Xin Kai Li

On the influence of lubricant properties on the dynamics of two-dimensional journal bearings

In dynamically loaded journal bearings it is important to predict and assess the performance of lubricants within the bearing with respect to friction, wear and load bearing capacity over a wide range of operating conditions. In this paper, a mathematical model is described which allows for a systematic study of the effects of shear-thinning, pressure-thickening and temperature-thinning viscosity on the dynamics and stability of a journal bearing. It is also shown that the thermal conductivity of the bearing can have a major effect on the minimum oil film thickness attained in the bearing.

Challenges in developing a multidimensional Feature Selective Validation implementation

Feature Selective Validation (FSV) was incorporated as core component of IEEE Std 1597.1. Recently, discussions have moved from ‘is quantitative comparison of data needed?’ to ‘how can this be applied to multidimensional data?’ The purpose of this paper is to present some of the latest thinking about the key challenges in developing a 1D model to unlimited dimensionality. In particular, the paper will present: (1) a revised mathematical framework for FSV, e.g. using tensor notation to simplify the mathematical representation. (2) A discussion on how the performance of n Dimensional FSV can be verified against human perception. (3) A review on the effects of data that oscillates between positive and negative data points, e.g. transients.

A transient thermal analysis for dynamically loaded bearings

A transient thermal analysis for a dynamic journal bearing system is presented in this paper based on a non-isothermal non-Newtonian fluid model. A spectral element approach is used to solve the full set of coupled equations (kinematics and constitutive) governing the flow of the lubricant, and an operator-splitting spectral element approximation is used to solve the dynamic energy equation. The transient thermal effects in the lubricant viscosity, non-Newtonian lubricant film thickness, variation of the journal rotating speed and time dependent applied load are investigated in this paper. The numerical results indicate that the thermal dynamic analysis plays an important role in the design of the journal bearing systems, especially, under large applied loads and high rotating speeds.

Perturbation solution of non-Newtonian lubrication with the convected Maxwell model

A fascinating and largely unsolved problem in tribology concerns the effect of visco-elasticity on lubrication flow characteristics. The paper has re-addressed this problem by using a perturbation method. The impact of the paper is that we theoretically provide an asymptotic solution based on the flow between two narrow surfaces with a convected Maxwell model and show that the viscoelasticity does indeed produce a beneficial effect on lubrication performance characteristics. We also prove that the solution given by Prof. Tichy, who is the chief editor of the Journal of Tribology, appears erroneous.

Three‐dimensional effects in dynamically loaded journal bearings

The effects of non-Newtonian lubricants on the dynamics of a 3D journal bearing are investigated using a moving spectral element method. Comparisons are made with the findings reported for the 2D case. The variation of L/D, the ratio of the length of the bearing to its diameter, is shown to have a significant effect on the stability properties of the journal. Copyright

Numerical Simulation of Oldroyd-B Fluid in a Contraction Channel

A spectral element method coupled with the elastic viscous split stress technique for computing viscoelastic flows is presented. The rate of deformation tensor is introduced as an additional variable in the momentum equation, but not in the constitutive equation. The nonlinear rheological model, Oldroyd-B, is chosen to simulate the flow of a viscoelastic fluid. Numerical solutions are investigated based on a planar 4:1 abrupt contraction channel flow benchmark problem with different Weissenberg numbers. The results show a good agreement with other numerical predictions.

A new immersed boundary method for compressible Navier–Stokes equations

This paper presents an immersed boundary method for compressible Navier–Stokes equations in irregular domains, based on a local radial basis function approximation. This approach allows one to define a reconstruction of the radial basis functions on each irregular interface cell to treat both the Dirichlet and Neumann boundary conditions accurately on the immersed interfaces. Several numerical examples, including problems with available analytical solutions and the well-documented flow past an airfoil, are presented to test the proposed method. The numerical results demonstrate that the proposed method provides accurate solutions for viscous compressible flows.

The Chebyshev spectral element approximation with exact quadratures

A new Chebyshev spectral element method has been developed in this paper, in which exact quadratures are used to overcome a shortfall of the Gauss-Chebyshev quadrature in variational spectral element projections. The method is validated with the Stokes and the Cauchy-Riemann problems. It is shown that an enhancement of the approximation convergence rate is attained, and numerical accuracy is much better than that from the Gauss-Lobatto-Legendre spectral element method. The paper addressed and assessed some of the issues concerning the numerical accuracy on the Chebyshev spectral element method.A new Chebyshev spectral element method is developed by using exact quadratures in computing spectral elements.The method is validated with the Stokes and the Cauchy-Riemann problems.Numerical results show that an enhancement of the approximation convergence rate is attained.Numerical accuracy is much better than that from other spectral element methods.

Non-Newtonian effects on lubricant thin-film flows

A long-standing question is readdressed as to whether the viscoelasticity can have a measurable effect on lubrication characteristics in thin-film flows. Specifically, a perturbation method based on the upper convected Maxwell constitutive equation is employed to analyze thin-film flows of a non-Newtonian fluid between two surfaces. The results show that there is a significant enhancement on the pressure field in the presence of viscoelasticity when the minimum thin-film thickness is sufficiently small. This mechanism suggests that viscoelasticity does indeed produce a beneficial effect on lubrication characteristics, which is consistent with experimental observations.

Smooth Interfaces for Spectral Element Approximations of Navier-Stokes Equations

A smoothing technique is developed to calculate the interface conditions of spectral element method for solving the incompressible Navier-Stokes equations. The first derivative of spectral element solution at the interface is calculated by using only the adjacent element information. Numerical simulations of an incompressible laminar fluid flow through a 2 : 1 planar contraction channel are presented for various Reynolds numbers.