Stress Analysis And Optimal Design Of Structures For Marine Cryogenic Tanks

Liquefied natural gas is clean and efficient,gradually replacing traditional diesel gasoline as fuel and widely used in transportation industries such as automobiles and ships.Marine cryogenic fuel tanks are important containers for storing liquefied natural gas fuel,and the working conditions are particularly complex when acting at sea.Therefore,it is of great significance to analyze the heat transfer,strength and fatigue of marine cryogenic fuel tanks,as well as to carry out reasonable optimization design.In this paper,a marine cryogenic fuel tank trial-produced by some cryogenic equipment company of Beijing is used as the research object.Workbench software is used to model the marine cryogenic fuel tank with a strap support structure,and perform finite element calculations and analysis of steady-state heat transfer and structural statics.The thermal stress intensity of marine low-temperature fuel tanks is analyzed,and the unreasonable design of the structure is changed and optimized.Due to the complex working conditions of the ship while operating at sea,the collision load analysis of the optimized fuel tank was carried out,and the fatigue accumulation damage of the marine cryogenic fuel tank was calculated according to the standards of the classification society.(1)Under the influence of temperature load and pressure load,a model of thermal-structural coupling of low-temperature fuel tank for marine is established,and the overall stress analysis of fuel tank is carried out.The results show that the virtual stress value at the connection between the horizontal pull belt and the reinforcement ring reaches 1632.2MPa,the analysis is that the pull belt support structure of the marine cryogenic fuel tank is the main structure of thermal conduction of the environment and contenter medium LNG,and both ends of the pull belt support structure are welded in a fixed way to the inner container and the reinforcement ring,so the pull belt support structure bears the effect of large temperature differential stress,and the structure needs to be improved and optimized.(2)In the improvement of the pull belt support structure of marine cryogenic fuel tank,the "U" structure,"Ω" structure and "double Ω" structure are mainly considered,and the overall finite element analysis of these three structural types of marine cryogenic fuel tank is carried out.The final results show that the three structures reduce the stress by 48.42%,80.65% and 84.94%,respectively,of which the "double Ω" structure is the best structure that can effectively reduce the pull band support temperature difference stress.The "double Ω" structure is optimized through parametric design,and the optimal size of the "double Ω" structure is calculated.The maximum stress of the optimized transverse tension band is located on the inner surface near the center of the "Ω" circle of the inner container.The value is 202.19 MPa,which is a local stress,and does not exceed the yield limit of 207 MPa of the material.It meets the structural strength requirements,but the necessary fatigue analysis of the marine fuel tank is required.(3)According to the collision conditions stipulated in the Rules for Natural Gas Fueled Ships,the marine low-temperature fuel tank is analyzed by finite element.The results show that under the condition of collision load,the influence of the outer container is less,while the maximum stress of the contenter head,the lateral pull belt and the head pull belt is 250.09 MPa,281.07 MPa and 408.94 MPa,all exceed the yield limit of the material 207 MPa,but below the material’s anti-pull limit 517 MPa,but are located on the local surface,and the cross-section is still in the elastic stage,so it can be seen that in the collision conditions under the action of this extreme load,Part of the structure of the marine cryogenic fuel tank will yield,but will not break.The structure meets the requirements of the crash test.(4)According to the fatigue analysis method stipulated in the standard of the Ship Structure Fatigue Intensity Guide of the China Classification Society,the fatigue accumulation damage under the operating conditions of the marine cryogenic fuel tank in the specification is calculated.The results showed that the fatigue cumulative damage degree of contenter and outer container was 0.0187 and 0.0062 respectively,and the fatigue accumulation damage degree at lateral pull belt and head pull belt was0.466 and 0.179,respectively,and the value was lower than 0.5,and the fatigue verification results were in line with the standard requirements.In this paper,steady-state heat transfer analysis,thermal stress intensity analysis and fatigue analysis are carried out on the finite element method of marine low-temperature fuel tank application,the results of which can provide theoretical basis for enterprise products to pass the evaluation of relevant institutions,as well as theoretical support for engineering applications.