声波探查砼裂缝深度的数学分析与实践     

王清玉 《水文地质工程地质》1993,20(4):58-59

本文仅就声波探查砼裂缝深度的可行性从数学角度进行了分析与论证,并给出了工程实例。  相似文献   

The role of wind direction in eolian transport on a narrow sandy beach     

Karl F. Nordstrom  Nancy L. Jackson 《地球表面变化过程与地形》1993,18(8):675-685

Comparison of eolian transport during five high-velocity wind events over a 29 day period on a narrow estuarine beach in Delaware Bay, New Jersey, USA, reveals the temporal variability of transport, due to changes in direction of wind approach. Mean wind speed measured 6 m above the dune crest for the five events ranged from 8·5 to 15·9 ms^?1. Mean wind direction was oblique to the shoreline (63° from shore-normal) during one event but was within 14° of shore-normal during the other events. Eolian transport is greatest during low tide and rising tide, when the beach source area is widest and when drying of surface sediments occurs. The quantity of sediment caught in a vertical trap for the five events varied from a total of 0·07 to 113·73 kgm^?1. Differences in temperature, relative humidity and moisture and salt content of surficial sediments were slight. Mean grain sizes ranged from 0·33 to 0·58 mm, causing slight differences in threshold shear velocity, but shear velocities exceeded the threshold required for transport during all events. Beach width, measured normal to the shoreline, varied from 15·5 to 18·0 m; beach slope differed by 0·5°. The oblique wind during one event created a source width nearly double the width during other days. Beach slope, measured in the direction of the wind, was less than half as steep as the slope measured normal to the shoreline. The amount of sand trapped during the oblique wind was over 20 times greater than any other event, even those with higher shear velocities. The ability of the beach surface to supply grains to the air stream is limited on narrow beaches, but increased source width, due to oblique wind approach, can partially overcome limitations of surface conditions on the beach.  相似文献   

广义帕累托分布在广东重现期风速计算中的应用     

王志春 《气象科技》2020,48(3):428-432

利用广东省86个国家气象观测站建站以来近70a的逐月最大风速序列和近20a(1999—2018年)的逐月最大风速序列,基于POT抽样法,分别采用三参数广义帕累托分布函数对各站的重现期风速进行了概率计算,计算过程中三参数广义帕累托分布函数分别采用矩估计(MOM)、极大似然估计(MLE)、似然矩估计(LM)和概率权矩估计(PWM)等4种参数估计方法,结合表征参数估计优良性的指标:均方根误差RMSE、拟合相对偏差和显著性水平为0.05的科莫戈洛夫检验拟合适度指标K_f对拟合效果进行检验,结果表明:基于POT抽样的概率权矩估计(PWM)拟合效果最好。  相似文献   

An Imaging Photon Counting Intensified CCD for High Speed Photometry     

P. Bergamini  G. Bonelli  A. Paizis  L. Tommasi  M. Uslenghi  R. Falomo  G. Tondello 《Experimental Astronomy》2000,10(4):457-471

The scientific performance evaluation of a photon countingimaging system is presented. The detector is constituted by an ICCD camera with RbTe photocathode(optimized for UV radiation), and dedicated electronics for the acquisition and analysis ofthe events. For each photon event on the CCD, a real-time centroid calculation is performed, inorder to reach spatial resolution down to 25 m FWHM. The system has been tested usingthe 182 cm telescope of the Asiago Observatory.A standard stars field through U Johnson filter,and the Crab pulsar (PSR 0531+21) were observed. From the photometric data, relative magnitudes of the standard stars have been derived, showing a goodlinearity of the detector in the range of flux under consideration, as expected fromprevious laboratory measurements.The pulsar's data have been processed by FFT and epoch foldingtechniques to testthe detector's timing performances in the highest resolutionmode (4.512 ms).These observations show that a space resolved time analysis ofperiodic sources can be performed with 10^-7 s accuracy.  相似文献   

Comments on: ‘The Neutral, Barotropic Planetary Boundary Layer, Capped by a Low-Level Inversion’ by G. D. Hess, Boundary-Layer Meteorology (2004) 110, pp. 319–355     

