Elliptical Bearing Research Articles

Dynamics modeling and fault diagnosis of flexible thin-walled elliptical bearings in harmonic reducers

Harmonic reducers, crucial in industrial robots for their high load capacity and low friction, often rely on Flexible Thin-Walled Bearings (FTWBs). However, these bearings are particularly prone to failure due to the cyclic alternating stress loads they experience, stemming from their unique elliptical structure. This study presents a dynamic model for the Flexible Thin-Walled Bearing (FTWB) using a finite element approach. Stress distribution and motion characteristics were analyzed, revealing maximum stress at major and minor axis positions during operation. The model was tested under three conditions: normal, outer ring fault, and inner ring fault. A vibration test rig was constructed to gather real vibration signals, enabling model validation and analysis of vibration signal characteristics under different conditions. This research sheds light on the mechanisms of impact and fault signal generation in FTWBs, offering valuable insights for dynamic analysis and fault diagnosis in FTWBs and harmonic drives.

Elliptical periodic shock of flexible thin-walled elliptical bearing and its separation using singular value decomposition of adding additional signal

Flexible thin-walled elliptical bearing (FTEB) is a new type of bearing, and its elliptical inner and outer rings make its vibration signal exhibit very unique characteristics, which are completely different from ordinary bearing. The experiment results of vibration detection show that the vibration signal of healthy FTEB presents elliptical periodic shocks, while ordinary bearing has no such shocks. The frequency composition of elliptical periodic shocks is determined. Elliptical periodic shocks are great interference to the fault periodic shocks, masking the waveform of fault periodic shocks and the fault characteristic frequency, thus concealing the fact of bearing failure. A new signal separation algorithm, singular value decomposition of adding additional signal (SVDAAS), is proposed to separate elliptical periodic shocks. By adding specific frequencies to the original signal, singular value distribution of the original signal can be changed so that the singular values corresponding to the specific frequencies can be identified and the desired frequency components can be separated by inverse singular value decomposition. SVDAAS can accurately extract single or multiple frequency components distributed in any frequency band. The shock signal separation example of the damaged FTEB shows that SVDAAS accurately separates the elliptical periodic shocks from the complex mixed periodic shocks, while the weak fault periodic shocks are unaffected, so that the fault status of FTEB is revealed. Compared with the popular frequency separation methods, SVDAAS obtains more accurate fault periodic shocks and stronger fault characteristic frequency.

Multidisciplinary design and optimization of journal bearing for high-power wind turbine speed increaser

With the increasing power of wind turbine generators (WTG), the failure rate of rolling bearings in wind turbines due to insufficient bearing capacity increases with the increase of bearing size. To overcome these challenges, this paper proposes a design optimization method for the rectangular groove elliptical sliding bearing (RGEB) of the WTG output shaft. This method can maximize the radial bearing capacity under the premise of ensuring that the oil film pressure is large, the end leakage and the temperature rise are small. The multidisciplinary design and modeling of RGEB are carried out according to the structure and working conditions of WTG. Based on computational fluid dynamics (CFD), the influence of the number of rectangular dynamic pressure grooves on the bearing performance is analyzed. The kriging model, BP neural network model, and SSA-BP model are constructed for each performance index of RGEB, to establish a high-precision combined surrogate model based on global error criterion. After establishing the optimization equation, the PSO and SQP combined optimization algorithm is used to optimize the optimal structural parameters. The results show that the bearing capacity of the optimized RGEB is 95.9% higher than that of the ordinary elliptical bearing (EB) without increasing the size and quality of the bearing. In addition, the combined surrogate model can effectively replace the expensive finite element model to deal with the WTG sliding-bearing optimization problem.

