Modified fish-bone model: A simplified MDOF model for simulation of seismic responses of moment resisting frames

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment–rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment frames. The proposed model is evaluated with respect to nonlinear dynamic analysis results of three classic moment resisting frames subjected to 94 records of FEMA-440 ground motion data set. Moreover, the adequacy of this model is compared with the fish-bone model and two predictors of nonlinear seismic demand. The statistical study of predicted interstory drift demonstrates the superiority of the proposed model over the fish-bone model and both seismic demand predictors.     

基于NLCCA的中国夏季降水与东亚夏季风关系的探讨

运用一种基于人工神经网络的非线性典型相关分析方法(NLCCA),对中国夏季降水与东亚夏季风之间的非线性关系进行了分析。结果表明,夏季降水对东亚夏季风的响应具有一定的非线性,当夏季风较强与较弱时,对应的中国夏季降水异常分布呈现明显的不对称性。夏季降水与夏季风之间的关系可分离为线性响应和非线性响应,其中非线性响应部分占总方差贡献的52.1%,说明我国夏季降水异常分布与东亚夏季风相互之间的关系既有线性特征也有非线性特征,非线性响应略显重要。     

两种土壤温度算法的对比分析

为了定量理解黄土高原土壤的物理特性和过程, 为进一步提高陆面模式对该地区地表能量平衡模拟能力奠定基础, 本文利用2005年黄土高原陆面过程试验中7月22～26日期间裸土地表观测站土壤温度观测资料, 采用热传导（结合数学拟合法)、热传导－对流两种方法分别计算了该地区土壤热扩散率。本文还利用热传导－对流方法计算0.05～0.1 m浅薄土壤层的热扩散率垂直梯度与水通量密度之和, 其值介于0.80×10-6～2.43×10-6m/s之间。在此基础之上, 以0.05 m深度的土壤层为上边界, 分别利用上述两种方法模拟0.10 m深度的土壤层温度, 结果表明: 由于忽略土壤的垂直不均匀性和水分的垂直运动而只考虑热传导过程, 热传导方法不仅高估了土壤温度振幅, 而且高估了位相的延迟。而热传导－对流方法对温度振幅和位相的模拟值与实际观测值吻合较好, 白天 (北京时间08:00～20:00) 的温度模拟值相对测量值的平均误差、 标准差和归一化标准差分别为0.19 K、0.18 K和0.08%。     

长时效的正压原始方程能量完全守恒(拟)谱模式

遵循误差反演补偿新计算原理,对正压原始方程传统气象全球拟谱模式方案进行了改造,构造了正压原始方程能量完全守恒全球拟增模式新计算方案,解决了正压原始方程的(非线性)计算稳定性问题和能量守恒整体性质保持问题,改进了相应正压原始方程传统气象全球拟谱模式方案的计算效能。新方案的数值试验表明:在计算实践上,新方案在解决能量守恒问题的同时,可解决(非线性)计算稳定性问题,并在一定条件下可解决非线性计算收敛性问题。进一步的比较数值试验还表明:在计算实践上,新方案具有在提高相应传统气象方案的计算精度,减少其计算量的同时,延长其计算时效,解决其中一类特定“气候漂移”问题方面的效用。本工作原理也适用于斜压原始方程情形。     

大气中一类非线性方程的非线性波解及周期的近似计算法

大气中许多模式可化为Ｆ＇＇＝ＡＦ／Ｆ＋Ｂ（ＡＢ≠０）一类非线性常微分方程。利用常微分方程定性理论说明了该方程存在非线性波解，讨论了其周期的计算问题，并求得了波解及其周期的近似表达式。     

ANNUAL VARIATIONS OF TEMPERATURE ON FOUR URBAN UNDERLYING SURFACES AND FITTING ANALYSIS

Based on the observed 2-year temperature data for four kinds of typical urban underlying surfaces, including asphalt, cement, bare land and grass land, the annual variations and influencing factors of land surface temperature are analyzed. Then fitting equations for surface temperature are established. It is shown that the annual variation of daily average, maximum and minimum temperature and daily temperature range on the four urban underlying surfaces is consistent with the change in air temperature. The difference of temperature on different underlying surfaces in the summer half year (May to October) is much more evident than that in the winter half year (December to the following April). The daily average and maximum temperatures of asphalt, cement, bare land and grass land are higher than air temperature due to the atmospheric heating in the daytime, with that of asphalt being the highest, followed in turn by cement, bare land and grass land. Moreover, the daily average, maximum and minimum temperature on the four urban underlying surfaces are strongly impacted by total cloud amount, daily average relative humidity and sunshine hours. The land surface can be cooled (warmed) by increased total cloud amount (relative humidity). The changes in temperature on bare land and grass land are influenced by both the total cloud amount and the daily average relative humidity. The temperature parameters of the four land surfaces are significantly correlated with daily average, maximum and minimum temperature, sunshine hours, daily average relative humidity and total cloud amount, respectively. The analysis also indicates that the range of fitting parameter of a linear regression equation between the surface temperature of the four kinds of typical land surface and the air temperature is from 0.809 to 0.971, passing the F-test with a confidence level of 0.99.     

