A NEW NUMERICAL METHOD FOR GROUNDWATER FlOW AND SOLUTE TRANSPORT USING VELOCITY FIELD
ert与染色示踪方法在土壤入渗监测中的应用
（2）根据ERT反演后计算得到的电阻率值，将其与实测的含水量数据用改进后的Archie公式拟合，获得了含水量与电阻率之间的定量关系，其拟合度为0.765，相关性较好，能较为准确地反映含水量与电阻率之间的关系。
（3）利用ERT监测田间土壤水分运动时，在入渗初期，入渗区域土壤的表层电阻率迅速降低，随着时间的延续，表层电阻率的变化逐渐减小；比较试验不同时刻土壤水分入渗剖面和亮蓝溶液入渗剖面，发现土壤水分的入渗速度比亮蓝溶液的入渗速度要快；在亮蓝溶液入渗的过程中，由于上部土壤会对亮蓝溶液产生吸附，所以在优先流区域引起电阻率变化的主要原因是水分的运动；在入渗量特别大时，水分会在渗透性较差的区域产生积聚。
（4）将系列二维电阻率剖面信息导入到V oxler软件转换成三维空间电阻率分布模型，得到了更加丰富的地电断面信息，可以更清晰地反映土壤水分入渗过程。
通过将二维电阻率剖面信息与三维电阻率立体信息相对比，发现三维电阻率模型能够准确地反映土壤水分运动过程。
（5）利用Photoshop图像处理软件将入渗试验结束时的土壤染色剖面图像处理成为二值图像，并统计分析土壤剖面染色比例在垂直方向上的变化，发现随着入渗量的增大，亮蓝的最大染色深度、均匀染色范围、优先流的均匀程度都随之增加。
关键词：土壤；ERT；染色示踪；水分入渗；Hydrus-1D；数值模拟Application of ERT and dye tracing method in monitoring soilwater infiltrationAbstractThe precipitation infiltrates to the soil and turns into soil water,then soil water flows through the unsaturated zone (or vadose zone) to the surface of groundwater and recharges groundwater. Soil water and groundwater are the most important components of water resources in arid and semi-arid regions. In order to ensure the sustainable utilization of water resources, it is necessary to estimate the groundwater recharge rate. In recent years, with the development of economy and the improvement of people's living standard, the water resources in Qingdao are becoming increasingly scarce. The Dagu river is an important water source in Qingdao, but it faces many problems such as the decline of groundwater level, the seawater intrusion, and the pollution of groundwater though the basin area is vast. So exploring the soil water infiltration process is one of the key researches on these issues. In the past twenty years, the Electrical Resistivity Tomography method (ERT) as a new hydro geophysical technology has been widely used in the study, because of its non-destruction, temporal continuity and high resolution characteristics. Otherwise, the dye tracer test has been paid more and more attention because it can clearly and intuitively reflect the soil water flow path.To understand the process of water movement in soil, this paper conducted a total indoor soil water infiltration experiment and field soil water infiltration experiment, analyzed in different infiltration conditions, water movement process in homogeneous soil and heterogeneous soils. In the indoor soil column infiltration experiments, the soil moisture sensor installed on different depth of soil column to monitor profile variation of soil moisture in water infiltration process. And using different models simulated water movement. The field water infiltration experiment was carried out in the Luncun of Jimo city in Dagu River downstream. Setting 2~4 measuring line, two frames were arranged in the center of the measuring line. The inner frame infiltrated 3g/L brilliant blue solution, while the outer frame infiltrated water, and the height of water and brilliant blue solution must keep 3 cm. Using the DCX-1G multi function and high density electrical instrument -- real-time imaging system (ERT) monitored variation of resistivity before infiltration and infiltration process and after the infiltration in situ. The 2-D resistivity information were collated and imported into the 3D V oxler software, realizing the conversion from two-dimensional to three-dimensional, it can observe the soil water infiltration process more clearly. And using Hydrus-1D software simulated soil water movement. At the end of the experiment, along the inner frame excavated section every 5~10 cm, and using the camera recorded the profile of dyes. The research of this paper drawsthe following conclusions:(1)Through the analysis of the indoor infiltration experiment, it was found that the infiltration rate of water was large at the beginning of infiltration, and the cumulative infiltration rate changed rapidly. With the passage of time, the infiltration rate decreased gradually and tended to be stable. The infiltration process can be simulated by Philip model and Kostiakov model, and the fitting degree of Kostiakov model was better; the process of infiltration and redistribution process can be simulated by Hydrus-1D,and the simulation results of the former was better, but the simulation results of the latter was slightly worse.(2)Through fitting the resistivity values calculated by ERT and measured the water content data used Archie formula, the quantitative relationship between them were determined, the fitting degree between them was 0.765, the correlation was good. So the fitting formula can accurately describe the quantitative relationship between resistivity and water content.(3)In the early infiltration, soil resistivity was decreased rapidly, with the passage of time, the variation of surface resistivity decreased. According to the comparison of resistivity between water infiltration profile and brilliant blue solution infiltration profile, it was found that water moved faster than brilliant blue. In the process of brilliant blue solution infiltration, the brilliant blue solution can be adsorpted by upper soil, so the main reason of resistivity changes in preferential flow area was water movement. And when the infiltration amount is large, the water will accumulate in the poor permeability region.(4)A series of 2D resistivity profile information loaded into the V oxler software and converted into a three-dimensional resistivity distribution model, which can be used to enrich the information of the geoelectric section. It was found that the 3D resistivity model can accurately reflect the process of soil water movement by comparing with the 2D resistivity profile.(5)The Photoshop image processing software was used to process the image of the soil profile to be a two value image. By statistical analysing soil profile changes in dyeing ratio in the vertical direction, it was found that with the infiltration volume increased, the maximum dyeing depth, uniform dyeing range, preferential flow uniformity increased.Key words: Soil; ERT; Dye tracer; Water infiltration;Hydrus-1D; Numerical simulation目录第一章绪论 (1)1.1 研究目的及意义 (1)1.2 国内外研究进展 (2)1.2.1 高密度电阻率成像法研究进展 (2)1.2.2 染色示踪技术研究进展 (3)1.2.3 土壤水分入渗研究进展 (5)1.3 主要研究内容与技术路线 (6)第二章实验材料与方法 (8)2.1 研究区概况 (8)2.2 土壤基本物理性质的测定 (8)2.3 土壤水分特征曲线的测定 (9)2.4 室内入渗实验 (14)2.5 田间入渗试验 (15)2.6 高密度电法简介 (16)2.7 Hydrus-1D模型简介 (20)第三章室内土柱水分入渗的时空变化及数值模拟 (22)3.1 累积入渗量随时间的变化特征 (22)3.2 土壤压力水头随时间变化规律 (23)3.3 不同模型模拟室内土柱水分运移 (27)3.3.1 Kostiakov模型和Philip模型模拟室内土柱水分运移 (27)3.3.2 Hydrus-1D模型模拟室内土柱水分运移 (29)第四章基于高密度电阻率成像法的田间土壤水分入渗过程 (34)4.1 土壤水分含量与电阻率之间的定量关系 (34)4.2 ERT二维反演土壤水分入渗过程 (35)4.2.1 异常点的剔除 (36)4.2.2 试验I土壤水分入渗过程 (37)4.2.3 试验II土壤水分入渗过程 (40)4.3 土壤水分入渗过程三维图像显示 (50)4.3.1 试验I土壤水分入渗过程三维图像显示 (51)4.3.2 试验II土壤水分入渗过程三维图像显示 (53)4.3.3 试验III土壤水分入渗过程三维图像显示 (55)4.4 Hydrus-1D模拟田间水分入渗过程 (57)第五章土壤染色示踪剖面分析 (64)5.1 土壤染色剖面图像处理 (64)5.1.1 土壤染色剖面图像获取 (64)5.1.2 土壤染色剖面图像处理过程 (65)5.2 染色剖面分析 (65)第六章结论与展望 (76)6.1 结论 (76)6.2 存在的不足及展望 (77)参考文献 (78)攻读学位期间的研究成果 (84)致谢 (85)学位论文独创性声明 (86)学位论文知识产权权属声明 (86)第一章绪论第一章绪论1.1 研究目的及意义土壤水是指存在于地表以下包气带中的水，在四水转化中具有重要地位，是联系地下水、地表水和大气水之间的纽带，是水资源的重要组成部分[1-3]。
groundwatermodeling system
groundwatermodeling systemGroundwater modeling systems are computer-based tools used to simulate and analyze the flow and behavior of groundwater in an aquifer. These systems typically consist of software programs that utilize mathematical models and algorithms to generate simulations and predictions of groundwater flow patterns, contaminant transport, and water resource management.Groundwater modeling systems can be used for a variety of purposes, including:1. Aquifer characterization: Groundwater models can help in assessing the physical properties and behavior of aquifers, such as permeability, hydraulic conductivity, and water level fluctuations.2. Water resource management: By simulating different scenarios, groundwater models can assist in decision-making related to water supply, allocation, and optimization of groundwater pumping rates.3. Contaminant transport analysis: Models can simulate the transport of contaminants in groundwater, helping to understand the potential impact of pollution sources and develop remediation strategies.4. Climate change impact assessment: Groundwater models can be used to assess the impact of climate change on groundwater resources, such as changes in recharge rates, water availability, and vulnerability to drought.5. Land-use planning and management: Models can assist inevaluating the potential impacts of land-use changes on groundwater resources, facilitating better land management decisions.Groundwater modeling systems typically require input data such as hydrogeological parameters, meteorological data, and information about groundwater extraction rates and contaminant sources. The output of these systems includes visualizations of groundwater flow patterns, water level fluctuations, contaminant concentrations, and various other parameters.Some widely used groundwater modeling systems include MODFLOW (developed by the US Geological Survey), FEFLOW, and Visual MODFLOW. These systems offer a range of features and capabilities, allowing hydrogeologists and water resource professionals to better understand and manage groundwater resources.。
托福阅读TPO28（试题+答案+译文）第1篇：Groundwater
托福阅读TPO28(试题+答案+译文)第1篇:Groundwater为了帮助大家备考托福。
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托福阅读原文【1】Most of the world’s potable water—freshwater suitable for drinking is accounted for by groundwater, which is stored in the pores and fractures in rocks. There is more than 50 times as much freshwater stored underground than in all the freshwater rivers and lakes at the surface. Nearly 50 percent of all groundwater is stored in the upper 1,000 meters of Earth. At greater depths within Earth, the pressure of the overlying rock causes pores and cracks to close, reducing the space that pore water can occupy, and almost complete closure occurs at a depth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.Aquifers, Porosity and Permeability【2】Groundwater is stored in a variety of rock types. A groundwater reservoir from which water can be extracted is called an aquifer. We can effectively think of an aquifer as a deposit of water. Extraction of water depends on two properties of the aquifer: porosity and permeability. Between sediment grains are spaces that can be filled with water. This pore space is known as porosity and is expressed as a percentage of the total rock volume. Porosity is important for water—storage capacity, but for water to flow through rocks, the pore spaces must be connected. The ability of water, or other fluids, to flow through the interconnected pore spaces in rocks is termed permeability. In the intergranular spaces of rocks, however, fluid must flowaround and between grains in a tortuous path; this winding path causes a resistance to flow. The rate at which the flowing water overcomes this resistance is related to the permeability of rock.【3】Sediment sorting and compaction influence permeability and porosity. The more poorly sorted or the more tightly compacted a sediment is, the lower its porosity and permeability. Sedimentary rocks—the most common rock type near the surface—are also the most common reservoirs for water because they contain the most space that can be filled with water. Sandstones generally make good aquifers, while finer-grained mudstones are typically impermeable. Impermeable rocks are referred to as aquicludes. Igneous and metamorphic rocks are more compact, commonly crystalline, and rarely contain spaces between grains. However, even igneous and metamorphic rocks may act as groundwater reservoirs if extensive fracturing occurs in such rocks and if the fracture system is interconnected.The Water Table【4】The water table is the underground boundary below which all the cracks and pores are filled with water. In some cases, the water table reaches Earth’s surface, where it is expressed as rivers, lakes and marshes. Typically, though, the water table may be tens or hundreds of meters below the surface. The water table is not flat but usually follows the contours of the topography. Above the water table is the vadose zone, through which rainwater percolates. Water in the vadose zone drains down to the water table, leaving behind a thin coating of water on mineral grains. The vadose zone supplies plant roots near the surface with water.【5】Because the surface of the water table is not flat but instead rises and falls with topography, groundwater is affectedby gravity in the same fashion as surface water. Groundwater flows downhill to topographic lows. If the water table intersects the land surface, groundwater will flow out onto the surface at springs, weather to be collected there or to subsequently flow farther along a drainage. Groundwater commonly collects in stream drainages but may remain entirely beneath the surface of dry stream-beds in arid regions. In particularly wet years, short stretches of an otherwise dry stream-bed may have flowing water because the water table rises to intersect the land surface.[Glossary]Sediment: materials (such as sand or small rocks) that are deposited by water, wind, or glacial ice.Topography: the shape of a surf ace such as Earth’s, including the rise and fall of such features as mountains and valleys.