基于接地弹簧及配点法的系统动态特性分析

核电设备和部件的动态特性包括其固有频率和相应模态。对于动态特性受支承条件影响的核电设备,将之简化为带接地弹簧的质量一弹簧系统．并分析接地弹簧刚度的变化对该系统动态特性的影响。在此基础上,从带罚数的有限元配点法出发,推导接地弹簧的有限元等价形式,证明接地弹簧刚度与罚数的等价性,并由此等价性,阐明支承条件在施加设备边界条件过程中所起的作用。     

基于NPSI方法的西安市地裂缝灾害链地表形变监测与演化态势分析

受构造背景、地下水采掘、活断层等因素的综合作用,西安市地裂缝于近年间不断加剧,引发多处不均匀地表沉降,并演化为对地表及地下建筑物均有强烈破坏作用的城市地质灾害链。为探明西安市地裂缝灾害链区域近年间的地表沉降态势、辨析不均匀沉降与地裂缝发育的联系,引入在城市地表形变监测精度和可靠性方面具有显著优势的网络化永久散射体时序雷达干涉测量（NPSI）方法,以2017年3月至2018年3月间成像的15期Sentinel-1A卫星SAR影像为数据源针对西安地区开展了时序监测分析,结合水准测量数据验证发现NPSI监测结果的精度达到 ±4.75 mm。实验结果表明：西安市地裂缝正向西南郊发育,地下水采掘及地上地下工程的建设在地裂缝发育趋势下加剧了不均匀沉降灾害,在形成地裂缝灾害链的鱼化寨、电子城、曲江新区以及地铁3号线等危害严重区域需要实时监测地裂缝发育趋势,并合理规划地下水开采及工程建设活动。相关研究结果可为路政、城建等部门的业务工作及相关研究提供参考信息。     

改进FCOS的二阶段SAR舰船检测算法

近年来无锚框的目标检测算法逐渐被应用于SAR舰船检测,其中FCOS算法摆脱了对锚框参数设置的依赖,对多尺度、多形态舰船检测的鲁棒性更好,但仍存在两个问题：第一、该算法直接进行逐像素点回归,因搜索空间过大、目标回归困难导致检测不够准确;第二、其中特征金字塔对低层特征利用仍有不足导致小目标大量漏检。针对上述问题基于FCOS进行改进,通过增加特征增强网络构建了二阶段无锚框检测算法。该网络作为第一阶段对检测过程进行精细化引导,同时增强了舰船特征表达能力。通过引入更多特征并增加跳跃连接改进特征金字塔,提高了低层特征利用率。在数据集SSDD和SAR-Ship-Dataset上的实验结果表明,平均准确率（mAP）相比FCOS分别提高9.5和3.4个百分点,相比其他主流舰船检测算法分别提高3.6和1.0个百分点,充分验证了所提算法的有效性。     

Unanticipated multiple seam stresses from pillar systems behaving as pseudo gob–case histories

Underground coal mining in the U.S. is conducted in numerous regions where previous workings exist above and/or below an actively mined seam. Miners know that overlying or underlying fully extracted coal areas, also known as gob regions, can result in abutment stresses that affect the active mining. If there was no full extraction, and the past mining consists entirely of intact pillars, the stresses on the active seam are usually minimal. However, experience has shown that in some situations there has been sufficient yielding in overlying or underlying pillar systems to cause stress transfer to the adjoining larger pillars or barriers, which in turn, transfer significant stresses onto the workings of the active seam. In other words, the overlying or underlying pillar system behaves as a ‘‘pseudo gob." The presence of a pseudo gob is often unexpected, and the consequences can be severe. This paper presents several case histories, summarized briefly below, that illustrate pseudo gob phenomenon:(1) pillar rib degradation at a West Virginia mine at 335 m depth that contributed to a rib roll fatality,(2) pillar rib deterioration at a Western Kentucky mine at 175 m depth that required pillar size adjustment and installation of supplemental bolting,(3) roof deterioration at an eastern Kentucky mine at 400 m depth that stopped mine advance and required redirecting the section development,(4) coal burst on development at an eastern Kentucky mine at 520 m depth that had no nearby pillar recovery, and(5) coal burst on development at a West Virginia mine at the relatively shallow depth of 335 m that also had no nearby pillar recovery. The paper provides guidance so that when an operation encounters a potential pseudo gob stress interaction the hazard can be mitigated based on an understanding of the mechanism encountered.     

