Study on Mixed Lubrication Performance of a New Type of Multi‐Liner Water‐Lubricated Stern Bearing Under Complex Working Conditions

In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic deformation of asperities and polymer matrix of the thrust pad, as well as the elastic deformation of the rubber support. The randomly distributed surface roughness of the thrust pad is generated by a mathematical model and shares the same distribution characteristics as the measured surface roughness. The Greenwood and Williamson asperity contact model and thin plate deformation model are combined to solve the asperities contact stress and deformation. Meanwhile, the bearing ML performance is compared with the results calculated by a thermohydrodynamic (THD) lubrication model and a thermo-elasto-hydrodynamic (TEHD) lubrication model, while the film thickness is also compared with measurements. The results show that the water film thickness calculated by the ML model is smaller than that by the THD model and the TEHD model, but the water film temperature is higher. The roughness has a great influence on the contact area ratio and the lubrication state, but little effect on the average film thickness. A higher roughness indicates a higher rotational speed required for the bearing to achieve full hydrodynamic lubrication. The film thickness calculated by the mixed lubrication model is closer to the measured results. Overall, it is proved that the mixed lubrication model can more accurately predict the lubrication performance of bearings. Compared to the thin plate deformation model, the elastic deformation simulation based on the half-infinite space model severely overestimates the elastic deformation of the pad surface, making it unsuitable for calculating the elastic deformation of the polymer matrix of the thrust pad under contact force or water film pressure. This ML deterministic model provides an effective means for high-precision prediction of the lubrication performance of the elastic supported water-lubricated thrust bearings coupled with multi-layer soft materials.

A slice method to determine the boundary conditions between the stern bearing and shaft by dividing the journal in the stern bearing into several slice elements along the axial direction is proposed for the first time. A comprehensive finite element model considering the nonlinear force of the water film and the flexibility of the propeller blade is established for a propeller-shaft system. The long bearing approximation is adopted to calculate the pressure distribution around each journal element in the stern bearing. The mode superposition method is employed. The nonlinear equation of motion is solved iteratively using the Newmark method. A parametric study is implemented to analyze the nonlinear vibration characteristics of the system. It is shown that the real motion state of the journal in the stern bearing can be simulated more precisely by the slice method proposed. The responses of the system alternate among period-one, quasi-periodic, multi-periodic, and chaotic motions as the rotating speed increases. The damping ratio has a significant effect on the dynamic characteristics of the propeller-shaft system. The motion of the system is unstable when the damping ratio is very small. At this time, the modes of the flexible propeller blades can be excited readily. The slice method, which can also be extensively used in similar rotor-bearing systems in the engineering field, is very simple and efficient to analyze the nonlinear vibration characteristics of a flexible propeller-shaft system supported by water film bearings.

The nonlinear time-domain lubrication characteristics of the hydrodynamic journal bearing system are studied in this paper. The motion equation of the hydrodynamic journal bearing system is established based on the balance of the relationship among the water film force, journal inertia force, and external load. The water film pressure distribution of the sliding bearing is calculated by the finite difference method. Firstly, the variation law of the water film pressure distribution with time under the external periodic load is calculated considering the inertial force of the journal. The influence of the initial eccentricity on the orbit of the journal center is studied. Secondly, the maximum water film pressure, the orbit of the journal center, eccentricity, water film pressure, and the minimum water film thickness of the bearing under the action of circumferential and unidirectional periodic external loads are calculated, and the effects of inertial force and rotational speed on the dynamic characteristics of the bearing are analyzed. Finally, the water film dynamic characteristics under low speed and heavy load are studied. The result shows that the pressure of the dimensionless water film caused by inertial force is reduced by 7 to 10 percent at the rotational speed between 200 r/min and 800 r/min, which means that the influence of inertia force cannot be ignored.

The 3D computational fluid dynamics (CFD) model and fluid structure interaction (FSI) model of water-lubricated rubber bearing with 10 axial grooves was built by ADINA and the influences of axial velocity, rotating speed on deformation of bearing bush and distribution of water film pressure are researched in this article. The results show that elastic deformation of bearing bush reduces water film pressure relative to rigid assumption; with the increasing of axial velocity, the deformation of bearing bush and water film pressure increases; and the axial velocity has a obvious influence on the front of bearing bush and water film pressure; with the increasing of bearing rotating speed, the deformation of bearing bush and water film pressure raises, but the deformation of bearing bush and water film pressure in water grooves are almost close to zero.

