Incremental approach to determination of image fragment displacements during vector field construction

An algorithm of constructing displacement vector fields, based on the incremental approach to estimating displacements of image fragments, is proposed. Application of this algorithm for processing model and experimental optical images is analyzed. Noise immunity of the incremental algorithm for determining displacements is compared with that of the combined algorithm developed by the authors. It is shown that the proposed incremental algorithm ensures a more noise-immune estimate of displacements in processing images of a deformation relief essentially varying in time.     

Dark field photoelectron emission microscopy of micron scale few layer graphene

We demonstrate dark field imaging in photoelectron emission microscopy (PEEM) of heterogeneous few layer graphene (FLG) furnace grown on SiC(000-1). Energy-filtered, threshold PEEM is used to locate distinct zones of FLG graphene. In each region, selected by a field aperture, the k-space information is imaged using appropriate transfer optics. By selecting the photoelectron intensity at a given wave vector and using the inverse transfer optics, dark field PEEM gives a spatial distribution of the angular photoelectron emission. In the results presented here, the wave vector coordinates of the Dirac cones characteristic of commensurate rotations of FLG on SiC(000-1) are selected providing a map of the commensurate rotations across the surface. This special type of contrast is therefore a method to map the spatial distribution of the local band structure and offers a new laboratory tool for the characterisation of technically relevant, microscopically structured matter.     

基于SVR-GA算法的广义加工空间机床切削稳定性预测与优化研究

针对机床零件加工位置和进给方向不确定造成刀尖频响函数变化,导致切削稳定性叶瓣图与无颤振工艺参数预测具有不确定性问题,提出一种耦合支持向量回归机(SVR)与遗传算法(GA)的切削稳定性预测与优化方法。该方法采用锤击法模态实验和空间坐标变换,获取样本空间不同加工位置与进给方向的刀尖频响函数;进而结合传统切削稳定性预测方法构建以各向运动部件位移、进给角度、主轴转速、切削宽度、每齿进给量为输入的极限切削深度SVR预测模型;采用该SVR模型作为切削稳定性约束建立材料切除率优化模型,通过遗传算法求解各运动轴位移、进给角度与切削参数的最优配置。以某型加工中心展开实例研究,实验结果表明获取的优化配置能实现稳定切削,验证了该方法的有效性。     

The influence of a vortex on a freely propagating laminar methane-air flame

The change in the NO emission indices (EINO) in a two-dimensional plane has been investigated, which is due to the interaction between a vortex and methane-air flames established at different equivalence ratios, by solving the field equation. After solving the field equation, the spatial distribution of G-values is obtained. The NO emission index is calculated after applying the appropriate relation between the G-values and the NO production rate or the mass fraction of methane obtained from the library of freely propagating flames created from detailed simulations. When a vortex exists in a reacting flow field, in general EINO slightly increases, whereas EINO is lowered in the vicinity of the vortex regardless of flow direction. A change in vortex size has negligible impact on EINO_T but increasing the vortex strength slightly increases EINOt in the domain of this study.     

Pressure field estimation from ultrasound Doppler velocity profiler for vortex-shedding flows

A novel algorithm of pressure field estimation based on ultrasound velocity profiler (UVP) is developed. The method consists of UVP measurement of velocity distribution in fluid flows and numerical analysis of the measured data using fluid dynamics equations. We introduce equation of continuity, incompressible Navier-Stokes equation and proper orthogonal decomposition (POD) into the basic algorithm, so that pressure field of space-time two-dimensional unsteady fluid flow is fully reconstructed. Since UVP is based on ultrasound Doppler principle, the local instantaneous pressure distribution is obtained non-intrusively. The performance of an algorithm is evaluated for vortex shedding flow behind a circular cylinder at Re = 1000. Considering the specification of UVP, the optimal method of experimental data conversion to pressure information is proposed. We have found that the one-dimensional velocity measurement by UVP upon Taylor's frozen hypothesis is suitable for evaluation of pressure field in wake of the cylinder. The present algorithm is also demonstrated for opaque fluid flows by considering vortex flow in milk.     

Optoelectronic scanning system upgrade by energy center localization methods

A problem of upgrading an optoelectronic scanning system with digital post-processing of the signal based on adequate methods of energy center localization is considered. An improved dynamic triangulation analysis technique is proposed by an example of industrial infrastructure damage detection. A modification of our previously published method aimed at searching for the energy center of an optoelectronic signal is described. Application of the artificial intelligence algorithm of compensation for the error of determining the angular coordinate in calculating the spatial coordinate through dynamic triangulation is demonstrated. Five energy center localization methods are developed and tested to select the best method. After implementation of these methods, digital compensation for the measurement error, and statistical data analysis, a non-parametric behavior of the data is identified. The Wilcoxon signed rank test is applied to improve the result further. For optical scanning systems, it is necessary to detect a light emitter mounted on the infrastructure being investigated to calculate its spatial coordinate by the energy center localization method.     

