Fatigue Analysis Of The Connecting Bolts Between The Top Cover And The Seat Ring Of The Turbine Based On Finite Element And Online Monitoring

With the development and utilization of clean energy in our country,our country’s hydropower industry has begun largely-scale construction since the middle of the last century.As one of the most important components of hydropower stations,which is supposed to pay more attention about safe operation.During the operation of the turbine,the top cover and seat ring of the turbine will be affected by huge water pressure and impact force.The bolt connecting the top cover and seat ring of the turbine is an important fastener to ensure the safe and stable operation of the turbine,and is one of the key components to ensure the sealing performance of the top cover.Once the failure of the connecting bolt,it will cause the serious consequences of flooding the plant,destroying the machine and even killing the factory.Therefore,it is necessary to carry out the strength analysis and fatigue analysis of the connecting bolt between the top cover and the seat ring of the turbine.The author takes the mixed flow turbine of a large hydropower station in Sichuan as the research object.Based on UG software,a three-dimensional parameter model of the turbine cap,seat ring and connecting bolt is established.The strength of connecting bolt is analyzed by using ANSYS Workbench commercial software and finite element analysis method.According to the typical working conditions,the maximum stress,the position of the dangerous section and the average stress of the section are calculated and analyzed.At the same time,the fatigue life of the connecting bolt of hydraulic turbine is preliminarily analyzed according to the results of calculation and analysis.According to the self-designed bolt intelligent monitoring system,the real-time monitoring data of bolt pretightening force and time are obtained,and the time-frequency combination method is adopted to analyze and process the data and calculate the fatigue life of bolts by short-time Fourier transform.According to the results of calculation and analysis,the stress alarm threshold is set in the intelligent bolt monitoring system,and the most dangerous bolt connection is monitored in real time,which can prevent the occurrence of safety accidents.The research shows that the average stress of the connecting bolt section under all working conditions is between 95 MPa and 175 MPa,which meets the strength requirements.Among the eight working conditions with bolt preload,the most unfavorable working conditions are the turbine load of 82.5MW,volute water pressure of 0.82 MPa,bolt preload of 295 k N.Under this working condition,the joint bolt has the maximum stress,the maximum equivalent stress is 580.96MPa,and the maximum deformation is 1.2374mm.The position of the dangerous section of the connecting bolt appears in the return groove or the joint of the first thread of the bolt,which is in accordance with the actual situation.The maximum bolt axial force collected by the bolt intelligent monitoring system is between 340 k N and 430 k N,that is,between 100MPa and 135 MPa.The results of strength analysis of coupling bolts by using finite element analysis method are in good agreement with the monitoring data of bolt intelligent monitoring system.At the same time,according to the monitoring data,the finite element analysis method and time-frequency analysis method were respectively used to conduct fatigue life analysis.The fatigue life of the connecting bolt was predicted to be 2.4694×10~5h by the finite element analysis method,and 1.9695×10~5h by the time-frequency analysis method.The fatigue life of the connecting bolt was estimated by combining these two methods.Therefore,the research method can provide the basis for the fatigue life prediction of the connecting bolt of the hydraulic turbine roof.