PCB CT Image Element Segmentation Model Optimizing the Semantic Perception of Connectivity Relationship

Computed Tomography(CT)is a commonly used technology in Printed Circuit Boards(PCB)non-destructive testing,and element segmentation of CT images is a key subsequent step.With the development of deep learning,researchers began to exploit the“pre-training and fine-tuning”training process for multi-element segmentation,reducing the time spent on manual annotation.However,the existing element segmentation model only focuses on the overall accuracy at the pixel level,ignoring whether the element connectivity relationship can be correctly identified.To this end,this paper proposes a PCB CT image element segmentation model optimizing the semantic perception of connectivity relationship(OSPC-seg).The overall training process adopts a“pre-training and fine-tuning”training process.A loss function that optimizes the semantic perception of circuit connectivity relationship(OSPC Loss)is designed from the aspect of alleviating the class imbalance problem and improving the correct connectivity rate.Also,the correct connectivity rate index(CCR)is proposed to evaluate the model’s connectivity relationship recognition capabilities.Experiments show that mIoU and CCR of OSPC-seg on our datasets are 90.1%and 97.0%,improved by 1.5%and 1.6%respectively compared with the baseline model.From visualization results,it can be seen that the segmentation performance of connection positions is significantly improved,which also demonstrates the effectiveness of OSPC-seg.

Image segmentation by level set evolution with region consistency constraint

Image segmentation is a key and fundamental problem in image processing,computer graphics,and computer vision.Level set based method for image segmentation is used widely for its topology flexibility and proper mathematical formulation.However,poor performance of existing level set models on noisy images and weak boundary limit its application in image segmentation.In this paper,we present a region consistency constraint term to measure the regional consistency on both sides of the boundary,this term defines the boundary of the image within a range,and hence increases the stability of the level set model.The term can make existing level set models significantly improve the efficiency of the algorithms on segmenting images with noise and weak boundary.Furthermore,this constraint term can make edge-based level set model overcome the defect of sensitivity to the initial contour.The experimental results show that our algorithm is efficient for image segmentation and outperform the existing state-of-art methods regarding images with noise and weak boundary.

Image segmentation of small defects in precision weldments with complex structure

In this paper, the X-ray nondestructive test method of small defects in precision weldments with complex structure was presented. To resolve the difficulty of defect segmentation in variable grey image, the image processing based on Visual Basic programming method was adopted. The methods of automatic contrast and partial grey stretch were used to enhance the X-ray detection image which has relatively low contrast, then automatic threshold method was carried out to segment the two high intensity zones, and weld zones which contain the small defects was extracted. Smoothing and sharpen processing were proceeded on the extracted weld zones, and small defects in X-ray detection image of weldments with complex structure were segmented by using the method of background subtraction in the end. The effects of raster were eliminated, and because of that the image processing was only proceeded on the extracted weld zones, the calculated speed using the above provided algorithm was improved.

Defect detection method based on 2D entropy image segmentation

In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization of ultrasonic D-scan image,clutter wave suppression and de-noising were presented firstly.Then,the image is processed by binaryzation using KSW 2 D entropy based on image segmentation method.The results showed that,the global threshold based segmentation method was somewhat ineffective for D-scan image because of under-segmentation.Especially,when the image is big in size,small targets which are composed by a small amount of pixels are often undetected.Whereas,local threshold based image segmentation method is effective in recognizing small defects because it takes local image character into account.

Prototype test study on mechanical characteristics of segmental lining structure of underwater railway shield tunnel

Based on the first unde rwater railway shield tunnel, the Shiziyang shield tunnel of Guangzhou Zhu- jiang River, the prototype test was carried out against its segmental lining structure by using ＂multi-function shield tunnel structure test system＂. And the mechanical characteristics of segmental lining structure using straight assembling and staggered assembling were studied deeply. The results showed that, the mechanical characteristics of segmental lining structure varied with the water pressures; especially after cracking, the high water pressure played a significant role in slowing down the growing inner force and deformation. It also testi- fied that the failure characteristics varied with straight assembling structure and staggered assembling structure. Shear thilurc often occurred near longitudinal seam when using straight assembling.