托福阅读试题1.In paragraph 1, why does the author mention "the pressure of the overlying rock"?A.To show how water can be forced deep under Earth's surface.B.To show why groundwater is more plentiful than surface freshwater.C.To correct a commonly made error about the location of groundwater.D.To explain why most groundwater lies near Earth's surface.2.According to paragraph 1, groundwater differs from the water in riversand lakes in terms of itsA.portability.efulness.C.abundance.D.cost.3.The word "extracted" in the passage(paragraph 2)is closest in meaning toed.B.poured.C.removed.D.kept out.4.The word "termed" in the passage(paragraph 2)is closest in meaning toA.considered.B.called.C.limited to.D.caused by.5.According to paragraph 2, what does porosity determine?A.The rate at which the aquifer's water overcomes resistance to flow.B.The amount of water that the aquifer can hold.C.The likelihood that fractures and joints will occur in the aquifer.D.The depth underground at which the aquifer lies.6.According to paragraph 2, what is the relationship between permeability and porosity?A.The more pores a rock has, the higher its porosity but the lower its permeability.B.Rocks with many internal spaces that are not connected with each other will have high porosity but low permeability.C.If water flows through a rock easily, it has high permeability but low porosity.D.Rocks that have high permeability have high porosity and vice versa.7.The word "compacted" in the passage(paragraphy 3)is closest in meaning toA.hard.pressed.C.heavy.D.deeply buried.8.According to paragraph 3, when can igneous rock serve as an aquifer?A.When it has many connected fractures.B.When it lies next to metamorphic rock.C.When it lies relatively near the surface.D.When it is crystalline.9.The word "coating" in the passage(paragraph 4)is closest in meaning toA.stream.B.barrier.C.amount.yer.10.Paragraph 4 implies which of the following about the rootsof plants?A.They prevent water from reaching the vadose zone.B.They mark the boundary between the vadose zone and the water tableC.They do not typically get their water from the water table.D.They help keep the water table from dropping farther.11.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage paragraph 5 ? Incorrect choices change the meaning in important ways or leave out essential information.A.Groundwater only flows out of the ground if the watertable intersects the land surface.B.If the land surface and the water table intersect, groundwater can flow underground.C.Groundwater may be drained if springs occur where the water table intersects the land surface.D.Where the water table meets the land surface, groundwater flows out through surface springs.12.Paragraph 5 implies which of the following about the level of the waterA.It may rise or fall from year to year, depending on annual rainfall.B.It does not vary in arid regions.C.It rarely intersects the land surface of most regions.D.It is unrelated to the rate at which groundwater flows.13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.Where would the sentence best fit? This is a consequence of the slow rate of movement of the groundwater, which often prevents the water table from attaining a flat (horizontal) level.The water table is the underground boundary below which all the cracksand pores are filled with water. In some cases, the water table reaches Earth's surface, where it is expressed as rivers, lakes and marshes. ■【A】Typically,though,the water table may be tens or hundreds of meters below the surface. ■【B】The water table is not flat but usually follows the contours of the topography. ■【C】Above the water table is the vadose zone, through which rainwater percolates. ■【D】Water in the vadosezone drains down to the water table, leaving behind a thin coating of water onmineral grains. The vadose zone supplies plant roots near the surface withwater.14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.Most of the world's potable water is stored as groundwater in the poresand fractures of underground rock, much of it at depths of less than 1,000 meters.A.Sedimentary rock may make poor aquifers because of tightly compacted sediment, which reduces porosity and permeability.B.Porosity is a measure of the empty space within rock while permeability measures the degree to which water can flow freely through rock.C.In arid regions, the water tables remain at a constant level far below the surface, preventing stream-beds from filling up even during wet years.D.Groundwater reservoirs are characterized by the porosity and permeability of the rock in which they lie, and these factors vary according to the type of rock.E.The vadose zone is typically dry because water does not stay in it, but instead percolates down to aquifers below or drains out through springs and streams.F.Although the water table usually follows the contours of the land surface, its level may vary from year to year and may intersect to the surface in places.托福阅读答案1.在高亮部分的描写之后，本段的最后一句出现了，therefore。
剑桥雅思阅读解析8（test2）
剑桥雅思阅读解析8(test2)店铺为大家整理收集了剑桥雅思阅读8真题解析：test2阅读原文解析，希望对各位考生的备考有所帮助,祝每位烤鸭考试顺利，都能取得好成绩!剑桥雅思阅读8原文(test2)READING PASSAGE 1You should spend about 20 minutes on Questions 1-13, which are based on Reading Passage 1 below.Sheet glass manufacture:the float processGlass, which has been made since the time of the Mesopotamians and Egyptians, is little more than a mixture of sand, soda ash and lime. When heated to about 1500 degrees Celsius (℃) this becomes a molten mass that hardens when slowly cooled. The first successful method for making clear, flat glass involved spinning. This method was very effective as the glass had not touched any surfaces between being soft and becoming hard, so it stayed perfectly unblemished, with a 'fire finish'. However, the process took a long time and was labour intensive.Nevertheless, demand for flat glass was very high and glassmakers across the world were looking for a method of making it continuously. The first continuous ribbon process involved squeezing molten glass through two hot rollers, similar to an old mangle. This allowed glass of virtually any thickness to be made non-stop, but the rollers would leave both sides of the glass marked, and these would then need to be ground and polished. This part of the process rubbed away around 20 per cent of the glass, and the machines were very expensive.The float process for making flat glass was invented by Alistair Pilkington. This process allows the manufacture of clear, tinted and coated glass for buildings, and clear and tinted glass for vehicles. Pilkington had been experimenting with improving the melting process, and in 1952 he had the idea of using a bed of molten metal to form the flat glass, eliminating altogether the need for rollers within the float bath. The metal had to melt at a temperature less than the hardening point of glass (about 600℃), but could not boil at a temperature below the temperature of the molten glass (about 1500℃). The best meta l for the job was tin.The rest of the concept relied on gravity, which guaranteed that the surface of the molten metal was perfectly flat and horizontal. Consequently, when pouring molten glass onto the molten tin, the underside of the glass would also be perfectly flat. If the glass were kept hot enough, it would flow over the molten tin until the top surface was also flat, horizontal and perfectly parallel to the bottom surface. Once the glass cooled to 604℃ or less it was too hard to mark and could be transported out of the cooling zone by rollers. The glass settled to a thickness of six millimetres because of surface tension interactions between the glass and the tin. By fortunate coincidence, 60 per cent of the flat glass market at that time was for six-millimetre glass.Pilkington built a pilot plant in 1953 and by 1955 he had convinced his company to build a full-scale plant. However, it took 14 months of non-stop production, costing the company ￡100,000 a month, before the plant produced any usable glass. Furthermore, once they succeeded in making marketable flat glass, the machine was turned off for a service to prepare it for years of continuous production. When it started up again it took another four months to get the process right again. They finallysucceeded in 1959 and there are now float plants all over the world, with each able to produce around 1000 tons of glass every day, non-stop for around 15 years.Float plants today make glass of near optical quality. Several processes —melting, refining, homogenising —take place simultaneously in the 2000 tonnes of molten glass in the furnace. They occur in separate zones in a complex glass flow driven by high temperatures. It adds up to a continuous melting process, lasting as long as 50 hours, that delivers glass smoothly and continuously to the float bath, and from there to a coating zone and finally a heat treatment zone, where stresses formed during cooling are relieved.The principle of float glass is unchanged since the 1950s. However, the product has changed dramatically, from a single thickness of 6.8 mm to a range from sub-millimetre to 25 mm, from a ribbon frequently marred by inclusions and bubbles to almost optical perfection. To ensure the highest quality, inspection takes place at every stage. Occasionally, a bubble is not removed during refining, a sand grain refuses to melt, a tremor in the tin puts ripples into the glass ribbon. Automated on-line inspection does two things. Firstly, it reveals process faults upstream that can be corrected. Inspection technology allows more than 100 million measurements a second to be made across the ribbon, locating flaws the unaided eye would be unable to see. Secondly, it enables computers downstream to steer cutters around flaws.Float glass is sold by the square metre, and at the final stage computers translate customer requirements into patterns of cuts designed to minimise waste.Questions 1-8Complete the table and diagram below.Choose NO MORE THAN TWO WORDS from the passage for each answer.Write your answers in boxes 1-8 on your answer sheet.Early methods of producing flat glassMethod Advantages Disadvantages1............Glass remained2........... ? Slow3.............RibbonCould produce glass sheets of varying 4.............non-stop process ? Glass was 5...........20% of glass rubbed awayMachines were expensive图片11Questions 9-13Do the following statements agree with the information given in Reading Passage 1?In boxes 9-13 on your answer sheet, writeTRUE if the statement agrees with the informationFALSE if the statement contradicts the informationNOT GIVEN if there is no information on this9 The metal used in the float process had to have specific properties.10 Pilkington invested some of his own money in his float plant.11 Pilkington’s first full-scale plant was an instant commercial success.12 The process invented by Pilkington has now beenimproved.13 Computers are better than humans at detecting faults in glass.READING PASSAGE 2You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 on the following pages.Question 14-17Reading passage 2 has six paragraphs, A-F.Choose the correct heading for paragraphs B and D-F from the list of headings below.Write the correct number, i-ix, in boxes 14-17 on your answer sheet.List of Headingsi Predicting climatic changesii The relevance of the Little Ice Age todayiii How cities contribute to climate change.iv Human impact on the climatev How past climatic conditions can be determinedvi A growing need for weather recordsvii A study covering a thousand yearsviii People have always responded to climate changeix Enough food at lastExample AnswerParagraph A Viii14 Paragraph BExample AnswerParagraph C V15 Paragraph D16 Paragraph E17 Paragraph FTHE LITTLE ICE AGEA This book will provide a detailed examination of the Little Ice Age and other climatic shifts, but, before I embark on that, let me provide a historical context. We tend to think of climate — as opposed to weather — as something unchanging, yet humanity has been at the mercy of climate change for its entire existence, with at least eight glacial episodes in the past 730,000 years. Our ancestors adapted to the universal but irregular global warming since the end of the last great Ice Age, around 10,000 years ago, with dazzling opportunism. They developed strategies for surviving harsh drought cycles, decades of heavy rainfall or unaccustomed cold; adopted agriculture and stock-raising, which revolutionised human life; and founded the world's first pre-industrial civilisations in Egypt, Mesopotamia and the Americas. But the price of sudden climate change, in famine, disease and suffering, was often high.B The Little Ice Age lasted from roughly 1300 until the middle of the nineteenth century. Only two centuries ago, Europe experienced a cycle of bitterly cold winters; mountain glaciers in the Swiss Alps were the lowest in recorded memory, and pack ice surrounded Iceland for much of the year. The climatic events of the Little Ice Age did more than help shape the modern world. They