Focusing on the abnormal vibration of a core pulling mixed flow pump, the vibration causes were explored by the tested signal analysis, and then the rotodynamic model was established based on the Lagrange equations, which complies with the energy conservation. Comparing the peak-peak va-lue and vibration frequency of tested signals with that of simulated signals, the simulation precision was verified, and the start-up characteristics, such as the shaft orbit and vibration frequency, were simulated to search the vibration mitigation measures. The test signal analysis shows that, the impact force at the start-up process causes the rotor misalignment, and the misalignment will reduce but not disappear when the pump′s rotational speed reaches the design value. The simulation results verify the precision of test analysis, and the internal connection between the accompanied impact force and units vibrations was studied. The powerful impact force is more likely to induce the severe vibration and misalignment. Because the accompanying impact force is induced by motor direct start, to improve unit start-up mode and reduce the impact force can weaken vibration and enhance the operation reliability effectively.
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