Trends and risk evolution of drought disasters in Tibet Region,China     

Chen  Qiong  Liu  Fenggui  Chen  Ruijie  Zhao  Zhilong  Zhang  Yili  Cui  Peng  Zheng  Du 《地理学报(英文版)》2019,29(11):1859-1875

Journal of Geographical Sciences - The risk posed by natural disasters can be largely reflected by hazard and vulnerability. The analysis of long-term hazard series can reveal the mechanisms by...  相似文献   

Penetration response of spudcans in layered sands     

《Applied Ocean Research》2019

The behaviour of spudcan foundations during the installation and preloading in two-layer sand sediments was investigated through large deformation finite element (LDFE) analyses. The LDFE analyses were carried out using the coupled Eulerian-Lagrangian approach, modifying Mohr-Coulomb soil model to capture hardening and subsequent softening effects of sand. Parametric analyses were undertaken varying the top layer thickness, relative density of sand and spudcan diameter. Both loose to medium dense-over-dense and dense-over-loose to medium dense sand deposits were explored. The results showed that, for the investigated relatively thin top layer thickness of ≤ 5 m, spudcan behaviour was dictated by the bottom sand layer with a minimal influence of the top layer. For assessing the penetration resistance profile in two-layer sands, the performance of the ISO, SNAME, InSafeJIP, and other existing theoretical design methods were evaluated.  相似文献   

A finite element approach for predicting the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay     

《Applied Ocean Research》2019

This paper presents a finite element approach to calculate the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay, in which a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure exists. A modified Mohr-Coulomb model characterized by incorporating a four-phase variation of the mobilized strength and dilation parameters with an equivalent accumulated plastic strain is developed and tested for the overlying dense silica sand. An extended Tresca model is used for the strain softening of the underlying clay. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength and dilation parameters as well as the spudcan geometries. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data, allowing the numerical study to be extended parametrically. The four-phase variation of the mobilized strength and dilation parameters involved in the progressive failure of the upper dense sand is parametrically studied and extended to cover the range of sand relative densities that are of practical interest. Additionally, comparisons with the typical existing LDFE analyses using both simple and sophisticated constitutive models are carried out. It shows that the present approach performs fairly well to calculate the full resistance profile of a spudcan deeply penetration in both thin and thick dense sand overlying clay, especially the peak and post-peak resistance, within around 5% of the corresponding centrifuge tests results.  相似文献   

相对剥夺视角下的乡村旅游地居民不规范行为研究 ——以江西婺源县李坑、思溪为例   总被引：3，自引：1，他引：2  

王文辉  白冰  张茵 《地理科学》2019,39(11):1814-1821

居民不规范行为危害性极大,传统相关研究多基于社会交换视角,存在一定局限。相对剥夺理论在研究人们的不规范行为上存在一定优势,但鲜有应用于旅游研究。以社区问题明显的李坑、思溪两村落为例,结合相对剥夺理论对居民不规范行为的成因和形式等进行了定性分析。与传统研究不同,发现居民不规范行为与其对旅游负面影响的纵向感知并无直接关系,而主要与横向剥夺感相关。研究表明,相对剥夺理论或可作为居民旅游态度和行为研究的新视角,并在预防和管控旅游地社区问题方面具有重要现实意义。  相似文献   

浮力装置触发深海管道水平向整体屈曲效果的数值模拟研究     

曹洋  张淑华  孙林 《海洋通报》2019,38(6):719-726

海洋油气资源的运输主要通过海底管道进行,管道在工作时受到较大的温度荷载,会产生整体屈曲变形。深海管道设计中常采用人为装置触发一定程度的水平向整体屈曲变形,来释放轴向的温度应力,浮力装置是常用的触发方式之一。本文通过数值模拟研究,分析了不同浮力大小和不同浮力施加范围下,管道水平向整体屈曲的临界屈曲力,得出临界屈曲力随浮力大小和施加范围变化的情况;并研究了不同土体阻力下,浮力装置触发整体屈曲的效果。研究表明,水平向土体阻力较大时,浮力装置触发水平向整体屈曲的效果较好。浮力装置的触发效果对轴向土体阻力不敏感。  相似文献   

A geospatial study of the drought impact on surface water reservoirs: study cases from Texas,USA     

