Analysis On Flow Induced Vibration Characteristics Of Open Channel Guide Wall Of Tongzilin Hydropower Station

According to the operation and operation of Tongzilin hydropower station over the years and the overall hydraulic model test results of the hydropower station,it can be seen that when the open channel flood discharge sluice and the river bed flood gate jointly discharge flood,the downstream water level of the open channel is relatively high,the energy dissipation effect in the channel is good,and the flood discharge flow pattern is stable.However,due to the change of power grid dispatching rules,the open channel is often faced with large-scale flood discharge by the flood gate of the open channel.At this time,the water depth in the channel is seriously insufficient,and the flow in the channel is easy to become a torrent.The discharged high-speed flow is strongly swirling and oscillating,which greatly increases the impact on the downstream hydraulic structures.In order to improve the energy dissipation efficiency of open channel,the relevant units put forward the scheme of adding 6m T-shaped pier + 8m continuous sill in the open channel from the hydraulic point of view.However,the additional auxiliary energy dissipator dissipates the energy of discharged water greatly,which will inevitably cause severe turbulence in the water body in the open channel,which can cause the guide wall and auxiliary energy dissipater to be strongly excited by flow pulsation,and the guide wall is used as the dam section It is necessary to pay special attention to its vibration characteristics under discharge condition.Therefore,in order to ensure the safe and stable operation of the power station,based on the existing research results,this paper studies the flow induced vibration law of the open channel guide wall of the hydropower station by combining the prototype observation and numerical simulation,and evaluates whether the auxiliary energy dissipation scheme will endanger the safety of the guide wall and auxiliary energy dissipater.The main contents are as follows:1 Based on the flow induced vibration displacement data of the guide wall obtained from prototype observation,the flow induced vibration characteristics of the guide wall are analyzed.The main analysis results are as follows: the vibration amplitude and mean s Euare deviation of each measuring point of the guide wall are within the allowable range,which indicates that the structure is safe under the prototype observation condition W the main fre Euency distribution of each measuring point is relatively fixed under different wor Iing conditions,which indicates that the dynamic characteristics of the guide wall are better under the prototype observation condition In order to be stable,the transverse vibration of measuring points 3 #,4 #and 5# in condition 3 is wea Iened,which is mainly caused by the vibration wea Iening of 1 ～ 3 Hz component from condition 2 to condition 3 and the vibration range of less than 1 Hz component moving bac Iward.2 The guide wall model established by ABAQUS verifies that the recognition error of NEx T-ERA is less than 2% without noise interference.Because of the low signal-to-noise ratio SNR of the prototype observation data of hydraulic structures,it is found that when the signal-to-noise ratio SNR is reduced to 7d B,the singular entropy technology can not determine the order of the system clearly.Therefore,the prototype observation data must be denoised first.In this paper,an improved denoising method based on empirical wavelet transform is proposed The fre Euency and damping errors of NEx T-ERA are about 5% when the signal-to-noise ratio is4 d B.It shows that the optimized algorithm has high accuracy and strong anti noise performance,and can be well applied to the wor Iing mode identification of hydraulic structures.Finally,the modal parameters of the guide wall of the open channel are identified by the optimized modal parameter identification method,and the fifth order wor Iing fre Euency is identified.3 Ta Iing the fifth order wor Iing fre Euency of modal identification of guide wall in Chapter 3 as the calibration standard,the finite element model parameters of ABAQUS guide wall are adjusted continuously to ma Ie the difference between the natural fre Euency of modal analysis and the wor Iing mode fre Euency as small as possible,so as to provide reliable finite element model for dynamic displacement calculation in Chapter 5.Comparing the natural fre Euency of the final correction model with the wor Iing modal fre Euency of the guide wall,it is found that the natural fre Euency has a certain increase,but it is within a reasonable range.The first five fre Euencies can basically correspond to the wor Iing mode fre Euency,indicating that the final numerical model can better reflect the dynamic characteristics of the structure.4 In order to judge the feasibility of the energy dissipation scheme of adding auxiliary energy dissipator in open channel from the perspective of mean s Euare deviation of flow induced vibration,the difference of dynamic characteristics of guide wall of open channel before and after setting auxiliary energy dissipator is analyzed by using the corrected finite element model of open channel guide wall in chapter 4 The vibration difference of guide wall in open channel should mainly consider the change of flow excitation before and after adding auxiliary energy dissipator.Then,the difference of vibration response of guide wall of open channel before and after setting auxiliary energy dissipator was simulated by prototype observation and numerical simulation.According to the simulation results,adding auxiliary energy dissipator did not change the distribution of vibration mean s Euare deviation of open channel guide wall,and the maximum measurement point of vibration mean s Euare deviation of three wor Iing conditions was still 2# measuring point,and the vibration mean s Euare deviation of each measuring point after adding auxiliary energy dissipater was added The maximum vibration mean s Euare error of auxiliary energy dissipater is 6.3 μm,which is within the allowable mean s Euare deviation of the structure.Therefore,it is judged that the auxiliary energy dissipater is safe in all wor Iing conditions.