Research on Static and Dynamic Characteristics of Gas-lubricated Microbearings for Microfluidic Devices

Aerodynamic journal microbearings with microtribological phenomena significantly influence the operating stability of microfluidic devices. The modified Reynolds equations including different rarefaction models are derived and are solved by the partial derivative method and relaxation iteration algorithm. The effects of Knudsen number and bearing parameters on the static and dynamic characteristics of microbearings are investigated in detail. The results show that the rarefaction effect plays a crucial role in the ultra-thin gas film lubrication. The maximum film pressure of Fukui–Kaneko (FK) model is lowest and the result in Boltzmann model is largest in small Knudsen number regions. As the Knudsen number increases further, the curve of FK model is coincident with that of the Boltzmann model in the transition regime. The direct stiffness coefficients of Boltzmann model increase with the increase of eccentricity ratio and aspect ratio, whereas the effect of Knudsen number on the damping coefficients yields a relatively complicated trend.

Investigation of Stall Flutter Based on Peters-ONERA Aerodynamic Model

The Peters model is used to simulate the linear aerodynamic force and ONERA stall model is used to simulate the nonlinear aerodynamic force. The state-space equation of the aeroelastic system is established by coupling the structural equation. In order to solve problems, Euler predictor corrector method is used in the time domain and eigenvalue analysis method is used in the frequency domain. The case of dynamic stall is simulated based on Peters-ONERA model and the results imply that the validity of the aerodynamic model. The effect of under relaxation iteration on the stability of static aeroelastic solution is studied. It is found that under relaxation iteration can improve the static aeroelastic solution stability. Then based on frequency and time domain methods, flutter critical characteristic and bifurcation phenomenon are studied. It is found that:(1) Under large angle of attack, the coupling between nonlinear aerodynamic modal and structure modal could induce the instability of the structure modal and single degree of freedom flutter. (2) Under different angles of attack, bifurcation characteristic of aeroelastic system is far different. (3) The sensitivity to the disturbance of the system is different in different ranges. When the disturbance increases, the aeroelastic system will change from stable state to limit cycle oscillation.

A Novel Iteration Model for Electromagnetic Scattering from Rough Surfaces

An iterative physical optics (IPO) is proposed to solve the extra large scale (e.g. larger than one thousand square lambda) electromagnetic (EM) scattering from randomly rough surfaces in this paper. The forward-backward methodology and its modification with under-relaxation iteration improve convergence and stability of the IPO; the fast far-field approximation (FaFFA) in the matrix-vector product reduces the computational complexity based on the scattering characteristics of rough surface. Through these techniques, this model can solve effectively the extra large scale scattering problem from the randomly rough surfaces.

Numerical Computation of Dynamic Character Coefficient of Journal Bearing

The purpose of this study is to determine the dynamic character coefficient of journal bearing with the consideration of bearing load direction and oil groove. Based on numerical differential method, the oil film pressure distribution on journal bearing is obtained with the point-by-point relaxation iteration method. Then, the dynamic characters are calculated by numerical integral algorithm.The calculation program is developed for the dynamic characteristics of journal bearing. The computation method provides a useful guide for the numerical simulation of rotary parts.