Research On Design And Direct Analysis Approach To Strength Of Structure Of Independent Type B Prismatic Tank

Independent Type B tank is a type of self-contained tanks that are simple to build and easy to maintain.As the demand for natural gas continues to increase all over the world,LNG carriers have received increasing attention as an important conveyance.Small and medium-sized LNG carriers adopting independent Type B tanks are gradually becoming a hot trend for the development of LNG carrier types because they can transport the natural gas to inland areas that are far from the sea or cannot be covered by pipelines.This paper proposes a design scheme for an independent Type B prismatic tank mounted on the LNG carrier and establishes a set of direct analysis approaches for the structural strength,temperature field,and thermal stress analysis of the tank.The work provides a reference for the design and construction of independent Type B tank in the future.First,a target ship is selected to help design the independent Type B tank for LNG carrier.The designs of the tank hull,insulating layer and support structure are given.Then,according to the classification rules,the motion parameters of the target ship are calculated,and on this basis,the design load on the ship is obtained.Based on the loading and movement status of the target ship and cargo tank,the load cases are selected,including the ultimate limit state and the accidental limit state.Structural strength analysis is performed in two steps to improve computational efficiency.The first step is to calculate the overall strength of the cargo tank,and the second step is to calculate the local strength of the support structure.The stress distributions of the cargo tank and support structure are obtained,and the influence of the variations in plate thickness on the strength of cargo tank is discussed.Next,a simplified heat transfer model of independent Type B tanks is established by defining the cabins.Based on the theory of heat transfer and experimental correlation,the heat transfer coefficient of the cabin is calculated.The thermal equilibrium equations of the cabins are set up.The values of plate thickness,material thermal conductivity,ambient temperature,and heat transfer coefficient are plugged into these equations.A matrix iteration method is developed to obtain the temperature field of the cargo tank.At last,based on the temperature field calculated in the previous step,sequentially coupled thermal-stress analysis of the independent Type B tank is performed by using ABAQUS,and the influence of low-temperature environment on the structural strength of the tank is discussed.Based on the classification rules and commercial software like ABAQUS and MATLAB,this paper establishes the direct analysis approaches for structural strength,temperature field and thermal stress analysis of the independent Type B prismatic tank,which has potential engineering practical value.