Time filter

Source Type

Zhu S.,Beihang University | Zhao D.,Beihang University | Wang F.,CSR Qingdao Sifang Locomotive and Rolling Stock Co.
Mathematical Problems in Engineering | Year: 2015

The data size of hyperspectral image is too large for storage and transmission, and it has become a bottleneck restricting its applications. So it is necessary to study a high efficiency compression method for hyperspectral image. Prediction encoding is easy to realize and has been studied widely in the hyperspectral image compression field. Fractal coding has the advantages of high compression ratio, resolution independence, and a fast decoding speed, but its application in the hyperspectral image compression field is not popular. In this paper, we propose a novel algorithm for hyperspectral image compression based on hybrid prediction and fractal. Intraband prediction is implemented to the first band and all the remaining bands are encoded by modified fractal coding algorithm. The proposed algorithm can effectively exploit the spectral correlation in hyperspectral image, since each range block is approximated by the domain block in the adjacent band, which is of the same size as the range block. Experimental results indicate that the proposed algorithm provides very promising performance at low bitrate. Compared to other algorithms, the encoding complexity is lower, the decoding quality has a great enhancement, and the PSNR can be increased by about 5 dB to 10 dB. © 2015 Shiping Zhu et al. Source

Xi Y.-H.,Beijing Jiaotong University | Mao J.,Beijing Jiaotong University | Gao L.,Beijing Jiaotong University | Yang G.-W.,CAS Institute of Mechanics | Qu W.-Q.,CSR Qingdao Sifang Locomotive and Rolling Stock Co.
Tiedao Xuebao/Journal of the China Railway Society | Year: 2012

The limited safe speed of a high-speed train under crosswind should be obtained by analyzing the aerodynamic and vehicle-track dynamic characteristics. A real high-speed train of Type CRH3 was taken for case study. The train was assumed to run on a plane area under 25 numerically simulated operating conditions when the train speeds were chosen as 200, 250, 300, 350 and 380 km/h, the crosswind velocities as 10, 15, 20, 25 and 30 m/s and the wind direction angle as 90°. The detailed characteristics of real bogies and pantographs and so on were taken into account. The dynamic vehicle-track charateristics corresponding to the above 25 operating conditions were calculated respectively and compared in line with the domestic measured track spectra and the German track spectra. In accordance with the National standards and technical specifications concerned, the relationship between the crosswind velocity and the maximum safe operating speed of the CRH3 train running on a plane area was found. The results will play a guiding role in control of safe operation of a train under crosswind. Source

Lu H.,Northeastern University China | Zhang Y.,Northeastern University China | Zhao C.,CSR Qingdao Sifang Locomotive and Rolling Stock Co. | Zhu L.,Northeastern University China
Jixie Gongcheng Xuebao/Journal of Mechanical Engineering | Year: 2012

Several potential failure modes may occur when mechanical components fail. For that all the failure modes have a certain impact on the reliability sensitivity of the components, it is necessary to take each failure mode into account as a reliability sensitivity estimation is performed. A reliability sensitivity analysis method for mechanical components with multiple failure modes is proposed. Concerning the unknown distributions of random variables, the random perturbation technique and the fourth moment method are employed to respectively calculate the first four moments and the reliability index of each performance function of the failure mode. The potential failure modes, only a few existed in the component, are regarded in series, and the failure of the component is thus the failure of a series system. The calculating formulas of reliability sensitivity with respect to the mean and variance of random variables are derived with the gradient method. The numerical example illustrates that the proposed method could quickly and effectively estimate the reliability sensitivity of the mechanical components with multiple failure modes, and is also applicable for nonlinear performance functions. ©2012 Journal of Mechanical Engineering. Source

Song X.,Northeastern University China | Wang J.,Northeastern University China | Li Q.,Northeastern University China | Wang H.,CSR Qingdao Sifang Locomotive and Rolling Stock Co.
2012 International Conference on Wireless Communications, Networking and Mobile Computing, WiCOM 2012 | Year: 2012

The constant modulus algorithm (CMA) has been known as blind adaptive beamforming because it requires no knowledge about the signal except that the transmitted signal waveform has a constant envelope. But in practical applications, the performance of the linearly constrained CMA is known to degrade severely in the presence of even slight signal steering vector mismatches. To account for the mismatches, a novel robust CMA algorithm is proposed via the oblique projection of signal steering vector. To improve robustness, the weight vector is optimized to involve minimization of a constant modulus algorithm objective function with penalty for the worst-case signal steering vector by the Lagrange multiplier method, in which the parameter can be precisely derived at each iterative step. Moreover, the performance analysis of the proposed algorithm is presented in this paper. The proposed robust constrained CMA provides a significantly improved robustness against the signal steering vector mismatches and improves the mean output array SINR as compared with the conventional constrained CMA. The simulation experiments have been carried out to demonstrate the superiority of the proposed algorithm on beampattern control and output SINR enhancement. © 2012 IEEE. Source

Ji S.,Shenyang Aerospace University | Meng X.,Shenyang Aerospace University | Ma L.,Shenyang Aerospace University | Lu H.,CSR Qingdao Sifang Locomotive and Rolling Stock Co. | Gao S.,Shenyang Aerospace University
Materials and Design | Year: 2015

Vertical compensation friction stir welding (VCFSW) was developed to solve the existence of a big gap at the interface between two workpieces to be welded. By a self-designed tool system with external stationary shoulder, VCFSW is successfully used to weld 6061-T6 aluminum alloy with the thickness of 4. mm, while 2024-T4 aluminum alloy is chosen as compensation material. When using a traditional tool, it is difficult for VCFSW to attain a sound joint if the width of compensation strip is no less than 1.5. mm. The self-designed stationary shoulder tool system is more suitable for VCFSW. Defect-free VCFSW joints using the self-designed stationary shoulder are attained when the widths of strip vary from 1. mm to 2. mm. For VCFSW process, increasing the rotational velocity and decreasing the welding speed are beneficial to break the compensation strip into pieces to get the higher quality welding joint. When the width of compensation strip is 1. mm, the tensile strength and elongation of joint by the stationary shoulder tool system reach the maximum of 75.1% and 58.8% of base material (BM) when using the welding speed of 50. mm/min and rotational velocity of 2000. rpm, respectively. The fracture surface morphology of VCFSW joint presents the typical ductile fracture. © 2014 Elsevier Ltd. Source

Discover hidden collaborations