Fatigue Safety Assessment of Concrete Continuous Rigid Frame Bridge Based on Rain Flow Counting Method and Health Monitoring Data

The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.

Filtering Method of Aero⁃engine Load Spectrum Based on Rain Flow Counting

A filtering method of aero-engine load spectrum based on the rain flow counting is proposed in this paper.Firstly,the original load spectrum is counted through the rain flow method to get the peak and valley values.Then,some data points in the original load spectrum are added between the peak and valley values.Finally,the filtering spectrum is obtained.The proposed method can reflect the path information of the original load spectrum.In addition,it can also eliminate the noise in the signal and improve the efficiency of signal processing,which is of practical significance for the research of aero-engine.

Changes in Low Energy Neutron Counts Rate near Ground Level Associated to Steady Rain

Measurements of neutron count rate （0.025 eV to 10 MeV） at ground level were performed with a single free （He-3） tube detectorthat is located near ground level in Aeronautical Institute of Technology （ITA） Silo Jos6 dos Campos, SP, Brazil. The data were collected uninterruptedly since February 28, 2016 to March 11, 2016. Based on the analysis of data obtained in this period, was possible to observe the occurrence of events, backscattering for example,with significant increases in the neutron count rate during about 3 days of steady rain for all nearby regions. These events seem to be correlated with changes in local weather conditions such as cloud coverage or rain-precipitation of weak intensity. It was reported that the non-observation of a single event seems to be an indicative of the production of a burst of neutrons by a lightning discharge near the detector. Some explanations about the increasing of low energy neutrons are suggested in this article.

The intensity detection of single-photon detectors based on photon counting probability density statistics

Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conven- tional methods adopt sampling gates with fixed width and count the triggered number of sampling gates, which is capable of obtaining photon counting probability to estimate the echo signal intensity. In this paper, we not only count the number of triggered sampling gates, but also record the triggered time position of photon counting pulses. The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions. Then Minimum Variance Unbiased Estimation （MVUE） method is used to estimate the echo signal intensity. Compared with conventional methods, this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information. Finally, a proof-of-principle laboratory system is established. The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.

THE SPATIOTEMPORAL CHARACTERISTICS OF LIGHT RAIN DAYS AND LOW CLOUD COVER UNDER HEAVY POLLUTION OVER SOUTH CHINA

By using the data set of light rain days and low cloud cover at 51 stations in South China(SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows:(1) The trends of light rain days and low cloud cover over SC are opposite(light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area.(2) The regression coefficients of light rain days and low cloud cover during 1960-2005 are4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level.(3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter.(4) There are two regions with large values of aerosol optical depth(AOD), which distribute in central and southern Guangxi and Pearl River Delta(PRD) of Guangdong, and the value of AOD in PRD is up to 0.7.The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.

Modelling and predicting low count child asthma hospital readmissions using General Additive Models

Background: Daily paediatric asthma readmissions within 28 days are a good example of a low count time series and not easily amenable to common time series methods used in studies of asthma seasonality and time trends. We sought to model and predict daily trends of childhood asthma readmissions over time inVictoria,Australia. Methods: We used a database of 75,000 childhood asthma admissions from the Department ofHealth,Victoria,Australiain 1997-2009. Daily admissions over time were modeled using a semi parametric Generalized Additive Model (GAM) and by sex and age group. Predictions were also estimated by using these models. Results: N = 2401 asthma readmissions within 28 days occurred during study period. Of these, n = 1358 (57%) were boys. Overall, seasonal peaks occurred in winter (30.5%) followed by autumn (28.6%) and then spring (24.6%) (p

基于马尔可夫模型的油菜花期低温阴雨灾害预测

花期低温阴雨是四川盆区油菜的主要气象灾害之一,本研究旨在通过预测四川盆区油菜花期低温阴雨灾害,为防灾减灾提供科学依据。本研究基于1961-2020年四川盆区101个站点油菜花期低温阴雨灾害损失评估结果,依据灾损率,将各站点60 a灾害序列划分为5个状态;利用马氏性检验筛选站点序列,选取满足预测条件的序列;对通过马氏性检验的站点序列,建立叠加马尔可夫链、加权马尔可夫链、改进叠加马尔可夫链、改进加权马尔可夫链模型预测油菜花期低温阴雨灾害,并对结果进行回代和预测检验。结果表明,4种模型均有一定的预测能力,其中改进后的模型预测总正确率较改进前有明显提高,且各等级灾害的预测正确率分布较改进前更加均匀,表明改进后的马尔可夫模型具有更好的预测效果。

