Study On Characteristics Of Vibration And Vibration Reduction In The Foundation And Ground Induced By Flood Discharge Of Wudongde Hydropower Station

Foundation and ground vibration induced by flood discharge is an extremely complex phenomena of fluid-solid interaction,which occurs in the complicated system including hydrodynamic load,dam,cushion pool,foundation and the ground.In view of the complexity of interaction between hydrodynamic load and structure due to flood discharge,the hydroelastic model test is an effective method to study the vibration characteristics induced by flood discharge of high dam.Currently,the study of foundation and ground vibration induced by flood discharge mainly focuses on a gravity dam,which adopts the form of underflow energy dissipation.In contrast,the water retaining structure of Wudongde Hydropower Station is arch dam.And the energy dissipator is the combination of ski jump energy dissipation and natural cushion pool.Therefore,the vibration source and dynamic response of the foundation and ground are also different.It's important and necessary to conduct special research on the foundation and ground vibration induced by flood discharge of high arch dam.The results can be used for reference in the future.Based on Wudongde hydroelastic model test,vibration acceleration of the foundation and ground was tested.According to the test results,the factors influencing the vibration distribution of the foundation and ground are analyzed qualitatively and the vibration distribution characteristics are studied.The vibration under different discharge and different opening modes was compared and analyzed.By refining the combination of opening modes under different discharge,the vibration reduction of the cushion pool was optimized.(1)In terms of the vibration sources,it can be attributed to impact load and flap load qualitatively.The impact load is generated by the impact of the water on the cushion,and the flap load acting on the bank slope is caused by the fluctuations of the water level in the cushion pool.The impact load mainly affects the distribution of vibration in the foundation and the slope below elevation 767 m.Since the depth of the cushion of Wudongde Hydropower Station can exceed 100 m,the impacted zone by water level fluctuations is mainly around elevation 827 m,so the flap load mainly affects the vibration distribution in the slope around elevation 827 m.(2)For three-direction vibration distribution along stake number,whether at the bottom of the plunge pool or on the bank slope,the vertical vibration should be greater than that in the horizontal direction.The water tongues from the surface orifices and mid-level outlets can have an important influence on the distribution of the vibration acceleration.When the mid-level outlets discharge,the peak of the vertical acceleration distribution along stakes appears in the downstream.In the case of surface orifices discharge or joint discharge,the peak appears in the upstream which is mainly affected by the water tongue from surface orifices.Due to the high water-head drop and high water-entry angle of surface orifices discharge,the influence of water tongue impact on the distribution of vertical vibration acceleration is greater than that of mid-level outlets.(3)With regard to the law of propagation of vibration along the elevation,the vertical acceleration distribution of the left and right banks around elevation 767 m is similar to that at the bottom,but its magnitude is smaller.While the vertical acceleration of the left and right banks around elevation 827 m is different.The vibration distribution is affected by many factors such as fluctuations of water level,discharge,opening mode,energy dissipation impact,slope trend of natural cushion pool and so on.When the discharge and the downstream water level are low,the influence of flap load is small.The root mean square of vertical acceleration at 827 m slope is basically less than 767 m.The root mean square of vibration acceleration in the whole cushion pool decreases from the bottom upward.When the discharge and the downstream water level are high,the root mean square of vertical acceleration at 827 m slope may be larger than 767 m.(4)In terms of the influence of discharge or opening mode on vibration distribution,in most cases,the larger the discharge is,the larger the root mean square of vibration acceleration is,and the magnitude of vibration acceleration in the plunge pool is approximately positively correlated with discharge.Under the same discharge,the influence of different opening modes on the vibration distribution is obvious.On the whole,surface orifices discharge has the largest vibration acceleration,the second is the mid-level outlets discharge.During the joint flood discharge(when the number of surface orifice is smaller than that of the mid-level outlet),flow energy is greatly consumed due to the collision of water tongue and the vibration acceleration is small.However,water level fluctuations in the cushion pool are more violent than other opening modes.Under the influence of the flap load and the slope trend,the vibration acceleration on the left slope around elevation 827 m becomes obviously larger.(5)For optimal operation of flood discharge,considering the vibration characteristics of foundation and slope,more opening modes were set under different discharge.It was concluded that when the discharge is small,the mid-level outlet discharging can be given priority because the overall vibration was relatively small.When the discharge is larger,the joint flood discharge must be adopted to meet the flood safety requirements.Then special attention should be paid to ensure the number of mid-level outlet n is larger than that of surface orifice m.If not,the vibration caused by flood discharge would be rather larger,even larger than that of surface orifice discharge.In order to reduce the vibration of foundation and ground,this kind of opening modes should be avoided in the actual operation process.