## 4 Conclusions  
This study carried out numerical simulations to investigate the seismic responses of both aboveground and underground LNG storage tanks, considering the combined effects of the FSSI. Through employing the VOF and FEM models, this study conducted simulated calculations of two-phase flow for the LNG liquid inside the tanks. Based on this study, the following conclusions can be drawn:  
1. After computing the modes of empty and full LNG storage tanks on the ground, we found that the frequency of full tanks is lower (3.193 Hz) than that of empty ones (3.714 Hz).
2. Due to the soil restraining the structure, the period and height of the liquid sloshing wave in underground tanks are 0.284 m and 1.9 s, smaller than those in aboveground tanks (0.392 m, 4.1 s). Excessive waves will impact the ceiling of the tank, causing adverse effects. Thus, underground full tanks are safer than aboveground full tanks.
3. Under earthquake loads, the deformation, acceleration, and stress of aboveground and underground tanks exhibit distinct patterns. The maximum relative horizontal displacement of an aboveground tank in a full state (136 mm) exceeds that in an empty state (122 mm), indicating that liquid sloshing significantly impacts the tank's structure. The maximum story drift of the underground full tank wall (37 mm) is less than that in an empty tank (41.5 mm). Meanwhile, both the acceleration and displacement of underground tanks are lower than those of aboveground tanks. Due to the influence of soil pressure, the stress in underground tanks exceeds that in aboveground tanks, both in the empty and full states.
4. The seismic response varies under different waves. Soft soil also has an amplifying effect on the deformation and stress response of structures. Therefore, in the seismic response analysis of structures, it is necessary to conduct parametric analysis under various seismic motions to ensure the safe operation of storage tanks under multiple seismic waves.  
Overall, underground tanks offer several advantages, including good seismic performance, land resource conservation, and relatively lower total costs. They are well suited for areas prone to earthquakes or where land resources are limited, making them deserving of wider application. At the same time, considering the groundwater seepage field and the characteristics of low-temperature LNG, further research is needed on the effects of thermal-fluid-structure coupling interactions.  
**Author Contributions**: Conceptualization, Y.Z. and H.L.; methodology, G.J.; validation, Y.Z.; formal analysis, X.X.; investigation, G.J. and M.Z.; resources, X.X.; data curation, Y.Z. and M.Z.; writing--original draft preparation, Y.Z.; writing--review and editing, X.X. and G.J.; visualization, M.Z.; project administration, X.X. and G.J.; funding acquisition, X.X. All authors have read and agreed to the published version of the manuscript.  
**Funding**: National Key R&D Program of China: grant nos. 2023 YFC3806701, 2023 YFC3806702, 2023 YFC3806705; National Natural Science Foundation of China: grant nos. 52038008, 52378408; Science and Technology Innovation Plan of Shanghai Science and Technology Commission: grant nos. 22 dz1203004, 23 YF1451400; State Grid Shanghai Municipal Electric Power Company: grant no. 52090W23000B.  
**Institutional Review Board Statement**: Not applicable.  
**Informed Consent Statement**: Not applicable.  
**Data Availability Statement**: Embargo on data due to commercial restrictions.  
**Conflicts of Interest**: Authors [PERSON], [PERSON] and [PERSON] were employed by the company China Shipbuilding NDRI Engineering Co., Ltd. Author [PERSON] was employed by the company CNOOC Gas and Power Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.