EOF模型分析北京周边气溶胶影响域气候变化显著性特征

利用1979~2000年TOMS气溶胶光学厚度和华北地区气象站日照时数、雾日数、低云量等资料以及EOF模型综合统计分析方法,研究冬季北京及周边城市群落的气溶胶分布特征及其对区域气候的影响效应问题,重点探讨了北京周边区域气候EOF模型特征向量变化显著区与气溶胶影响效应的相关联系.分析多年平均冬季TOMS气溶胶光学厚度的区域分布,发现北京及其南部周边地区“马蹄型”大地形谷地内存在南北向带状大范围相对稳定的气溶胶浓度高值区空间分布;冬季气溶胶光学厚度在北京与周边地区存在高相关影响区,在此气溶胶相互影响显著区,冬季气溶胶光学厚度与雾日数、低云量呈年际变化“同位相”特征,表明特定区域大气环流背景下,北京及周边地区气溶胶变化对该地区低云量、雾日数的年际变化存在影响效应.进一步通过EOF模型特征分析,揭示出华北地区冬季日照时数减少、低云量和雾日数增多气候变化区及其长期演变趋势,尤其EOF模型第一特征向量中日照时数、雾日数及低云量变化显著区与其20世纪80~90年代偏差显著区近似重合,且这些变化特征显著区域均与北京周边南北向带状气溶胶光学厚度高值区及其高相关区呈对应关系;日照时数、雾日数、低云量EOF模型第一特征向量时间系数与区域平均气溶胶光学厚度年际变化呈“同位相”特征,且均呈长期演变上升趋势.EOF模型分析描述出北京南部周边地区冬季日照时数减少、低云量和雾日数增多的区域气候变化主体特征,揭示出区域气溶胶影响效应,即多年平均冬季气溶胶光学厚度高值区以及日照时数、低云量和雾日数EOF模型第一特征向量变化显著区均位于北京南部周边城市群落区域,上述相关分布特征揭示出北京南部周边城市群落影响域存在气溶胶气候效应区域性增强的变化趋势.     

水平井生产测井组合仪模拟井测量数据分析与模型建立

由于水平油水两相流局部流速及局部相含率沿管径方向存在复杂分布,致使其流量及相含率测量非常困难.本文利用伞集流涡轮流量计、电导传感器、过流式电容传感器构成的生产测井组合仪,在水平油水两相流模拟井中开展了动态实验,分析了流动特性及管子角度倾斜对涡轮流量计及含水率传感器响应特性的影响.根据电容及电导传感器在不同总流量及含水率范围的响应分辨特性,分别采用变系数漂移模型及统计模型预测分相流量,发现变系数漂移模型能够自适应调整模型中的流型参数,且对油水两相分相流量具有较高预测精度.     

储层岩石流动电位频散特性的数学模拟

利用储层岩石流动电位的频散特性评价复杂储层已经成为勘探地球物理领域关注的热点,但是目前还没有形成基于储层岩石储渗特性及电化学性质的具有普遍指导意义的理论方法和数学模型.本文利用微观毛管理论,通过随时间谐变条件下渗流场和电流场的耦合模型,建立了描述储层岩石流动电位频散特性的数学方法,定量分析了频率域储层岩石动态渗透率、动电耦合系数和流动电位耦合系数随储层岩石孔隙度、溶液浓度和阳离子交换量的变化规律.研究结果表明:储层岩石流动电位频散特性是储层流体惯性力与流体黏滞力相互作用的结果.储层岩石孔隙度越大,储层维持流体原有运动状态的能力越大,临界频率越小;储层岩石的溶液浓度和阳离子交换量对临界频率没有影响.储层岩石的孔隙度越大,流体流动能力越强,流动电位各耦合系数的数值越大;溶液浓度越小或阳离子交换量越大,孔隙固液界面的双电层作用越强,各耦合系数的数值越大.     

苏、 鲁、 豫、 皖交界及南黄海地区地磁监测与分析

通过在苏、 鲁、 豫、 皖交界及南黄海地区开展地磁基本场矢量测量、 数据处理和分析, 计算了该区域地磁基本场和地磁异常场总强度和水平强度的曲面样条模型, 并绘制相应的地磁图和地磁异常图, 探索研究局部地磁基本场的变化特征。 分析结果表明, 通过区域地磁基本场矢量测量, 能相对精细地反应区域地磁基本场空间分布, 分辨存在的地磁基本场异常, 为地震中长期预报提供科学数据和相关地球物理场变化背景。     