湖北省持续低温雨雪过程评估与分析

气候变化背景下,极端持续低温雨雪过程时有发生,给社会生活带来诸多不利影响,为了进一步评估持续低温雨雪天气,对湖北省单站持续低温雨雪过程的评估指标进行了修订,同时建立区域性持续低温雨雪过程评估模型,并将修订后的评估指标应用于湖北省单站及区域性持续低温雨雪过程的梳理及分析。结果表明:(1)湖北省最严重的5次区域性持续低温雨雪过程分别出现在1954、1969、1977、1984和2008年,最严重的是1954年12月24日-1955年1月18日的过程,其次是2008年1月12日-2008年2月5日的过程。(2)湖北省区域性持续低温雨雪过程的易发区主要集中在鄂西的高山或半高山地区、江汉平原荆州一带、汉江河谷一带、鄂东南南部低山平原地区以及鄂东北山脉的缺口处。(3)气候变暖的背景下,湖北省单站和区域性持续低温雨雪过程均是在20世纪80年代前发生次数多,90年代后属于减少的阶段,但其强度更趋极端。

基于损伤等效的直立锁边屋面板动态抗风揭试验方法

围护结构在台风等极端风下的抗风性能需要依靠动态试验测定,试验周期长导致成本高且模拟研究受限。基于直立锁边屋面板材料的损伤本构模型,通过疲劳分析研究荷载幅值对材料损伤影响,提出简化荷载序列组合。借助雨流计数法统计测点风压时程得到基于损伤等效的简化荷载循环,提出动态抗风揭试验方法。参照不同试验方法开展抗风揭试验,通过对比发现,试验方法对屋面板风揭破坏过程影响不明显。除永久塑性变形外,该文试验方法与现有试验方法下屋面板损坏现象基本一致,屋面板均为撕裂破坏。不同试验方法下屋面板承载力差异在10%~20%间。该文试验方法加载周期小于1h,现有试验方法加载周期则大于20h。在屋面板风揭破坏过程、承载力等抗风揭性能差异不大情况下,该文试验方法可大幅降低试验周期,为开展模拟研究奠定基础。

微弱光探测器光谱响应测量装置

为满足光子计数类型光电探测器光谱响应度的计量需求,建立了微弱光探测器光谱响应测量装置,其特点是可在pW级单色光功率水平下实现光谱比较测量。设计了可调式亮度源,与色散相减双光栅单色仪密闭耦合后实现了6个量级的功率可调单色光输出,可适用于不同光子探测器的线性工作区间,波长范围覆盖330~1 100 nm。设计的密闭准直光路使系统可在正常照明环境下工作,降低了实验环境要求。以集成fA级电流放大器的标准探测器为参考,实现被测光子探测器计数率在1×10^(6)个/s量级的光谱响应度测量。基于LabView编写了专用的控制及数据采集软件,实现了自动化测量。对系统的各项计量特性进行了实验,在330~1 100 nm波段内完成了光子探测器相对光谱响应度测量,相对扩展不确定度为(2.5~3.8)%,k=2。

数据中心发展进展

本文采用文献调研的方法,研究了中国数据中心在新型基础设施建设等策略下的市场规模与发展趋势,并对比了中外数据中心发展特点及政策导向。本文分析了近年来中国数据中心耗电量、算力规模、机架数等关键指标的变化趋势。结果表明:我国数据中心市场规模将保持持续增长态势,增长率将保持在20%以上。“东数西算”政策驱动下,未来数据中心将朝着高效化、大型化、绿色化的新兴数据中心发展。冷却技术的高速发展将助力数据中心能效不断提升,使电能使用效率降至1.1左右。

我国南方西南和中东部区域两次持续性低温雨雪过程与关键环流系统的关系研究

利用NCEP再分析资料和国家气象信息中心提供的753站逐日气温和降水资料,对比分析了我国南方西南和中东部区域两次持续10 d以上的低温雨雪过程,结果表明:(1)两次过程中欧亚大陆中高纬东亚大槽均加深,但环流形势有差异。西南过程呈现"北高南低"形势,关键脊区在贝加尔湖,而中东部区域过程"北高南低"和"西高东低"形势共存,关键脊区从乌拉尔山延伸至贝加尔湖。两次过程异常的环流与北大西洋向东传播的波列有关。(2)西南过程关键脊区提前过程3 d发展并东移至贝加尔湖,形成稳定形势;而中东部区域过程关键脊区提前过程一周发展,在开始日达最强。两次过程均伴随蒙古高压东移南压使地面降温,500 hPa关键脊区超前蒙古高压2 d变化。西南过程降温主要受到冷平流和绝热冷却影响,而中东部区域过程主要受到冷平流的影响。(3)西南过程水汽来自孟加拉湾,只受南支槽支配。中东部区域过程水汽来自孟加拉湾、南海和西太平洋,由南支槽和西太平副热带高压的共同影响。两次过程水汽正收支主要来自南边界。