Vertical load capacities of roof truss cross members

Trusses used for roof support in coal mines are constructed of two grouted bolts installed at opposing forty-five degree angles into the roof and a cross member that ties the angled bolts together. The load on the cross member is vertical, which is transverse to the longitudinal axis, and therefore the cross member is loaded in the weakest direction. Laboratory tests were conducted to determine the vertical load capacity and deflection of three different types of cross members. Single-point load tests, with the load applied in the center of the specimen and double-point load tests, with a span of 2.4 m, were conducted. For the single-point load configuration, the yield of the 25 mm solid bar cross member was nominally 98 kN of vertical load, achieved at 42 cm of deflection. For cable cross members, yield was not achieved even after 45 cm of deflection. Peak vertical loads were about 89 kN for 17 mm cables and67 kN for the 15 mm cables. For the double-point load configurations, the 25 mm solid bar cross members yielded at 150 kN of vertical load and 25 cm of deflection. At 25 cm of deflection individual cable strands started breaking at 133 and 111 kN of vertical load for the 17 and 15 mm cable cross members respectively.     

Numerical simulation of land subsidence and verification of its character for an iron mine using sublevel caving

Combined with a digital bored photography system and in-situ statistics concerning the joints and fissures of both ore-body and surrounding rock,a 2D discrete model was constructed using UDEC.The stress field and displacement field changes of different sublevel stoping systems were also studied.Changes in the overlying rock strata settlement pattern has been analyzed and validated by in-situ monitoring data.The results show that:in the caving process,there exists an obvious delay and jump for the overlying rock strata displacement over time,and a stable arch can be formed in the process of caving,which leads to hidden goafs.Disturbed by the mining activity,a stress increase occurred in both the hanging wall and the foot wall,demonstrating a hump-shaped distribution pattern.From the comparison between simulation results and in-situ monitoring results,land subsidence shows a slow-development,suddenfailure,slow-development cycle pattern,which leads eventually to a stable state.This pattern validates the existence of balanced arch and hidden goafs.     

Location of steel reinforcement in concrete using ground penetrating radar and neural networks

Ground-penetrating radar is becoming increasingly popular for use as a non-destructive assessment method for investigating reinforced concrete structures. The amount of data collected however can be very large and take a significant level of subjective experience to interpret. This study focuses upon the use of a neural network approach to automate and facilitate the post-processing of ground penetrating radar results. The radar data is reduced to a simplified data set by using an edge detection routine. Signal reflections from reinforcing bars displaying a hyperbolic image format are detected using a multi-layer perceptron (MLP) network with a single hidden layer containing 8 nodes to recognise a simplified hyperbolic shape. Training and testing of the network was carried out making use of an emulsion analogue tank, simulating the properties of concrete, and using real concrete specimens. The results showed that the use of a MLP neural network approach could be quite effective in automating the identification and location of embedded steel reinforcing bars from a radar investigation. Accurate estimation of depth, or cover, requires a reliable knowledge of the dielectric properties of the concrete, and recent work using a specially-developed wideband horn antenna for direct determination of in situ properties is also outlined.     

探地雷达在混凝土板钢筋检测中的应用

介绍探地雷达技术应用于混凝土结构无损检测的原理,针对其在确定钢筋直径以及钢筋笼中单根钢筋位置的检测难点,制作了一块带有多根单独钢筋及双层钢筋网的混凝土板,并使用1.2GHz的雷达天线采用反射法对板进行了检测。检测结果表明,雷达可以分辨出双层钢筋的位置,并给出估计钢筋直径的方法以及可分辨钢筋的最小间距。     

基于高频地波雷达的无角度双站雷达目标跟踪算法

高频地波雷达对于远距离目标难以给出准确的方位角观测信息,从而严重影响超视距目标的跟踪精度。为此,提出一种基于高度参数化扩展卡尔曼滤波（HPEKF）的无角度双站雷达目标跟踪算法,仅需要2部雷达得到距离和径向速度信息。通过 HPEKF技术可以对目标进行三维定位与跟踪,忽略雷达量测的方位角信息,较好地弥补当目标距离较远时测量角度精度不够精确的问题,扩展了算法的应用环境。仿真实验结果验证了该算法的可行性和有效性。     

基于高亮模型匹配的SAR建筑物高度反演方法

针对高分辨率SAR图像中的建筑物高度提取问题,提出了一种基于高亮模型匹配的建筑物高度反演方法。通过对建筑物的成像特征进行分析构建出高亮特征模型,建立模型与SAR图像之间的匹配度函数,运用多种群遗传算法对匹配度函数进行优化搜索出最优的高度参数。基于模拟和实测SAR图像的实验结果表明该算法可以用于SAR图像建筑物高度反演,并具有较高的反演精度。