用能量法研究深直井管柱最大转速与正弦屈曲时临界轴向力间的关系

通过考虑离心力对钻柱屈曲的影响，运用能量法研究了钻柱最大转速与正弦屈曲时临界轴向力间的关系，进而得到了转速－轴向临界力的数学模型。综合考虑钻柱惯性离心力和自重的影响，我们发现，在工作状态下，钻柱的临界压力会明显地小于静态时的临界力，这对实际的钻探工程来说具有十分重要的指导意义。     

海冰对圆台结构的作用力及结构相互遮蔽关系

利用非冻结模型冰进行海冰对圆台结构上的水平和垂直冰作用力物理模拟试验研究, 给出作用在单圆台结构上水平和垂直冰力上限值同抗弯强度的包络线关系. 对于同类型的圆台, 能够依照一定模型比尺下的模型冰抗弯强度确定作用在圆台上的冰作用力试验值, 然后按照相似比尺复原到原型冰力. 当相邻两个圆台结构物距离比较近时, 圆台结构物之间会发生相互遮蔽. 通过系列不同相邻结构间距和夹角的物理模拟试验, 结合几何投影关系和圆台结构物前冰层的破碎特点及前人已有简单结构的试验理论关系形式, 利用新的物理模拟数据拟合出两个圆台结构之间冰力遮蔽系数同几何遮蔽系数的试验关系.     

考虑斜坡效应的基桩屈曲临界荷载分析

以某实际工程桩为原型,根据相似理论设计并完成了斜坡基桩竖向承载室内模型试验,分析了不同坡度及桩长条件下斜坡基桩屈曲临界荷载,获得了基桩屈曲临界荷载理论计算公式及拟合公式。研究表明:竖向荷载作用下,基桩荷载-位移曲线均无明显拐点,且桩顶沉降、水平位移均随坡度或桩长的增加而增大,斜坡基桩的屈曲失稳破坏模型非常显著。斜坡基桩的屈曲临界荷载值由桩顶沉降和水平变形共同控制,斜坡坡度越大或基桩自由段越长,其屈曲临界荷载及竖向承载折减系数越小,斜坡效应越明显。对比分析表明,由理论公式和拟合公式计算得到的结果与模型试验结果均吻合较好,最大误差尚不足10%,验证了模型试验、计算理论及拟合公式的合理性,其成果可以为实际工程设计提供参考。     

关于渗流的力及其应用

饱和渗流是岩土体失稳的重要因素。叙述了渗流产生的消极破坏力“浮力”和积极破坏力“渗透力”。较详细地讨论了渗流各力之间的相互转换关系及其在管涌滑坡问题中的正确应用;并特别推荐引用渗透力计算滑坡问题具有简便、精确的优点。并指出了在计算中和设计规范中引用渗流力方面的误解。     

拖曳锚与安装缆绳相互作用力计算方法研究

深水系泊系统及其系泊基础的研发已成为国际海洋工程领域的前沿和关键课题,拖曳锚因其在承载力和深水安装中的诸多优势而具有良好的发展前景。在拖曳锚安装过程中,锚板与安装缆绳在系缆点处发生复杂的相互作用,分析二者之间的相互作用可等价为分析系缆点拖曳力的大小,研究拖曳锚与安装缆绳相互作用力的计算方法对认识锚板在海床土中的受力以及确定拖曳锚安装船的吨位具有重要指导意义。分别基于嵌入缆绳和拖曳锚在海床土中的力学模型,首次推导出适用于黏性土和无黏性土的系缆点拖曳力表达式,并开展模型试验验证,对比两类拖曳力计算方法的精度和稳定性,结果表明,两类计算方法均能合理预测系缆点拖曳力,但基于拖曳锚受力模型获得的表达式更为精确和稳定;通过参数考察,探究系缆点拖曳力预测模型中各参数的影响效应;经过与试验对比,给出关键参数的建议取值,该取值对研究结构与土体的相互作用问题具有重要参考价值。     

半圆型结构冰压力的物理模拟试验研究

利用DUT-1非冻结合成模型冰开展1:25冰对半圆型构件的物理模拟试验研究. 首先用简单的斜面构件的物理模拟试验检验了整体试验装置和技术设备的可靠性, 然后以同样比尺进行2种冰厚在5个不同水位条件的系列试验, 获得了模型冰排在半圆型构件前的破碎堆积现象和作用于构件上的水平和垂直作用力过程.结合实测模型冰物理和力学指标, 通过优化组合, 拟合出半圆型防波堤冰荷载的试验公式. 这些公式包含了冰对半圆型结构的弯曲破坏作用力、挤压破坏作用力及爬坡和堆积作用力.     

