基于小波包域噪声能量分布的脉冲噪声消除

针对信号被平稳脉冲噪声污染的场合,提出了一种从含噪信号中检测脉冲噪声并降噪的脉冲噪声消除方法.该方法选择脉冲噪声能量相比含噪信号能量最为显著的小波包树节点,并利用该节点小波包系数重构信号进而检测脉冲噪声的时域分布.在降噪中,该方法于小波包域内估计脉冲噪声的能量分布并依据估计结果计算每段脉冲噪声的滤波阀值.将该方法用语音增强实验验证,结果表明所提出的检测算法能获得较好的检测结果,而提出的降噪算法能显著地改善信噪比,获得较好的降噪效果.将文中的检测算法应用于轴承故障检测的信号预处理,进一步验证了方法的有效性.     

基于小波变换的图像降噪技术研究

根据小波变换和噪声信号的能量分布特性,提出了一种先用小波变换对含噪图像进行多尺度分解,求出各尺度小波变换高频系数的噪声方差和阈值,利用各尺度的阈值对高频系数进行处理,然后利用小波变换系数重构图像,实现图像降噪的方法;实验结果说明该方法既可以有效地降低噪声,又可以较好地保持图像细节。     

基于Symlets小波滤波的滚珠丝杠伺服进给系统频响特性辨识

高速、高加速度条件下,滚珠丝杠进给系统所具有的弹性特性会对其频率响应特性造成很大影响.通过分析转矩输入信号和加速度输出信号的幅值和相位关系可以实现对进给系统频响特性的辨识.通过集中质量方法对弹性滚珠丝杠传动系统进行建模,由拉格朗日能量法和状态空间分析对系统的频响特性进行计算.并进一步利用试验方法完成进给系统频响特性的辨识.为了减少量化噪声、白噪声和有色噪声对辨识信号的影响,提出通过Symlets小波滤波方法对有限差分方法得到的加速度信号进行小波滤波处理后,再进行幅值和相位信号的提取和频响函数的拟合.仿真和试验最终证明Symlets小波滤波方法能有效地减少噪声对加速度信号的影响,提取出有效信号,实现对进给系统频响特性更为精确地辨识.     

变分模态分解和熵理论在超声信号降噪中的应用

针对超声检测信号中结构噪声难以去除的问题,提出了一种变分模态分解(Variational Mode Decomposition,VMD)和小波能量熵阈值(Wavelet Energy Entropy Threshold,WEET)联合降噪的算法.分析了含噪系统熵增的特性以及结构噪声在不同时间段的分布特征,提出了用小波能量熵表征信号的含噪状态,并以小波能量熵最大子区间的小波系数参与计算各个尺度层的阈值.对仿真及实测信号进行处理,结果表明,该方法(VMD-WEET)能很好地抑制超声回波信号中存在的白噪声及结构噪声,还原了准确的波形特征,验证了其有效性.     

超声波测距系统中的小波去噪方法研究

针对远距离超声波测距系统中回波信号信噪比低的问题,采用小波变换对超声波的回波信号进行去噪处理.为取得较好的去噪效果,对小波变换的参数选取进行了研究.根据小波基的特性,通过能量与能量熵选取最优小波基;基于回波信号噪声的白噪声特征,采用白噪声检验自适应确定分解层数;引入参考噪声信号,确定小波系数处理阈值,并选用一种结合软、...     

一种自适应小波消噪方法

为了消除噪声对被测信号的干扰,有效提取信号中的有用成分,根据信号和噪声小波变换系数的不同特性,在分析了传统阈值方法局限性的基础上,提出了一种自适应小波消噪方法.该方法首先对被测信号进行小波分解,并改进了阈值量化公式,使其具有能量分布自适应的降噪能力;然后,利用类别方差作为判别依据,选取使得类别方差最大和类内方差最小的阈值作为最佳的阈值.并根据每层分解后的小波系数进行自适应的阈值确定;最后,对信号进行重构,通过分解、阈值处理和重构等过程实现小波消噪.仿真信号和轴承故障诊断的实例结果表明该方法可在强噪声背景下消除噪声干扰,有效提取出滚动轴承的早期故障频率.     

基于小波变换的低场脉冲核磁共振系统高斯白噪声估计

介绍了以小波分析理论为基础，结合小波阈值去噪算法找到一种有效的噪声分离方法。采用该方法从实际低场脉冲核磁共振系统噪声信号中分离出高斯白噪声并对其进行了参数估计。该方法还可以用于其它信号处理领域高斯白噪声的估计。     

基于小波包变换的电磁超声接收信号特征提取

使用改进的功率谱函数对电磁超声缺陷信号进行了缺陷的定性分析,使用小波包能量谱对电磁超声缺陷接收信号进行了特征提取,从小波包的小波函数选取、分解层次及特征参数的噪声鲁棒性3个方面开展了讨论分析.结果表明:通过选择适当的小波函数和小波包分解层次,小波包能量谱的能量比可以精细地反映信号的特征;基于小波包能量谱的特征参数具有良好的损伤敏感性及噪声鲁棒性,能在强噪声影响下实现对EMAT不同损伤类型的判别.     

一种轴承故障诊断的改进型小波包包络方法

小波包包络法是轴承振动信号分析中的一种重要方法,使用该方法可以对包含有故障特征频率的各频段信号进行分析,能够滤去噪声信号,有效地提取轴承的故障信息。在小波包分解时,对小波包细节信号的选取目前常用的是基于细节系数能量的方法,但该方法在信噪比较小的情况下对信号分析效果一般,结合自相关和互相关的特性,提出了一种改进型的小波包包络方法,为小波包分解中细节信号的选取提供了一定的理论依据,提高了小波包在轴承故障诊断中的判断准确度。     

基于完全抗混叠DTCWPT和包络谱熵的轴承故障诊断

针对经典小波包和双树复小波包(dual tree complex wavelet package transform,DTCWPT)能量泄漏和频率混叠的缺陷,提出完全抗混叠的DTCWPT改进算法,该算法解决了经典小波包存在负频率以及经典小波包和DTCWPT滤波器频率不完全截止问题。根据高斯白噪声频率充满整个频带的特性,通过小波包变换对高斯白噪声进行分解,利用频带能量泄漏的定量分析方法,验证了改进DTCWPT具有完全的抗频带能量泄漏特性。将改进DTCWPT方法和包络谱熵引入到轴承故障诊断中,该方法的核心是:对轴承振动信号进行改进DTCWPT变换得到不同尺度的分解信号,分别计算各分解信号的包络谱熵,合并熵值较小的几个分量信号的包络谱,最后根据合并的包络谱来检测轴承故障。该方法在消除经典小波包变换和DTCWPT频率混叠和能量泄漏的同时还解决了小波包分量选择盲目的问题。最后应用轴承故障试验数据对该方法进行试验验证,结果表明:改进DTCWPT结合包络谱熵选择的方法能够很好提取出轴承故障特征频率的基频、倍频,提高了轴承故障的诊断效果。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.