Due to the low viscosity of water, the water film is not easy to form, and the water-lubricated bearing system has the characteristics of airtightness. Therefore, it is difficult to obtain an accurate water film pressure distribution through experiments. Aiming at the loss of water film pressure in the process of water film pressure transmission caused by L-type pipeline in the existing wireless sensor testing methods for water film pressure, a mathematical model of water-lubricated bearing system pipeline pressure loss is established by numerical analysis method, and the corresponding physical model is established by using ANSYS software. The mechanism of pressure loss is studied by simulation. Finally, the test results were corrected and analyzed. The results show that the higher the flow rate of lubricating water at the inlet of the pipeline, the greater the pressure loss of the water film; the higher the shaft speed, the greater the local pressure loss; the longer the pipeline, the greater the pressure loss of the straight pipe section of the L-shaped pipeline, and the dynamic condition of the pipeline The pressure loss and energy loss are much more severe than static conditions.

In this paper, we focus on the hydrodynamic lubrication properties of different meshing pair profiles (the gate-rotor tooth flank shape and the corresponding screw thread flank shape) of water-flooded single screw compressors. A test rig was designed to verify whether the water flowing through the meshing pair clearance could take load. Three specimens with different profiles were tested under the water-flooded condition. The balance position of the specimen, the water film thickness under different applied load and the effective water film carrying capacity were tested. A numerical model was proposed to calculate the water film pressure distribution and the effective water film carrying capacity under different film thickness. The numerical solutions were compared with the test results and showed good coherence. The results show that the three specimens can all get balanced under the water film torques and can restore balance after disturbances. The water film at the leading flank of the specimen with multicolumns enveloped profile has the largest water film pressure peak and effective carrying capacity. This study can be applicable in the design of single screw compressors meshing pair profile.

PurposeThis study aims to investigate mixed lubrication performances of stern bearing in a misaligned state considering turbulence and bearing deformation impacts.Design/methodology/approachA mixed lubrication model of stern bearing is established. The generalized average Reynolds equation governing the turbulent flow of lubricant is analyzed by considering the interaction of bearing elastic deformation, asperity contact pressure and film pressure. The bearing behaviors including minimum film thickness, hydrodynamic pressure, asperity friction force and frictional coefficient are studied under different models. The correctness of this model is verified by comparing it with that of the published data.FindingsNumerical results indicate that elastic deformation noticeably decreases the maximum film pressure, the asperity contact force and the friction coefficient in the mixed lubrication stage. The effect of elastic deformation and turbulence reduces the transition speed from mixed to liquid lubrication.Originality/valueThis model includes both turbulence and bearing deformation impacts on journal bearing performances. It is expected that the numerical results can provide useful information to establish a stern bearing exposed to mixed lubrication conditions.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0352/

The deformation of marine water-lubricated stern bearing which the lining materials are polymer materials is much bigger than the bearing built with metal materials. So, in order to improve the calculate accuracy of elastic hydrodynamic, it is necessary to consider the deformation of the lining. Both pressure and thickness distributions of water film which contrasts with the hydrodynamic lubrication are presented by the Reynolds equation, and combining with the elastic deformation of the stern bearing solved by using the finite element method theory. The result shows that the stern bearing water film pressure of elastic hydrodynamic lubrication is lower than that of hydrodynamic lubrication, while the water film thickness is larger.

Tangential leakage loss is the primary factor that significantly affects the output performance of oil-free scroll expanders. A scroll expander can function under different operating conditions, and the flow of tangential leakage and generation mechanism is different. This study employed computational fluid dynamics to investigate the unsteady flow characteristics of the tangential leakage flow of a scroll expander with air as the working fluid. Consequently, the effects of different radial gap sizes, rotational speeds, inlet pressures, and temperatures on the tangential leakage were discussed. The tangential leakage decreased with increases in the scroll expander rotational speed, inlet pressure, and temperature, and decreased with decrease in radial clearance. With an equal-proportional increase in radial clearance, the flow form of the gas in the first expansion and back-pressure chambers became more complicated; when the radial clearance increased from 0.2 to 0.5 mm, the volumetric efficiency of the scroll expander decreased by approximately 5.0521%. Moreover, because of the large radial clearance, the tangential leakage flow maintained a subsonic flow. Further, the tangential leakage decreased with increase in rotational speed, and when the rotational speed increased from 2000 to 5000 r/min, the volumetric efficiency increased by approximately 8.7565%.

