High Fidelity Simulation of Rotordynamic Morton Effect by Nonlinear Transient Approach

The present study is focused on accurate prediction of Morton effect problem including journal asymmetric heating and the corresponding long period amplitude oscillations using a nonlinear time transient rotordynamic simulation. For the analysis of the Morton effect problem, variable viscosity Reynolds equation and three-dimensional energy equation are coupled via temperature and viscosity, and solved simultaneously. Three-dimensional heat transfer equations of bearing and shaft are modeled by a finite element method, and thermally coupled with the fluid film via heat flux boundary condition. Asymmetric heat flux into the synchronously whirling rotor is solved by the orbit time averaged heat flux from fluid film to the spinning journal surface. The journal orbit is calculated by the nonlinear transient dynamic analysis of rotor-bearing system with variable time step numerical integration scheme. For the computation time reduction, modal coordinate transformation is adopted for dynamic and thermal transient analysis. This research explains how the thermal bow induced imbalance force develops in spinning journal with time, and how the vibration level is affected by the thermal bow vector.

This dissertation is also focused on a new modeling method of three-dimensional thermo-elasto-hydro-dynamic cylindrical pivot tilting pad journal bearing (TPJB). For the computational efficiency, modal coordinate transformation is utilized in the flexible pad dynamic model, and pad dynamic behavior is represented only by means of modal coordinate. Fluid film thickness is calculated by a newly developed node based method, where pad arbitrary thermal and elastic deformation, and journal thermal expansion are taken into account simultaneously. This paper presents a new analysis method for a thermo-elasto-hydro-dynamic tilting-pad journal bearing system to reach a static equilibrium condition adopting nonlinear transient dynamic solver. In the nonlinear transient dynamic solver, physical and modal coordinates co-exist for computational efficiency, and transformation between modal and physical coordinate is performed at each numerical integration time step. Nonlinear time transient dynamic analysis and steady thermal analysis are combined to find the static equilibrium condition of the TPJB system, where the singular matrix issue of flexible pad finite element (FE) model is resolved.