are the deeply important context for the current unprecedented global warming. The Little Ice Age was far from a deep freeze, however; rather an irregular seesaw of rapid climatic shifts, few lasting more than a quarter-century, driven by complex and still little understood interactions between the atmosphere and the ocean. The seesaw brought cycles of intensely cold winters and easterly winds, then switched abruptly to years of heavy spring and early summer rains, mild winters,and frequent Atlantic storms, or to periods of droughts, light northeasterly winds, and summer heat waves.C Reconstructing the climate changes of the past is extremely difficult, because systematic weather observations began only a few centuries ago, in Europe and North America. Records from India and tropical Africa are even more recent. For the time before records began, we have only 'proxy records' reconstructed largely from tree rings and ice cores, supplemented by a few incomplete written accounts. We now have hundreds of tree-ring records from throughout the northern hemisphere, and many from south of the equator, too, amplified with a growing body of temperature data from ice cores drilled in Antarctica, Greenland, the Peruvian Andes, and other locations, we are close to a knowledge of annual summer and winter temperature variations over much of the northern hemisphere going back 600 years.D This book is a narrative history of climatic shifts during the past ten centuries, and some of the ways in which people in Europe adapted to them. Part One describes the Medieval Warm Period, roughly 900 to 1200. During these three centuries, Norse voyagers from Northern Europe explored northern seas, settled Greenland, and visited North America. It was not a time of uniform warmth, for then, as always since the Great Ice Age, there were constant shifts in rainfall and temperature. Mean European temperatures were about the same as today, perhaps slightly cooler.E It is known that the Little Ice Age cooling began in Greenland and the Arctic in about 1200. As the Arctic ice pack spread southward, Norse voyages to the west were rerouted into the open Atlantic, then ended altogether. Storminess increased in the North Atlantic and North Sea. Colder, much wetter weatherdescended on Europe between 1315 and 1319, when thousands perished in a continent-wide famine. By 1400, the weather had become decidedly more unpredictable and stormier, with sudden shifts and lower temperatures that culminated in the cold decades of the late sixteenth century. Fish were a vital commodity in growing towns and cities, where food supplies were a constant concern. Dried cod and herring were already the staples of the European fish trade, but changes in water temperatures forced fishing fleets to work further offshore. The Basques, Dutch, and English developed the first offshore fishing boats adapted to a colder and stormier Atlantic. A gradual agricultural revolution in northern Europe stemmed from concerns over food supplies at a time of rising populations. The revolution involved intensive commercial farming and the growing of animal fodder on land not previously used for crops. The increased productivity from farmland made some countries self-sufficient in grain and livestock and offered effective protection against famine.F Global temperatures began to rise slowly after 1850, with the beginning of the Modern Warm Period. There was a vast migration from Europe by land-hungry farmers and others, to which the famine caused by the Irish potato blight contributed, to North America, Australia, New Zealand, and southern Africa. Millions of hectares of forest and woodland fell before the newcomers' axes between 1850 and 1890, as intensive European farming methods expanded across the world. The unprecedented land clearance released vast quantities of carbon dioxide into the atmosphere, triggering for the first time humanly caused global warming. Temperatures climbed more rapidly in the twentieth century as the use of fossil fuels proliferated and greenhouse gas levels continued to soar. The rise has been even steeper since theearly 1980s. The Little Ice Age has given way to a new climatic regime, marked by prolonged and steady warming. At the same time, extreme weather events like Category 5 hurricanes are becoming more frequent.Questions 18-22Complete the summary using the list of words, A-I, below.Write the correct letter, A-I, in boxes 18-22 on your answer sheet.Weather during the Little Ice AgeDocumentation of past weather conditions is limited: our main sources of knowledge of conditions in the distant past are 18...........and 19.................. We can deduce that the Little Ice Age was a time of 20.............. , rather than of consistent freezing. Within it there were some periods of very cold winters, other of 21...............and heavy rain, and yet others that saw 22................with no rain at all.A climatic shiftsB ice coresC tree ringsD glaciersE interactionsF weather observationsG heat waves H storms I written accountsQuestions 23-26Classify the following events as occurring during theA Medieval Warm PeriodB Little Ice AgeC Modern Warm PeriodWrite the correct letter, A, B or C, in boxes 23-26 on your answer sheet.23 Many Europeans started farming abroad.24 The cutting down of trees began to affect the climate.25 Europeans discovered other lands.26 Changes took place in fishing patterns.READING PASSAGE 3You should spend about 20 minutes on Questions 27-40, which are based on Reading Passage 3 on the following pages.Questions 27-32Reading Passage 3 has six paragraphs, A-F.Choose the correct heading for each paragraph from the list of headings below.Write the correct number, i-viii, in boxes 27-32 on your answer sheet.List of Headingsi The difficulties of talking about smellsii The role of smell in personal relationshipsiii Future studies into smelliv The relationship between the brain and the nosev The interpretation of smells as a factor in defining groups vi Why our sense of smell is not appreciatedvii Smell is our superior senseviii The relationship between smell and feelings27 paragraph A28 paragraph B29 paragraph C30 paragraph D31 paragraph E32 paragraph FThe meaning and power of smellThe sense of smell, or olfaction, is powerful. Odours affect us on a physical, psychological and social level. For the most part, however, we breathe in the aromas which surround us without being consciously aware of their importance to us. It is only when the faculty of smell is impaired for some reason that we begin torealise the essential role the sense of smell plays in our sense of well-beingA A survey conducted by Anthony Synott at Montreal's Concordia University asked participants to comment on how important smell was to them in their lives. It became apparent that smell can evoke strong emotional responses. A scent associated with a good experience can bring a rush of joy, while a foul odour or one associated with a bad memory may make us grimace with disgust. Respondents to the survey noted that many of their olfactory likes and dislikes were based on emotional associations. Such associations can be powerful enough so that odours that we would generally label unpleasant become agreeable, and those that we would generally consider fragrant become disagreeable for particular individuals. The perception of smell, therefore, consists not only of the sensation of the odours themselves, but of the experiences and emotions associated with them.B Odours are also essential cues in social bonding. One respondent to the survey believed that there is no true emotional bonding without touching and smelling a loved one. In fact, infants recognise the odours of their mothers soon after birth and adults can often identify their children or spouses by scent. In one well-known test, women and men were able to distinguish by smell alone clothing worn by their marriage partners from similar clothing worn by other people. Most of the subjects would probably never have given much thought to odour as a cue for identifying family members before being involved in the test, but as the experiment revealed, even when not consciously considered, smells register.C In spite of its importance to our emotional and sensorylives, smell is probably the most undervalued sense in many cultures. The reason often given for the low regard in which smell is held is that, in comparison with its importance among animals, the human sense of smell is feeble and undeveloped. While it is true that the olfactory powers of humans are nothing like as fine as those possessed by certain animals, they are still remarkably acute. Our noses are able to recognise thousands of smells, and to perceive odours which are present only in extremely small quantities.D Smell, however, is a highly elusive phenomenon. Odours, unlike colours, for instance, cannot be named in many languages because the specific vocabulary simply doesn't exist. ‘It smells like…,’ we have to say when describing an odour, struggling to express our olfactory experience. Nor can odours be recorded: there is no effective way to either capture or store them over time. In the realm of olfaction, we must make do with descriptions and recollections. This has implications for olfactory research.E Most of the research on smell undertaken to date has been of a physical scientific nature. Significant advances have been made in the understanding of the biological and chemical nature of olfaction, but many fundamental questions have yet to be answered. Researchers have still to decide whether smell is one sense or two — one responding to odours proper and the other registering odourless chemicals in the air. Other unanswered questions are whether the nose is the only part of the body affected by odours, and how smells can be measured objectively given the non-physical components. Questions like these mean that interest in the psychology of smell is inevitably set to play an increasingly important role for researchers.F However, smell is not simply a biological and psychologicalphenomenon. Smell is cultural, hence it is a social and historical phenomenon. Odours are invested with cultural values: smells that are considered to be offensive in some cultures may be perfectly acceptable in others. Therefore, our sense of smell is a means of, and model for, interacting with the world. Different smells can provide us with intimate and emotionally charged experiences and the value that we attach to these experiences is interiorised by the members of society in a deeply personal way. Importantly, our commonly held feelings about smells can help distinguish us from other cultures. The study of the cultural history of smell is, therefore, in a very real sense, an investigation into the essence of human culture.Questions 33-36Choose the correct letter, A, B, C or D.Write the correct letter in boxes 33-36 on your answer sheet.33 According to the introduction, we become aware of the importance of smell whenA we discover a new smell.B we experience a powerful smell.C our ability to smell is damaged.D we are surrounded by odours.34 The experiment described in paragraph BA shows how we make use of smell without realising it.B demonstrates that family members have a similar smell.C proves that a sense of smell is learnt.D compares the sense of smell in males and females.35 What is the write doing in paragraph C?A supporting other researchB making a proposalC rejecting a common beliefD describing limitations36 What does the write suggest about the study of smell in the atmosphere in paragraph E?A The measurement of smell is becoming more accurate.B Researchers believe smell is a purely physical reaction.C Most smells are inoffensive.D Smell is yet to be defined.Questions 37-40Complete the sentences below.Choose ONE WORD ONLY from the passage for each answer.Write your answers in boxes 37-40 on your answer sheet.37 Tests have shown that odours can help people recognise the.......... belonging to their husbands and wives.38 Certain linguistic groups may have difficulty describing smell because they lack the appropriate ................ .39 The sense of smell may involve response to................ which do not smell, in addition to obvious odours.40 Odours regarded as unpleasant in certain.................are not regarded as unpleasant in others.剑桥雅思阅读8原文参考译文(test2)PASSAGE 1 参考译文：玻璃板制造：浮法工艺早在美索不达米亚时期和古埃及时期人们就开始制造玻璃，当时制作出的玻璃只不过是沙子、碳酸钠和石灰的混合物而已。
最新托福阅读tpo1-Groundwater地下水原题解析
incredible that there can be enough space in the "solid" ground underfoot to hold
all this water.
地下水是指渗入到地下并将所有岩石孔隙填满的水。到现在为止，大气水是最丰富的地
下水资源， 是地下水在水循环中的一个环节。 普通的大气水会从地表、 降水以 及湖泊河流侵
water; this is the groundwater that circulates as part of the water
cycle. Ordinary
meteoric water is water tห้องสมุดไป่ตู้at has soaked into the ground from the surface, from
米。
In lowland country almost any spot on the ground may overlie what was once the bed of a river that has since become buried by soil; if they are now below the water ’ s upper surface (the water table), the gravels and sands of the former riverbed, and its sandbars, will be saturated with groundwater.