ABSTRACTExperimental research on the water film pressure of water-lubricated rubber bearings with multiple grooves (WLRBMG) was carried out. A test rig was designed that could measure various performance of WLRBMG to further study the properties of the bearing. The experimental results indicated that film pressure circumferential distribution of WLRBMG was different from that of conventional rigid bearings. The relatively low water film pressure led to a partial contact between the shaft and rubber bearings, which will cause significant rubber deformation. Integration of the friction coefficient and orbit of the shaft center also suggest that the WLRBMG operated in mixed lubrication. The multigroove structure had a significant influence on the film pressure circumferential distribution of WLRBMG. By detailed analysis of the experimental results, some properties and working mechanism of the WLRBMG have been found and demonstrated.

Water-lubricated rubber bearings are widely used in the propulsion shafting of military craft and ships. These bearings may wear down after a period of service, and consequently, their lubrication characteristics will change, affecting the operation of the shaft. Hydrodynamic lubrication characteristics of water-lubricated rubber bearings with partial wear at the bottom are studied by finite difference method. The steady-state characteristics of water-lubricated rubber bearings with wear and elastic deformation of rubber liner considered are solved with successive over-relaxation iteration method, and the dynamic characteristics are further calculated with finite perturbation method. The results show that water film thickness and distribution of water film pressure is significantly changed by wear. With the same eccentricity ratio, the maximum water film pressure, load capacity, attitude angle, and friction force are reduced by wear, but the friction coefficient is increased by wear. Under the same load, the minimum water film thickness and the maximum water film pressure are slightly affected by wear, the eccentricity ratio increases with the increase of wear, and the attitude angle and the friction coefficient decrease with the increase of wear. For large eccentricity ratios, the direct stiffness coefficients and direct damping coefficients are decreased by wear. The maximum allowable wear depth is approximately 1/6 of the bearing clearance.

The affect of the thrust pad inclination and ratio of length to breadth (L/B) on the lubricity of a water-lubricated thrust bearing is studied in numerical method. The research results indicate that when the elastic deformation is considered, the distribution of both water film thickness and pressure presents to be paraboloid. With the increase of thrust pad inclination, both maximum water-film pressure and the friction coefficient increase, and the minimum water-film thickness decreases first and then increases; when the L/B increases in the range of 1~2, both maximum water-film pressure and the friction coefficient increase, but the minimum water-film thickness decreases.

Surface topography plays an important role in mixed lubrication. However, the influence of the surface topography's morphological characteristics on lubrication performance is still not fully understood. In this article, we employ digital filtering and the Johnson transformation system, and we use a mixed plasto-elastohydrodynamic lubrication model to simulate the lubricated contact between rough spherical surfaces with different morphological characteristic parameters. The influence of skewness, kurtosis, and the wavelength factor, that is, the ratio between the autocorrelation lengths in the transversal and longitudinal directions, on contact pressure, film thickness, and von Mises (subsurface) stress, is examined with the mixed plasto-elastohydrodynamic lubrication model. The results confirm that plastic deformation leads to lower pressure distribution, distributed over a larger contact area than the pure elastohydrodynamic lubrication solution. Moreover, it is found that an increase in the kurtosis may improve the lubrication performance, while the opposite is true for the skewness and the wavelength factor. We believe that the insights obtained by means of the numerical simulations presented herein, would facilitate the design and manufacturing processes of the surfaces used for machine elements operating in the mixed plasto-elastohydrodynamic lubrication regime.

Transient load has a huge impact on the life and stability of water-lubricated bearings. In this paper work, CFD software is used to analyse the dynamic characteristic of water lubricated bearings under different transient loads of 500N, 1000N, 2000N and 3000N. The water film pressure contour distribution at different transient time was given. The time-varying relationships between the different transient loads with bearing forces, the journal displacement, the maximum value of water film pressure as well as the minimum value of water film thickness are obtained. The results show that with the increase of transient load, the effective bearing area of dynamic water pressure film decreases, and the maximum pressure increases. The bearing forces, the journal displacement, the maximum value of water film pressure as well as the minimum value of water film thickness will increase fast.

To study the effect of surface texture on the tribological characteristics of ship’s water-lubricated rubber bearings, the surface texture modification technology is applied to the friction surface of the lining, and the tribological characteristics of the surface texture are studied. The tribological characteristics of the flow field, such as velocity change, water film pressure distribution, and the influence of water film thickness on the surface texture flow field were discussed by simulation analysis. The results show that the average velocity is decreased on the texture surface, and the water film pressure obtained by the inclined cylinder pitted surface texture is the least.