A view on capsizing under direct and parametric wave excitation

The behavior of a ship that is simultaneously heaving, swaying and rolling in waves is examined by using an early developed model by Thompson et al. [Thompson, J. M. T., Rainey, R. C. T. and Soliman, M. S. (1992) Mechanics of ship capsize under direct and parametric wave excitation. Philosophical Transactions of the Royal Society London A 338, 471-490]. A second-order nonlinear differential equation has been used as a mathematical model which is analyzed by using numerical methods to obtain geometrical phase space techniques of nonlinear dynamics. Bifurcation diagrams and Poincaré maps are two of the geometrical techniques used in this study. The result of the calculation is given to allow the naval architect to make a self comparison.     

Assessing sediment transport dynamics from energy perspective by using the instrumented particle

Sediment transport has been extensively studied. There is still a need to learn more about the mechanisms that make bed particles move, which is caused by turbulent flow in the low transport stages(above the motion threshold and below continuous transport). This work is focused on the use of an advanced tool to obtain a better perception of sediment transport dynamical methods: an instrumented particle equipped with a micro-electromechanical systems(MEMS) sensor. Particle transport experiments w...     

河口区斜压梯度对余水位的累积影响及其机制探讨

余水位（即潮平均水位）是河口区径潮相互作用的典型结果,研究其形成演变机制对探讨河口区的水资源高效开发利用具有重要科学意义。本文基于不同径潮边界条件下的三维斜压水动力数值模拟及切比雪夫机制分解,初步探讨了概化地形条件下斜压梯度对余水位沿程变化的影响。数值模拟结果表明:河口区余水位的沿程变化明显受径流量、潮波振幅、辐聚地形及斜压梯度等因素的共同影响,斜压梯度对余水位的影响是一种累积效应且影响区域集中在回水区,同时其影响强度具有明显的大小潮变化、洪枯季变化。利用数值模型提供的水位及流速场信息,通过切比雪夫分解非线性摩擦项分离出控制余水位变化的3个主要因素,即径流、潮流和径潮相互作用因子,并与斜压梯度产生的余水位进行对比分析,结果表明:回水区域余水位主要以径潮相互作用因子为主导;斜压梯度对余水位影响主要体现在小潮期间,有可能成为影响余水位变化的主控因子。     

Spatio-temporal Characteristics of Area Coverage and Observation Geometry of the MISR Land-surface BRF Product: A Case Study of the Central Part of Northeast Asia

The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.     

Key morphological changes and their linkages with stream power and land-use changes in the Upper Tapi River basin,India

Knowledge on spatio-temporal variations in planform, hydraulic geometry, and bed-level variations of alluvial streams is required for planning and development of hydraulic structures and bank protection works. In the current study, a Geographic Information System (GIS) has been used to analyze topographical maps, multi-temporal remotely sensed imagery, and hydrologic and hydraulic data to extract the morphological parameters of the Upper Tapi River, India. The river has been found to have consistent migration towards the northern direction, with erosion/deposition on right/left banks. The river has not experienced any major meander except in the lower reaches of the Upper Tapi Gorge and minor braiding conditions at the location where the river emerges from mountainous topography to the plain region. The analyzed river cross sections were found to be depth dominated, and contain large flows within the channel banks. The cross-sections exhibited moderate channel bed adjustments in 1994, 2006, and 2007 wherein excessive sediment flux and stream power were capable of causing morphological changes in the river. High intensity rainfall in the subcatchment resulted in high sediment flux into the river during 1994, which was reported to cause significant aggradation at the downgauging station. The analysis of sediment flux into the river in conjunction with decadal land use land cover, revealed that sediment yield from the catchment was reduced during 2000–2010 due to an increase in water bodies in the form of minor hydraulic structures. The entry of comparatively less sediment laden water into the river, resulted in moderate bed degradation especially in 2006 and 2007 as observed at the downstream station. The methodology applied in the current study is generic in nature and can be applied to other rivers to identify their morphological issues.     