地电阻率三维影响系数及其应用

采用有限元数值方法,计算了对称四极装置观测时测区介质对地电阻率观测的三维影响系数分布。计算结果表明,表层介质整体影响系数为正和为负时,表层介质各区域影响系数的分布形态相近,不同层状电性结构三维影响系数分布形态也相似。在地表二维平面,影响系数在供电电极和测量电极之间存在近似椭圆的负区域,其余区域影响系数为正。沿测线垂直剖面,影响系数在供电电极和测量电极之间存在近似半椭圆的负区域,其余区域影响系数为正。在三维空间上,观测系统布设于地表时影响系数为负的区域位于供电电极和测量电极间的近似半椭球区域,影响系数在靠近电极附近显著大于其余区域。在测区地表局部介质电阻率发生变化时,可依据影响系数分布定性地分析其对地电阻率观测的影响,为进一步实验和数值模型定量分析提供参考。     

基于实测PM_(2.5)、能见度和相对湿度分辨雾霾的新方法

霾是由于气溶胶增多或相对湿度增大引起气溶胶吸湿增长而导致的能见度降低的现象,而雾是气溶胶经过活化变成雾滴而造成的低能见度事件,在气象观测中如何对两者进行准确区分一直是一个存在争议的问题.本文以雾和霾在物理性质上的客观区别为基础,介绍了一种全新的基于实测PM2.5、能见度和相对湿度来分辨雾和霾的新方法.通过对当地历史观测的气溶胶谱分布数据进行拟合和统计,并结合气溶胶吸湿增长特性计算得到判别参考值.通过将实际测量的PM2.5、能见度和相对湿度与判别参考值相比对,来估计当前状况是雾或霾的概率.本方法可操作性强,基于常规观测仪器即可实现.     

珠江三角洲海相沉积软土压缩和剪切变形特性试验研究

为了研究近代海相沉积软土的变形特征,本文对珠江三角洲河口地区的全新世海相沉积的软土进行了室内单轴压缩与不同围压下作用下的三轴固结不排水(CU)、不固结不排水(UU)的剪切试验。试验结果表明:原状土和重塑土样的孔隙比随压力的增大而下降,且与加压方式有密切关系,加压幅度越小,土的扰动破坏越小;原状土样固结系数随着压力增加而递减,整体近似符合指数函数分布,重塑土样固结系数随着压力增加逐渐增大,整体近似符合线性函数分布。在相同的固结压力下,原状土样的强度低于重塑土样的强度。土样的应力应变曲线为应变硬化型,且围压对重塑土的影响小于原状土。     

带焊缝圆灯柱气动特性及焊缝影响机理研究

为了研究某实桥带焊缝圆灯柱的气动特性以及焊缝对灯柱涡激振动的影响机理,开展了灯柱刚性节段测压模型风洞试验,测试了无焊缝工况以及0°～180°焊缝位置的灯柱周向压力分布,分析了灯柱气动力以及流体卡门涡脱强度,揭示了焊缝对灯柱涡激振动的影响机理。研究结果表明：焊缝对灯柱的气动特性影响显著,不同的焊缝位置可以激发不同的流动模式,当焊缝在灯柱前驻点或者原分离点后侧时,灯柱气动特性受焊缝影响较小。当焊缝在B区域(21°～33°)和C区域(36°～63°)时,流体在焊缝附近发生分离-再附-再分离现象,卡门涡脱强度降低,灯柱的涡激振动被抑制。当焊缝在D区域(63°～78°)时,流体在焊缝位置直接涡脱,伴随着脉动风压和卡门涡脱强度的增强,使灯柱的涡激振动增大;焊缝尺寸的变化不会改变灯柱的气动力系数随焊缝位置的变化规律,但是可能会影响涡激振动风速锁定区间和振动幅值。     

全长粘结型锚杆锚固性能研究

利用全长粘结型锚杆的Mindlin解,对锚固体的应力分布及抗拔力进行了理论分析,导出了抗拔承载力计算式,并结合新疆高昌故城土建筑遗址保护工程,就影响锚固体应力分布及锚固力的因素进行了探讨.结果表明,锚固体应力不能均匀地分布在锚固长度上,随着荷载的增加,应力分布区域变化不大;锚固长度存在临界值,超过该值时增加锚固长度对锚固力的影响甚微;锚杆直径越粗,锚固体上的剪应力分布越均匀,但工程选用时应结合岩土体特性.研究结果可为全长粘结型锚杆加固小型土体的设计理论和施工应用提供一定的数据储备和理论支持.     

江苏及邻区中小地震能量场的时空变化分析

采用随机能量场的概念,将地震活动能量场看作时间和空间的随机函数场,用自然正交函数展开的分析方法,研究江苏及邻区自1970年1月至2007年12月的中小地震(2.1≤M_L≤4.5)能量场变化特征,以及主要典型能量场的时间"权重"系数的变化特征.结果显示:前7个典型场的展开精度为0.9244.研究区内不同构造块体的地震活动能量场强度存在明显差异,其中下扬子块体的苏中、苏南地区及南黄海海域的地震背景能量值高于其他地区;从典型场的分布来看,该区域对研究区能量场的影响也最为显著.前6个主要典型场的时间"权重"系数随时间的变化幅度与研究区大部分中强震之间在时间上存在很强的相关性.     

