Fluid-Solid Interaction And Structural Optimization For LNG Tank Container Based On Railway Impact Test

Liquefied natural gas referred to as LNG is a colorless fluid in liquid conditions,which is formed after pretreatment and a series of ultra-low temperature liquefaction of natural gas,and its main component is methane,which is a flammable and explosive medium.Tank containers is the main transportation equipment of LNG when it is transported by rail.LNG tank container is a type of mobile pressure vessel that places high vacuum double insulated cryogenic liquid storage tanks within the framework of international standard containers.In the process of railway transportation,due to the heavy longitudinal impact of the vehicle loaded with LNG tank container in the daily shunting or slipping operation,as well as when the train is suddenly started and emergency braking is made.The external longitudinal instantaneous impact force will make the vehicle and tank state of motion change sharply,and at the same time stimulate the transient disturbance of the fluid medium in the tank.The impact force caused by the acceleration change of the medium in the tank.The impact force caused by the shaking of the medium will change the stress state of the structure.The structure may cause local structural cracking,deformation,etc.,and even lead to LNG leakage,which is a safety hazard.In order to ensure the safety of railway transportation of LNG tank containers,the structural strength of the tank container must meet the requirements of the railway impact test.However,the actual impact test cost is high and the cycle is long,and it is necessary to calculate the dynamic response of the fluid-solid interaction strength under the action of railway shock load with the computer-aided simulation.Existing tank strength simulation related research usually uses traditional methods to equate dynamic problems with static problems for simulation analysis.The effects of the fluid medium in the tank are treated as static loads,applied to the area of action in the form of additional equivalent inertial forces.In fact,in railway transportation,the tank is caused by external impacts to change the movement of the fluid medium in the tank,and the fluid reacts to the structure,which belongs to the fluid-solid interaction kinetic impact problem over a longer impact period.Therefore,it is not reasonable to analyze the dynamic problem by static methods,on the one hand,it cannot truly reflect the time domain response of the impact process;on the other hand,it cannot accurately simulate the fluid-solid interaction impact of the medium in the tank and the tank structure in the actual process.In this paper,the simulation of the fluid-solid interaction intensity of the LNG tank is carried out taking a company’s CGBIS-40-0.62-1AA LNG tank container as an example,Which combined with the finite element solution method of vehicle dynamics and fluidsolid interaction.This includes the following:Firstly,the multibody dynamics software SIMAPACK was used to establish a tank container dynamics model to simulate the railway impact test.The acceleration time domain curve and impact response data of the tank container in the process of railway impact test are obtained by solving the established dynamic model,and compared with the actual impact test data,the reliability of the tank container impact test dynamic model and the impact response result is verified.Secondly,the ANSYS platform is used to create finite element models of the LNG tank container structure and the media in the tank container separately for tank flowstructure interaction calculations.According to the design parameters and patterns provided by the manufacturer,the structure is simplified,and a three-dimensional solid model of the LNG tank container structure is established.The structural finite element model includes defining material properties,loads and constraints,etc.,and the fluid part includes defining basic parameters,motion parameters and coupling interfaces.Verify the accuracy of the finite element model by calculating the hydrostatic pressureThirdly,the impact acceleration time domain response obtained by the tank container impact test dynamic model is used as the impact load input for finite element calculation,and the tank container strength simulation calculation is carried out by single and bidirectional fluid-solid interaction methods,respectively.The calculation results obtained by the simulation methods of single and bidirectional fluid-solid interaction are compared with the actual experimental stress results,and the bidirectional fluid-solid interaction results are closer to the reality.According to the results of bidirectional fluidsolid interaction,the maximum stress and maximum deformation of the tank container in the whole impact process are analyzed,and the strength is checked to identify the weak parts of the force.Finally,According to the two-way coupling calculation results,the structure design optimization of the frame structure is carried out.Reasonable sampling is performed by the design of experiments method,the design variables initiate the size change of the frame model,and the fluid-solid interaction calculation is performed on the sample scheme,and the variable parameters are selected based on the generated response surface to determine the design space.The multi-objective genetic algorithm is used to obtain the optimal design size,which meets the lightweight design requirements while achieving the purpose of reducing stress,and improves the overall stress condition of the framework.In the tank container design stage,the impact load of fluid-solid interaction simulation is obtained by comparing and accurate dynamic modeling of impact test,and the impact of railway impact on the strength of fluid-solid interaction of LNG tank container is faithfully reflected.The structural optimization design can effectively predict the impact strength of the tank container and obtain the information required for its structural improvement,shorten the development,design,testing and other cycles,and save test costs and time costs.This study has practical significance for ensuring the safety of LNG railway transportation in China,and provides ideas for the structural strength assessment and design improvement of LNG container and the railway impact test in the future.