基于压电复合材料的梳状柔性宽带表面波传感器有限元设计

为检测厚板和厚壁管道表面缺陷。采用1-3型压电复合材料结合有限元方法设计了一种柔性非等间距梳状宽带表面波传感器。首先优化了复合材料参数。当复合材料宽高比小于0.6,压电相体积百分比为70%时为最佳参数。然后采用优化得到的压电复合材料,设计了宽度渐变和厚度渐变的传感器,并进行了频率响应,指向性和缺陷检测模拟。结果表明,设计的传感器-3 dB带宽达到420 kHz,指向性良好,并且能够在不同频率实现缺陷检测。为传感器实物制作提供了理论基础。     

电容式微机械超声传感器(CMUT)声场特性分析

为研究CMUT指向性,将CMUT微元看成圆形活塞式换能器,根据指向性函数的理论,计算出CMUT微元的指向性公式,依据Bridge乘积原理,推导出了一种计算CMUT阵元、CMUT一维线阵和CMUT面阵指向性公式,并利用MATLAB软件对CMUT微元、阵元、线阵和面阵指向性进行了仿真分析,得出CMUT类型对指向性、主瓣宽度和旁瓣的影响,证实了多维模型的优势,为CMUT结构优化设计提供了基础。基于CMUT微元声场理论分析基础,根据瑞利-索末菲积分公式推导出CMUT阵元、CMUT阵列的辐射声场分布函数,并仿真验证了其聚焦和指向性性能。     

基于阵元指向性的复合材料曲面结构超声表面契合法研究

采用相控阵超声结合表面契合法(Surface adaptive ultrasonic,SAUL)检测复合材料曲面结构过程中周向缺陷检测分辨力低,给缺陷定量带来困难。为提高SAUL的检测能力,以T700/环氧树脂T形长桁为研究对象,建立弹性各向异性有限元模型,并对照弹性各向同性情况分析其声传播规律,发现弹性各向异性和层间反射共同作用导致肋板处形成明显噪声。在此基础上,基于阵元指向性开展曲面结构成像检测研究,结果表明：引入阵元指向性校正系数对声源脉冲信号幅值进行优化,降低探头频率,可使阵元声场更适应曲面结构,从而减弱两侧肋板反射,提高成像质量。针对周向长度4.5 mm、深1.5 mm的分层缺陷,改进后的SAUL方法对应仿真和试验中周向缺陷长度定量误差较常规SAUL结果分别减小7.4%和13.1%,表明优化阵元指向性可有效改善SAUL周向检测分辨力,提高复合材料曲面结构超声检测缺陷定量水平,具有推广应用价值。     

一种高信噪比电磁声表面波传感器及在厚壁管道检测中的应用

为了提高在自激自收模式下接收信号的信噪比,自行研制一种不同结构配置的电磁声表面波传感器,分析其提高信噪比的机制及影响其信噪比的因素。在自激自收模式下,由于所研制的传感器中磁铁与线圈间存在间隔,降低了磁铁中超声波的影响,进而提高了信噪比。研究结果表明,接收信号的信噪比不仅与提离距离(磁铁与线圈的间隔)有关,而且与其中心频率成正相关关系。所研制的3个不同中心频率电磁声表面波传感器性能测试结果表明,其实测中心频率与设计值一致,其指向性与理论分析相吻合。采用所研制的表面波传感器对标准样块上不同深度的缺陷进行检测,试验结果表明,当缺陷深度约达表面波波长的1/4时,即可检测到该缺陷。进一步选用中心频率1.0 MHz的表面波传感器,实现了对厚壁管道上周向矩形槽、轴向矩形槽和平底孔3种类型缺陷的检测。     

漏磁传感器励磁结构影响因素分析及优化设计

漏磁检测中励磁结构的磁化能力是影响漏磁传感器缺陷检测能力的一个重要因素。根据交流漏磁检测原理,建立二维漏磁检测参数化有限元仿真模型,研究磁心的形状和尺寸、励磁线圈的位置和绕组长度、磁屏蔽层厚度等励磁结构参数对漏磁检测信号的影响。同时,将参数化有限元分析与遗传优化算法相结合,发展一种励磁结构尺寸参数的有限元模拟遗传优化设计方法,实现了漏磁传感器中磁极间距与磁极宽度等关键尺寸的优化。仿真及检测试验结果表明,传感器的励磁结构参数对漏磁检测结果具有很大影响,优化后的励磁结构可有效提高漏磁传感器的缺陷检测性能。提出的基于参数化有限元的遗传优化方法为漏磁检测中其余影响参数的优化提供了可行的参考方法。     

