A Multiple Criteria Decision Modelling approach to selection of estimation techniques for fitting extreme floods

The problem of fitting a probability distribution, here log-Pearson Type III distribution, to extreme floods is considered from the point of view of two numerical and three non-numerical criteria. The six techniques of fitting considered include classical techniques (maximum likelihood, moments of logarithms of flows) and new methods such as mixed moments and the generalized method of moments developed by two of the co-authors. The latter method consists of fitting the distribution using moments of different order, in particular the SAM method (Sundry Averages Method) uses the moments of order 0 (geometric mean), 1 (arithmetic mean), –1 (harmonic mean) and leads to a smaller variance of the parameters. The criteria used to select the method of parameter estimation are:

The two-component extreme value distribution for flood frequency analysis: Derivation of a new estimation method

The two component extreme value (TCEV) distribution has recently been shown to account for most of the characteristics of the real flood experience. A new method of parameter estimation for this distribution is derived using the principle of maximum entropy (POME). This method of parameter estimation is suitable for application in both the site-specific and regional cases and appears simpler than the maximum likelihood estimation method. Statistical properties of the regionalized estimation were evaluated using a Monte Carlo approach and compared with those of the maximum likelihood regional estimators.     

基于核主成分分析的时间域航空电磁去噪方法

时间域航空电磁数据往往在测量过程中受到天然和人文噪声的干扰.如果不能很好滤除这些电磁噪声,那么将会降低资料质量、影响反演的精度,甚至获得错误的解释结果.本文提出了一种基于核主成分分析的去噪方法,通过核主成分分析提取叠加后衰减曲线的主成分,然后使用能量占比方法分离反映地下介质的有效信号和噪声,最后使用反映地下介质的特定成分进行重构.本文所推荐的去噪方法不仅能剔除天然噪声,例如天电产生的尖脉冲或者振荡,而且能有效地抑制人文噪声.分别使用基于核主成分分析的去噪方法,以及AeroTEM软件的处理方法对同样的吊舱式时间域直升机航空电磁勘查系统实测数据进行处理,并比较其结果.处理结果表明：所推荐的去噪方法要优于AeroTEM软件.     

基于易损性的基础隔震结构地震动选取方法研究

对基础隔震结构进行动力弹塑性时程分析时,地震记录的选择是关键.提出基于基础隔震结构弹塑性动力放大系数谱进行地震记录选取的方法:首先采用动力弹塑性时程分析方法对基础隔震结构的两自由度简化模型进行分析,得到结构的动力放大系数谱;然后采用谱匹配的方法选取地震记录,对一8层混凝土框架结构的基础隔震结构进行增量动力分析、地震易损...     

计算结构首次穿越时间概率密度函数的新方法

本文在M adsen等提出的积分方程方法基础上,采用单点FORM方法计算结构首次穿越问题中的条件穿越率、联合穿越率及首次穿越时间概率密度。提出的新方法计算简单,结果精确,适于进行脆性结构的首次穿越破坏分析。     

随机结构动力可靠度分析的极值概率密度方法

提出了随机结构动力可靠度分析的极值概率密度方法。基于概率密度演化的基本思想,构造一个虚拟随机过程,使得随机结构动力反应的极值为该虚拟随机过程的截口随机变量。进而．采用概率密度演化方法,建立概率密度演化方程并求解给出随机结构动力反应的极值分布。在安全域内积分即可给出结构动力可靠度,当安全界限为随机变量时,采用这一方法几乎不增加额外的工作量,与随机模拟结果的比较表明,本文建议方法具有良好的精度和效率。     

Skyline‐based ground motion selection method for nonlinear time history analysis of building structures

This paper develops a novel ground motion selection procedure for nonlinear time history analysis of critical structures. The skyline query originated from computer science is first introduced, including its concept and related algorithms. Then, the ground motion selection procedure based on skyline query is developed. Meanwhile, a new five‐dimensional vector‐valued intensity measure is defined as a critical ingredient of the selection procedure to measure the damage potential of ground motions. Finally, the process of the selection procedure is illustrated through examples of three shear models, and its efficiency is also validated. Through the examples of three shear models, the ground motion selection procedure based on skyline query proposed in this paper is proven to be capable of selecting a limited set of ground motions with high damage potentials for the nonlinear time history analysis purpose. Copyright © 2012 John Wiley & Sons, Ltd.     

基于卡方分布函数的辐射带电子蝴蝶状投掷角分布的优化判别方法

受不同物理过程影响,辐射带电子呈现多种投掷角分布类型,其中蝴蝶状分布尤为引人关注,其特征为通量在90°投掷角附近有极小值、在较低投掷角处达到峰值.现有研究普遍通过对几个特定投掷角间的通量比值进行限定来识别蝴蝶状分布,然而,该方法所挑选的电子分布并不一定符合蝴蝶状分布特征,这为准确研究电子蝴蝶状分布的现象学规律及其背后物理机制带来了一定困难.针对该问题,本文建立了一个基于卡方分布函数的判别模型,通过比较电子观测通量剖面与模型模拟的理想蝴蝶状分布剖面的相似性来判别电子蝴蝶状分布.使用范艾伦卫星上REPT仪器提供的L-shell > 3空间区域内两组不同投掷角分辨率的电子通量数据对该判别方法进行验证,结果表明该方法能明显提升判别效果,分别使基于17个投掷角和36个投掷角的电子通量数据判别蝴蝶状分布的误判率下降12.6%和27.5%.本文的分析结果证实了提高投掷角精度有利于准确确定辐射带电子的投掷角分布类型,发展的模型方法也对深入开展地球与行星磁层中电子蝴蝶状分布的统计学研究具有重要价值.

