Multiaxial Fatigue Analysis on Reeled Deepwater Steel Catenary Risers with Girth Weld Defects

In the present study, we simulated the reel-lay installation process of deepwater steel catenary risers (SCRs) using the finite element method and proposed multiaxial fatigue analysis for reeled SCRs. The reel-lay method is one of the most efficient and economical pipeline installation methods. However, material properties of reeled risers may change, especially in the weld zone, which can affect the fatigue performance. Applying finite element analysis (FEA), we simulated an installation load history through the reel, aligner, and straightener and analyzed the property variations. The impact of weld defects during the installation process, lack of penetration and lack of fusion, was also discussed. Based on the FEA results, we used the Brown-Miller criterion combined with the critical plane approach to predict the fatigue life of reeled and non-reeled models. The results indicated that a weld defect has a significant influence on the material properties of a riser, and the reel-lay method can significantly reduce the fatigue life of SCRs. The analysis conclusion can help designers understand the mechanical performance of welds during reel-lay installation.     

利用位置签到数据探索城市热点与商圈

众源地理数据（Crowd Sourcing Geographic Data）是指由大众采集并向大众开放共享的地理空间数据。众源位置签到数据作为众源地理数据的一种,客观真实的反映了大众日常生活行为,包含大量丰富的社会化属性信息。本文提出了一种基于众源位置签到数据的城市热点探测与商圈挖掘方法,首先对位置签到数据时空分布特性进行了研究,设计并提出了众源位置签到数据时空数据库模型;其次,提出了位置签到数据探索性空间分析方法,通过对众源位置签到数据的空间聚类分析,实现基于位置签到数据的商圈热点探测;最后,以武汉市为例,对街旁网截止2011年9月30日的众源位置签到数据进行了城市热点探测与商圈挖掘分析实验,结果表明,基于众源位置签到数据挖掘的武汉市商圈分布与城市规划商圈具有强相关性,可用于城市社会经济发展预测与区域经济规划。     

利用C_SURF配准的空基视频运动目标检测

针对传统的车辆检测算法的性能易受低空移动平台影响造成相机自运动以及外界的干扰等问题,提出了一种基于改进的C_SURF彩色特征稳像和光流法向量相结合的方法来解决低空视频中的运动车辆检测问题。通过图像稳像消除了相机的自运动和外界干扰问题,提高了运动车辆的检测性能。实验结果显示,该方法不仅在检测车辆方面可以获得更好的检测性能,在复杂的背景环境下也能有效地检测运动车辆。     

基于道路网矢量数据的遥感影像道路损毁检测

利用面向对象方法对地震后高分辨率遥感影像上的道路进行多尺度分割和分类.通过融合地震前道路网矢量数据与地震后遥感影像,提出一种基于自适应模板的道路损毁检测方法.试验结果证明,该方法能够快速、准确地对损毁信息进行提取.     

基于体元分析的三维建筑物模型结构化分割方法

针对现有三维模型分割方法在建筑物基本结构特征识别方面存在的不足,提出一种基于体元分析的三维建筑物模型结构化分割方法。该方法首先通过体元化和内部距离参数计算在模型内部构建分层距离场,然后采用局部极值判别方法从各层距离场中提取出对建筑物结构、形状分布具有代表意义的中心体元,并基于中心体元和内、外部体元聚类找到建筑物在空间组成上相互独立的结构单元,最后依据体元分析结果对原始建筑物模型进行表面分割。试验结果表明,该方法能够对不同风格的建筑物模型进行有效分割,具有极强的稳健性。     

空间认知驱动的自适应路径引导

为了生成符合人们认知习惯、反映用户空间知识并易于利用自然语言表达的路径引导, 提出了一个将路径抽象为一系列结构统一、具有时序性和多粒度性且可以被加工为指导用户沿路径前进的短语或句子的指示单元的表达框架,并说明了利用环境结构、路径特征、先验知识等上下文因素生成多粒度的指示单元, 从中选择最合适的指示单元, 进而实现自适应路径引导的方法。通过与传统的采用“Distance-to-Turn”模式的路径引导进行对比可以发现, 基于空间认知的自适应路径引导更加符合人们描述路径的方式, 能够降低用户的认知压力并提高导航的效率。     

利用低空视频检测道路车辆

针对背景像素的移动,提出了SURF特征稳像和光流法向量相结合的新方法来解决低空视频的道路车辆检测。首先,检测两帧图像的SURF特征;再用最近邻匹配得到两幅图像的匹配点对;随后结合RANSAC和最小二乘法计算全局运动参数向量,获得稳定的帧;最后,根据稳定的帧计算光流法向量,并检测出运动车辆。实验结果表明,基于SURF算子的图像稳像算法在不损失稳像精度的前提下,能够提高图像稳像算法的速度,所提方法能够有效地检测出运动车辆。     

Sea Surface Temperature Extremes of Different Intensity in the China Seas During the Global Warming Acceleration and Hiatus Periods

Based on the daily OISST V2 with 0.25o horizontal resolutions, we study the variations of sea surface temperature (SST) extremes in the China Seas for different segments of the period 1982-2013. The two segments include the warming acceleration period from 1982 to 1997 and hiatus period from 1998 to 2013 when the global surface mean temperature (GSMT) was not significantly warming as expected during the past decades, or even cooling in some areas. First, we construct the regional average time series over the entire China Seas (15o–45oN, 105o–130oE) for these SST extremes. During the hiatus period, the regionally averaged 10th, 1th and 0.1th percentile of SSTs in each year decreased significantly by 0.40°C, 0.56°C and 0.58°C per decade, respectively. The regionally averaged 90th, 99th and 99.9th percentile of SSTs in each year decreased slightly or insignificantly. Our work confirmed that the regional hiatus was primarily reflected by wintertime cold extremes. Spatially, the trends of cold extremes in different intensity were non-uniformly distributed. Cold extremes in the near-shore areas are much more sensitivity to the global warming hiatus. Hot extremes trends exhibited non-significant tendency in the China Seas during the hiatus period. In word, the variations of the SST extremes in the two periods were non-uniform spatially and asymmetric seasonally. It is unexpected that the hot and cold extremes of each year in 1998–2013 were still higher than those extremes in 1982–1997. It is obvious that relative to the warming acceleration period, hot extremes are far more likely to occur in the recent hiatus as a result of a 0.3°C warmer shift in the mean temperature distribution. Moreover, hot extremes in the China Seas will be sustained or amplified with the end of warming hiatus and the continuous anthropogenic warming.     

城市3维地理信息系统研究的几个焦点问题

指出当前国际国内在城市3维地理信息系统领域的一些研究焦点，并概括城市3维地理信息系统应具备的一些特征。     

大型水电工程百米级引水竖井的病害检测技术

大型水电站引水道竖井段的混凝土病害检测,直接涉及水电站的安全运行。针对大型水电站百米级引水竖井数据获取与病害检测的国际性难题,本文提出一种以无人系留飞艇为浮空装载平台,集成多传感器的百米级垂直竖井检测方案;自主研制了竖井环境适应性强的圆柱形无人系留飞艇浮空装载平台,集成全景CCD相机、三维激光扫描仪、惯性导航测量单元、气压高度计、照明模块、控制模块等多传感器,自主研制了全球首台百米级竖井数据获取与病害检测装备,于2017年5-7月在云南糯扎渡水电厂2、3、4号200 m级引水道竖井现场进行了试验。结果表明,检测装置能够满足大型水电站百米级竖井引水道的检修工作,填补了百米级竖井检测的国际空白,具有较好的应用前景。