基于模态分析的厚壁管道周向导波检测的研究

厚壁管道中结构的不连续会改变周向导波的传播特性,从而影响对检测信号的判断,因而研究厚壁管道中周向导波传播特性以及缺陷对周向导波传播的影响是实现厚壁管道系统检测的基础。从厚壁管道的频散曲线出发,分析了厚壁管道周向导波频散曲线的不同特征,同时研究了入射角对厚壁管道检测性能的影响。在优化选取最优入射角度的情况下,利用小波分析结合数据拟合的方法研究了该角度下导波在厚壁管道中的模态转换特征,计算出周向导波在厚壁管道不同距离处的实际传播速度,区分出了导波的模态,并以此为基础在厚壁管中引入切槽缺陷,采用实验方法研究了缺陷大小对导波幅值、模态转换的影响规律。该研究为厚壁管道周向导波检测提供了参考。     

油气管道柔性测径传感器设计及其结构优化

油气管道测径技术是检测管内通径变化、保障管道安全的重要手段。针对传统薄铝盘测径板无法检测多处缺陷且不可重复使用等问题,本文设计了一种柔性测径传感器,其通过置于聚氨酯柔性测径盘中的电阻应变片测量遇阻时的应变变化,实现管内缺陷量化检测。结合ABAQUS软件建立应变片和聚氨酯密封盘的耦合模型,分析产生拉压变形时的应变输出特性,并基于敏感栅应变趋势,寻找应变片最优放置位置。通过柔性测径传感器性能检测实验台,对柔性测径传感器的功能进行测试。最后结合BP神经网络与遗传算法得出使传感器检测性能最佳的结构参数。研究结果表明,对于DN200的管道,当测径盘外径为97.5%的管道内径,测径盘厚度19 mm,测径盘瓣间距8 mm时,柔性测径传感器能较好表征凹陷的几何尺寸,对于油气管道变形检测作业具有一定的工程应用价值。     

基于三轴融合的漏磁内检测数据缺陷反演方法研究

在管道漏磁检测中,缺陷反演是管道故障诊断的核心部分。 考虑漏磁信号的复杂性以及管道环境的多变性,常用的缺 陷反演方法多采用传感器单轴信息,从而导致缺陷反演面临缺陷估计尺寸精度低、模型通用性差的问题,难以满足实际应用需 求。 本文提出基于三轴融合的漏磁内检测数据缺陷反演算法,显著提高漏磁缺陷反演精度。 该方法主要由两部分组成,首先, 利用提出的加权随机森林算法分别实现单轴信号的缺陷反演;其次,通过本文设计的模糊推理系统实现三轴反演结果决策融 合,进而得到精确的缺陷估计尺寸。 最后,通过仿真数据与实际管道数据实现该方法的评估。 实验结果表明,该方法缺陷反演 的长度精度提升 23% ,宽度精度提升 13% ,深度精度提升 14. 7% ,具有较好的实验效果。     

基于TOFD周向扫查的厚壁管道倾斜裂纹精准定量

利用超声衍射时差法(TOFD)对厚壁管道实施周向扫查时,曲率表面与直通波路径不重合,引起倾斜裂纹长度和角度定量误差。为实现深层裂纹检测,提高探头中心距(PCS)进一步增加检测误差。考虑管道外壁曲率半径、PCS与裂纹端点深度之间的几何关系,开展厚壁管道倾斜裂纹精准定量研究。推导厚壁管道TOFD检测周向扫查时,裂纹长度和倾斜角度定量公式,并对比优化前后检测误差。仿真研究表明,对壁厚30.0 mm,外壁曲率半径148.0 mm的碳钢管道内,长度4.0 mm,倾斜角度10°～50°的裂纹实施检测时,长度和倾斜角度定量误差分别下降可达0.10 mm和1.58°。实验针对碳钢管道试块中长度4.0 mm,倾斜角度30°的裂纹,长度和倾斜角度定量误差从0.30 mm和2.74°,降低至0.27 mm和0.28°。所述方法可适用于不同曲率管道内部倾斜裂纹定量检测,应用范围较广。     

管道超声导波分段时间反转检测方法研究

超声导波时间反转聚焦是实现管道小缺陷检测的一项常用技术,但目前使用时需要预判缺陷大致位置以确定时反窗的起点及宽度,在实际工程使用中往往难以实现。针对此问题,提出一种基于超声导波分段时间反转的管道检测方法。该方法将管道待检区域划分为多段区间,分别对不同区间段各阵元的常规导波检测信号进行时间反转,然后将各区间段的时反信号依次作为激励信号重新激发对应阵元,以获取各段区间的时反检测信号。仿真和试验结果表明,当某区间段的时反检测信号的信噪比优于常规导波检测时,可判定该区间段内存在缺陷,并能进一步精确计算出缺陷具体位置,反之,则可判定该区间段内不存在缺陷。通过分段时间反转检测可实现对管道整个待检区域中的小缺陷的有效检测。     

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.     

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.     

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....     

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.