阅读原文：
Groundwater is the word used to describe water that saturates the ground, filling
稳定渗流分析的局部间断伽辽金有限元法
稳定渗流分析的局部间断伽辽金有限元法何朝葵;速宝玉;盛金昌【摘要】Based on the characteristics of the steady seepage equation, a basic calculation formula of the local discontinuous Galerkin finite element method for steady seepage analysis was deduced according to the principle of the method, and the feasibility of the formula was studied. The variational formula of the basic formula was analyzed with consideration of the stability and boundedness of the bilinear operator in the variational formula. The Lax-Milgram theorem was used to verify the existence and uniqueness of the solution of the basic formula, in order to demonstrate that the local discontinuous Galerkin finite element method is applicableto steady seepage analysis. Through a priori error analysis, the formula was proved to have p + 1-order accurate approximations, indicating that the local discontinuous Galerkin finite element method is a high-precision numerical method compared with commonly used finite element methods.%针对稳定渗流分析问题的特征,依据局部间断伽辽金有限元法原理,推导出稳定渗流分析问题的局部间断迦辽金有限元法基本计算格式,并对该计算格式的有效性进行探讨.通过分析基本计算格式相应的变分形式,考虑变分形式中双线性算子的稳定性及有界性,利用Lax-Milgram定理论证这一基本计算格式解的存在性、唯一性,从而证明局部间断伽辽金有限元法可以用来处理稳定渗流分析问题.通过对该格式的解进行先验误差分析,证明其近似解具有p+1阶的精度,表明相对于一般的有限元法来说,局部间断伽辽金有限元法是一种高精度的数值计算方法.【期刊名称】《河海大学学报（自然科学版）》【年(卷),期】2012(040)002【总页数】5页(P206-210)【关键词】渗流;间断有限元;局部间断伽辽金有限元;误差分析【作者】何朝葵;速宝玉;盛金昌【作者单位】河海大学水利水电学院,江苏南京210098;河海大学理学院,江苏南京210098;河海大学水利水电学院,江苏南京210098;河海大学水利水电学院,江苏南京210098【正文语种】中文【中图分类】O357.3间断有限元法[1-3]是一种在有限元法、有限体积法和有限差分法基础上发展起来的数值计算方法，它的特点在于允许插值函数在剖分单元边界处不连续，使得其在处理大梯度问题上具有独特的优势，并使其在多个领域得到广泛的应用[2-4].国外部分学者对间断有限元法在椭圆问题上的应用进行了分析[5-6]，国内则鲜见这方面的文献.局部间断伽辽金有限元法[2，7](the local discontinuous Galerkin methods，简称LDG法)是间断有限元法中最有效的方法之一，它具有良好的稳定性.笔者主要从理论上分析LDG法在稳定渗流分析问题中的应用.1 渗流方程稳定渗流方程及定解条件如下:式中:Ω——求解区域;H——水头函数;k——渗透系数(考虑各向同性，分片常数情形);ΓD，ΓN——第一类边界和第二类边界，且∂Ω=ΓD∪ΓN;n——边界ΓN上的外法线方向单位向量;g D，g N——常数.2 LDG法原理把水力梯度σ=k▽H作为中间变量，则式(1)中的二阶方程化为一阶方程组:假设 T h为Ω的1个剖分，E表示其中的任意1个单元，n E表示E的单位外法线方向向量.用σh和H h表示单元内插值函数，LDG法允许插值函数在单元边界处不连续，故插值函数在单元边界上的值用数值流通量[1-3]替代.数值流通量定义如下:若e为单元E和单元E′的公共边界，用 n E表示单元E在边界e上的外法线单位向量，H h，E和σh，E分别表示 H h和σh在边界上单元E侧的值，则有式中:α——边界e上的常数;β——边界e上的常向量.在式(2)中第1个方程两边分别乘以测试函数v，在第2个方程两边分别乘以测试向量函数τ，然后在每个单元上积分，得式中:▽h——单元内梯度算子;k E——单元E的渗透系数.单元方程(式(3)和式(4))通过数值流通量建立联系，构成整体代数方程.3 基本计算格式相对于剖分 T h，ε表示剖分单元边界的集合，ε0表示区域内部的单元边界的集合，εD表示在ΓD上的单元边界的集合，εN表示在ΓN上的单元边界的集合，要求ε=ε0+εD+εN.把式(3)和式(4)相对于剖分 T h在求解域Ω上对所有单元叠加，整理得式(5)和式(6)就称为渗流问题的LDG法基本计算格式.4 变分形式的稳定性和有界性若引入3个算子，则由式(6)可得σh在有限元空间∑h上的L 2投影:式中∏为投影算子.把式(7)代入式(5)，整理得基本计算格式的变分形式为其中显然B h(H h，v)是对称双线性算子.为证明变分的稳定性和有界性，定义如下半范数和范数[8-10]:式中‖u‖和分别为单元E上的Sobolev范数和半范数.在证明之前，先看下面的引理[9].引理其中C是与h无关的常数.证明再由L2投影的稳定性可得不等式(9).利用引理可以得 B h(H h，v)的稳定性，即对∀v∈V h有同样利用引理亦可得到B h(v，v)的有界性，即对∀v，w∈V h有结合引理有因而根据Lax-Milgram定理知变分问题B h(H h，v)=F h(v)存在唯一解.5 误差估计设H为渗流问题(式(1))的解，H I为相对剖分 T h下的某一插值函数，则由插值函数局部估计有其中的常数C仅与插值函数的次数p和单元E的最小角度有关.为了得到LDG法数值解误差的L2估计，先看2个定理[11]:定理1 若H为式(1)的解，H I为H的某个插值函数，则存在正数C使得式(13)成立.证明由迹不等式知存在常数C，使得定理2 若H为式(1)的解，H h为式(8)的解，则存在正数C使得式(15)成立.证明设 H I为 H的分片插值函数，由式(11)和式(12)有所以，再由三角不等式‖|H-H h|‖Ω=‖|H-H I+H I-H h|‖Ω ≤‖|H-H I|‖Ω+‖|H I-H h|‖Ω，结合定理 1得式(15).由定理1和定理2可得到误差的L2估计.定理3 若 H为式(1)的解，H h为式(8)的解，则存在正数C使得式(16)成立.证明由于LDG法的数值流通量是守恒的，因而变分格式(8)是自相容的，即对∀v∈H2(T h)有B h(v，，其中ψ为方程-Δψ=g，(x，y)∈ Ω以及ψ=0，(x，y)∈ ∂Ω的解[10].若取g=H-H h，则有B h(v，ψ)=(H-H h，v)，∀v ∈ V h.设ψI为ψ的线性插值，则根据椭圆边值问题的正则性，有2，Ω≤C2‖H-H h‖0，Ω，其中常数 C2只与Ω有关.结合式(15)即得‖H-H h ‖0，Ω ≤Chp+1p+1 ，Ω.6 结语间断有限元法已推广到水动力、气动力学等多个领域.笔者通过对稳定渗流分析的局部间断伽辽金有限元法的理论分析，给出其计算格式，并论证说明该格式具有良好的稳定性.论证结果表明，运用局部间断伽辽金有限元法来处理稳定渗流分析是有效的;在运用本文格式计算时，可以通过选取正交的基函数来简化整体代数方程组.对这一方法的近似解进行的先验误差分析表明其具有p+1阶精度，所以相对于一般的有限元法来说，局部间断伽辽金有限元法是一种具有较高精度的数值计算方法.关于局部间断伽辽金有限元法在渗流问题上的一些具体计算及验证可见文献[12]，其他一些结论笔者正在整理中.参考文献:【相关文献】[1]REED WH，HILL T R.Triangular mesh methods for the neutron transportequation[R].Alamos:Los Alamos Scientific Laboratory，1973.[2]COCKBURN B，KAMIADAKISG，SHU Chi-wang，et al.Discontinuous Galerkin Methods[M].Berlin:Spring Verlag，2000:89-101.[3]刘儒勋，舒其望.计算流体力学的若干新方法[M].北京:科学出版社，2003:159-179.[4]FAGHERAZZIS，FURBISH D J，RASETARINERA P，et al.Application of the discontinuous spectral Galerkinmethod togroundwater flow[J].Advances in Water Resources，2004，27:129-140.[5]ARNOLD DN，BREZZIF，COCKBURN B，et al.Unified analysis of discontinuous Galerkinmethodsfor elliptic problems[J].SIAM J Numer Anal，2002，39(5):1749-1779. [6]CASTILLO P.Performance of discontinuous Galerkin methods for elliptic pde's[J].SIAM JSci Comput，2002 ，24(2):524-547.[7]COCKBURN B，SHU Chi-wang.The local discontinuous Galerkin finite element method for convection-diffusion systems[J].SIAM J Numer Anal，1998，35:2440-2463.[8]CASTILLO P，PERUGIA I，SCHOTZAU D.An a priori error analysis of the local discontinuous Galerkin method for elliptic problems[J].SIAM JNumer Anal，2000，38:1676-1706.[9]PERUGIA I，SCHOTZAU D.An hp-analysis of the local discontinuous Galerkin method for diffusion problems[J].JSci Comp，2002，17:561-571.[10]肖捷，刘韶鹏.求解间断系数椭圆型问题的一种改进的DG方法[J].计算数学，2007，29(4):377-390.(XIAO Jie，LIU Shao-peng.A modified DG method for elliptic problems with discontinuous coefficients[J].Journal of Cumputational Mathematics，2007，29(4):377-390.(in Chinese)).[11]LEEMA ，SHINJY.Error estimiates for a discontinuous Galerkinmethod for elliptic problems[J].Appl Math&Computing，2006，21(1/2):189-201.[12]何朝葵，速宝玉，盛金昌，等.用局部间断伽辽金有限元法分析渗流场[J].水利水电科技进展，2010，30(2):21-23.(HE Zhao-kui，SU Bao-yu，SHENG Jin-chang，et al.Analysis of seepage field for aquifer problems by the local discontinuous Galerkinmethod[J].Advances in Science and Technology of Water Resources，2010，30(2):21-23.(in Chinese)).。
SWAT-MODFLOW耦合模型在地下水量均衡分析中的应用
第18卷第6期2020年12月南水北调与水利科技(中英文)Vol.18No.6 South-to-North Water Transfers and Water Science&Technology Dec.2020DOI:10.13476/ki.nsbdqk.2020.0130张琳琳.崔亚莉，梁桂星.等.SWAT-M()DFL()W耦合模型在地下水量均衡分析中的应用［J］.南水北调与水利科技(中英文)，2020,18(6):176-183.ZHANG L L,CUI Y L.LIANG G X,et al.Application of SWAT-M()DFLOW coupling model in groundwater balance analysis］〕］.South-terNorth Water Transfers and Water Science&Technology,2020»18(6):176-183.(in Chi^ nese)SWAT-MODFLOW耦合模型在地下水量均衡分析中的应用张琳琳1,崔亚莉I,梁桂星“2,梁灵君3,王晓阳1(1.中国地质大学(北京)水资源与环境学院，北京100083；2.北京市地热研究院，北京102218；3.北京市水文总站，北京100089)摘要:利用地下水-地表水半松散耦合数值模拟方法，选取北京市苏密怀地区为典型地区，以长时间序列SWAT模型获取的平原区地下水补给量和山区对平原区地下水补给量作为传递变量，分别代替MODFLOW模型中降雨入渗补给量和山前侧向补给量的研究思路,建立半松散式SWAT-MODFLOW耦合模型,利用地下水位校验耦合模型并对苏密怀地区地下水水量平衡进行分析。
