Pressure Dam Bearings Research Articles

Performance characteristics of two-lobe pressure dam bearings with micropolar lubrication

A circular bearing experiences the instability problem due to oil whirl, causing violent vibrations at high speed. Two-lobe pressure dam bearing is a solution to the instability arising in high-speed rotating machineries. The paper presents the various static and dynamic characteristics of two-lobe pressure dam bearings, while operating with micropolar fluid. The modified Reynolds equation used to model the lubrication is solved using the finite element method. Performance characteristics such as load, attitude angle, critical mass, threshold speed and whirl frequency are computed, presented graphically and analysed. A detailed comparison of the performance characteristics is done for various micropolar and dam parameters. It is concluded that bearing performance is significantly influenced by dam parameters (dam angles) and micropolar parameters (coupling number and characteristics length).

Effect ofL/DRatio on the Performance of Two-Lobe Pressure Dam Bearing: Micropolar Lubricated

Two-lobe pressure dam bearings are commonly used in high speed rotating machineries. Their use is considered more stable than plain cylindrical bearings. Such bearings have a dam in the upper half whereas the lower half is provided with a relief track. Performance of two-lobe pressure dam bearings under micropolar fluid is evaluated. Finite element method is used to solve the modified Reynolds equation. Fluid film pressures are obtained by solving modified Reynolds equation. Thus pressure obtained is used to find performance characteristics of this bearing. The dynamic performance characteristics are studied at variousL/Dratios. ThreeL/Dratios are considered 1.6, 2.0, and 2.4 for the analysis purpose. Results obtained are presented for various micropolar parameters. Results show that stability of two-lobe pressure dam bearings increases with decrease in aspect ratio (L/D).

API 610 BB5 펌프 개발을 위한 로터다이나믹 특성분석

This paper deals with the detail rotordynamic analysis for BB5 eight stages pump as development of API 610 BB5 type pump. Dry-run analytical model, not considering operating fluid, and wet-run analytical model, considering operating fluid are established. In addition, plain circular and pressure dam bearings are chosen and it was discussed that each bearing has an effect on dynamic characteristics of pump rotor system. A rotordynamic analysis includes the critical speed map, Campbell diagram, stability, and unbalance response. As results, it was predicted that rated speed of the pump rotor passes through 1st critical speed in dry-run condition regardless of bearings, however, it was verified that, in wet-run condition, the rotor system doesn’t have critical speeds even if more than twice rated speed. Hence the resonance problem caused by the critical speeds does not happen since actual operating is in wet-run condition including operating fluid. As a result of unbalance response analysis, the pump rotor has stable vibration response at rated speed, regardless of operating fluid and the proposed bearing types.

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.

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.

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.

A Feature of Tapered Pressure-Dam Bearings.

This paper treats dynamic and static features of a sliding circular bearing with tapered grooves on its upper and lower sides. This bearing is called a tapered pressure-dam bearing in the present paper and designed in order to reduce lubricant pressure at high rotational speed. The preceding features of the bearing are analyzed by numerically solving the Reynolds equation and a heatconduction equation, considering the change of the ludricant temperature. The results show the designed bearing has a smaller value of cross-coupled stiffness coefficients when it is compared with a full circular bearing. Moreover, a Jeffcott rotor is used to investigate the stability characteristics of the bearing, and some design paremeters of the bearing are numerically determined to achieve good stability at high rotational speed. A comparison of the stability with a full circular bearing shows the proposed bearing possesses a better stability feature for a higher frequency region.

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.

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.

Static and Dynamic Characteristics of Orthogonally-Displaced Pressure Dam Bearings

An orthogonally-displaced pressure dam bearing is obtained by horizontally displacing the two halves of an elliptical pressure dam bearing. This bearing is more stable than the other pressure dam and fixed geometry bearings. This paper describes the static characteristics such as film pressures, oil flow, friction, etc., and dynamic characteristics, namely spring and damping coefficients and the stability threshold speed of this bearing supporting both rigid and flexible rotors.

Stability of Finite Orthogonally-Displaced Pressure Dam Bearings

During assembly, if the centers of the two halves of an elliptical pressure dam bearing are displaced horizontally, the bearing so obtained is termed orthogonally-displaced pressure dam bearing. The present paper describes the dynamic behavior of this bearing.

Experiments on the Stability of an Overhung Rotor in Pressure-Dam and Multilobe Bearings

Four sets of bearings were tested on a three-mass overhung flexible rotor: axial-groove, pressure-dam, and two sets of preloaded (0.75 and 0.40) multilobe bearings. The first and second critical speeds were observed at 3200 and 6800 rpm; predicted values were 2960 and 7420, respectively. The instability thresholds were observed to depend strongly on the load orientations for the axial-groove and multilobe bearing. The maximum instability thresholds (optimum load direction for the axial-groove, multilobe (m = 0.75), and multilobe (m = 0.40) bearings were 6700 rpm, 9200 rpm, and 6800 rpm, respectively. For the pressure-dam bearings, it was 6400 rpm and was predicted to be 5800 rpm. The lowest instability threshold for the axial-groove and multilobe bearings were 5750 rpm, 7600 rpm, and 6200 rpm, respectively. When known unbalances were added to the rotor in the pressure-dam bearings, the stability threshold was increased to above the safe running range of the rotor and a brief instability was observed as th...

