用变分方法估算淮河流域总体输送系数

利用2001年6～7月间在安徽肥西的边界层观测资料,利用变分方法计算地面动量通量和感热通量,进而分别估算该处动量总体输送系数和感热总体输送系数。用变分方法计算的地面粗糙度为0.03m。在中性条件下,10m高处平均动量总体输送系数和感热总体输送系数分别为4.83×10-3和3.81×10-3,比值是1.27。总体输送系数具有明显的日变化特征,中午时段最大,夜晚最小;总体输送系数与大气稳定度存在明显关联,文中给出它们之间的拟合关系式;随着高度的增加总体输送系数减少,但减少幅度逐渐变小。     

半潜式超大型浮式结构水动力系数研究

以半潜式超大型浮式结构在动力响应分析中的各水动力系数为研究对象,经理论推导得到D’Alembert动力学方程中的移动式海上基地(MOB)单模块运动的结构质量、结构附加质量、静恢复力系数的简易计算公式。以MOB的"三模块模型"为例,研究其在6级海况浪向角为0°~90°条件下,各模块的附加质量系数及静恢复力系数的历时规律,以实例MOB中的第1个模块为代表展示了计算结果,并统计其最大值与文献资料中的结果进行对比。结果表明:运用本理论公式计算的结果与文献中所得结果相似,可验证本理论公式的正确性、可行性与合理性,为求解半潜式超大型浮式结构模块动力响应位移及转角提供简便的方法。     

应用屏障进行被动隔振的研究综述

人工振动作为一种新形式的环境污染,被列为世界七大环境公害之一。各种形式的人工振动都涉及弹性波的产生和传播,在既有振源与保护区之间设立屏障来切断弹性波的传播路径,衰减振动能量,降低振动幅度,是目前国际上普通采用的隔振措施。屏障按几何构造可分为两类:连续屏障和非连续屏障。对国内外两类屏障的隔振理论和试验研究进行简述,得出的结论为:(1)连续屏障隔振效果好,但对于低频振源,屏障的深度需达到十几米以上(近似于R波的半波长),在软土和高地下水位地区的工程造价非常高,施工难度也非常大;(2)非连续屏障施工方便,不受深度和场地的限制,不需要进行额外的支护和维护,多排非连续屏障具有更广泛的应用前景。今后应注重和加强多排非连续屏障隔振的三维理论分析和吸振新材料的试验研究。     

非连续变形分析中时间步及弹簧刚度取值研究

非连续变形分析（DDA）是一种隐式求解的动力学计算方法,且采用在块体界面加减刚硬弹簧的方式来满足块体界面无张拉和无嵌入的接触准则,其中时间步长和弹簧刚度两个物理量的取值直接影响DDA的计算结果。基于对DDA时间步和弹簧刚度在程序运行过程中的调整策略和块体接触的简化力学概念模型,研究了惯性力在DDA收敛求解中的作用过程。采用数值模拟试验对自由落体和斜面单滑块模型在3种力学状态下的相关力学问题进行了数值模拟研究,通过对自由落体运动的模拟,研究了时间步长单一因素对计算结果的影响规律,并初步确定了时间步长的合理取值区间。在此基础上,采用斜面单滑块模型,研究了时间步长和弹簧刚度对计算结果的共同影响,确定了不同时间步长条件下弹簧刚度的合理取值区间。研究成果表明,合适的时间步长和弹簧刚度的取值组合构成一个单连通参数取值域,当时间步和弹簧刚度的取值组合位于此“域”范围内时,DDA的计算结果是合理的。     

Behaviour of the geomagnetic field during the Matuyama–Brunhes polarity transition

The ability to derive Gauss coefficients, up to and including degree 3, and their variation through a geomagnetic polarity transition is studied using simulated palaeomagnetic data. It is concluded that for a specified distribution of palaeomagnetic sites reasonable estimates of the behaviour of the coefficients can be derived even when uncertainties in the data, and in the compilation of contemporaneous records, are considered. Published palaeomagnetic records of the Matuyama–Brunhes transition are then used as basis for deriving the variation of the Gauss coefficients over a 32 kyear period encompassing the reversal. Individual records are interpolated to uniform time intervals of 0.5 kyear and put on to a common time scale by correlating between sites the variation in the latitude of VGP's through the reversal. Relative palaeointensity data are scaled by the geocentric axial dipole field intensity for 2000 at each site, and the Gauss coefficients derived by a matrix inversion employing singular value decomposition. The derived variation with time of the Gauss coefficients suggests that, over the time span of the data, the dipole and non-dipole fields have approximately equal intensities. Plots of the variation of the surface vertical magnetic field through the reversal suggest that immediately prior to the reversal a large patch of reverse flux appears in the southern hemisphere. This may subsequently have been responsible for the weakening of the vertical field leading into the reversal. A similar patch of reverse flux is observed some 20–15 kyear prior to the actual reversal and may be associated with an observed excursion in VGPs at several sites.     