Laboratory Research on Effective Test Area of Short-Crested Waves Generated by Two-Sided Segmented Wavemakers

The size and shape of the effective test area are crucial to consider when short-crested waves are created by segmented wavemakers. The range of the effective test area of short-crested waves simulated by two-sided segmented wavemakers is analyzed in this paper. The experimental investigation on the wave field distribution of short-crested waves generated by two-sided segmented wavemakers is conducted by using an array of wave gauges. Wave spectra and directional spreading function are analyzed and the results show that when the main direction is at a certain angle with the normal line of wave generators, the wave field of 3D short-crested waves generated by two-sided segmented wavemakers has good spatial uniformity within the model test area. The effective test area can provide good wave environments for seakeeping model tests of various ocean engineering structures in the deep ocean engineering basin.

Dynamic behaviors of rockslides subjected to brittle failure of locked segments

Locked segments are recognized as a critical role that controls the stability of rock slopes but remain an unclear and challenging problem with respect to their role incorporated into the failure mechanism.In order to study the effect of the locked segments on the initial failure process of rockslides,thirty-six groups of locked segment specimens with three different lithologies were prepared,direct shear tests were carried out to obtain the accelerations caused by brittle failure of the locked segment specimens.Experiment results showed that the maximum accelerations caused by the brittle failure of locked segment specimens was 2.91 g in the horizontal direction,and 3.18 g in the vertical direction.We took the Wangjiayan rockslide in 2008 Wenchuan earthquake as an example,the critical balance condition of the sliding mass under combined effect of gravity and accelerations induced by brittle failure of locked segment was analyzed,which indicated that the initial failure process of the Wangjiayan rockslides was notably influenced by the existence of the locked segment.The departure acceleration and direction of the Wangjiayan rockslide were proposed.The study results can provide a new insight into the understanding of the initial failure mechanism of rockslides with locked segments.

Mechanical performances of shield tunnel segments under asymmetric unloading induced by pit excavation

To explore the stress and deformation responses,as well as the failure characteristics of the shield tunnel segment of Hangzhou Metro under the influences of pit excavation and other surrounding projects,a self-developed“shield tunnel segment hydraulic loading system”was used to carry out full-scale loading tests on the three-ring staggered assembled segments.The structural performances and failure process of the tunnel segment under step-by-step asymmetric unloading were studied.A safety index was proposed to describe the bearing capacity of the segment.Next,a finite element model(FEM)was established to analyze the bearing capacity of segment using the test results.Finally,the effect of reinforcement with a steel plate on the deformation and bearing capacity of the segment was analyzed.The results showed that under asymmetric unloading,the peak value and amplitude of the bending moment on the near unloading side converged with a greater value than those on the far side.The concrete internal force exhibited a directional transformation at different load stages.Cracks first appeared at the 180inner arc surface of the bottom standard block and then expanded to both sides,while the rate of crack propagation of the outer arc surface was relatively lower.The bearing capacity of the segments can be evaluated by the combination of the factors,e.g.the residual bearing capacity coefficient,moment transfer coefficient,and characterization coefficient.The segments approaching failure can facilitate the increase in the residual bearing capacity coefficient by more than 50%.This can provide guidance for the service assessment of metro tunnel operations.

Cyclic test and numerical study of seismic performance of precast segmental concrete double-columns

The comparative research on the seismic performance of grouted sleeve connected pier(GS)and prestressed precast segmental concrete pier(PC)is mostly carried out by numerical simulation.In this study,the GS pier and the PC pier of the new railway project from Hetian to Ruoqiang are taken into consideration.Two kinds of 1/5-scale assembled double-column specimens are made,and the quasi-static tests are carried out.The overall seismic performance of the two spliced piers is studied,and compared in terms of failure mechanism,bearing capacity,ductility,stiffness and energy dissipation capacity.The results show that the failure modes of both GS pier and PC pier are characterized by bending.However,the specific failure location and form are different.The GS pier presents a complete hysteretic curve,large equivalent stiffness and strong energy dissipation capacity.The hysteretic area of the PC pier is small.However,it has good self-reset ability and quasi-static residual displacement.Finite element models are set up using DispBeamColumn fiber elements and ZeroLength elements.The models that are calibrated with the test data can effectively simulate the damage development under monotonic loading.The load−displacement curves are in good agreement with the backbone curves of the test results.

