A multiple-time-scale algorithm is developed to numerically simulate certain structural components in civil structures where local defects inevitably exist. Spatially, the size of local defects is relatively small com...A multiple-time-scale algorithm is developed to numerically simulate certain structural components in civil structures where local defects inevitably exist. Spatially, the size of local defects is relatively small compared to the structural scale. Different length scales should be adopted considering the efficiency and computational cost. In the principle of physics, different length scales are stipulated to correspond to different time scales. This concept lays the foundation of the framework for this multiple-time-scale algorithm. A multiple-time-scale algorithm, which involves different time steps for different regions, while enforcing the compatibility of displacement, force and stress fields across the interface, is proposed. Furthermore, a defected beam component is studied as a numerical sample. The structural component is divided into two regions： a coarse one and a fine one; a micro-defect exists in the fine region and the finite element sizes of the two regions are diametrically different. Correspondingly, two different time steps are adopted. With dynamic load applied to the beam, stress and displacement distribution of the defected beam is investigated from the global and local perspectives. The numerical sample reflects that the proposed algorithm is physically rational and computationally efficient in the potential damage simulation of civil structures.展开更多
高比例可再生能源并网和多样化负荷接入加剧了新型配电系统高运行成本和高电压偏差运行风险。针对目前新型配电系统配置阶段未在多时间尺度下考虑运行风险和多元时空灵活性资源协同配置的问题,提出考虑运行风险的新型配电系统多元时空...高比例可再生能源并网和多样化负荷接入加剧了新型配电系统高运行成本和高电压偏差运行风险。针对目前新型配电系统配置阶段未在多时间尺度下考虑运行风险和多元时空灵活性资源协同配置的问题,提出考虑运行风险的新型配电系统多元时空灵活性资源协同配置模型。首先,采用蒙特卡洛抽样和Kmeans聚类算法生成源-荷场景集,并利用多尺度形态学算法对源-荷曲线波形进行多尺度分解;然后,基于条件风险价值(conditional value at risk,CVaR)理论量化评估配电系统多时间尺度运行风险,并在此基础上建立考虑运行风险的新型配电系统多元时空灵活性资源双层配置模型。其中,上层以配电系统年综合成本最小为目标函数对多元时空灵活性资源进行协同配置,下层以期望损失值和基于CVaR的运行风险值最小为目标对系统进行运行优化。最后,通过改进的IEEE 33节点系统进行算例分析,结果表明:所提方法可以有效降低配电系统高运行成本和高电压偏差的运行风险。展开更多
基金supports from NSFC(No.11302078)China Postdoctoral Science Foundation(No.2013M531139)Shanghai Postdoctoral Sustentation Fund(No.12R21412000)
文摘A multiple-time-scale algorithm is developed to numerically simulate certain structural components in civil structures where local defects inevitably exist. Spatially, the size of local defects is relatively small compared to the structural scale. Different length scales should be adopted considering the efficiency and computational cost. In the principle of physics, different length scales are stipulated to correspond to different time scales. This concept lays the foundation of the framework for this multiple-time-scale algorithm. A multiple-time-scale algorithm, which involves different time steps for different regions, while enforcing the compatibility of displacement, force and stress fields across the interface, is proposed. Furthermore, a defected beam component is studied as a numerical sample. The structural component is divided into two regions： a coarse one and a fine one; a micro-defect exists in the fine region and the finite element sizes of the two regions are diametrically different. Correspondingly, two different time steps are adopted. With dynamic load applied to the beam, stress and displacement distribution of the defected beam is investigated from the global and local perspectives. The numerical sample reflects that the proposed algorithm is physically rational and computationally efficient in the potential damage simulation of civil structures.
文摘高比例可再生能源并网和多样化负荷接入加剧了新型配电系统高运行成本和高电压偏差运行风险。针对目前新型配电系统配置阶段未在多时间尺度下考虑运行风险和多元时空灵活性资源协同配置的问题,提出考虑运行风险的新型配电系统多元时空灵活性资源协同配置模型。首先,采用蒙特卡洛抽样和Kmeans聚类算法生成源-荷场景集,并利用多尺度形态学算法对源-荷曲线波形进行多尺度分解;然后,基于条件风险价值(conditional value at risk,CVaR)理论量化评估配电系统多时间尺度运行风险,并在此基础上建立考虑运行风险的新型配电系统多元时空灵活性资源双层配置模型。其中,上层以配电系统年综合成本最小为目标函数对多元时空灵活性资源进行协同配置,下层以期望损失值和基于CVaR的运行风险值最小为目标对系统进行运行优化。最后,通过改进的IEEE 33节点系统进行算例分析,结果表明:所提方法可以有效降低配电系统高运行成本和高电压偏差的运行风险。
文摘【目的】针对我国南方地区云雨频繁、耕地细碎及多熟种植所造成的耕地种植强度(cropping intensity,CI)提取与动态监测不确定性问题,拟充分发挥多尺度遥感观测的优势,实现2000—2021年湖北省耕地CI的高效精准提取,并解析区域农业生产格局的时空演变规律。【方法】协同250 m MODIS归一化差值植被指数(NDVI)和30 m Landsat NDVI时序数据,分别利用STARFM、ESTARFM、STNLFFM和GF-SG 4种典型的时空融合算法生成高时空分辨率NDVI数据,从光谱保真度(AD/RMSE)、空间细节精度(Edge/LBP)及CI提取效果对融合数据进行综合评估。利用优选的时空融合算法生成2000—2021年湖北省30 m/8 d时空分辨率NDVI数据集,并基于物候的峰值探测法,开展长时序耕地种植强度提取及时空演变分析。【结果】与其他3种时空融合算法相比,GF-SG算法在光谱保真度与空间细节精度方面表现最佳(|AD|<0.021,RMSE<0.111,|Edge|<0.55,|LBP|<0.10),利用该算法重构的NDVI时序数据集提取耕地CI的精度提升了0.02%—5.53%。基于地面实地采样数据开展精度评价,湖北省耕地CI分类的总体精度达86.60%。2000—2021年耕地CI时空演变分析显示,研究区每5年约有20%—25%的耕地发生种植强度转变,其中2005—2010年变动最显著(25.79%),2010—2015年变动最小(20.07%)。主导转变类型由“一熟转二熟”(13.49%)逐步演变为“二熟转一熟”(9.35%)和“一熟转休耕”(4.90%)。【结论】近20年来湖北省形成以“一熟为主、二熟与休耕共存”的多元耕作格局,耕地CI演变由政策引导、劳动力变化、资源投入与种植结构调整等因素共同驱动。通过协同MODIS与Landsat多尺度遥感数据构建的高时空分辨率NDVI数据集,可有效支撑复杂农业景观下长时序耕地CI的高效精准提取,可为农业生产管理与耕地保护政策制定提供重要支撑。