Droplet breakup in subsurface oil releases – Part 1: Experimental study of droplet breakup and effectiveness of dispersant injection

Size distribution of oil droplets formed in deep water oil and gas blowouts have strong impact on the fate of the oil in the environment. However, very limited data on droplet distributions from subsurface releases exist. The objective of this study has been to establish a laboratory facility to study droplet size versus release conditions (rates and nozzle diameters), oil properties and injection of dispersants (injection techniques and dispersant types). This paper presents this facility (6 m high, 3 m wide, containing 40 m³ of sea water) and introductory data. Injection of dispersant lowers the interfacial tension between oil and water and cause a significant reduction in droplet size. Most of this data show a good fit to existing Weber scaling equations. Some interesting deviations due to dispersant treatment are further analyzed and used to develop modified algorithms for predicting droplet sizes in a second paper (Johansen et al., 2013).     

Oil slicks on water surface: Breakup,coalescence, and droplet formation under breaking waves

The ability to calculate the oil droplet size distribution (DSD) and its dynamic behavior in the water column is important in oil spill modeling. Breaking waves disperse oil from a surface slick into the water column as droplets of varying sizes. Oil droplets undergo further breakup and coalescence in the water column due to the turbulence. Available models simulate oil DSD based on empirical/equilibrium equations. However, the oil DSD evolution due to subsequent droplet breakup and coalescence in the water column can be best represented by a dynamic population model. This paper develops a phenomenological model to calculate the oil DSD in wave breaking conditions and ocean turbulence and is based on droplet breakup and coalescence. Its results are compared with data from laboratory experiments that include different oil types, different weathering times, and different breaking wave heights. The model comparisons showed a good agreement with experimental data.     

The relationship between oil droplet size and upper ocean turbulence

Oil spilled at sea often forms oil droplets in stormy conditions. This paper examines possible mechanisms which generate the oil droplets. When droplet Reynolds numbers are large, the dynamic pressure force of turbulent flows is the cause of droplet breakup. Using dimensional analysis, Hinze (1955, A.I.Ch.E. Journal 1, 289–295) obtained a formula for the maximum size of oil droplets that can survive the pressure force. When droplet Reynolds numbers are small, however, viscous shear associated with small turbulent eddies is the cause of breakup. For the shear mechanism, we obtain estimates of droplet size as a function of energy dissipation rate, the ratio of oil-to-water viscosity and the surface tension coefficient.

The two formulae are applied to oil spills in the ocean. At dissipation rates expected in breaking waves, the pressure force is the dominant breakup mechanism and can generate oil droplets with radii of hundreds of microns. However, when chemical dispersants are used to treat an oil slick and significantly reduce the oil-water interfacial tension, viscous shear is the dominant breakup mechanism and oil droplets with radii of tens of microns can be generated. Viscous shear is also the mechanism for disintegrating water-in-oil emulsions and the size of a typical emulsion blob is estimated to be tens of millimeters.     

Size distribution models of fog and cloud droplets and their volume extinction coefficients at visible and infrared wavelengths

Based on the average variability of the skewness with respect to the droplet mode radius, a wide set of mean size-distribution models is presented in terms of the modified gamma function for fog and stratified cloud droplets. These models appear appropriate for giving reliable size-distribution curves relative to the various formation stages of the droplet population both in fogs and in stratus and stratocumulus clouds.The corresponding volume extinction coefficient has been computed at various wavelengths from 0.4 to 17 m using Van de Hulst's (1957) approximation multiplied by Deirmendjian's (1960) correction factors. This set of theoretical extinction data has been compared with experimental extinction measurements performed in atmospheres characterized by a marked thermal inversion for describing the evolutionary features of the water droplet size distribution within the whole ground layer.     

A smoothed particle hydrodynamics model for droplet and film flow on smooth and rough fracture surfaces

Flow on fracture surfaces has been identified by many authors as an important flow process in unsaturated fractured rock formations. Given the complexity of flow dynamics on such small scales, robust numerical methods have to be employed in order to capture the highly dynamic interfaces and flow intermittency. In this work we use a three-dimensional multiphase Smoothed Particle Hydrodynamics (SPH) model to simulate surface tension dominated flow on smooth fracture surfaces. We model droplet and film flow over a wide range of contact angles and Reynolds numbers encountered in such flows on rock surfaces. We validate our model via comparison with existing empirical and semi-analytical solutions for droplet flow. We use the SPH model to investigate the occurrence of adsorbed trailing films left behind droplets under various flow conditions and its importance for the flow dynamics when films and droplets coexist. It is shown that flow velocities are higher on prewetted surfaces covered by a thin film which is qualitatively attributed to the enhanced dynamic wetting and dewetting at the trailing and advancing contact lines. Finally, we demonstrate that the SPH model can be used to study flow on rough surfaces.     

