模拟三维裂纹问题的多尺度扩展有限元法

扩展有限元法模拟裂纹时独立于网格,因此该方法是目前求解裂纹问题最有效的数值方法。为了在计算代价不大的情况,实现大型结构分析中考虑小裂纹或提高裂纹附近精度,在裂纹附近一般采用小尺度单元,其他区域采用大尺度单元。提出了分析三维裂纹问题的多尺度扩展有限元法,在需要的地方采用小尺度单元。基于点插值构造了六面体任意节点单元。所有尺度单元都采用8节点六面体单元,这样六面体任意节点单元可方便有效地连接不同尺度单元。采用互作用积分法计算三维应力强度因子。边裂纹和中心圆裂纹算例分析结果表明,该方法是正确和有效的。     

台湾海峡西南部海域春季悬浮体及沉积物来源与输运机制

台湾海峡作为连接东海和南海的重要通道,其悬浮体和沉积物的来源和输运格局非常复杂。2005年4~5月利用带有浊度传感器和荧光传感器的SD204型CTD对台湾海峡西南部海域627个站位的悬浮体特性进行了综合调查,并采集了底层沉积物。在室内分别利用英国Marlvern公司生产的Mastersizer 2000型激光粒度仪和德国ELEMENTOR公司生产的ELEMENTOR varioELIII型元素分析仪对表层沉积物进行了粒度分析和沉积物碳、氮含量测定,结果表明,台湾海峡西南部海域春季受粤东沿岸流、韩江冲淡水、九龙江冲淡水及台湾海峡混合水影响,其中粤东沿岸流在向北输运过程中影响强度逐渐减弱,韩江冲淡水影响范围较大,并且在西南季风的控制下向东北方向输运;长时间尺度的沉积物输运格局表明,近岸沉积物由岸向海输运,远海地区沉积物由海向岸输运,并且在汕尾南部海域、南澳岛东南部海域形成了沉积物的汇聚区,沉积物以陆源为主;表层沉积物的输运过程受控于区域内水团、悬浮体分布及运动格局;在春季上升流形成早期尽管叶绿素荧光值相对较低,但其对表层沉积物的输运过程起着非常重要的控制作用。     

考虑主余震作用下的核岛厂房结构易损性研究

一次强震常伴随着多次余震作用,且时间间隔较短。研究表明,主震诱发的系列余震会对原有结构造成进一步的累积损伤。核岛厂房结构作为核反应堆的最后一道防线,其在服役期间可能遭受主震和余震的累积作用。参考我国现行规范,定义了四类性能水准(PL)和三种极限状态(LS),以混凝土最大应变作为结构破坏指数(DI),以谱加速度S_a作为地震动强度指标(IM),提出一种考虑主余震序列作用下核岛厂房结构的易损性评估方法。选取PEER数据库地震记录,采用增量动力分析方法,给出了AP1000核岛厂房在420条主余震序列地震作用下的易损性曲线。定量分析了主震强度和主余震谱加速度比对核岛厂房结构易损性的影响。结果表明:核岛厂房的超越概率随着余震强度的增大而增大;余震在主震对结构损伤的基础上会加重核岛厂房的附加损伤;随着主余震谱加速度比从0.5增加到1.0时,核岛厂房结构破坏状态超越概率提高了10%～40%。     

黄河口及其邻近水域强壮箭虫密度的时空分布及其与环境因子的关系

为探究强壮箭虫（Sagitta crassa）在黄河口及其邻近水域的时空分布特征及其与生物和非生物环境等因子的关系,本文依据2013—2014年在黄河口及其邻近水域6个航次的调查数据,采用丛生指标（I）、聚块性指标（A）和负二项分布参数的倒数（C_A）等聚集指标,分析了强壮箭虫的空间分布特征;应用广义可加模型（GAM）研究了强壮箭虫密度的时空分布和环境因子的关系。结果表明,黄河口及其邻近水域强壮箭虫平均密度为21.85 ind/m3,春、秋季高,冬、夏季低;其密度的空间分布以黄河入海口附近水域为密集中心,向远岸水域逐渐降低;强壮箭虫在黄河口及其邻近水域的聚集特征随密度的变化存在两次聚集和两次扩散;水深、表层水温和浮游桡足类密度是影响其密度时空分布的主要因子,总偏差解释率为55.11%,强壮箭虫密度随水深的增加而减小,随表层水温的升高先增加后减小,随桡足类密度的增加而增加。强壮箭虫密度受黄河口及其邻近水域环境因子变动的影响,具有明显的季节变化和空间分布规律。     