球形颗粒紧密堆积状态时的吸力分析

根据圆液面假设和热力学基本原理,研究了球形颗粒紧密堆积模式在水封闭状态（状态2）时的吸力特性,得到了状态2中3类吸力和3类等效吸力与饱和度的定量关系和以接触角和饱和度或饱和半径为参数的吸力比表达式。进一步的研究表明,在状态2中吸力比都小于1,与基于松散堆积模式在水封闭状态（状态1）时得到的结果比较后可知,随着颗粒排列密实度的增大,相对于基质吸力,张力吸力的作用将有所降低但仍然不可忽视。另外,随饱和度变化,状态2中的3类吸力,特别是3类等效吸力的变化趋势与基于状态1得到的结论基本一致。在状态2中,对数吸力比与饱和半径呈明显的线性关系,吸力比与饱和度也呈明显的线性关系,前者与状态1中的吸力演化规律一致,而后者则存在较大不同。     

Plot and small‐watershed scale runoff from two reclaimed surface‐mined watersheds in Alberta

Infiltration excess overland flow has been identified as the dominant flow pathway in recently reclaimed surface mined watersheds as a result of compaction and sorting during the reclamation procedure. Therefore, there could be a fairly direct relationship between runoff generated from the hillslopes to that measured at the watershed outlet. A 3‐year study was initiated in 1993 to determine how well surface runoff at a watershed scale could be predicted from 1‐m² runoff frames placed on hillslopes in two reclaimed surface‐mined watersheds in central Alberta. Runoff from the hillslope frames suggests outlet discharge should be high from the 3\4‐ha Sandy Subsoil Watershed and much less for the 9\8‐ha West Watershed, but the opposite occurred. Most of the hillslope runoff from the Sandy Subsoil Watershed infiltrated once it reached the channel and depression storage played an insignificant role in determining runoff. In contrast, most of the runoff from the West Watershed originated from rain falling directly on the saturated channel (depression storage) or near‐channel saturated areas, rather than the hillslopes. Neither watershed runoff magnitude nor timing could be predicted from the same parameters for hillslope runoff frames for either reclaimed watershed. Copyright © 2000 John Wiley & Sons, Ltd.     

陇中黄土高原半干旱区总体输送系数的特征

利用在陇中黄土高原半干旱区2003年10月—2005年7月获得的近地层梯度观测资料,采用空气动力学法,计算了动量和感热总体输送系数。结果表明,陇中黄土高原半干旱区动量和感热总体输送系数均存在明显的日变化特征,夏季中午左右分别达到5.6×10-3和6.7×10-3。受下垫面植被的影响,在一年中呈现出双峰型特征,第一峰值出现在春小麦拔节—黄熟期,次高值出现在10月初。动量和感热总体输送系数平均值分别为2.9×10-3和3.1×10-3。当大气处于不稳定状态时,总体输送系数随着风速的增大而减小;相反当大气处于稳定状态时,随着风速的增大而增大。陇中黄土高原半干旱区的总体输送系数高于戈壁、平原草地和海洋下垫面的值,但低于青藏高原草地和城市下垫面的值。     

敦煌戈壁不同近地层大气稳定度下的感热交换系数

首先利用空气动力学法,计算分析了敦煌戈壁2000年9月—2001年9月的感热交换系数Ch的特征,计算得到Ch的年平均值为0.00203±0.00045。敦煌戈壁的Ch在近中性和中性条件下(-0.01<ζ<0.01,ζ为Monin-Obukhov大气稳定度参数)为常数,Chn≈0.0020;在稳定条件下(ζ≥0.01),Ch比较小,随地表风速的增大而增大,趋于Chn,它们之间存在的关系是:Ch=0.0012 0.0003ln(V);在不稳定条件下(ζ≤-0.01),Ch比较大,随地表风速的增大而减小,也趋于Chn,它们之间存在的关系是:Ch=0.0026-0.0002ln(V)。本文还利用地表温度、一层气温和一层风速近似计算了总体Richardson数Rb,判定大气的层结稳定度,再根据该稳定度来选择感热交换系数。     

不同下垫面湍流输送计算方法的研究

文章应用三种不同下垫面近地面层风速和温度梯度资料，代入风速和温度廓线公式，迭代求得感热通量及热量交换系数。确定Kh /Kw与稳定参数ξ的关系式。分别利用空气动力学方法和波文比能量平衡法计算潜热通量，并进行了比较。