Concentration–discharge relationships reflect chemostatic characteristics of US catchments

Concentration–discharge relationships have been widely used as clues to the hydrochemical processes that control runoff chemistry. Here we examine concentration–discharge relationships for solutes produced primarily by mineral weathering in 59 geochemically diverse US catchments. We show that these catchments exhibit nearly chemostatic behaviour; their stream concentrations of weathering products such as Ca, Mg, Na, and Si typically vary by factors of only 3 to 20 while discharge varies by several orders of magnitude. Similar patterns are observed at the inter‐annual time scale. This behaviour implies that solute concentrations in stream water are not determined by simple dilution of a fixed solute flux by a variable flux of water, and that rates of solute production and/or mobilization must be nearly proportional to water fluxes, both on storm and inter‐annual timescales. We compared these catchments' concentration–discharge relationships to the predictions of several simple hydrological and geochemical models. Most of these models can be forced to approximately fit the observed concentration–discharge relationships, but often only by assuming unrealistic or internally inconsistent parameter values. We propose a new model that also fits the data and may be more robust. We suggest possible tests of the new model for future studies. The relative stability of concentration under widely varying discharge may help make aquatic environments habitable. It also implies that fluxes of weathering solutes in streams, and thus fluxes of alkalinity to the oceans, are determined primarily by water fluxes. Thus, hydrology may be a major driver of the ocean‐alkalinity feedback regulating climate change. Copyright © 2009 John Wiley & Sons, Ltd.     

INTERMODAL TRANSPORTATION IN NORTH AMERICA AND THE DEVELOPMENT OF INLAND LOAD CENTERS*

This paper analyzes the changes that are transforming intermodal transportation in the United States and Canada. Traffic is being concentrated at a relatively small number of inland load centers that serve as regional truck distribution points, and are linked by high volume dedicated train services. Both theoretical and practical implications of the changes are examined, and a range of research questions are presented.     

冲击荷载作用下新型延展式张力腿平台时域分析

延展式张力腿平台是一种适用于深水油气开采的海洋平台结构。提出一种新型平台由四个立柱和一个环形浮箱连接而成,环形浮箱是由四个箱型梁焊接而成。根据给出的南海海域的海况条件和相应的规范计算结构的环境载荷,运用SESAM软件Deep C模块,考虑风、浪、流等环境荷载的作用和张力腿系统的非线性影响,进行了时域耦合分析,得到了平台的运动位移时程、张力腿系统张力时程和张力极值等。模拟波浪破碎作为冲击载荷,得到张力腿平台在冲击荷载作用下的运动位移时程、张力腿系统的张力时程。研究结果表明:该新型平台具有良好的运动响应,张力筋腱应力满足安全要求;在冲击载荷作用下新型平台的运动响应也满足要求。     

An Experimental Study on A Trapezoidal Pendulum Wave Energy Converter in Regular Waves

Experimental studies were conducted on a trapezoidal pendulum wave energy converter in regular waves. To obtain the incident wave height, the analytical method (AM) was used to separate the incident and reflected waves propagating in a wave flume by analysing wave records measured at two locations. The response amplitude operator (RAO), primary conversion efficiency and the total conversion efficiency of the wave energy converter were studied; furthermore, the power take-off damping coefficients corresponding to the load resistances in the experiment were also obtained. The findings demonstrate that the natural period for a pendulum wave energy converter is relatively large. A lower load resistance gives rise to a larger damping coefficient. The model shows relatively higher wave energy conversion efficiency in the range of 1.0?1.2 s for the incident wave period. The maximum primary conversion efficiency achieved was 55.5%, and the maximum overall conversion efficiency was 39.4%.     

Ultimate Load Capacity of Offshore Pipeline with Arbitrary Shape Corrosion Defects

A set of generalized solutions are proposed for estimating ultimate load capacity of pipeline with arbitrary corrosion shapes subjected to combined internal pressure, axial force and bending moment. Isotropic and anisotropic material characteristics in longitudinal and circumferential direction of pipeline are also considered in the proposed equations. Simplified numerical method is used to solve the generalized expressions. The comparisons of numerical results based generalized solutions and full-scale experimental results are carried out. The predicted results agree reasonably well with the experiment results. Meanwhile, the effects of corrosion shapes and locations on the ultimate load capacity are studied.     

