基于小波包尺度-能量占比的变压器三相不平衡绕组振动特征辨识

针对变压器不平衡运行模式绕组振动问题,研究变压器不平衡运行模式振动原理,构建不平衡运行模式下的绕组电磁-振动模型,利用小波包变换进行振动信号的分解重构,研究不同频域尺度的能量分布规律,提出了基于尺度-能量占比的振动特征辨识方法。通过动模实验获取绕组振动信息,通过小波包分解重构信号确定尺度-能量占比特征值,研究不平衡运行绕组振动特性,为变压器不平衡异常工况提供新的诊断手段。变压器正常运行时,二倍频分量信号占总信号能量的46.72%,当不平衡运行α为-20%、20%时,二倍频能量占比分别下降75.67%和升高42.07%,且不平衡运行时三相绕组振动特征差异较大,所产生的不平衡振动力矩将会危害变压器绕组整体结构的稳定性。

基于小波尺度-能量的钢绞线张拉力识别研究

目的研究预应力钢绞线长期服役后剩余应力水平,开展无损检测方法评估剩余应力.方法以工程中常用的钢绞线为研究对象,进行钢绞线逐级加载实验与超声导波实验,对端面传感器与侧面传感器采集到的导波信号进行小波分析与多尺度分析;定义不同拉力状况下能量特征向量Ej之间的差值为LWE,能量Shannon熵特征向量Sj之间的差值为LWES,并以该值作为钢绞线张拉力识别指标.结果随着张拉力的增大,实测导波信号幅值降低,其频谱图幅值也降低,能量分布发生了改变;不同张拉力下,小波能量在尺度上分布有相似的规律,其峰值随张拉力的增大而下降;识别指标LWE和LWES随张拉力变化显著,线性规律强,可靠性系数R2均在0.94以上,传感器布置策略对其影响较小.结论构建的识别指标均能识别出钢绞线张拉力的变化,与小波尺度-能量Shannon熵图相比,小波尺度-能量图更能清晰地观察到能量随张拉力的变化趋势,基于小波能量的识别指标LWE敏感系数K值更大,可靠性越高,识别效果更佳.

尺度-小波能量谱在滚动轴承故障诊断中的应用

针对滚动轴承故障振动信号的特点 ,构造脉冲响应小波 ,采用连续小波变换的方法来提取滚动轴承故障振动信号的特征 ,在此基础上提出了一种滚动轴承故障诊断方法 :尺度 -小波能量谱比较法。通过对具有外圈缺陷、内圈缺陷的滚动轴承振动信号的分析 ,说明尺度 -小波能量谱比较法不仅能检测到滚动轴承故障的存在 ,而且能有效地识别滚动轴承的故障模式。

基于尺度-小波能量谱和神经网络的内燃机故障诊断

为了对内燃机气门及活塞连杆组故障进行有效地诊断，通过试验测取内燃机在不同故障下的振动信号，利用连续小波变换得到信号在不同尺度上的能量分布，即信号的尺度小波能量谱。其能量主要分布于尺度范围1～32，且相同故障模式下的尺度小波能量谱呈现出相似性，不同故障模式之间的尺度一小波能量谱存在很大的差异性，以此作为不同故障模式的信号特征，结合BP神经网络方法，实现了对待检信号的正确识别。

基于尺度-小波能量谱的舰船轴频电场检测算法

为了检测复杂海况下的舰船轴频电场信号,文章通过连续小波变换分析了海洋环境电场和舰船轴频电场的实测信号,计算其尺度-小波能量谱并找出两者差异。根据两者在不同尺度内能量分布的差异,在一定特征尺度内提取能量和为特征值,并根据环境变化,设置具有自适应功能的动态阈值,通过滑动检测的方法实时检测信号。算法由高信噪比和低信噪比的实测数据验证。结果表明该算法在高信噪比时检测率达100%,没有出现虚警和漏警,在低信噪比时也能较好地检测到目标信号。该算法具有较强的稳健性和较好的检测效果,为舰船轴频电场信号的检测提供了一种新方法。

基于改进灰色关联度及尺度-小波能量谱的输电线路故障选相

提出基于改进灰色关联度和尺度-小波能量谱的输电线路故障选相新方法,依据尺度-小波能量谱分析提取暂态故障特征,再由改进灰色关联度分析来确定故障相别。对故障线路三相电流信号进行小波分析,获取各尺度下的小波变换系数,计算尺度-小波能量谱;采用改进的灰色关联度算法对故障信号能谱和参考序列进行关联度分析,根据最大关联度原则确定故障类型。仿真表明,该方法能准确地判断故障相别。

基于尺度—小波能量谱的船舶水压场信号检测

为了有效地从风浪背景中检测船舶水压场信号,本文利用连续小波变换分析了实测海浪水压场与船舶水压场的尺度—小波能量谱,根据两者的能量差异,提取某一特征尺度范围内的能量和为特征,采用滑动检测方法对信号进行实时检测.通过实测数据和仿真数据对该检测算法进行验证,结果表明此方法在低信噪比情况下,能较好的检测到目标信号.

