Abstract：Step and pulse loads are the transient loads with sharply and dramatically changing amplitudes. Therefore, when these loads are acted on a rotor, the axial centre of the rotor may be altered, resulting in a sudden change in bearings lubrication condition. A seawater desalination pump unit can experience different transient loads during startup, stopping and rotational speed variation. A fluid-structure interaction(FSI)model for the water lubricated bearing-rotor system in a seawater desalination pump unit was established to explore changes in lubrication condition and vibration dynamics under a transient load. Effects of rotor elastic deformation at different time instances on the circumferential pressure distribution, water film bearing capacity and axial centre position were analyzed by using CFD(computational fluid dynamics)and FSI methods when the rotor system was subject to step, rectangular and triangular pulse loads, respectively. The results showed that the axial centre position, file bearing capacity and maximum pressure in film can change greatly and exhibit a certain oscillation process under a transient load. Due to a pulse load applied in a limited period of time, once it disappears, the axial centre will restore its original balance position; for a step load, however, the centre will move to a new equilibrium position.
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