水电站旁通洞的水力特性模型试验

对拟建水库的长、短旁通洞排沙效果进行了水工模型试验研究,试验中率定了旁通洞的泄流能力;观测了旁通洞进口及洞内流态;测量了长、短旁通洞在正常水位下,宣泄不同流量时的含沙量等。试验结果表明:在闸门全开情况下,长、短旁通洞的泄流能力均超过200m3/s;在输沙模数1200t/km2考虑下,长旁通洞方案中水典型年过机年平均含沙量为51.3g/m3,短旁通洞方案中水典型年过机年平均含沙量为59.0g/m3。研究结果证明:长、短旁通洞泄流能力均满足分流要求、旁通洞进口段与导流洞结合段无不良流态、短旁通洞的输沙能力略优于长旁通洞方案。     

公伯峡水电站导流洞安全监测分析评价

公伯峡水电站导流洞下闸蓄水1个月后对导流洞导0+159 m-导0+214 m段进行了封堵,但导流洞导0+214 m下游段改建为右岸旋流式泄洪洞下平洞段的漩流洞、水垫塘和退水洞,为此导流洞导0+214 m以下洞身段安全运行直接影响右岸泄洪洞泄洪.文章对公伯峡水电站导流洞导0+214 m以下洞身4个监测断面监测资料进行全面...     

某隧道从施工横洞进入正洞施工方案研究

某高速公路隧道全长4847m,位于海拔2300m的高原,服务隧道先行贯通,为加快施工进度,从施工横洞进入正洞施工,该文详细介绍了通过服务隧道的施工横洞进入正洞正向开挖、反向开挖的施工方案,该方案在实施过程中取得了良好的效果。     

粉煤灰堆积体地层连拱隧道开挖错距影响分析

粉煤灰堆积体自稳能力差,受力即破碎成散颗粒,隧道穿越粉煤灰场区时失稳围岩对施工安全构成极大威胁。以盐坪坝连拱隧道为依托,根据粉煤灰力学性质对比选用了塑性-硬化本构,通过有限差分软件FLAC3D对不同开挖错距进行数值模拟,设置中导洞上下台阶以及左右洞开挖错距工况分别为5m、10m和15m,研究不同开挖错距对粉煤灰堆积地层中双连拱隧道的围岩和结构的影响。结果表明：中导洞台阶开挖错距不宜超过10m,15m错距相比10m错距应力最大值增长了36.82%,左右洞采用小开挖错距可以有效减少中导洞拱顶位移；中导洞开挖完成后左右洞拱顶竖向位移已达到其总沉降量约50%,左洞拱顶沉降位移与开挖错距近似线性增长,后行洞开挖过程中对先行洞造成的影响较大；主洞采用不同开挖错距时应力积聚分布在不同位置,开挖错距大于10m后结构受力增幅快速增长,15m错距相比10m错距应力最大值增长了17.28%。可见主洞开挖错距不宜超过10m。     

浅议引水隧洞掌子面涌水处理技术

正概述石兜水库新建的引水隧洞担负着向厦门市供应原水的重任,该隧洞总长4285.30m,断面为城门洞形,洞径为3.6m,隧洞出口与下游供水管道相连接,为同时满足往下游坂头水库放水要求,在隧洞中部设一施工支洞兼作坂头水库放水洞,支洞断面为城门洞形总长535m,洞径为3.0m。2012年4月     

鼠类对吉林西部春季草原环境的影响研究

通过铗日法和洞道调查,得知吉林省松嫩平原北大岗草原分布有5种草原鼠：即达乌尔黄鼠、黑线仓鼠、草原鼢鼠、五趾跳鼠、缺齿鼹。鼠洞密度为29个/hm2。鼠类活动使草原平均覆盖率下降29.2%,平均高度降低4.8 cm,使丰富度指数降低16.1%,使草原鲜重生物量下降51.2 g/m2;干重生物量下降36.1g/m2,使一部分...     

湖南洛塔屋檐洞地下河系统BP人工神经网络分析

采用湖南洛塔地区屋檐洞地下河系统降水—径流资料训练BP人工神经网络,建立了该系统的径流预测模型.通过降水对径流的贡献率进行快速流和慢速流的划分,屋檐洞地下河系统的快速流与慢速流比例接近2∶3.以可直接开发利用的慢速流计,屋檐洞地下河系统地下水允许开采量为0.363 2×108m3/a.     