全球资料同化中误差协方差三维结构的准确估计与应用Ⅰ:观测空间协方差的准确估计

观测误差与背景误差协方差在四维资料同化和业务资料分析系统中起到决定性作用,它决定着观测信息与背景初猜值信息的相对重要性以及这些信息在空间及不同变量间的扩展方式.由于实际大气的真值并不知道,需要发展不同的技巧来估计观测误差与背景误差协方差,其中在观测空间利用观测与背景初猜值之差来分离观测误差与背景误差协方差的方法估计出的结果较为准确,其估计出的观测误差可直接用于资料分析系统中,背景误差可作为标尺来度量其他方法估计结果的可靠性.文章采用国家气象中心T213L31全球中期分析预报系统的6 h预报作为背景初猜场及同时段冬夏两个季节的北半球探空,利用贝塞尔函数拟合方法来分离观测误差与背景误差协方差,并比较了东亚区、北美区、欧洲区3个探空资料均匀密集区的区域与季节变化结果.结果表明,观测空间拟合方法所要求的水平均质、各向同性在欧洲区和北美区成立程度较好,在东亚区略差,使用时需要斟酌.此外均方差区域间差别较大,在冬季明显大于夏季,温度场偏大0.2 K,风场偏大0.9 m/s.温度场在400 hPa以下与150 hPa以上,背景误差略小于观测误差,而在200-300 hPa,背景误差略大一些.风场的特点与温度场比较一致.温度与风场背景误差主要集中在前40波,并在20波左右达到最大,水平相关季节区域差别不大,而温度垂直相关比风场窄,两者相关范围比较大的波数主要集中在前20波.此外利用贝塞尔函数拟合方法获得结果的分析表明,在质量场中不同区域季节间温度误差的稳定性要明显好于高度场,涡度散度的稳定性要明显好于流函数和势函数,特别是对于特征长度更为明显.这表明利用贝塞尔函数拟合方法获得的结果对校准在全球资料同化中采用温度、涡度散度作为资料同化的分析变量具有一定的优势.     

On the evolution of finite-amplitude disturbance to the barotropic and baroclinic quasigeostrophic flows

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区域气候模式侧边界的处理对东亚夏季风降水模拟的影响

在区域气候模式模拟中,侧边界的作用是引入大尺度强迫场。如何处理好侧边界,即大尺度强迫场和区域气候模式本身之间的关系问题,对于区域气候模式模拟和预报东亚夏季风降水具有重要意义。本文利用美国纽约州立大学Albany分校的区域气候模式（SUNYA-ReCM）,设计了两种不同的侧边界处理方法,来探讨侧边界对东亚夏季风降水模拟的影响。驱动区域模式的大尺度强迫场来自欧洲中期天气预报中心（ECMWF）及热带海洋大气研究计划（TOGA）的分析资料场。试验结果表明:（1）当模式的区域较大时,采用较小的侧边界缓冲区会在缓冲区与模式内部的交界处产生不连续;扩大缓冲区并且考虑不同尺度强迫在垂直方向上的不同作用,可以避免这一缺陷。（2）更重要的是采用后一种方案,即减少了区域气候模式在模拟大尺度环流场方面所起的作用,使得模式更多地依赖侧边界来得到更真实的、对东亚夏季风降水起重大影响的一些气流,如副高、西南季风和南海季风,对东亚夏季风降水无论是在大小上还是在雨带位置的演变上都能进行更好的模拟。     

Geotechnical design with apparent seismic safety factors well-bellow 1

The paper demonstrates that whereas often in seismic geotechnical design it is not realistically feasible to design with ample factor of safety against failure as is done in static design, an “engineering” apparent seismic factor of safety less than 1 does not imply failure. Examples from slope stability and foundation rocking illustrate the concept. It is also shown that in many cases it may be beneficial to under-design the foundation by accepting substantial uplifting and/or full mobilization of bearing capacity failure mechanisms.