考虑渗流力的海床临界冲刷机理及计算方法

从波浪引起的海床内部渗流与床面泥沙运动耦合的角度出发,研究波浪作用下海床临界冲刷机理及计算方法。研究表明,波浪作用下床面泥沙起动及冲刷是一个不断向下发展的过程,最终达到一个临界冲刷深度。波浪引起的渗流力能够显著降低泥沙的临界起动切应力,促进泥沙起动,是影响海床冲刷的一个重要因素。将渗流力引入到传统泥沙起动公式中,推导并给出了波浪作用下海床临界冲刷深度的计算方法。结合室内和现场两个算例,很好地解释了波浪水槽试验中海床"流化"现象和黄河水下三角洲粉砂流冲沟等灾害地貌特征及成因,初步验证了该方法用于评价和计算海床冲刷的有效性。     

考虑渗流力的海床临界冲刷机理及计算方法

从波浪引起的海床内部渗流与床面泥沙运动耦合的角度出发,研究波浪作用下海床临界冲刷机理及计算方法。研究表明,波浪作用下床面泥沙起动及冲刷是一个不断向下发展的过程,最终达到一个临界冲刷深度。波浪引起的渗流力能够显著降低泥沙的临界起动切应力,促进泥沙起动,是影响海床冲刷的一个重要因素。将渗流力引入到传统泥沙起动公式中,推导并给出了波浪作用下海床临界冲刷深度的计算方法。结合室内和现场两个算例,很好地解释了波浪水槽试验中海床"流化"现象和黄河水下三角洲粉砂流冲沟等灾害地貌特征及成因,初步验证了该方法用于评价和计算海床冲刷的有效性。     

静水压力作用下圆拱正对称失稳临界力的求解

按Ｒｉｔｚ法求得铰支和固支圆拱受静水压力作用时,具有高精度的正对称失稳临界力的第３次近似值。在圆拱临界力的求解中,还可同时导得圆环以不同波数失稳的临界力的精确值。     

静水压力艇下圆拱正对称失稳临界力的求解

按Ｒｉｔｚ法求得铰支和固支受水压力作用时,具有高精度的正对称失稳临界力的第３次近似值。在圆拱临界力的求解中,还可同时导得圆不以不同波数失稳的临界力的精确值。     

Glacio-isostasy and Glacial Ice Load at Law Dome, Wilkes Land, East Antarctica

The Holocene sea-level high stand or “marine limit” in Wilkes Land, East Antarctica, reached 30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 ¹⁴C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 ¹⁴C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105°–160° E) suggests that a similar ice load of up to 1000 m existed along the EAIS margin between Wilkes Land and Oates Land.     

累积海冰密集度及其在认识北极海冰快速变化的作用

为定量分析北冰洋海冰密集度年际差异,提出并采用累积海冰密集度(ASIC)概念。利用SSMR/SSMI的分辨率为25 km的海冰密集度数据,分别研究了1979—2011年北极海冰在融冰期(4~9月)和结冰期(10月至翌年3月)的变化过程以及2个冰期内ASIC的区域差异。研究发现,在1979—1989年、1989—1999年和1999—2009年期间,融冰期海冰发生明显变化的范围都远远大于结冰期海冰发生明显变化的范围。1998—2010年,融冰期内发生加速融化的海区并没有都出现结冰期冰量减小的现象。在此期间融冰期ASIC减小,结冰期ASIC也减小的海域仅集中在楚克奇海、新地岛北部海域以及格陵兰岛东西海岸。融冰期ASIC减小,而结冰期ASIC无明显变化的海域包括波弗特海、东西伯利亚海、拉普捷夫海和喀拉海。这些区域与局地陆地径流侵入的海域重合。研究发现,在这些区域,融冰期ASIC减少是陆地径流增大加速海冰融化引起的。在结冰期,陆地径流加速海水结冰的作用消除融冰期海水吸收大量太阳辐射能后发生推迟结冰的现象,使得ASIC无明显变化。融冰期ASIC减小,而结冰期ASIC增大的区域只有白令海。研究结果证明累积海冰密集度能够去除海冰高频变化而只表现低频变化,能够描述海冰的年际变化特征。同时由于海冰变化与海洋中其他物理参数存在显著关系,变T的ASIC可以更加方便地描述次表层叶绿素最大值层深度的变化。     

