三阶Stokes型随机波浪载荷谱研究     

马汝建  赵锡平 《海洋科学》2002,26(11):38-43

应用非线性谱分析理论，对三阶Stokes型随机波浪载荷谱进行了分析，将波面方程及海水质点的水平速度用一阶波面的非线性组表示，导出了随机波浪谱的表达式。为了便于求解随机波浪的载荷谱，将阻力项展开为幂级数式，并应用非线性谱分析理论，确定了幂级数的系数，进而将波浪载荷表示为一阶波面及其导数的非线性组合，最后得出波浪载荷谱密度的表达式，并应用数值分析方法，得出单位桩柱波浪力及总波浪力谱密度。  相似文献   

Models for the origin of accretionary lapilli   总被引：1，自引：0，他引：1  

R. Schumacher  H. -U. Schmincke 《Bulletin of Volcanology》1995,56(8):626-639

Binding between initially cohesionless ash particles to form concentric accretionary lapilli is provided primarily by the capillary forces of liquid bridges from condensed moisture and by electrostatic attraction. Capillary forces are strong bonds if the particles are in close contact, but they decrease rapidly with increasing particle spacing. Electrostatic attraction between charged ash particles is much weaker but effective over larger distances, increasing the frequency of collision between them.Experimental results of liquid film binding of volcanic ash showed that agglomeration was most successful between 15 and 25 wt.%, defining the agglomeration window for the formation of accretionary lapilli. Below 5–10 wt.% and above about 25–30 wt.% of water, concentric agglomeration was inhibited. Particles <350 m could be selected from a wider particle population in the experiments using only small amounts of water, which can explain the growth of accretionary lapilli in pyroclastic surges around agglomeration nuclei. Experiments testing the behavior of volcanic ash in electric fields showed that ash clusters formed instantaneously when the ash entered the field between a corona discharge gun and a grounded metal plate. The maximum grain size incorporated into the artificial clusters was about 180 m but >90 wt.% of ash was <45 m.Accretionary lapilli form in turbulent ash clouds when particles carrying liquid films of condensed moisture collide with each other and when the binding forces exceed the grain dispersive forces. Larger particles >500 m act as agglomeration nuclei in surges, accreting ash <350 m around them. In pyroclastic flows the aggregates are thought to originate from already size-sorted ash at the interface between the lower avalanche part of the flow and its overriding elutriation cloud. The fine-grained rims around accretionary lapilli found close to source are interpreted to be accreted dominantly by electrostatic attraction of very fine ash similar to clustering in elutriation clouds.  相似文献   

直流电法勘探中"干扰场"形成机理、表现特征及应用浅析     

周金华  黄经明  覃永炎  黄革非 《华南地质与矿产》2007,(3):70-74

电法勘探野外观测中常遇到干扰电场,影响观测精度和工作效率,有时甚至使观测无法开展。对干扰场进行研究,从干扰场中获取有用信息,把干扰场应用于地质找矿中有着十分重要的意义。经观测发现,干扰场以直流脉冲型为主;以直流渐变型和低频波动型为辅。通过己知矿区的试验应用表明:在良导矿床和构造破碎带上,干扰场强度有明显的异常出现,表明干扰场异常与矿体及其他物化探异常有一定的对应关系,异常形态及走向与矿体的走向和产状有关,且干扰场异常具有重现性和规律性。通过对干扰场的研究,可解决一些地质问题。  相似文献   

新疆于田绿洲荒漠交错带土地利用变化的社会驱动力研究   总被引：15，自引：15，他引：15  

王国友  塔西甫拉提·特依拜  谭灵芝 《中国沙漠》2006,26(2):259-263

 以新疆于田绿洲为例,在遥感手段对图形分析的基础之上，从景观特征上为于田绿洲土地利用变化的具体表现提供空间分析功能。结合多年的调查数据和统计资料，通过研究区遥感分类影像获得的不同土地利用类型的面积变化和转移趋势，运用SPSS软件获得于田绿洲荒漠交错带土地利用变化的综合驱动力方程，包括经济发展、人口增长、和政治经济政策等个方面。获得了影响该研究区土地利用变化的社会影响因子。结果表明，20世纪90年代以来于田地区人口的增长是土地利用/覆盖变化最主要驱动力因素，其次是牲畜头数的增长以及采樵量的变化。  相似文献   

黑河中游土地利用/覆盖变化驱动力的定量分析   总被引：13，自引：4，他引：13  

张勃  毛彦成  柳景峰 《干旱区地理》2006,29(5):726-730

以1981-2005年间近25年数据为基础,定量分析了绿洲区土地利用/覆盖变化的社会经济与自然驱动力。文中对指标进行了相关分析、主成分分析和回归分析,对社会经济和自然驱动力的10个指标综合分析和对比,确定绿洲区土地利用/覆盖变化的主要驱动因子,阐明干旱区绿洲土地利用/覆盖变化的驱动机制。结果表明:黑河中游土地利用/覆盖变化驱动力的第一主成分、第二主成分和第三主成分的贡献率分别为50.501%、17.819%和17.480%,反映出绿洲土地利用/覆盖变化驱动力因子的综合性与复杂性,其中,社会经济驱动力在黑河中游LUCC中起到主导作用,自然驱动力相对来说作用较小。  相似文献   

