Torsional Vibration Analysis Of High Speed Turbine With Gearbox

Severe torsional vibration will cause damage to the shafting of the steam turbine unit,which will not only cause unit accidents,but also affect the normal operation of the relevant system,thus causing economic losses.For large power steam turbines,the torsional vibration of the shafting system has been relatively mature.The characteristics of this type of steam turbine are composed of a limited number of setting rotors,which can be mass-produced.The rotor structure of the same model is relatively fixed,and the dynamic characteristics are basically unchanged.For individualized industrial steam turbines,the rotor structure is different due to the wide variety of steam parameters,power,speed,etc.Although such shafting torsional vibration can be solved by finite element modeling,it requires a longer design cycle.It is unable to meet the market demand with large output and short delivery time,especially the shaft belt gearbox unit makes the situation more complicated,and the torsional vibration calculation problem is more prominent.How to quickly solve this kind of shafting twist under the premise of meeting engineering precision is the key research content of this paper.The calculation model of the traditional multi-segment lumped mass method for calculating the natural frequency of torsional vibration is studied in the torsional vibration of the large-span shafting system,and the limitation of the equivalent diameter simplification method in the existing calculation method is found.In this paper,the equivalent diameter method recommended in the API684 standard is first proposed and introduced in the multi-stage lumped mass method model to calculate the torsional vibration,and the strain energy method is used to verify that the stepped axis,the cone axis and the interference axis are solved by the above method.It is reasonable to solve the problem of large error of the original method and shorten the design cycle.For units with gearboxes,the gear pair is generally equivalent to a rigid body,that is,the meshing stiffness is infinite,but there is gear torsional deformation when the actual gear pair is running.Therefore,the problem of large error in some shafting torsional vibration calculations sometimes occurs..High-precision meshing stiffness can be modeled using finite element method,but there is also a problem of long design cycles.This paper introduces the simplified meshing stiffness calculation method recommended in the API684 standard,and verifies the rationality of the above meshing stiffness simplification method by finite element method.Finally,the torsional vibration natural frequency is solved by the simplified equivalent diameter and compared with the strain energy method,the error is small.In addition,torsional vibration analysis is performed on the actual running unit,and the shafting modeling method described can be used to obtain the natural frequency of the torsional vibration.