Zachary Asbury 《地理信息系统科学与遥感》2019,56(6):894-910

Satellite images have been used historically to measure and monitor fluctuations in the surface water reservoirs. This study integrates remote sensing and Geographic Information System (GIS) technologies to investigate the impact of drought on 10 selected surface water reservoirs in San Angelo and Dallas, Texas. Oscillations in summer and winter months throughout the 2005–2016 period were assessed using multispectral images from Landsat-5, ?7, and ?8, and changes in the reservoirs were characterized and correlated against local climate data of each reservoir. For quantitative comparisons of the time-series measurements, a robust density slicing approach was employed to classify the range of values of the raster cells in the near-infrared band of Landsat images for each lake into three desired classes (deep water, shallow water, and dry area) based on the natural breaks inherent in the dataset. Statistical analysis shows that the overall accuracy of the classification is about 94%, which demonstrates the efficiency of the density slicer to accurately estimate surface water area changes from an individual Landsat band. Shrinkage in the surface water area over the study period reveals the concrete impact that the drought along with other factors have on the 10 selected lakes. The San Angelo lakes located in west central Texas experienced a nearly consistent pattern of change during most of the study period; whereas the Dallas lakes in northeast Texas followed the oscillating pattern of drought and correlated closely to the local conditions. Shockingly, the extreme drought caused complete vanishing of several lakes, and consequently Texas had to remove them from its recreational plans. Our new findings can certainly help with the water resource management in Texas and our study approach can be adapted for monitoring lake oscillations in other areas across the world. This geospatial study demonstrates the societal benefits from incorporating remote sensing and GIS in investigating geo-environmental problems associated with severe climate changes.  相似文献   

顾及空间非平稳特征的遥感干旱监测     

朱欣然  黄长平  吴波  苏华  焦文哲  张立福 《遥感学报》2019,23(3):487-500

遥感技术具备实时快速、时空连续、广覆盖尺度等独特优势,在全球气候恶化大背景下,利用遥感干旱监测方法相比于传统地面监测手段,能够提供实时、准确、稳定的旱情信息,辅助科学决策。目前常用遥感旱情监测方法大多依赖全域性数学模型建模,假定了旱情模式的空间平稳特性,因而难以准确反映旱情模式的局部差异特征。本文提出利用地理加权回归模型GWR (Geographically Weighted Regression),考虑旱情模式的空间非平稳特性,综合多种遥感地面旱情监测指数,以实现传统全域旱情监测模型的局部优化。以美国大陆为研究区,监测2002年—2011年共10年的旱情状态。研究表明,GWR模型能够提供空间变化的局部最佳估计模型参数,监测结果更加吻合标准美国旱情监测USDM (U.S Drought Monitor)验证数据,且与地面实测值的最高相关系数R达到0.8552,均方根误差RMSE达到0.972,显著优于其他遥感旱情监测模型。GWR模型具备空间非平稳探测优势,实现了旱情模式的局部精细探测,能够显著提升遥感旱情监测精度,具备较好的应用前景。  相似文献   

随机森林算法在全球干旱评估中的应用   总被引：2，自引：0，他引：2  

方秀琴  郭晓萌  袁玲  杨露露  任立良  朱求安 《地球信息科学学报》2021,23(6):1040-1049

干旱是发生频率最高,造成社会、经济损失和生态破坏最严重、最广泛的自然灾害之一,因此对干旱进行可靠、有效的评估十分重要.本文以月平均降水、月平均温度、月最高温度、月最低温度、土壤湿度、蒸散发、NDVI、叶绿素荧光等作为解释变量,以基于SPI的干旱等级作为目标变量,采用随机森林算法,以2007-2012年的数据作为训练数据...  相似文献   

潜艇指挥台围壳对阻力和伴流场影响数值研究   总被引：2，自引：0，他引：2  

吴方良  吴晓光  马运义  张志国  何汉保 《海洋工程》2009,27(3):91-99

采用Reynolds平均Navier-Stokes(RANS)方法计算潜艇三维粘性流场,分析潜艇指挥台围壳对潜艇水动力性能的影响.采用全附体SUBOFF模型验证了CFD方法,通过将螺旋桨盘面处的实效伴流场、艇体表面压力分布以及模型总阻力的模拟结果与Taylor船池的实验结果进行对比.比较结果显示CFD计算结果与实验数据具有很好的一致性,表明CFD方法可以用于潜艇指挥台围壳设计的水动力计算.通过数值计算研究指挥台围壳的高度和在艇上的分布位置对其后方的流场、螺旋桨盘面处的伴流场和阻力的影响.  相似文献   

利用NOAA-AVHRR数据分析1982-2001年间中国植被的动态变化(英文)   总被引：1，自引：0，他引：1  

HABIB Aziz Salim  陈晓玲  龚健雅  王海燕  张俐 《地球空间信息科学学报》2009,12(2):146-153

The authors derived the normalized difference vegetation index (NDVI) from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index (NDVI) in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China’s vegetation cover h...  相似文献