De-noising of wayside acoustic signal from train bearings based on variable digital filtering

In the wayside Acoustic Defective Bearing Detector (ADBD) system, the recorded signal usually includes both the sound from train bearings and the other disturbance sources. The fact of heavy noise corruption and the Doppler Effect of multi-source acoustic signals would badly reduce the effectiveness of online defect detection of the ADBD system. In order to extract useful information from the multi-source signal with Doppler Effect, this paper proposes an effective de-noising method based on the variable digital filter (VDF) for the ADBD system. Specifically, the ridge extraction based on Short-Time Fourier Transform (STFT) is applied to estimate the instantaneous frequencies (IFs), with which the fitting IF curves based on the Morse theory of theoretical acoustics could be achieved by using the nonlinear curve-fitting so that the parameters of the initial position of the acoustic sources could be calculated. By the aid of these parameters, the IFs according to the target train bearing could be then extracted. After that, the FIR variable digital filters could be designed with all the IFs which match the Morse theory with Doppler Shift so that the noise from the other parts could be effectively restrained after filtering the original signal. The effectiveness of this method is verified by means of a simulation with multi-frequency signals and applications to diagnosis of train roller bearing defects. Results indicate that the proposed method is effective.     

Computational investigation toward selective collection of water particles containing odorous molecules by electrostatic spraying

The necessity of odor sensing has been increasing from environmental and health standpoints. Here, we propose the novel concept of a small device which can select odor molecules based on electrostatic spraying. For high selectivity of the target gas or odor, we conducted computational fluid dynamics coupled with an electrostatic field, as well as measurements by particle image velocimetry and anemometry. The computational model successfully reproduced characteristic features of ionic wind. Different trajectories of charged particles were computationally obtained owing to their electrical mobility. The results imply that different materials might be separated by the arrangement of the collecting electrode.     

Optical coherence tomography based particle image velocimetry (OCT-PIV) of polymer flows

The measurement of spatially resolved velocity distributions is crucial for modelling flow and for understanding properties of materials produced in extrusion processes. Traditional methods for flow visualization such as particle image velocimetry (PIV) rely on optically transparent media and cannot be applied to turbid polymer melts. Here we present optical coherence tomography as an imaging technique for PIV data processing that allows for measuring a sequence of time resolved images even in turbid media. Time-resolved OCT images of a glass-fibre polymer compound were acquired during an extrusion process in a slit die. The images are post-processed by ensemble cross-correlation to calculate spatially resolved velocity vector fields. The results compared well with velocity data obtained by Doppler-OCT. Overall, this new technique (OCT-PIV) represents an important extension of PIV to turbid materials by the use of OCT.     

Doppler程序对金红石型TiO2的空位缺陷研究

金红石型TiO2是一种非常好的稀磁半导体材料,其自身的本征缺陷与室温铁磁性起源密切相关。本文利用Doppler程序在广义梯度理论（GGA）的基础上,计算了正电子在金红石型TiO2块材中不同缺陷处的湮没寿命。主要包括自由态正电子的湮没寿命,单空位和双空位处束缚态正电子的湮没寿命。并从理论上给出了含有空位缺陷时金红石型TiO2的符合多普勒展宽能谱。     

激光驱动含能复合飞片速度特性

采用真空磁控溅射方法制备了CuO/Al2O3/Al,(CuO/Al)Ⅱ/CuO/Al2O3/Al,(CuO/Al)Ⅷ/Al2O3/Al三种复合飞片,利用激光共聚焦显微镜和扫描电镜对复合飞片进行表征,结果表明,不同材料膜层的分界面清晰可见,复合薄膜的表面结构致密,颗粒基本尺寸可以达到nm级,均匀性好。利用光子多普勒测速技术对三种复合飞片速度进行测量,结果表明:将飞片靶放置在空气电离点偏前的位置(入射激光方向),增大聚焦光斑,能改善激光电离空气引起的能量屏蔽作用;含能烧蚀层CuO/Al的存在,有助于提高飞片速度。在含能薄膜烧蚀层厚度一定的情况下,增大周期、减小每层薄膜厚度,有助于提高含能薄膜反应程度,减小飞片上升沿时间。在同等激光能量密度下,(CuO/Al)Ⅷ/Al2O3/Al的上升沿时间低于(CuO/Al)Ⅱ/CuO/Al2O3/Al。     

Evaluating practical measurements of fire-induced vent flows with stereoscopic PIV

Stereoscopic particle image velocimetry (SPIV) was applied to a fire-induced doorway flow to provide the velocity field for computations of the mass flow rate of air into an enclosure. For a flow of uniform temperature and concentration, the technique met all of the requirements to provide the best estimate of the mass flow rate. Simultaneous measurements of vertical distributions of velocity and temperature were also conducted with conventional vent flow techniques, bi-directional probes and thermocouples. Correction factors for mass flow rate computations using the conventional techniques were determined based on comparisons to the SPIV results. An average correction factor of unity was determined for the bi-directional probe technique thus further confirming the utilization of velocity distributions acquired using the technique in mass flow rate computations. An average correction factor of 0.69 was determined for mass flow rates computed from vertical temperature distributions inside and outside the enclosure. This agrees with average correction factors determined in previous studies. The results from the present study suggest that the conventional techniques, which are practical and affordable for routine fire testing, may be applied with greater confidence for fires up to 500 kW.     

