Abstract
When operating actual pumps, we need to check the stability limit. This paper suggests the reduction method of rotor system to 2 DOF, and simplified method for prediction of the stability limit. First, we set up the rotor shape, and stiffness and damping at journal bearings and annular seal. Then we check unstable mode by complex eigenvalue analysis with strict model (1D-FEM) and 2 DOF model, and prove 2 DOF model is enough for stability analysis. Next, we define λΩ for presenting cross stiffness of oil film dynamic property offered by Bently-Muszynska into 2 DOF model. 2 DOF model consists of whirl (rigid rotor) mode and whip (shaft bending) mode. Using the reduced model, we analyze the stability problem focusing on stability limit states. As a result, we found that the stability limit is equal to intersection of λΩ line and curve of undamped natural frequency ω1.
