Determination of ductility factor considering different hysteretic models

In current seismic design procedures, base shear is calculated by the elastic strength demand divided by the strength reduction factor. This factor is well known as the response modification factor, R, which accounts for ductility, overstrength, redundancy, and damping of a structural system. In this study, the R factor accounting for ductility is called the ‘ductility factor’, R_μ. The R_μ factor is defined as the ratio of elastic strength demand imposed on the SDOF system to inelastic strength demand for a given ductility ratio. The R_μ factor allows a system to behave inelastically within the target ductility ratio during the design level earthquake ground motion. The objective of this study is to determine the ductility factor considering different hysteretic models. It usually requires large computational efforts to determine the R_μ factor. In order to reduce the computational efforts, the R_μ factor is prepared as a functional form in this study. For this purpose, statistical studies are carried out using forty different earthquake ground motions recorded at a stiff soil site. The R_μ factor is assumed to be a function of the characteristic parameters of each hysteretic model, target ductility ratio and structural period. The effects of each hysteretic model to the R_μ factor are also discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Automated calibration applied to watershed‐scale flow simulations

Complexity in simulating the hydrological response in large watersheds over long times has prompted a significant need for procedures for automatic calibration. Such a procedure is implemented in the basin‐scale hydrological model (BSHM), a physically based distributed parameter watershed model. BSHM simulates the most important basin‐scale hydrological processes, such as overland flow, groundwater flow and stream–aquifer interaction in watersheds. Here, the emphasis is on estimating the groundwater parameters with water levels in wells and groundwater baseflows selected as the calibration targets. The best set of parameters is selected from within plausible ranges of parameters by adjusting the values of hydraulic conductivity, storativity, groundwater recharge and stream bed permeability. The baseflow is determined from stream flow hydrographs by using an empirical scheme validated using a chemical approach to hydrograph separation. Field studies determined that the specific conductance for components of the composite hydrograph were sufficiently unique to make the chemical approach feasible. The method was applied to the Big Darby Creek Watershed, Ohio. The parameter set selected for the groundwater system provides a good fit with the estimated baseflow and observed water well data. Copyright © 1999 John Wiley & Sons, Ltd.     

Compactification and cosmic string phenomenology

A U(1) model of gravitational, Higgs and, gauge fields is analysed. Two phases of the system are considered. In the case with broken symmetry we have the Nielsen-Olesen configuration. In the symmetric phase we find a space-time metric S² × E₁². This appears in full analogy to the Freund-Rubin compactification due to an antisymmeric tensor field. The connection of these structures with cosmic string phenomenology is analysed.     

数值预报AI气象大模型国际发展动态研究

数值预报是研究地球系统的重要工具,有助于加深科学家对大气、海洋、气候和环境等复杂系统之间相互作用和变化过程的理解,在防灾减灾、气候变化和环境治理等方面发挥着不可或缺的作用。随着模式复杂度和分辨率的提高,传统数值模式在气候变化研究和气候预测方面取得了迅速的进展,但也面临一些挑战,需要得到数据同化、集合耦合、高性能计算和不确定性分析等多方面的支持。而近年来,“AI+气象”的交叉研究在气象领域引起了广泛关注。基于多种深度学习架构的人工智能大模型,依托强大的计算资源和海量的数据进行训练,能够以新的科学范式进行高效数值预报。气象大模型不断涌现,一些科技公司如华为、英伟达、DeepMind、谷歌、微软等,以及国内外高校如清华大学、复旦大学、密歇根大学、莱斯大学等发布了多个涵盖临近预报、短时预报、中期预报和延伸期预报等不同领域的气象大模型。这标志着人工智能与气象领域的交叉融合已经达到新的高度。尽管气象大模型在现阶段取得了较大突破,但其发展仍然面临弱可解释性、泛化能力不足、极端事件预报强度偏低、智能预报结果过平滑、深度学习框架能力需要拓展等诸多挑战。     

