Effect of pier shape and pier alignment on the equilibrium scour depth at single piers

The equilibrium scour depth at uniform single bridge piers depends on a large number of variables,including the pier horizontal cross-section shape and its alignment angle towards the flow direction.The influence of these variables has been studied by only a few researchers,mostly,on the basis of tests that were far from approaching equilibrium.This experimental study aims at revisiting the influence of piers' shape and alignment on local scouring for length-width ratios smaller than or equal to 4,by increasing the experimental evidence.Fifty five long-duration laboratory tests were run under steady,clear-water flow,close to the threshold for initiation of sediment motion.Five pier shapes were considered:circular,rectangular square-nosed,rectangular round-nosed,oblong,and zero-spacing(packed) pile-groups;the tested skew-angles were 0°,30°,45°,60°,and 90°.It was concluded that i) the shape factor can be taken as 1.0,for rectangular round-nosed and oblong cross-section piers,and as 1.2,for rectangular squarenosed and packed pile-group cross-section piers,ii) the shape factor does not vary significantly with the duration of tests,this way confirming the robustness of the shape factors reported to date,iii) the effect of shape is present at skewed piers although the associated coefficients remain in the narrow range of1.0-1.2,and iv) for length-width ratios smaller than 4,the shape factor is of the same order of magnitude as the skew angle factor and should not be neglected.     

不同纵波速度介质中炸药震源激发数值模拟研究

震源激发是影响地震勘探效果的一个重要因素,在油气勘探中需要选择合适的震源参数以获取较好的地震记录。本文以数值模拟方法为基础,通过使用ANSYS/LS-DYNA软件,对单井条件下不同岩土介质中柱状炸药震源激发进行了对比研究,计算得到相应的地震子波。通过对比分析各组参数对应的地震子波振幅和频谱,选择合适的激发参数。研究结果表明,在纵波速度较低的介质中,中低爆速、细长药柱炸药激发产生的地震子波频率高、能量大,而在纵波速度较高的介质中,高爆速、短粗药柱炸药激发产生的地震子波频率高、能量大。该研究结果与实际勘探结果比较符合,可为实际勘探中激发参数的选择提供参考。      

任意形状工作面沉陷预测的概率积分法及其应用

概率积分法是煤矿开采沉陷预测的重要方法,可适用于缓倾斜、倾斜煤层开采地表移动分布曲线符合正态分布规律的地表移动和变形计算。针对原方法对任意形状工作面存在的不足,在原有走向和倾向概率积分函数的基础上,以走向和倾向为基准划分积分函数区域,在该区域内剖分非结构化的三角形单元作为二重积分的基本单位;通过坐标旋转变换的二重积分换元法,转化为以直线为上、下限的二重积分,计算旋转后的影响半径,对新的二重积分采用复合辛普森数值积分公式,积分得出地表任意点在基本三角形开采单元下的积分下沉值;最后,通过叠加计算完成任意点、任意形状工作面概率积分法的沉陷预测计算。算法在GIS系统下实现,实例应用效果良好,可为“三下”采煤提供地表移动预测计算的支持。     

Structural identification with incomplete output‐only data and independence of measured information for shear‐type systems

Structural identification is the inverse problem of estimating physical parameters of a structural system from its vibration response measurements. Incomplete instrumentation and ambient vibration testing generally result in incomplete and arbitrarily normalized measured modal information, often leading to an ill‐conditioned inverse problem and non‐unique identification results. The identifiability of any parameter set of interest depends on the amount of independent available information. In this paper, we consider the identifiability of the mass and stiffness parameters of shear‐type systems in output‐only situations with incomplete instrumentation. A mode shape expansion‐cum‐mass normalization approach is presented to obtain the complete mass normalized mode shape matrix, starting from the incomplete non‐normalized modes identified using any operational modal analysis technique. An analysis is presented to determine the minimum independent information carried by any given sensor set‐up. This is used to determine the minimum necessary number and location of sensors from the point of view of minimum necessary information for identification. The different theoretical discussions are illustrated using numerical simulations and shake table experiments. It is shown that the proposed identification algorithm is able to obtain reliably accurate physical parameter estimates under the constraints of minimal instrumentation, minimal a priori information, and unmeasured input. The sensor placement rules can be used in experiment design to determine the necessary number and location of sensors on the monitored system. John Wiley & Sons, Ltd.     

