磁場中で回転するロータでは，ある回転数以上でロータの導体部に生ずるローレン ツ力に起因した不安定振動が発生することが知られている。本研究では直流磁場中 のロータ動特性評価を目的とし，磁場の感度解析を適用してロータへの磁気作用力 を求めそれを減衰定数，ばね定数として表現することで，ロータの動特性を従来の 回転軸振動解析システム上で扱えるようにした。本手法の妥当性はモデル試験によ り検証され，直流磁場中のロータ安定性について設計段階での定量評価が可能とな った。　（著者抄録）

Subsynchronous vibration sometimes occurs on rotors operating in static magnetic field. The vibration of this type is considered as a self-excited vibration caused by Lorent'z force, but its dynamical mechanism has not cleared yet. This paper describes the destabilizing force from both experimental and theoretical works. It is suggested to apply the method used for oil film bearings to the Lorent'z force acting system. This method deals with 8 parameters to describe the dynamic characteristics of the system. The perturbation method of the Lorent'z force using FEM analysis of the magnetic field is applied to obtain those parameters. The calculation shows that the Lorent'z force acts as not only damping but also cross coupled stiffness, and these results have a good agreement with the experimental data of the test rotor. From this study, the stability check of rotors operating in static magnetic field is possible at the design stage.