结果表明:该方法可以提高地下水模型的精度，耦合模型较传统算法计算得到的降雨入渗补给量减少了0・54亿占/a,反映出当下垫面条件发生变化和包气带厚度增加时,含水层的降水补给量减少。
托福阅读tpo 1 Groundwater 地下水原题解析
阅读原文：Groundwater is the word used to describe water that saturates the ground, filling all the available spaces. By far the most abundant type of groundwater is meteoric water; this is the groundwater that circulates as part of the water cycle. Ordinary meteoric water is water that has soaked into the ground from the surface, from precipitation (rain and snow) and from lakes and streams. There it remains, sometimes for long periods, before emerging at the surface again. At first thought it seems incredible that there can be enough space in the "solid" ground underfoot to hold all this water.地下水是指渗入到地下并将所有岩石孔隙填满的水。
到现在为止，大气水是最丰富的地下水资源，是地下水在水循环中的一个环节。
普通的大气水会从地表、降水以及湖泊河流侵入到地下。
在再次冒出地表之前，这些地下水有时会长时间留在地下。
最初让人觉得难以置信的是，在我们脚下“坚实的”土地中竟然有足够的空间能储存这么些水。
The necessary space is there, however, in many forms. The commonest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel. Beds of this material, out of sight beneath the soil, are common. They are found wherever fast rivers carrying loads of coarse sediment once flowed. For example, as the great ice sheets that covered North America during the last ice age steadily melted away, huge volumes of water flowed from them. The water was always laden with pebbles, gravel, and sand, known as glacial outwash, that was deposited as the flow slowed down.然而，地下水所需的储存空间多种多样。
【doc】绘制流网的数值计算方法
绘制流网的数值计算方法水利水运科学研究1994年6月tan一是一或d—dx一0式中口为与轴的夹角,和分别为在和轴向的分量.(2)式为描述流线的流线方程,对二维渗流场都适用.在地下水(假定为不可压缩)的渗流问题中,有渗流连续性方程+:0drdV故流线方程(2)式则为全微分方程(=』z(1)(2)(4)或d妇,)一d+d=Vdy—dx(5)得渗流速度与流函数的关系为y一1:型}J由Darcy定律fa一一到薹}㈣【J及(6)式可得'+雾一(—k)啬+k(耄一雾)(8)式中,,及为Darcy渗透系数;,)为水头函数.可见,当渗流域为各向同性域时(一,一=O),流函数,)满足Laplace微分方程;当域中介质为各向异性体时≠,一≠O),流函数不满足Laplace方程.再由(6)和(7)式可得(k警+b)+(k箬+)一o(9)因此,当渗流域由各向同性体组成时,有+等=o㈣,.av.…或V?V一0(11)表明流网中流线与等水头线互为正交,流网为一正交型曲线网络图.反之,在各向异性庠渗流场中,(10)或(n)式均不等于0.即流网流线与等水头线不正交,流网为一斜交型曲线网第1,z期朱岳明等t绘制流同的数值计算方法络图.三,流网的数值计算在渗流域S内,(6)式的两边分别对y及徽分,整理得流函数的Passion型徽分方程+等+警一=o0.0.…再沿面域S的边界曲线r对(6)式分别乘以和n,相加得(12)式解的Neumaun边界条件+=一(13)式中n和,为边界曲线r的外法线方向余弦i渗流速度和,是水头函数的梯度函数,可用有限元法先计算出水头函数在域中的分布,再求得和.如引入单元内水头函数,y)的有限元法插值式,)一∑Ⅳ.(14)则有一一∑∑k警+b警警+警(15)式中,M和m分别为单元结点的水头值,插值基函数和单元结点数固已有水头函数的有限元离散解,和V只是位置坐标的函数.根据变分原理,由(12)和(13)式构成的流函数的解为下述泛函Ⅱ()的驻值点一盯[吉c丢cc警一一f'一nV,)dP(16)因有V=dPⅡ主(VDdS及一JJV,)dS(16)式.q-简化为)一盯[丢(-f-W¨-+,一(17)把(15)式代/k(17)式并在单元内引入流函数的有限元插值(18)式,);∑Ⅳj(18)则在计算域S内,对(17)式进行有限元法的离散运算及单元传导矩阵和左,右端项的集合组装后,可得标准型有限元法线性支配方程水利水运科学研究1994年6月I-K2{}一{Q)(19)式中的{}为流函数的未知结点值向量.~(18)am(19)式,每个单元对系数矩阵[]和右端项{Q}中相应元素的作用分别为b:盯(警警+警警jacz.:=Ⅱ{警[耋ckiaN,+b警]～警[喜ck警+]cz式中为单元的面域}f,j=1.2'..?,m.(19)式的解就为流函数(z,y)的有限元解.有了水头函数,y)和流函数(z,y)的有限元数值解,再经过有限元解后处理子程序的计算,整理后,即可得绘制流网所需的所有技术数据或直接在计算机上绘制出高精度的流网.事实上,(13)式把渗流场中流函数的强制性第一类边界条件(,)一(,y)转化成了第二类自然边界条件,避开了渗出面上流函数事先不易确定的问题,使流网的数值计算大为简化.为了消除系数矩阵[]的奇异性并使解唯一性,在解(19)式前,可根据问题的性质及其物理意义,对某些结点直接引入已知值,如位于浸润线上结点的值为0.0;位于计算域底部不透水面上结点的值为总渗流量q(或取相对值100).四,算例(一)土提中无压渗流场的流网计算'图2为一均质各向同性土堤中无压Fi.P要誊ed印渗流场流网的计算结果,流线与荨水头"ow.ughhomo~eneoandisotop线互为正交,计算域为ABCDEA,上,下游水头分别为6.0和2.0.在求解水头函数的分布及确定浸润线位置时,采用结点虚流量法[3}在求解流函数(,y)的分布时,令浸润线AD上所有结点的值为0.0.劫一盟赴-rdlD第l,2期朱岳明等绘制谎同的数值计算方法(二)闸坝下成层各向异性地基中流网的计算图3为某一水闸下非均质成层各向异性体地基中流网的计算结果.在计算域中,视闸体混凝土为不透水体,厚 2.0rn,深40.0m的棍凝土防渗板桩也为相对不透水体,约40m深的强透水砂砾覆盖层为均质各向异性透水体,其Dare),渗透张量为吡=(m/d)r2.320,01一lo.o1.16J如/s)覆盖层下为水平向层状岩体,其渗透张量为嘲,一[c…m闸坝上,下游水头分别为20.0m和5.0m,计算中令位于闸底板面上结点的=0.0,位于z一一100.0m,z一150.0m和=一100.0m的边界面上的结点满足=舢(为总渗流量). 图3非均质各向异性闸基域中的斜交型流网F.3Tiltedflowztetofeon|inedseepageflowthrou暮hinhomogeneousandanlsotroplc foundationof8sluice如图3所示,在一一40.0m的地基材料分界面上,因受渗流越流量连续性条件的约束,流线与等势线均发生折射;又因材料均为各向异性体,尽管渗透方向与整体坐标和Y轴同向(==O),流线斜交于等水头线,流网为斜交网络图.这种流网难以用徒手勾画, 也不便由模型试验中得到.124水刺水运科学研究1994年6月(三)非均质土石坝中流网的计算图4为一壤土质宽心墙非均质各向同性体土石坝中渗流流网的计算结果.该坝高30.0m,底宽160.Om,心墙底宽96.Om,坝上,下游水头分别为148.Om和130.Om.整个渗流计算域主要由四种透水性不同的材料组成t一区为壤土质宽心墙体,其渗透系数h;1.16×10一m/s}二区为上,下游坝坡区的粗砂砾填筑区,其岛一L16×10～m/s{三区为深选50.Om的细砂砾覆盖层,其=1.16X10-5m/s;四区为覆盖层下的砂质岩层,其h= 1.16×10一m,s.":,\\汹l—?.'.....'..一1160—————————卜—一l伽———图4壤土质宽心墙土石坝中的流网F.4Flowtofseepagethroughanearthdam该坝虽在各子区域内介质为各向同性体,流线与等水头线正交,但在一70.0m和一120.Om等不同透水体的分界面上流线和等水头线均发生折射,使得流网的形态复杂化.显然,流网也不宜用徒手勾画.五,结语(一)本文介绍的方法适用于各种非均质,各向异性域中复杂流网的绘制工作.与传统的几种方法相比,尤其适用于材料分界面处流线和等水头线均折射及各向异性域中斜交流网的绘制.(二)求解漉函数(z,)时.虽基于已求解得水头函数z,)的基础上,但采用的是饲一种网格.(三)在非均质域中,困在相邻材料区的分界线上流线和等水头线均要发生折射,为了提高流网的计算及绘制精度,对这些分界线区单元,应布置得相对密一些.同理?在水力梯度变化较大的有关阻水及排水区,单元也应布置得小些.∞+占●上第l,2期朱岳明等:绘制浇两的数值箅方法12j参考文献1HarrME.GroundwaterandSeepage.LondonlMCGraw—HillBookCompany.19622AahoJ.Finiteelementseepageflownets.IntJforNumericalaMAnalysis MethodsinGeomechanlcs,1984l8t297—3033ZhuYueming,WangRuyun,XuHongbo.Someadaptivetechnlquesfor solutionoffreesurfaceseepageflowthrougharchdamabutments.In±Procof theIntSymposiumonArchDams,1992 NumericalmethodfordrawingflownetofseepageZhuYuemlng(HohaiUniversity)HeJian(ZheiiangProvinceWaterConservancy,~[anagement)ShaoJingdong(ChenduHydroelectricInvestigation,DesignandResearchInstituteofMOE,M~VR) AbstractAtthefirst.thefundamentaltheoryandcharacteristicoftheflownetsof2-D.DarcyS seepageflowproblemareintroduced.Basedonthevariationalprincipleandfiniteelementmethod,thenumericalmethodandthecorrespondingcalculationexpressionsarepresented indetail.Threeillustrativeexamplesaboutthenumerlzationanddrawingoftheflownets ofseepagesthroughembankmentandsluicefoundationaresuccessfullygiven.Themethod hasfoundamentlysolutedtheproblemthatallofthecomplicatedflownetsingeoengineer—ingmaybenumericallydrawnwithquickandhighprecision.Keywords:seepage,flownet,finiteelementmethod,numericalcalculation,tWO,dimensionaIflOW。
Many_world’s_large_lakes_are_drying_up_许多大型湖泊处境危险李
Crazy English 2023.10一研究小组研发了一项新技术，即使用了各种卫星和模型的数据跟踪世界上近2,000个大型湖泊和水库的水位变化，并对这些湖泊及水库的储水变化趋势和原因进行了详细分析。
让我们一起来看看吧。
