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91.
Kun‐xia Yu Lars Gottschalk Xiang Zhang Peng Li Zhanbin Li Lihua Xiong Qian Sun 《水文研究》2018,32(12):1844-1857
An approach for nonstationary low‐flow frequency analysis is developed and demonstrated on a dataset from the rivers on the Loess Plateau of China. Nonstationary low‐flow frequency analysis has drawn significant attention in recent years by establishing relationships between low‐flow series and explanatory variables series, but few studies have tested whether the time‐varying moments of low flow can be fully described by the time‐varying moments of the explanatory variables. In this research, the low‐flow distributions are analytically derived from the 2 basic explanatory variables—the recession duration and the recession coefficient—with the assumption that the recession duration and recession coefficient variables follow exponential and gamma distributions, respectively; the derived low‐flow distributions are applied to test whether the time‐varying moments of explanatory variables can explain the nonstationarities found in the low‐flow variable. The effects of ecosystem construction measures, that is, check dam, terrace, forest, and grassland, on the recession duration and recession coefficient are further discussed. Daily flow series from 11 hydrological stations from the Loess Plateau are used and processed with a moving average technique. Low‐flow data are extracted following the pit under threshold approach. Six of the 11 low‐flow series show significant nonstationarities at the 5% significance level, and the trend curves of the moments of low flow are in close agreement with the curves estimated from the derived distribution with time‐dependent moments of the recession duration and time‐constant moments of the recession coefficient. It is indicated that the nonstationarity in the low‐flow distribution results from the nonstationarity in the recession duration in all 6 cases, and the increase in the recession duration is resulted from large‐scale ecosystem constructions rather than climate change. The large‐scale ecosystem constructions are found to have more influence on the decrease in streamflow than on the increase in watershed storage, thus resulting in the reduction of low flow. A high return period for the initial fixed design value decreases dramatically with an increasing recession duration. 相似文献
92.
In scientific communication, ambiguities in term usage can go unnoticed due not only to the distance between reader and writer but also to the existence of highly specialized scientific subcommunities. This commentary therefore aims at raising awareness about the use of terms that have different meanings within different hydrological subcommunities such as field hydrology, hydrological modelling, or statistical hydrology. To do so, we discuss the use of the following commonly used hydrological terms: sample, runoff, discharge, and streamflow. We performed three types of analyses to provide evidence of term usage and understanding, including both qualitative and quantitative approaches: a drawing exercise, a survey, and a literature corpus analysis. These analyses allow for a comparison of spontaneous definitions and the actual use of these terms in scientific publications. Our various information sources revealed that the dialogue between hydrologists within and across subdisciplines is substantially influenced by personal conceptualizations of terms that are not always shared across conversational partners. The terms discussed and illustrated in this commentary have to be seen as a small sample used to demonstrate the need for a thoughtful use of hydrological terms when communicating research, not only to a general audience but even across subdisciplines within hydrology. 相似文献
93.
94.
文章采用SWOT-AHP分析法对舟山海岛休闲业的优势、劣势、机遇和挑战4方面设定指标14项,并进行研究分析,结果表明:舟山海岛休闲产业有良好的区位、资源和政策优势,舟山海岛休闲产业面临的形势,依次为:机遇、优势、劣势、威胁,产业优势和机遇处于利好位置,但同时面临着一系列如缺乏统一规划、产品特色不突出、缺乏完善的管理体制机制、竞争中同质化情况明显等问题。针对此现状及问题提出科学规划可持续发展、完善管理体制机制、强化市场宣传,提升知名度、倡导生态旅游,提升环保意识、加强产品创新及人才培养等建议,以促进舟山海岛休闲业的稳步发展,给舟山及我国海岛休闲业的发展提供一些参考,以实现我国海岛休闲产业的品质化与多元化,促进海岛休闲产业的蓬勃发展。 相似文献
95.
在无气象数据的条件下,提出一种基于集合经验模态分解(EEMD)和季节性自回归移动平均模型(SARIMA)的对流层延迟(ZTD)预报新方法,并分别选取长春、上海、乌鲁木齐3个地区4个季节的ZTD数据进行预测分析。结果表明,基于EEMD-SARIMA的ZTD改正预报模型能够满足不同地区、不同季节下的ZTD估计需求,是一种高精度的ZTD预报方法。 相似文献
96.
Determining sediment provenance allows a better understanding of fluvial palaeo-dynamics, and identifying involved watersheds, at broad spatio-temporal scales. Conventional approaches for source identification are usually based on the physical, mineralogical, geochemical, magnetic or isotopic properties of sediments. Rapid, non-destructive and, in well-established contexts, highly accurate, mid-infrared spectroscopy is an alternative method for investigating sediment sources. The present research objectives are: (i) to use the mid-infrared spectroscopy method to discriminate the provenance of fine sediments, by applying discriminant analysis on a large set of reference samples from three different watersheds in the Upper Rhine area (associated with the Rhine, Ill and Vosges tributaries); (ii) to clarify whether the provenance spectra signatures are influenced by riverine depositional contexts (bars versus banks) and, to some extent, by grain size and/or high organic matter content; and (iii) to apply the mid-infrared spectroscopy – discriminant analysis method to a study of fluvial palaeo-dynamics and determine the provenance of palaeo-channel infillings. Three main sedimentary sources, divided into eight sub-categories, have been characterized by 196 modern reference samples from 78 collecting sites. Discriminant analysis displayed a strong separating power by classifying correctly the origin of samples without any inter-group overlap, independently from the geomorphological context (bar or bank) and associated slight changes in organic matter contents or grain size. Mid-infrared spectroscopy – discriminant analysis investigations of the palaeo-channel infill, complemented by radiocarbon dates and mineralogical data, allowed reconstructing general trends for the local morpho-sedimentary dynamics over the last ca 12 millennia. 相似文献
97.
