. Based on the concept of holistic risk evaluation, the authors carried out lifecycle structural optimization of mid-ship section of a double hull tanker in this study. For the evaluation of environmental risk, the method of life cycle assessment (LCA) is introduced to evaluate the CO₂ emission. Also, evaluation of environmental pollution is carried out by using oil outflow calculation shown in the MARPOL. For the evaluation of the risk of failure, the authors carried out structural reliability analysis of longitudinal strength of the ship. Then, the authors carried out the following five optimization problems, (1) Minimization of construction cost, (2) Maximization of life cycle benefit (LCB) considering the risk of oil outflow, (3) Maximization of LCB considering the risk of CO₂ emission, (4) Maximization of LCB considering the risk of failure, and (5) Maximization of LCB considering the holistic risk. Finally, the optimum solutions of these five problems are compared to discuss about the advantage of the design of ship structures based on the holistic risk evaluation.