拉深件成型裂纹的非平稳信号处理及状态识别

为了对金属拉深件成型时裂纹所产生的非平稳信号进行处理,最终提取到声发射信号的特征参数,从而进行金属制件的状态识别,首先,以Matlab数据处理软件为工具,采用小波包分析对金属板料拉深成型实验中采集到的声发射信号进行多维正交分解；然后,对信号进行平滑、消除趋势项、差分处理得到平稳信号,剔除了噪声信号带来的影响;最后,采用时序分析建立各分解信号的自回归模型以提取声发射信号的特征参数,以此进行制件的状态识别,并通过实验加以验证.研究结果表明,通过此方法将金属拉深制件成型时裂纹的非平稳信号转换为平稳信号,再经时序分析提取到了声发射信号的特征参数及其分布图,根据其分布图能够判定金属制件有无裂纹状态.     

基于声发射技术的拉深过程中润滑状态分析

采用发射技术监测了拉深过程中的润滑状态.在干摩擦和润滑脂润滑下,进行了拉深成形实验,并分析了不同润滑状态下拉深过程中声发射信号的能量、振铃计数、信号幅度等参数的变化规律.结果表明,拉深中产生声发射信号对润滑状态非常灵敏,随着润滑状态改善,拉深过程中产生的声发射信号能量、振铃计数、信号幅度参数等均呈下降趋势;通过对声发射信号分析可以判断拉深件的摩擦状况,即将声发射技术引入金属板材拉深中的摩擦状态的监测是可行的.     

单通道AE信号盲分离的飞机构件监测方法研究

基于声发射(AE)技术的飞机结构件疲劳裂纹检测是飞机健康状态识别的一种有效方法。由于声发射信号的瞬态性、不确定性、微弱性和易受机电干扰性,使声发射检测技术很大程度上已演变成信号处理问题,目前多数研究报道的是单源声发射信号的降噪处理。然而,在实际应用中,不仅结构件出现疲劳裂纹时会产生AE信号,而且紧耦合的结构体之间也会因冲击载荷产生弹性波,以至观测信号一般是多源AE混合信号,波的传播时延的存在使得信号混合方式为卷积混合。针对目前测试方法不能正确识别AE信号,以致难以识别结构体是否存在疲劳裂纹的问题,提出一种具有信号源个数估计的单通道非负矩阵分解解卷积盲源分离算法。首先采用经验模态分解方法将单通道混合信号分解为多个本征模态函数;然后采用主成分分析法估计信号源个数,并重构观测信号;最后通过非负矩阵分解解卷积得到各个源信号。实验结果表明,单通道盲源分离算法能正确分离AE信号,为飞机关键结构件的疲劳裂纹监测提供了一种方法。     

风力机叶片多裂纹扩展声发射信号的特征识别

针对风力机叶片蒙皮多裂纹难以状态识别的问题,根据裂纹扩展释放能量的过程,推导主裂纹扩展AE信号的表达式,从而明晰了主裂纹扩展的AE信号特性及其与应力变化之间的关联。由于多裂纹扩展AE信号为卷积混合模型,提出一种对具有非平稳、非线性特性的卷积混合AE信号特征提取的方法,以输出信号的广义能量作为目标函数得到盲解卷的滤波器迭代式,采用Godard算法通过输出信号与估计值的误差调整滤波器系数,并根据相似系数选择适当的非线性函数以减少采集设备对AE信号的影响。最后在裂纹扩展试验中,预制不同尺寸的多缺陷,对叶片试件同时施加激振载荷和循环载荷,每间隔一定的循环次数采集不同状态的AE信号,同时采用具有非全局性的瞬时频率和特征尺度来识别多裂纹在不同扩展状态下的特征,从而明晰了信号特征与多裂纹生存状态的关联,形成了识别多裂纹复合材料损伤的评价机制。     

金属拉深件裂纹AE信号特征参数提取的实验

通过设计的三层BP神经网络对实验采集的11个声发射信号参数进行特征提取。首先,根据均方根误差确定隐含层中神经元的数量为12个,然后计算各声发射参数对表征裂纹信号灵敏度的大小,逐步删除灵敏度较小的声发射参数,以达到降低训练时输入信号维数的目的。最后确定选取幅度(X1)、振铃计数(X3)、能量(X6)、持续时间(X7)、时间消耗(X9)五个特征参数能够有效地识别金属拉深件裂纹。实验研究对于减少金属拉深件裂纹定位时的繁琐的参数计算具有重要意义。     

