Study On Vibration Characteristics Of The Diversion Pipeline Region Of Pumped Storage Power Station

When the pumped storage power stations are getting stronger day by day,the vibration caused by the operation of power station has attracted more and more attention.The pulsating load generated by the flow passage will elicit vibration of the diversion power system,owing to the operation characteristics of high head and bidirectional frequent start-up,which can be transmitted from the pipeline and plant structure to the surrounding rock,and then to nearby ground,resulting in ground vibration and buzzing noise,thus impacting the safety of surroundings and affecting the inhabitants.Based on the analysis of vibration sources,this article established the3 d finite element model of the hydropower plant and “pipeline-surrounding rock-ground” finite-infinite element coupling model which aimed to investigate the characteristics of vibration sources and response of pumped storage power station as well as diversion pipeline.The main research contents are as follows:(1)Study on vibration sources characteristics of pumped storage region.This paper calculated the theoretical frequencies of all kinds of vibration sources in hydropower plant structure for resonance checking.In allusion to the blade-passing frequency and double blade-passing frequency,the forced vibration modes of the diversion pipeline system were calculated by the method of hydraulic impedance and transfer matrix,thus the pressure distribution along the diversion pipeline was settled.The engineering calculation results show that the pressure distribution along the diversion pipeline under the double blade-passing frequency is about 50% higher than that under the blade-passing frequency.(2)Study on response characteristics of underground powerhouse.This paper carried out modal analysis and dynamic response calculation,which depended on the three-dimensional finite element model of underground powerhouse.According to the engineering calculation results,the fundamental frequencies of powerhouse are greatly staggered with the theoretical frequencies of all kinds of vibration sources,so it will not cause resonance.The maximum vibration displacement of each calculation point of the powerhouse structure meets the design requirements as well as revealing the distribution of large vibration displacement in hydropower plant structure,which provides a theoretical reference for the layout of measurement points for site vibration testing.(3)Study on ground vibration characteristics of diversion pipeline region.This paper established the “pipeline-surrounding rock-ground” finite-infinite element coupling model,which solved the problems of vibration wave propagation in infinite domain simulation.Through the finite-infinite element coupling model,this article studied the vibration characteristics of diversion pipeline under different excitation sources.What was more,the sensitivity analysis of the influencing factors was investigated.This study finds that compared with one double blade frequency,the vibration intensity induced by two double blade frequency is larger.Besides,the surface vibration intensity will attenuate 7%～33% considering the faultage.This article also finds that the surface vibration intensity will decrease by 10%approximately when unit load decreases from 175 MW to 245 MW,suggesting that the surface vibration intensity will decrease with the increase of unit load.(4)Study on damping measures of diversion pipeline region.Comparing with engineering examples,this paper established the “pipeline-surrounding rock-ground”finite-infinite element coupling model to analyze the damping effect of different cushion thickness and elastic modulus,which is based on original model.The analysis shows that the larger the cushion thickness is,the better damping effect is.And the lower the elastic modulus of cushion material is,the more prominent damping effect is.When the cushion thickness is 30 mm,the surface vibration intensity will decrease by 38%～65%.When the elastic modulus of cushion material is 0.8MPa,the surface vibration intensity will decrease by 44%～71%.