Quantifying the suspended sediment discharge to the ocean from the Markham River,Papua New Guinea     

Ora Renagi  Peter Ridd  Thomas Stieglitz 《Continental Shelf Research》2010

The Markham River is a small river draining a tropical mountain range with altitudes between 1000 and 3000 m and discharges directly into a submarine canyon, the head of which is at 30 m depth and reaches depths of 500 m only 4 km from the shore. As such, the Markham discharge system serves as a possible analogue for rivers discharging onto margins during low stands of sea-level. Located in a tectonically active area and with high rainfall, sediment supply is high and episodic and is sometimes related to catastrophic mountain landslides. The river has an estimated sediment load of 12 Mt yr⁻¹. Occasionally, high energy flows are generated at the river mouth which is evident from the channel morphology and sediment distribution. Profiles of salinity and suspended sediment concentrations (SSC) show that sediment is dispersed via a plume with components at both the surface, intermediate depth along isopycnal surfaces and near the sea bed. The dispersal pattern of the surface freshwater plume is largely determined by the buoyancy force. The surface plume is very thin with salinity gradients 15 ppt m⁻¹ while a Richardson number greater than unity suggested that the mixing zone is highly stratified. Estimates of the horizontal sediment flux gradient of the surface plume along the estuary axis suggest that about 80% of the sediment discharged is lost from the plume within a distance of 2 km from the river mouth. Particle fall velocities estimated from the vertical flux indicate values less than those of flocculated material. Layers of sediment with SSCs between 500 and 1000 mg l⁻¹ were observed at intermediate depths and near the seabed during periods of both high and intermediate discharge. The mass of sediment in a SSC layer at intermediate depths between 150 and 250 m within the canyon channel was estimated to be equivalent to an average of 2 to 3 days of Markham sediment discharge. SSCs near the seabed of between 250 and 750 mg l⁻¹ suggest that layers of significantly elevated density exist near the seabed, moving under the influence of gravity down steep seabed slopes of the Markham canyon.  相似文献   

双重孔隙介质中P1波在自由边界上的反射   总被引：1，自引：0，他引：1  

贺鹏飞  夏唐代  刘志军  陈炜昀 《岩土力学》2016,37(6):1753-1761

对双重孔隙介质波动中的体波及P1波在半空间自由透水和不透水边界上的反射问题进行了详细的理论求解。通过数值计算,对双重孔隙介质中4种体波的弥散和衰减特性,以及不同边界上反射波振幅反射系数随P1波入射角和频率的变化进行了分析。结果表明：（1）P1、P2、P3和S波均具有弥散和衰减特性,P1波传播最快而衰减最慢,P3波传播最慢而衰减最快;（2）随着入射角的增大,反射P2、P3和S波的振幅反射系数均先增大后减小,反射P1波则先减小后增大,且边界透水条件对反射P2和P3波的振幅反射系数影响显著,对P1和S波的影响较小,但透水和不透水边界下振幅反射系数随入射角的变化趋势一致;（3）反射P2、P3波的振幅反射系数均随频率的增大而增大,且不透水边界下反射P2波的振幅反射系数大于透水边界下的反射系数,而反射P3波则相反;（4）随着频率增大,透水边界下反射P1波的振幅反射系数先增大后减小,不透水边界下先减小后增大再减小,反射S波的振幅反射系数随频率变化情况则与P1波相反。  相似文献   

不同地表条件下土壤冻结、融化规律分析   总被引：1，自引：0，他引：1  

杜琦 《地下水》2009,31(4):27-29

土壤温度是土壤热状况的综合表征指标,以深耕休闲裸地作为对照,分析了不同地表条件下土壤的冻融过程。结果表明,土壤的冻融作用具有阶段性,不同冻融阶段,土壤具有不同的冻结、融化特点。不同地表处理条件土壤的冻结、融化特点亦不同。  相似文献   

