有限水域近水面气流演化特征试验研究

气流作为湖泊、湿地等有限水域的主要驱动力之一,其演化特征是研究水-气间能量与物质传递的基础,决定了水域水环境与水生态格局,具有重要研究意义.采用室内风洞水槽,通过设置不同试验风速,研究近水面气流与风速和吹程的响应关系与演化特征,并将光滑壁面条件下的气流特征作为试验对照组,分析时间域内风速垂向分布形式、摩阻风速、特征粗糙...     

A new drain spacing formula

Abstract

A drain spacing formula is derived considering the variation in radial flux and the area above the drain level in the radial flow zone. The extent of the radial flow zone is ascertained by applying a mass balance and differentiability criterion of the water surface profile at the interface of radial and Dupuit-Forchheimer flow zones. The radial flow zone extends from the centre of the tile drain a distance of 2/π times the depth to impervious layer below the drain. For a normal ratio of recharge rate to hydraulic conductivity (R/K ≤ 0.0025), the water surface profile in the radial flow zone computed using Hooghoudt's formula is very different from the profile obtained by the new drain spacing formula; however, Hooghoudt's formula computes the maximum water table height which marginally differs from that found by the present method. For a ratio of high recharge rate to hydraulic conductivity (R/K = 0.1) and close drain spacing (L/D = 2), the difference in the maximum heights is 21%. Hooghoudt's formula overestimates the maximum water table position for L/D < 40. Unlike Hooghoudt's equivalent depth, the equivalent depth obtained using the present method is a function of the ratio of recharge rate to hydraulic conductivity.     

Wind set-up of water level in a river

The wind set-up of water level in a river is of great importance in many practical cases, notably in the river mouth section where the slope of the free water table is very small (sometimes 10⁻⁵) and the wind shear stress acting at the water surface generates significant changes in the vertical velocity profile. If the wind is blowing opposite to the main flow, an increase of water depth is observed. In the outlet area, the increase of water depth can reach up to 0.5 m (Lower Odra River). The paper presents an analysis of wind set-up of water level based on hydrodynamic principles.     

Seasonal formation and movement of the thermocline in lakes

Summary The work described deals with the formation and movement of the thermocline on a lake during the summer season. The formation requires an input of mechanical energy from the wind stress as well as an input of heat from solar radiation or from the air. The depth of the thermocline is shown to be nearly proportional to the ratio of the energy input to the heat input and the thermocline sinks or ascends as one input is greater or less than the other. Formulae are found for the variation of the energyE with the cumulative effect of the wind speed, the temperature difference between the water and air if positive, and the depth of the thermocline. A similar formula is obtained forQ the heat input against the total number of hours of sunshine and the positive water-air temperature difference. From these two formulae it is possible to derive a formula for the thermocline depth entirely in terms of meteorological data and surface temperatures of the water for the season.     

Vertical concentration profile of nonuniform sediment

A new formula for the concentration profile of nonuniform sediment is derived using the diffusion differential equation with equilibrium bed concentration.The interaction coefficient for nonuniform sediment particles as a function of both relative diameter and geometric standard deviation of nonuniform sediment is taken into account in the settling velocity.The diffusion coefficient is obtained from the logarithmic velocity profile.This new formula possesses several advantages as follows:(1)avoids theoretical defect of the Rouse formula,which states that the sediment concentration is infinite at the bottom and zero at the water surface.(2)suitable for an arbitrary fraction of nonuniform sediment,and(3)easy to apply with a simple form.The formula yields less difference among concentration profiles for various particles than that for uniform sediment and reveals the lawfor fractional concentration distribution of nonuniform sediment.The calculated concentration agrees well with the measured data from the Yangtze River.     

