The e!ect of a hydrodynamic thrust bearing on the dynamics of a rotor-bearing system is investigated systematically in this paper. The action of a thrust bearing is described as forces and moments in a static state and a series of dynamic coe$cients in a dynamic state which are calculated from the Reynolds equation and its perturbed forms by using the boundary elements method. A lumped-mass model for system motion based on the Myklestad transfer matrix method is formulated considering the e!ects of thrust bearings and axial load. An interative procedure is proposed to sovle the indeterminate problem of load-sharing among journal bearings due to the introduction of thrust bearings. The e!ects of such parameters as sti!ness of shaft, static loads of journal bearings, position of lumped mass, position of thrust bearing and arrangement of thrust bearings on the action of thrust bearings are discussed. The nature of this action reveals that thrust bearings not only provide sti!ness and damping in a dynamic state, but also change the static de#ection of the shaft, and thereby in#uence the static load-sharing of journal bearings. The present research helps to explain the variation of dynamic characteristics of a machine due to the introduction of thrust bearings, and also provide theoretical basis for the dynamic design considering the e!ect of thrust bearings. 1999 Academic Press 0022-460X/99/440833#40 $30.00/0 * *x h 12 *p *x # * *y h 12 *p *y " 2 *h * # *h *t . (1) H *p *h Q N r dr d , k5 X " H *p * H r dr d , d5 X " H *p * R H r dr d , k5 XR " H *p * H r dr d , d5 XR " H *p * Q H r dr d , k+ VF " H *p *h N r cos dr d , d+ VF " H *p *hQ N r cos dr d , k+ V " H *p * H r cos dr d , d+ V " H *p * R H r cos dr d , DYNAMICS OF A ROTOR-BEARING SYSTEM 837 k+ VR " H *p * H r cos dr d , d+ VR " H *p * Q H r cos dr d , k+ WF " H ! *p *h N r sin dr d , d+ WF " H ! *p *h Q N r sin dr d , k+ W " H ! *p * H r sin dr d , d+ W " H ! *p R H r sin dr d , k+ WR " H ! *p * H r sin dr d , d+ WR " H ! *p * Q H r sin dr d . (10)