Many world s large lakes are drying up许多大型湖泊处境危险山东 李全忠1 More than 50 percent of large lakes in the world are losing water, according to agroundbreaking new assessment published in Science . The main causes are warming climate and unsustainable human consumption.2 Lead author Fangfang Yao, a climate fellow at the University of Virginia, said this isthe first comprehensive assessment of trends and drivers of global lake water storage variability based on an array (一系列) of satellites and models.3 The team used 250,000 lake⁃area pictures captured by satellites between 1992 and 2020 to survey the area of 1,972 of Earth s large lakes. They collected water levels from nine satellite altimeters and used long⁃term water levels to reduce any uncertainty. For lakes without a long⁃term level record, they used recent water measurements made by newer instruments on satellites. Combining current level measurements with longer⁃term area measurements allowed scientists to understand the changes in lake levels over decades.4 The results were striking: 53 percent of lakes globally experienced a decline in water storage. Yao and his colleagues also assessed storage trends in reservoirs (水库). They found that nearly two⁃thirds of Earth s large reservoirs experienced significant water losses. “Sedimentation (沉积作用) dominated the global storage decline in existing reservoirs,” said Ben Livneh, also a co⁃author, CIRES fellow, and associate professor of engineering at主题语境：自然生态篇幅：312词建议用时：7分钟44CU Boulder. In long⁃established reservoirs—those that were filled before 1992—sedimen⁃tation was more important than droughts and heavy rainfall years.5 Globally, freshwater lakes and reservoirs store 87 percent of the planet s fresh water, making them a valuable resource for both humans and ecosystems. Unlike rivers, lakes are not well monitored, yet they provide water for a large part of humanity—even more than rivers. It is estimated that roughly one⁃quarter of the world s population, 2billion people, lives in the basin of a drying lake, which indicates an urgent need to incorpor⁃ate human consumption, climate change, and sedimentation impacts into sustainable water resources management.ReadingCheckDetailGistDetail Inference 1. What problem does the new study focus on?A. Severe water shortage of global big lakes.B. An increase in the waste of water resources.C. Human activities damaging effects on lakes.D. The importance of lakes to Earth ecosystems.2. What is paragraph 3 mainly about?A. The introduction to Earth s big lakes.B. The difficulties of measuring water levels.C. The process of scientists conducting the research.D. The advantages of applying satellites to collecting data.3. What is the main cause of the storage decline in reservoirs?A. Sedimentation.B. Frequent rainfall.C. Long⁃term droughts.D. Excessive use of water.4. What does the author suggest in the last paragraph?A. Limiting the development of lake resources.B. Taking urgent action to control human consumption.C. Solving the water problem of people around drying lakes.D. Improving the management of sustainable water resources.45疯狂英语 （新读写）Crazy English 2023.10LanguageStudyⅠ. Difficult sentence in the textIt is estimated that roughly one⁃quarter of the world s population, 2 billion people, lives in the basin of a drying lake, which indicates an urgent need to incorporate human consumption, climate change, and sedimentation impacts into sustainable water resources management. 据估计，大约四分之一的世界人口，即约20亿人生活在干燥的湖泊流域，这表明迫切需要将人类消耗、气候变化和沉积的影响纳入可持续的水资源管理。
GMS论文：基于GMS的矿井涌水量预测分析
GMS论文：基于GMS的矿井涌水量预测分析【中文摘要】矿井涌水量是确定矿床水文地质条件复杂程度的重要指标,更是生产设计部门制定开采方案,确定矿坑排水能力、制定疏干措施,防止重大矿井水害的重要依据。
矿井涌水量的预测研究与煤矿安全生产关系重大,一直以来倍受重视。
本文以山西省朔南煤田为研究区,利用地下水数值模拟软件GMS中集成的MODFLOW2000对井田地下水流运动进行了数值模拟,对井田先期开采地段开采后的矿井涌水量进行了预测分析。
在分析研究区地质条件的基础上,针对地层岩性和地质构造特点,对井田地层进行了概化,结合工作区地质勘探钻孔资料,建立了丰予井田地质模型。
通过分析区域含水层水文地质特征,地下水补给、径流、排泄等水文地质条件,对井田含水层进行了概化,结合对井田充水因素的分析,建立了丰予井田水文地质概念模型。
依据研究区水文地质条件,结合以往工作经验及专家分析意见,对研究区边界条件进行了设定,以井田水文地质概念模型为依据建立了地下水数学模型。
利用井田地质模型,按水文地质概念模型含水岩组概化原则,使用GMS软件,建立丰予井田水文地质体,依据所建立的数学模型,根据边界条件,采用网格法建立丰予井田数值模型,通过求解数值模型进行不同开采情况下的矿井涌水量预测,并与大井法矿井涌水量预测结果进行了对比。
由于煤田开拓方案尚未确定,本次研究以井田初步设计中先期开采地段的初期采区为研究重点。
研究区范围内包括了古生代、中生代的马家沟组、本溪组、太原组、山西组地层和新生代松散沉积物,本次研究将其概化为31个大的层次,将含水层概化为9个含水岩组和一个稳定的隔水岩组。
数值模拟主要针对初期采区4号煤层全部开采后和4号、9号煤层全部开采后的矿井最大涌水量进行了预测。
研究结果表明:开采山西组、太原组的4、6、9号煤层,二叠系上中隔水岩组可以起到隔水层作用,不会造成新生界地下水的大量渗漏;在4号煤层开采后矿井稳定最大涌水量为12910m3/d,略大于大井法预测结果9993.64m3/d;在4号、9号煤层开采后矿井稳定最大涌水量为19385m3/d,比大井法的预测结果29673.8m3/d小。
小学上册第6次英语第1单元寒假试卷
小学上册英语第1单元寒假试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The tree provides shade and _______ (这棵树提供阴凉和_______).2.The raccoon is known for its _________. (聪明)3.She is ___ (reading/writing) a poem.4.Which vehicle runs on tracks?A. CarB. BusC. TrainD. BicycleC5.My teacher is a ______. She loves to inspire creativity.6.Which shape has three sides?A. SquareB. TriangleC. CircleD. RectangleB7.The _____ (cantaloupe) is a sweet melon.8.I can ___ (see/hear) you.9.What is the name of the famous composer known for "The Nutcracker"?A. Johann StraussB. Igor StravinskyC. Pyotr Ilyich TchaikovskyD. Ludwig van BeethovenC10.The flowers are _______ (美丽的).11.What kind of animal is a parrot?A. MammalB. ReptileC. BirdD. Fish12. A ________ (草坪) is nice for playing games.13.Chemical reactions can be classified as ______ or exothermic.14.I enjoy learning about different ______ (语言) and cultures. It helps me understand the world better.15.The sunset is ______ and beautiful. (colorful)16.I have a pet __________ at home.17.What do you call a baby cat?A. PuppyB. KittenC. CubD. ChickB18.The reaction of baking soda and vinegar produces ______.19.The chemical formula for water is _____.20.They are ___ the game. (winning)21.__________ (反应动力学) examines the speed and mechanisms of reactions.22.What do you call a large area of flat land?A. MountainB. ValleyC. PlainD. HillC23.Which part of the plant is usually green and makes food?A. RootB. StemC. LeafD. FlowerC24.My sister loves to ________.25.What is the currency used in the UK?A. DollarB. EuroC. PoundD. Yen26.The __________ (英国宪法) is based on many documents.27.I feed my puppy with ________.28.What do we call a scientist who studies rocks and minerals?A. GeologistB. BiologistC. ChemistD. Environmentalist29. A mixture of two or more elements can create a new ______.30.What do you call a large body of freshwater flowing toward the sea?A. LakeB. RiverC. StreamD. CreekB31. A ______ is a large area of elevated land.32.The chemical formula for chromium trioxide is _______.33.I saw a _____ (兔子) nibbling on a carrot.34.The weather is ___ (warm) today.35.The ancient Greeks believed in the power of _____.36.What do we call the study of matter and its interactions?A. ChemistryB. PhysicsC. BiologyD. GeologyA37.I like to make ______ for my friends' birthdays.38. A _______ is a method of separating components based on their boiling points.39.I ________ to play games.40.We should always _____ (尊重) nature and its resources.41.What is the name of the famous bear in "The Jungle Book"?A. BalooB. BagheeraC. Shere KhanD. KaaA42.The _______ (Arab Spring) was a series of protests in the Arab world.43.There are five _____ (flowers) in the garden.44.The eagle flies high in the ______ (天空).45.An interesting place I have visited is __________, and I liked it because__________.46.What do you call a baby swan?A. CygnetB. DucklingC. GoslingD. FlapperA47. A snail can sleep for ______ (几个月).48.My sister enjoys __________ (参加) workshops.49.The ______ of a flower can sometimes determine its fragrance. (花的结构有时会决定它的香气。
