Characteristics Of Tilting-pad Journal Bearing Research Articles

The impact of installation deviation on the lubricating characteristics of a 1000 MW giant hydropower unit’s tilting-pad journal bearing

Abstract With the trend towards larger and higher capacity units, tilting-pad journal bearings are being increasingly used in hydropower units. Through thermo-hydrodynamic (THD) analysis, it is possible to establish pressure differential equations that consider the change in oil viscosity with temperature, which is essential to ensure safe operation of the bearing. Further research on the flowing characteristics of tilting-pad journal bearings, especially about installation deviations, is essential for giant hydropower unit. This study establishes a three-dimensional model of a 1000 MW hydropower unit’s turbine journal bearing to investigate temperature, pressure distribution, and load under various installation deviation scenarios. The findings aim to optimize the design and engineering practices of tilting-pad bearings in rotating machinery, meeting the evolving needs of the power industry.

Numerical and experimental study on dynamic characteristics of tilting-pad journal bearings considering pivot stiffness in a vertical rotor system

Purpose The purpose of this paper is to study the influence of pivot stiffness on the dynamic characteristics of tilting-pad journal bearings (TPJBs) and the stability of the bearing-rotor system. Design/methodology/approach A theoretical numerical model is established, and the influences of pivot stiffness on TPJBs and a bearing-rotor system are analyzed. Then, two kinds of pivot structures with different stiffness are designed and the vibration characteristics are tested on the vertical rotor bearing test bench. Findings The pivot stiffness has an obvious effect on the dynamic characteristics of the TPJBs and the stability of the bearing-rotor system. As a result of appropriate pivot stiffness, the critical speed and the vibration amplification factor can be reduced, the logarithmic decay rate and the stability of the rotor system can be effectively increased. While the journal whirl orbit is smoother and the rubbing is obviously reduced when the bearings have flexible pivots. Originality/value The influence of pivot stiffness on TPJBs and a vertical rotor-bearing system is studied by theoretical and experimental methods.

Design of Tilting-Pad Journal Bearings Considering Bearing Clearance Uncertainty and Reliability Analysis

The dynamic characteristics of tilting-pad journal bearings (TPJBs) are strongly related to their geometric parameters, most importantly the bearing clearance. In turn, the bearing clearance in TPJBs is strongly dependent on the machining tolerances of the bearing parts and their assembling. Considering that, the machining tolerances of the pads can be of the same magnitude order of the oil film thickness in the bearing, it is uncertain that the TPJB will have the originally designed geometry after assembling. Therefore, the resultant dynamic characteristics of the TPJB also become uncertain. In this work, we present an investigation of tilting-pad bearings and their equivalent dynamic coefficients when subjected to dimensional variability. First, we perform a stochastic analysis of the system using a thermo-hydrodynamic (THD) model of the tilting-pad bearing and considering the bearing clearance in each pad as an independent random variable (varying between minimum and maximum values). We show that the scattering of the results of the dynamic coefficients is limited by the values obtained from TPJBs with all pads with maximum or minimum possible clearances. Second, we apply the concepts of reliability analysis to develop a design procedure for tilting-pad bearings. This design methodology considers the results obtained in the stochastic analysis and it allows the Engineer to appropriately design the bearing for a given probability of success or, inversely, a given probability of failure. Such approach assures a level of reliability to the dynamic coefficients of designed TPJBs in face of their dimensional variability.

Numerical and Experimental Research on Dynamic Characteristics of Tilting-pad Journal Bearing of Pivot Stiffness and Damping

In view of the characteristic of the tile which swings and slightly vibrates through geometric direction of preload, an analytical model for vibration of entire dynamic characteristics of tilting pad bearing and its corresponding simplified dynamic model of 8 parameters are made. Based on this theory, the tilting-pad journal bearing of pivot stiffness and damping is designed. The resilient pads are set between the tiles and the bearings, thus, the pivots of the tiles are put on the resilient pads and a small clearance is left between the resilient pads and the bearings. Therefore, the oil can be shared by the small clearance and the bearing lubrication system, and that can cause squeeze film damping effect which improves the damping coefficient of the system. According to different processing technic, two kinds of tilting-pad journal bearing of pivot stiffness and damping are designed, and their dynamic characteristics are worked out by numercial and experimental research. The result shows that the tilting-pad journal bearing of pivot stiffness and damping can increase the first-order damping of rotor-bearing system and thus improve system's stability obviously.

Effects of Load Direction on the Static and Dynamic Characteristics of Tilting-Pad Journal Bearings

This paper studies the static and dynamic characteristics of tilting-pad journal bearings (TPJBs) with the load directions different from either of the two typical load directions of LOP (Load On Pad) and LBP (Load Between Pads). Theoretical results show that the effects of the load direction on the static and dynamic characteristics are found in the range of low Sommerfeld number S and increase with the decrease of S. The cross-coupling terms of spring and damping coefficients are no longer zero if the load direction is different from LOP and LBP, but the cross-coupling spring coefficients are equal, which indicates that the non-zero cross-coupling terms of the spring coefficients do not cause the self-excited vibration.

