Papers by Author: Jin Quan Xu

Abstract: In this study, a coupled methodology is proposed for the aerodynamic behavior of wind turbine airfoils. The idea is to combine a Navier-Stokes solver with a free vortex model. The zone for the calculation of CFD is confined to the surrounding of the airfoil, whilst the free vortex model accounts for the far field of the airfoil. The flow around the airfoil is assumed to be two-dimensional (2D) incompressible fully turbulent flow, which is modeled by two equation turbulence models. The computed aerodynamic coefficients are presented for two wind turbine airfoils and compared with wind tunnel data.

Abstract: Fretting fatigue has grasped strong interest in last decades, some quantitative methods for the evaluation of fretting fatigue were developed. However, only very few studies have been reported on fretting wear, especially on its mechanical model and evaluation method. In this study, cumulative plastic strain is analyzed by FEM. To obtain accurate plastic strain, the shape change due to the plastic deformation has been taken into account. It is found that the cumulative plastic strain will be saturated after several hundred cycles at the initial fretting stage. Considering that fretting wear is very small during this early stage, as it can be observed from the fretting test, the wear at the contact interface before the saturation of cumulative plastic strain can be neglected. Since the saturated cumulative plastic deformation represents the stable deformation of the contact interface, it is proposed that the fretting wear can be characterized by the saturated cumulative plastic strain and accumulative shear stress. With this method, the wear profile of the specimen is predicted. By comparing FEM results with the experimental results of fretting wear, the proposed wear formulation is validated.

Abstract: This paper presents a PMAC-based combined CNC machine that integrates technologies of ultrasonic machining, electrical discharge machining and high speed grinding. As a multifunctional machine, it can provide diverse machining methods for different materials. For hard and brittle materials, it can conduct ultrasonic machining and high-speed grinding respectively or in a combined form; for conductive hard and brittle materials, electrical discharge machining with or without ultrasonic vibration could be implemented. Driven by AC servomotors, the mechanical structure of the vertical machine is mainly composed of a cross workbench for work piece handling, and a spindle head for tool feeding or high speed rotating. Besides those mentioned above, the system management program, the pulse power generator as well as the ultrasonic generator are also analyzed in this paper. Experimental results show that this machine has a wide range of application indeed and is suitable for various materials processing.

Abstract: Fourier transform profilometry in 3-D measurement based on wavelet digital filter is presented in this paper. Before phase demodulation, original modulated grating image is handled with wavelet transform in order to remove the background components and high frequency. This method resolves spectrum overlapping at some extent and reduces the requirement of low-pass filter.