Juan Carlos Bergmann 《Boundary-Layer Meteorology》2006,119(1):171-179

Precision measurements indicate that the stability capping of the neutral planetary boundary layer (PBL) that leads to a reduced PBL height is caused by the very stable upper part of the PBL, rather than by an overlying inversion. Radiative processes related to liquid water in boundary-layer clouds seem to play the key role for the formation of the stable upper PBL. The famous Leipzig Profile – generally considered as an example of a neutral PBL – has been included in Hess’s analysis because its PBL height is considerably lower than the ca. 3000 m to be expected by numerical models in truly neutral conditions. An analysis of the original observations reveals that the Leipzig PBL was stable and that it can be consistently treated as a ‘normal’ stable PBL with a height of ca. 700 m. A further finding is that the super-geostrophic PBL wind speed maxima predicted by almost all models are not observed in near-steady-state conditions. For the ‘ranking’ of analytical models versus numerical models, the comparisons with measurements show that the analytical models perform comparably well and even partially better than the numerical models.  相似文献   

濮阳近50a风速变化特征及突变分析     

Xu Qiaozhen  Wu Jianhe  Han Xiangbin  Xu Qing′e  Wang Chunling  Jia Jinming 《河南气象》2007,(Z1)

利用线性分析方法,分析了濮阳近50 a平均风速、大风日数的变化特征,并利用滑动的t检验法分析了风速突变,结果显示:年平均风速以0.498(m/s)/10 a的倾向率减少,大风和扬沙日数分别以2.7 d/10 a和5.6 d/10 a的倾向率减少;平均风速,大风、扬沙日数在20世纪80年代初期发生突变。  相似文献   

极端干旱荒漠区典型晴天大气热力边界层结构分析   总被引：3，自引：1，他引：3  

张强  赵映东  王胜  马芳 《地球科学进展》2007,22(11):1150-1159

利用极端干旱区敦煌野外观测试验资料，分析了极端干旱荒漠区夏季典型晴天位温、风速、比湿等主要物理要素的垂直结构特征及其地表热力和近地层大气运动特征的日变化规律。发现在极端干旱地区夏季晴天大气热力边界层结构十分独特。在夜间，贴地逆温层最低在900 m以上，最厚可以达到1 750 m，逆温层上面的残余层一般能达到4 000 m左右的高度。在白天，位温超绝热递减层高达1 000 m，超绝热递减层上面的混合层最高达3 700 m，混合层顶上还有大约450 m甚至更厚的夹卷层。当白天对流层发展达到残余层以后，混合层的发展明显加快。风速和比湿垂直廓线特征很好地印证了大气热力边界层独特的结构特征，地表热力和近地层大气运动特征也为这种独特的大气热力边界层结构提供了较好的物理支持。  相似文献   

对建筑场地类别划分方法的探讨     

任志善  朱金泰  李明恩 《岩土工程技术》2007,21(5):243-245,249

判定场地类别是岩土工程勘察要解决的主要问题之一。科学地确定场地类别可以用来指导建筑抗震设计。判定场地类别的方法目前主要依据规范法进行。在按规范法进行判定场地类别时,由于场地沉积土层的差异、建筑物基础埋深的不同或采用基础型式的不同、场地标高的不同,有时会产生一些矛盾。对这些矛盾提出了初步解决的建议,供业内人士参考及批评指正。  相似文献   

Pulsatory characteristics of wind velocity in sand flow over typical underlying surfaces     

ZHANG KeCun  QU JianJun  ZU RuiPing & FANG HaiYan Key Laboratory of Desert  Desertification  Cold  Arid Regions Environmental  Engineering Research Institute  Chinese Academy of Sciences  Lanzhou  China 《中国科学D辑(英文版)》2007,50(2):247-253

Pulsatory characteristics of wind velocity in sand flow over Gobi and mobile sand surface have been investigated experimentally in the wind tunnel. The primary goal of this paper is to reveal the relation- ship between pulsatory characteristics of instantaneous wind speed in sand flow and the motion state of sand grains. For a given underlying surface, pulsation of wind velocities in sand flow on different heights has a good correlation. As the space distance among different heights increases, fluctuation of instantaneous wind speed presents a decreasing trend and its amplitude is closely related to the mo- tion state of sand grains and their transport. Pulsatory intensity increases with the indicated wind speed, but its relative value does not depend on it, only agrees with height.  相似文献   

城市区域屋顶上与地上的风速和温度特征分析   总被引：17，自引：5，他引：12  

张一平  彭贵芬 《地理科学》1998,18(1):45-52

以低纬的城市昆明为研究对象,利用城内外屋顶上和地上的风速和温度实测资料,分析了研究较少的,做为城市第二热力面的屋顶面附近的风度温特征,变化规律及其与地上的差异,得到了一些有益的结果。  相似文献