Application of vortons to calculate vibrations of a beam in spatial flow

The modification of the meshless vortex method to solve associated spatial problems of hydroelasticity is described. Symmetrical vorton segments and vorton frames on the surface of a body are used. The obtained algorithm is applied to analyze vibrations of a beam in a subsonic flow. Results of the calculation of a model problem are given.     

A method for measuring the dynamics of velocity vector fields in a turbulent flow using smoke image-visualization videos

A new optical method for determining flow-velocity vector fields that allows investigations of unsteady and fast processes is described. The method is based on measuring the displacements of turbulent structures, which are visualized in a light sheet, within a fixed time interval between consecutive video frames. The method was tested using measurements of pulsating-flow velocity. It was shown that the difference between the mean flow velocity in the investigated flow measured using this method and a hot-wire anemometer does not exceed 1%, while the deviation of the rms velocity pulsations is within 4.5%.     

基于粒子群算法的二维Otsu阈值分割法

二维Otsu方法同时考虑了图像的灰度信息和像素间的空间邻域信息,是一种有效的图像分割方法。针对二维Otsu方法计算量大的特点,采用粒子群算法来求解最优二维阈值向量。通过分别用快速递推算法和改进粒子群算法对显微细胞图像的实验表明,后者不仅能得到理想的分割效果,且相较于前者,计算量大大减少,达到了快速分割的目的,有利于提高图像处理的实时性。     

Discrete positions method in kinematics and control of spatial linkagesEine methode der diskreten lagen in der kinematik und steuerung der bewegungen raumlicher mechanismen

Using the screw theory in the field of infinitesimal displacements, the first and second order transfer functions of spatial kinematic chains are algebrised. Based on this, a method of finite increments of the relative displacements in the joints is offered. Finally, an algorithm for the control strategy of open kinematic chains of manipulators and robots was evolved using an imaginary closing of the kinematic chain while bearing in mind the conditions for instantaneous mobility (transitory).     

A light field measurement system through PSF estimation by a morphology-based method

Light field imaging technology can obtain three-dimensional (3D) information of a test surface in a single exposure. Traditional light field reconstruction algorithms not only take a long time to trace back to the original image, but also require the exact parameters of the light field system, such as the position and posture of a microlens array (MLA), which will cause errors in the reconstructed image if these parameters cannot be precisely obtained. This paper proposes a reconstruction algorithm for light field imaging based on the point spread function (PSF), which does not require prior knowledge of the system. The accurate PSF derivation process of a light field system is presented, and modeling and simulation were conducted to obtain the relationship between the spatial distribution characteristics and the PSF of the light field system. A morphology-based method is proposed to analyze the overlapping area of the subimages of light field images to identify the accurate spatial location of the MLA used in the system, which is thereafter used to accurately refocus light field imaging. A light field system is built to verify the algorithm's effectiveness. Experimental results show that the measurement accuracy is increased over 41.0％compared with the traditional method by measuring a step standard. The accuracy of parameters is also improved through a microstructure measurement with a peak-to-valley value of 25.4％and root mean square value of 23.5％improvement. This further validates that the algorithm can effectively improve the refocusing efficiency and the accuracy of the light field imaging results with the superiority of refocusing light field imaging without prior knowledge of the system. The proposed method provides a new solution for fast and accurate 3D measurement based on a light field.     

多孔射流式通风的流场特性分析

为了分析多孔射流风机作用下风场的流场特性,文中采用CFD方法,对多孔射流式风场模型内部流场进行了数值模拟,对比分析了不同喷嘴数量及排布方式对流场性能的影响,并引入涡动力学理论,分析了流场内涡结构的分布发展规律及其对流体掺混的影响。结果表明：喷嘴的数量及排布方式对流场性能有显著影响,外围喷嘴会对中心喷嘴的流动起到限制作用;流向涡对流体掺混效果的作用比展向涡大,在涡量一定的情况下,流向涡尺度越大、衰减越快,流体间的混合效果越好,流场稳定性越高。流场内速度及涡动力学分布表明,流场稳定性随着喷嘴数量的增加而显著提高,因此在保证经济性的前提下应尽量采用数量多的喷嘴排布方式。     

改进时频分析和特征融合在内燃机故障诊断中的应用

针对基于内燃机振动信号的故障识别诊断问题,首先提出一种基于阈值筛选的变分模态分解(VMD)、玛基诺-希尔时频分布(MHD)的时频分析方法,该方法针对Cohen类时频分布存在的交叉干扰项问题,通过阈值筛选法确定VMD算法的分解层数,从而将内燃机振动信号分解成一系列单分量模态信号,然后对单分量信号进行MHD时频表征及线性叠加得到时频聚集性优良、物理意义明确的振动信号时频谱图。再通过局部非负矩阵分解(LNMF)对时频图像特征进行提取,将提取的特征与振动信号时域参数进行特征融合,得到融合特征向量。对支持向量机(SVM)采用改进粒子群优化算法进行参数优选,然后对特征向量进行训练和测试,实现了内燃机的故障识别诊断。将该方法应用于内燃机气门间隙故障8种工况下缸盖振动信号的识别诊断试验,结果表明,该方法能够对不同工况振动信号进行有效识别分类。通过参数优选,最高识别率达到了99.17%,同时对比传统的最近邻分类器的分类结果,证明了该方法的优越性。     

