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1.
Input energy is the principal component of the energy balance equation. It is beneficial to determine, through its components, how the recoverable and irrecoverable energies are distributed within the structural elements. Several equations and attenuation relations to define mass-normalized input energy spectra exist in the literature. They are mainly proposed for elastic systems subjected to far-fault EQs. There is a lack of experimental verification of these proposed spectra. In this paper, experimental assessment was performed to the existing spectra, and further improvements were accomplished. For this purpose, steel cantilever columns were tested on the shake table for two specific historical EQs coincidently having similar spectral acceleration values. Based on the experimental results, a three-part mass-normalized relative input energy spectrum was formulated including soil type, EQ (corner period, intensity, duration, spectral acceleration, and velocity), and structural behavioral characteristics (period and structural damping). The proposed input energy spectrum was experimentally calibrated and numerically validated for various EQs featuring near- and far-field types. Analytical and experimental comparisons were made between the previously developed spectrum and the newly proposed one. The validation studies and the statistical evaluations exposed that the proposed spectrum yielded better agreement with the experimental and numerical results.  相似文献   
2.
刘敏  姜会明  姜天龙 《地理科学》2020,40(12):2037-2045
按照粮食的产销情况,将全国划分为3类粮食功能区域,利用固定效应模型和门槛效应模型分析了农机投入对农业绿色全要素生产率(GTFP)的影响及门槛效应的区域差异。结果表明:农机投入对农业GTFP的影响程度存在区域异质性,农机投入对粮食主销区农业GTFP提升的促进作用最大,粮食产销平衡区次之,粮食主产区最小;农机投入对农业GTFP的影响路径亦存在区域差异,粮食主产区和产销平衡区的农机投入通过促进农业技术效率和农业技术进步进而推动农业GTFP提升,粮食主销区的农机投入通过促进农业技术进步推动农业GTFP提升;农机投入对粮食主产区农业GTFP的影响存在双门槛效应,对粮食主销区和产销平衡区农业GTFP的影响存在单门槛效应。  相似文献   
3.
The isotopic composition of precipitation (D and 18O) has been widely used as an input signal in water tracer studies. Whereas much recent effort has been put into developing methodologies to improve our understanding and modelling of hydrological processes (e.g., transit‐time distributions or young water fractions), less attention has been paid to the spatio‐temporal variability of the isotopic composition of precipitation, used as input signal in these studies. Here, we investigated the uncertainty in isotope‐based hydrograph separation due to the spatio‐temporal variability of the isotopic composition of precipitation. The study was carried out in a Mediterranean headwater catchment (0.56 km2). Rainfall and throughfall samples were collected at three locations across this relatively small catchment, and stream water samples were collected at the outlet. Results showed that throughout an event, the spatial variability of the input signal had a higher impact on hydrograph separation results than its temporal variability. However, differences in isotope‐based hydrograph separation determined preevent water due to the spatio‐temporal variability were different between events and ranged between 1 and 14%. Based on catchment‐scale isoscapes, the most representative sampling location could also be identified. This study confirms that even in small headwater catchments, spatio‐temporal variability can be significant. Therefore, it is important to characterize this variability and identify the best sampling strategy to reduce the uncertainty in our understanding of catchment hydrological processes.  相似文献   
4.
To investigate the sources of particulate organic matter (POM) and the impact of Three Gorges Dam (TGD), two large lakes and erosion processes on determining the composition and flux of POM in low water discharge periods along the middle and lower Changjiang, suspended particulate samples were collected along the middle and lower reaches of the Changjiang (Yangtze River) in January 2008. Organic geochemistry of bulk sediment (particulate organic carbon, organic carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ13C) and grain size) and biomarker of bulk sediment (lignin phenols) were measured to trace the sources of POM. The range of C/N ratios (6.4–8.9), δ13C (?24.3‰ – ?26.2‰) and lignin phenols concentration Λ8 (0.45 mg/100 mg OC‐2.00 mg/100 mg OC) of POM suggested that POM originated from the mixture of soil, plant tissue and autochthonous organic matter (OM) during the dry season. POM from lakes contained a higher portion of terrestrial OM than the mainstream, which was related to sand mining and hydropower erosion processes. A three end‐member model based on δ13C and Λ8 was performed. The results indicated that soil contributed approximately 50% of OM to the POM, which is the dominant OM source in most stations. POM composition was affected by total suspended matter (TSM) and grain size composition, and the direct OM input from two lakes and channel erosion induced OM. The lower TSM concentration in January 2008 was mainly caused by seasonal variations; the impact from the TGD in the dry season was relatively small. A box model indicated that more than 90% of the terrestrial OM transported by the Changjiang in January 2008 was from the middle and lower drainage basins. Channel erosion induced OM, and contributions from Poyang Lake were the major terrestrial OM sources in the dry season. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
5.