轴向受压矩形开孔板极限强度近似计算

针对受均匀轴向压力的矩形开孔板剩余极限强度的问题,考虑矩形板中间开圆孔和腰圆孔两种典型形状,四种边界条件下,以板的柔度系数、开孔率为主要影响参数通过大量非线性有限元数值计算分析,采用一种新的拟合方式提出了矩形开孔板轴向受压剩余极限强度的简化计算公式,新经验公式能够很好地反映开孔所导致板极限强度的衰减趋势。将所提出的经验公式计算结果分别与相应的试验结果、非线性有限元计算结果及其他经验公式计算结果进行对比分析。结果表明所提出的经验公式相比已有的经验公式计算更为准确,适用范围更广,可以用来预报不同边界条件下轴向均匀受压开孔矩形板的极限强度。     

西太平洋暖池时空分布特征及其与ENSO的关系

应用NCEP/NCAR SST资料和SODA海温资料,分析研究了热带太平洋海温场的变化特征,讨论了气候突变前后热带西太平洋暖池(以下简称WPWP)形态的显著变化及其差异,由此重新界定了WPWP的范围,并进一步分析了WPWP的时空变化特征。结果表明,新界定的WPWP气候平均场与前人定义的气候平均场分布特征基本相同,但也存在一定的差异。新界定的WPWP的优点在于它不仅能够客观反映出气候(海洋)突变前后西太平洋暖池的时空变化特征,而且重要的是可以避免由前人定义的WPWP与东太平洋暖池合为一体的现象发生,从而避免人为地计算WPWP面积变化带来的结果差异。新界定的WPWP平均深度可达130 m左右,呈现出西浅东深的"耳状"分布特征,在冬春季节,南北(经向)窄东西(纬向)宽,呈纬向带状分布;在夏秋季节,WP-WP明显向北扩展。平均深度最大中心位于(5°S,180°)附近。由WPWP区域不同深度的异常海温变化与Niño3指数的相关分析可知,WPWP次表层异常海温变化与Niño3指数呈显著的负相关关系,而与表层的异常海温的关系并不密切,这一结果进一步证明了西太平洋暖池对ENSO的贡献是来自次表层异常海温的东传。     

An extension of the Airy theory for linear waves into shallow water

As a fully developed (Airy) wave propagates from deep into shallow water, its crest becomes more peaked while the trough flattens out. The median crest diameter MCD, defined as the distance between the wave flanks under the crest at a level halfway between the crest and trough, therefore decreases relative to the similarly defined median trough diameter MTD, which remains constant up to the breaking point. The MCD is directly related to other wave characteristics, which enables water particle velocities to be calculated for any water depth without having to recur to more complex, higher-order Stokes, cnoidal or Fenton theories. Over a nearly horizontal bottom, most fully developed wave characteristics can be expressed as functions of the wave period T_w. It is shown that the horizontal particle velocity at the bottom under the breaker crest is at least 9 times faster than under the breaker trough, which explains why sediment is transported landward under fair weather conditions. The proposed equations also shed new light on the formation of spilling, plunging and surging/collapsing breakers.     

颗粒级配与形状对钙质砂渗透性的影响

钙质砂是富存于热带海洋环境（包括中国南海海域）中的一种特殊岩土介质,具有不同于陆源砂的水理性质。采用传统常水头渗流试验,首先探究了不同不均匀系数和曲率系数条件下级配对钙质砂渗透性的影响。针对钙质砂的颗粒形状特性,采用扫描电镜（SEM）与图像处理技术,引入球度 和圆度X的比值 从三维空间角度上对颗粒形状进行了定量描述。并在粒径区间、相对密实度相同的条件下,通过与福建标准砂、玻璃珠进行对比试验来考察钙质砂渗透特性,从而进一步探究颗粒形状对钙质砂渗透性的影响。试验结果表明,钙质砂渗透性随着颗粒粒径不均匀系数和曲率系数的增大而增大,符合级配对一般砂土渗透性的影响规律;钙质砂颗粒形状具有较强的结构性和不均匀性,同等密实度下钙质砂的渗透性小于陆源的石英砂。本研究获得的钙质砂渗透规律对今后南海岛礁填筑和海上平台基础工程设计具有一定的指导意义。     

岩爆的洞室效应

岩爆是高地应力区地下工程开挖中常见的一种地质灾害。目前岩爆的发生条件多从地应力条件、地层岩性、岩体结构、埋深和地形、地质构造作用、水文地质条件、开挖爆破等因素开展研究。文章提出通过改变洞室断面形态及尺寸预防岩爆发生的思路,在单因素分析条件下,通过有限元软件模拟不同洞室形状和尺寸的开挖,分析探讨同一尺寸、不同洞室形状下的岩爆强度和同一洞室形状、不同尺寸下的岩爆强度。结果表明：岩爆存在洞室形状效应,同一尺寸下,椭圆（谐洞）是对减少岩爆最有利的洞形,半圆直墙形和圆形其次,半圆形最差;岩爆存在洞室尺寸效应,同一洞室形状下的岩爆都随洞室开挖尺寸的增大而增强。同时,通过双曲线和指数函数的拟合表明,岩爆强度不会无限上涨,而是最终趋于一个稳定值。     

面积测量设计中地块形状与界址点误差关系

分析了面积设计误差与界址点误差的关系,推导了根据面积设计误差确定界址点误差的计算公式,得到了最适合设计时求解界址点误差的图形形状。