## 4 Case Study
### Stage B: Sustainability Evaluation by SF DEMATEL-EDAS Method  
#### 4.3.1 Evaluation Criteria Identification and Weighting  
On the other hand, this study implemented a multi-criteria evaluation of sustainability for the proposed locations. The evaluation criteria are recommended by experts and previous studies as shown in Table 5[8; 17; 57; 58; 59]. Next, the experts provide linguistic pairwise comparisons of the influence between the criteria as illustrated in Table 14. Under the assumption of experts' equally weights, the aggregated SF direct influence matrix is established according to Equation (14) and presented in Table 6. As shown in Table 7, the SF total influence matrix is established by Steps 5 and 6, which were mentioned in Section 3.3.  
Table 15 and Figure 6 illustrate the results of Steps 7, 8, and 9 in the SF DEMATEL-EDAS procedure mentioned above. From Figure 6, it can be seen that experts are most concerned with the costs (11.34%) and potential tourism impacts (11.04%) of WWSs. The costs such as installation, operation, maintenance, and local labor are significantly dependent on the location of the WWS. In addition, the potential effects of WWS on the tourism industry are of great concern to experts because it contributes more than six percent to Vietnam's economy [60]. The social acceptability (10.29%), proximity to industrial area (10.70%), and vessel density (10.93%) are approximately equally weighted groups of criteria. The next lower weighted group includes potential fisheries impact (9.73%), proximity to seaports (9.48%), vessel density (9.51%), and military activities (9.51%). Although the western Pacific region has many sovereignty issues, experts consider geopolitical factor (7.03%) with the lowest weight to assess the sustainability of WWSs.  
\begin{table}
\begin{tabular}{c c} \hline
**Notation** & **Evaluation Criteria** \\ \hline EC1 & Vessel density \\ EC2 & Costs \\ EC3 & Military activities \\ EC4 & Geopolitical issues \\ EC5 & Proximity to conservation area \\ EC6 & Proximity to Seaports \\ EC7 & Proximity to Industrial Area \\ EC8 & Potential tourism impact \\ EC9 & Potential fisheries impact \\ EC10 & Social acceptability \\ \hline \end{tabular}
\end{table}
Table 5: List of evaluation criteria.  
Table 3. By using SWAM, individual spherical fuzzy decision matrices are synthesized to form a spherical fuzzy decision matrix as shown in Table A6. Based on the spherical fuzzy decision matrix, the average spherical fuzzy solution was determined according to Equation (34) and as shown in Table A7. The defuzzification process for the spherical fuzzy decision matrix and the spherical fuzzy averaging solution was performed and is illustrated as shown in Table A8. Tables A9 and A10 present the positive distances from the average solution and the negative distance from the average solution as Equations (37) and (38). Continuing to perform the calculations according to Step 13 and Step 14 as mentioned in Section 3.3, the results of assessing the sustainability of the locations are presented in Table 8. According to the ranking results, WWS-11, WWS-13, and WWS-7 ranked first three in terms of sustainability. In contrast, at the bottom of the sustainability rankings are WWS-17, WWS-16, and WWS-10, respectively.