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针对构件外表面局部区域遭受随机点蚀损伤的圆管截面,考虑点蚀随机特性的影响,建立包含点蚀坑细节的精细有限元模型;在多种腐蚀强度下,研究局部腐蚀的点蚀区分布位置(沿轴向和周向分布位置变化)及其形状(点蚀区长度和宽度独立或联合变化)影响轴压极限强度退化的规律;并比较局部随机点蚀与局部均匀腐蚀引起构件极限强度退化的差异。研究结果表明,尽管局部随机点蚀与最大初始几何缺陷的耦合作用会使极限强度的退化趋于严重,但是总体而言点蚀区分布位置变化对圆管极限强度的退化没有显著的影响。此外,同等腐蚀体积和腐蚀面积下,相比于长窄式局部腐蚀,短宽式局部腐蚀会引起更严重的极限强度退化,在严重腐蚀情形下后者导致的强度退化会高出25.5%;相比于局部均匀腐蚀,局部随机点蚀会导致更剧烈的极限强度退化,其不利影响可高出20.7%。 相似文献
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由于煤炭开采而形成的塌陷区地形形态复杂,本文利用分形插值理论模拟了塌陷区地形。在Matlab语言环境下,实现了塌陷区基于遗传算法求取无标度区最优解和基于FBM分形插值算法,在此基础上求解分形特征参数H和σ。对概率积分法预计的数据进行分形内插绘制地表下沉图,取得了理想的效果。 相似文献
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对于定量热红外遥感的一些思考 总被引:38,自引:4,他引:38
作者根据在热红外遥感工作中的长期实践经验,介绍了热红外遥感的现状,特别指出了定量反演地表温度的难点---地物比辐射率的测定和区域范围内的比辐射率估算。文中提出了定量热红外遥感研究中常见的一些问题。最后,讨论了定量热红外遥感的未来发展趋势和目前现实工作的对策,旨在抛砖引玉,以求得热红外定量遥感的发展。 相似文献
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改进的热惯量模式及遥感土壤水分 总被引:9,自引:0,他引:9
本文提出一个考虑地表显热通量及潜热通量的热惯量模式。模式利用了地面定标的方法并充分利用了热象图的空间分布信息,因而较大幅度地提高了估算土壤水分含量的精度。 相似文献
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It is more and more popular to estimate the exchange of water vapor, heat and CO2fluxes between the land surface and the atmosphere using the eddy covariance technique. To get believable fluxes, it is necessary to correct the observations based on the different surface conditions and to determine relevant techinical parameters. The raw 10 Hz eddy covariance data observed in the Yucheng and Changbai Mountains stations were recalculated by various averaging periods (from 1 to 720 min) respectively, and the recalculated results were compared with the results calculated by the averaging period of 30 mins. Meanwhile, the distinctions of fluxes calculated by different averaging periods were analyzed. The continuous 15 days observations over wheat fields in the Yucheng station were mainly analyzed. The results are shown that: (i) In the Yucheng station, compared with the observations by 30 min, when the averaging period changes from 10 to 60 min, the variations of the eddy-covariance estimates of fluxes were less than 2%; when the averaging period changes less than 10 min, the estimate of fluxes reduced obviously with the reduction of the averaging period (the max relative error was -12%); and when the averaging period exceeds 120 min, the eddy covariance estimates of fluxes will be increased and become unsteady (the max relative error is over 10%); (ii) the eddy covariance estimates of fluxes over wheat field in the Yucheng station suggusted that it is much better to take 10 min as an averaging period in studying diurnal change of fluxes, and take 30min for a long-term flux observation; and (iii) normalized ratio was put forward to determine the range of averaging period of eddy covariance measurements. By comparing the observations over farmlands and those over forests, it is indicated that the increase of eddy covariance estimates over tall forest was more than that over short vegetation when the averaging period increased. 相似文献
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Based on the improved interaction mechanism of two-layer model, this paper proposed Pixel Component Arranging and Comparing Algorithm (PCACA) and theoretically positioning algorithm, estimated the true temperature of mixed pixel in four extreme points in combination with the measurements of dry and wet points in calibration fields and improved the reliability of positioning dry and wet line. A new two-layer energy-separation algorithm was proposed,which was simple and direct without resistance network parameters for each pixel. We also proposed a new thought about the effect of advection. The albedo of mixed pixel was also separated with PCACA. In combination with two-layer energy-separation algorithm, the net radiation of mixed pixel was separated to overcome the uncertainty of conventional energy-separation algorithm using Beer's Law. Through the validation of retrieval result, this method is proved to be feasible and operational. At the same time, the uncertainty of this algorithm was objectively analyzed. 相似文献
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高出海平面的洋岛和低于海平面的海山是成熟大洋最重要的特征。笔者通过野外调查,于西藏自治区贡嘎县昌果乡普夏东侧的“原桑日群”中新识别出普夏洋岛。通对普夏洋岛的岩石学、地球化学研究及锆石U-Pb定年,认为普夏洋岛具有典型的“玄武岩+灰岩”岩石组合,其中的玄武岩为典型的洋岛玄武岩,形成于以成熟洋壳为基底的洋岛海山环境。普夏洋岛玄武岩的锆石U-Pb定年结果为203.9±1.6Ma和219.5±2.0Ma,表明其形成时代为晚三叠世。综合研究认为,普夏洋岛是雅鲁藏布江特提斯洋发现的较早的洋岛海山之一,证明雅鲁藏布江新特提斯洋在三叠纪已具有成熟的洋壳,普夏洋岛是雅鲁藏布江新特提斯洋向北俯冲形成的桑日群增生杂岩的重要组成部分。普夏洋岛的发现,丰富了新特提斯洋的研究内容,为反演研究区地质构造演化提供了新证据。 相似文献