On the morphology of radial sand ridges     

Weina Zhang  Xiaohe Zhang  Huiming Huang  Yigang Wang  Sergio Fagherazzi 《地球表面变化过程与地形》2020,45(11):2613-2630

We use a hydrodynamic model applied to an idealized fan-shaped basin to explore the morphology and dynamics of radial sand ridges in a convergent coastal system. A positive morphological feedback between channel incision and flow redistribution is responsible for the formation of the channel-ridge pattern. The selection mechanism of bottom wavelength is associated with flow concentration in the deeper part of the channels. Our results are compared to sediment and hydraulic dynamics in the radial sand ridges (RSRs) in China. In a convergent, sloping basin the tangentially averaged tidal velocity peaks at 47 km from the apex. This distance is similar to the arc distance, 62 km, where the RSRs are most incised. An offshore shift in tidal phase results in stronger flows near the north coastline, explaining the presence of asymmetric channel patterns. A numerical stability analysis indicates that small radial oscillations with a wavelength of 10° to 15° maximize the velocity in the troughs. This oscillation wavelength also emerges in the RSRs, which display a peak in spectral energy at a radial wavelength between 25° to 37.5°. High-resolution numerical simulations in the RSRs confirm that flow concentration occurs in the deeper part of the channels, keeping them flushed. We therefore conclude that the RSRs display morphometric characteristics similar to other tidal incisions, like tidal inlets and intertidal channels. This result further supports the dominant role of tidal prism and related peak velocities in incising coastal landscapes. © 2020 John Wiley & Sons, Ltd.  相似文献   

Inter- and intra-annual trend analysis of water level and flow in the middle and lower reaches of the Ganjiang River,China     

Di Zhu  Yue Ben  Xinfa Xu 《水文科学杂志》2020,65(12):2128-2141

ABSTRACT

The Ganjiang River is the largest tributary of Poyang Lake in China, and its hydrological regime variation greatly affects the utilization of regional water resources and the ecological environment of the lake. In this study, a novel trend analysis method, the Moving Average over Shifting Horizon (MASH), was applied to investigate the inter- and intra-annual trends of flow and water level from 1976 to 2016 at the Xiajiang and the Waizhou hydrological stations in the Ganjiang River. The Significant Change Rate Method (SCRM) was proposed to determine the MASH averaging parameters. The trend analysis results show a statistically significant decrease in water level series throughout the year and the relationship of flow and water level have changed greatly at the Waizhou station. The sediment load reduction, large-scale sand mining and water level decrease of Poyang Lake are identified as the main causes for the water level decrease.  相似文献   

连续弯箱梁自行车桥地震响应分析          下载免费PDF全文

施有志  林四新  阮建凑  林树枝 《地震工程学报》2020,42(5):1208-1216

为研究厦门市弯箱梁自行车桥的地震响应规律，采用SAP2000有限元软件建立自行车高架桥三维壳体模型，在考虑多遇地震和罕遇地震水准作用及不同加载方向的基础上，分别采用反应谱分析法和时程分析法进行该桥的动力响应分析。结果表明：自行车桥z方向位移分量最大，且z方向分量极值均发生在曲线分叉段；相对剪力而言，桥墩竖向支反力相对较小；E1和E2地震水准响应情况随时间的变化趋势基本一致，桥梁结构未进入塑形状态，抗震性能良好，安全性指标较高；反应谱法计算得到的响应包络值相对3条不同的地震时程结果的峰值大，在实际桥梁抗震分析过程中需要综合考虑两者的分析结果。文章研究结果对今后自行车桥设计和抗震性能分析具有指导意义，并可为研究者对该类桥的进一步研究提供借鉴。  相似文献   

Estimating the starting time and identifying the type of urbanization based on dense time series of landsat-derived Vegetation-Impervious-Soil (V-I-S) maps – A case study of North Taiwan from 1990 to 2015     

