基于分数阶傅里叶变换的振动信号分析

通过仿真实验验证了分数阶傅里叶变换可以抑制高斯噪声,检测出chirp信号。通过机械振动实验进一步验证了分数阶傅里叶变换不仅可以分析平稳振动信号,而且分析非平稳振动信号比传统傅里叶变换更客观地表达出信号的频谱,提取出非平稳成分。     

分数阶傅立叶变换的线性调频信号降噪

本文在分数阶Fourier变换原理的基础上,提出了一种基于分数阶傅里叶变换的线性调频（LFM）信号的滤波方法,利用该变换等同于对信号在时频平面进行旋转,将混迭有噪声的信号以特定的旋转角作分数阶傅里叶变换,使得信号与噪声在变换域中的交迭达到最小：然后通过窄带通滤波器对LFM信号进行抽取,再经过分数阶傅里叶反变换,恢复出原信号。     

混响背景下基于分数阶傅里叶变换的自适应LMS滤波算法

针对强混响背景下经典的最小均方误差(Least Mean Square,LMS)滤波算法难以有效地实现信混分离的问题,提出一种基于分数阶傅里叶变换的自适应LMS算法。首先将混响信号和自适应LMS滤波算法中的参考信号进行分数阶傅里叶变换,寻找最优变换域,并在分数阶域进行带通滤波,然后将得到的信号进行分数阶傅里叶反变换,最后将基于正态分布曲线的变步长LMS算法应用于此混响条件下进行滤波。仿真和海试数据验证结果表明,在信混比为0 dB的情况下,算法仍可以有效地滤除混响,使信混比提高6dB。     

基于分数阶傅里叶变换的NURBS曲面拟合

为了实现对自由曲面模型的高精度非均匀有理B样条(NURBS)曲面拟合,提出了一种基于分数阶傅里叶变换的NURBS曲面拟合方法.首先,借助分数阶傅里叶变换对自由曲面模型点云数据的高程图像展开分析,从中提取出表征自由曲面表面三维结构的特征点;然后,利用外切圆取点法结合提取的特征点选取用于NURBS曲面拟合的数据点;最后,利...     

基于频率-波数分析的激光Lamb波传播特性试验研究

Lamb波的频散和多模态特性,使得利用Lamb波信号的时域或频域特征实现缺陷的定量检测具有一定的困难。提出了一种在频率-波数内分析激光Lamb波传播特性的方法。基于全光学型激光超声检测系统,脉冲激光在固定位置激励,连续激光一维线扫描接收,获得时间-空间波场信号,可直观地显示激光Lamb波信号的传播特性以及激光Lamb波与缺陷之间的作用规律。采用二维傅里叶变换将波场信号从时间-空间域转换到频率-波数域,可有效识别信号中包含的各模态信息。为了保留空间信息,借鉴短时傅里叶变换的思想,采用短空间二维傅里叶变换得到沿扫描路径上波数的分布,从中可直观看出缺陷的位置。采用带通滤波结合连续小波变换的方法对短空间二维傅里叶变换的结果进行了优化。分别在有、无缺陷铝板中进行了试验研究,试验结果验证了该方法的有效性。     

基于样本熵和分数阶傅里叶变换的滚动轴承故障特征提取

提出了一种基于样本熵和分数阶傅里叶变换的故障特征提取新方法。这种方法的核心思想是首先把原始数据空间中可分性较差的数据映射到合适的分数阶空间,然后计算并比较经过合适阶次分数阶傅里叶变换后数据的样本熵,从而实现故障的特征提取。实测数据的研究结果表明,用这种方法提取信号特征,能增强不同故障模式的可分性,可以容易地将正常滚动轴承、内圈故障、外圈故障和滚动体故障的信号区分。     

飞机颤振试飞试验信号的广义时频滤波

针对飞机颤振试飞试验信号噪声过大的问题,提出了一种广义时频域滤波算法。算法采用分数阶傅里叶变换对线性扫频激励及其响应信号进行广义时频分析,利用该类信号在分数阶傅里叶域内的聚焦特性,有效提取真实响应信号,达到信噪分离的目的。给出了具体的滤波算法,并将其应用于仿真算例和实际试飞数据,结果表明该方法可显著提高信号的信噪比。     

基于FRFT的齿轮振动信号故障特征提取

研究了典型齿轮故障振动信号在分数阶傅里叶变换（FRVF）域的分布特征,并在此基础上分析了该信号在FRFT循环域（CFRFD）的分布特征,提出了FRFT循环处理（CFRFT）方法,实现了信号在CFRFD的能量积累。通过仿真实验验证了低信噪比条件下,CFRFT对齿轮振动信号的故障特征提取能力及有效性。     

基于分数阶傅里叶变换的邻近阶比分离研究

提出了一种基于分数阶傅里叶变换（Fractional Fourier Transform, FRFT）的邻近阶比分离方法。根据变速器输入轴转速信号及传动比确定FRFT最佳阶次,对变速器升速过程振动信号进行最佳阶次FRFT,在该分数阶域分离邻近阶比分量,并对分离出的单分量信号进行阶比分析。试验结果表明,根据转速信号确定FRFT最佳阶次,准确、快速、鲁棒性好,并具有自适应性;最佳阶次的FRFT能准确分离提取邻近阶比分量,对分离出的目标阶比分量进行单分量分析,能有效解决邻近阶比胶合问题。     

基于线性调频信号二次相位变换的主动声呐目标速度估计

分数阶傅里叶变换常用于主动声呐线性调频信号的分析,通过搜索变换参数可以估计目标的相对速度.但是由于其参数搜索计算量偏大,在自主式水下航行器等计算力有限的小平台难以实时处理.针对该问题提出了一种基于二次相位变换的线性调频信号速度估计方法,根据多普勒频移后线性调频信号的二次相位变换的解析解,分析了二次相位变换后变换域频谱展...     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from