无中导洞连拱隧道掌子面纵向间距优化

作为一种大跨径地下结构形式连拱隧道结构复杂,无中导洞法能在提高施工速度的基础上降低中隔墙渗漏水。为研究连拱隧道无中导洞法施工活动对隧道先后行洞的影响程度,以陈家滩隧道为研究对象通过数值模拟,研究了不同间距下先后行洞的影响范围、先后行洞的影响程度以及中隔墙的倾覆趋势。结果表明：当先行洞开挖至控制截面5m范围内对围岩的影响最大,其围岩位移释放系数增量达到了40%以上;超过控制截面10 m时其围岩释放系数达到了93%以上,影响程度较小;超过20 m时影响程度可以忽略。当先后行洞纵向间距大于35 m时影响程度S值接近10%,纵向间距大于40 m时S值小于10%。从中隔墙的倾覆程度来看当先行洞开挖完成时,中隔墙的倾斜程度达到最大,倾斜角约为3.28×10-4;而纵向间距大于30 m时倾斜角差值为0.351×10-4,此时中隔墙倾斜程度较大极差较小,有利于中隔墙受力。故先后行洞开挖掌子面纵向间距建议控制在30 m~40 m左右。     

贵州黔西县水西洞洞穴成因及价值研究

黔西县水西洞主要呈NE-NEE向发育于下三叠统茅草铺组(T_1m)可溶岩层内,由五条主洞及三个洞厅组成,实测长度为10557. 13 m,最低点高程762. 12 m,最高点高程920 m,高差达157. 88 m。洞道形态呈拱形、梯形、三角形等,洞穴次生碳酸钙沉积物充分发育,不同类型的沉积物通常相伴生,部分洞段分布较密集,规模体量较大,多沿层理、节理发育,造型较美观,具有极高的观赏价值和美学价值。冲积物主要为粘土及粉砂。水西洞形成经历了深潜期、渗流期及半悬托期三个阶段,是区域地质构造演化的反映,洞内广泛分布的石笋是了解古气候演变的重要载体,具有较高的科学价值。     

塔河风化壳储层典型单元注水方式优化研究

风化壳古岩溶作用形成的缝洞型油藏是塔河油田奥陶系油藏的主要储层类型,其由于缝洞发育,非均质性极强。目前在注水开发过程中,部分缝洞单元注水效果变差。为强化注水效果,利用数值模拟方法研究了塔河某油藏典型生产单元的最佳注水方式组合。根据注水见效期、稳定期以及调整期的含水率特点,通过对注水方式的组合优化模拟,论证了最佳注水组合的模式及注采参数。模拟结果显示,最佳注水组合为先温和持续注水,后周期注水,最终转为脉冲注水的模式。基于该油藏参数,三种注水方式的参数的优化结果为持续注水强度200 m3/d,常规周期注水采用长注短停注60 d停15 d的方式,脉冲注水为(100~200)m3/d间隔30 d的方式间歇注入。     

Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago

Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20?metres, in less than 500?years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the B?lling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.     

Recent and episodic volcanic and glacial activity on Mars revealed by the High Resolution Stereo Camera

The large-area coverage at a resolution of 10-20 metres per pixel in colour and three dimensions with the High Resolution Stereo Camera Experiment on the European Space Agency Mars Express Mission has made it possible to study the time-stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of Mars. Here we show that calderas on five major volcanoes on Mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history, with phases of activity as young as two million years, suggesting that the volcanoes are potentially still active today. Glacial deposits at the base of the Olympus Mons escarpment show evidence for repeated phases of activity as recently as about four million years ago. Morphological evidence is found that snow and ice deposition on the Olympus construct at elevations of more than 7,000 metres led to episodes of glacial activity at this height. Even now, water ice protected by an insulating layer of dust may be present at high altitudes on Olympus Mons.     

不同海拔高度对视觉机能的影响

人在不同海拔高度(4000米以下),对红、绿色能正确辨认;对黄、白色在海拔3980米时出现错辨;对蓝色则从海拔2640米以上开始产生错辨,尤其在距离120米处错辨率达72.7%,在海拔3980米距离为120米处错辨率达78.8％.结果表明:视觉机能减弱不仅与高原低氧而且与疲劳因素有关.     

