Analysis On Structural Statics And Dynamics Of Large Vacuum Powder Insulated Cryogenic Spherical Tank

With the rapid development of modern economy,large-scale vacuum powder insulated cryogenic spherical tank has been widely used in petrochemical,urban gas,aerospace and metallurgy fields.The inner vessel of the spherical tank stores cryogenic liquid and bears liquid pressure,the jacket space is vacuumized and the outer shell is at ambient temperature.At the same time,the thermal load,structural load and possible seismic load need to be considered,so the force is more complicated.The safety of each component of the spherical tank is related to the smooth operation of the whole process.The thermal insulation jacket in the large-scale vacuum powder insulated cryogenic spherical tank has a good thermal insulation effect,and it will also affect the deformation and force of the spherical tank.At present,the research on the thermal insulation jacket mainly focuses on the thermal insulation performance,while the research on the static and dynamic characteristics of the spherical tank structure is less.In addition,the temperature difference between the inner vessel and the outer shell under normal operating conditions and the direction of the seismic force in the event of an earthquake will all affect the performance of each component of the spherical tank.Based on this,the finite element method（FEM）is used to analyze the structure statics and dynamics of a 500 m3vacuum powder insulated cryogenic spherical tank,the influence of the thermal insulation jacket and thermal load on the static characteristics and the influence of the thermal insulation jacket and seismic force direction on the dynamic characteristics of the spherical tank were studied.The main conclusions are as follows:（1）According to the design principle of limit state,the structural statics and dynamics analysis of the spherical tank are carried out by selecting the more destructive ULS combined working conditions,so the structural strength of the spherical tank under the most dangerous condition is obtained.When the strength of the spherical tank is checked,the static strength and stability problems of the spherical tank can be solved by the limit load method and the stress classification method respectively.（2）The main factors affecting heat leakage of the spherical tank were studied.When the piping system is not considered,the external heat mainly leaks into the inner vessel through the thermal insulation jacket,glass fiber reinforced plastic（FRP）and tension strap.Taking the storage of LO₂ as an example,the heat leaking into the inner vessel through the above three ways accounted for 78.05%,21.65%,and 0.30%of the total heat leakage of the spherical tank respectively.The thermal insulation jacket and FRP are the main components that affect the heat leakage of the spherical tank.（3）The models of spherical tank with and without thermal insulation jacket were established,and the influence of the thermal insulation jacket and thermal load on the static characteristics of each component of the spherical tank were analyzed.When the effect of thermal load is considered,the existence of the thermal insulation jacket reduces the maximum displacement deformation of each component of the spherical tank;the thermal insulation jacket has a small effect on the inner vessel and the tension strap,but reduces the stress of the outer shell,FRP and pillar,and makes the stress change along the analysis path more gentle.For the spherical tank model with thermal insulation jacket,the existence of thermal load increases the maximum displacement deformation of each component of the spherical tank;In addition to reducing the stress of the outer shell far away from the stress concentration position,the thermal load also reduces the equivalent stress values of the inner vessel,FRP,tension strap and pillar in varying degrees,and makes the stress change along the analysis path more intense.（4）The modal analysis of the spherical tank models with and without insulation layer was carried out.The vibration of the spherical tank occurs at the shell part in the low-order mode,and occurs at the tie rod part in the middle and high-order modes,and the displacement deformation of the shell is less than that of the tie rod.（5）Based on the modal analysis,the seismic response analysis was carried out,and the influence of the direction of the seismic force and the thermal insulation jacket on the dynamic characteristics of the spherical tank was studied.Under the action of seismic load,the displacement deformation of the spherical tank mainly occur in the horizontal direction,and there is a stress concentration at the connection part of the upper ear plate and the pillar.Compared with the spherical tank mid-span model,the maximum displacement deformation of the centering model in the horizontal and vertical directions increased by 29.86%and 30.71%respectively,and the maximum equivalent stress value has increased by 19.73%.Therefore,the displacement deformation and stress distribution of the mid-span model are better than those of the centering model.Compared with the model without thermal insulation jacket,the maximum displacement deformation of the model with thermal insulation jacket in the horizontal and vertical directions are reduced by 26.17%and34.82%respectively,and the maximum equivalent stress value is reduced by 5.90%.Therefore,the existence of thermal insulation jacket can effectively reduce the displacement deformation and equivalent stress of the spherical tank under the seismic response.