低温阴雨天气对农作物的影响

对黑龙江省部分地区20年以来4—5月5 cm土壤温度和降水量的研究。分析粮食减产的原因,得出的结论是由于土壤温度低、降水少严重影响农作物生长,导致粮食减产。针对低温阴雨天气带来的危害,应采取的应对措施和面对恶劣天气带来的不利因素进行补救措施进行了探讨。

基于损伤力学的矿用定向钻机金属结构寿命评估

针对ZYL-15000D型煤矿用履带式全液压定向钻机底座寿命评估,首先通过Q345B钢的脉动循环加载拉伸疲劳试验数据,拟合得到应力幅值和寿命的关系式,经由应力修正和安全系数的选取,转换得到对称循环下的应力幅值和寿命的关系式。结合基于损伤力学推导出的损伤退化模型,根据Q345B钢试验数据拟合确定损伤退化模型中的待定参数,将Q345B钢对称循环下应力幅值和寿命的关系式代入,得到Q345B钢的疲劳损伤退化模型。然后借助ABAQUS对钻机整机进行结构分析,得到钻机底座的危险点位置(即应力最大处),在该型号样机试验台上通过应变片测得钻机底座危险点处的应力—时间历程。最后采用雨流计数和应力修正,对测得的随机载荷谱进行处理得到雨流计数直方图(应力均值-幅值-循环次数),再转换为对称循环载荷的形式,代入确定的疲劳损伤退化模型中,评估钻机底座的疲劳寿命。

我国南方两次低温雨雪天气成因对比分析

2018年末和2021年末我国南方分别发生了一次大范围的低温雨雪天气,通过对比分析两次低温雨雪天气成因,结果表明:两次过程期间,对流层中层中高纬阻塞流场显著,阻高位于贝加尔湖西侧,脊前偏北气流在下游横槽后部堆积,使得西伯利亚高压强度增强。东传的Rossby波在阻高区域发生能量频散,利于阻高减弱、崩溃,横槽转竖引导槽后冷空气南下,导致地面强烈降温,同时在西伯利亚高压东侧和南侧,低频风温度平流是造成强降温的主要原因。低纬南支槽活跃,向北的暖湿空气与中高纬南下的冷空气汇合,造成我国南方大范围的低温雨雪、冻雨天气。与2018年过程相比,2021年过程持续时间较短,降水范围小,关键区域降温幅度更大,是因为2021年过程期间Rossby波能量频散更快,阻高维持时间较短,冷空气从中高纬地区直接南下侵袭我国,而2018年冷空气在贝加尔湖附近发生堆积、西折,向南渗透时势力减弱。

区域海气耦合模式WON在东南亚低纬高原一次强降水事件模拟中的应用

为改善东南亚低纬高原区(LLHSA)降水模拟的性能,提高降水预报准确性,本文采用大气环流模式WRF(4.2版)和海洋分量模式NEMO(3.4版),用耦合器OASIS3-MCT进行桥接,得到区域海气耦合模式WRF-OASIS-NEMO(WON)。大气和海洋分量模式都配置成相同的Arakawa-C网格,水平空间分辨率设为0.25°,耦合频次设置为逐小时,便于模拟海洋和大气环流相耦合的中尺度运动特征。为评估WON模式的模拟性能,选取2020年8月16-18日的强降水过程为例,与单独WRF模式的模拟效果进行比较分析。WON和WRF模式模拟的降水大值区位于高原东北部和中西部地区,平均日降水量约为20 mm·d^(-1),与观测事实基本相符。WON模式改善了WRF模式在高原南部降水偏多而在高原西北部降水偏少的模拟偏差。WON模式改善了降水动力条件的模拟效果,在高原中南部气旋式环流增强,在高原西侧反气旋式环流增强,进而改善了WRF模式在高原南部周围降水偏少,高原西北部降水偏多的模拟偏差。WRF和WON模式均能再现垂直螺旋度的发展特征,即在对流层中低层为正垂直螺旋度发展,而在对流层高层为负垂直螺旋度发展。两个模式在雨带西部400 hPa高度层附近垂直螺旋度模拟偏强,而在600~700 hPa高度层上垂直螺旋度模拟偏弱。WON模式相对于WRF模式的改进区域主要集中在雨带中西部地区。本次强降水的水汽来源包括孟湾的西南水汽输送和中国南海的偏南水汽输送。WRF模式和WON模式均能较好地重现相关水汽通量特征。WRF模式在孟湾北部水汽辐合偏强,而在中国南海水汽向北输送偏弱。WON模式主要改善了WRF模式在中国南海水汽输送偏弱的模拟偏差。WON模式改善降水模拟效果的主要原因是孟湾海表热通量交换导致孟湾中低层大气偏冷偏干,大气对流活动减弱,在孟湾北部形成的低层反气旋偏差改善了本次强降水过程动力条件和水汽条件的模拟效果。