针对现有烟包上包机存在的占地面积过大,易发生掉包以及移动困难等问题,设计了一种基于可编程逻辑控制器(PLC)控制的新型烟包上包机。该设备采用提升链条为输送装置,可以对烟包进行垂直运输,从而减小占地面积;以托盘作为烟包输送的载体,可以使烟包在上包过程中放置平稳,减小掉包的可能性。利用SolidWorks软件完成整机机械结构的三维建模,采用PLC控制系统来控制烟包上包机的上包作业流程。与传统的烟包上包机相比,该新型烟包上包机具有占地面积小,上包作业过程运行平稳,操作简单轻便等优点,可适应多种工作场所。 相似文献
98.
Wei-Cui Ding Ting-Dong Li Xuan-Hua Chen Jian-Ping Chen Sheng-Lin Xu Yi-Ping Zhang Bing Li Qiang Yang 《地学前缘(英文版)》2020,(2):651-663
The West Junggar Orogenic Belt(WJOB)in northwestern Xinjiang,China,is located in the core of the western part of the Central Asian Orogenic Belt(CAOB).It has suffered two stage tectonic evolutions in Phanerozoic,before and after the ocean–continental conversion in Late Paleozoic.The later on intracontinental deformation,characterized by the development of the NE-trending West Junggar sinistral strike-slip fault system(WJFS)since Late Carboniferous and Early Permian,and the NW-trending Chingiz-Junggar dextral strike-slip fault(CJF)in Mesozoic and Cenozoic,has an important significance for the tectonic evolution of the WJOB and the CAOB.In this paper,we conduct geometric and kinematic analyses of the WJOB,based on field geological survey and structural interpretation of remote sensing image data.Using some piercing points such as truncated plutons and anticlines,an average magnitude of^73 km for the left-lateral strike-slip is calculated for the Darabut Fault,a major fault of the WJFS.Some partial of the displacement should be accommodated by strike-slip fault-related folds developed during the strike-slip faulting.Circular and curved faults,asymmetrical folds,and irregular contribution of ultramafic bodies,implies potential opposite vertical rotation of the Miao’ergou and the Akebasitao batholiths,resulted from the sinistral strike-slipping along the Darabut Fault.Due to conjugate shearing set of the sinistral WJFS and the dextral CJF since Early Mesozoic,superimposed folds formed with N–S convergence in southwestern part of the WJOB. 相似文献
99.
Omid Ghaffaripour Golnaz A. Esgandani Arman Khoshghalb Babak Shahbodaghkhan 《国际地质力学数值与分析法杂志》2019,43(11):1919-1955
This paper presents the first application of an advanced meshfree method, ie, the edge-based smoothed point interpolation method (ESPIM), in simulation of the coupled hydro-mechanical behaviour of unsaturated porous media. In the proposed technique, the problem domain is spatially discretised using a triangular background mesh, and the polynomial point interpolation method combined with a simple node selection scheme is adopted for creating nodal shape functions. Smoothing domains are formed on top of the background mesh, and a constant smoothed strain, created by applying the smoothing operation over the smoothing domains, is assigned to each smoothing domain. The deformation and flow models are developed based on the equilibrium equation of the mixture, and linear momentum and mass balance equations of the fluid phases, respectively. The effective stress approach is followed to account for the coupling between the flow and deformation models. Further coupling among the phases is captured through a hysteretic soil water retention model that evolves with changes in void ratio. An advanced elastoplastic constitutive model within the context of the bounding surface plasticity theory is employed for predicting the nonlinear behaviour of soil skeleton. Time discretisation is performed by adopting a three-point discretisation method with growing time steps to avoid temporal instabilities. A modified Newton-Raphson framework is designed for dealing with nonlinearities of the discretised system of equations. The performance of the numerical model is examined through a number of numerical examples. The state-of-the-art computational scheme developed is useful for simulation of geotechnical engineering problems involving unsaturated soils. 相似文献
100.
原有非连续变形分析(DDA)采用一阶近似后的位移增量表达式更新块体构形,推导相关子矩阵,且对不同时步计算出的应变增量直接叠加,当模拟的块体发生大转动时往往会产生较大误差。为考虑块体转动与变形的耦合作用,引入先变形、后转动的块体位移增量表达式。重新推导了惯性力子矩阵,将块体转动时的离心力与科氏力加到荷载矩阵中。计算时对应变分量及其相关变量进行坐标变换与修正,并采用新引入的位移增量表达式计算块体顶点位移,进行后接触修正与更新块体构形。数值算例表明,改进后的程序能够消除转动带来的误差,自动考虑了块体转动时离心力和科氏力引起的变形,应变计算精度更高。改进方法克服了块体体积自由膨胀、应变场畸变等问题,给出了合理的块体应变。 相似文献