Three-Dimensional Dynamic Model of TEHD Tilting-Pad Journal Bearing-Part II: Parametric Studies
Suh, Junho(Department of Mechanical Engineering, Texas A&M Un)
United States | Journal of Tribology
2015-10 | 바로가기
Cited by 29
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Journal of Tribology
Published: October 2015
Junho Suh, Alan Palazzolo
Department of Mechanical Engineering, Texas A&M University
This paper presents a new analysis method for a thermo-elasto-hydro-dynamic (TEHD) tilting pad journal bearing (TPJB) system to reach a static equilibrium condition adopting nonlinear transient dynamic solver, whereas earlier studies have used iteration schemes such as Newton–Raphson method. The theoretical TPJB model discussed in Part I of this research is combined into a newly developed algorithm to perform a bearing dynamic analysis and present dynamic coefficients. In the nonlinear transient dynamic solver, physical and modal coordinates coexist for computational efficiency, and transformation between modal and physical coordinate is performed at each numerical integration time step. Variable time step Runge–Kutta numerical integration scheme is adopted for a reliable and fast calculation. 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. The flexible pad TPJB model was verified by comparison with other numerical results. Simulation results corresponding with the theoretical model explained in Part I are presented and discussed. It explains how the TPJB dynamic behavior is influenced by a number of eigenvector of flexible pad FE model and pad thickness. Preload change under fluid and thermal load is examined.
This study presented a new modeling method and algorithm for the evaluation of the static equilibrium condition of the flexible pad and pivot TPJB, adopting nonlinear transient dynamic analysis. This study can be summarized as follows:
Nonlinear transient dynamic analysis is adopted to avoid the singular matrix problem of flexible pad FE model under the fluid load on pad and produce more realistic pad deformation.
For the computation time reduction, modal coordinate transformation is adopted for the analysis of the flexible pad FE model.
At each time step of the transient dynamic analysis, coordinate transformation is performed to produce the film thickness in the physical coordinate and the pad elastic deformation in the modal coordinate.
For the verification of the new TPJB model, flexible pad model only with the consideration of the rigid body mode was simulated and compared with the rigid pad TPJB model. Each TPJB model showed identical result.
The simulation results were compared with the experimental work of Kulhanek and Childs  research, and they agreed well with 20% maximum error of stiffness coefficients and 30% maximum error of damping coefficient. Current numerical model predicted higher stiffness coefficients and lower damping values than the experimental work. Cross coupled terms are also simulated compared with Kulhanek and Childs  research. This study predicted much lower cross coupled terms with less than 1% of direct terms.
Static equilibrium condition and dynamic coefficients are simulated with varying number of modes of the FE pad. The 1st bending mode was found to have the biggest influence on the TPJB dynamic behavior.
Three pad models with different thicknesses are simulated and compared each other. The drop rate of the damping coefficient due to the reduced pad thickness was bigger than that of the stiffness coefficient.
The preload change due to the thermal and elastic deformation was simulated. At the thinnest pad, preload change induced by elastic deformation was bigger than that induced by the thermal deformation.
Both elastic and thermal deformations were found to increase the bearing pad preload.
Present study can be extended to a nonlinear time transient rotordynamic analysis with a large imbalance motion.
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