Continuous flushing of contaminants from ballast water tanks     

Eames I  Landeryou M  Greig A  Snellings J 《Marine pollution bulletin》2008,56(2):250-260

The transport of non-indigenous species (NIS) with ship ballast water is a major environmental problem. The International Maritime Organisation (IMO) have recommended that ballast tanks are flushed through with sea water to remove NIS contaminants. The flushing efficiency is studied using mathematical models and a scaled experimental model of a ballast tank. The density contrast between the ballast water and water used for flushing is important when the Froude number Fr(w)=U(w)/sqr rt|g(')|H < 1 (defined in terms of average horizontal flow U(w), reduced buoyancy g', and H the vertical dimension in the tank). When denser water is used to flush a ballast tank, from below, it efficiently displaces lighter ballast water; but flushing through with light water creates a buoyant gravity current which effectively short circuits part of the tank. When Fr(w)>1, the density contrast between the ballast water and water used for flushing is not important and flushing is controlled by a bulk Péclet number, Pe(w). For Pe(w)<1 perfect mixing occurs, while for Pe(w)>1 displacement flushing occurs. Laboratory experiments of flushing were performed using a model two-dimensional ballast tank employing dye attenuation to measure the whole concentration field and these experiments confirm the essential features of the mathematical models. The results of this study are discussed in the context of current IMO flushing protocols.  相似文献   

Physical and coupled fully three-dimensional numerical modeling of pressurized bottom outlet flushing processes in reservoirs     

Ousmane Sawadogo  Gerrit R. Basson  Simon Schneiderbauer 《国际泥沙研究》2019,34(5):461-474

Sediment deposition in reservoirs is an important research topic in engineering practice. Reservoir sedimentation has the potential to affect ood levels, drainage for agricultural land, pump station and hydropower operation as well as navigation. This paper describes the development of a coupled fully three-dimensional (3D) numerical model for the prediction of the local sediment ushing scour upstream of the bottom outlet. The presented numerical model solves the Navier-Stokes equations in conjunction with the k- turbulence model which includes both sediment transport and hydrodynamic parameters. The proposed coupled fully 3D numerical model is used to simulate experimental tests based on non-cohesive sediment. The geometric features of the scour hole (temporal and spatial hole devel- opment) upstream of the bottom outlet were reasonably well predicted compared to the experimental data. Furthermore, the velocity eld upstream of the bottom outlet was in good agreement with mea- surements. The proposed numerical model for bottom outlet ushing was, therefore, validated because of its ability to accurately predict the scour hole development during the ushing process. The proposed numerical model can be considered reliable provided that the model is correctly calibrated and set up to re ect the conditions of a particular case study.  相似文献   

Response characteristics of DOC flushing in an alpine catchment     

Elizabeth W. Boyer  George M. Hornberger  Kenneth E. Bencala  Diane M. McKnight 《水文研究》1997,11(12):1635-1647

The spatial distribution of source areas and associated residence times of water in the catchment are significant factors controlling the annual cycles of dissolved organic carbon (DOC) concentration in Deer Creek (Summit County, Colorado). During spring snowmelt (April–August 1992), stream DOC concentrations increased with the rising limb of the hydrograph, peaked before maximum discharge, then declined rapidly as melting continued. We investigated catchment sources of DOC to streamflow, measuring DOC in tension lysimeters, groundwater wells, snow and streamflow. Lysimeter data indicate that near-surface soil horizons are a primary contributor of DOC to streamflow during spring snowmelt. Concentrations of DOC in the lysimeters decrease rapidly during the melt period, supporting the hypothesis that hydrological flushing of catchment soils is the primary mechanism affecting the temporal variation of DOC in Deer Creek. Time constants of DOC flushing, characterizing the exponential decay of DOC concentration in the upper soil horizon, ranged from 10 to 30 days for the 10 lysimeter sites. Differences in the rate of flushing are influenced by topographical position, with near-stream riparian soils flushed more quickly than soils located further upslope. Variation in the amount of distribution of accumulated snow, and asynchronous melting of the snowpack across the landscape, staggered the onset of the spring flush throughout the catchment, prolonging the period of increased concentrations of DOC in the stream. Streamflow integrates the catchment-scale flushing responses, yielding a time constant associated with the recession of DOC in the stream channel (84 days) that is significantly longer than the time constants observed for particular locations in the upper soil. © 1997 John Wiley & Sons, Ltd.  相似文献   

深圳市征地拆迁信息系统的设计与实现     

卢永华 《测绘信息与工程》2010,35(6):23-24,27

提出了征地拆迁信息管理系统的总体目标和建设内容,陈述了系统的结构设计和数据库设计,分析了系统的主要技术特点。  相似文献   

Investigation of hydraulics transport time scales within the Arvand River estuary,Iran          下载免费PDF全文

