基于神经网络的自适应滤波技术及其在超声检测中的应用

为满足超声无损检测和评价在新材料和新构件上应用的需求,提出了一种基于神经网络的自适应滤波器,使其兼具自适应滤波和非线性处理的能力。该滤波器是在线性自适应滤波器中引入一非线性隐含层而构成,在对该滤波器的结构和收敛性进行详细研究的基础上,实现了一种自适应噪声消除器并应用于超声检测中的材料噪声消除。实验结果证实:利用这种滤波器构成的材料噪声消除器比采用线性自适应滤波器具有更强的降噪能力。     

阀门流场的数值模拟及流噪声的实验研究

采用非结构、非交错网格的有限体积法求解用二方程模型封闭的雷诺平均N S方程组 ,对水管路系统中 3种常见阀门的三维分离流动进行数值模拟。模拟结果表明 ,随着蝶阀、闸阀和球阀开度的减小 ,流体在蝶阀背面、球阀阀门内外分别形成两个方向相反的漩涡 ,闸阀的漩涡出现在挡板与管道的壁角处 ,并且漩涡在阀门下游逐渐消失。同时实验表明 ,阀门下游的流噪声大于阀门上游的流噪声 ,涡声是阀门噪声的主要来源     

Elastic–plastic spherical contact under combined normal and tangential loading in full stick

The behavior of an elastic–plastic contact between a deformable sphere and a rigid flat under combined normal and tangential loading with full stick contact condition is investigated theoretically. Sliding inception is treated as a plastic yield failure mechanism, which allows static friction modeling under highly adhesive conditions. Several contact parameters such as: junction tangential stiffness, static friction force and static friction coefficient are extensively investigated. The phenomenon of junction growth and the evolution of the plastic zone in the contact region are briefly described. It is found that at low normal dimensionless loads the static friction coefficient decreases sharply with increasing normal load, in breach with the classical laws of friction. As the normal load further increases the static friction coefficient approaches a constant value that is about 0.3 for many material properties combinations.     

实验数据RBF神经网络模型中噪声的处理方法

实验数据的非线性建模,是对各种仪器、设备的性能进行校正和补偿的基础.讨论了神经网络非线性建模时数据中的噪声成分造成的过拟合现象以及对模型精度的影响,针对RBF网络给出了2种提高建模精度的方法建模数据预处理法和网络参数优化法.在数据预处理方法中,根据建模样本的特点,分别采用滑动平均法和灰色模型法对原始建模数据进行修正,并分析了它们的适用场合;对于后一种方法,选择径向基函数分布宽度和学习目标进行优化.以精密平台为例进行了实验,通过对其定位误差的测量、建模和预测,证明了上述各种方法的有效性,特别是后一种方法,可以得到非常高的建模精度.     

Atmospheric effects of friction,friction noise and wear with silicon and diamond. Part II. SEM tribometry of silicon in vacuum and hydrogen

Scanning electron microscope (SEM) tribometric data on polycrystalline silicon (poly-Si) vs. poly-Si, Si(100) vs. Si(100) and Si(111) vs. Si(111) interfaces, obtained in Torr and in 0.2 Torr partial pressure of hydrogen gas ( ) from room temperature to 850^°C, were performed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology described in part I of this paper series. The results indicate a highly beneficial friction- and wear-reducing regime within a relatively narrow thermal region. This desirable region coincides with some chemisorption of excited species of molecular hydrogen just before the mass thermal desorption of surface hydrides. These data represent the tribochemical equivalent of a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking in molecular hydrogen. The also exerts a moderating influence on the size of the friction noise at all test temperatures. However, the general level of friction beyond the beneficial thermal region is high. In parallel, the general wear rate of Si representative of the entire range of standard thermal ramping in both atmospheric environments is in the extremely high 10^-12m³/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude reduction in the wear rate over those measured under standard thermal ramping conditions. Although the results confirm previous findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microbearings and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen at surface temperatures between 100 and 300^°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于8PSK 和16PSK 调制的全双工RoF 系统研究