Twenty-first-century warming of a large Antarctic ice-shelf cavity by a redirected coastal current

The Antarctic ice sheet loses mass at its fringes bordering the Southern Ocean. At this boundary, warm circumpolar water can override the continental slope front, reaching the grounding line through submarine glacial troughs and causing high rates of melting at the deep ice-shelf bases. The interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice-mass loss. Here we show that a redirection of the coastal current into the Filchner Trough and underneath the Filchner-Ronne Ice Shelf during the second half of the twenty-first century would lead to increased movement of warm waters into the deep southern ice-shelf cavity. Water temperatures in the cavity would increase by more than 2 degrees Celsius and boost average basal melting from 0.2 metres, or 82 billion tonnes, per year to almost 4 metres, or 1,600 billion tonnes, per year. Our results, which are based on the output of a coupled ice-ocean model forced by a range of atmospheric outputs from the HadCM3 climate model, suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern Weddell Sea due to thinning of the formerly consolidated sea-ice cover. The projected ice loss at the base of the Filchner-Ronne Ice Shelf represents 80 per cent of the present Antarctic surface mass balance. Thus, the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of Antarctic ice streams and ice shelves, and global sea level rise.     

A globally coherent fingerprint of climate change impacts across natural systems

Causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local, short-term biological changes. Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends across diverse species and geographic regions; however, debates within the Intergovernmental Panel on Climate Change (IPCC) reveal several definitions of a 'systematic trend'. Here, we explore these differences, apply diverse analyses to more than 1,700 species, and show that recent biological trends match climate change predictions. Global meta-analyses documented significant range shifts averaging 6.1 km per decade towards the poles (or metres per decade upward), and significant mean advancement of spring events by 2.3 days per decade. We define a diagnostic fingerprint of temporal and spatial 'sign-switching' responses uniquely predicted by twentieth century climate trends. Among appropriate long-term/large-scale/multi-species data sets, this diagnostic fingerprint was found for 279 species. This suite of analyses generates 'very high confidence' (as laid down by the IPCC) that climate change is already affecting living systems.     

长江防洪堤南京段设计洪水风险分析

长江南京段洪水位存在明显上升的趋势,为确保新水情下防洪堤的安全,首先分析了引起该河段水位上升的原因,然后按３种方案研究了今后长江南京段出现不同水位的风险度,研究结果表明,长江南京段水位突破历史最高值１０．２２ｍ的重现期为２７年,１００年一遇的设计洪水位达１０．８ｍ左右。     

新疆尼雅河一场罕见的特大洪水成因分析

1999年8月初，昆仑山北坡诸河相继发生了罕见的特大灾害性洪水，尤其是位于和田地区的尼雅河出现了1969～2005年间实测最大洪峰流量649m^3／s，是该河历年第二大洪峰流量的3倍多。经调查、计算与分析，“99．8”洪水属特殊洪水类型，洪水暴涨暴落现象十分突出，同时，分析了此次特大灾害性洪水的发生过程特性及成因。     

Endangered species: Pan-Atlantic leatherback turtle movements

The overall extent of habitat use by leatherback turtles in the North Atlantic, and hence their possible interactions with longline fisheries, is unknown. Here we use long-term satellite telemetry to reveal that leatherbacks range throughout the North Atlantic, indicating that closing limited areas to longline fisheries will probably have only partial success in reducing turtle bycatch. Although turtles dive very deeply on occasion (one descended to a maximum depth of 1,230 metres, which represents the deepest dive ever recorded for a reptile), they generally restrict their diving to less than 250 metres, which increases the chance that they will encounter longline hooks.     

Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet

During the last interglacial period (the Eemian), global sea level was at least three metres, and probably more than five metres, higher than at present. Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6-7 metres. But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet, with model studies attributing only 1-2 m of sea-level rise to meltwater from Greenland. This result was considered consistent with ice core evidence, although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period. Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses. Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian, and plausibly contributed 4-5.5 m to the sea-level highstand during that period. We conclude that the high sea level during the last interglacial period most probably included a large contribution from Greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the West Antarctic ice sheet.     

深水湿法焊接气孔问题研究

根据水下湿法焊条在压力舱内焊接的试验结果，讨论了焊接水深(10～80m)对焊缝金属气孔生成的影响。指出：水下湿法焊接由于焊接冶金及熔池结晶的特殊性，容易生产内气孔．而外气孔则当水深增加至较深的深度时(一般为60m)才开始出现，且内外气孔数量均随水深的增加而增加；通过研究气孔数量随焊缝金属残余氢含量及氧含量变化的趋势，推断出水下湿法焊接气孔主要属于氢气孔。