Computational fluid dynamics study to investigate the performance of fluid film journal bearings with different geometries

The geometry of a hydrodynamic journal bearing plays a vital role in the rotating machinery. In this work, the performance characteristics of the plain and elliptical journal bearings are carried using Computational Fluid Dynamics (CFD) approach. An alternative approach to thermo-hydrodynamic analysis is presented assuming that all the heat that is generated by viscous shear in the fluid film is dissipated only in the fluid (no heat conduction through the boundaries). The effect of lubricant viscosity and bearing geometry on the pressure distribution is presented. The analysis is done for a wide range of speed (500–1000 rpm.) and lubricant viscosity at 1000 N load. In this paper, the theoretical results obtained are validated by computational methodology. The pressure distribution in the elliptical bearing is highly increased as compared to the plain bearing. The percentage increase upto 370.44 % is observed in the elliptical bearing. The Computational Fluid Dynamics (CFD) method can be very useful tool for study on the bearing lubrication problem and can accurately predict the performance characteristics of hydrodynamic journal bearing.

Theoretical Comparison of Characteristics between Elliptical and Conventional Hydrodynamic Journal Bearing

In this research, two subjects are presented. The first one was, studying the effect of the ellipticity ratio on the bearing performance characteristics (flow rate, load number, power absorbed, and stiffness coefficients), where three different values of the ellipticity ratio (0.5, 1, and 1.5) were studied and the conventional bearing was considered as a reference for comparison with the elliptical bearing of different values of ellipticity ratio to demonstrate the effect of ellipticity ratio on the bearing performance, while the other aspect was, studying the effect of aspect ratio on the elliptical bearing performance. Three different values of aspect ratio (0.5, 1, and 1.5) were studied. This was achieved within the range (0.1 - 0.8) for the eccentricity ratio. The finite difference method was used to solve Reynold’s equation numerically to obtain the pressure distribution on the bearing surface and then the bearing characteristics were computed. The computer program (Matlab R2015a) was used for solving the equations used in this study. From the results, it was observed that increasing the ellipticity ratio gives an increase in the flow rate values and a decrease in the (load number, power losses, Krr, Kss, |Krs| and Ksr) values, while, increasing the aspect ratio gives an increase in the (flow rate, power losses, Krr, Kss, |Krs| and Ksr) values and a decrease in the load number values. It was also observed that the elliptical bearing has a (higher flow rate, lower load capacity, and less power losses), than the conventional bearing. In addition, the elliptical bearing has higher principle stiffness coefficients (Krr and Kss) in the region (n<0.41) and (n<0.66), respectively, and lower cross-coupling stiffness coefficients (Krs and Ksr), than the conventional bearing.

Study on antifriction mechanism of surface textured elliptical bearings

Abstract The surface micro texture can improve the surface tribological properties of friction pairs. As a two oil wedge bearing, elliptical bearing can restrain the journal whirl and maintain the stable operation. In the manuscript, the surface micro-texture is combined with elliptical bearing, and the influence of micro-texture shape, micro-texture depth and micro-texture radius on oil film pressure, bearing capacity and friction coefficient of elliptical bearing is studied by theoretical calculation and experimental research. The results show that with the increase of micro-texture depth, the bearing capacity first increases and then decreases; and when the dimensionless texture depth is 0.03, the bearing friction is the lowest and the bearing capacity is the highest. When the dimensionless radius of the micro texture is v3, the lubrication performance of the bearing is the best. When the shape of micro-texture is circle or triangular, the lubrication performance of elliptical bearing can be improved.

Linear and Nonlinear Performance Analysis of Hydrodynamic Journal Bearings with Different Geometries

In rotor dynamics, a traditional way of representing the dynamics of hydrodynamic bearings is using stiffness/damping coefficients. It is thus necessary to carry out a linearization of hydrodynamic forces around the shaft’s equilibrium position. However, hydrodynamic bearings have highly nonlinear nature, depending on operating conditions. Therefore, this paper discusses the applicability of these linear/nonlinear approaches using a computational model of the rotating system, where the finite element method is used for rotor modelling and the finite volume method for bearing calculation. The main goal is to investigate the boundaries for linear approximation of the hydrodynamic forces present in lobed hydrodynamic bearings, with the system operating under high loading conditions. Several numerical simulations were performed varying preload parameter and rotating speed. A comparison of the system’s responses, in time domain (shaft orbits) and frequency domain (full spectrum), is made for linear and nonlinear models. Results showed that trilobed bearings are more susceptible to nonlinearities, even in situations of smaller vibration amplitudes, while elliptical bearings are sensitive only under larger vibration amplitudes. These analyses are of great importance for mapping the influence of nonlinearities in different types of lobed hydrodynamic bearings with fixed geometry, varying the preload parameter to verify the influence on the system’s dynamic response. This study is important and serves as the basis for cases of monitoring and fault diagnosis (in the field of structural health monitoring) since it is crucial to distinguish what would be a fault signature or a standard nonlinear effect created by the use of hydrodynamic bearings.

