## 4 Results and Discussion
### FE Results  
The equivalent von Misses stress contour for various cases extracted from the FE simulation is shown in Figure 3. The results indicated that among the studied materials for compartments, the highest von Misses stress was created in the steel compartment. The highest intensity of tension was observed at the edges of the walls. This means that these areas are more sensitive and should be given more attention in the design stage.  
The deflection of different structures is demonstrated in Figure 4. From this figure, it is clear that the maximum deflection was generated in the compartment made of aluminum and at a depth of 20 m. The strength of the structure decreased as deformation increased. Therefore, it can be said that the parts that have more deformation are more exposed to damage.  
The results obtained from FE analysis, including critical stress and value of deformation, are summarized in Table 5.  
The first three shape modes of the buckling phenomenon of different materials are shown in Figure 5. The results reveal that the shape mode is independent of material. Therefore, the type of buckling can be specified using the buckling mode shapes in the structure.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Material** & **Critical Value of N** & \(n\) & \(m\) & \(a\) & \(b\) & \(t\) & **No. Sheet** \\ \hline \multirow{8}{*}{Steel} & \(3.01\times 10^{7}\) & 1 & 1 & 798 & 868 & 38 & 1 \\ \cline{2-8}  & \(7.16\times 10^{7}\) & 2 & 1 & 798 & 868 & 38 & 2 \\ \cline{2-8}  & \(1.8\times 10^{7}\) & 1 & 1 & 868 & 1522 & 38 & 3 \\ \cline{2-8}  & \(3.2\times 10^{7}\) & 2 & 1 & 868 & 1522 & 38 & 4 \\ \cline{2-8}  & \(2\times 10^{7}\) & 1 & 1 & 798 & 1522 & 38 & 5 \\ \cline{2-8}  & \(3.4\times 10^{7}\) & 2 & 1 & 798 & 1522 & 38 & 6 \\ \hline \multirow{8}{*}{Aluminum (depth of 20 m)} & \(6.5\times 10^{6}\) & 1 & 1 & 798 & 868 & 32 & 1 \\ \cline{2-8}  & \(1.5\times 10^{7}\) & 2 & 1 & 798 & 868 & 32 & 2 \\ \cline{2-8}  & \(3.9\times 10^{6}\) & 1 & 1 & 868 & 1522 & 32 & 3 \\ \cline{2-8}  & \(6.8\times 10^{6}\) & 2 & 1 & 868 & 1522 & 32 & 4 \\ \cline{2-8}  & \(4.5\times 10^{6}\) & 1 & 1 & 798 & 1522 & 32 & 5 \\ \cline{2-8}  & \(7.3\times 10^{6}\) & 2 & 1 & 798 & 1522 & 32 & 6 \\ \hline \multirow{8}{*}{Aluminum (depth of 60 m)} & \(3.2\times 10^{7}\) & 1 & 1 & 798 & 868 & 55 & 1 \\ \cline{2-8}  & \(7.7\times 10^{7}\) & 2 & 1 & 798 & 868 & 55 & 2 \\ \cline{1-1} \cline{2-8}  & \(1.9\times 10^{7}\) & 1 & 1 & 868 & 1522 & 55 & 3 \\ \cline{1-1} \cline{2-8}  & \(3.4\times 10^{7}\) & 2 & 1 & 868 & 1522 & 55 & 4 \\ \cline{1-1} \cline{2-8}  & \(3.2\times 10^{7}\) & 1 & 1 & 798 & 1522 & 55 & 5 \\ \cline{1-1} \cline{2-8}  & \(3.7\times 10^{7}\) & 2 & 1 & 798 & 1522 & 55 & 6 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Buckling results obtained using the analytical solution.  
Figure 4: Deflection contours as FE results for various cases of compartments: (**a**) steel compartment, (**b**) aluminum compartment (depth of 20 m), and (**c**) aluminum compartment (depth of 60 m).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compartment Type** & **Maximum Deformation (mm)** & **Critical Stress (Mpa)** & **Safety Factor** \\ \hline St 60 & 0.586 & 241 & 3 \\ \hline Al + depth 20 & 8.69 & 117 & 2.4 \\ \hline Al + depth 60 & 4.73 & 188 & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Critical stress and deformation extracted from FE software.  
Figure 3: Contours of von Misses stress for various compartments: (**a**) steel compartment, (**b**) aluminum compartment (depth of 20 m), and (**c**) aluminum compartment (depth of 60 m).  
The buckling factor (BF) is the factor of safety against buckling or the ratio of the buckling loads to the applied loads. Table 6 illustrates the interpretation of possible BF values for different cases. From this Table, it is clear that the steel structure had a higher buckling strength than the aluminum structure. Moreover, for aluminum, the value of BF increased by increasing the immersion depth.