Numerical Simulation Of Temperature Field And Study On Cutting Efficiency For Emergency CO₂ Jet Cutting Of Accident Ships

With the rapid development of social and economic society,the demand for dangerous and hazardous goods transportation has increased annually in various industries during production.As a result,the risk of underwater navigation by ships in river channels is also increasing.In cases of ship accidents,it is necessary to urgently transport goods and rescue trapped personnel,and it is necessary to quickly cut the ship body.Therefore,urgent emergency cutting technology with high efficiency and safety is urgently needed.Currently,liquid carbon dioxide jet cutting has gradually received attention from people due to its technical advantages of high cutting efficiency,no residue,and low risk during cold cutting.In order to better explain the destruction characteristics and cutting efficiency of liquid carbon dioxide jet cutting of high-temperature steel,this article uses a modeling software to simulate the heat transfer and steel cutting process of liquid carbon dioxide jet striking high-temperature steel.This provides a theoretical basis for emergency rescue cutting technology in the emergency treatment of underwater ships in river channels.The main work and conclusions are as follows:（1）Using FLUENT finite element software to simulate the liquid carbon dioxide jet flow field characteristics,it is concluded that the jet velocity increases with the increase of nozzle inlet pressure,when the nozzle inlet pressure is 30MPa,35MPa and 40MPa respectively,the maximum velocity of the jet is 284.4m/s,307.6m/s and 330.1m/s respectively,it can be seen that for every 5MPa increase in the inlet pressure,the jet The velocity of the core increases by an average of 7.73%.The pressure value also increases gradually with the increase in nozzle inlet pressure,but the increase gradually decreases.（2）Liquid carbon dioxide jet impact steel plate within a short period of time,high temperature steel plate surface temperature difference will reach a large,the internal temperature gradient increases,along the thickness direction,the cooling rate decreasing trend is obvious.With the passage of time,the temperature of the surface layer of the steel plate decreases,and the heat exchange capacity of the jet is weakened,the internal heat conduction occupies a dominant role,the internal temperature distribution of the steel plate tends to be uniform,the internal temperature gradient will gradually decrease,the cooling rate in the direction of the thickness of the steel plate gradually decreases,the decreasing trend becomes slower.（3）LS-DYNA software was used to simulate the damage process of high temperature steel plates cut by liquid carbon dioxide jets.In the early stage of steel plate damage,the stresses are concentrated at the side edges;in the middle stage of damage,the maximum stress area gradually concentrates and increases in the normal direction,and the stresses weaken and dissipate in a mushroom-like shape;in the late stage of damage,the SPH particles completely pass through the steel plate,and the damage area is about 1.4 times the size of the jet diameter.The higher the steel plate temperature,the higher the normal stress of the jet cutting steel plate,the deeper the erosion depth,the better the shape of the cut,but the damage range of the steel plate first increases and then decreases.（4）As the jet pressure increases,the time taken by the liquid carbon dioxide jet and the water jet decreases linearly and the time difference between the two increases gradually,indicating that the higher the jet pressure,the better the cutting performance of the liquid carbon dioxide jet compared to the water jet when cutting targets.In the range of 500MPa-800MPa,the average increase in cutting efficiency of the liquid CO₂ jet is14.2%for every 100MPa increase in jet pressure.In the range of 2mm-5mm target spacing,there is an optimum target spacing of 4mm,which results in the shortest cutting time and highest cutting efficiency.