     

A fuzzy‐based simulation method for modelling hydrological processes under uncertainty

In this study, a fuzzy‐based simulation method (FBSM) is developed for modelling hydrological processes associated with vague information through coupling fuzzy vertex analysis technique with distributed hydrological model. The FBSM can handle uncertainties existed as fuzzy sets in the hydrological modelling systems, and solutions under an associated number of α‐cut levels can be generated by solving 2ⁿ deterministic models. The lower reach of the Tarim River Basin in China is selected as a study case for demonstrating applicability of the proposed method. The developed model is calibrated and validated against observed groundwater elevation for four wells during the period 2000–2001, and generally performed acceptable for model Nash–Sutcliffe coefficient (R2) and correlation coefficient (R). The R2 is approximately over 0·65 and the correlation coefficient is higher than 0·90. Based on the technique of fuzzy simulation, the uncertainties of two parameters (K_H and LC) are reflected under different α‐cut levels. The results indicate that, under a lower degree of plausibility, the interval between the lower and upper bounds of the groundwater elevation is wider; conversely, a higher degree of plausibility would lead to a narrow interval. The main effect of K_H is more significant than the effect of LC at most well sites. The proposed method is useful for studying hydrological processes within a system containing multiple factors with uncertainties and providing support for identifying proper water resources management strategies. Copyright © 2010 John Wiley & Sons, Ltd.     

基于UPFs的珊瑚岛礁场地地震反应分析方法研究

合理且高效地模拟珊瑚砂非线性动力特性、远场无限地基辐射阻尼以及海域岛礁动水压力的影响是进行珊瑚岛礁抗震安全分析的关键技术问题.以通用有限元软件ANSYS为研究工具,基于UPFs二次开发灵活性的特点,建立了适用于珊瑚砂地基条件下的岛礁场地地震反应分析时域计算模型.通过创建一种新的珊瑚砂等价线性单元描述岛礁场地的非线性动力...     

Mountain ordering: A method for classifying mountains based on their morphometry

A new method for classifying mountain morphology, ‘mountain ordering,’ is proposed, and quantitative expressions for various morphological parameters of two ordered mountains in northern Japan were obtained using this method. Mountain order was defined in terms of the closed contour lines on a topographic map. A set of closed, concentric contour lines defines a first-order mountain. Higher-order mountains can be defined as a set of closed contour lines that contain lower-order mountains and that have only one closed contour line for each elevation; they are identified as m + 1th-order mountains, where m represents the order of the enclosed, lower-order mountains. The geomorphometry for a mountain ordered according to this definition permits the identification of systematic relationships between various morphological parameters. The relationships between mountain order and these morphological parameters follow a form similar to that of Horton's laws, and permit the calculation of the ratios of number, area and height; these parameters are sufficient to express the magnitude of a mountain's dissection. The size–frequency distribution for area and height shows self-similarity for ordered mountains, and determines their fractal dimensions. Furthermore, the relationship between area and height, which has the form of a power function, describes the relief structure of ordered mountains. Copyright © 1999 John Wiley & Sons, Ltd.     

幂函数剪切模量成层土非线性地震反应的半解析算法

运用文献[1]所建议的动态应力一应变关系及其推广的Masing加卸载准则,考虑土料在地震等产生的不规则加载条件下的非线性滞回特征,将增量法与相应场地地震线性反应解析解[2]相结合,提出了该动力非线性方程的半解析时域算法,基于改进的一维剪切梁模型,对剪切模量是其深度的某一幂函数的成层非均质土层,建立了求解土体地震反应的非线性分析技术。针对文献[2]中的土层剖面,做了计算、分析和讨论。     

基于统计学的地震显著平静阈值估计

提出具有统计学意义的地震显著平静阈值估算方法,用于中国大陆及川滇、新疆和华北地区中强震活动分析,在不同区域得到不同起始震级的显著平静阈值范围。结果显示:(1)中国大陆7级、6级和5级地震显著平静的阈值范围分别为3.9—6.2年、7.9—9.6个月和62—70天;(2)川滇地区6级和5级地震显著平静的阈值范围分别为2.1—2.9年和7.0—8.5个月;(3)新疆地区6级和5级地震显著平静的阈值范围分别为2.6—4.0年和8.5—10.5个月;(4)华北地区6级和5级地震显著平静的阈值范围分别为11.7—23.4年和5.2—7.7年。     