岬间海湾平面平衡形态研究进展

岬间海湾平面平衡形态规律的研究是砂质海岸稳定与演变研究的重要内容。简要回顾了岬间海湾平面形态规律的研究进展,着重介绍了海湾平衡形态的五个模型。通过评述平衡形态模型的优缺点,指出机理分析和经验拟合相结合应该为以后海湾平面平衡形态规律的研究发展方向,并论述了我国岬间砂质海湾平面平衡形态研究的重要意义。     

Laboratory study and predictive modeling for thaw subsidence in deep permafrost

Oil wells on the North Slope of Alaska pass through deep deposits of permafrost. The heat transferred during their operation causes localized thawing, resulting in ground subsidence adjacent to the well casings. This subsidence has a damaging effect, causing the casings to compress, deform, and potentially fail. This paper presents the results of a laboratory study of the thaw consolidation strain of deep permafrost and its predictive modeling. Tests were performed to determine strains due to thaw and post-thaw loading, as well as soil index properties. Results, together with data from an earlier testing program, were used to produce empirical models for predicting strains and ground subsidence. Four distinct strain cases were analyzed with three models by multiple regression analyses, and the best-fitting model was selected for each case. Models were further compared in a ground subsidence prediction using a shared subsurface profile. Laboratory results indicate that strains due to thaw and post-thaw testing in deep core permafrost are insensitive to depth and are more strongly influenced by stress redistributions and the presence of ice lenses and inclusions. Modeling results show that the most statistically valid and useful models were those constructed using moisture content, porosity, and degree of saturation. The applicability of these models was validated by comparison with results from Finite Element modeling.     

Long-term behaviour of the stellar brightness in eclipsing minima of SV Cam

Es wird das zeitliche Verhalten der Helligkeit in den zentralen Bedeckungen beider Komponenten von SV Cam – beobachtet zwischen 1973 und 1980 durch PATKOS – analysiert, um das von Busso u. a. aus Helligkeitsvariationen außerhalb der Bedeckungen abgeleitete Sternaktivitätsmodell für diesen Stern zu testen. Ihre Entdeckung eines Zyklus von ungefähr 10 Jahren bestätigt sich aus den Beobachtungen im Hauptminimum, wogegen aus den Beobachtungen des Nebenminimums eine eindeutige Feststellung der Zykluslänge nicht möglich war. Es ist klar erkennbar, daß der Zyklus von Kurzzeitfluktuationen überlagert wird, welche in charakteristischen Zeiten von einigen Tagen bis hin zu Monaten verlaufen. Diese Fluktuationen sind nicht nur während des Hauptminimums, sondern auch während des Nebenminimums zu beobachten. Korrelationen zwischen den Fluktuationen zu diesen beiden Bahnphasen sprechen dafür, daß die Primärkomponente im System SV Cam den Hauptbeitrag zu den beobachteten Helligkeitsvariationen liefert.     

城市模型研究的发展趋势及展望

从内容、空间尺度、时间维、综合程度、建模方式、复杂程度和数学方法等方面对目前的城市模型进行了系统的分类。论述了城市模型研究的发展趋势：模型研究内容日益丰富和多元化;从静态模拟到动态模拟发展;从子系统模拟向综合系统模拟发展;遥感和GIS的应用以及与城市模型的集成。对城市模型研究的未来发展进行了展望,认为未来的城市模型开发应基于综合方法的思想,注重加强城市基本理论和多学科交叉研究,强调城市模拟的动态性和综合性。充分借助遥感与GIS等技术手段进行研究。     

基于元胞模型的河道纵剖面调整动态模拟

纵剖面的调整是河道演化的重要内容,其对于河道整治及水沙灾害机理研究都具有重要意义。利用多年观测资料可以较为精确地分析和推断河道纵剖面的调整过程。但是,这种方法不能从过程机理上对纵剖面的调整进行模拟分析。而自然条件下河道边界条件的复杂性使得对河道纵剖面演化的物理过程模拟有很大困难。元胞自动机是一个时间、空间和状态都离散的动力模型,是研究复杂系统动态演化过程的有力工具。本文以黄河尾闾河道为例,利用一维元胞模型对河道纵剖面的调整进行动态模拟。模拟揭示了河道纵剖面在初始形态、不同水沙组合以及河道延伸等情况下的演化规律与趋势。