Dynamic Response Modeling and Morton-Effect Stability Assessment of Three-Pad Tilting-Pad Journal Bearings in Nuclear Steam Turbine Generator Units

Periodic abnormal vibration in large pressurized water reactor (PWR) nuclear steam turbine generator units is difficult to diagnose because the parameter-level link among three-pad tilting-pad journal bearings, oil-film thermal asymmetry, and possible Morton-effect susceptibility remains insufficiently quantified. This study investigates an ARABELLE-type unit and establishes a finite-difference bearing rotor model by solving the oil-film thickness equation, Reynolds pressure equation, two-dimensional energy equation, pad moment balance, and linearized stiffness and damping coefficients. The bearing load, radial clearance, rotational speed, and inlet oil temperature are examined as controllable variables, while only the calculated pad temperature rises are directly validated against field measurements from eight support bearings. The calculated temperature rise deviations range from −7% to 8%, with a root-mean-square deviation of approximately 0.32 °C and a mean absolute percentage error of approximately 4.2%. The model results suggest that the load and speed mainly intensify the total oil-film heating, whereas the radial clearance and inlet oil temperature more directly govern the circumferential temperature difference, used here as an indirect indicator of the Morton effect risk. For the investigated Bearing 3, a radial clearance near 0.52 mm and an inlet oil temperature of 48–52 °C are suggested as bearing-specific operating windows for reducing thermal imbalance while maintaining engineering stability. The main contribution is a traceable engineering chain from field abnormal vibration to three-pad bearing thermal asymmetry, cautious Morton-effect risk interpretation, and operational adjustment for large nuclear rotating machinery.