格陵兰冰盖表面消融研究进展

冰盖表面消融是格陵兰冰盖物质平衡的重要组成部分, 已成为近年来格陵兰冰盖研究的热点. 格陵兰冰盖表面消融研究的关键在于理解冰盖融水的产生、 运移和释放等水文过程, 需要解决如下关键科学问题: 1) 冰盖表面产生了多少融水;2)冰盖表面水文系统具有什么特征; 3)冰盖表面融水如何影响冰盖运动; 围绕这些科学问题, 总结了格陵兰冰盖表面消融的研究进展. 冰盖表面消融建模、 冰盖表面湖的信息提取与面积特征变化、 深度反演与体积量算等是目前研究冰盖表面融水量的主要途径, 冰盖表面湖、 冰盖表面径流、 锅穴与冰裂隙等表面水文要素的空间分布规律研究则可用于揭示冰盖表面水文系统特征, 冰盖表面融水与冰盖运动速率的关系、 表面融水进入冰盖内部与底部的水文过程是目前揭示表面融水如何影响冰盖运动的主要手段.     

东南极洲中山站附近1年生海冰的发育和结构特征及其对生物群落的影响(英)

Sea ice growth, characteristics and ice algal biomass were measured at four sites off Zhongshan Station (66°22, 24" S, 76°22, 40" E), East Antarctica in 1992. The ice formed in late March,grew stablely and reached its highest thickness of 174 cm in November and December. The difference　between measured ice thickness and the calculated values from the classical Stephen formula are small,suggesting that the heat flux from the ocean to the underside of the ice at this area is not obvious.The results of sea ice analysis show that the sea ice consists mainly of congelation ice, and the frazil　ice only occurs at the top of sea ice, no snow or platelet ice is found. When the ice thickness reached its　　highest values in late spring, congelation ice contained average 89. 5 % of the total column crystal 　structure, the remaining 10. 5% consisted of frazil ice, and the ice thicknesses above the congelation ice layers were mostly consistent throughout the year, suggesting that the sea ice developed in a relativelycalm environment after the top layer of ice had formed and grew downwards only.Congelation ice fabrics shows frequent moderate to strong alignments at almost all depths, and thedegree of preferred orientation mostly increased with depths. In the sub--structure of congelation ice,the plate width are in a range of 0. 55 to 1. 05 mm with an average value of 0. 76 mm. No apparent pattern occurs in its vertical profiles.Ice crystal composition is one of the major factors influencing the ice algal biomass, and the effectsof crystal alignments and ice plate width of congelation ice are not apparent.     

2003年南极威德尔海至普里兹湾之间海冰分布研究

Ship-based sea ice observation data (concentrations,ice thickness,topography and overlying snow cover) were collected from Middle Weddell Sea to Prydz Bay,Antarctic during the period of 4 to 17 Jan 2003.Antarctic ice chart of first week of Jan 2003 was derived from National Ice Center (NIC).The compared analysis of sea ice concentrations and thickness distributions were conducted though in situ data and NIC chart.Results from sea ice concentration-analysis indicated the presence of large-scale open water between 2000 and 4100 km along transit route resulted from sea ice drifting.We describe the existence of mostly smooth first-year sea ice in study region ranged between 30 and 120 era.We also display the derived overlying snow coverage.Our results reveal the strong correspondence between ship-based observations and remotely sensed ice charts whatever in ice concentrations and ice thickness distributions.     