Amir Etemad‐Shahidi  Mostafa Pirnia  Hengameh Moshfeghi  Charles Lemckert 《水文研究》2014,28(25):6006-6015

Transport time scales are key parameters for understanding the hydrodynamic and biochemical processes within estuaries. In this study, the flushing and residence times within the Arvand River estuary have been estimated using a two‐dimensional hydrodynamic model called CE‐QUAL‐W2. The model has been calibrated and verified by two different sets of field data and using the k‐ε vertical eddy diffusivity scheme. Flushing time has been estimated using different methods such as the tidal prism and fraction of freshwater methods. Moreover, residence times have been investigated using pulse residence time, estuarine residence time and remnant function approaches. The results have shown that different methods yield different time scales, and freshwater inflow has the greatest impact upon estimation of residence time, whereas tidal circulation hardly contributes to residence time at all. It has also been shown that the neap‐spring circulation and start phase of simulations have negligible effects on the Arvand's time scales. The investigation of bathymetry showed that two sills of the estuary tend to significantly increase residence time. Understanding the applicability of these time scales and their estimation approaches helps us to evaluate the water quality management of estuaries. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

寨上矿区复杂地层钻探技术   总被引：5，自引：0，他引：5       下载免费PDF全文

尹建国  刘青山  夏文彬  杨增智 《探矿工程》2012,39(6):42-45

针对甘肃省岷县寨上矿区构造发育,地层破碎,断裂带厚度大,钻孔缩径、漏失、坍塌,岩心采取率低,孔内事故多等钻进难题,采用植物胶泥浆、PAB无固相冲洗液、多层套管护壁技术,以及试验运用Q系列钻具和射流式绳索取心局部反循环钻具取心等措施,取得了较好的效果。  相似文献   

陕西金龙山矿区复杂地层典型钻孔施工工艺          下载免费PDF全文

习辉  王政敏  杨增智 《探矿工程》2014,41(8):29-32

介绍了陕西金龙山矿区ZK744孔钻探施工工艺,重点阐述了冲洗液护壁堵漏技术,总结了钻孔前期施工失败的教训和后期施工的成功经验,可为类似矿区的钻孔施工提供借鉴。  相似文献   

The role of inflow magnitude and frequency on plankton communities from the Guadalupe Estuary,Texas, USA: Findings from microcosm experiments     

Carrie J. Miller  Daniel L. Roelke  Stephen E. Davis  Hsiu-Ping Li  George Gable 《Estuarine, Coastal and Shelf Science》2008

Changes in magnitude and frequency of inflow results in subsequent alterations in the delivery of nutrients essential for phytoplankton growth and competition producing variations in community composition and nutritional value of phytoplankton. Zooplankton demographics are likely directly influenced by pulsed inflows due to flushing losses, whereas they are also indirectly affected by changes in prey quality. In this study, we report the potential effect of pulsed inflows on the plankton community of the Guadalupe Estuary. Microcosms were used that allowed control of light intensity and photoperiod, turbulence, temperature, nutrient loading, and flushing magnitude and periodicity. Our microcosm experiments were novel as they utilized natural plankton communities, thereby allowing the simultaneous interaction between hydrology, resource availability and grazing. Results show differences in microcosms according to magnitude and frequency of flushing. For example, copepod population density was greatest at the annual mean inflow magnitude. At half the annual mean inflow a decline in prey quality likely resulted in poorer grazer performance, and at double the annual mean inflow magnitude increased flushing losses prevented the incidence of higher copepod densities. Similarly, pulsed inflows resulted in greater copepod population densities, higher overall phytoplankton biomass, and dominance of centric diatoms (known to be faster growing and more edible). While reduced freshwater inflow associated with increasing anthropogenic demands often strains the needs of estuarine systems, the effects of reduced river input may be alleviated with several management options including manipulation of the timing, frequency, and magnitude of freshwater inflows. Before implications for management can be discerned from these findings, however, larger scale experiments are needed focus on the roles of inflow magnitude and frequency.  相似文献   

Hydrological versus biogeochemical controls on catchment nitrate export: a test of the flushing mechanism     

Carlos J. Ocampo  Carolyn E. Oldham  Murugesu Sivapalan  Jeffrey V. Turner 《水文研究》2006,20(20):4269-4286

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新疆哈密白山钼矿深孔钻探施工工艺          下载免费PDF全文

马德义  贾宏福  廖志新  付兆友  盖志鹏 《探矿工程》2011,38(5):28-31

介绍了新疆哈密白山钼矿深孔钻探施工工艺。就深孔施工的一些关键问题,如钻孔结构,设备选型,钻头选择,冲洗液选用与维护,深孔防斜等进行了探讨。  相似文献