Hysteretic behavior of post-tensioned precast segmental CFT double-column piers

Considering the desirable behavior of concrete filled steel tube(CFT)columns and the complicated behavior of segmental double-column piers under cyclic loads,three post-tensioned precast segmental CFT double-column pier specimens were tested to extend their application in moderate and high seismicity areas.The effects of the number of CFT segments and the steel endplates as energy dissipaters on the seismic behavior of the piers were evaluated.The experimental results show that the segmental piers exhibited stable hysteretic behavior with small residual displacements under cyclic loads.All the tested specimens achieved a drift ratio no less than 13%without significant damage and strength deterioration due to the desirable behavior of CFT columns.Since the deformation of segmental columns was mainly concentrated at the column-footing interfaces,the increase of the segment numbers for each column had no obvious effects on the loading capacity but reduced the initial stiffness of the specimens.The use of steel endplates improved the bearing capacity,stiffness and energy dissipation of segmental piers,but weakened their self-centering capacity.Fiber models were also proposed to simulate the hysteretic behavior of the tested specimens,and the influences of segment numbers and prestress levels on seismic behavior were further studied.

柔性光伏系统颤振性能的节段模型试验研究

柔性光伏支架的频率低、质量轻,极易在风荷载作用下发生大幅振动。以某实际柔性光伏项目为工程背景,借鉴桥梁抗风的研究经验,对该柔性光伏支架的颤振性能进行研究。首先,考虑严格的相似比关系,设计并制作了弹性悬挂节段模型系统,并对其动力特性进行了测试;然后,进行不同光伏组件倾角(-39°~+39°)下的弹性悬挂节段模型测振风洞试验,研究光伏组件风致响应随风速的变化规律,得到各倾角下柔性光伏节段模型的颤振临界风速值,探讨2种气动措施对提高柔性光伏支架颤振稳定性的效果。结果表明:在0°~39°的正倾角工况下,柔性光伏支架的颤振临界风速随光伏组件倾角的增大,呈现先减小后增大的趋势,最小颤振临界风速出现在12°~21°光伏组件倾角范围内,折算成实际风速为9.6m/s;在-39°~0°的负倾角工况下,颤振临界风速随光伏组件倾角的增大,也呈现先减小后增大的趋势,最小颤振临界风速出现在-21°~-12°光伏组件倾角范围内,折算成实际风速为10.1m/s;设置中央稳定板的气动措施难以有效提高柔性光伏支架的颤振临界风速。

带定位榫盾构隧道管片接头剪切力学行为研究

外套于盾构隧道管片螺栓的空心圆锥筒定位抗剪构件定位榫能有效控制盾构管片错台量和错台值,与管片、螺栓共同形成“管片-定位榫-弯螺栓”接头.为探明盾构隧道管片受压工况、“管片-定位榫-弯螺栓”接头在剪切荷载作用下的结构力学特征和破坏机理,以内径7.5 m、外径8.3 m、弯螺栓连接的盾构隧道衬砌环的纵向接头为例,首先,建立三维有限元模型,对轴力分别为196、392、588和784 kN4种工况的接头剪切破坏全过程进行数值模拟;然后,对接头剪切破坏过程、定位榫和螺栓力学及变形特征、管片接缝面变形破坏特征进行分析;最后,采用原型剪切破坏试验对数值模拟结果进行印证和补充研究.研究结果表明:盾构隧道“管片-定位榫-弯螺栓”接头剪切破坏全过程分为接触面静摩擦、定位榫弹性变形、定位榫塑性错动和螺栓剪切破坏4个阶段;定位榫弹性变形阶段,定位榫表现为“压扁”形态,定位榫塑性错动阶段,定位榫拱顶外侧首先出现塑性屈服区,随着剪切荷载的增加,塑性区将扩展到定位榫端部和横断面内大部分区域,塑性破损过程中定位榫将超过其承载能力的外部剪切荷载转移给螺栓;螺栓杆体受力从定位榫塑性错动阶段开始,最终加载侧杆体将发生“拉直”破坏、固定侧杆体将发生弯剪破坏;管片接缝面混凝土从定位榫塑性错动阶段后期出现塑性区,初始位于榫槽内水平两侧,随着剪力增加,塑性区将向周边扩展,最终与管片内弧面手孔塑性区连通,形成“手孔-螺栓孔-手孔”塑性破坏域.