This article illustrates the results of a study aimed at developing a methodology for the automatic identification of the seismic input at outcropping rock sites and flat topographic conditions necessary to carry out non-linear dynamic analysis of structures and geotechnical systems. The seismic input is provided in terms of a set of 7 natural accelerograms recorded on outcropping rock and satisfying the average spectral compatibility requirements prescribed by the Italian seismic code (NTC08).The study focuses on the territory encompassing Tuscany region in Central Italy and it has been carried out for six return periods, which are 50, 75, 101, 475, 712 and 949 years. The procedure involved four main steps: (1) grouping of the response spectra with similar features; (2) definition of the reference response spectrum for each group; (3) selection of spectrum-compatible accelerograms using the reference response spectrum of each group; and (4) linear scaling of the accelerograms to satisfy the compatibility requirement with respect to other response spectra of the group. The last step is implemented through an interactive, user-friendly program named SCALCONA 2.0, which provides the seismic input in agreement with the site location and return period specified by the user. The program is freely available at the following web site: http://www.rete.toscana.it/sett/pta/sismica/01informazione/banchedati/input_sismici/progettazione/index.htm.  相似文献   
6.
考虑到多维地震输入对网架结构的不利影响,基于形状记忆合金超弹性,研制出一种兼具自复位、高耗能及放大功能于一体的形状记忆合金复合黏滞阻尼器(Hybrid Shape Memory Alloy Viscous Dampers,简称HSMAVD),并通过试验研究该阻尼器在循环荷载作用下的力学性能;然后以平面四角锥网架模型为基础,将该阻尼器替换部分网架结构杆件,并分析该阻尼器减震控制效果。结果表明形状记忆合金与黏滞阻尼器复合后具有良好的协同工作能力,可有效发挥形状记忆合金的超弹性和黏滞阻尼器的速度相关特性,使其具有稳定的滞回性能和良好的耗能能力;采用阻尼杆件替换原杆件的方法既能对结构进行有效的减震控制,又不改变原有的结构形式,是一种优越的减震控制方法,并为HSMAVD被动控制系统在结构抗震中的实际应用提供新思路。  相似文献   
7.
姚虞  刘天云  张建民 《地震工程学报》2015,37(2):324-328,348
提出三维问题的波函数组合法求解不规则河谷的散射问题,应用到高面板坝动力有限元计算的地震动输入中,可以满足非一致输入的要求,并回避人工边界对外行波的反射问题。重点介绍三维问题的波函数组合法的理论推导和程序的算例验证,并给出将该方法应用到高面板坝地震动输入的基本步骤。  相似文献   
8.
9.
江西鄱阳湖地区土壤酸化与人为源氮的关系   总被引:4,自引:0,他引:4  
江西鄱阳湖地区是我国土壤酸化严重的地区之一,对比研究区多目标区域地球化学调查与第二次土壤普查资料发现,研究区土壤酸化趋势严重,强酸性土壤占研究区面积比例由58.22%上升到78.44%;赣江、抚河水系入湖区和饶河流域表层土壤酸化明显。研究区因施肥、大气干湿沉降和灌溉输入到农田的氮素分别为123.84 kg.hm-.2a-1、74.13 kg.hm-.2a-1、11.02 kg.hm-.2a-1。研究区因人为氮带入农田的H+为18.67 kmol.hm-.2a-1。化肥氮是引起土壤酸化的主控因素,氮沉降也是影响土壤酸化的主要因素之一。土壤pH与氮含量呈较差负相关,说明土壤中的有机氮对土壤酸化作用有限,增施有机肥和复合肥,适当减少氮肥,特别是铵态氮肥的比例,可以补充盐基物质的相对不足,达到缓解土壤酸化的作用。土壤pH与钙含量呈极显著正相关,适量增施含钙物质可以有效地防止表层土壤酸度降低。  相似文献   
10.
Fuzzy logic controller (FLC) performance is greatly dependent on its inference rules. In most cases, the more rules being applied to an FLC, the accuracy of the control action is enhanced. Nevertheless, a large set of rules requires more computation time. As a result, an FLC implementation requires fast and high performance processors. This paper describes a simplified control scheme to design a fuzzy logic controller (FLC) for an underwater vehicle namely, deep submergence rescue vehicle (DSRV). The proposed method, known as the single input fuzzy logic controller (SIFLC), reduces the conventional two-input FLC (CFLC) to a single input FLC. The SIFLC offers significant reduction in rule inferences and simplifies the tuning process of control parameters. The performance of the proposed controller is validated via simulation by using the marine systems simulator (MSS) on the Matlab/Simulink® platform. During simulation, the DSRV is subjected to ocean wave disturbances. The results indicate that the SIFLC, Mamdani and Sugeno type CFLC give identical response to the same input sets. However, an SIFLC requires very minimum tuning effort and its execution time is in the orders of two magnitudes less than CFLC.  相似文献   
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