Hydrodynamic Lubrication in a Nanoscale Bearing

2009 ◽  
Vol 60-61 ◽  
pp. 1-5 ◽  
Author(s):  
Chang Zheng Xiang ◽  
Yu Juan Wang ◽  
Yun Fei Chen
Keyword(s):  
Liquid Water ◽  
Effective Viscosity ◽  
Hydrodynamic Lubrication ◽  
Load Capacity ◽  
Water Film ◽  
Hydrodynamic Pressure ◽  
Shear Velocity ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
High Shear

Nonequilibrium molecular dynamics simulation is used to simulate the hydrodynamics lubrication in the nanoscale bearing. A physical model of the nanascale bearing that the thin liquid water film confined between two solid walls has been set up. The simulation results indicate that the hydrodynamic pressure profiles as the macroscopic state are formed in nanoscale bearings. The hydrodynamic pressure increases with increasing shear velocity, and corresponding load capacity also increases with increasing sliding velocity of the upper driven wall. These results are in accordance with classical Reynolds’ theory about hydrodynamic lubrication. On the other hand, the shear thinning behavior of the liquid water film appears, so that effective viscosity decreases under high shear velocity. Although effective viscosity of water film decreases under high shear velocity, this phenomenon doesn’t affect the hydrodynamic lubrication of the nanoscale bearing.

Hydrodynamic Pressure of Thrust Step Bearings

2009 ◽  
Author(s):  
Shuangbiao Liu ◽  
W. Wayne Chen ◽  
Diann Y. Hua
Keyword(s):  
Analytical Solution ◽  
Coordinate System ◽  
Laplace Equation ◽  
Analytical Solutions ◽  
Hydrodynamic Lubrication ◽  
Load Capacity ◽  
Hydrodynamic Pressure ◽  
Finite Width ◽  
Cylindrical Coordinate ◽  
Lubrication Models

Step bearings are frequently used in industry for better load capacity. Analytical solutions to the Rayleigh step bearing and a rectangular slider with a finite width are available in literature, but none for a fan-shaped thrust step bearing. This study starts with a known solution to the Laplace equation in a cylindrical coordinate system, which is in the form of infinite summation. An analytical solution to pressure is derived in this paper for hydrodynamic lubrication problems encountered in the fan-shaped step bearing. The presented solutions can be useful for designers to maximize bearing performance as well as for researchers to benchmark numerical lubrication models.

Hydrodynamic lubrication in nanoscale bearings under high shear velocity

2006 ◽  
Vol 125 (8) ◽  
pp. 084702 ◽  
Author(s):  
Yunfei Chen ◽  
Deyu Li ◽  
Kai Jiang ◽  
Juekuan Yang ◽  
Xiaohui Wang ◽  
...  
Keyword(s):  
Hydrodynamic Lubrication ◽  
Shear Velocity ◽  
High Shear

A hydrodynamic lubrication model and comparative analysis for coupled microgroove journal-thrust bearings lubricated with water

2019 ◽  
Vol 234 (11) ◽  
pp. 1755-1770
Author(s):  
Guo Xiang ◽  
Yanfeng Han ◽  
Renxiang Chen ◽  
Jiaxu Wang ◽  
Xiaokang Ni ◽  
...  
Keyword(s):  
Thrust Bearing ◽  
Hydrodynamic Lubrication ◽  
Load Capacity ◽  
Mutual Effect ◽  
Hydrodynamic Pressure ◽  
Isosceles Triangle ◽  
Maximum Load ◽  
Hydrodynamic Effect ◽  
Thrust Bearings ◽  
Lubrication Performance

The novelty of this study is to develop a hydrodynamic lubrication numerical model for coupled microgroove journal-thrust bearings (or coupled bearings) under water-lubricated condition. In the present model, the continuity of the hydrodynamic pressure and the fluid field (or coupled hydrodynamic effect) at common boundary is considered to reveal the mutual effect between the hydrodynamic behavior of the journal bearing and the thrust bearing. The lubrication performances of the coupled microgroove bearing with three bottom shapes, i.e., isosceles triangle, right triangle, and left triangle, are studied comparatively. Additionally, the effects of the microgroove depth on the lubrication performances of the coupled bearing are discussed. The present study reveals that the coupled hydrodynamic effect generated by the coupled bearing can improve the lubrication performance for both the journal and the thrust bearing. The microgroove with left triangle bottom shape yields the optimal lubrication performance as compared to the other two. There is an optimal groove depth that generates the maximum load capacity and the minimum friction coefficient for both the journal and the thrust bearing.