基于大涡模拟的小区气候态精细化风环境模拟试验     

姜平  刘晓冉  朱宇  曾文馨  朱浩楠 《气候与环境研究》2020,25(2):139-152

对具有复杂下垫面的小区精细化风环境进行数值模拟是当前城市气象研究的热点,而针对具有复杂地形的山地型城市（如重庆）的研究还比较匮乏。本文采用能显式分辨下垫面陡峭地形和复杂建筑物的计算流体力学（CFD）模式对重庆市渝北区龙湖社区气候态下的精细化风环境进行高分辨率的数值模拟。结果表明,下垫面能显著调节小区内风场的分布,风速大值区主要出现在九龙湖等开阔区域以及与中尺度背景入流方向一致的街道中。在夏季,小区整体风场以东南风为主,而其他3个季节则以偏东风为主。4个季节中,夏季小区内的风速最大,平均风速为0.3 m/s左右,局地能出现大于背景风的风速,可达0.8 m/s;其他3个季节的风速则较弱,区域平均的风速在0.2 m/s左右。不同的建筑物布局对局地风环境的影响也不同:单个孤立高层建筑迎风面的近地面存在明显地绕流,局地风速有所增加,而在背风面则形成尾流区,水平风速较低;在低矮分散的建筑群,建筑物的整体高度不高,区域内流场相对来说比较一致,风速较大,有利于小区的通风;在密集高层建筑群内,由于建筑物群本身的布局比较封闭,加之不同建筑物的环流场存在相互干扰及影响,使得小区近地面风速几乎为零,不利于小区通风和污染物扩散。建筑物的这些影响在城市冠层内尤为明显,高度越高这种影响越弱。  相似文献   

基于三维激光扫描的地铁隧道连续形变监测数据处理软件系统   总被引：1，自引：0，他引：1  

康志忠  托雷  王保前  谢远成 《测绘工程》2013,(5):82-86,96

利用地基三维激光扫描技术所具有的“形测量”特点,结合高精度、高空间分辨率的多时相点云数据,实现地铁隧道连续形变监测数据处理的软件系统。系统的主要功能包括：点云拼接、隧道中轴线拟合、断面连续截取、形变分析以及成果输出等。结合对上海某地铁隧道的多期激光扫描数据的处理,展示软件的主要功能和技术流程,最后对系统的应用前景进行阐述。  相似文献   

Global photometric properties of Asteroid (4) Vesta observed with Dawn Framing Camera     

Jian-Yang Li  Lucille Le Corre  Stefan E. Schröder  Vishnu Reddy  Brett W. Denevi  Bonnie J. Buratti  Stefano Mottola  Martin Hoffmann  Pablo Gutierrez-Marques  Andreas Nathues  Christopher T. Russell  Carol A. Raymond 《Icarus》2013

Dawn spacecraft orbited Vesta for more than one year and collected a huge volume of multispectral, high-resolution data in the visible wavelengths with the Framing Camera. We present a detailed disk-integrated and disk-resolved photometric analysis using the Framing Camera images with the Minnaert model and the Hapke model, and report our results about the global photometric properties of Vesta. The photometric properties of Vesta show weak or no dependence on wavelengths, except for the albedo. At 554 nm, the global average geometric albedo of Vesta is 0.38 ± 0.04, and the Bond albedo range is 0.20 ± 0.02. The bolometric Bond albedo is 0.18 ± 0.01. The phase function of Vesta is similar to those of S-type asteroids. Vesta’s surface shows a single-peaked albedo distribution with a full-width-half-max ∼17% relative to the global average. This width is much smaller than the full range of albedos (from ∼0.55× to >2× global average) in localized bright and dark areas of a few tens of km in sizes, and is probably a consequence of significant regolith mixing on the global scale. Rheasilvia basin is ∼10% brighter than the global average. The phase reddening of Vesta measured from Dawn Framing Camera images is comparable or slightly stronger than that of Eros as measured by the Near Earth Asteroid Rendezvous mission, but weaker than previous measurements based on ground-based observations of Vesta and laboratory measurements of HED meteorites. The photometric behaviors of Vesta are best described by the Hapke model and the Akimov disk-function, when compared with the Minnaert model, Lommel–Seeliger model, and Lommel–Seeliger–Lambertian model. The traditional approach for photometric correction is validated for Vesta for >99% of its surface where reflectance is within ±30% of global average.  相似文献   