Stability Analysis of Finite Offset-Halves Pressure Dam Bearing

Cylindrical pressure dam bearings are manufactured in two halves. During assembly, intentionally or accidentally, the centers of two halves may get displaced. This paper analytically analyzes the dynamic behavior of a cylindrical pressure dam bearing having centers of both halves displaced. Hence the bearing is termed as offset-halves pressure dam bearing. It has been observed that stability of a cylindrical pressure dam bearing can be increased many times by displacing the centers of two halves. The bearing so obtained is even superior to elliptical and half-elliptical pressure dam bearings in stability. A simple and inexpensive method of increasing stability of cylindrical pressure dam bearings has been analytically analyzed in this paper.

Dynamic Analysis of Finite Half-Elliptical Pressure Dam Bearings with Rotor Flexibility Effects

This paper presents an analytical study of dynamic characteristics of half-elliptical pressure dam bearings. One half (either upper or lower) of these bearings is elliptical, while the other half is circular. A step or pressure dam is cut in the upper half bearing surface. The lower half bearing surface is provided with a deep groove or relief-track. These bearings have been analyzed by the finite-element method. The results have been computed for dimensionless rotor flexibilities of 0.0, 0.5, 1.0, 2.0, and 4.0. Dynamic characteristics such as stiffness and damping coefficients, and stability threshold speed are presented in the form of graphs. It has been determined that half-elliptical pressure dam bearings are superior to circular pressure dam bearings in stability for bearings having same design parameters. Both these half-elliptical pressure dam bearings have almost identical dynamic characteristics. Rotor flexibility adversely affects the stability of these bearings and its effect is pronounced at h...

Stability of Finite Elliptical Pressure Dam Bearings with Rotor Flexibility Effects

The stability of two-axial groove cylindrical journal bearing is improved by milling a step or pressure dam in the upper half surface and by cutting a deep groove or relief-track in the lower half surface. Dynamic analysis of elliptical bearings having similar construction of dam and relief-track, called elliptical pressure dam bearings, has revealed that these bearings are far more stable than ordinary cylindrical, cylindrical pressure dam, elliptical, three-lobe, etc., when supporting a rigid rotor. In this paper, the stability of finite elliptical pressure dam bearings supporting flexible rotors is discussed. The dimensionless rotor flexibilities selected are 0.5, 1.0, 2.0, and 4.0, which cover almost the entire range of practical interest. Effects of design parameters such as vertical preset, L/D ratio, Sommerfeld number, dam location and relief-track width ratio on the stability of these bearings, corresponding to various dimensionless rotor flexibilities are presented in the form of graphs. Also, the effect of turbulence over the entire bearing surface has been included. The bearings have been analyzed by finite-element method. It has been found out that rotor flexibility adversely affects the stability of elliptical pressure dam bearings. The effect is pronounced at high Sommerfeld numbers. However, the zone of infinite stability remains unaffected with rotor flexibility.

Experiments on the Stability and Response of a Flexible Rotor in Three Types of Journal Bearings

Three sets of bearings were tested on a three-mass flexible rotor: axial-groove, pressure-dam and preloaded three-lobe, and the instability thresholds and unbalance responses were determined. The pressure-dam bearings were designed for maximum rigid rotor stability; the three-lobe bearings had preload factors of approximately 0.75. Rotor first and second critical speeds were observed at 2550 and 9800 rpm, respectively. The instability thresholds and unbalance responses at the first critical speed for the axial-groove and three-lobe bearings were found to be strongly dependent on the load orientation. Maximum stability limits of 6550, 7400 and 10 400 rpm were found for the axial-groove, pressure-dam, and three-lobe bearings, respectively. Thus, the preloaded three-lobe bearings were the only set that allowed this particular rotor to operate above the second critical speed. The experimental data were also compared to theoretical predictions. Differences in instability thresholds of up to 37 percent were rea...

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.

An Experimental Investigation on the Response of a Flexible Rotor Mounted in Pressure Dam Bearings

The response of a flexible rotor mounted in six bearing sets has been experimentally determined. One set of axial groove bearings and five sets of pressure dam bearings were tested. Conventional synchronous tracking was used in the analysis and other techniques utilizing an FFT analyzer were developed. The stability of the system was seen to strongly depend on the design of the step bearings. The dam bearings were also noted to lock into subsynchronous whip during deceleration after the system went unstable. The response of the system with varying degrees of unbalance is also analyzed and several structural resonances of the rotor system are discussed.

Experimental Study of Three Journal Bearings with a Flexible Rotor

The unbalance response and stability of a simple flexible rotor was tested over a speed range with three different types of journal bearings: axial groove, pressure dam and tilting pad. Measurements were made of total rotor response, synchronous response and frequency spectrums at various running speeds and at selected locations along the shaft. Axial groove bearings were better for low-speed use and near the critical speed but oil whip occurred at approximately twice the first rotor critical speed. Two sets of pressure dam bearings with different geometries were tested and both controlled vibrations at the critical speed. Whip occurred at twice and thrice the critical speed for the two pressure dam bearings. Tilting-pad beatings exhibited large vibration amplitudes near the critical speed, but did not go into oil whip at speeds up to three times the first rotor critical speed. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979