Performance of three-lobe pressure-dam bearings

The use of multi-lobe bearings, considered to be more stable than ordinary circular bearings in industry is increasing daily. Studies have shown that performance can be further improved if pressure dams are incorporated into these bearings. Analysis of two-lobe pressure dam bearings has been reported in the literature. The present work was carried out to assess the performance of a three-lobe bearing with pressure dams. The results show that the performance of a three-lobe pressure-dam bearing is far superior to that of an ordinary three-lobe bearing.     

Effects of lubricant viscosity on the experimental response of a three-Mass flexible rotor in two types of journal bearings

Preloaded three-lobe and pressure dam bearings were tested with a three-mass flexible rotor. The oil viscosity was varied. The resulting changes in the instability threshold were measured and were found to depend markedly on oil viscosity. Data were compared with theoretical stability map predictions. The data were typically 50% higher than predicted for the three-lobe bearing and were within ±30% for the pressure dam bearing. Although the predictions are not quantitatively correct, the correct trends are predicted, i.e. the experimental and theoretical stability maps show the same trends for instability thresholds as functions of the Sommerfeld number.     

Performance characteristics of tilted three-lobe journal bearing configurations

A tilted three-lobe journal bearing is a geometric variation of the usual symmetric three-lobe configuration. This investigation of the performance characteristics of the three-lobe configurations over a wide range of tilt angles shows that, within a specific range of tilt angles, the tilted configurations exhibit superior dynamic performance to the usual symmetric three-lobe bearing.     

Effects of elastic deformation of a bearing liner on performance of finite offset-halves pressure dam bearings

The elastic effects of the liner of a hydrodynamic bearing are considered to be very significant, since they are found to influence the performance of the bearing considerably. The study of bearings such as circular, ordinary two-lobe, elliptical pressure dam etc. has already been reported. This paper describes the elastohydrodynamic study of an offsethalves pressure dam bearing, which is one of the common types of two-lobe bearings. The flexibility of the liner is represented by a dimensionless deformation coefficient. The results indicate that with the flexibility of the liner, the zone of infinite stability increases, whereas the minimum threshold speed first decreases and then increases in the investigated range. Rotor flexibility adversely affects the minimum threshold speed, but the zone of infinite stability remains unaffected.     

Static and Dynamic Characteristics of Four-Lobe Pressure-Dam Bearings

The stability of ordinary journal bearings is found to increase by the use of multi-lobes. Studies have shown that performance can be further improved by incorporation of pressure dams into these bearings. This paper analyses the performance of a four-lobe pressure-dam bearing which is produced by incorporating two pressure dams on the upper two lobes and two relief-tracks on the lower two lobes of an ordinary four-lobe bearing. The results show that the performance of a four-lobe bearing with pressure dams is superior to that of an ordinary four-lobe bearing.     

On Performance Characteristics of Three-Lobe Porous Hydrodynamic Journal Bearings

This paper presents an analysis of a three-lobe porous hydrodynamic journal bearing for its static and dynamic performance characteristics. The performance characteristics of the bearing have been computed and presented in graphical form for a wide range of permeability parameter to investigate the effect of porosity on bearing performance. The stability margin of the three-lobe journal bearing system, in terms of crtical mass of journal, has been established using Routh's criteria. The nature of transient motion of the journal has been analyzed using the complex eigen values of characteristic equation and motion trajectories obtained by numerical integration of equations of motion.     

Stability Analysis of Four-Lobe Pressure-Dam Bearings

This paper analyzes the dynamic behavior of a new type of bearing, namely, four-lobe pressure-dam bearing. It is produced by incorporating two pressure dams in the upper two lobes and two relief tracks in the lower two lobes of an ordinary four-lobe bearing. The characteristic curves of this type of bearing show that it is much more stable as compared to an ordinary four-lobe bearing. A study of the performance characteristics of this type of bearing is also undertaken.     

