Dynamic Analysis Of Multistage Centrifugal Pump Rotor System With Uncertain Sliding Bearing Parameters

As a key equipment for fluid transportation,multistage centrifugal pump is widely used in large industrial and military fields such as chemical,petroleum,firepower,and aerospace.At present,the multistage centrifugal pump mainly develops in the direction of high head,high speed,high pressure and high flow rate,and its operation stability is affected and restricted by the critical speed.Therefore,the research on the construction of multistage centrifugal pump rotor dynamics model and its dynamic characteristics prediction is an important technical means to ensure the working reliability of multistage centrifugal pump.It is beneficial to prolong pump set life and improve economic benefits,and has practical engineering application value.The dynamic model of the traditional centrifugal pump rotor system is established based on the bearing dynamic characteristic coefficient calculated from the nominal value of the bearing structure parameter,which leads to the difference between the theoretical prediction of the dynamic characteristic of the rotor system and the actual operating performance.Aiming at the uncertainty of dynamic characteristics of rotor system of multistage centrifugal pump caused by manufacturing errors of sliding bearing structural parameters,this thesis takes the critical speed of rotor system as the research object,and studies the prediction of dynamic characteristics of rotor system of multistage centrifugal pump within the range of sliding bearing structural parameters.The main research contents are as follows:First,the fluid lubrication theory of journal bearing and the solution method of bearing dynamic characteristic coefficient are studied,and the Reynolds equation which obeys the generalized fluid lubrication theory of journal bearing is established.The five-point difference method,the over-relaxation iteration method and the small parameter method were compiled using MATLAB to complete the calculation of the oil film pressure value,oil film thickness distribution,bearing capacity,deflection angle position,end discharge flow rate,and stiffness damping coefficient of the sliding bearing.The influence of bearing structure parameters on oil film characteristics and stiffness and damping coefficients are analyzed.And it provides a theoretical basis for the subsequent establishment of the finite element model of the multi-stage centrifugal pump bearing-rotor system.Then,the kinematic equations of each unit of multistage centrifugal pump and the overall kinematic differential equations of rotor system are deduced theoretically.Taking a high-pressure centrifugal pump of a company as an example,the finite element simulation model of multistage centrifugal pump rotor system beam element-spring damping element-lumped mass point was established by using ANSYS virtual simulation platform.After meshing and setting constraints,the natural frequency and critical speed of the rotor system are solved,and then the influence of the manufacturing error of the bearing structure parameters on the dynamic characteristics of the rotor system is analyzed.And lay the foundation for the subsequent establishment of the optimization model of the critical speed of the sliding bearing-rotor system.Finally,the uncertain dynamic characteristics of multistage centrifugal pump rotor system caused by the manufacturing error of sliding bearing structural parameters are discussed.Based on rotor system dynamics simulation and improved particle swarm optimization(PSO),this thesis proposes a robust prediction method for the critical speed of the rotor system.This method establishes a dynamic model of the rotor system through the dynamic characteristic coefficients associated with the structural parameters of the sliding bearing.Furthermore,an optimization model is established with the structural parameters of the sliding bearing as the variable and the critical speed of the rotor system as the goal,and the critical speed extreme value of the dynamic model of the rotor system is calculated by combining with the improved PSO simulation.A large number of samples are sampled by Monte Carlo,and the effectiveness of PSO results is verified by repeated calculation for a long time.