《International Journal of Applied Earth Observation and Geoinformation》2020

Land cover and land use change (LCLUC) is a global phenomenon, and LCLUC in urbanizing regions has substantial impacts on humans and their environments. In this paper, a semi-automatic approach to identifying the type and starting time of urbanization was developed and tested based on dense time series of Vegetation-Impervious-Soil (V-I-S) maps derived from Landsat surface reflectance imagery. The accuracy of modeled V-I-S fractions and the estimated time of initial change in impervious cover were assessed. North Taiwan, one of the regions of the island of Taiwan that experienced the greatest urban LCLUC, was chosen as a test area, and the study period is 1990 to 2015, a period of substantial urbanization. In total, 295 dates of Landsat imagery were used to create 295 V-I-S fraction maps that were used to construct fractional cover time series for each pixel. Root Mean Square Error (RMSE)s for the modeled Vegetation, Impervious, and Soil were 25 %, 22 %, 24 % respectively. The time of Urban Expansion is estimated by logistic regression applied to Impervious cover time series, while the time of change for Urban Renewal is determined by the period of brief Soil exposure. The identified location and estimated time for newly urbanized lands were generally accurate, with 80% of Urban Expansion estimated within ±2.4 years. However, the accuracy of identified Urban Renewal was relatively low. Our approach to identifying Urban Expansion with dense time series of Landsat imagery is shown to be reliable, while Urban Renewal identification is not.  相似文献   

Analysis and Comparison for Fusion Algorithms of Time Transfer     

WANG Wei-xiong  DONG Shao-wu  WU Wen-jun  GUO Dong  ZHANG Jian 《Chinese Astronomy and Astrophysics》2021,45(2):224-235

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基于斩波轮技术的K波段接收机噪声校准研究          下载免费PDF全文

王凯  王洋  陈卯蒸  段雪峰  闫浩  马军  陈晨雨  曹亮 《天文学报》2020,61(1):1

接收机是射电天文中用于探测微弱射电信号的重要接收设备.接收机的强度校准就是将接收机对射电源的响应转换为天文意义上的流量密度.常规方法就是使用经典的冷热负载法,将接收机自身的强度响应转换为一个等效的温度值,之后再据此对射电源做进一步标定.通过搭建基于斩波轮技术的K波段接收机强度校准平台,使用斩波轮法测试K波段常温接收机的噪声温度,并与传统冷热负载法的测试结果进行比对.结果显示,在晴好天气条件下,斩波轮法在30°、90°仰角下噪声温度的最大测试误差为7.5%和8.4%,可以很好地应用于实际噪声温度测试中;但在5°仰角测试中,由于过低仰角引入了地面噪声,使得斩波轮法的测试误差上升至20%–30%之间而无法使用.希望在此基础上进一步开展K波段天空亮温度的理论计算与实测,从而完善斩波轮技术的应用,使之可以满足在不同气象条件下的噪声校准测试需求.  相似文献   

基于分段副产物瞬时选择性的反应器网络综合     

胡仰栋  周勇  伍联营 《中国海洋大学学报(自然科学版)》2020,50(3):61-66

针对第三类反应体系的反应器网络综合问题,提出将串联反应以反应物到目的产物的反应步数为依据的新分段策略。通过比较不分段目的产物、不分段目的产物和中间产品、分段副产物和分段目的产物这四种不同的瞬时选择性,提出以分段副产物瞬时选择性为参数,以其对关键组分浓度或转化率的导数为依据选择各阶段最合适的反应器,以目的产物总选择性最大为目标采用遗传算法优化反应器网络。通过三个实例验证了本文所建立方法在解决复杂反应反应器网络综合问题的有效性,且本方法同样适用于简单反应体系。  相似文献   

中国土地利用空间格局刻画方法研究   总被引：7，自引：1，他引：6  

鞠洪润  左丽君  张增祥  赵晓丽  汪潇  温庆可  刘芳  徐进勇  刘斌  易玲  胡顺光  孙菲菲  汤占中 《地理学报》2020,75(1):143-159

