滑动屋盖摩擦控制系统对地震频谱和结构刚度的鲁棒性

地震功率谱密度函数的频率范围和结构刚度变化对滑动屋盖摩擦控制系统减震效果的影响分析表明 :控制系统减震效果对地震功率谱的频域宽窄不敏感 ,而对功率谱所覆盖的结构自振频率敏感 ;结构刚度发生± 15 %的变化对减震效果的影响不大。分析还表明 ,滑动屋盖摩擦控制系统对于结构非线性地震反应有显著的减震作用     

通过改进节点性能确保火灾下钢框架结构的鲁棒性

介绍了钢框架结构火灾下鲁棒性的背景知识,建议对于非常重要的建筑结构,抗火安全设计必须包括通常设计中尚未考虑到的意外破坏模式。文章辨识了结构意外破坏的不同模式,并提出了保证结构安全性的可行方法。本文主要介绍了如何利用梁的悬链线效应,使荷栽从受损结构重新分配到相邻结构,该效应是梁受弯承载力状态的一种转变。为确保钢梁中悬链线效应的充分发展,最重要的是要保证节点具有足够的抗拉承栽力与转动能力。本文提出了一种节点转动能力需求的量纲分析方法,并根据一些试验结果,介绍了英国常用的梁柱节点可到达的转动能力。虽然一些延性较好的节点在升温时能够达到10°的转动能力,但当钢的温度非常高时,其仍不能满足使悬链线效应充分形成时所需要的转动能力（〉15°）。随后,讨论了如何提高节点的转动能力,包括：采用具有较好延性的节点（例如开反向槽口的节点）,改进节点的细部构造（如将节点的受拉区移近至受压区,并为螺栓开槽型孔）和采用更强的、延性更好的由耐火钢制成的螺栓。这些提出的节点技术需要与节点在其他设计要求下的性能要求相协调（如刚度）,为满足不同的结构性能要求,找到最优的节点设计方法,仍需要更深入的研究。     

Testing the robustness of the physically-based ECOMAG model with respect to changing conditions

Abstract

The robustness of the physically-based, semi-distributed hydrological model ECOMAG with respect to changing (climatic or land-use) conditions was evaluated for two basins, considered within the modelling workshop held in the frame of the 2013 IAHS conference in Göteborg, Sweden. The first basin, the Garonne River basin, France, is characterized mostly by changes in climatic conditions, while the second, Obyån Creek, Sweden, was exposed to drastic land cover change due to deforestation. Tests were conducted to evaluate the model’s ability to simulate with acceptable accuracy the changing hydrological regime of each basin and to retain, in the process, relatively stable values of the parameters. Acceptable performance of the ECOMAG model was obtained under the different combinations of the calibration/evaluation periods, including, importantly, the periods of hydrological regime changes in both basins.     

A fine-grained perspective on the robustness of global cargo ship transportation networks

The robustness of cargo ship transportation networks is essential to the stability of the world trade system. The current research mainly focuses on the coarse-grained, holistic cargo ship transportation network while ignoring the structural diversity of different sub-networks. In this paper, we evaluate the robustness of the global cargo ship transportation network based on the most recent Automatic Identification System (AIS) data available. First, we subdivide three typical cargo ship transportation networks (i.e., oil tanker, container ship and bulk carrier) from the original cargo ship transportation network. Then, we design statistical indices based on complex network theory and employ four attack strategies, including random attack and three intentional attacks (i.e., degree-based attack, betweenness- based attack and flux-based attack) to evaluate the robustness of the three typical cargo ship transportation networks. Finally, we compare the integrity of the remaining ports of the network when a small proportion of ports lose their function. The results show that 1) compared with the holistic cargo ship transportation network, the fine-grain-based cargo ship transportation networks can fully reflect the pattern and process of global cargo transportation; 2) different cargo ship networks behave heterogeneously in terms of their robustness, with the container network being the weakest and the bulk carrier network being the strongest; and 3) small-scale intentional attacks may have significant influence on the integrity of the container network but a minor impact on the bulk carrier and oil tanker transportation networks. These conclusions can help improve the decision support capabilities in maritime transportation planning and emergency response and facilitate the establishment of a more reliable maritime transportation system.     

