An improved concentrated mass method for analysis of the mechanics modes of a four-stage pump rotor system

Abstract

To improve the calculation accuracy for the mechanics mode of a double-support four-stage centrifugal pump rotor system (FCPRS), a simplified mathematical model derived from “four segments-four concentrations” and an ANSYS model were used to solve the model of a D-type FCPRS with balanced mass. Based on ourresults, we present an improved mathematical model combining "five segments-four concentrations" and the modal resistance-bending stiffness (RBS) correction coefficient. Moreover, the calculation results of the impeller mass eccentricity from the optimized model were compared with those from ANSYS simulations. The natural frequencies (NF) from the concentrated mass method (CMM) are slightly lower than those obtained from ANSYS. After optimization, the errors of the first four orders of NFs decreased from 1.13%, 1.24%, 7.62%, and 7.96% to 0.79%, 0.90%, 4.17%, and 4.51%, respectively. The NFs of each order increase slightly in the case of impeller mass eccentricity. The low-order NF increases slightly and the high-order NF decreases when the impeller in the middle is eccentric. The NF error obtained via the optimized CMM for the impeller with eccentric mass is slightly larger than that for the impeller without eccentricity.