舰船地震波信号的小波能量谱检测算法

本文基于滑动小波能量谱提出一种新的舰船地震波信号实时检测算法,首先利用小波变换对实测信号进行尺度-小波能量谱分析,获得信号在尺度-小波能量谱上的特点,然后基于该特点选取一段频带内的能量和作为检测特征量,最后通过比较特征量与阈值的大小,并根据一定的检测规则,完成对舰船地震波信号的实时检测。实测数据和仿真数据表明,该检测算法能够实时地完成对目标信号的检测,且在信噪比为-15 dB时,检测概率达到96%。

Dynamic Properties of Two-Dimensional Polydisperse Granular Gases

We propose a two-dimensional model of polydisperse granular mixtures with a power-law size distribution in the presence of stochastic driving. A fractal dimension D is introduced as a measurement of the inhomogeneity of the size distribution of particles. We define the global and partial granular temperatures of the multi-component mixture. By direct simulation Monte Carlo, we investigate how the inhomogeneity of the size distribution influences the dynamic properties of the mixture, focusing on the granular temperature, dissipated energy, velocity distribution, spatial clusterization, and collision time. We get the following results： a single granular temperature does not characterize a multi-component mixture and each species attains its own ＂granular temperature＂; The velocity deviation from Gaussian distribution becomes more and more pronounced and the partial density of the assembly is more inhomogeneous with the increasing value of the fractal dimension D; The global granular temperature decreases and average dissipated energy per particle increases as the value olD augments.

Critical Dimension for Stable Self-Gravitating Stars in AdS

We study the self-gravitating stars with a linear equation of state, P = aρ, in AdS space, where a is a constant parameter. There exists a critical dimension, beyond which the stars are always stable with any central energy density; below which there exists a maximal mass configuration for a certain central energy density and when the central energy density continues to increase, the configuration becomes unstable. We find that the critical dimension depends on the parameter a, it runs from d = 11.1429 to 10.1291 as a varies from a = 0 to 1. The lowest integer dimension for a dynamically stable self-gravitating configuration should be d = 12 for any a E [0, 1] rather than d = 11, the latter is the case of self-gravitating radiation configurations in AdS space.

基于Morlet小波变换的滚动轴承早期故障特征提取研究

针对轴承故障初期振动信号中的特征成分极易被噪声信号淹没而不能及时检测的问题,结合Morlet小波变换降噪的基本原理,提出一种由尺度相关能量分布确定最优尺度参数的方法,从而在该尺度下对信号滤波来提取冲击特征成分。以最小Shannon熵优化Morlet小波的形状参数,实现母小波与信号故障特征的最佳匹配;以最优Morlet小波在不同变换尺度下的小波系数绘制尺度-能量谱,利用信号故障特征能量在特定尺度范围内聚集的特性,从谱图的极值点中选择滤波效果最好的尺度参数。对轴承全寿命数据的实际应用结果表明,与信号的均方根趋势相比,该方法能够提前从信号中提取微弱故障特征并检测到轴承的外圈故障,为轴承早期故障诊断提供了一种有效途径。

焊接裂纹金属磁记忆信号的特征提取与应用

金属磁记忆检测技术是一种新兴的对铁磁性材料进行早期损伤诊断的无损检测方法。通过对焊接裂纹磁记忆信号的小波能量谱特征进行研究表明,与无裂纹时相比,含有焊接裂纹信息的金属磁记忆信号,其尺度-小波能量谱的分布范围广,能量水平高,且能量达到峰值以后,呈指数规律下降,据此可以判定被测试件中是否含有裂纹缺陷;其空间-小波能量集中程度较无裂纹时高,而能量集中的位置恰好就是焊接裂纹存在的位置。

基于连续小波变换的湖底回波特征提取

提出了以多尺度连续小波变换值矩阵的奇异值作为识别特征矢量的方法,并利用该方法对湖底回波实测数据进行特征提取与分类。理论分析与仿真试验结果表明,相对于时间-小波能量和尺度-小波能量特征提取法而言,该方法可得到更好的类内紧致性和类间可分性,以及更佳的分类效果。

A new adaptive bending method using closed loop feedback control

As the competition from companies in low cost countries increases,the need for more automated production which reduces labour cost while improving product quality is required.A new rotary compression bending set-up with automated closed-loop feedback control is thus being developed.By transferring in-process measurement data into an algorithm for predicting springback and bend angle prior to the unloading sequence,the dimensional accuracy is improved.This work focuses on the development of this steering model.Since the method used does not increase cycle time,it is attractive for high-volume industrial applications.More than 150 bending tests of AA6060 extrusions were conducted to determine the capability of the technology.The results show that by activating the automated closed-loop feedback system,the dimensional accuracy of the bent parts is more than three times better than that obtained by traditional compression bending.Since the steering model permits the direct use of additional process data,such as instant wall thickness and cross sectional distortions,it is believed that extension of the measurement capabilities would improve the accuracy of the methodology even further.