Effects of Scratches on Lubrication Performance of Elliptical Bearing and Stability of Rotor System

Effects of Scratches on Lubrication Performance of Elliptical Bearing and Stability of Rotor System

Thermo-hydrodynamic simulation study of twin-groove elliptical (two-lobe) journal bearing of steam turbine with experimental investigations

The present paper reports an experimental and theoretical investigation on performance behaviour of twin-groove elliptical (two-lobe) white metal hydrodynamic journal bearing used in steam turbines. The experiments are performed on a fully automatic journal bearing test rig with provisions to various operating conditions (i.e. load, speed, and lubricant temperature). The performance behaviour in terms of coefficient of friction, lubricant inlet temperature, load carrying capacity, journal displacement, weight loss etc. has been presented. In addition to this, numerical investigations have also been performed with the numerical solution of governing Reynolds equation using FEM (finite element method) technique and Jakobsson-Floberg-Olsson (JFO) boundary condition. The experimentally obtained and theoretical results have been correlated.

Static thermal performance evaluation of elliptical journal bearings with nanolubricants

Journal bearings of different configurations have been extensively used in turbomachinery and power generating equipments. Although circular bearings have simplest configuration and commonly used journal bearings, non-circular bearings such as multi-lobe and elliptical bearings have an added advantage of lower lubrication film temperature alongwith stable operation. In this study, static thermal performance of pure elliptical bearing lubricated with nanoparticles based mineral oils has been studied at different eccentricity ratios and bearing speeds. Two types of nanoparticles, namely, CuO and TiO2 with 0.5, 1.0 and 2.0 wt.% concentrations have been separately added in three different viscosity grades of oils. The effect of nanoparticles on thermo-physical properties of oil was considered to compute bearing performance parameters (pressure distribution, load capacity, oil temperature and power losses). Bearing model was generated by taking into account the modified Krieger Dougherty method to determine viscosity at different combinations of oils and nanoparticles. The findings indicate the increase in maximum pressure and load capacity with addition of nanoparticles and this increase was more pronounced at higher concentrations of nanoparticles and at higher viscosity grade oils. Load capacity was found to be increased by 14.24% and 9.21% with 2 wt% concentration of TiO2 and CuO nanoparticles respectively in base oil (AW68) at eccentricity ratio of 0.7. An increase in load capacity with nanolubricants was achieved without an appreciable increase in oil temperature.

Theoretical and experimental dynamics analysis of rotor-bearing system supported by elliptical bearings

PurposeHigh power and speed are new demands for rotating machinery which needs the journal bearings with high dynamic characteristics. The critical speed of the rotor-bearing system is one of the most significant parameters to evaluate the dynamic characteristics. This paper aims to investigate the theoretical and experimental analysis of a rotor system supported by large diameter elliptical bearings.Design/methodology/approachTo obtain the theoretical and experimental support for rotor-bearing system design, dynamic characteristics theoretical analysis based on the finite difference method is given and an experiment focuses on critical speed identification is carried out.FindingsThe theoretical calculation results indicate that the critical speed is near to 800 rpm and there is no large vibration amplitude round working speed (1,500 rpm). Using the test bench in the factory unit, vibration data including three experimental processes are obtained. According to the vibration data, the critical speed is identified which also indicates that it is stable when working at 1,500 rpm.Originality/valueThe design method for the rotor system supported by large diameter elliptical bearing can be obtained by the theoretical and experimental results shown in this paper.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0122/

Bearing type influence on vibration activity at coasting of bent double-span rotor with skew-symmetric residual unbalance

The paper is dedicated to study the dependence of vibration activity at coasting of high-temperature segment of turbine unit (TU), which includes high pressure and medium-low pressure rotors (HPR-MLPR system) with skew-symmetric residual unbalance of each rotor, from frequently used types of bearings. Six-block segmental and elliptical bearings are considered. The study takes into account the presence of unrecoverable initial deflection of the shaft. Calculations are performed for turbine model K-300-23.5. Detailed analysis of results is performed.

