## 4 Analysis of Vibration Data
### Efficeint Vibration Design  
Table 8 summarizes the vibration velocity values after applying and analyzing the changed design from Cases 1 to 5. The vibration value of the original model was set as the reference value, and the results of the other cases were compared to that of Case 1. The results revealed that the reinforcement of the internal support of the water tank was the most efficient design for vibration reduction. In addition, the maximum vibration value for each axial direction according to the case was represented in a graph, as shown in Figure 14. When only the upper end of the pump connected to the pipe was reinforced, the vibration reduced in the Y direction, but slightly increased in the Z direction. Additionally, if the structure is reinforced in each axial direction between the impeller part and the water tank, there is an overall vibration reduction effect, but the vibration velocity does not satisfy the requirement of 4 mm/s or less. When the length of the strainer is increased, the pressure reduced and there was a slight vibration reduction effect, but the flow rate reduced significantly, and an increase in the existing RPM value is required to increase the flow rate. This is not an effective design change because it eventually results in a vibration increase problem.  
Figure 12: Vibration velocity according to the axial direction: (**a**) Case 2; (**b**) Case 3; (**c**) Case 4.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Case No.**} & \multirow{2}{*}{**Contents**} & \multicolumn{3}{c}{**Max. Vibration Velocity (mm/s)**} & \multicolumn{1}{c}{**Vibration**} \\ \cline{3-6}  & & **X** & **Y** & **Z** & **Reduction Rate Based** \\  & & **Direction** & **Direction** & **Direction** & **on Max. Value (\%)** \\ \hline
1 & Original model & 4.14 & 4.46 & 3.71 & Default value \\ \hline
2 &
\begin{tabular}{c} Pump top \\ reinforcement \\ \end{tabular} & 4.13 & 4.42 & 3.73 & 0.9 \\ \hline
3 &
\begin{tabular}{c} Structural \\ reinforcement of \\ the impeller part \\ \end{tabular} & 4.91 & 4.07 & 3.59 & 9 \\ \hline
4 &
\begin{tabular}{c} Change strainer \\ length \\ \end{tabular} & 4.01 & 4.25 & 3.64 & 4.6 \\ \hline
5-1 &
\begin{tabular}{c} Water tank \\ structure \\ reinforcement (1) \\ \end{tabular} & 3.87 & 3.97 & 3.58 & 11 \\ \hline
5-2 &
\begin{tabular}{c} Water tank \\ structure \\ reinforcement (2) \\ \end{tabular} & 3.76 & 3.82 & 3.52 & 14.3 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Vibration velocity data according to design change.  
Figure 13: Vibration velocity based on the axial direction: (**a**) Case 5-1; (**b**) Case 5-2.  
Among the designs, Case 5, in which the internal support of the water tank was reinforced, satisfied the vibration velocity requirement of 4 mm/s or less. As a value close to 4 mm/s was achieved in the Y direction when the periphery of the impeller was reinforced, the most efficient design is to reinforce the internal support of the water tank as a whole to achieve a notable vibration reduction effect. Nevertheless, if the vibration regulations are satisfied, it is efficient to reinforce only the periphery of the impeller in consideration of the cost aspect.