三油楔固定瓦滑动轴承空间安装方位对其性能影响的研究

以三油楔固定瓦滑动轴承为研究对象,采用数值模拟方法,深入探讨了轴瓦空间安装位置（轴承安装角）对三油楔固定瓦滑动轴承静动特性和稳定性的影响,得出了三油楔固定瓦滑动轴承静动特性和稳定性随轴承安装角变化而变化的一系列规律性曲线,并进行了理论分析。     

Stability analysis of orthogonally displaced bearings

Journal bearings operating at high speeds often exhibit vibrational instability. Circular bearings are known to be prone to vibrations and, in general, a non-circular bearing geometry enhances shaft stability. Among the several possible configurations of non-circular bearings, elliptical, offset, three-lobe and tilted three-lobe bearings have attracted attention. The present analysis is a theoretical prediction of stability for a hybrid two-lobe bearing obtained by displacing the lobe centres of an elliptical bearing. It has been found that an orthogonally displaced bearing is more stable than the hitherto known bearings and at the same time it is easier to manufacture. Numerical results have been presented for nine combinations of horizontal and vertical displacements of lobes and three $\text{L}\text{D}$ ratios so that a suitable profile and $\text{L}\text{D}$ ratio can be selected by a designer in a specific application.     

A study of elastohydrodynamic effects in a three-lobe journal bearing

The effect of flexibility of bearing liner on the static and dynamic performance characteristics of a three-lobe journal bearing was studied. The three-dimensional Navier-Stokes and the continuity equations governing the lubricant flow in the clearance space of the journal bearing, and the three-dimensional e elasticity equations governing the displacement field in the bearing liner, were solved by using the finite element method and an iteration scheme. The static and dynamic performance characteristics were calculated at various eccentricities for a wide range of values of deformation coefficients which take into account the flexibility of the bearing liner.     

Combined Effect of Turbulence,Load Orientation and Rotor Flexibility on the Performance of Three-Lobe Bearings

A three-lobe journal bearing is analytically investigated to determine its dynamic performance when three main parameters, i.e. turbulence, load orientation, and rotor flexibility are varied. Reynolds numbers up to 12000, rotor dimensionless flexibilities up to 4, and load orientations up to 30 degrees on either side of the vertical load line are considered. Thus, almost all cases of practical interest are studied. The stability of a three-lobe bearing improves due to turbulence at high Sommerfeld numbers (more than 0.6) for a rigid rotor, while it is virtually the same for flexible rotors. Conversely, the load orientation has a pronounced effect on stability for both rigid and flexible rotors.     

Severity Estimation of Cracked Shaft Vibrations within Fluid Film Bearings

The equations of motion, with four degrees of freedom, taking into consideration the flexibility, damping and cross coupling of the fluid film bearings are derived for a cracked Jeffcott rotor supported on fluid film bearings.

Dimensionless equations are developed for dynamic radial load, dynamic pressure developed in the fluid film bearings and coefficient of dissipation considering the journal vibrations in two harmonics; bearing fluid film stiffness and damping coefficients. These are applied to a cracked Jeffcott rotor supported on different types of bearings, i.e., cylindrical journal bearings, offset cylindrical bearings, tilting pad journal bearings and three-lobe bearings. Based on the allowable dynamic pressure developed in the fluid bearings, the severity of cracked shaft and allowable crack depths are estimated in this study. Measurement of dynamic pressure and dissipation for monitoring the crack growth is suggested. However, 2x vibration is the best indicator of cracks in the shafts.     

Effects of Three-Lobe Bearing Geometries on the Unbalance Response of a Flexible Rotor

The synchronous response due to unbalance was studied both theoretically and experimentally for a three-mass rotor mounted in three-lobe and axial-groove bearings. Offset factor, preload factor and load orientation were parametrically varied for the three-lobe bearings. Theoretical predictions indicate that low preload factors (with offset factors of 0.5) result in the smallest critical speed responses. Also, for a preload factor of 0.75, offset factors of approximately 0.65 minimize the critical speed response. Experimental data for peak responses agree within 42 percent (usually much less) of predictions. Reasons for the differences are attributed to the predicted bearing stiffness and damping coefficients.     