Separating wheat from chaff: Diatom taxon selection usingan artificial neural network pruning algorithm

This study addresses the question of what diatom taxa to includein a modern calibration set based on their relative contribution in apalaeolimnological calibration model. Using a pruning algorithm for ArtificialNeural Networks (ANNs) which determines the functionality of individual taxa interms of model performance, we pruned the Surface Water Acidification Project(SWAP) pH-diatom data-set until the predictive performance of thepruned set (as assessed by a jackknifing procedure) was statistically differentfrom the initial full-set. Our results, based on the validation at each5% data-set reduction, show that (i) 85% of the taxa canbe removed without any effect on the pH model calibration performance, and (ii)that the complexity and the dimensionality reduction of the model by theremoval of these non-essential or redundant taxa greatly improve therobustness of the calibration. A comparison between the commonly usedmarginal criteria for inclusion (species tolerance andHill's N2) and our functionality criterion shows that the importance ofeach taxon in an ANN palaeolimnological model calibration does not appear todepend on these marginal characteristics.     

随机系统稳健自适应控制

对具有未建模动态特性且时滞任意的多维随机系统,通过采用有界外来激励和随机变界截尾方法,本文建立了推广最小二乘（ＥＬＳ）算法和加权ＥＬＳ算法的稳健估计,进而得到间接自适应模型参考控制的稳健性     

基于粒子群优化的理论变异函数拟合方法研究

变异函数是地统计学中区域化变量空间结构分析和空间局部插值的主要分析工具.理论变异函数模型的获取是地质统计学中的基础性工作,它是了解区域化变量的变异特征、进一步对地质统计学计算的必要环节.针对现有的理论变异函数的拟合方法,如人工拟合法、线性规划拟合法、加权多项式拟合法、目标规划拟合法等的不足之处,充分利用粒子群优化算法在求解非线性优化问题时具有的全局寻优的特点,提出基于粒子群优化的理论变异函数拟合方法.在实例应用中,分别利用粒子群优化算法和加权多项式拟合方法进行理论变异函数拟合,交叉验证结果表明粒子群优化算法预测精度较高,具有较强的稳健性.     

Deriving hydrological signatures from soil moisture data

Soil moisture is an important variable in hydrological studies, but has been little used for model evaluation due to its high sensitivity to local conditions. We explore the possibility to derive hydrological signatures from soil moisture data that could overcome this limitation and be helpful for model evaluation. A set of eight hydrological signatures was built, encompassing long-term to short-term time scales. These signatures were tested according to robustness, representativeness and discriminatory power, using in situ data sets from New Zealand, including national network and experimental watershed data. Field capacity, type of soil moisture distribution, and starting dates of seasonal transitions typically meet the criteria, subject to uniform sensor depths and homogeneous land uses. Durations of seasonal transitions and event-based signatures showed higher variability and lower discriminatory power. In general, long-term signatures are more robust, more representative of large areas, and have a high discriminatory power, thus showing a good potential for use in diagnostic evaluation of regional models.     

Modified model-based control of shake tables for online acceleration tracking

The interest in shake tables stems from a need to simulate earthquake behavior in laboratory settings. However, the inherent properties and nonlinearities associated with electromechanical and servohydraulic shake tables, combined with issues of table-structure interaction, make accurate reproduction of earthquake acceleration time histories a challenging problem. The classical approach to control shake tables has been the Transfer Function Iteration (TFI) method. The tuning of the TFI controller is an offline iterative process, conducted using small amplitude ground motions. Effective compensation is not achievable for system nonlinearities that are not projected in the iterative tuning process. To address this problem, researchers have developed online compensation techniques, which can maintain tracking performance for the earthquake signals more effectively. Model-based controllers (MBC) are a class of online controllers which use an identified model of the shake table-structure for compensation. The MBC employs feedforward and feedback controllers to ensure that the shake table tracks a specified earthquake ground motion despite the presence of table and structural nonlinearities. However, the feedback controllers in MBC do not always maintain tracking accuracy and can result in loss of robustness when changes occur in the shake table and structure dynamics. This paper introduces a modified model-based controller (mMBC) for acceleration tracking as an improvement on the existing MBC architecture. A stability condition is introduced to assess the robustness of the new modified control architecture. Through numerical and experimental studies, the improved tracking robustness of the mMBC architecture is demonstrated.     

Six factors which affect the condition number of matrices associated with kriging

Determining kriging weights to estimate some variable of interest at a given point in the field involves solving a system of linear equations. The matrix of this linear system is subject to numerical instability, and this instability is measured by the matrix condition number. Six parameters in the kriging process have been identified which directly affect this condition number. Analysis of a series of 648 experiments gives some insight on these parameters, and how the condition number relates to kriging variance.