An Analytical Complete Model of Tilting-Pad Journal Bearing Considering Pivot Stiffness and Damping

Abstract Considering the freedom of pad tilting and pad translation along preload orientation, an analytical complete model, as well as mathematical method, which contains 2n+2 degrees of freedom, is presented for calculating the dynamical characteristics of tilting-pad journal bearing. Based on the motion relationship of shaft and pad, the local coordinate system, the generalized displacement, and the generalized force vector are chosen. The concise transformation of generalized displacement, generalized force, and its Jacobian matrix between the local and global coordinate systems are built up in matrix form. A fast algorithm using the Newton–Raphson method for calculating the equilibrium position of journal and pads is proposed. The eight reduced stiffness and damping coefficients can be obtained assuming that the journal and all pads are subject to harmonic vibration. Numerical results show that the reduced damping coefficients and the threshold speed can be effectively enhanced by giving suitable pad pivot stiffness and damping simultaneously, and this analytical method can be applied to analyze dynamical behavior of the tilting-pad journal bearing rotor system.

An analytical model for complete dynamical coefficients of a tilting-pad journal bearing

An analytical model as well as calculation method is presented for the complete dynamic characteristics of tilting-pad journal bearing. Using this model, the global oil-film forces, stiffness and damping coefficients acting on the journal and all pads can be calculated in a highly concise expression. To improve the computational efficiency, a fast algorithm for calculating the oil-film force and Jacobian of the local pad system is proposed and the Newton–Raphson method is used for solving the equilibrium positions of the journal and all pads. Taking a rigid rotor symmetrically supported on two identical five-shoe tilting-pad journal bearing as an example, the complete dynamic characteristics, damping natural frequency and the stability are calculated. Compared with the traditional reduced model, the numerical results show that the dynamic characteristics can be calculated efficiently and succinctly. The stability can also be overestimated by using the reduced model.

Effect of Angular Spring and Angular Damping of Oil Film on the Stability Characteristics of Tilting-Pad Journal Bearings

Effect of Angular Spring and Angular Damping of Oil Film on the Stability Characteristics of Tilting-Pad Journal Bearings

Rotordynamic Characteristics of Flexure-Pivot Tilting-Pad Journal Bearings

Many of today's modern turbomachines, especially those running at high speeds and high power ratings, require the superior stability characteristics of tilting-pad journal bearings to prevent rotor-dynamic instabilities. Until now, the design complexity of tilting-pad bearings has precluded their use in many small, high-volume applications where cost and size are important. This paper introduces a new one-piece journal bearing design, the flexure-pivot bearing, that offers many of the beneficial rotodynamic advantages of tilting-pad bearings, without the complexities of a multi-piece design. Performance data for a flexure-pivot bearing is shown for an application requiring a highly stable design, illustrating the effectiveness of the flexure-pivot bearing in offering rotordynamic stability approaching that of a tilting-pad bearing. Presented at the 47th Annual Meeting In Philadelphia, Pennsylvania May 4–7, 1992

Inlet Pressure Effects on the Static and Dynamic Characteristics of Tilting-Pad Journal Bearings.

In this paper, the effect of inlet pressure at the bearing entrance on the static and dynamic characteristics of finite-width tilting-pad journal bearings is investigated theoretically. The inlet pressure for a finite-width pad is obtained by assuming the conservation of mechanical energy in the midplane in front of the bearing inlet and a proper polynomial expression as an inlet pressure distribution in the lateral direction. The film pressure is numerically calculated using the inlet pressure as the pressure boundary condition at the leading edge of each pad. Numerical results with or without inlet pressure for a wide range of eccentricity ratios or Sommerfeld numbers are compared. The analysis shows that there is a significant influence of the inlet pressure on the dynamic characteristics of tilting-pad journal bearings, especially on the stiffness coefficient.

An Influence of Fluid Inertia Forces on the Dynarnic Characteristics of Tilting-pad Journal Bearings in Turbulent Flow

In this paper, an influence of fluid inertia forces on the dynamic characteristics of tilting-pad journal bearings in turbulent flow is investigated theoretically. Applying the generalized turbulent lubrication equation with inertia effects to the centrally pivoted 2-pads journal bearings, the dynamic oil film forces are obtained. And linearizing the forces around the static equilibrium position under the assumption of a small displacement of journal center, the static and dynamic characteristics such as the Sommerfeld number, the dynamic oil film coefficients and the pad critical mass are calculated for three slenderness ratios, λ= 0.6, 1.0 and 2.0. It is found that the fluid inertia forces affect significantly the dynamic oil film coefficients but insignificantly the Sommerfeld number and the pad critical mass.