HHT Analysis And Application Of Dam Structure Vibration Signal

With the vigorous development of new energy industry in China.Hydropower plays an increasingly important role in China’s power supply.Tibet is rich in water resources,the reserves are the second largest in the country,more than 400 hydropower stations have been built so far,but because Tibet is located in the Himalaya-Mediterranean seismic belt,and frequent geological activities,it is of great practical significance to study the response of dam to earthquake vibration once dam break is caused by earthquake.In this paper,Hilbert-Huang transform(HHT)analysis method is used as the main analysis method of seismic vibration signals,use MATLAB,ABAQUS and other auxiliary software as calculation tools,the response process of dam structure under earthquake vibration excitation is analyzed from three dimensions: resonance frequency,vibration acceleration and vibration energy,provide a theoretical reference for the seismic design of subsequent dams.In this paper,based on analysis of HHT method to do the following work:(1)To study the problem of end-point effects in the process of empirical mode decomposition.Through the comparative analysis it is concluded that the most suitable dam vibration signal endpoint effect suppression method-Neural network method.Superimpose two low frequency signals into a composite signal,using the HHT analysis of the analog signal,Almost complete restoration of all the physical information of the original signal,and the self-adaptability,accuracy and rationality of the HHT analysis method for seismic vibration signals are verified.At the same time,it is verified that the neural network algorithm has a good inhibitory effect on the end effect.Finally using HHT analysis of real seismic vibration signal,calculate the percentage of the energy of each IMF component energy in the total energy of the original signal,especially between 6 ～ 21 Hz,energy in the frequency domain is mainly concentrated in the range of 91.1%,and it is less distributed at high frequencies,accounting for about 0.9%.It is proved that the energy of seismic vibration signal is mainly concentrated in low frequency and lasts for a long time,the resonant frequency of the dam should be avoided between 6～21Hz,then reduce the damage to the dam due to resonance frequency,and provide a theoretical basis for the seismic design of the dam structure in the future.(2)According to the real parameters of a dam in Tibet,ABAQUS is used to carry out three-dimensional mathematical modeling of the dam,obtained a three-dimensional simulation model of the dam based on the infinite element method.Using ABAQUS to carry out three-dimensional mathematical modeling of the dam,and obtain a three-dimensional simulation model of the dam based on the infinite element method.The vibration acceleration response of the dam model is analyzed,it can be seen from the results that the dam axial direction,river direction,vertical direction appeared strong earthquake stage(3～6.5s),and has the amplification effect to the vibration acceleration,but due to the damping effect,the acceleration time history curve of the crest of the dam is lagging compared with the input seismic wave.At the same time,with the increase of the dam elevation,the amplification coefficients of the acceleration of the axial vibration along the river and the dam are increasing.(3)Firstly,based on the energy spectrum analysis method,the time relation between the energy extreme value of dam vibration and the input seismic wave extreme value is analyzed,it is proved that the energy extremum time of vibration response is always obviously lagging behind the maximum energy extremum time of excitation,moreover,the time of reaching the extreme energy value along the river direction,the axial direction and the vertical direction of the dam are not consistent.The extreme energy is reached first in the downstream direction,and finally in the vertical direction.Then select 8 measuring points in the vertical direction,it is found that with the increase of the height,the vibration energy magnifies more and more,and the vibration energy of the dam crest is obviously greater than that of the dam bottom,which requires strengthening the seismic design of the dam crest.At the same time,the amplification factor of the vibration energy along the river direction is obviously higher than the axial and vertical direction of the dam,and the variation of the amplification factor of the vertical vibration energy is small,which indicates that the direction along the river direction is the concentrated direction of the vibration energy of the dam,which provides theoretical support for the seismic design of the dam structure.