To study the effect of surface roughness on the lubrication characteristics of water-lubricated rubber bearings (WLRBs) when the stern shaft is tilted, the surface roughness of the bearings was measured by a surface roughness measuring instrument. Considering the tilting stern shaft and surface roughness, a mathematical model was constructed and water film thickness equation was deduced. By adopting the finite difference method, the film thickness and pressure distribution of WLRBs with tilt angle and roughness were analysed. The effects of tilt angle on film thickness and pressure under different surface roughness amplitudes and wavelengths were studied, and the results were then compared with those of smooth surface bearings without tilt angle. Finally, the minimum film thickness and maximum film pressure were analysed. The results showed that when the tilt of rotor and surface roughness of bearing were considered simultaneously, the film thickness exhibited a jagged distribution in the circumferential direction and decreased gradually in the axial direction. The film pressure had slightly irregular fluctuations and a sharp pressure peak. The tilt angle and roughness reduced the minimum film thickness, and the film thickness difference increased. The film pressure increased rapidly and local pressure exhibited slight, sudden changes. The surface roughness amplitude and wavelength had a considerable influence on the water film thickness, and the roughness amplitude had a clear effect on the film pressure. As the roughness amplitude increased, the minimum film thickness gradually declined and film pressure peak fluctuation grew. As the roughness wavelength increased, the film thickness fluctuated irregularly within a certain range of magnitude, and the minimum film thickness was almost constant.
To study the lubrication characteristics of water-lubricated rubber bearings (WLRBs) in-mixed flow state, based on the classical laminar and turbulent lubrication theories, the mixed-flow lubrication equations were established for WLRBs. Adopted the finite difference method, the variation of Reynolds number, water film thickness and pressure with eccentricity, rotational speed and length-to-diameter ratio under mixed-flow lubrication model were investigated. The results show that the mixed-flow lubrication equations are more suitable for WLRBs in actual operating conditions than the laminar and turbulent theories. In the mixed-flow lubrication model, the Reynolds number decreases when the eccentricity increases in pressure-bearing zone; meanwhile, it increases with the rotational speeds. The water film thickness decreases when the eccentricity increases. The film pressure increases with eccentricity and rotational speed. This study can provide reference for the accurate analysis of WLRBs lubrication characteristics under actual engineering applications. K E Y W O R D Smixed-flow state, the Reynolds number, water film pressure, water film thickness, water lubricated rubber bearings
To study the lubrication characteristics of water-lubricated rubber bearings under high-Reynolds-number operating conditions, four different turbulent lubrication mathematical models are used. With these models, adopting the finite difference method, initially, the distributions of the Reynolds number, water film thickness, lining deformation, and film pressure are analyzed. Second, for the same models, the variation in the Reynolds number with the eccentricity is investigated. Third, the bearing capacity and maximum film pressure variation with the eccentricity, rotating speed, and clearance ratio for the four turbulent lubrication models are examined. The results show that the lining deformation and maximum film pressure of the above models are larger than those of laminar lubrication models, and according to the importance of descending orders, they are as follows: Aokihiro-Harada Masahiro turbulence model, Ng–Pan model, Constantinescu model, and Hirs model; the type of the lubrication model has a little effect on the Reynolds number. The bearing capacity and film pressure calculated by the turbulent lubrication models are much higher than those by the laminar lubrication model, and the laminar flow assumption is no longer applicable to the actual operating conditions of the water-lubricated rubber bearings at a high Reynolds number. Concurrently, the Aokihiro-Harada Masahiro turbulent lubrication theory is more accurate than the other three lubrication models. With the increase in the eccentricity and rotational speed, the bearing capacity and maximum film pressure increase non-linearly and approximately linearly, respectively. By contrast, with the increase in the clearance ratio, the bearing capacity exhibits a non-linear decrease, whereas the pressure increases approximately linearly.
In order to obtain the loading capacity and its variation of the squeeze-film air bearing, taking an air bearing as the research object, the structure model and the equivalent disk model of the squeeze-film air bearing are established. The modal analysis of the designed structure is carried out, the mode of the bearing structure in the ultrasonic frequency range and the working squeeze frequency of the bearing are obtained. At the same time, the influence of air film thickness on the load characteristics of squeeze-film air bearing is analyzed by the fluid-solid coupling method. The relationship between air film thickness and loading capacity, and the relationship between contact area and loading capacity are obtained respectively by above method. The results show that reducing the gap between the bearing bush and the rotor, increasing the amplitude of the bearing bush and increasing the contact area between the bearing bush and the rotor can improve the loading capacity of the squeeze-film air bearing.
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