Multi-Physics Coupling Dynamics Simulation of Thermally Induced Vibration of Magnetically Suspended Rotor in Small and Micro Nuclear Reactors

The power conversion system of a small micro-reactor has strict requirements on the compactness of the rotating mechanical support. Although the active magnetic bearing is an ideal choice, the thermally induced vibration caused by it may destroy the stability of the system. As such, this study proposes a multi-physics coupling simulation framework, which integrates electromagnetic, thermal, and mechanical multi-physics coupling mechanisms and quantifies the stability of the system under thermal-induced vibration in the frequency domain. Firstly, the equivalent magnetic circuit and electromagnetic finite element modeling and calculation of the compressor rotor are carried out. In the case of the maximum AC current of 10 A, the equivalent stiffness of the magnetic pole is 4.21 × 10⁸ N/m and 2.1 × 10⁸ N/m, and the eddy current loss of the rotor is 4.17496 W. Based on the eddy current loss, a magneto-thermal coupling model is established to reveal the temperature gradient distribution and the thermal sensitivity coefficient of the journal is 0.006. Subsequently, the thermal stress and equivalent stiffness are coupled to the rotor dynamics equation, and the maximum amplitude of the rotor is obtained at a value of 0.001 mm. Finally, the critical stability threshold of the system is determined by a Nyquist diagram, and the results show that the system is stable as a whole. In this paper, the quantitative analysis of the cross-scale coupling mechanism of electromagnetic, thermal, and mechanical multi-physical fields is realized, which provides a systematic analysis method for the thermally induced vibration of magnetically suspended rotors and has important engineering significance for high power density rotating mechanical systems in small micro-reactors.