宜兴丁蜀镇土地质量地球化学等级评价中的空间分析

在江苏宜兴丁蜀镇土地质量地球化学等级评价中,以当地的土地利用类型图（层）为基础,采用图层交叠分析和Voronoi图相结合的方法,对评价单元作了进一步的划分,并确定了各单元的控制样点。取得了样点与控制单元之间的良好对应效果。概述了部分相关空间分析的算法。     

数值模拟方法验证光透法监测流体饱和度的有效性:以非均质孔隙介质中的水/气两相流为例

光透法作为一种安全经济的非侵入监测方法广泛应用于室内砂箱多相流实验中,但该方法在局部空间点上结果的可 靠性尚缺乏验证。鉴于当前难以采用实验手段直接进行局部监测点取样验证光透法结果,本文以非均质孔隙介质中的水/气 两相流为例,基于砂箱实验开展了数值模拟研究以进行论证。研究表明：（1） 模拟结果中气体在非均质含水层中的迁移规 律、展布形态和饱和度分布总体上再现了光透法的测量结果。（2） 数值模拟和光透法得到的6个局部点饱和度数据在各时 刻均拟合较好。同时选取12个时刻共5316个监测点的饱和度数据进行分析,其决定系数达0.94,这表明模拟结果从统计 角度较好地验证了光透法在局部点监测上的有效性,两者间的差异主要由人工填砂导致的介质“不均匀”引起。（3） 气体 总量方面,实测排水值、模拟结果与光透法计算结果均拟合较好。因此数值模拟结果系统地验证了光透法监测流体饱和度 的有效性。     

语义与几何相结合的道路网融合研究与实现

道路网是最重要的地理空间要素之一,空间数据融合能够把不同来源道路空间数据或信息加以结合,以获得信息量更丰富或更适于处理、分析、决策的新的数据集。传统的方法受限于道路网数据模型、属性数据类型以及缺少唯一标识的属性信息,道路网融合方法多以各个弧段或道路的位置、形状、方向等几何特征进行匹配,而忽略了道路的语义匹配。本文在数据来源与技术分析的基础上,提出了一种在工程化应用中可行的语义与几何相结合的道路网匹配方法,并通过FME实现空间数据融合,旨在为两个或多个道路网数据融合、联动更新提供方法参考。     

超高压——高压剪切带

超高压－高压剪切带是大陆碰撞造山过程中变质－变形分解作用形成的一类特殊的剪切带。剪切带内的构造以含柯石英、金刚石等超高压－高压矿物的榴辉岩、面理化超基性－基性岩、片麻岩、大理岩为特征，具有复杂的变形组构和变形历史。最终形成布丁－基质或残斑－基质结构。深入研究超高压－高压剪切带的几何学、运动学和流变学特征，对分析超高压－高压变质岩石的形成－折返过程及碰撞造山动力学，具有重要的实际和理论意义。     

三峡工程运用对近期荆江段平滩河槽形态调整的影响

针对近期荆江段河槽形态的显著调整,定量研究了三峡工程运用对其造成的影响。计算了2002—2013年该河段断面及河段尺度的平滩河槽形态参数,并建立这些参数与宜昌站汛期水流冲刷强度的经验关系。还原了在无三峡工程时宜昌站的水沙数据,计算了相应的河槽形态参数,分析了有、无三峡工程时荆江段河槽形态调整的差异。计算结果表明:三峡工程运用后近期荆江段平均河床比降略有调平,河段平滩水深逐年增加,但平滩河宽变化较小,使得河相系数减少6.7%~10.3%;无三峡工程时平滩河槽形态调整较缓,河段平滩水深及面积的增幅分别仅占有三峡工程时的16%和18%。故三峡工程运用没有改变近期荆江段河槽形态趋于窄深的调整趋势,但一定程度上加快了调整过程。