Intelligent technology-based control of motion and vibration using MR dampers

Due to their intrinsically nonlinear characteristics, development of control strategies that are implementable and can fully utilize the capabilities of semiactive control devices is an important and challenging task. In this study, two control strategies are proposed for protecting buildings against dynamic hazards, such as severe earthquakes and strong winds, using one of the most promising semiactive control devices, the magnetorheological (MR) damper. The first control strategy is implemented by introducing an inverse neural network (NN) model of the MR damper. These NN models provide direct estimation of the voltage that is required to produce a target control force calculated from some optimal control algorithms. The major objective of this research is to provide an effective means for implementation of the MR damper with existing control algorithms. The second control strategy involves the design of a fuzzy controller and an adaptation law. The control objective is to minimize the difference between some desirable responses and the response of the combined system by adaptively adjusting the MR damper. The use of the adaptation law eliminates the need to acquire characteristics of the combined system in advance. Because the control strategy based on the combination of the fuzzy controller and the adaptation law doesn’t require a prior knowledge of the combined building-damper system, this approach provides a robust control strategy that can be used to protect nonlinear or uncertain structures subjected to random loads. Supported by: Hong Kong Research Grant Council Competitive Earmarked Research Grant HKUST 6218 / 99E and by the National Science Foundation under grant CMS 99-00234.     

Morphological Investigations in the River Odra

Since 1992, the Federal Institute of Hydrology (Bundesanstalt für Gewässerkunde – BfG) performs morphological investigations in the river Odra downstream from the confluence of the river Neiße (Nysa Luzycka). The results of these investigations give a clear insight into the morphodynamic behaviour of this part of the river and indicate that on average 380 000 t of suspended solids and 130 000 t of bed load are transported by the river Odra at Hohensaaten per year, with a distinct seasonal variability in the case of suspended solids. Detailed studies on type and composition of the bed substrates have revealed that the river bottom is composed of very fine material: at Ratzdorf already 75 % of the bed material is finer than 2 mm, at Widuchowa almost all of the river bed material consists of sand finer than 0.63 mm. Because of the high sensitivity of the river bottom to discharge increases and the corresponding increases of bottom shear stress sand was found to be the dominating fraction of the suspended load in case of extreme flood events.     

THE SENSITIVITY OF TWO DISTRIBUTED NON-POINT SOURCE POLLUTION MODELS TO THE SPATIAL ARRANGEMENT OF THE LANDSCAPE

Distributed hydrological models are becoming increasingly complex with respect to spatial phenomena, and with the widespread availability of spatial data from GIS, this trend is likely to increase. In all such models the spatial arrangement of phenomena, such as soil properties and land-use categories is fundamental, and so the arrangement should have an influence on the model output. Testing for this influence we term spatial sensitivity analysis. Here, we report on the spatial sensitivity of two widely used models, AgNPS (agricultural non-point source pollution model) and ANSWERS (areal nonpoint source watershed environment response simulation). The input spatial data were subjected to spatially random mixing to varying degrees, such that the organized landscape became disorganized. The chemical discharge from AgNPS, and the sediment and water discharge from ANSWERS, are examined. In both cases most outputs exhibited little or no sensitivity to the spatial distribution of most input data. Only infiltration-related inputs produced large variations, but these changes were not in the sense that might have been predicted. Although the analytical methods used require further refinement, there must now be some doubt as to the validity of the models, and whether they repay their computational complexity. Furthermore, it is felt that spatial sensitivity analysis should become a fundamental part of the verification of all such models. © 1997 by 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。     

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.     

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。     

Review of methods for the detection and estimation of trends with emphasis on water quality applications

Methods for the detection and estimation of trends which are suitable for the type of data sets available from water quality and atmospheric deposition monitoring programmes are considered. Parametric and non-parametric methods which are based on the assumption of monotonic trend and which account for seasonality through blocking on season are described. The topics included are heterogeneity of trend, missing data, covariates, censored data, serial dependence and multivariate extensions. The basis for the non-parametric methods being the method of choice for current large data sets of short to moderate length is reviewed. A more general definition of trend as the component of gradual change over time is consistent with another group of methods and some examples are given. Spatial temporal data sets and longer temporal records are also briefly considered. A broad overview of the topic of trend analysis is given, with technicalities left to the references cited. The necessity of defining what is meant by trend in the context of the design and objectives of the programme is emphasized, as is the need to model the variability in the data more generally.