The effect of a simple shear flow upon the coalescence rate of water droplets

There is some experimental evidence by Schotland (1957) and by Telford and Cottis (1964) that there is an interaction region associated with the wake of a small droplet such that other droplets inside this region eventually collide with that droplet. It is shown that the existence of such a region produces a significant collision rate between droplets of comparable size in a vertical shear flow. The general features of the collision process are in agreement with the experimental results of Jonas and Goldsmith (1972).     

Density effects on solute release from streambeds

Contaminants that entered the streambed during previous surface water pollution events can be released to the stream, causing secondary pollution of the stream and impacting its eco-environmental condition. By means of laboratory experiments and numerical simulations, we investigated density effects on the release of solute from periodic bedforms. The results show that solute release from the upper streambed is driven by bedform-induced convection, and that density effects generally inhibit the solute release from the lower streambed. Density gradients modify the pore water flow patterns and form circulating flows in the area of lower streambed. The formation of circulating flows is affected by density gradients associated with the solute concentration and horizontal pressure gradients induced by stream slope. The circulating flows near the bottom of the streambed enhance mixing of the hyporheic zone and the ambient flow zone.     

Parameters affecting maximum fluid transport in large aperture fractures

We present results of laboratory experiments to study the behavior of liquids moving in unsaturated wide-aperture fractures. A 5-mm-thick glass plate cut with a 1.7-mm aperture was used as a fractured rock analog to study behavior of film and capillary droplet flow modes. Flow rates ranged between 0.6 and 6.0 ml/min. Variability in the ambient barometric pressure, resulting from weather conditions, seemed to play a role in the natural selection of flow mode. For droplet mode, constant input conditions resulted in highly variable transport properties within the fracture. The advancing meniscus exhibited a dynamic contact angle that was a function of the droplet speed and much larger than the static contact angle. Flow rate was reduced due to the larger contact angle. Analytical expressions for droplet velocity and flow capacity are presented as a function of the dynamic rather than the static contact angle.     

Influence of water pressure dynamics and fluid flow on the streaming‐potential response for unsaturated conditions

Streaming‐potentials are produced by electrokinetic effects in relation to fluid flow and are used for geophysical prospecting. The aim of this study is to model streaming potential measurements for unsaturated conditions using an empirical approach. A conceptual model is applied to streaming potential measurements obtained from two drainage experiments in sand. The streaming potential data presented here show a non‐monotonous behaviour with increasing water saturation, following a pattern that cannot be predicted by existing models. A model involving quasi‐static and dynamic components is proposed to reproduce the streaming potential measurements. The dynamic component is based on the first time derivative of the driving pore pressure. The influence of this component is investigated with respect to fluid velocity, which is very different between the two experiments. The results demonstrate that the dynamic component is predominant at the onset of drainage in experiments with the slowest water flow. On the other hand, its influence appears to vanish with increasing drainage velocity. Our results suggest that fluid flow and water distribution at the pore scale have an important influence on the streaming potential response for unsaturated conditions. We propose to explain this specific streaming potential response in terms of the behaviour of both rock/water interface and water/air interfaces created during desaturation processes. The water/air interfaces are negatively charged, as also observed in the case of water/rock interfaces. Both the surface area and the flow velocity across these interfaces are thought to contribute to the non‐monotonous behaviour of the streaming potential coefficient as well as the variations in its amplitude. The non‐monotonous behaviour of air/water interfaces created during the flow was highlighted as it was measured and modelled by studies published in the literature. The streaming potential coefficient can increase to about 10 to 40 when water saturation decreases. Such an increase is possible if the amount of water/air interfaces is increased in sufficient amount, which can be the case.     

Small-scale modelling of the physiochemical impacts of CO2 leaked from sub-seabed reservoirs or pipelines within the North Sea and surrounding waters

A two-fluid, small scale numerical ocean model was developed to simulate plume dynamics and increases in water acidity due to leakages of CO₂ from potential sub-seabed reservoirs erupting, or pipeline breaching into the North Sea. The location of a leak of such magnitude is unpredictable; therefore, multiple scenarios are modelled with the physiochemical impact measured in terms of the movement and dissolution of the leaked CO₂. A correlation for the drag coefficient of bubbles/droplets free rising in seawater is presented and a sub-model to predict the initial bubble/droplet size forming on the seafloor is proposed. With the case studies investigated, the leaked bubbles/droplets fully dissolve before reaching the water surface, where the solution will be dispersed into the larger scale ocean waters. The tools developed can be extended to various locations to model the sudden eruption, which is vital in determining the fate of the CO₂ within the local waters.