土地利用空间格局研究是土地利用/覆盖变化（LUCC）理论和实践的基础,对土地利用空间格局进行有效刻画有利于国土资源空间优化,提升土地利用规划和管理水平。由于土地利用空间格局的研究范畴尚不明晰,目前土地利用空间格局的研究对形状、斑块分布和结构等方面关注较少,缺乏对不同土地利用类型间相互关系的研究;同时,格局指标繁多且存在较大的相关性,如何建立指标与土地利用空间格局的对应关系值得进一步研究。本文在深刻理解土地利用空间格局内涵的基础上,将面积、形状和斑块分布总结为土地利用几何特征,将结构和多样性总结为土地利用类型特征,建立了土地利用空间格局刻画指标体系,利用模糊C均值聚类分析,明确了指标与空间格局间的对应关系。结果表明,中国土地利用几何特征可以划分为简单大斑块型、复杂大斑块型、复杂小斑块型、简单小斑块型和散布型五种,不同的几何特征反映了不同土地利用类型的面积、形状和斑块分布的特点,体现了区域土地利用类型的组合关系。2010年中国土地利用共存在61种不同的结构,但主要的结构类型仅有14种,结构特征具有明显的空间聚集性,体现了不同土地利用类型的空间分异性。中国土地利用多样性以3~5类为主,占比达66.69%,其特征总体上呈现“东北、东南高,西北低”的态势。该研究丰富了土地利用空间格局研究的理论体系,填补了中国土地利用整体空间格局刻画的空白。  相似文献   

Adding the missing third and fourth dimensions to trajectory analysis in carbonate systems     

Philipp Tesch  Robert S. Reece  James R. Markello  Juan Carlos Laya  Michael C. Pope 《Basin Research》2020,32(2):388-401

We developed a seismic geomorphology-based procedure to enhance traditional trajectory analysis with the ability to visualize and quantify lateral variability along carbonate prograding-margin types (ramps and rimmed shelves) in 3D and 4D. This quantitative approach analysed the shelf break geometric evolution of the Oligo-Miocene carbonate clinoform system in the Browse Basin and delineated the feedback between antecedent topography and carbonate system response as controlling factor on shelf break rugosity. Our geometrical analysis identified a systematic shift in the large-scale average shelf break strike direction over a transect of 10 km from 62° to 55° in the Oligo-Miocene interval of the Browse Basin, which is likely controlled by far-field allogenic forcing from the Timor Trough collision zone. Plotting of 3D shelf break trajectories represents a convenient way to visualize the lateral variability in shelf break evolution. Shelf break trajectories that indicate contemporaneous along-strike progradation and retrogradation correlate with phases of autogenic slope system re-organization and may be a proxy for morphological stability of the shelf break. Shelf break rugosity and shelf break trajectory rugosity are not inherited parameters and antecedent topography does not dictate long-term differential movement of the shelf margin through successive depositional sequences. The autogenic carbonate system response to antecedent topography smooths high-rugosity areas by filling accommodation and maintains a relatively constant shelf break rugosity of ~150 m. Color-coding of the vertical component in the shelf break trajectory captures the creation and filling of accommodation, and highlights areas of the transect that are likely to yield inconsistent 2D sequence stratigraphic interpretations.  相似文献   

基于组合权重与灰色关联度分析法的地铁深基坑开挖稳定性评价     

郎秋玲  王伟  高成梁 《吉林大学学报(地球科学版)》2020,50(6):1823-1832

伴随着城市的快速发展，地铁深基坑工程越来越多。在开挖过程中如何对其稳定性进行评价，是当前需要重点关注的问题。以成都地铁十七号线凤溪站深基坑支护开挖工程为依托，利用层次分析确定的主观权重与利用熵值法确定的客观权重计算获得组合权重，并与灰色关联度分析法相结合，通过现场数据采集并进行综合评判，客观评价地铁深基坑开挖的稳定性。结果表明，各监测项目对基坑稳定性的重要程度从大到小依次为桩顶水平位移（0.29）、地表沉降（0.24）、建筑物沉降（0.19）、桩顶沉降（0.18）、内支撑轴力（0.10），基坑稳定性综合评判结果等级为"非常好"。所建立的评价模型可为类似地铁深基坑开挖稳定性评价提供新的方法。  相似文献