Influence of the Bearing Type on Vibration Activity of a Double-Span Rotor with a Skew-Symmetric Residual Imbalance

The dependence of the vibration activity of the high-temperature part of a turbo-unit containing a high-pressure rotor and a medium–low–pressure rotor under a skew-symmetric residual imbalance of each of the rotors on the type of bearings most often used is studied. Six-pad segmental and elliptical bearings are considered. The presence of unavoidable deflection of a shafting is taken into account in the study. The calculations are performed for the turbine of K-300-23.5 type manufactured by PJSC Power machines at the Leningrad Mechanical plant (LMP). The results obtained are analyzed.

Geometrical analysis of elliptical journal bearings and its effects on friction and load capacity

Elliptical bearings are one type of non-circular journal bearings which has two main advantages over the conventional circular bearings: lower temperature rise and lower vibrations. In this study, the energy equation and Reynolds equation are simultaneously solved under adiabatic boundary conditions. The predicted pressure and temperature are compared to the results of published literature for verification purposes. A parametric study is then conducted on the effect of geometrical parameters of the elliptical journal bearing on the load capacity, friction force, pressure, and oil temperature. Effect of geometric parameters of the bearing on the performance is studied. The results show that non-circularity parameter is the most influential parameter in the bearing, and an increase in the non-circularity results in the decrease in maximum pressure and temperature as well as the friction force. Increasing the eccentricity ratio, on the other hand, will cause an increase in the pressure, temperature, and the friction force. Changes in the angle between the major axis of the bearing and load direction decrease the load-carrying capacity and the non-dimensional pressure and results in an increase in the friction coefficient.

Dynamic behaviors of a high-speed turbocharger rotor on elliptical floating-ring bearings

Floating-ring bearings are commonly used in automotive turbocharger applications due to their low cost and their suitability under extreme rotation speeds. This type of bearings, however, can become a source of noise due to oil whirl-induced sub-synchronous vibrations. The scope of this paper is to examine whether the concept of a floating-ring bearing with an elliptical clearance might be a solution to suppress sub-synchronous vibrations. A very time-efficient approximate solution for the Reynolds equation to the geometry of elliptical bearings is presented. The nonlinear dynamic behaviors of a turbocharger rotor supported by two concepts of elliptical floating-ring bearings are systematically investigated using run-up simulations. For the first concept of elliptical floating-ring bearings i.e. the outer bearing of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(b) in the article), some studies have pointed out that its steady-state and dynamic performances are superior to plain cylindrical floating-ring bearings but, the nonlinear run-up simulation results shown that this type of elliptical floating-ring bearings is not conducive to reduce the self-excited vibration levels. However, for the second type of elliptical floating-ring bearings i.e. both the inner and outer films of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(c) in the article), it is shown that the sub-synchronous vibrations have been considerably suppressed. Hence, the second noncircular floating-ring bearing design is an attractive measure to suppress self-excited vibrations.[Figure: see text]

Experimental study for performance evaluation of steadily loaded true elliptical and orthogonally displaced non-circular journal bearing profiles

Purpose The non-circular journal bearings may be used over circular journal bearings because of their superior thermal stability. The paper aims at experimental study of thermal performance of two different true elliptical and orthogonally displaced non-circular journal bearing profiles. Design/methodology/approach The experiments have been conducted on a specially designed test rig which simultaneously evaluates oil film pressure and temperature along the circumference of non-circular journal bearing. The tests are conducted for the designed true elliptical and orthogonally displaced journal bearing at three different rotational speeds of 2,000, 3,000 and 4,000 rpm under the influence of steadily applied load varied from 0.5 to 2.0 kN. The data collected during experimentation have been used to evaluate thermal performance parameters such as maximum pressure, flow rate and effective temperature of the bearings under study. Findings It has been observed experimentally that two lobes of pressure and temperature have been obtained for both the elliptical and orthogonally displaced journal bearing. The negative pressure zone (cavitation area) has been observed to be reduced along the circumference for both the journal bearings which results in less thermal degradation of an oil as compared to circular journal bearing. The oil film pressure and temperature increases with the increase in radial load of both the bearings. The maximum temperature rise of oil film is more in case of elliptical bearing as compared to the orthogonally displaced bearing. Originality/value The experimental data presented in this paper will help the designers to select such kind of non-circular journal bearing for various applications. The designed bearings have resulted in reduced cavitation zone and two positive pressure lobes have been observed which may result in application of such bearings as an alternate for circular journal bearing.

