Robust parametric approach for tracking control of an air-breathing hypersonic cruise vehicle

To realize the stabilization and the tracking of flight control for an air-breathing hypersonic cruise vehicle, the linearization of the longitudinal model under trimmed cruise condition is processed firstly. Furthermore, the flight control problem is formulated as a robust model tracking control problem. And then, based on the robust parametric approach, eigenstructure assignment and reference model tracking theory, a parametric optimization method for robust controller design is presented. The simulation results show the effectiveness of the proposed approach.     

Ultrasonic Nondestructive Signals Processing Based on Matching Pursuit with Gabor Dictionary

The success of ultrasonic nondestructive testing technology depends not only on the generation and measurement of the desired waveform, but also on the signal processing of the measured waves. The traditional time-domain methods have been partly successful in identifying small cracks, but not so successful in estimating crack size, especially in strong backscattering noise. Sparse signal representation can provide sparse information that represents the signal time-frequency signature, which can also be used in processing ultrasonic nondestructive signals. A novel ultrasonic nondestructive signal processing algorithm based on signal sparse representation is proposed. In order to suppress noise, matching pursuit algorithm with Gabor dictionary is selected as the signal decomposition method. Precise echoes information, such as crack location and size, can be estimated by quantitative analysis with Gabor atom. To verify the performance, the proposed algorithm is applied to computer simulation signal and experimental ultrasonic signals which represent multiple backscattered echoes from a thin metal plate with artificial holes. The results show that this algorithm not only has an excellent performance even when dealing with signals in the presence of strong noise, but also is successful in estimating crack location and size. Moreover, the algorithm can be applied to data compression of ultrasonic nondestructive signal.     

Synthesis,characterization, and infrared-emissivity study of Ni–P–CB nanocomposite coatings by electroless process

The Ni–P–CB (carbon black) nanocomposite coatings have been successfully deposited on an ABS plastic matrix via electroless plating process. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectrometry techniques were employed to examine the surface morphology and structure of the as-plated coating. Energy dispersive spectroscopy (EDS) was adopted to obtain the component analysis of the Ni–P–CB composite coating, and the infrared emissivity of the coating was determined by the IRE-I Infrared Emissometer. SEM and XRD results indicated that the nanoparticles were dispersed homogeneously in the Ni–P coating; the result of EDS showed that the increased rate of CB content is in correspondence with its concentration. In the case that CB concentration is lower than 4 g/L, the increase rate is sharp, whereas when the concentration is higher than 4 g/L, the increase rate is reduced significantly. Furthermore, study of infrared emissivity shows that the nanocomposite coatings possessed low emissivity value. A comparison of the infrared emissivity dependence on surface resistivity obtained from the analysis of the experimental results and those calculated using the Hagen–Rubens relation indicates that the Hagen–Rubens relation is good for modeling the infrared emissivity of the Ni–P–CB nanocomposite coatings.     

A User Parameter-Free Robust Adaptive Beamformer Based on General Linear Combination in Tandem with Steering Vector Estimation

If there is a mismatch between the assumed steering vector (SV) and the real value, the performance of adaptive beamforming methods is degraded. When the signal SV is known exactly but the sample size is small, the performance degradation can also occur. The second kind of degradation is mainly due to the mismatch between the sample covariance matrix and the real one. Almost all existing robust adaptive beamformers are proposed to improve the robustness against these two types of mismatch. Indeed, most of them are user parameter dependent, and the user parameter-free robust beamformers are scarce. As one of the shrinkage methods, the general linear combination (GLC) based beamformer is a good user parameter-free robust beamformer. However, it is only suitable for the scenarios with low sample size and/or small SV mismatch. In this paper, we propose a new robust beamformer, and it is based on general linear combination in tandem with SV estimation (GLCSVE). The proposed approach is superior to GLC in two aspects. One is that the GLCSVE beamformer performs well not only with small but also with large sample size. The other is that the GLCSVE can effectively deal with a large range of SV mismatch. Moreover, the proposed GLCSVE approach is a user parameter-free robust beamformer, and is more suitable for application than the parameter dependent approaches. The idea of our method can also be used to enhance other shrinkage based beamformers.     

基于静电收集型固体核径迹氡探测器尺寸的蒙特卡罗方法优化

设计了一种新型的基于静电收集的固体核径迹探测器,并利用蒙特卡罗方法对其尺寸进行优化模拟,确定最优尺寸使装置达到效能最大化,结果表明转换系数作为优化对象随着探测器直径的增大而近似线性增加,当管子半径增大到2 cm后曲线逐渐变缓,而后在约等于3 cm处转换系数基本不再增加甚至有下降的趋势,由此可得出结论探测器半径取3 cm...     