基于精确权函数的仪器响应失真校正方法与算例

当前,经仪器响应失真校正后,加速度计有效观测频带通常为0至1倍自振频率,这限制了强震仪应用领域的延拓。有鉴于此,本文提出一个基于精确权函数的仪器响应失真校正方法并给出一个验证算例。分析表明:较之现有方法,新方法兼有高精度和高效率的优点,并可以将力平衡式加速度计的有效观测频带至少延拓3倍,对于拓展强震仪的应用领域具有重要意义。     

A Woodbury solution method for efficient seismic collapse analysis of space truss structures based on hybrid nonlinearity separation

This study presents a fast algorithm for collapse behavior simulation of space truss structures under extreme earthquake excitation by introducing the Woodbury formula to efficiently solve the structural response caused by material and geometric nonlinearity (hybrid nonlinearity). The Woodbury formula, which is an efficient tool in mathematics for solving low-rank perturbation problems, has successfully been used to improve the efficiency of local material nonlinear analysis but still has difficulties with seismic collapse analysis in which geometric nonlinearity should be considered. In this study, by implementing stiffness matrix decomposition according to the unchanged reference configuration, the effects of hybrid nonlinearity on the change in tangent stiffness of truss structures are uniformly formulated in the form of hybrid nonlinear perturbation to the reference elastic stiffness. Thus, a hybrid nonlinearity separated governing equation can be established, in which the hybrid nonlinear behaviors are depicted by the additional nonlinear degrees of freedom (NLDOFs) separated from the reference system. This allows for employing the Woodbury formula to perform seismic collapse analysis of space truss structures for avoiding the repeated updating of the global stiffness. To overcome the adverse effect of the large NLDOF number caused by the global characteristics of geometric nonlinearity on the efficiency advantages of the Woodbury formula during seismic collapse analysis, an element state judgment strategy and an adaptive restart mechanism are presented to activate only a small number of NLDOFs within critical local regions. The accuracy and efficiency of the proposed method are verified by two numerical examples.     

基于图像分析的双台面波相速度频散曲线快速提取方法

双台波形的互相关方法是面波相速度频散曲线提取的一种常用方法。传统的方法精度不高,效率较低。本文提出了一种基于图像分析的频散曲线快速提取方法,采用图像显示互相关振幅矩阵,且提出了快速追踪整条频散曲线的算法,并用Matlab编写了交互式的处理软件。基于这种方法编写的资料处理软件提高了双台相速度频散曲线提取的速度和精度,为大批量处理地震数据资料提供了坚实的软件基础。基于图像分析的方法可以更为清晰地展现出双台问的面波频散曲线的特征,对频散曲线的识别和分析也提供了更为有效的研究工具。     

基于龙门山断裂带中段平行逆断层格局 和动力学背景的特征地震数值模拟实验

本文构建一种应用有限元开展特征地震数值模拟的新方法, 并以龙门山断裂带中段的浅层构造和动力学机制为背景, 研究了平行逆冲断层分布格局对区域地震活动性的影响. 结果表明, 从断层活动相互影响的角度看, 包含3条平行逆断层的断裂带的整体地震活动性并不适用严格周期的特征地震模型, 当断层间距在20 km以下时, 随着断层间距的缩短, 对单条断层应用特征地震模型的适用性会逐渐降低. 龙门山断裂带中段的模拟计算结果显示, 后山断裂的地震活动相对独立, 区域活动性和中央断裂的断层活动很可能不适用严格周期的特征地震模型.      

A comparison of high‐resolution specific conductance‐based end‐member mixing analysis and a graphical method for baseflow separation of four streams in hydrologically challenging agricultural watersheds

Quantifying the relative contributions of different sources of water to a stream hydrograph is important for understanding the hydrology and water quality dynamics of a given watershed. To compare the performance of two methods of hydrograph separation, a graphical program [baseflow index (BFI)] and an end‐member mixing analysis that used high‐resolution specific conductance measurements (SC‐EMMA) were used to estimate daily and average long‐term slowflow additions of water to four small, primarily agricultural streams with different dominant sources of water (natural groundwater, overland flow, subsurface drain outflow, and groundwater from irrigation). Because the result of hydrograph separation by SC‐EMMA is strongly related to the choice of slowflow and fastflow end‐member values, a sensitivity analysis was conducted based on the various approaches reported in the literature to inform the selection of end‐members. There were substantial discrepancies among the BFI and SC‐EMMA, and neither method produced reasonable results for all four streams. Streams that had a small difference in the SC of slowflow compared with fastflow or did not have a monotonic relationship between streamflow and stream SC posed a challenge to the SC‐EMMA method. The utility of the graphical BFI program was limited in the stream that had only gradual changes in streamflow. The results of this comparison suggest that the two methods may be quantifying different sources of water. Even though both methods are easy to apply, they should be applied with consideration of the streamflow and/or SC characteristics of a stream, especially where anthropogenic water sources (irrigation and subsurface drainage) are present. Copyright © 2014 John Wiley & Sons, Ltd.