Transfort of oxygen,nutrients and carbonates by the Kuroshio Current

Measured concentrations of dissolved oxygen, phosphate, silicate, total alkalinity and calculated total CO₂ in a section between 121° E and 125° E across the Kuroshio near 22° N off Taiwan and the geostrophic velocity were used to estimate the gross transport of oxygen, nutrients and carbonates. The flux of dissolved oxygen is 6.7×10⁶ mol/s northward and 0.9×10⁶ mol/s southward. The net flux equals 5.8×10⁶ mol/s down-stream. The northward flux of phosphate is 22.6×10³ mol/s; the southward flux is 1.4×10³ mol/s. The net phosphate flux is 21.2×10³ mol/s northward. The flux of silicate is 967×10³ northward and 59×10³ mol/s southward; the net transport is 908×10³ mol/s down-stream. The flux of alkalinity is 75.5×10⁶ mol/s northward, and 10.8×10⁶ mol/s southward, the net flux is 64.7×10⁶ mol/s northward. For total CO₂ the transport is 73.4×10⁶ mol/s northward and 10.8×10⁶ mol/s southward, or a net transport of 62.6×10⁶ mol/s horthward.     

Current and thermohaline characteristics of the Arabian Sea during January 1998

Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area.     

鄂尔多斯盆地都思兔河流域白垩系含水层特征及供水前景分析

在鄂尔多斯盆地都思兔河流域供水水文地质详查的基础上,通过水文地质钻探、抽水试验、样品分析等手段,查明了流域含水层的结构、埋深以及含水层和隔水层在水平和垂直方向上的变化规律,探讨了各含水层之间的水力联系,并求取了含水层的水文地质参数;对比圈定了包乐浩晓、巴彦布拉格、好勒包勒吉3处富水区;采用地下水流数值模拟方法对上述3处富水区地下水开采量进行计算,提出了27种地下水开采方案,并经过对比得到地下水开采推荐方案。结果表明:包乐浩晓、巴彦布拉格、好勒包勒吉3处富水区主要补给为侧向径流及大气降水入渗补给,排泄方式以潜水面蒸发及向河流排泄为主;在地下水浅埋区,结合含水层单井涌水量的大小,确定采用管井开采方式、中段悬挂式非完整井结构,平均布井,井深300m,单一开采白垩系环河组的地下水,最大限度夺取潜水蒸发排泄量;根据推荐方案,上述3个富水区总开采量达到123 500m3/d,可为该地区地下水资源开发与利用提供技术保障。     

成都市城市热岛效应分析

城市热岛效应是城市气候最显著的特征之一。基于地理信息系统和不同时次的遥感影像,探讨成都市地表温度、热岛强度、热岛等级的分布特征及其演变。结果表明:成都市热岛效应明显且夜间夏强冬弱,地表温度呈条状分布;日间城市多数区域属于弱热岛以上等级,中心城区偏向强热岛和极强热岛,夜间强热岛面积扩张,冬季热岛等级增加明显;2002~2012年,城市热岛等级增加,强热岛面积扩张,但存在昼夜和季节性差异。     

Non-uniform across-shelf variations in thickness, grain size, and frequency of turbidites in a transgressive outer-shelf, the Middle Pleistocene Kakinokidai Formation, Boso Peninsula, Japan

Across-shelf variations in thickness, grain size, and frequency of sandstone beds in a transgressive outer-shelf succession were investigated from the Middle Pleistocene (ca. 0.7 Ma) Kakinokidai Formation on the Boso Peninsula, Japan. The transgressive deposits are generally muddy and contain slumps and slump scars. The intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge-complex deposits in the southwestern upslope area during storm events. Mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed-by-bed correlation of the outer-shelf sandstone beds. Although, overall, thickness, grain size, and frequency of sandstone beds decrease in the downslope direction, some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits. These sandstone beds subsequently thicken and fine, and finally thin out in the farther downslope area. In addition to the local thinning of sandstone beds, the frequency of sandstone beds first decreases and then increases in the farther offshore direction. From this evidence, we concluded that these non-uniform patterns of across-outer-shelf variations in thickness, grain size, and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents, along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer-shelf floor. These physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds, compared with the bed-shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand-stage shelf systems.     

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