## 5 Structural Strength Assessment of the LNG CCS  
This study has been carried out to confirm that the use of the suggested method with appropriate parameters for the sloshing assessment provides an effective method of investigating LNG CCS design. Figure 15 shows the fluid motion and volume fraction of the fluid column at impact time in the FSI analysis. In Figure 15, the red region is the volume fraction of the LNG fluid column, and the blue indicates the volume fraction of the gas region. The fluid column shows the process of impact and diffusion over time. The fluid column uniformly impacts the interface. The maximum pressure induced by the fluid column model is approximately 0.8 MPa with a duration of 0.0067 s, as shown in Figure 16. The pressure history shows that after the maximum pressure is generated, the subsequent pressure due to the fluid force is generated. Therefore, sloshing fluid flow modeled as incompressible fluids present a need for a compressible flow model for fluid and gas. This is possible since the CFD approach allows us to specify an order that satisfies the dynamic behavior. When calculating the structural response of Mark III CCS by the FSI model, the results for each timestep are shown in Figure 17. The maximum equivalent stress occurred in the mastic member connected with the hull, with a maximum of about 3.3 MPa and a maximum deformation of about 2.6 mm. In addition, the results were compared with the structural safety review criteria presented in the ABS guidance to verify the structural safety of the Mark III LNG CCS applied through the FSI analysis results. According to the guidance, the structural safety reviews of LNG CCS are evaluated by each structural member: plywood, R-PUF, and mastic [6]. Table 1 summarizes the maximum structural response for each member calculated through FSI analysis. In addition, the values shown in bracket \"()\" in Table 1 are the safety reference values for each member presented in ABS guidance. The results showed that all of the calculated results met safety standards.  
Figure 14: Local FSI model using a fluid column: (**a**) schematic configuration of the FSI model; (**b**) volume fraction of the multi-phase in fluid domain.  
Figure 16: Max. pressure history from the fluid column model.  
Figure 15: Local FSI model using a fluid column: (**a**) at 0.001 s; (**b**) at 0.002 s; (**c**) at 0.005 s; (**d**) at 0.008 s; (**e**) at 0.01 s; (**f**) 0.015 s.  
Although a simple LNG CCS model was applied to calculate the structural response by the FSI analysis, the validity of the strength evaluation process of LNG CCS was reviewed using the proposed FSI model.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Max. Stress [MPa]**} & \multicolumn{2}{c}{**Max.**} \\ \hline  & **Equivalent** & **Horizontal** & **Vertical** & **Shear** & **Deformation** \\ \hline Whole CCS & 3.32 & - & - & - & 2.6 \\ Plywood & 6.8 & 0.3 (40) & 1.21 (2) & 1.32 (2.8) & \\ R-PUF & 0.21 & 0.26 (2.4) & 0.36 (1.4) & 0.06 (1.4) & \\ Mastic & 1.69 (15) & - & - & - & 2.6 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Structural responses review of Mark III CCS by ABS guidance [6].  
Figure 17: Von-Mises stress distribution and max deformation in CCS: (**a**) at 0.001 s; (**b**) 0.002 s; (**c**) 0.005 s; (**d**) 0.008 s; (**e**) 0.010 s; (**f**) 0.015 s.