Green’s function of the linearized Saint-Venant equations in laminar and turbulent flows

In the present paper, an analytical expression of the Green’s function of linearized Saint-Venant equations (LSVEs) for shallow water waves is provided and applied to analyse the propagation of a perturbation superposed to a uniform flow. Independently of the kinematic character of the base flow, i.e., subcritical or supercritical uniform flow, the effects of a non-uniform vertical velocity profile and a non-constant resistance coefficient are accounted for. The use of the Darcy-Weisbach friction law allows a unified treatment of both laminar and turbulent conditions. The influence on the wave evolution of the wall roughness and the fluid viscosity are finally discussed, showing that in turbulent regime the assumption of constant friction coefficient may lead to an underestimation of both amplification and damping factors on the wave fronts, especially at low Reynolds numbers. This conclusion has to be accounted for, particularly in describing hyper-concentrated suspensions or other kinds of Newtonian mixtures, for which the high values of the kinematic viscosity may lead to relatively low Reynolds numbers.     

G: Fracture energy,friction and dissipation in earthquakes

Recent estimates of fracture energy G ^′ in earthquakes show a power-law dependence with slip u which can be summarized as G ^′ ∝ u ^a where a is a positive real slightly larger than one. For cracks with sliding friction, fracture energy can be equated to G _f : the post-failure integral of the dynamic weakening curve. If the dominant dissipative process in earthquakes is friction, G ^′ and G _f should be comparable and show a similar scaling with slip. We test this hypothesis by analyzing experiments performed on various cohesive and non-cohesive rock types, under wet and dry conditions, with imposed deformation typical of seismic slip (normal stress of tens of MPa, target slip velocity > 1 m/s and fast accelerations ≈ 6.5 m/s²). The resulting fracture energy G _f is similar to the seismological estimates, with G _f and G ^′ being comparable over most of the slip range. However, G _f appears to saturate after several meters of slip, while in most of the reported earthquake sequences, G ^′ appears to increase further and surpasses G _f at large magnitudes. We analyze several possible causes of such discrepancy, in particular, additional off-fault damage in large natural earthquakes.     

差分GPS实现探地雷达图像地形校正方法研究

针对在地形起伏较大的区域探地雷达获取的图像不能表达地形变化的缺点,通过探地雷达与差分GPS同步采集记录数据,实现探地雷达图像与GPS数据时间同步,选择某一标准水准面为参考面,根据时间位移和线性插值方法,将探地雷达数据进行时深转换,从而实现探地雷达地形校正。探地雷达图像地形校正前后对比表明此方法在保留地下介质体水平方向分布特征的同时,实现了探地雷达图像在垂直方向的精确校正,对地下目标的解译和精确定位有很大的帮助,对浅层活动断层探测具有一定的实际意义。      

新疆库车坳陷克拉苏冲断带白垩系辫状河三角洲沉积特征及其与储集层发育的关系*

新疆库车坳陷克拉苏冲断带白垩系巴什基奇克组一、二段是一套由细砂岩、中粗砂岩、含砾砂岩、粉砂岩及泥岩组成的碎屑岩组合。通过30余口钻井(包括6口新取心井)的岩心、测井、录井、薄片及粒度等资料的分析, 结合区域地质资料, 确认克拉苏冲断带巴什基奇克组一、二段发育砂质辫状河三角洲沉积。其岩性以岩屑砂岩为主;粒度概率曲线具有牵引流特征;砂体中发育楔状交错层理及冲刷、充填构造等丰富的强水动力沉积构造及间断正韵律;砂体延伸远、面积大展布稳定, 砂地比值高;发育水下分流河道、分流间湾等微相。据三角洲砂体的岩性、沉积构造及沉积序列等特征, 建立了三角洲沉积模式。稳定的构造背景、开阔的盆地、丰富的物源供给使得研究区辫状河三角洲前缘沉积非常发育, 其以水下分流河道沉积为主体, 物性好, 砂体延伸远, 可向盆地中央方向推进35～60km, 砂体纵横叠置, 为岩性油气藏的形成提供了有利的储集空间。     

常熟地震台伸缩仪运行分析

对常熟地震台2008—2011年SS-Y伸缩仪观测资料的连续率、噪声水平及M2波振幅因子的相对中误差等指标的质量评定表明:1)在无雷害情况下,伸缩仪连续率在99.6%以上;2)噪声水平及M2波振幅因子的相对中误差等指标均符合形变观测规范要求,较为稳定;3)SS-Y伸缩仪主要受气压及降雨干扰,降雨干扰最大。     

澜沧江―湄公河地区地形地貌划分

地形地貌反映了地质构造运动特征,是影响和制约区域经济社会发展的基础。本研究以澜沧江-湄公河地区1:250 000TM遥感影像图为基础,考虑到本区新构造运动异常活跃以及微地貌的特殊性,结合其坡度形态及海拔高度,采用成因类型-成因形态-物质形态-坡度形态-微地貌形态的方法进行地貌类型划分研究。采用地势起伏度分级、野外查证等方法进一步验证了地貌划分成果,结果表明本次地形地貌划分研究较好地反映了客观实际。     

