## 4 Analysis of Vibration Data
### Comparison of Data According to Design Factors  
Figure 11 shows the vibration data for the original model (case 1) without structural reinforcement. This data was confirmed based on the six points shown in Figure 3, and data were secured for 4-7 s when the fluid was in the saturation state. The maximum vibration velocity along the X, Y, and Z-axis was 4.14, 4.46, and 3.71 mm/s, respectively, and the largest vibration value was observed in the Y direction, which is the gravity direction. This indicates that the design satisfied the vibration velocity requirement of 4.5 mm/s or less, which is the reference value before the change. Therefore, the results of the reinforced structures were analyzed based on the vibration value of Case 1.  
Figure 12 shows the vibration data for each axial direction of Cases 2 to 4. For Case 2, in which the upper part of the pump connected to the pipe was reinforced, a maximum vibration velocity of 4.42 mm/s was observed in the Y direction. Compared to that of the original model, this corresponded to a decrease of approximately 0.9%, indicating that the design did not efficiently reduce vibration. In addition, for Case 3 in which the impeller part was reinforced in each axial direction, a maximum vibration velocity of 4.07 mm/s was observed in the Y direction. This indicates that if the impeller part is fixed, the vibration reduced by approximately 9%; however, this is unsuitable for the design because the vibration value is higher than 4 mm/s. For Case 4 in which the length of the strainer at the lower end of the pump was increased, a reduction in vibration was expected owing to a decrease in pressure; however, a maximum vibration velocity of 4.25 mm/s was observed in the Y direction. Although the vibration reduced by approximately 4.6%, it cannot be regarded as an efficient design compared to Case 2.  
Figure 10: Comparison of mode shape according to structural reinforcement.  
For Case 5, the analysis was performed by dividing the internal support of the water tank into the case where only the impeller part was reinforced and the case where the entire support was reinforced. While the overall reinforced form was more stable in terms of vibration when performing the modal analysis, it is also important to consider the cost aspect. Therefore, if the vibration regulations are satisfied when only the periphery of the impeller part is reinforced, it is unnecessary to reinforce the entire structure. Figure 13 shows the results for Case 5. Case 5-1 is a case where only the periphery of the impeller was reinforced, and a maximum vibration velocity of 3.97 mm/s was observed in the Y direction. In addition, Case 5-2 achieved a maximum vibration velocity of 3.82 mm/s. Compared to the original model, the vibration of Case 5-1 and 5-2 reduced by 11 and 14.3%, respectively. As the vibration velocity of both Cases 5-1 and 5-2 was less than 4 mm/s, the results indicated that the reinforcement of the internal support of the water tank effectively reduced the vibration.  
Figure 11: Case 1—vibration velocity according to the axial direction: (**a**) Axial direction display; (**b**) X direction; (**c**) Y direction; (**d**) Z direction.