Benchmark computations for flows around a stationary cylinder with high Reynolds numbers by RANS-overset grid approach

The aim of this paper is to evaluate the accuracy, stability and efficiency of the overset grid approach coupled with the RANS (Reynolds Averaged Navier-Stokes) model via the benchmark computations of flows around a stationary smooth circular cylinder. Two dimensional numerical results are presented within a wide range of Reynolds numbers (6.31 × 10⁴ ∼ 7.57 × 10⁵) including the critical flow regime. All the simulations are carried out using the RANS solver pimpleFoam provided by OpenFOAM, an open source CFD (Computational Fluid Dynamics) toolkit. Firstly, a grid convergence study is performed. The results of the time-averaged drag and lift force coefficients, root-mean square value of lift force coefficient and Strouhal number (St number) are then compared with the experimental data. The velocity, vorticity fields and pressure distribution are also given. One main conclusion is that the numerical solutions in regard to a fixed cylinderare not deteriorated due to the implementation of the overset grid. Furthermore, it can be an appealing approach to facilitate simulations of Vortex Induced Vibrations (VIV), which involves grid deformation. The present study is a good start to implement the overset grid to solve VIV problems in the future.     

四种海水透明度现场测量方法的对比分析及发展趋势研究

随着海洋探测的不断发展,海水透明度作为海水光学性质的一个重要参量,也越来越受到人们的关注。文章对比分析了4种海水透明度现场测量方法:透明度盘法~([1])、光纤式高光谱剖面测量法~([2])、激光衰减测量法~([3])和基于双光路原理的海水IOPs高光谱测量法~([4]),主要分析了4种方法的测量原理,对比各自的优缺点,并提出了海水透明度测量未来发展设想。     

巴黎气候会议对全球长期目标的新发展

巴黎气候会议（COP21）达成了包括《巴黎协定》在内的重要成果,丰富和深化了应对气候变化的一揽子长期目标。1.5℃温升控制目标意味着全球管控气候风险的政治意愿得到强化,减缓温室气体排放的路径得到初步勾勒。在未来的科学评估和政治谈判中,全球各区域甚至是各个排放大国的排放空间、排放路径和减缓需求将会进一步清晰化和定量化,还会丰富和深化自上而下的国际气候合作规则,结合当前以国家自主决定贡献（INDC）为特征的、主要以自下而上方式推进全球气候治理的新模式,将对发展中国家、尤其是发展中排放大国的排放配额与发展空间产生重要影响,并进一步影响各国制定其国家贡献目标与行动的自主性。     

滇西牟定—香格里拉电性剖面及深部构造

通过对滇西NW—SE向牟定—香格里拉大地电磁测深剖面的反演并结合地质构造、小震精定位资料,综合分析了剖面经过地区的深部构造.在滇西北地区深部发育一规模巨大的近水平产出地壳高导层,此高导层从香格里拉一直延伸到永胜盆地以东,沿剖面水平延伸超过200km.地壳高导层又可分为两段,两段高导层在剖面上形成两个香蕉型相连的复合形态,高导层之上的高阻体则形成两个碗型相连的复合结构,碗型内部有向东倾斜的相对低阻带存在.滇西北地区整体构造格架可以解译为一套两个主推覆面构成的叠瓦式推覆系统,两个主推覆面高低起伏形成总长度超过250km的底部滑脱带.第一个主推覆面的长度超过150km,并在丽江东部上翘到接近地表,小金河断裂是其延伸到地表的主要破裂带.第二个主推覆面长度超过120km,过程海断裂后上翘并在永胜以东地区出露地表.根据反向低阻带影像,可以推断推覆体反冲构造发育,在玉龙山至丽江以东和永胜盆地西缘至平川盆地东缘形成两处冲起构造.推覆面在剖面上呈现出平缓-陡峭-再平缓-再陡峭的断坪和断坡相间的阶梯状结构.     

2014年8月3日云南鲁甸6.5级地震序列破裂过程研究

本文利用主地震相对定位法,对2014年鲁甸MS6.5地震序列中的8月3日—9月30日地震进行了重新定位,借助于时空图像分析方法,对本次地震破裂过程进行了分析,得到如下结果:(1)2014年鲁甸MS6.5地震主要沿NW向破裂,存在沿NE向破裂的成分,但是NE向破裂并不明显;(2)地震破裂时,主要从主震震中处往ES方向传播,破裂带长度大约为10km,破裂面近乎直立;(3)余震活动主要集中于主震上方区域,震源深度大于主震的余震稀少.根据上述结果,结合当地的地震构造情况和本次地震的震源机制解,分析表明,本次地震的破裂面为NW向,其发震断层为包谷垴—小河断裂的可能性很大.     