基于AE与STFT的变桨轴承裂纹诊断研究

由于变桨轴承不完全转动的工作特殊性,基于振动或应变等常规监测手段难以奏效,为此提出一种基于声发射(acoustic emission,简称AE)技术监测方法获取信号,并采用短时傅里叶方法(short time Fourier transform,简称STFT)进行分析诊断的方法。首先,研究了AE技术的信号采集方法,推导了STFT的原理及过程,并在某风电机组变桨轴承上进行实验验证;其次,先后在时域、频域及时频域对有裂纹数据和无裂纹数据进行对比,发现时频域基于STFT分析方法可以有效发现裂纹;最后,通过新的裂纹数据进行验证,可以确认裂纹特征。结果表明:AE信号能较好地获取变桨轴承的状态信息,STFT分析方法可以较好地识别裂纹故障,较少受工况或其他因素的影响,有较高的实用价值。     

运用声发射技术监测金属塑性成型过程中润滑状态的研究

为监测金属塑性成型过程中的润滑状态,采用运用声发射技术,通过对无润滑和有润滑时金属塑性变形过程和摩擦过程的监测及对比,分别研究了金属摩擦声发射信号和塑性变形声发射信号.结果表明,不同材料摩擦产生的声发射信号数值上大小不同,同种材料摩擦声发射信号数值上小于塑性变形声发射信号;采用声发射技术,基于实时波形和声发射信号参数的平均值都能监测金属塑性成型时的润滑状态.     

声发射技术在金属板材拉深成形润滑剂配方优化中的应用

以聚四氟乙烯(PTFE)、石墨(C)、锡青铜(CuO)、环氧树脂(E44)、聚酰胺、无水乙醇、液体石蜡为原料,合成一种摩擦性能优异的固液润滑剂;利用声发射技术及马氏距离判别法对该固液润滑剂的润滑性能进行考察。结果表明:声发射技术及马氏距离判别法能准确实现对裂纹状态的识别,反映固液润滑剂在对板料拉深时的润滑性能,进而可对润滑剂配比进行优化。当聚四氟乙烯与石墨含量之比为2.5∶1时,润滑效果良好,拉深件畚斗无初试裂纹产生。     

基于深度强化学习与有限元仿真集成的拉深成形控制

金属板材拉深过程中的压边力是决定成品质量的关键参数,传统压边力控制方法往往需要对高度非线性的拉深过程进行建模,导致其控制结果与实际存在较大偏差。提出一种基于深度强化学习与有限元仿真集成的金属板材拉深过程控制模型,利用深度神经网络强大的预测能力来提取拉深加工过程中的状态信息并进行可靠预测,结合强化学习的决策能力来进行压边力控制策略的学习优化,避免了精确系统动力学模型的拟合以及先验知识的获取。同时,针对板材拉深加工中常见的拉裂质量缺陷与起皱质量缺陷,建立拉深成形性能评价函数,为深度强化学习提供回报信号来指导学习过程,并利用有限元仿真构成深度强化学习的环境模型。试验表明,深度强化学习模型能够有效地进行压边力控制策略优化,有效提高产品质量。所提出的压边力控制模型利用无模型的深度强化学习,能避免拉深过程的系统模型拟合,可提高压边力控制策略的控制效果,同时结合循环神经网络能解决板材拉深加工过程中的部分可观察性问题。     

采用小波神经网络的刀具故障诊断

为了有效的进行刀具状态监测，采用小波神经网络的松散型结合对刀具进行故障诊断。通过小波变换提取刀具磨损声发射（AE）信号的特征．即对AE信号进行小波分解，提取了5个频段的均方根值作为神经网络的输入，来识别刀具磨损状态。试验表明，均方根值完全可以作为刀具磨损过程中产生AE信号的特征向量。仿真结果表明，基于小波神经网络的刀具故障诊断对刀具磨损状态的识别效率高．该方法是有效的。     

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...     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

考虑进油孔有限长滑动轴承油膜力的近似解析解

针对具有进油孔的有限长滑动轴承油膜力求解问题,采用变分原理和分离变量法,求得了有限长滑动轴承油膜压力分布的近似解析表达式。将油膜压力分布的近似解析表达式在油膜存在区域上进行积分,即得到了油膜力。将提出的计算有限长滑动轴承油膜力方法与无限长轴承模型、有限元方法的计算结果进行了比较,发现了提出的方法与有限元方法的计算结果很接近。最后,研究了进油孔位置和进油压力对油膜存在区域、油膜力等的影响,研究结果表明进油孔位置和进油压力对油膜存在区域和油膜力有较大的影响。     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

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.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

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....     

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.