基于稀疏分解的多分量线性调频信号参数估计∗

本文提出了一种多分量线性调频信号的参数估计方法。基于过完备Gabor字典的Matching Pursuit算法,可以将信号表示为Gabor原子的线性组合。这些原子有效的揭示了信号的内在时频结构特征,是信号的一种稀疏表示。本文直接利用分解得到的稀疏信息对信号中调频分量的调频率、初始频率和结束频率进行估计。仿真结果显示,该方法适用于存在强有意干扰或者有色噪声的环境。     

A SAR image method of detecting target changes using two-dimensional scattering centre characteristics

Remote-sensing image interpretations and applications require information on changes in the target. In high-resolution synthetic aperture radar (SAR) images, multi-scattering centres reflect the characteristics of target scattering, but not those of point targets or point scattering. Total scattering is the vector summation of each scattering centre. These scattering centres include shape and structural information of the target. When a target changes, both the scattering characteristics and the scattering centres change. In this way, changes in the centres may cancel out changes in the target. This article proposes a new method of change detection for SAR image targets using the two-dimensional scattering centre characteristics (TDSCC). This method is here called the TDSCC algorithm. This algorithm differs from other change detection algorithms that are based on image fields. General change detection algorithms require accurate registration. Otherwise, the change information is inaccurate. The TDSCC method is a feature-level or target-level change detection algorithm and it does not require registration operation. Therefore, it avoids errors in change information. The experimental data have confirmed the feasibility of the proposed algorithm.     

Numerical modeling of a low temperature high velocity air fuel spraying process with injection of liquid and metal particles

An analysis of a low temperature high velocity air fuel (LTHVAF) thermal spray process is presented using computational fluid dynamics (CFD). The originality of the process lies in the injection of liquid (water) upstream of the powder injection to control to gas temperature and, therefore, the heat transfer to the injected particles. First, computation fluid dynamic techniques are implemented to solve the mass, momentum, and energy conservation equations in the gas phase. A turbulence model based on the renormalized group theory (RNG) is used for the turbulent flow field. The gas dynamic data are, then, used to model the behavior of the liquid droplets and particles in the gas flow field. The calculated results show that the liquid flow rate should range between 20 and 30 kg/h to achieve the optimal gas characteristics for particle treatment. They also show that particle velocity and temperature are strongly affected by particle size. At the gun exit, the particle velocity and temperature range between 700 and 300 m/s and between 900 and 400 K, respectively, for Cu and Ni particles with size distributions of 1 to 50 μm. As expected, the smaller particles have higher velocity and temperature. The metal coatings (Nickel and copper) produced by the LTHVAF spray process are characterized by low oxide content, low residual stresses, high deposition rates, and good bonding to the substrate.     

Structures and potential energy functions for ground states of PuU and U2 molecules

Pu-Pu,Pu-U and U-U interatomic potentials must be known in molecular dynamics (MD) calculation of the effects of U recoil nucleus produced by self irradiation on physical properties and phase stability in δ-Pu.Because of the lack of experimental data for fitting Pu-U and U-U potentials,electronic states and potential data of PuU and U2 molecules are obtained by ab initio calculations with B3LYP hybrid exchange-correlation functional.The valence electrons of Pu and U atoms are treated with contraction basis sets,and the cores are approximated with relativistic effective core potential.The results show that electronic states for the ground states are X11Σu+ and X9Σg+.The pair potential data are fitted with the Murrell-Sorbie analytical potential function.The LDA+U calculations on the Pu-U intermetallic compound are performed with Perdew and Wang exchange-correlation functional at the spin-polarized level.The material parameters,such as the cohesive energies,elastic constants,and bulk modulus,are used to fit the 0-K universal Rose EOS,so the Pu-U EAM potential model is obtained.     

基于矩阵形式的否定选择算法研究

现有的状态空间表示形式和匹配规则已经成为否定选择算法研究的瓶颈。为此,该文将状态空间从向量扩展到矩阵,提出了一种基于矩阵形式的否定选择算法。引入矩阵表示自我和非我空间,定义了元素匹配距离,在此基础上建立了双向匹配规则;同时根据状态空间特征建立了基于覆盖检验的检测器生成算法。实验结果表明该算法性能明显优于实值否定选择算法,有效解决了检测率和误报率联动的问题,且能产生更为高效的检测器。