INTERNATIONALE GLAZIOLOGISCHE GRÖNLANDEXPEDITION, 1957–1959

Abstract

Equations are derived for vapor transport within a constant flux layer of the atmosphere. The physical model is based on the Reynolds analogy for fully turbulent flow, so that vapor and momentum flux are assumed similar. The shear stress is deduced from analysis of the wind profile by means of equations available for non-neutral conditions. Empirical expressions are proposed using the friction velocity rather than the wind velocity at a given level in order to take account of the stability of the air.     

海陆风及沿海风速廓线在风电场风速预报中的应用

为了建立沿海风功率预报系统,本文探讨了中国沿海风电场风速预报问题,并利用数值模式RAMS对海陆风进行了模拟研究.发现海陆风发生时,海风和陆风阶段风速廓线存在较大差异,海风阶段风速的垂直切变明显小于陆风阶段.海陆风发生时,风速会呈现有规律的变化,即海风和陆风分别有两个时段：风速增加时段和风速减少时段.在为沿海风电场提供风速预报时,当模式预报到海陆风发生时,可以利用海陆风的这种特点,使用统计方法对预报出的风速进行有效的订正.并发现即使没有海陆风发生,当风向为海洋吹向陆地时,风速随高度的垂直切变同样小于陆地吹向海洋的时段.利用统计方法根据不同风向时风速廓线的特性,把数值模式计算高度上的预报结果,精确地插值到风机涡轮高度,会很大程度上减少风速预报的误差及风功率预报环节的误差.     

Experimental study of wind solitons

A soliton mechanism of formation of rogue waves in the sea is considered. With this in view, a series of experiments was carried out in a ring aerohydrocanal. It was shown that, in the case of long waves (shallow water), a soliton may form under the effect of wind. With increasing wind velocity and decreasing liquid depth, the height of the soliton increases and its forward profile becomes steeper. The result is the formation of a bore. In a sea, such process of wind wave development can lead to the formation of rogue or freak waves. Measurements in the Setun R. have shown that the height of the rings induced by throwing a body into water always decreased in the field of counter flow.     

The stationary and non-stationary wind profile

Summary A method is presented which permits the separation of the non-stationary part of the wind profile from the stationary or smoothed profile. Very little a priori assumption is made, thus, the results can be considered to render information of general purpose. The establishment of the stationary wind profile creates a variable reference with altitude which is necessary for turbulence investigations.     

Bagnold's kink: A physical feature of a wind velocity profile modified by blown sand?

Bagnold (1941) made detailed measurements of the wind profile modified by blown sand. He noted that each velocity profile appeared to be kinked and suggested that the position of the kink corresponded to the height at which an average or a characteristic trajectory extracted the bulk of its momentum from the wind. However, Anderson and Haff (1988) have shown that in aeolian sand transport the grain cloud is made up from a distribution of trajectory paths and that it was an over-simplification to attempt to describe the complex behaviour of the grain cloud in terms of a single representative trajectory. These recent developments leave the nature and even the existence of the kink observed by Bagnold (1941) open to question. This paper shows that a kink is indeed a physical feature of the modified wind velocity profile and that it is caused, as Bagnold (1941) suggested, by a maximum, occurring at some height above the surface, in the momentum extracted by the grains from the wind. Further comments are made on both the form of the modified wind velocity profile and the fluid shear stress profile in the grain layer. In particular these comments, based upon a theoretical analysis, suggest an experimental means to measure the mean surface fluid shear stress and to gain, from accurately measured wind profiles, a greater insight into the grain cloud which caused the modification.     