高三英语科学前沿动态单选题50题(答案解析)
高三英语科学前沿动态单选题50题(答案解析)1.Scientists have made a breakthrough in the field of artificial intelligence. The new technology is called deep learning. What is deep learning?A.A kind of softwareB.A branch of mathematicsC.A method of machine learningD.A type of computer hardware答案：C。
deep learning 是深度学习，是一种机器学习的方法。
选项A，它不是一种软件；选项B，不是数学的一个分支；选项D，不是一种计算机硬件。
2.The latest scientific discovery is a new element. What is an element?A.A compoundB.A mixtureC.A substance made up of only one kind of atomD.A solution答案：C。
element 是元素，是由一种原子组成的物质。
选项A，compound 是化合物；选项B，mixture 是混合物；选项D，solution 是溶液。
3.In the field of space exploration, a satellite is launched. What is a satellite?A.A spaceshipB.A planetC.An object that orbits a planet or other celestial bodyD.A star答案：C。
satellite 是卫星，是围绕行星或其他天体运行的物体。
选项A，spaceship 是宇宙飞船；选项B，planet 是行星；选项D，star 是恒星。
“蒸发悖论”在秦岭南北地区的探讨
“蒸发悖论”在秦岭南北地区的探讨蒋冲;王飞;刘思洁;穆兴民;李锐;刘焱序【摘要】潜在蒸散量(ET0)是大气蒸发的估计值,已经广泛应用于灌溉管理和无实测蒸发资料地区的估算.分析ET0的时空变化是研究水资源对气候变化响应的基础工作,同时对于农业水资源的优化利用也具有重要意义.根据秦岭南北47个气象站1960-2011年逐日数据,利用FAO Penman-Monteith公式计算出各站的潜在蒸散量(ET0),研究了气温、降水与ET0之间的长期变化趋势关系,对导致ET0下降的主要原因进行了讨论,着重对秦岭南北地区是否存在“蒸发悖论”进行验证.结果表明:(1)秦岭南北整体气温经历了先降后升的变化过程,1993年为突变年份,1960-1993年的降温速率和1994-2011年的升温速率均表现出由南向北递减的规律,1960-2011年整体升温速率由北向南递减.(2)1979年和1993年是ET0变化的转折点,以1979和1993为界ET0经历了“升—降—降”的变化阶段.1960-1979年仅汉水流域和巴巫谷地存在“蒸发悖论”现象,1980-1993、1994-2011和1960-2011年3个时段区域整体和各子区均发现了“蒸发悖论”现象.秋季后18a 和52a整体以及冬季前34a和52a整体均存在“蒸发悖论”现象,冬季最为明显.(3)近52年整体降水表现出不显著的下降趋势,相较于年尺度,夏季降水与ET0逆向变化趋势更为明显.(4)年尺度上,太阳辐射(日照时数)下降引起的潜热通量减少是造成ET0下降即“蒸发悖论”现象的主要原因.季节尺度,春季ET0下降的主导因素为风速,其它季节均为太阳辐射(日照时数).【期刊名称】《生态学报》【年(卷),期】2013(033)003【总页数】12页(P844-855)【关键词】秦岭南北;潜在蒸散量;蒸发悖论;气温;降水【作者】蒋冲;王飞;刘思洁;穆兴民;李锐;刘焱序【作者单位】西北农林科技大学资源环境学院,杨凌712100;西北农林科技大学资源环境学院,杨凌712100;中国科学院水利部水土保持研究所,杨凌712100;北京大学遥感与地理信息系统研究所,北京100871;西北农林科技大学资源环境学院,杨凌712100;中国科学院水利部水土保持研究所,杨凌712100;西北农林科技大学资源环境学院,杨凌712100;中国科学院水利部水土保持研究所,杨凌712100;陕西师范大学旅游与环境学院,西安710062【正文语种】中文潜在蒸散量(ET0)是指在一定气象条件下水分供应不受限制时，某一固定下垫面土壤蒸发量和植物蒸腾量的总和，它是实际蒸散量的理论上限，也是计算实际蒸散量的基础，又被称之为参考作物蒸散量［1-4］。
地下水数值模拟模型简介.ppt
Introduction to Groundwater Model
优化（自动）调参法
设含水层参数分区为L个，含水层参数为Si、 Ki(i=1,…,L)。模拟区内共有观测点n个，模 拟时期（应力期）m个。则：
hsij-第i点（i=1,…,n）、第j个应力期(j=1,…,m) 的模型计算地下水位，它是含水层参数Si、 Ki (i=1,…,L)的函数。
hrij-第i点（i=1,…,n）、第j个应力期(j=1,…,m) 的实际观测地下水位。
Introduction to Groundwater Model
Groundwater Model_Math Model
Mass Balance
Qinput Qoutput Q
Darcy’s Law
q K dh dl
Boundary Conditions
First Type Second Type Mixed Type
Contents
What is Groundwater Model? Problems about GW Development Groundwater Model_Math Model Solving GW Flow Equation Numerical Methods Calibration of the Model
Introduction to Groundwater Model
Calibration of the Model
基于三维渗流数值模拟的调蓄水池地下水渗流影响分析
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（ＳｈａａｎｘｉＰｒｏｖｉｎｃｅＩｎｓｔｉｔｕｔｅｏｆＷａｔｅｒＲｅｓｏｕｒｃｅｓａｎｄＥｌｅｃｔｒｉｃＰｏｗｅｒＩｎｖｅｓｔｉｇａｔｉｏｎａｎｄＤｅｓｉｇｎ，Ｘｉ’ａｎ，Ｓｈａａｎｘｉ７１０００１，Ｃｈｉｎａ）
第 １８卷第 ２期 ２０２０年 ４月
水利与建筑工程学报
ＪｏｕｒｎａｌｏｆＷａｔｅｒＲｅｓｏｕｒｃｅｓａｎｄＡｒｃｈｉｔｅｃｔｕｒａｌＥｎｇｉｎｅｅｒｉｎｇ
ＤＯＩ：１０．３９６９／ｊ．ｉｓｓｎ．１６７２－１１４４．２０２０．０２．０４４
基于三维渗流数值模拟的调蓄水池 地下水渗流影响分析
Ｖｏｌ．１８Ｎｏ．２ Ａｐｒ．，２０２０
收稿日期：２０１９１２１０ 修稿日期：２０２００１１７ 作者简介：许建建（１９７６—），男，陕西富平人，高级工程师，主要从事水利工程设计、污水处理及再生利用研究工作。
Ｅｍａｉｌ：ｘｕｊｊ２０７６０５１７＠１６３．ｃｏｍ
第 ２期 许建建，等：基于三维渗流数值模拟的调蓄水池地下水渗流影响分析
许建建，惠焕利，裴旭阳
（陕西省水利电力勘测设计研究院，陕西 西安 ７１０００１）
摘 要：依据实测的调蓄池地形、地质数据，通过 Ｓｕｒｆｅｒ三维地图处理软件对数据预处理，采用 Ｖｉｓｕａｌ ＭＯＤＦＬＯＷ Ｆｌｅｘ地下水三维渗流数值模拟软件，建立了调蓄水池三维渗流数值模型，利用有限差分法模 拟地下水流动，分别计算了在设计水位时天然地基条件下水池地下水的三维渗流场和采取灰土垫层加 土工膜防渗措施后的地下水三维渗流场，根据渗流场分析了调蓄水池蓄水后形成的地下水渗流对周边 铁路、村庄及沟道临谷渗漏的影响，解决了复杂地形、地质条件下大型调蓄水池不能采用单一公式进行 多维度分析渗流场的难题，为调蓄水池设计的可行性、安全性提供了参考依据。 关键Ｕ４４１＋．３３ 文献标识码：Ａ 文章编号：１６７２—１１４４（２０２０）０２—０２５６—０７
基于不确定性分析的地下水污染超标风险预警
基于不确定性分析的地下水污染超标风险预警李久辉;卢文喜;常振波;李明彧;苗添升;赵莹;张将伟【摘要】Groundwater contamination prediction could be achieved through the numerical simulation model of groundwater contaminant transport.In order to analyze the influence of the uncertainty of parameters in the model, Monte Carlo method was used to analyze the uncertainty of the model output in this paper,In order to reduce the complexity of the numerical simulation model, the sensitivity analysis method was used to select the random variables in the model.To reduce the calculated load generated by the numerical simulation model called repeated, set up Krig surrogate model instead of the numerical simulation model to complete the simulation process. The results showed that the probability density function integral could be used to estimate the groundwater contamination risk and the contamination concentration range under different confidence level. Thedistribution of contaminant plume could estimate different level pollution cover acreage of the study area and the classification contamination risk early warning could estimate the contamination plume distribution of the study area in different contamination risk; Groundwater contamination risk warning, which was based on the uncertainty analysis of groundwater contaminant transport numerical simulation could forecast the groundwater problem more objectivily.%地下水污染预测可以通过地下水污染质运移数值模拟模型予以实现,为分析模型参数取值不确定性对模型输出结果的影响,本文运用蒙特卡洛方法对模型输出结果进行不确定性分析.为降低数值模拟模型复杂程度,运用灵敏度分析方法筛选对模型影响较大参数作为模型中随机变量;为减少重复调用数值模拟模型产生的计算负荷,在保证一定精度前提下,运用克里格方法建立模拟模型的替代模型完成模拟过程.结果表明:应用概率密度函数积分可以估计地下水遭受污染风险与不同置信程度下污染物浓度区间.污染羽分布图与分级污染超标风险预警图可以分别对研究区不同等级污染覆盖面积和研究区不同污染风险对应污染羽分布进行估计.基于污染质运移数值模拟不确定性分析的地下水污染超标风险预警可以更加客观地对地下水污染问题进行预测.