Simulation studies on static thermal behaviour of true elliptical and orthogonally displaced non-circular journal bearing

Purpose The current trend of modern industry is to use machineries which rotate at high speed along with the capability of carrying heavy rotor loads. This paper aims at static thermal analysis of two different profiles of non-circular journal bearings – a true elliptical bearing and orthogonal bearing. Design/methodology/approach The Reynolds equation has been solved through finite difference method to compute the oil film pressure. Parabolic temperature profile approximation technique has been used to solve the energy equation and thus used for computation of various bearing performance characteristics such as thermo-hydrodynamic oil film pressure, temperature, load capacity, Sommerfeld number and power loss characteristics across the bearing. The effect of ellipticity ratio on the bearing performance characteristics has also been obtained for both the elliptical and vertical offset bearing using three different commercially available grades of oil (Hydrol 32, 68 and 100). Findings It has been observed that the thermo-hydrodynamic pressure and temperature rise of the oil film is less in orthogonal bearing as compared to the true elliptical bearing for same operating conditions. The effect of ellipticity ratio of non-circularity on bearing performance parameters have been observed to be less in case of elliptical bearing as compared to orthogonal bearing. It has been concluded that though the rise in oil film temperature is high for true elliptical bearing, but still it should be preferred over orthogonal profile under study, as it has comparably good load-carrying capacity. Originality/value The performance parametric analysis will help the designers to select such kind of non-circular journal bearing for various applications.

Analysis of the Stability of Elliptical Journal Bearings under Vapor Cavitation Erosion

The phenomenon of lubricant cavitation in hydrodynamic bearings and its effect on the stability has been rigorously studied and reported in the literatures. In certain cases, cavitation has significant effect on the dynamic and stability characteristics of the rotor-bearing system. With a proper control of the cavitation condition and groove location, stability can be achieved over a wide range of operating speed, in the case of elliptical journal bearings. On the other hand, the stability is not affected by the presence of vapor cavitation, in the case of multi-lobe journal bearings with the oil supplied at atmospheric pressure. For the unstable, submerged, circular bearings, vapor cavitation phenomena results in a distinctive vibration response observable on the vibration plots. The stability of the elliptical journal bearings under the influence of vapor cavitation erosion was analyzed. It is found that vapor cavitation erosion on elliptical bearings results in instability of the whirling shaft. Collapse of the vapor cavitation bubbles causes erosion wear that falls within the pressure zone of the elliptical bearing, thus causing the instability.

A Comparative Performance Analysis of Gas Lubricated Cylindrical and Elliptical Journal Bearings

The finite element method is employed to perform a comparative analysis of gas lubricated cylindrical and elliptical journal bearings in this work. A finite element procedure, based on the Galerkin weighted residual method, is specially devised to solve the zeroth- and first-order lubrication equations for plain cylindrical and non-cylindrical hydrodynamic journal bearings running on thin gas fluid films. Load-carrying capacity and dynamic force coefficients of gas cylindrical and elliptical journal bearings are computed for some geometric and operating parameters, such as journal eccentricity ratio and rotational speed. Several comparative curves of steady-state and dynamic bearing characteristics depict the differences in the behavior of some gas lubricated fixed-geometry journal bearings.

SOME GEOMETRICAL DATA FOR THE ELLIPTICAL BEARINGS IN ARTIFICIAL ROBOTS

In this paper are considered analogies between elliptical-slide bearing occurring in artificial robots and elliptical natural human joints as well artificial human femoral prosthesis. The comparisons between elliptical human femoral prosthesis and mechanical spherical bearings indicate the advantages implicated from the use of elliptical slide bearings. To