INS/Doppler组合导航中安装偏角的在线估计

INS和Doppler在载机上安装时存在安装偏角,会对组合导航精度产生影响.为此,提出了一种新的INS/Doppler组合导航算法,将标度因数和安装偏角作为状态变量进行估计.在分析Doppler输出误差模型的基础上,详细推导了组合导航算法模型,并进行了仿真.仿真结果表明,在载机正常飞行并适当机动的情况下,该组合导航算法能够准确对标度因数和安装偏角进行估计,标度因数的估计精度为0.4‰,安装偏角的估计精度为0.1′-0.3′,从而提高了导航精度.     

Defocus and binocular vision based stereo particle pairing method for 3D particle tracking velocimetry

We propose a new method, based on the depth-from-defocus technique and binocular vision, for solving the stereo particle pairing problem in 3D particle tracking velocimetry (PTV). Firstly, the apparent particle depth is measured with a single camera, using the depth-from-defocus technique. Secondly, a strict mathematical model of the particle-to-particle correspondence relationship between the left and right images, taking into account the refractions at the interfaces in the optical path, is presented, with the assumption that the apparent particle depth is measured. Thirdly, based on the apparent particle depth and particle-to-particle correspondence relationship, the epipoplar line is truncated into a short line segment by cutting off, where the apparent particle depth extends beyond its estimated range. For the first time, the range of the blur circle radius is employed as an additional stereo particle pairing constraint. Finally, the optimal pairing particle is selected by applying the epipolar line segment and blur circle radius constraints. The experimental results show that the rate of correct pairing is significantly improved compared with the epipolar line nearest neighbor analysis, especially when the particle density is increasing.     

3D particle positioning by using the Fraunhofer criterion

In particle tracking velocimetry, the necessary information is the 3D location of a given particle in space. This information can be obtained by examining the real image or by analyzing the interference fringe recorded on a digital camera. In this work, we measure the three-dimensional position of spherical particles by calculating the Central Spot Size of the interference pattern of a particle diffraction image. The Central Spot Size is obtained by combining the Continuous Wavelet transform and circle Hough transform. The Continuous Wavelet transform allow us in only one step enhanced quality of particle images and sets a threshold to select properly places where a Central Spot Size appear in order to determine its size via the Hough transform. The size and centroid of the Central Spot Size render z and x-y position of a particle image, respectively. The Central Spot Size is related to a criterion of a simplified theory given by the Fraunhofer theory in order to obtain z particle position. Our approach has been applied to simulated and experimental particle images. Simulated particle images show good agreement between actual and calculated Central Spot Size. An average relative error of 0.5% and 1.12% for x-y and z directions, respectively, was found in the analysis. Our experimental particle images were obtained from particle motion inside a channel. The quality of the particle images determines the accuracy of the calculation of the Central Spot Size of a particle image.     

Ultrasound velocimetry of ferrofluid spin-up flow measurements using a spherical coil assembly to impose a uniform rotating magnetic field

Ferrofluid spin-up flow is studied within a sphere subjected to a uniform rotating magnetic field from two surrounding spherical coils carrying sinusoidally varying currents at right angles and 90° phase difference. Ultrasound velocimetry measurements in a full sphere of ferrofluid shows no measureable flow. There is significant bulk flow in a partially filled sphere (1-14 mm/s) of ferrofluid or a finite height cylinder of ferrofluid with no cover (1-4 mm/s) placed in the spherical coil apparatus. The flow is due to free surface effects and the non-uniform magnetic field associated with the shape demagnetizing effects. Flow is also observed in the fully filled ferrofluid sphere (1-20 mm/s) when the field is made non-uniform by adding a permanent magnet or a DC or AC excited small solenoidal coil. This confirms that a non-uniform magnetic field or a non-uniform distribution of magnetization due to a non-uniform magnetic field are causes of spin-up flow in ferrofluids with no free surface, while tangential magnetic surface stress contributes to flow in the presence of a free surface.Recent work has fitted velocity flow measurements of ferrofluid filled finite height cylinders with no free surface, subjected to uniform rotating magnetic fields, neglecting the container shape effects which cause non-uniform demagnetizing fields, and resulting in much larger non-physical effective values of spin viscosity η′∼10⁻⁸−10⁻¹² N s than those obtained from theoretical spin diffusion analysis where η′≤10⁻¹⁸ N s. COMSOL Multiphysics finite element computer simulations of spherical geometry in a uniform rotating magnetic field using non-physically large experimental fit values of spin viscosity η′∼10⁻⁸−10⁻¹² N s with a zero spin-velocity boundary condition at the outer wall predicts measureable flow, while simulations setting spin viscosity to zero (η′=0) results in negligible flow, in agreement with the ultrasound velocimetry measurements. COMSOL simulations also confirm that a non-uniform rotating magnetic field or a uniform rotating magnetic field with a non-uniform distribution of magnetization due to an external magnet or a current carrying coil can drive a measureable flow in an infinitely long ferrofluid cylinder with zero spin viscosity (η′=0).