## 2 Prototype Test for the Vibration of the Hydraulic Gate
### Vibration of the Surface Outlet Radial Gate  
The surface outlets are designed as a WES overflow weir with an 11-m-wide cross section and 12-m-high gate piers to restrict flow in the lateral direction. It is noted that the bottom edge of the 3# surface outlet gate is in contact with the discharge flow when the gate opening ratios are 0%, 25% and 50% (i.e., the cases 4, 5 and 6). Moreover, for the cases 7 and 8, the gate opening ratios are further increased to 75% and 100%, thus the surface outlet gate is uplifted and its bottom edge is separated from the discharge flow. Therefore, the discharge volume cannot be controlled by the hydraulic gate in cases 7 and 8. As shown in Figure 6, the test point placement on the 3# surface outlet gate was given and triaxial acceleration sensors were installed at each measuring point.  
In Figures 7 and 8, the RMSs and dominant frequencies of the acceleration histories measured at each test point on 3# surface outlet gate in different cases are illustrated. The x-, y- and z- directions for the test points on surface outlet gate have the same meanings as those for the test points on mid-level outlet gate.  
Due to the limited number of sensors, all of the acceleration sensors were installed on the 3# surface outlet gate to meticulously monitor its vibration condition. As shown in Figure 7, it was found that small vibration occurs when only the surface outlet gates are opened (e.g., case 3) and the surface orifice gate vibration is significantly amplified when the mid-level orifice gate is fully opened (e.g., cases 4 to 8). According to the experience of management personnel, the surface gate vibration under working condition 2 can be clearly identified with the naked eye and the vibration is so strong that people cannot stand on the concrete cover directly above the surface gate. In addition, the obvious vibration of the 1#, 2# and 4# surface orifice gates is also observed in cases 2 and 4 to 8 by the operation and maintenance personnel in this hydropower station, although we do not have detailed data. Therefore, the conclusion can be drawn that the intense vibration of surface orifice gate is mainly induced by the mid-level orifice gate vibration.  
As shown in Figure 7a, the x-directional accelerations of the 3# surface outlet gate first decrease with the increasing of its opening and then the accelerations do not decrease any more when the bottom of the hydraulic gate is separated from the discharge flow in cases 7 and 8 (i.e., the opening is equal to or greater than 75%). Considering the y- and z-directional accelerations illustrated in Figure 7b,c, the aforementioned varying tendency is approximately satisfied, but is not as obvious as that shown in Figure 7a. Moreover, as illustrated in Figure 7d, the variation trend of the sum of the acceleration vectors in different directions during the gate opening process is almost the same as the varying tendency of x-directional acceleration. The vibration mode of the surface outlet gate is further investigated and compared with the numerical analysis results in Section 4.  
Figure 8 illustrates that the dominant frequencies of the acceleration histories in different cases are mainly distributed in a narrow range from 27.5 to 28.5 Hz. It is noted that the dominant frequencies for the vibrations of the surface outlet gate are very similar to those for the vibration of the mid-level outlet gate, which verified the aforementioned analysis that the exciting force generated by the mid-level  
Figure 6: Test point placement on 3# surface orifice gate.  
-orifice gate vibration contributes significantly to the surface orifice gate vibration. The dominant frequencies higher than 40 Hz (shown in Figure 8) are probably caused by the vibration of the accessory structures on the gate (e.g., the staircase and its handrail), signal distortion and interfering signals generated by the vehicles and construction process.