# Seismic Analysis of a Large LNG Tank Considering Different Site Conditions
## 4 Seismic Analysis of a Large Liquefied Natural Gas (LNG) Tank
### Results  
The simulation of a large LNG tank using the SPH-FEM algorithm is entirely performed on an ordinary personal computer. The computer has an Intel(R) Core(TM) i7-8700 CPU @ 4.10 GHz processor and an installation memory of 16.00 GB. Out of the 12 seismic waves in four site classes, the San Fernando seismic wave produces the largest stress on the outer and inner tank under different liquid volume. Therefore, in Figures 7 and 8, the San Fernando wave is selected to compare the maximum stress experienced by the outer and \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Site Class** & **Event** & **Station** & **Time** & **Vs30** \\ \hline \multirow{3}{*}{I} & Ground Motion (GM) 1: Tangshan Aftershock & Qianan Lanhe Bridge & 1976.8.6 & - \\  & GM2: Imperial Valley & Sup-Superstition Mountain & 1979.10.15 & 362 \\  & GM3: San Fernando & Fsd-Santa Felicia Dam & 1971.2.9 & 389 \\ \hline \multirow{3}{*}{II} & GM4: Imperial Valley-01 & El Centro Array9 & 1940.518 & 213 \\  & GM5: Northridge-01 & Northridge-Sucitory & 1994.117 & 281 \\  & GM6: Kerr Country, California & Taft Lincoln School Tunnel & 1994.117 & 385 \\ \hline \multirow{3}{*}{III} & GM7: Kobe & Nishi-Akashi & 1995.1.16 & 609 \\  & GM8: Hollister & Holl Diff Array \#1 & 1986.1.26 & 215 \\  & GM9: Landers & Indo-Coachella Canal & 1992.6.28 & 339 \\ \hline \multirow{3}{*}{IV} & GM10: Tangshan Aftershock & Tianjin Hospital & 1976.11.15 & - \\  & GM11: Cape Mendocino & Fortuna-Fortuna Blvd & 1992.4.25 & 457 \\  & GM12: Loma Prieta & Alameda Nas Hanger & 1989.10.18 & 190 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Details of 12 ground motions. Figure 6: Acceleration response spectra for ground motions and for code specifications; (**a**) Site class I, (**b**) Site class II, (**c**) Site class III, (**d**) Site class IV. inner tank at different liquid volumes. In addition, to compare the maximum stress at different site conditions in Figures 9 and 10, each site is represented by one of the three seismic waves that produces the greatest stress on the outer and inner tank. Therefore, Taft, Hollister, and Loma Prieta are selected for Class II, Class III, and Class IV, respectively. Furthermore, when comparing the four different site conditions, each model is filled with 100% LNG, which produces the greatest von Mises stress on the outer and inner tank compared to other liquid volumes. In general, stress distribution on the outer tank exhibits a symmetrical trend about the X- and Z-axis. Figure 7 shows the respective maximum stress of the outer tank with LNG levels of 25%, 50%, 75% and 100%. Under the same liquid level, the level of stress on the outer tank is the largest in Class I, followed by Class II, Class III and Class IV, though their values are relatively similar. In addition, under the same site class, the stress distribution on the outer tank is minimally affected by different liquid levels. On the other hand, the location of maximum stress on the outer tank changes depending on liquid level. With LNG liquid levels of 25% and 50%, the maximum stress of the outer tank is located at the dome; however, with LNG liquid levels of 75% and 100%, the maximum stress of the outer tank is at the bottom of the tank. This phenomenon occurs because gravity plays a more important role than pressure with LNG liquid levels of 25% and 50%, and pressure at the bottom increases at a much faster rate relative to the dome as liquid level rises. Furthermore, the maximum stress of the outer tank is nearly identical at the liquid level of 25%, 50%, and 75%, but the maximum stress of the outer tank increases significantly from 75% liquid level to 100% liquid level. As a result, more extensive design  
Figure 7: The maximum von Mises stress distribution on the outer tank at different LNG liquid levels under San Fernando seismic wave; (**a**) At 25% full, (**b**) At 50% full, (**c**) At 75% full, (**d**) At 100% full. and analysis considerations should be paid to the dome and bottom of large LNG tanks depending on the liquid level.