【期刊名称】《中国环境科学》【年(卷),期】2017(037)006【总页数】8页(P2270-2277)【关键词】地下水污染;数值模拟模型;蒙特卡洛方法;克里格替代模型;不确定性分析【作者】李久辉;卢文喜;常振波;李明彧;苗添升;赵莹;张将伟【作者单位】吉林大学地下水与资源环境教育部重点实验室,吉林长春 130012;吉林大学环境与资源学院,吉林长春 130012;吉林大学地下水与资源环境教育部重点实验室,吉林长春 130012;吉林大学环境与资源学院,吉林长春 130012;吉林大学地下水与资源环境教育部重点实验室,吉林长春 130012;吉林大学环境与资源学院,吉林长春 130012;吉林大学地下水与资源环境教育部重点实验室,吉林长春 130012;吉林大学环境与资源学院,吉林长春 130012;吉林大学地下水与资源环境教育部重点实验室,吉林长春 130012;吉林大学环境与资源学院,吉林长春 130012;吉林大学地下水与资源环境教育部重点实验室,吉林长春 130012;吉林大学环境与资源学院,吉林长春 130012;吉林大学地下水与资源环境教育部重点实验室,吉林长春130012;吉林大学环境与资源学院,吉林长春 130012【正文语种】中文【中图分类】X523地下水污染预测可以运用地下水污染质运移数值模拟模型予以实现.过去地下水中溶质运移模拟多采用确定性模型求解,没有将水文地质参数获取的不确定性考虑在内,其结果参考价值不高,基于其结果的地下水污染预测与评价亦不够可靠,严重影响污染预防与污染治理相关措施实施,使污染得不到及时处理与改善,导致地下水环境及生态环境污染进一步恶化.故研究参数的不确定性对模型输出结果的影响对于地下水污染预测与风险预警是十分必要的.近年来不确定性分析研究在国内外发展迅速.水文地质参数不确定性与地下水研究结合层出不穷,但多用于水资源量评价,Kuczera等[1]将降雨量模型不确定性分析结果与降雨数据评估相结合,具有实际意义;曾献奎等[2]将地下水流概念模型不确定性分析应用于模型预测精度研究,使与地下水相关研究的不确定性分析进一步发展;束龙仓等[3]将水文地质参数不确定性分析与地下水补给量研究相结合,来评价地下水补给量离散程度,不确性分析多用于水量评价,在水质问题研究领域却很少见,直到欧阳琦等[4], 苗添升等[5]将不确定性分析结果与地下水遭受污染风险相结合,水质预测与不确定性分析结合才有所进展.根据前人经验,将不确定性分析与地下水污染预测相结合,运用灵敏度分析方法筛选出对数值模拟模型输出结果影响较大的参数,作为模型中随机变量以降低模型复杂程度;为减少重复调用模拟模型产生的计算负荷,在保证一定精度前提下,运用克里格方法建立数值模拟模型的替代模型完成蒙特卡洛模拟,最后对蒙特卡洛结果进行统计分析.利用概率密度函数估计不同置信程度的污染物浓度范围;运用数理统计方法分析研究区各个有限差分网格(运用 GMS软件剖分离散得到的差分网格)污染物浓度值服从分布规律,实现对研究区地下水不同程度污染的污染羽分布预测与分级污染超标风险预警,为地下水污染预测提供更多选择依据.1.1 蒙特卡洛方法本文以蒙特卡洛方法作为不确定性分析的的总体研究思路.蒙特卡洛方法的主要思想是当待求解的问题是某种随机事件出现的概率,或者是某个随机变量的期望值时,通过“实验”统计的方法,用这个随机事件在实验中出现的频率对随机事件发生的概率进行估计,或者利用实验中随机事件的数字特征,作为研究问题的解.在研究过程中无论随机事件结果满足何种分布,在模拟次数足够多的情况下,都可以得到一个比较精确的概率分布[6].文中将污染质运移数值模型视为“实验”发生器,将模型输出的污染物浓度结果视为研究区污染问题这一随机事件出现的结果,最后利用输出的污染物浓度结果估计地下水污染事件总体.1.2 模型建立建立一个东西长 1000m,南北宽 550m,含水层厚度为20m的研究区,含水层为均质各向同性潜水非稳定流,初始水位为16m,水流方向由西至东;区域内地表平坦,南侧Г2及北侧Г4均为隔水边界;西侧Г1有一河流,切穿潜水含水层且与其具有较好的水力联系,河流水位稳定为18m;东侧Г3有一湖泊,水位稳定为16m.研究区在垂向上均匀的接受大气降水补给,年平均降水量为580mm;在忽略蒸发腾散消耗量前提下,地下水排泄方式主要是人工开采,井1、2,3抽水量均为500m3/d.区内一化工厂污水未经处理泄漏到地下含水层中,污水污染物浓度为 400mg/L,泄漏量为600m3/d.将污染物视为不会发生化学变化及生物转化与迁移的稳定污染物.潜水含水层中污染物的初始浓度为零,定水头边界Г1,Г3与隔水边界Г2,Г4分别视为零浓度边界和零通量边界.根据研究区概况,为更好地对研究区污染质运移情况进行研究,利用GMS将研究区剖分离散为220个有限差分网格,区内剖分情况及观测井与污染源位置详见图1：根据研究区水文地质条件建立研究区的地下水水流数值模型：式中：K为含水层渗透系数,m/d;H为潜水水位,m; B为潜水含水层底板高程,m;Q 为人工开采强度,m/d;R为降水入渗补给量,m/d;μ为含水层给水度,无量纲;S为模拟区范围;Г1,Г3为定水头边界;Г2,Г4为零流量边界;Kn为边界法向量上的渗透系数,m.污染质随水流运移,在建好的地下水水流数值模型基础之上,建立地下水污染质运移数值模型：式中：S为模拟区范围;Г1,Г3为定浓度边界;Г2,Г4为零弥散通量边界;n为含水层介质的孔隙度,无量纲;c为污染质浓度,mg/L;Dx,Dy为水动力弥散系数在x、y方向的分量,m2/d;x yv v、为渗透流速v在x、y方向上的分量, m/d; I为单位时间单位液相体积内溶质质量的增减量,mg/(d⋅m3).在建立好研究区的污染质运移数值模型基础之上,利用GMS软件将研究区剖分为220个有限差分网格,然后利用其MODFLOW工具箱和MT3DMS工具箱模拟15年后研究区污染质运移情况.为了简化模型计算,可以将对模型影响较小的随机参数作为定值输入模型,影响较大的参数作为随机变量输入模型,为实现这一研究过程,应该运用有效方法对模型中多个随机参数进行逐一筛选.1.3 灵敏度分析方法筛选随机参数运用灵敏度分析方法筛选出对污染质运移数值模型输出结果影响较大的参数,可以在提高研究精度同时减少计算负荷.灵敏度分析常用的两种分析方法是全局灵敏度分析方法和局部灵敏度分析方法[7].灵敏度分析应用广泛,束龙仓,王茂枚等[8]对灵敏度分析方法进行了阐述,并将局部灵敏度分析和全局灵敏度分析引入地下水数值模型,来模拟塔里木河下游地下水水位变化情况.文中采用局部灵敏度分析方法筛选随机参数.局部灵敏度分析即利用参数求偏导数反映参数变化对结果影响程度的大小,来选择影响较大参数,公式如下：式中：Sk是灵敏度系数;αk是输入模型参数值;△αk是输入模型参数变化量;yi(αk+△αk)是参数变化△αk时,模型输出结果;yi(αk)是参数为αk时模型输出结果.灵敏度系数越大,说明此参数对模型输出结果影响越大.时,先将模型中参数取波动均值见表 1,输出污染物浓度,然后分别将模型中某个随机参数加减20%,10%,其他参数不变,利用式(3)筛选出2个灵敏度系数较大的参数作为随机变量.根据图 2可知,对模型输出结果影响较大的2个随机参数分别是渗透系数和纵向弥散系数.将渗透系数和纵向弥散系数作为随机变量,其它参数取波动均值(定值)输入模型.为实现渗透系数和纵向弥散系数两个随机变量在参数变化范围内多组不同取值,应该选择适当的方法对两个随机参数分别抽样取值.1.4 拉丁超立方方法运用拉丁超立法抽样方法对筛选出的两个随机参数分别抽样取值,可以有效的降低参数的抽样误差,使参数取值具有代表性.拉丁超立法抽样方法是将服从某个分布的参数在其波动范围内进行等概率分层,并在每一层中抽取相同数量的参数组成参数样本的一种抽样方法.根据前人经验总结,渗透系数,纵向弥散系数服从分布如表1所示[9].运用MATLAB利用拉丁超立方方法对渗透系数,纵向弥散系数分别抽样取值.对渗透系数,纵向弥散系数分别抽样 50组,运用污染质运移数值模拟模型求解,输出井1、2、3的50组污染质浓度结果.因为少量的数据没有办法支撑地下水污染预测研究,多次重复调用模拟模型又会产生大量的计算负荷,且耗时较长,故利用模拟模型的 50组随机参数与输出结果数据集建立克里格替代模型代替模拟模型求解.1.5 建立替代模型在保证一定精度前提下,为减少运用污染质运移数值模拟模型的计算负荷建立数值模拟模型的替代模型完成蒙特卡洛过程.此次研究选择克里格内插法建立替代模型.克里格方法由南非地质学家 Krige[10]提出的一种插值方法,它从变量的相关性和变异性出发,利用方差的变化表达空间的变化,在引入似然函数估计误差最小的情况下,通过已知观察点估计未知观察点.目前克里格方法被延伸为一种建立替代模型的方法,替代模型做为一种黑箱模型[11],应用于多个工程领域.替代模型建立可以按以下步骤实现：式中：y(x)是替代模型中要求解的污染物浓度值;(x)是 y(x)的估计值,可以分为两部分,f(x)Tβ为线性回归部分,z(x)为随机部分;f(x)=[f1(x), f2(x),…，fk(x)]为已知模型的基函数;待定参数β = [β1,β 2,… ,β k]为基函数系数,可以利用训练数据求出;随机部分z(x)满足下列条件：式中：R(xi,xj)为任意两采样点 xi,xj之间的空间相关关系方程,也称关联函数,文中采用 EXP型的关联函数：式中：θk为待定参数;xi为第i个样本的k维坐标.k根据克里格模型,在点 x处的响应值 y(x)的估计值为：式中：r( x)为点x与n个采样点(x1,x2 ,…, xn)的相关向r( x) =[R( x, x1 ),R( x, x 2 ),… ,R( x, x n)];y为n个采样点对应的响应值,为n×1阶向量;β为线性回归部分的待定参数,通过最优线性无偏估计可以求得：式中：R为n个采样点相关系数组成的n×n阶相关矩阵：方差2σ 估计值用(10)式确定：替代模型的建立可以通过求解上面的非线性无约束优化问题[12]来实现.待定参数θk求出后,通过建立的替代模型可获得待求响应值. θk可以通过无约束优化(11)式求得[13-14]：由图 3可知替代模型输出的污染物浓度与检验样本的相对误差均小于 1%,误差较小,故认为替代模型精度较高,可以代替模拟模型求解.再次利用拉丁超立方方法对渗透系数和纵向弥散系数分别抽样1000组,输入克里格替代模型代替模拟模型求解,得到井1、2、3的各1000组污染物浓度值.对井1、2、3的各1000组污染物浓度值进行统计与分析.2.1 观测井污染预测与分析2.1.1 污染物浓度统计分析对 3口观测井的各1000组污染物浓度值各项统计指标进行统计,绘制3口观测井污染浓度直方图.结合图4和表2可知,井2污染物波动范围较大,分布较井1,3分散,可能原因是井2位于地下水流向下方,与污染源距离较远且相对来讲靠近定水头边界,这些因素的综合影响导致井 2中污染物浓度波动较大.且浓度与井1,3相比偏高,原因可能井2位于地下水流向一侧,污染质在水流携带作用下运移加快,导致其浓度偏高.井 1,3与隔水边界距离相等,与污染源距离有微小差距.故2口井污染浓度相差较小,波动区间也比较相近.2.1.2 污染超标风险预警为了对观测井中污染物浓度进行更具体的统计分析,应用偏度·峰度检验法[15]对替代模型输出浓度值服从分布进行检验.偏度·峰度检验法是检验数据是否服从正态分布的一种数学方法,方法原理是利用数据样本计算出样本峰度,偏度与正态分布总体峰度,偏度的近似程度来判断数据是否来自正态分布总体. 利用峰度·偏度检验法检验出3口观测井中污染物浓度值在满足显著水平为α=1%、置信程度为 1-α=99%时来自正态分布总体.井 1、2、3污染物浓度值的拟合情况见图5：在评价井中地下水遭受污染风险时可以对1000组污染物浓度值进行正态分布拟合,求出拟合的正态概率密度函数,对正态概率密度函数进行积分求出地下水受污染风险,公式见(12)：式中：P是观测井污染风险大小;f(x)是污染物浓度值服从的概率密度函数;σ为正态分布的标准差;μ是正态分布的均值;m是污染物超标标准.将污染物浓度超过120mg/L视为轻度污染,超过 200mg/L 视为较严重污染,超过280mg/L视为重度污染,利用(12)式进行积分求出井1、2、3为轻度污染风险分别为99.94%、98.47%、74.50%;为较严重和严重污染风险均为0%,根据风险评价结果可知3口井相比井3受污染风险较小,相比于井1和井2,井3更适合做水源.对正态概率密度函数积分可以得到井1、2、3中污染物浓度在置信程度分别为80%、60%、40%, 20%时地下水污染物浓度波动区间,见表3.2.2 研究区污染预测与分析2.2.1 污染羽范围分布预测与分析为预测研究区污染羽分布范围,利用替代模型输出研究区220个剖分网格的各1000组污染物浓度的均值绘制不同程度污染的污染羽分布图.污染物浓度超过 120mg/L的区域为轻度污染区域,超过200mg/L区域为较严重污染区域,超过 280mg/L为严重污染区域,利用均值绘制图6,根据图6可知 15年后研究区受污染总面积约为 175000m2占研究区总面积的 32%,其中严重污染覆盖面积最约为90000m2占研究区总面积16%.根据研究区被污染面积大小,决策者可以提前准备污染治理工作,根据研究区发展情况规划需要治理的污染面积.2.2.2 研究区污染分级风险预警为对研究区遭受污染风险进行预警,统计替代模型输出的研究区220个剖分网格的各1000组污染物浓度输出值服从的分布规律,根据统计结果,分析各剖分网格受不同程度污染风险,对研究区不同程度污染的不同污染超标风险对应污染羽分布进行预测.由污染超标风险预警图(图 7～图 9)可知在污染超标风险相同情况下,污染羽覆盖范围随污染级别增大反而有减小态势.对于相同程度污染,随污染风险置信程度增高,污染羽分布有减小态势,若选择污染风险为99%时的区域作为重点污染治理区,需要治理面积可由污染超标风险预警图计算得到.根据资金,设备,人员情况,也可以选择相信其它污染风险对应的污染面积进行治理.除此之外,可以根据研究区能够承受的污染风险上限对污染问题进行提前防治工作.也可以将污染超标风险预警图与研究区内人口密度及生活情况相结合,确定更经济更清洁的水源位置.结合污染风险预警图可以看出相同污染程度下,井3受污染风险最小,与井1、2比较,井3更适合做水源.3.1 运用灵敏度分析方法筛选出渗透系数与纵向弥散系数作为数值模拟模型中随机变量,在保证一定精度前提下建立模拟模型的替代模型完成蒙特卡洛模拟过程,可大幅度减小计算负荷,对于工程领域的研究工作具有实践意义.3.2 利用概率密度函数可以对地下水遭受污染风险与不同置信程度的污染物浓度范围进行估计;污染羽分布图可以对研究区不同等级污染的污染羽覆盖面积进行估计,分级污染风险预警图可以对研究区不同污染等级的污染超标风险进行预警.3.3 基于污染质运移数值模拟不确定性分析的地下水污染超标风险研究与确定性的地下水污染问题研究相比,可以对地下水污染进行更加客观的预测,为决策者提供更多选择依据,对于地下水污染研究有重大意义.【相关文献】[1]Kuczera G, Kavetski D, Franks S, et al. 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