利用能量法由沿轨扰动位数据恢复位系数精度分析     

邹贤才  李建成  徐新禹  王正涛 《武汉大学学报(信息科学版)》2006,31(11):1011-1014

讨论了在基于能量法确定地球重力场模型的过程中，利用最小二乘方法由沿轨扰动位数据解算位系数时法方程的特性，在该问题中，法方程只与卫星轨道有关。基于这一特点，阐明了最小二乘解算结果与是否使用参考重力场模型是无关的。在此基础上，根据不同的噪声水平，模拟了4种不同精度的沿轨扰动位观测值。分别进行了重力场模型恢复并分析了其恢复精度。结果表明，在现有加速度计校准水平下，能量法恢复重力场模型难以达到动力法的精度，用于时变研究尚存在一定的困难。  相似文献   

The evaporation of the charged and uncharged water drops suspended in a wind tunnel     

Rohini V. Bhalwankar  A. B. Sathe  A. K. Kamra 《Journal of Earth System Science》2004,113(2):129-138

A laboratory experiment has been performed to study the effect of ventilation on the rate of evaporation of the millimeter sized charged and uncharged water drops suspended in a vertical wind tunnel. The linear relationship,f _u = 0.907 + 0.282X, observed between the mean ventilation coefficient, f_u, and a non-dimensional parameterX, (X =N _Sc,v ^1/3 N _Re ^1/2 whereN _Sc,uis Schmidt number andN _Reis Reynold’s number) is in agreement with the results of earlier investigations for uncharged water drops. However, in case of charged drops carrying 10^-10C of charge, this relationship gets modified tof _u = 0.4877 + 0.149X. Thus, the rate of evaporation of charged drops is slower than that of uncharged drops of the same size. Oscillations of the drop and the change in airflow around drops are suggested to contribute to lowering of the ventilation coefficients for charged drops. Applicability of the results to a small fraction of highly charged raindrops falling through the sub-cloud layer below thunderstorm is discussed. The relaxation time required for a ventilated drop to reach its equilibrium temperature increases with the drop size and is higher for the charged than for the uncharged drops. It is concluded that in a given distance, charged drops will evaporate less than that of uncharged drops.  相似文献   

In-situ Measurements of Cutter Forces on Boring Machine at Äspö Hard Rock Laboratory Part I. Laboratory Calibration and In-situ Measurements     

Z. X. Zhang  S. Q. Kou  X. C. Tan  P.-A. Lindqvist 《Rock Mechanics and Rock Engineering》2003,36(1):39-61

Summary This paper presents the testing methods used and the results obtained in an investigation of the cutter forces on a Boretec DS 1.6 boring machine during field boring in ?sp? Hard Rock Laboratory. Two button cutters, one front cutter and one gauge cutter, were used in the field measurements. A total of 6 strain gauges were bonded on the shaft of each cutter. And each group of two gauges was used to measure a one-orthogonal cutter force component, i.e. the normal force, tangential force, and side force, respectively. In order to measure the cutter forces successfully, a telemetry system composed of a transmitter and a receiver was employed to transfer the signals from the strain gauges to a computer.  A three-direction-loading system was employed in the laboratory calibration so as to solve the force-coupling problem appearing in the cutter force measurements. Correspondingly, a mathematical treatment of the force-coupling problem was performed. Then, by means of the established testing system, which was proved successful in the laboratory, the normal force, tangential force, and side force of the two button cutters on the boring machine were measured in the field. In addition, the penetration rate, thrust, and rotation speed of the boring machine were also recorded in the field. The results show the following. (1) A force-coupling phenomenon really exists and it should be considered. (2) All three directional force components always show quite a high peak value every few seconds. (3) The cutter forces of the front cutter are always much larger than the respective cutter forces of the gauge cutter. Moreover, as expected, the normal force of each cutter is much larger than the tangential force and side force of the cutter in question. Received October 5, 2001; accepted June 25, 2002; Published online November 19, 2002  相似文献   

石门─长沙铁路产业带建设研究     

朱翔 《热带地理》1998,(4)

阐述石长铁路的概况和经济地理意义,提出构建石长铁路产业带的具体思路和对策措施,指出应采取点轴开发模式,兴建加工制造业和能源工业走廊以及一系列商品农业基地,并作为沟通我国东部与西部的枢纽地带。  相似文献   

稻田水量转换观测及模拟实验研究     

汪汉林  青先国  吴金水  谢小立 《湿地科学》2004,2(4):290-295

对双季稻田水量转换 10年 (1991～ 2 0 0 0年 )定位观测 ,以及模拟不同水源条件的稻田水管理模式 ,解析田间水量转换的 5年 (1998～ 2 0 0 2年 )实验结果表明 ,稻田不同水管理田间水量转换有明显差异 ,常规管理田间耗水量的分配为 :腾发量占总耗水量 1/ 2 ,翻耕整地占 1/ 6 ,植物构成占 1/ 2 1,田间渗漏占 1/ 14 ,其他环境耗水 (维持 )占 1/ 5。长年水层灌溉田间腾发量和维持性环境耗水量偏大 ;耕灌雨养管理翻耕整地和田间渗漏耗水比例过高。水分生产力 (以年度单位面积上每耗水 1mm的产量计为kg/ (mm·hm2 ·a) ) ,稻谷产量 ,长年水层灌溉与常规管水一致 ,为 6 .6 5kg/ (mm·hm2 ·a) ,耕灌雨养处理较低 ,为 6 .13kg/ (mm·hm2 ·a)。群体光合累积效应处理间差异表现与产量差异表现相同 ,早稻差异很小 ,晚稻差异显著。叶片水分生产效率 ,早稻以水层灌溉最大 ,晚稻是常规管理最大 ,耕灌雨养处理早晚稻都较小。不同生育期这种大小关系也有变化  相似文献