单线激光雷达扫描的矿车装载量核算方法

面向露天矿山生产对于矿车装载量核算的需求,本文提出了一种利用单线激光雷达扫描的矿车装载量自动核算方法。该方法首先采用固定式单线激光雷达对目标车辆进行俯视扫描,基于车辆形态特征分割出载荷物顶部点云;然后经时态校正,并与预先构建的车辆信息数据库进行匹配,重建出载荷物的三维表面模型;最后通过对载荷物表面模型的切片积分实现方量核算。以齐大山铁矿运输为例,对多台矿车装载量进行核算测试。结果表明,本文方法可在车辆正常行驶的情况下实时获取载荷物的表面三维点云,平均建模误差为2.54 cm,装载方量核算误差为1.17%。     

堆载下单桩负摩阻力工作性状非线性数值分析

利用三维非线性数值方法对一算例在堆载作用下桩侧负摩阻力进行了计算分析。计算结果揭示了摩擦型、端承型桩负摩阻力工作性状的异同;分析了堆载速度、桩顶荷载对负摩阻力的影响:堆载越快,负摩阻力越小;在无桩顶荷载作用下,由负摩阻力引起的下拉荷载最大,可视为常规方法设计的上限值;桩顶荷载与堆载施工顺序对负摩阻力的影响也很大,先施加桩顶荷载,后进行堆载所产生的负摩阻力最大,反之最小。     

Late Ordovician climbing‐dune cross‐stratification: a signature of outburst floods in proglacial outwash environments?

Climbing dune‐scale cross‐statification is described from Late Ordovician paraglacial successions of the Murzuq Basin (SW Libya). This depositional facies is comprised of medium‐grained to coarse‐grained sandstones that typically involve 0·3 to 1 m high, 3 to 5 m in wavelength, asymmetrical laminations. Most often stoss‐depositional structures have been generated, with preservation of the topographies of formative bedforms. Climbing‐dune cross‐stratification related to the migration of lower‐flow regime dune trains is thus identified. Related architecture and facies sequences are described from two case studies: (i) erosion‐based sandstone sheets; and (ii) a deeply incised channel. The former characterized the distal outwash plain and the fluvial/subaqueous transition of related deltaic wedges, while the latter formed in an ice‐proximal segment of the outwash plain. In erosion‐based sand sheets, climbing‐dune cross‐stratification results from unconfined mouth‐bar deposition related to expanding, sediment‐laden flows entering a water body. Within incised channels, climbing‐dune cross‐stratification formed over eddy‐related side bars reflecting deposition under recirculating flow conditions generated at channel bends. Associated facies sequences record glacier outburst floods that occurred during early stages of deglaciation and were temporally and spatially linked with subglacial drainage events involving tunnel valleys. The primary control on the formation of climbing‐dune cross‐stratification is a combination between high‐magnitude flows and sediment supply limitations, which lead to the generation of sediment‐charged stream flows characterized by a significant, relatively coarse‐grained, sand‐sized suspension‐load concentration, with a virtual absence of very coarse to gravelly bedload. The high rate of coarse‐grained sand fallout in sediment‐laden flows following flow expansion throughout mouth bars or in eddy‐related side bars resulted in high rates of transfer of sands from suspension to the bed, net deposition on bedform stoss‐sides and generation of widespread climbing‐dune cross‐stratification. The later structure has no equivalent in the glacial record, either in the ancient or in the Quaternary literature, but analogues are recognized in some flood‐dominated depositional systems of foreland basins.     

自升式钻井平台悬臂梁负荷试验方法研究

悬臂梁负荷试验是自升式钻井平台建造完工交付使用之前的关键试验项目之一.以200 ft自升式钻井平台“海洋石油923”为例,针对悬臂梁负荷试验方法做出了探索研究,试验结果表明,此方法行之有效,具有操作简便,安全可靠的优点,为其它类似工程项目的顺利实施提供了宝贵的经验和借鉴.     

Electricity generation and cooling water use: UK pathways to 2050

Thermoelectric generation contributes to 80% of global electricity production. Cooling of thermoelectric plants is often achieved by water abstractions from the natural environment. In England and Wales, the electricity sector is responsible for approximately half of all water abstractions and 40% of non-tidal surface water abstractions. We present a model that quantifies current water use of the UK electricity sector and use it to test six decarbonisation pathways to 2050. The pathways consist of a variety of generation technologies, with associated cooling methods, water use factors and cooling water sources. We find that up to 2030, water use across the six pathways is fairly consistent and all achieve significant reductions in both carbon and water intensity, based upon a transition to closed loop and hybrid cooling systems. From 2030 to 2050 our results diverge. Pathways with high levels of carbon capture and storage result in freshwater consumption that exceeds current levels (37–107%), and a consumptive intensity that is 30–69% higher. Risks to the aquatic environment will be intensified if generation with carbon capture and storage is clustered. Pathways of high nuclear capacity result in tidal and coastal abstraction that exceed current levels by 148–399%. Whilst reducing freshwater abstractions, the marine environment will be impacted if a shortage of coastal sites leads to clustering of nuclear reactors and concentration of heated water discharges. The pathway with the highest level of renewables has both lowest abstraction and consumption of water. Freshwater consumption can also be minimised through use of hybrid cooling, which despite marginally higher costs and emissions, would reduce dependence on scarce water resources thus increase security of supply.