误码率(bit error rate, BER)是信号传输质量的重要衡量指标,为了对比分析8进制相移键控(eight hexadecimal phase shift keying, 8PSK)与16进制相移键控(sixteen hexadecimal phase shift keying, 16PSK)信号的传输性能,建立了一个全双工光载无线通信(radio over fiber, RoF)链路模型。系统的下行链路是对基于马赫增德尔调制器(Maher-Zehnder modulator, MZM)的抑制奇次边带两路信号,分别进行8PSK和16PSK调制。上行链路是取下行链路中一路未被调制的抑制奇次边带信号,作为上行基带信号的载波信号,节约系统的成本。该系统分别在不同的光信噪比(optical signal to noise ratio, OSNR)和不同传输距离条件下,仿真分析了下行链路两种调制信号的光谱图及误码率曲线,通过分析接收信号的星座图和误码特性证明:与16PSK信号相比,当OSNR 25时, 8PSK信号误码率量级可以达到10-4(lg BER-3),当传输距离为40 km时, 8PSK的误码率为4.8×10-3(lg BER=-2.32),仍然可以有效传输数据信息。且在不同OSNR和不同传输距离条件下, 8PSK的误码率均低于16PSK,因此8PSK具有更可靠的传输性能,且更适用于远距离传输。     

Network Sorting Algorithm of Multi-Frequency Signal with Adaptive SNR

An signal noise ratio (SNR) adaptive sorting algorithm using the time-frequency (TF) sparsity of frequency-hopping (FH) signal is proposed in this paper.Firstly,the Gabor transformation is used as TF transformation in the system and a sorting model is established under undetermined condition;then the SNR adaptive pivot threshold setting method is used to find the TF single source.The mixed matrix is estimated according to the TF matrix of single source.Lastly,signal sorting is realized through improved subspace projection combined with relative power deviation of source.Theoretical analysis and simulation results show that this algorithm has good effectiveness and performance.     

Pipelined robust M-estimate adaptive second-order Volterra filter against impulsive noise

The main limits on adaptive Volterra filters are their computational complexity in practical implementation and significant performance degradation under the impulsive noise environment. In this paper, a low-complexity pipelined robust M-estimate second-order Volterra (PRMSOV) filter is proposed to reduce the computational burdens of the Volterra filter and enhance the robustness against impulsive noise. The PRMSOV filter consists of a number of extended second-order Volterra (SOV) modules without feedback input cascaded in a chained form. To apply to the modular architecture, the modified normalized least mean M-estimate (NLMM) algorithms are derived to suppress the effect of impulsive noise on the nonlinear and linear combiner subsections, respectively. Since the SOV-NLMM modules in the PRMSOV can operate simultaneously in a pipelined parallelism fashion, they can give a significant improvement of computational efficiency and robustness against impulsive noise. The stability and convergence on nonlinear and linear combiner subsections are also analyzed with the contaminated Gaussian (CG) noise model. Simulations on nonlinear system identification and speech prediction show the proposed PRMSOV filter has better performance than the conventional SOV filter and joint process pipelined SOV (JPPSOV) filter under impulsive noise environment. The initial convergence, steady-state error, robustness and computational complexity are also better than the SOV and JPPSOV filters.     

Glowworm swarm optimization algorithm with topsis for solving multiple objective environmental economic dispatch problem

A new glowworm swarm optimization (GSO) algorithm is proposed to find the optimal solution for multiple objective environmental economic dispatch (MOEED) problem. In this proposed approach, technique for order preference similar to an ideal solution (TOPSIS) is employed as an overall fitness ranking tool to evaluate the multiple objectives simultaneously. In addition, a time varying step size is incorporated in the GSO algorithm to get better performance. Finally, to evaluate the feasibility and effectiveness of the proposed combination of GSO algorithm with TOPSIS (GSO–T) approach is examined in four different test cases. Simulation results have revealed the capabilities of the proposed GSO–T approach to find the optimal solution for MOEED problem. The comparison with own coded weighted sum method incorporated GSO (WGSO) and other methods reported in literatures exhibit the superiority of the proposed GSO–T approach and also the results confirm the potential of the proposed GSO–T approach to solve the MOEED problem.     

Modeling the dynamic properties of fibre-reinforced concrete with different coating technologies of multifilament yarns

The dynamic behaviour of fibre-reinforced, cementitious composite materials is gaining increasing interest. With respect to service life dynamic loading just under the elastic limit of the material at hand is relevant to practical applications, for the resulting (stress-)waves may be focused within regions of the heterogeneous composite material. This local overstraining of the material may lead to deterioration of the structural element. In this contribution, the effect of the set-up of the reinforcing fibres on the wave scattering behaviour is investigated. Special attention is paid to layered centric configurations of these fibres, as it occurs e. g. within textile-reinforced concrete (TRC). A mechanical model is developed and solved analytically providing an efficient and robust method to describe the dynamic behaviour of given fibre configurations. This method is needed for materials which have to be described mechanically before the manufacturing process – as it is the case for TRC. The proposed model also allows for planning experiments and thus is of additional value. It is shown that the inner structure of the fibres does influence the amplitude response spectra and consequently the proposed method also may be used for non-destructively detecting the inner structure of the multifilament yarns and other related objects.