张力腿平台局部节点强度可靠度分析方法

局部节点可靠度分析对张力腿平台(TLP)整体安全性评估具有重要意义。提出了一个TLP平台局部节点可靠度的分析方法,首先对TLP平台整体进行分析,统计局部节点各种失效模式并得到典型失效模式及对应的典型荷载工况;然后应用改进的子模型技术对TLP平台局部节点进行极限承载能力分析,确定了局部节点在典型荷载工况下的极限承载力;对局部节点极限承载力及南海某区域的波浪荷载进行统计分析,得到其概率统计特性;在此基础上计算了TLP平台局部节点对应典型失效模式下的可靠度指标。通过算例分析表明,该TLP平台各节点可靠度指标值均大于3.1;立柱与浮箱连接节点在不同荷载工况下失效模式不同,而立柱与甲板连接节点易发生管交汇处剪切破坏。为TLP平台的安全性评估提供了一种有效的分析方法,具有一定的理论价值及实用价值。     

Experimental tests on full‐scale RC unretrofitted frame and retrofitted with buckling‐restrained braces

The results of experimental tests carried out on reinforced concrete (RC) full‐scale 2‐storey 2‐bays framed buildings are presented. The unretrofitted frame was designed for gravity loads only and without seismic details; such frame was assumed as a benchmark system in this study. A similar RC frame was retrofitted with buckling‐restrained braces (BRBs). The earthquake structural performance of both prototypes was investigated experimentally using displacement‐controlled pushover static and cyclic lateral loads. Modal response properties of the prototypes were also determined before and after the occurrence of structural damage. The results of the dynamic response analyses were utilized to assess the existing design rules for the estimation of the elastic and inelastic period of vibrations. Similarly, the values of equivalent damping were compared with code‐base relationships. It was found that the existing formulations need major revisions when they are used to predict the structural response of as‐built RC framed buildings. The equivalent damping ratio ξ_eq was augmented by more than 50% when the BRBs was employed as bracing system. For the retrofitted frame, the overstrength Ω and the ductility µ are 1.6 and 4.1, respectively; the estimated R‐factor is 6.5. The use of BRBs is thus a viable means to enhance efficiently the lateral stiffness and strength, the energy absorption and dissipation capacity of the existing RC substandard frame buildings. The foundation systems and the existing members of the superstructure are generally not overstressed as the seismic demand imposed on them can be controlled by the axial stiffness and the yielding force of the BRBs. Copyright © 2011 John Wiley & Sons, Ltd.     

Equivalent mechanical models of sloshing fluid in arbitrary‐section aqueducts

This paper reports on a semi‐analytical/numerical method to model sloshing water in an arbitrarily shaped aqueduct. The water motion is assumed to be inviscid, compressible, and linear (small displacement). The transverse sloshing fluid in an aqueduct is equivalently simplified as a fixed rigid mass M₀ and a mass–spring system (M₁, K₁). According to a rule that the actual fluid (computed with finite element model) and its equivalent mechanical model have the same first sloshing frequency and acting effects on the aqueduct, the analytical solutions of the fixed (impulsive) mass M₀, sloshing (convective) massM₁, spring stiffness K₁, and their locations in the aqueduct body are acquired by the least squares (curve fitting) algorithm. Applying this equivalent principle, the equivalent mechanical models are respectively obtained for the sloshing water in rectangular, semicircular, U‐shaped, and trapezoid aqueducts. The equivalent principle and fluid models are validated through comparison investigations involving rectangular and U‐shaped aqueducts. The dynamic properties and seismic responses of the original and equivalent systems are simulated, compared, and discussed for a U‐shaped aqueduct bridge. The main purpose of this paper is to provide a simplified model of sloshing fluid for the seismic/wind‐resistant computation of the support structures of the aqueduct bridge. Copyright © 2011 John Wiley & Sons, Ltd.     

RASC/CASC: Example of Creative Application of Statistics in Geology

RASC/CASC is a computer-based system for quantitative stratigraphic analysis developed by Agterberg, Gradstein, and co-workers. The application of the system to the Neogene biostratigraphy of the Pearl River Mouth Basin demonstrates the advantages of the system. The occurrence data of hundreds of fossils from dozens of wells are analyzed objectively based on established stratigraphic and statistical rules embedded in the system. Through permutation of the score matrix, the optimum sequence of fossil events is obtained. The calculation of inter-fossil distances allows the automated biostratigraphic zonation and the age-event correlation. Then the regional geological timetable is constructed and the inter-well chronological correlation and high-resolution subsidence analysis becomes possible, even for wells with incomplete fossil records. Uncertainty at each step is quantified. While all these are important accomplishments in a stratigraphic study, results of the study also help identify problems in allocation of fossil events and dating lithologic divisions.