Shape of Compact Toroidal Dimensions T_θ~d and Casimir Effect on M^D×T_θ~d Spacetime

We study the influence of the shape of compact a scalar field. We examine both the massive and the massless dimensions to the Casimir energy and Casimir force of scalar field. The total spacetime topology is M^D × Tθ2, where M^D） is the D-dimensional Minkowski spacetime and Tθ2 the twisted torus described by R1, R2, and 8. For the case R1 = R2 we found that the massive bulk scalar field Casimir energy is singular for D=even and this singularity is R-dependent and remains even when the force is calculated. Also the massless Casimir energy and force is regular only for D = 4 （!）. This is very interesting phenomenologically. We examine the energy and force as a function of 8. Also we address the stabilization problem of the compact space. We also briefly discuss some phenomenological implications.

Near ground air temperature calculation model based on heat transfer of vertical turbulent and horizontal air flow

In order to calculate the air temperature of the near surface layer in urban environment,the surface layer air was divided into several sections in the vertical direction,and some energy balance equations were developed for each air layer,in which the heat exchange due to vertical turbulence and horizontal air flow was taken into account.Then,the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls.Moreover,the measured air temperatures in a small area(with a horizontal scale of less than 500 m) and a large area(with a horizontal scale of more than 1 000 m) in Guangzhou in summer were used to validate the proposed model.The calculated results accord well with the measured ones,with a maximum relative error of 4.18%.It is thus concluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.

Pairing superfluidity in spin-orbit coupled ultracold Fermi gases

We review some recent progresses on the study of ultracold Fermi gases with synthetic spin-orbit coupling.In particular,we focus on the pairing superfluidity in these systems at zero temperature.Recent studies have shown that different forms of spin-orbit coupling in various spatial dimensions can lead to a wealth of novel pairing superfluidity.A common theme of these variations is the emergence of new pairing mechanisms which are direct results of spin-orbit-coupling-modified single-particle dispersion spectra.As different configurations can give rise to single-particle dispersion spectra with drastic differences in symmetry,spin dependence and low-energy density of states,spin-orbit coupling is potentially a powerful tool of quantum control,which,when combined with other available control schemes in ultracold atomic gases,will enable us to engineer novel states of matter.

Atom-continuum coupled model for thermo-mechanical behavior of materials in micro-nano scales

In this paper,an atom-continuum coupled model for thermo-mechanical behaviors in micro-nano scales is presented.A representative volume element consisting of atom clusters is used to represent the microstructure of materials.The atom motions in the RVE are divided into two phases,structural deformations and thermal vibrations.For the structural deformations,nonlinear and nonlocal deformation at atomic scales is considered.The atomistic-continuum equations are constructed based on momentum and energy conservation law.The non-locality and nonlinearity of atomistic interactions are built into the thermo-mechanical constitutive equations.The coupled atomistic-continuum thermal-mechanical simulation process is also suggested in this work.

High-efficiency laser-irradiation spheroidizing of NiCo_2O_4 nanomaterials

We realized the desired spheroidizing of NiCo_2O_4 nanomaterials by laser irradiating NiCo_2O_4 suspensions with different concentrations. The results reveal that the as-prepared samples are desired spheres with the maximal average size of 568 nm and the superior dispersity, which were obtained at the energy density of 0.30 J·pulse^(-1)·cm^(-2) and NiCo_2O_4 suspension concentration of 0.2 mg·mL^(-1). However, the phase segregation, which was induced by large amounts of solid redox of Co^(3+)/Co^(2+) and Ni^(3+)/Ni^(2+), also appears in the laser-irradiation process.

Nonadiabatic acceleration of plasma sheet ions related to ion cyclotron waves

The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons by magnetic field dipolarization is hard to occur at X>–10 RE because the time-scale of dipolarization(several minutes) is much larger than the gyroperiod of protons there(several seconds). In this paper, we present a case of nonadiabatic acceleration of plasma sheet ions observed by Cluster on October 30, 2006 at(XGSM, YGSM)=(-7.7, 4.7) RE. The nonadiabatic acceleration of ions is caused not by previously reported magnetospheric dipolarization but by the ultra low frequency(ULF) waves during magnetospheric dipolarization. The nonadiabatic acceleration of ions generates a new energy flux structure of ions, which is characterized by the usual energy flux increase of ions(28–80 ke V) and a concurrent energy flux decrease of ions in a lower energy range(10 e V–20 ke V). These new observations constitute a complete physical picture: The lower energy ions absorb the wave energy, and thus get accelerated to higher energy. We use a nonadiabatic model to interpret the ion energy flux variations. Both analytic and simulation results are in good agreement with the observations. This indicates that the nonadiabatic acceleration associated with ULF waves superposed on dipolarized magnetic field is an effective mechanism for ion energization in the near-Earth plasma sheet. The presented energy flux structures can be used as a proxy to identify the similar dynamic process.