Efficient 3D nonlinear Winkler model for shallow foundations     

H. El Ganainy  M.H. El Naggar 《Soil Dynamics and Earthquake Engineering》2009

This paper presents a new practical modeling approach, based on the beam-on-a-nonlinear Winkler foundation (BNWF) model, to simulate the 3D rocking, vertical and horizontal responses of shallow foundations using structural elements that are readily available in the element library of commercially available structural analysis programs. An assemblage of a moment-rotation hinge, shear hinge connected in series with an elastic frame member attached to the bottom end of ground story columns was proposed to model the response of the footing under combined action of vertical, horizontal and moment loading. To couple the responses of these hinges, two bounding surfaces equations were introduced and derived mathematically: a surface that defines the interaction between the rocking and vertical capacities of the footing along its width and length; and a surface that defines the interaction between the horizontal capacities of the footing along its width and length. Simple calculation steps to evaluate the geometric and mechanical properties of the proposed assemblage of structural elements are provided. The proposed modeling approach was verified using experimental results from large scale model foundations subjected to cyclic loading. Based on this study, it was found that the proposed assemblage can be reliably used in modeling the rocking and horizontal responses of shallow foundations under cyclic loading.  相似文献   

Review of Global Ocean Intermediate Water Masses: 1.Part A, the Neutral Density Surface (the ‘McDougall Surface’) as a Study Frame for Water-Mass Analysis     

Yuzhu You )  )  * ) The University of Sydney Institute of Marine Science 《中国海洋大学学报(英文版)》2006,(3)

1Preface Todescribeoceanicintermediatewatermasses,itis necessarytohaveawell definedstudyframeorsurfacebecauseofthefluctuationnatureofintermediatewa ters.Itiswellunderstoodthatoceanicwater mass mixingdoesnotalignwitheitheraconstantgeopoten tialdepthorapropertysurfacesuchastemperature,salinity,pressureanddensitysurfacesbutfollowsa neutraldensitysurface.Thisisbecauseawaterparcelmovesasmalldistanceisentropicallyandadiabaticallyontheneutraldensitysurfacewithoutdoingworka gainstabuoyantrestoringforc…  相似文献   

SOFTWARE REVIEWS     

《The Professional geographer》1988,40(3):343-347

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The early Cretaceous marine transgression and its significance for landscape interpretation     

《The Australian geographer》1991,22(2):178-184

Significant elements of the Australian landscape date from Mesozoic or earlier times. Australia did not separate completely from other Gondwanan components until Early Tertiary times and these Mesozoic and older elements can therefore be regarded as Gondwanan. During the separation and northern drift of the continent and particularly in Late Jurassic and earlier Cretaceous times the sea invaded and spread across much of the erstwhile landmass. The associated sediments not only covered and preserved much of the pre‐existing land surface, but they also augmented the effects of thalassostatic loading of the basins, causing further subsidence. Hinge lines developed near the coastal zones of the times, so that subsidence of the basins caused adjacent land masses to rise. Many old land surfaces have been re‐exposed at the former oceanic margins, but epigene forms are preserved high in the relief on the uplifted blocks. They survive partly because, as Crickmay (1976) suggested, rivers effectively erode at and near their channels; the divides remain untouched. A reinforcement effect also operates because the valleys are wet sites, the interfluves dry. Hence weathering and erosion proceed apace in the former while the latter are stable, allowing palaeoforms to survive.  相似文献