北极涛动低空大气环流特征及其与太阳活动的联系

通过北极涛动AO正负位相时期北半球1000 hPa月平均位势高度、位势高度距平和气温月距平图对比分析可知,北极区域异常增暖时期对应着AO负位相时期,而北极区域异常偏冷时期对应着AO正位相时期,说明北极区域气温异常变化是决定AO异常变化的重要因子.逐次滤波法分析可知,冬季1月北极涛动现象表现出十分清楚的与太阳活动密切联系的准110a世纪周期和准22a年代际周期,具体表现为：（1）冬季1月北极涛动现象具有十分清楚的与太阳活动密切联系的准110a世纪周期.准110a世纪周期对于北极涛动指数的方差贡献率达到44.4%,是冬季1月北极涛动现象最显著的世纪际变化特征.（2）谱分析结果表明,滤除准110a世纪周期变化以后的1月北极涛动指数具有显著的22a周期,其方差贡献率达到18.5%,乃仅次于准110a世纪周期之后北极涛动指数年代际变化重要特征.对比分析表明,太阳活动尤其是太阳磁场磁性指数变化与1月北极涛动22a周期变化呈密切的反相关关系,二者变化趋势基本相反,即多数情况当太阳磁性指数MI由最低值转为上升以后都可引起北极涛动AO由最高值转为下降;当太阳磁性指数MI由最高值转为下降以后都可引起北极涛动AO由最低值转为上升.综上所述,北极涛动的准110a世纪周期变化、22a年代际周期变化对于北极涛动方差贡献率达到62.9%,标志着太阳活动是北极涛动的重要驱动因子.     

基于相对质心震中的地震破裂方向性测定方法研究:以2008年云南盈江MS6.0地震为例

地震破裂方向性参数包含了断层几何形态、破裂长度等信息,对于地震灾害评估、孕震机理研究具有重要意义.但是基于点源近似的震源矩中心张量机制解(CMT)或断层面解(fault plane solution)只能给出两个节面,无法确定破裂断层面.本文提出一种基于质心与起始震中的差异确定发震断层的方法,该方法利用P波到时来测定主震与参考地震间相对起始震中,同时利用波形反演震源机制过程中的主震时移与参考地震时移之差测定相对质心震中,在假定单侧破裂的情形下,根据时移之差随方位角的变化推断破裂断层面.本文使用该方法研究了2008年云南盈江M_S6.0走滑型地震,发现其破裂方向与其他方法结果一致.由于该方法基于相对起始震中和质心震中,可有效削弱速度结构模型不准确以及地震绝对位置误差带来的影响,应可适用于其他类似类型6级左右地震的破裂方向性研究,但仍需进一步工作对其进行验证.     

地震记录的时间域反褶积、仿真及在地震计方位角相对测量中的应用

介绍了一种用冲击不变法从速度响应平坦地震计二阶传递函数设计得到的递归滤波方法,比用双线性变换得到的递归滤波系数少,因此使用更方便.作者用此方法作了反褶积与仿真的数值实验和实际地震记录的短周期仿真试验,仿真结果与实际仪器记录符合较好;并将此法应用于地震计方位角的相关分析法相对测量,结果与不仿真的相关分析测量相比更接近寻北仪的绝对测量结果.     

The numerical and empirical evaluation of chimneys considering soil structure interaction and high-temperature effects

During the past strong ground motions, chimneys constructed according to international standards are representative of similar structures at industrial areas throughout the world, including those collapsed or moderately damaged in earthquake-prone regions. This is due to the specialty of structural characteristics and the special loads acting on the structure such as earthquakes, wind and differences in the level of temperature, etc. In this context, the researchers and designers should focus on the dynamic behavior of chimneys especially under high temperature and seismic effects. For this purpose, the main focus of this study is to evaluate the dynamic response of a chimney under the above-mentioned effects considering soil-structure interaction (SSI). A 52 m steel chimney in Yeşilyurt township of Samsun City in Turkey was studied. The in-situ model testing and numerical models were compared. Before the commissioning of the chimney, a series of tests was realized to define its dynamic characteristics in case of no-heat and after the fabric got to work, the same tests were repeated for the same sensor locations to understand the heat effect on the dynamic response of the chimney. The ambient vibration tests are proven to be fast and practical procedures to identify the dynamic characteristics of those structures. The dynamic testing of the towers promises a widespread use, as the identification of seismic vulnerability of such structures becomes increasingly important. The data presented in this study are considered to be useful for the researchers and engineers, for whom the temperature and SSI effects on steel chimneys are a concern. Using the modal analysis techniques, presented finite element simulation for the soil/pile foundation-chimney interaction system is verified. The results of modal analyses using numerical solutions are shown to have acceptable accuracy compared with results obtained by in-situ test. The present study also aims to provide designers with material examples about the influence of these on the seismic performance of steel chimneys by means of reflecting the changes in the dynamic behavior.     

The effect of microporosity on transport properties in porous media

Sizeable amounts of connected microporosity with various origins can have a profound effect on important petrophysical properties of a porous medium such as (absolute/relative) permeability and capillary pressure relationships. We construct pore-throat networks that incorporate both intergranular porosity and microporosity. The latter originates from two separate mechanisms: partial dissolution of grains and pore fillings (e.g. clay). We then use the reconstructed network models to estimate the medium flow properties. In this work, we develop unique network construction algorithms and simulate capillary pressure–saturation and relative permeability–saturation curves for cases with inhomogeneous distributions of pores and micropores. Furthermore, we provide a modeling framework for variable amounts of cement and connectivity of the intergranular porosity and quantifying the conditions under which microporosity dominates transport properties. In the extreme case of a disconnected inter-granular network due to cementation a range of saturations within which neither fluid phase is capable of flowing emerges. To our knowledge, this is the first flexible pore scale model, from first principles, to successfully approach this behavior observed in tight reservoirs.