## 5 Discussion
### Relationship of Discharge, Loads and Vertical Vibration  
[PERSON] and [PERSON] (2018) reckoned that the gate stream-wise vibration was excited by upstream pressure fluctuations caused by flow discharge variations. [PERSON] et al. (2018) confirmed that the main reason for the pressure pulsation was velocity pulsation caused by turbulence through experiment and numerical analysis. Those results indicated that there was a certain relationship between the gate vibration and flow discharge. Figure 10 exhibits the discharge difference between 'flow1' and 'flow2' for a service gate height of 4.0 m. 'down' means direct closing and 'vibration' denotes vibratory closing. The fluctuation of the discharge difference in vibratory closing is greater than that direct closing. When the upstream water depth increases, the discharge variation gradually increases. Moreover, the variation is also related to the service gate height. If the service gate is in the large gate opening, the outflow condition behind the emergency gate is open and the relationship between flow discharge and gate vibration is weak. While the service gate is in the small gate opening, gate vibration increases the discharge fluctuation. At this stage, the discharge of 'flow1' is less than that of 'flow2', and the fluid from the gate shaft needs to be supplemented with the downstream fluid. Once the fluid in gate shaft has completely drained, the air from the gate shaft enters the downstream. When the emergency gate opening rate is less than 0.1, the outflow condition is stable open-flow, and the discharge fluctuation for the two closing modes is relatively small. [PERSON] and [PERSON] (2018) pointed out that gate vertical vibration caused the variation in effective flow area and discharge pulsation. The discharge pulsation and its inertia effect produced the variation in pressure difference. The pressure difference would lead to the  
Figure 10: Discharge difference of monitoring: (**a**) water depth 85 m; and (**b**) water depth 100 m.  
variation in hydrodynamic loads of the gate plate and affect the flow discharge in turn. Table 4 presents the correlation analysis of the flow discharge and hydrodynamic loads. With a decrease in the discharge, the gate bottom load, gate top load and downstream plate load decrease, while the upstream plate load and gate seal load increase. Meanwhile, the areas where the flow discharge have a great influence on the loads are concentrated in the upstream plate and gate bottom. Comparing to the relationship between the flow discharge, gate plate pressure and vertical vibration in terms of their numerical results, we can draw the conclusion that the vertical vibration has little influence on the discharge and gate plate pressure at a large opening rate. At a small opening rate, however, there is a strong correlation between the vertical vibration and the plate pressure due to the drastic flow pattern behind the gate. The correlation is related to the service gate height. Figure 11 presents the relationships between panel momentum. When the opening rate decreases, the momentum initially increases and then decreases. There is a momentum peak at a certain opening rate. An increase in the upstream water depth directly causes the flow discharge and velocity to increase. Nevertheless, the increased upstream water depth has no significant effect on the position of the peak. When the service gate height increases from 1.0 m to 4.0 m, the opening rate corresponding to the momentum peak increases from \(e\) = 0.1 to \(e\) = 0.4, meaning that the peak position is mainly related to the service gate height. The reason for this phenomenon is that the downstream boundary directly affects the outflow condition and makes the open-flow behind the gate appear in advance, which causes the opening rate to increase.