Molecular Simulation on Explosive Boiling of Water on a Hot Copper Plate

2013 ◽  
Author(s):  
Yijin Mao ◽  
Yuwen Zhang
Keyword(s):  
Liquid Film ◽  
Liquid Water ◽  
Water Film ◽  
Copper Plate ◽  
Dynamics Simulation ◽  
Bulk Liquid ◽  
Water Molecules ◽  
Confined Space ◽  
Explosive Boiling ◽  
Short Period

In this paper, molecular dynamics simulation is carried out to study the explosive boiling of liquid water film heated by a hot copper plate in a confined space. A more physically-sound thermostat is applied to control the temperature of the metal plate and then to heat water molecules that are placed in the elastic wall confined simulation domain. The results show that liquid water molecules close to the plate are instantly overheated and undergo an explosive phase transition. A huge pressure in the region between liquid film and hot copper plate formed at the beginning and leads to a low density vapor region by partially vaporizing water film. A non-vaporization molecular layer, with a constant density of 0.2 g/cm3, tightly attached to the surface of the plate is observed. The z-component of COM (center of mass) trajectory of the liquid film in the confined space is tracked and analyzed. The one-dimensional density profile indicates the water film have a piston-like motion after short period of explosive boiling. Temperatures at three corresponding regions, which are vapor, liquid, and vapor from the top plate surface, are also computed and analyzed along with the piston-like motion of the bulk liquid film.

scholarly journals A New Method to Calculate Water Film Stiffness and Damping for Water Lubricated Bearing with Multiple Axial Grooves

2020 ◽  
Vol 33 (1) ◽  
Author(s):  
Guojun Ren
Keyword(s):  
Analytical Procedure ◽  
Load Capacity ◽  
Water Film ◽  
New Method ◽  
Hard Materials ◽  
Stiffness And Damping ◽  
Film Stiffness ◽  
Hydro Turbines

Abstract Water lubricated guide bearings for hydro turbines and pumps are conventionally designed with multiple axial grooves to provide effectively cooling and flushing away abrasives. Due to the variety of groove configuration in terms of number and size, a predication of their performance is difficult. This paper deals with an analytical procedure to investigate groove effect on load capacity, stiffness and damping for this type of bearing where it is considered as an assembly of many inclined slide bearings. The result can be applied to bearings made of hard materials combined with low bearing pressure.

Dynamical Behavior and Flow Mechanism of Fluid in Nanochannel by Molecular Dynamics Simulation

2009 ◽  
Author(s):  
Juanfang Liu ◽  
Chao Liu ◽  
Qin Li
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Dynamical Behavior ◽  
Velocity Profiles ◽  
The Other ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Interfacial Region ◽  
Flow Mechanism ◽  
Bulk Fluid

The flow properties and dynamical behavior of fluid in a nanochannel were investigated by nonequilibrium molecular dynamics simulation. First of all, the locale distribution of molecules in the channel is found to be strongly inhomogeneous compared to the bulk fluid. In the vicinity of the wall, portion of the fluid molecules are absorbed on the surface of wall due to the strong interaction of the atoms between the wall and liquid, so that the fluid density in the contact region would be much larger than one of the bulk fluid. But in the other region, the local density value approaches one of the bulk fluids with the increasing distance from the wall. This oscillatory behavior of density resulted in different motion behavior of molecules in the different region of nanochannel. The molecular behavior in the interfacial region is remarkably different from those of fluid atoms in the center of channel and wall atoms, which posses both the motion properties of bulk liquids and a solid atom. At the molecular level, macroscopic continuum hypothesis failed, that is, the results predicted by the Navier-Stoke equations deviate from the simulation data adopted by molecular dynamics simulation. In the paper, the velocity profiles for the channels with different width were plotted, which demonstrated that the time-averaged velocity profiles was not quadratic when the channel width was less than 10 molecular diameters. But on the other cases, the velocity profiles will agree well with the analytical solution based on the NS theory. The molecular dynamics simulation method can withdraw the important microscopical information from the simulation process, which benefit to analyze the flow mechanism at such length scale channel.

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