Research Of Optimization For Slant Transitional Plate In Wing Tank Of VLCC

Oil tanker is one of most famous ship in the world and is the foundation of ship building. As the largest ship in oil tankers, VLCC (short for Very Large Oil Carrier) has a large capacity and better economical efficiency. It becomes the most important ship in oil transportation.By research, in recent years,70 percent of ships whose length is over 200 meters were broken by fatigue problems. What's more, fatigue problem in top corner and bottom corner are outstanding. The design of top corner and bottom corner structure is quite important especially for large ships and the optimization of the slant transitional plate in wing tank of VLCC is necessary. The objective ship of this study is a 30.8 million tons VLCC, the main works are as follow:(1) Analyze the rules about fatigue strength ruled by CSR and introduce nominal stress method based on regulation and hot spot stress method based on finite element method.(2) Carry out two optimization method:arrange longitudinal stiffeners at tip of arc plate and arrange longitudinal stiffeners at center of arc plate. Compare the optimization method and the traditional method and get the comparison results about the fatigue strength, structure arrangement and the construction method. Calculate the fatigue results by regulation method and finite element method to prove the improvement of the fatigue strength of the corner.(3) Optimize the top corner and bottom corner according to the construction method and get a better construction method.(4) By comparison, the new plan can improve stress concentration problem, improve fatigue strength, more easy to be constructed, be more accurate and can also reduce the cost. What's more, arranging longitudinal stiffeners at center of arc plate is better than arranging longitudinal stiffeners at tip of arc plate. Arranging longitudinal stiffeners at center of arc plate can improve fatigue strength obviously.(5) Analyze the construction method of arc plate. This method can be applied to the connection of inner shell or slant inner shell with horizontal girders. The feasibility analysis is carried out according to the construction.Fatigue strength at corner is an important problem of large ship. The fatigue strength is related with the safety and the service life of a ship. What's more, the construction of corner is difficult. The optimization method carried out in the title can improve the fatigue strength and be more easily to construction and reduce the cost. So the optimization of the structure is very necessary, which can provide technical support for design and construction of VLCC.