海冰反照率参数化方案的研究回顾

在全球变暖的背景下,北极海冰在发生快速变化,海冰覆盖范围明显减小,厚度显著变薄,积雪/海冰—反照率正反馈机制在此背景下变得愈发重要。气候系统和单一海冰模式采用了从简单到复杂的海冰反照率参数化方案。首先对模式中的海冰反照率参数化进行了回顾,并结合对现有卫星反照率产品问题的分析,概述了前人对参数化的评估研究工作。在此基础上进一步讨论了气候模式中海冰反照率参数化方案存在的问题,一方面目前的反照率参数化对海冰融池和冰间水道等物理过程的考虑还不够完善,另一方面反照率参数化方案的发展受到观测数据可用性的制约。最后对参数化的发展方向进行了初步探讨。     

冰层空气反循环连续取芯钻具：结构设计与冰芯卡断数值模拟

冰心包含大量的古气候资料和古生物学信息,这些信息对于从远古到现代的气候变化和生物进化都很重要。如何高效快速地获取无污染的冰心是极地科学家的一个重要课题。冰层空气反循环钻具采用双壁钻杆形成反循环通道,内管提供了从钻头底部到表面的冰屑和冰心的连续通道。钻具通过卡断机构卡断冰心,通过反循环通道不断运移冰心,从而实现连续钻具连续取心。本文采用ABAQUS软件对冰心卡断过程进行分析,运用XFEM断裂准则以及Explicit显式方法求解,选出适宜的卡断器尺寸和中心通道尺寸,从而得到更好的反循环钻进效果。     

Ice stream influence on West Greenland Ice Sheet dynamics during the Last Glacial Maximum

This paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central West Greenland, and explores the evidence for a cross‐shelf ice stream at the Last Glacial Maximum (LGM). To the east of Sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow‐flowing ice sheet areas. At the coast, the effects of regional flow convergence, caused by coastal fjord orientation, routed ice into the Sisimiut/Itilleq area where it formed an ice stream onset zone. This funnelled ice into an offshore trough (Holsteinsborg Dyb), resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream (Holsteinsborg Isbrae). To the south of this, striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast, but were later redirected by the Itilleq Fjord ice which turned southwestward due to diffluent flow and deflection by Holsteinsborg Isbrae. Roches moutonnées in this area have low elongation ratios and high bedform density, but do not provide unequivocal support for ice streaming, as they are a product of both bedrock structure and changes in ice flow direction, rather than enhanced flow velocities. Cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca. 755–810 m above sea level in this region. Such ice thickness enabled Holsteinsborg Isbrae to reach the mid/outer continental shelf during the LGM, and to contribute to the formation of a trough mouth fan and the Outer Hellefisk moraines. Initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the Bølling Interstadial at ca. 14.5 cal. ka BP. Between 12 and 10 cal. ka BP both increased air and ocean temperatures post the Younger Dryas, and peak sea‐level rise up to the marine limit, caused accelerated thinning and marginal retreat through calving, although dating evidence suggests ice streams remained along the inner shelf/coast boundary until at least ca. 10 cal. ka BP, their longevity maintained by increased ice thickness and ice discharge. Copyright © 2009 John Wiley & Sons, Ltd.     

东南极冰盖/冰架变化监测与预测技术研究

南北极是研究全球变化的关键区域。＂十一五＂期间我国在南极地区系统开展了东南极冰盖/冰架变化监测与预测技术研究,对认识全球气候变化具有重要作用。通过项目实施,建立和发展了一批现场观测体系,发展了冰盖观测新技术并集成应用于东南极冰盖的综合观测,拓展了对冰穹A地区的新认识和新发现;在冰穹A边缘地区钻取的一支浅冰芯恢复了过去约780年的气候记录,记录了东南极地区存在小冰期的明显证据;发展了东南极冰盖积累和等时年层流动模型,研究在冰盖浅层、中层和深部的变化特征,反演了冰穹A地区的古积累率分布。本文概要介绍该项目基本情况。