江西双季早稻播种育秧期低温连阴雨灾害分析

基于江西省82个国家气象站点1961—2023年的逐日气象资料,研究了江西省双季早稻播种育秧期低温连阴雨气象灾害风险,结果表明:1961—2023年江西省早稻播种育秧期平均气温以0.379℃/10 a的速度升高,日照时数呈先减后增趋势;不同等级低温连阴雨灾害发生天数均呈先增后减趋势,高频区发生在1980s、1990s,2000年以后则发生较少;2001—2023年的整体发生频率比1961—2000年的低,但高频区向赣西北转移,赣东北和赣中有所减弱;综合风险等级显示,高风险区主要分布在抚州市、吉安市、萍乡市、宜春市、南昌市和九江市,中风险区主要包括赣南北部和赣东北地区,低风险区以赣南南部地区为主。

全数字PET关键器件硅光电倍增器研究进展

近年来,硅光电倍增器(SiPM)凭借其出色的性能表现,已经成为正电子发射断层成像(PET)中的首选光电转换器件。SiPM具有单光子分辨能力和低于100 ps的时间分辨率,使得精确测量光子到达时间成为可能,催生了飞行时间PET、光子计数计算机断层扫描、正电子素寿命显像等新兴应用领域,这些应用又对SiPM的性能提出了更高的挑战。因此,如何将SiPM性能推进至其物理极限已成为新一代SiPM的研究的关键方向。在传统的SiPM架构中,信号经过多次处理和模数转换,带来噪声增加和时间性能恶化的问题,从而限制了SiPM的性能潜力。随着半导体制造工艺的快速发展,SiPM可在标准CMOS工艺节点上制造,标志着可以将数字逻辑集成在SiPM器件内,这是SiPM领域的一次重大突破,使我们能在单一SiPM内实现更精确的时间、能量、位置信息获取,为推进SiPM达到性能极限提供了一条可能的途径。本文综述SiPM的发展历史、工作原理和性能参数,分析传统SiPM的局限性,梳理数字SiPM研究的关键问题,介绍当前几种数字化SiPM架构,最后对数字SiPM的关键技术进行总结和展望。

过渡循环对风力机疲劳评估的影响及修正

随着风力机的装机容量和尺寸的不断增大,其运行环境更为复杂,疲劳问题突出,需要准确预测风力机结构遭受的实际疲劳损伤。通过对1.5 MW风力机的塔底应变进行长期监测,研究了不同方法在处理雨流计数后残余数据点问题上的准确性。首先,通过采用不同的计算时窗,分析过渡循环对疲劳损伤的影响,选择的计算时窗越短,得到的疲劳损伤误差越大,当计算时窗为10 min时,误差达到了20.7%。然后,使用残波串联法处理残余数据点,此时选择不同的计算时窗得到的损伤值均与将监测时段内所有数据作为连续序列得到的结果相同,证明了该方法在处理雨流残余数据时的准确性。该成果为风力机结构疲劳损伤在线预测提供了解决方法,可以更加准确的得到构件的实时损伤。

基于YOLO的低成本且轻量化的秧苗计数研究

农业生产中需要对秧苗进行计数以获取种子质量和种植密度等评估信息,而小规模批量育种环境下存在人工依赖程度高、软硬件设备差的情况。针对此问题,文中以唇形科植物为例,提出了一种低成本、轻量化的秧苗计数方法。首先提出数据集的快速构建方法,以降低数据集成本;然后通过改进YOLO模型颈部特征融合部分和精简头部来保证模型轻量高效,并添加改进的通道注意力方法以改善图像低分辨率造成的漏检率过高问题,构建了秧苗计数模型Seedet。实验结果表明,与YOLOv5s模型相比,Seedet的模型参数与计算量分别降低了73.45%和47.59%,检测精确率和速度分别提高了3.987%和70.09%。文中提出的计数方法更适合于低成本场景下的秧苗计数,促进了农业生产中深度学习的落地应用。