声纹的变压器放电与机械故障诊断研究*

变压器中的一些放电和机械故障会产生异常声音,可用于故障检测。据此,本文提出基于可听声的变压器放电和机械故障诊断方法。针对机械故障声音与变压器本体噪声特征相似易混淆的问题提出改进小波包-BP神经网络算法,与传统小波包-BP神经网络算法相比声音的识别率提高了5.7%。为提高声音识别系统的泛化性,提出基于梅尔对数频谱和卷积神经网络的声音识别算法。两种算法相互验证,提高了系统的可靠性。在真实变压器油箱中模拟了不同类型放电和机械故障。试验结果表明,本文提出的两种方法能成功识别放电和机械故障的声音,声音识别率分别为99.6％和97.57％。     

Variable shape or variable diameter flattop beam tailored by using an adaptive weight FFT-based iterative algorithm and a phase-only liquid crystal spatial light modulator

The variable shape or variable diameter flattop beam shaping technique by using an adaptive weight FFT-based iterative algorithm (AWFFT-IA) and a phase-only liquid crystal spatial light modulator (PO-LCSLM) is demonstrated. The algorithm is used to design the phase distribution for tailoring central symmetric laser beam into the desired shape or diameter flattop beam, the PO-LCSLM serves as dynamically programmable phase filters, which depend on the designed phase distributions, to retard the incident wavefront as we would expect. The experimental results show that the technique can realize variable shape or variable diameter flattop beam shaping.     

等离子体羽中氧原子的光谱强度分布

大气压等离子体羽放电产生的低温等离子体由于不需要真空装置,可以对复杂材料进行三维处理等,在工业上具有广泛的应用前景。本工作利用等离子体针放电装置在大气压空气中产生了稳定的等离子体羽。通过光谱测量,发现等离子体羽发射谱中存在777.5和844.6nm的氧原子谱线。这表明在大气压空气放电中产生了具有高化学活性的氧原子。通过光谱学方法研究了氧原子谱线强度的空间分布,发现靠近电极处氧原子谱线强度远大于其他位置。为了对这一现象进行解释,利用光电倍增管对等离子体羽的发光信号进行了空间分辨测量,发现靠近电极处发光信号宽度远大于其他位置的发光信号宽度。这些结果对大气压空气等离子体羽在杀菌消毒等领域的应用具有重要意义。     

金属管(杆)横驻波演示实验

对两端自由金属管(杆)弯曲振动实验进行了分析,对观察到的现象给出了相应的解释.     

基于最小二乘法的声速测定实验数据处理及分析

用振幅极大值法比振幅极小值法测声速的误差小和声波在传播过程中声压按指数函数关系衰减。     

浅谈杯鼓实验中空气柱的选频作用

本文首先通过杯鼓实验得到了不同空气柱长度下杯内声波的频域图,然后基于波动理论解析分析了边界振动有衰减时空气柱的共振频率及振幅,结果表明空气柱长度在声波传播过程中具有明显的选频作用。     

颗粒固体弹性势能的声波性质

基于大量静止颗粒堆积而成的物体属于非线性弹性体的观点,计算了其弹性势能的声速表达式(考虑圆柱对称和沿主应力方向传播的平面波情形).通过与己报道的一些实验数据的对比,认为精密的声学方法能够测定势能中的所有材料参数,因此是研究这类材料非线性弹性行为细节的一个重要观测手段,但需要对样品的所有应力、密度和均匀程度进行全面仔细的监控.     

星载宽波段大气痕量气体临边探测仪光学设计

为满足大气痕量气体临边探测的迫切需求,克服传统Czerny-Turner光谱仪由于像散大导致空间分辨率低的缺点,设计了一种可以在宽波段内同时校正像散的改进型Czerny-Turner光谱仪,光谱范围为0.3～0.7μm,全视场角为2.4°,焦距为120mm,相对孔径为1∶6.将离轴抛物面镜与改进型Czerny-Turner光谱仪匹配设计了一个临边探测仪光学系统并运用光学设计软件ZEMAX对临边探测仪光学系统进行了光线追迹和优化并对设计结果进行了分析,结果表明该系统的像散得到充分校正,光学系统在各个谱段的光学传递函数均达到0.69以上,完全满足设计指标要求,也证明了所提出的在宽波段内同时像散校正方法是可行的.     

Elastic moduli of η‐Ta2N3, a tough self‐healing material,via laser ultrasonics

The elastic moduli of the dense polycrystalline oxygen‐bearing η‐Ta₂N₃, a novel hard and tough high‐pressure (HP) material, were measured using the laser ultrasonic technique. The bulk modulus was determined to be B₀ = 281(15) GPa which is only ～11% below that from HP compression measurements. Our value of the shear modulus G₀ = 123(2) GPa is below those ones predicted theoretically for model structures. The discrepancies in G₀ could be due to a substitution of an‐ ions and the formation of cation vacancies in η‐Ta₂N₃. Self‐healing behaviour of η‐Ta₂N₃ by mechanical polishing was observed and confirmed by two independent experimental methods. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison between mathematical modeling and experimental identification of a spatial slider–crank mechanism

In this paper, Hamilton’s principle, Lagrange multiplier, geometric constraints, partitioning method and Baumgarte stabilization method (BSM) are employed to derive the dynamic equations of a spatial slider–crank mechanism that is driven by a servomotor. The formulation considers the effects of links masses, external forces and motor electric inputs. Comparing dynamic responses between the experimental results and numerical simulations, dynamic modeling gives a wonderful interpretation for the spatial slider–crank mechanism. In this paper, a new identification method based on real-coded genetic algorithm (RGA) is presented to identify the parameters of a spatial slider–crank mechanism. The method promotes the calculation efficiency very much, and is calculated by real-code without the operations of encoding and decoding. The results of numerical simulations and experimental results prove that the identification method is feasible. The contributions of this paper are that the comparison of mathematical modeling and identification between numerical simulations and experimental results are all realized.