Analysis On The Structure Dynamic Of Large-scale LNG Storage Tank

LNG is a kind of safe, clean, economic, efficient and high-quality energy, and when the raw natural gas is pretreated and cooled to-162? at atmospheric pressure, LNG will be obtained. LNG volume is only 1/625 of nature gas, so LNG has the advantages of convenient storage and transportation, and has become an important application form in the natural gas storage field. In order to meet the LNG extensive use needs, LNG storage capacity is growing, and as the LNG storage device, the volume of LNG storage tank will also increase accordingly. Based on the investigation results on the damage extent of the earthquake to the large-scale LNG storage, the local buckling of tank wall, which includes the elephant foot instability and the diamond instability, is the most common damage form, and with the increasing of the tank volume, the influence of the earthquake to the tank safety is more serious. Once the large-scale LNG storage tank is damaged under the seismic action, the serious consequences will be caused, so the study on the safety of large-scale LNG storage tank is particularly important. For large-scale LNG storage tank, the thermal insulation layer is taken as the mian component, and now the study on the influences of the thermal insulation layer to the thermal insulation of storage tank is the mian, then, the study on the influences of the thermal insulation layer to the structural dynamical characteristic of storage tank is less. In addition, the seismic response of large-scale LNG storage tank under the horizontal seismic action is widely discussed, and the seismic responses of storage tank under the vertical seismic action as well as under the horizontal and vertical seismic actions are rarely analyzed. The working combination in the ultimate limit state was selected based on GB50009-2012 Load code of building structures, then, the structural dynamical characteristic of large-scale LNG storage tank was analyzed, and the influences of thermal insulation layer to the structural dynamical characteristic of large-scale LNG storage tank were studied, and the seismic responses of large-scale LNG storage tank under the vertical seismic action as well as under the horizontal and vertical seismic actions were also discussed.The 2×104m3 LNG storage tank of single capacity, which is supported by domestic certain LNG storage and distribution station, was set as the research object, and the models with thermal insulation layer and without thermal insulation layer were established, respectively, and the modal analysis of the two models were carried out. The result shows that the inherent frequency and the maximum displacement deformation of the storage tank with thermal insulation layer are all bigger than without thermal insulation layer, and the vibration of the storage tank with thermal insulation layer mainly occurs in the vault and without thermal insulation layer mainly occurs in the tank wall.On the basis of the modal analysis, the seismic responses of the storage tank with thermal insulation layer and without thermal insulation layer under the horizontal seismic action were analyzed, respectively. The result shows that under the horizontal seismic action, for the storage tank with thermal insulation layer, the displacement deformation and the equivalent stress in the horizontal and vertical directions all occur in the vault, and for the storage tank without thermal insulation layer, the displacement deformation and the equivalent stress in the horizontal and vertical directions occur in the valut and the tank wall and the maximum equivalent stress occurs in the bottom of the tank wall and the displacement deformation and the equivalent stress are all bigger than with thermal insulation layer. Therfore, under the seismic response the thermal insulation layer changes the displacement deformation position and the stress distribution, and reduces the displacement deformation and the equivalent stress, then, for the storage tank with thermal insulation layer, the occurring positions of the displacement deformation and the stress avoid the buckling failure postions in the bottom of the tank wall and the tank safety is furtherly ensured.The seismic response of the storage tank with thermal insulation layer under the vertical seismic action was discussed. The result shows that for the storage tank with thermal insulation layer, the maximum displacement deformations in the horizontal and vertical directions as well as the equivalent stress under the vertical seismic action are all less than under the horizontal seismic action, so on the influences of seismic action, the horizontal seismic action is the main factor of influencing the structural dynamical characteristic of large-scale LNG storage tank.Besides, the seismic responses of the storage tank with thermal insulation layer under the horizontal and verstical seismic actions were also analyzed. The result shows that for the storage tank with thermal insulation layer, the occurring positions of the displacement deformation and the equivalent stress under the horizontal and vertical seismic actions are basically the same with under the horizontal seismic action, and only slightly numerically bigger than under the horizontal seismic action, once again, the horizontal seismic action is the main factor of influencing the structural dynamical characteristic of large-scale LNG storage tank.The study results provide the theoretical reference basis for the design and the check of large-scale LNG storage tanks, and ensure the safe operation of the actual tanks, and have the great significance to the localization design and construction of large-scale LNG storage tanks.