Optimization in PIV algorithm for visualizing vortices in bubble wake

The PIV (Particle image velocimetry) is the most commonly used method for flow field observation because of its high efficiency and non-interference to the flow field. This study aims to clarify the optimal parameter conditions used in the cross-correlation algorithm of PIV for flow fields with vortices. The influence factors on the error of the cross-correlation algorithm are analyzed and discussed using a synthetic flow field, including the seeding conditions, the velocity gradient and vortex size. It is confirmed that the minimum particle number density per interrogation window is about 10, which generally limits the minimum size of the window. For a vortex, when the vortex size is fixed, the velocity gradient corresponding to the characteristic velocity both controls the lower and upper limitation of window size. For a relatively small vortex, generally a window not larger than the vortex size is asked. Then, a strategy to improve the observation based on the existing equipment is discussed and applied to visualize a rising bubble wake based on LIF (Laser-induced fluorescence) images.     

EXPERIMENTAL INVESTIGATION OF TIP CLEARANCE FLOW FOR AN AXIAL FLOW FAN ROTOR

The flow field in the tip region of an axial ventilation fan is investigated with a particle image velocimeter (PIV) system at the design condition. Flow fields with three different tip clearances are surveyed on three different circumferential planes, respectively. The phase-locked average method is used to investigate the generation and the development of a tip leakage vortex. The result from PIV system is compared with that from a particle dynamics anemometer(PDA) system. Both data are in good agreement and the structure of the tip leakage vortex for the rotor is illustrated. The characteristic of a leakage vortex is described in both velocity vectors and vortical contours. The unsteadiness of the leakage vortex and the position of the vortex are surveyed in detail, which interprets the discrepancy between the numerical simulation and PDA experimental results to a certain extent. The center loci of tip leakage vortex at different times and the mean center loci of the leakage vortex are displayed particularly. Finally, the trajectories of the tip leakage vortex by the experimental measurement are compared with predictions from the existing models for high speed and high-pressure compressors and turbines when appropriately interpreted. A good agreement is obtained.     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

优化预测运动矢量的快速运动估计算法

提出了一种优化预测运动矢量的快速运动估计算法。在对预测运动矢量研究的基础上,根据序列图像中运动矢量的中心-中值偏置分布特性和矢量间的时空相关性,结合运动矢量的相似度分析,选用中心、中值和时间相关的三个矢量作为基本预测矢量。设置相似门限来减少由三个空间相邻块预测矢量带来的大量冗余信息,对算法中关键的门限技术进行了改进。实验结果证明,本文算法对各种类型的运动序列都有很强的自适应性,在保持搜索准确度的同时,可大幅度提高运动估计的速度,其平均搜索速度是FS的208倍,明显优于PMVFAST的146倍、MVFAST的77倍、DS的55倍,提高了视频压缩中现有的运动估计算法的性能。     

湍流信道下光空间调制信号的压缩感知检测

在光空间调制系统中采用最大似然检测算法可以获得最优的误码性能,但算法的译码复杂度限制了其实际应用。本文依据光空间调制激光器映射向量,并结合脉冲位置调制方式下的脉冲向量构建了具有稀疏特性的发送信号。基于该稀疏特性,采用正交匹配追踪算法提出了一种基于压缩感知理论的光空间调制信号检测方法。仿真结果表明:该方法以少量误码性能损失为代价极大地降低了信号检测的复杂度。当激光器数目为64时,相比于最大似然检测算法,本文所提方法的复杂度降低了99.54%。同时,由于稀疏性的引入,该方法更适合于具有大规模激光器的无线光通信系统。     

Dynamic contact stress analysis using a compliant sensor array

A flexible sensor array has been developed for the measurement of contact stress distribution between flexible bodies. The array incorporates 960 contact geometry modulation resistive (CGMR) transducers to provide a spatial resolution of 10 mm × 10 mm. The high flexibility of the array and its special structure enable it to comply with the very large displacements of the interface between the human body and a flexible cushion. In addition, a method and instrument have been developed to measure, digitize and record dynamic contact stress distributions with a sampling rate of up to 300 frames per second (960 sensors/frame). Measurements performed using this system under static and dynamic conditions are consistent with those performed through the contact pressure display (CPD) method. The new method has been used by the authers and their associates to obtain basic data required for the new field of cushioning mechanics.     

基于小波变换的涡街流量计信号处理方法

涡街流量计有许多优点,应用比较广泛。但是,涡街流量计易于受到由管道振动和流场扰动引起的噪声干扰。涡待流量计中的处理电路不能保证仪表在工业现场的测量精度。本文研究基于小波变换的涡街流量计信号处理方法。本文介绍小波变换的基本原理和快速算法,分析小波滤波器的幅频特性,研究调整滤波器中心频率的方法,给出涡街信号的处理过程,进行仿真和实验测试。仿真和实验结果表明,小波变换能有效地减小了噪声影响,使频率测量的精度高,处理实时。小波变换是涡街流量计信号处理的一种新方法。