环端面不平整条件下衬砌管片抗剪承载特性研究

在衬砌管片拼装过程中难免出现环端面不平整(或环缝间垫片局部脱空)的情形,进而在顶推力作用下管片容易产生局部开裂破损,严重时甚至危及衬砌结构安全。鉴于此,以衬砌管片抗剪原型试验为基础,在ABAQUS数值分析平台上建立P2型标准块管片的精细化模型,管片上部设置千斤顶靴板,底部设置垫片并使右侧垫片脱空。在靴板上逐级施加均布荷载,以分析局部脱空情况下衬砌管片在逐级顶推力作用下的力学响应,探讨环端面不平整条件下衬砌管片的裂缝发展过程及抗剪承载特性。数值模拟结果表明:顶推力加载至850 kN,管片脱空端竖向位移达到2 mm,管片内弧面上部出现第1道裂缝,内置钢筋仍处于弹性阶段;加载至1120 kN,脱空端竖向位移达到6 mm,内弧面上出现2道新裂缝,同时第1道裂缝进一步扩展形成内外贯穿性裂缝,即管片裂缝发展过程大致为内弧面→上环端面→外弧面,且裂缝附近上层纵向钢筋达到屈服强度;考虑到内外贯穿裂缝给衬砌管片带来较大渗漏水隐患,认为P2型标准块管片的抗剪承载力(即屈服荷载)约为1120 kN。将数值模拟结果与原型试验结果进行对比,二者所得管片裂缝分布与扩展规律大致一致,抗剪承载力基本相符,验证了数值模拟结果的可靠性。研究成果可为盾构隧道的衬砌设计与掘进施工提供参考依据。

大盾构管片最不利上浮状态下三维形变特征模型试验方案设计

隧道施工期管片所受浆液浮力并非恒定,壁后浆液压力的不均匀分布会导致管片变形和隧道环的位错损伤。为减弱或避免因管片上浮造成的结构病害,通过自主设计研发一种考虑千斤顶水平推力、围岩压力以及同步注浆上浮力作用的管片三维加载模型试验系统,对大直径管片最不利上浮状态下的瞬时变形进行分析。试验装置由围压加载装置和非均布上浮力加载装置组成,可实现单点或多点同步加卸载;模型试验采用不同刚度弹簧模拟上浮期隧道与地层之间的相互作用;根据相似理论对管片模型和连接螺栓进行精细化设计和加工;根据实际工程中试验段的围压对模型围压初始值进行换算,并将动、静态上浮力相结合,提出更符合工程实际的盾构隧道横、纵向上浮力分析模型。结果表明:在拱底非均布上浮力的作用下,拱底竖向位移和收敛变形沿纵向均近似呈对数正态分布,其最大值均出现在脱出盾尾后第3环;各环管片的收敛变形与拱底竖向位移近似呈线性关系,斜率介于0.63~1.49之间;模型试验结果与实测数据相吻合。研究成果可为盾构隧道管片抗浮设计和施工提供一定的技术支持。

高压断路器操动机构驱动电机及其控制技术研究

高压断路器操动机构用电机驱动提高了断路器运行的可靠性与可控性,因此设计了一套适用于126 kV真空断路器的电机操动机构。基于操动机构动力学分析结果确定驱动电机转矩、转速要求,提出一种有限转角永磁无刷电机设计方案,研制样机进行联机试验完成动作要求检验。在此基础上,设计分段转矩控制策略,结合驱动电机输出转矩需求将操动机构的运动过程分为4个阶段,从降低触头碰撞、避免预击穿现象发生、提高断路器工作可靠性角度对各阶段电机输出转矩进行动态调节。结果表明:所研制的驱动电机配合分段转矩控制策略,在保证灭弧室对操动机构动作时间、动作速度要求的前提下,实现了操动机构的运动过程优化和工作可靠性提高,促进了断路器智能化操作进程。

焊缝缺陷三维成像及亚像素定量方法研究

为实现工业设备中焊缝结构内部缺陷准确地定量分析,针对构造缺陷三维重构模型时缺陷图谱的过分割和欠分割导致定量分析不够精确的问题,提出了一种基于图谱颜色分割的新算法。利用该算法处理缺陷切片并进行三维重构获取其长度,应用Canny算子与三次样条插值法结合获取缺陷亚像素边缘,基于缺陷区域连通标记算法和累加法可获取缺陷面积和体积的方法。研究结果表明:与实际数据对比,未焊透、未熔合、夹渣缺陷重构的长度误差分别为8.18%、5%、9.62%,基于此对分割缺陷的亚像素边缘内连通域进行标记以准确地获取其面积及体积。该方法能够在不破坏焊缝结构的情况下即时获取焊缝内部缺陷的形貌并对其进行精准且全面的定量分析。