Comparative study of four gas-lubricated noncircular journal bearing configurations

Offset-halves, lemon-bore, three-lobe and four-lobe bearing performance has been compared at the same load capacity and speed. Both steady state and stability characteristics have been considered.     

Analysis of non-circular gas bearings including skewed axes

The steady state performance characteristics of non-circular gas bearings with journal bearing axes parallel and skewed are presented. The incremental finite element formulation suggested by Reddi and Chu was extended to obtain results for elliptical and three-lobe bearings. The validity of the method was checked with the results obtained by Pinkus.     

A Pressure Dam Bearing Analysis with Adiabatic Thermal Effects©

To improve the stability of fixed geometry journal bearings in high-speed rotating machinery, pressure dam or stepped bearings have often been used in place of plain or other bearings. Despite their long history and wide range of applications in industry, only isoviscous analyses have been reported in the literature. Since stability problems usually occur at relatively high speeds where considerable heating occurs, it is desirable to include the thermal effects in pressure dam bearing analysis. This study presents a full adiabatic thermohydrodynamic analysis for pressure dam bearings. The theoretical results show that the pressure and temperature distributions on a stepped pad are quite different from those on a smooth pad. The thermal effects have significant influence on the predicted bearing performance, such as journal eccentricity, dynamic coefficients, and rotor stability. The example of a flexible rotor indicates improved stability prediction with the thermal effects included.     

螺旋槽-波锥坝组合型非接触式机械密封性能分析

针对液体润滑非接触式机械密封在低黏环境下承载性能不足的问题,提出一种新型螺旋槽-波锥坝动静压组合型机械密封结构,采用MATLAB软件利用有限差分法求解考虑质量守恒空化边界的雷诺方程,并将组合槽与螺旋槽、波锥坝的密封性能进行比较,进一步分析不同结构参数与工况参数对组合槽性能参数的影响规律。结果表明:新槽型波数与螺旋槽数重合时组合密封在径向出现2个压力峰值,相较于单一槽型结构拥有更好的承载能力与较小的摩擦扭矩;液膜力与泄漏量随波锥比或径向宽度比的增加而增大,外径压力和转速越大,组合槽的承载性能提升越显著,但外径压力的升高会造成较大的径向泄漏。组合槽结合了波锥槽的静压承载与螺旋槽的动压承载综合优势,将有效提升液体润滑非接触式机械密封在低黏环境下的润滑性能。     

Effects of Excitation Frequency and Orbit Magnitude on the Dynamic Characteristics of a Highly Preloaded Three-Lobe Journal Bearing

The independent effects of excitation frequency and excitation magnitude on experimentally derived bearing coefficients for a highly preloaded three-lobe journal bearing were studied. The effect of excitation frequency was determined by applying external dynamic forces at half-synchronous, synchronous, and twice synchronous frequencies with respect to the operating speed. Effect of excitation magnitude was independently determined by applying either three or four different amplitudes of excitation force to the bearing resulting in orbit sizes ranging up to 30% of clearance. Applying static forces to the bearing housing controlled the Sommerfeld number, and thus, the static operating position. Data was reduced as linear dynamic coefficients, and presented relative to excitation frequency and excitation magnitude over a range of Sommerfeld numbers from 0.2 to 3.0 and operating eccentricities from 0.3 to 0.9. In general, neither excitation frequency nor excitation magnitude was shown to have a measurable effect over the ranges studied.     

A comparative study of the thermal behaviour of profile bore bearings

This paper describes principally a theoretical analysis of the thermal behaviour of offset half, orthogonally displaced, three-lobe and four-lobe bearing geometries. The thermal analysis illustrates the implication of type selection with regard to the parameters of load-carrying ability, power loss, lubricant requirements and operating temperatures. The comparisons show that for all profiles considered, they have inferior load-carrying ability when compared with the cylindrical geometry along with significantly larger lubricant supply requirements. Thermal effects in profile bore bearings are less extreme than those encountered in the cylindrical profile.