基于分段涂层时域反射探头的天然气水合物测试平台开发及实验研究

该文基于分段涂层时域反射(time-domain reflectometry,TDR)探头,开发了一套用于开展海洋沉积物中水合物模拟实验和TDR响应测试的平台。平台的硬件部分包括样品容器、TDR测试单元、温度测量单元;软件部分包括TDR测试单元和温度测量单元软件。通过标定TDR探头参数、校正分段涂层影响,平台可同步测量高电导率海洋沉积物表观介电常数和电导率。用四氢呋喃水合物模拟天然气水合物,在天然海砂中模拟其生成分解过程并进行了TDR测试,通过分析水合物生成过程中TDR测试的表观介电常数和电导率动态变化特征、讨论水合物饱和度的影响规律,验证了该测试平台的可靠性。基于理论分析分别建立了基于表观介电常数、电导率以及两者联合的水合物饱和度计算模型,实验数据检验结果表明联合模型的水合物饱和度计算误差最低。

底部填芯多节段预制拼装空心桥墩抗震性能试验研究

为提高预应力连接预制节段拼装桥墩的抗震性能及施工便捷性,设计了一种底部填芯多节段预制拼装空心桥墩并进行了抗震试验研究。提出了该新型预制节段拼装桥墩填芯高度设计方法,设计了底部填芯预制节段拼装桥墩缩尺模型并开展了拟静力试验测试。基于试验结果分析了该新型桥墩在水平循环往复作用下的裂缝发展过程、失效模式、滞回性能、延性性能、耗能能力及桥墩接缝的开口大小等抗震性能。研究结果表明:所发展的底部填芯多节段预制拼装空心桥墩的失效模式为底部节段混凝土局部压溃,但范围较小,所提填芯高度的设计方法可行,可以使桥墩实现预期失效模式。该新型桥墩具有较小的残余位移、优异的耗能能力与延性性能,这表明此桥墩具有优异的抗震性能。

北京地铁盾构隧道渗漏病害成因及对管片结构的影响研究

为揭示城市盾构隧道渗漏病害的形成机制,对北京地铁部分盾构隧道渗漏病害的主要类型、位置及程度进行统计分析。通过现场检测、地质雷达及内窥镜探测等手段,探究盾构隧道渗漏病害机制及成因,并通过数值模拟研究管片接缝渗漏时的地层变形规律及管片结构内力特征。研究表明:1)盾构管片接缝渗漏为主要的盾构隧道渗漏类型,占比超过60%,渗漏发生的位置集中在拱顶,以滴漏为主。2)盾构隧道渗漏水的主要内因是管片接缝处的不均匀变形,主要外因是地下水迅速升高导致存在渗漏隐患的隧道位于水位以下;同时,隧道周边地层更易形成富水体,增大了隧道渗漏病害的发生概率。3)盾构管片接缝处渗漏位置越靠近拱底,渗漏越严重,渗漏附近地层孔隙水压力消散的数值、最终达到稳定时的地表沉降越大。4)接缝局部渗漏导致的管片结构椭圆化变形较小,更易使结构出现向下且倾向渗漏点位方向的偏移;另外,渗漏位置变化相比渗漏程度对管片结构内力的影响大。

采用大直径灌浆套筒连接的预制桥墩抗震性能研究

为探究墩台处采用大直径灌浆套筒连接的预制装配式桥墩抗震性能,进行拟静力试验及有限元分析。设计、制作2个采用大直径灌浆套筒(主筋直径40 mm)连接的预制装配式桥墩(预制桥墩)及1个现浇桥墩开展拟静力试验,对2类试件的试验现象、破坏形态、滞回曲线和承载能力进行对比分析,并采用有限元法对预制桥墩混凝土、套筒及连接钢筋的受力性能进行研究。试验结果表明:在水平循环荷载作用下,预制桥墩与现浇桥墩一致表现为弯剪破坏,但墩底区域破坏形式不同,现浇桥墩主要表现为柱脚混凝土大面积压碎,而预制桥墩的破坏现象更为严重,集中表现为套筒四周混凝土成块压碎剥落;相较于现浇桥墩,预制桥墩的承载能力平均值偏小5.2%,位移延性系数平均值偏小2.7%,预制桥墩力学性能与现浇桥墩相当。有限元分析结果表明:预制桥墩会在套筒顶部和桥墩底部出现2个塑性区,且预制桥墩中大直径灌浆套筒的受力状态以轴向受力为主,按照轴向受力进行套筒设计可满足其在桥墩结构中的受力要求;预制桥墩在墩底混凝土破坏后,其主筋和灌浆料仍保持可靠粘结,采用大直径灌浆套筒连接的预制桥墩抗震性能良好。