A model for the numerical simulation of tephra fall deposits

A simple semianalytical model to simulate ash dispersion and deposition produced by sustained Plinian and sub-Plinian eruption columns based on the 2D advection–dispersion equation was applied. The eruption column acts as a vertical line source with a given mass distribution and neglects the complex dynamics within the eruption column. Thus, the use of the model is limited to areas far from the vent where the dynamics of the eruption column play a minor role. Vertical wind and diffusion components are considered negligible with respect to the horizontal ones. The dispersion and deposition of particles in the model is only governed by gravitational settling, horizontal eddy diffusion, and wind advection. The model accounts for different types and size classes of a user-defined number of particle classes and changing settling velocity with altitude. In as much as wind profiles are considered constant on the entire domain, the model validity is limited to medium-range distances (about 30–200 km away from the source).The model was used to reconstruct the tephra fall deposit from the documented Plinian eruption of Mt. Vesuvius, Italy, in 79 A.D. In this case, the model was able to broadly reproduce the characteristic medium-range tephra deposit. The results support the validity of the model, which has the advantage of being simple and fast to compute. It has the potential to serve as a simple tool for predicting the distribution of ash fall of hypothetical or real eruptions of a given magnitude and a given wind profile. Using a statistical set of frequent wind profiles, it also was used to construct air fall hazard maps of the most likely affected areas around active volcanoes where a large eruption is expected to occur.     

On Wind Profiles over Developing Wind Wave in the Water-Air Interface

The results of studying the vertical profile of wind velocity and the vortex-formation mechanism in the atmospheric layer immediately adjacent to the water surface under the condition of developing wind wave are considered. Materials of field and laboratory experiments are used.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 295–300.Original Russian Text Copyright © 2005 by Anisimova, Pokazeev, Soboleva, A. Speranskaya, O. Speranskaya.     

Hydrodynamic basis of formation of large-scale water circulation in the Caspian Sea: 2. Numerical calculations

The contributions of wind, water baroclinicity, and evaporation to the formation of water circulation over the depressions of the Middle and Southern Caspian are calculated numerically. The results show that all three factors—the wind, baroclinicity, and evaporation—are involved in the formation and maintenance of cyclonic water circulation over the depressions. The hydrodynamic basis of the formation of upwelling at the western and eastern coasts of the Middle Caspian are analyzed. A hypothesis is proposed regarding a more complicated, binuclear structure of the upwelling at the eastern shore of the Middle Caspian, and a theoretical substantiation of this hypothesis is given. From theoretical considerations, it is derived that the upwelling at the western shore of the Middle Caspian is of wind nature, but is governed by the integral effect of the spatial distribution of wind, rather than local alongshore wind.     

西藏高原斜压对流边界层风、温、湿廓线特征

利用1998年夏季第2次青藏高原大气科学试验当雄观测站的边界层观测资料以及拉萨、改则和武汉等地探空资料,分析讨论西藏高原斜压对流边界层风、温、湿廓线的特征. 研究结果表明,高原地区白天对流边界层发展可高达2200m,显著超过中纬度平原地区和海面上对流边界层高度. 高原对流边界层中温度廓线具有较好的混合特征,湿度廓线有时在某一高度上出现湿度极大值. 高原对流边界层内热量和水汽收支分析表明,水平平流作用对边界层结构具有重要作用. 在对流边界层中平均风速垂直分布存在风切变现象. 水平温度梯度形成较强的斜压性是形成边界层风切变的主要原因.     

钠多普勒激光雷达回波光子数仿真及大气参数反演

钠多普勒激光雷达利用中层顶区域的钠原子作为示踪物,探测中层顶区域大气风场和温度剖面.本文主要分析钠多普勒激光雷达的探测原理和大气参数反演算法.利用MSISE和HWM93等大气模型给出背景大气温度、密度及风场,并给定钠原子数密度剖面,从激光雷达方程出发,模拟计算了激光雷达的瑞利散射和钠共振荧光散射回波光子数.利用模拟的回波光子数剖面数据,反演得到大气温度、视线风速和钠原子数密度剖面,反演结果与模拟计算用的背景参数符合很好,验证了这一反演方法的正确性.分析了激光频率偏移和激光线宽变化对反演精度的影响.     

反演含有低速带的上地幔速度结构的一个公式

本文在Gerver和Markushevich以及McMechan对Herglotz-Wiechert-Bateman公式作推广的基础上,提出了一个反演含有低速带的上地幔速度结构的简明公式。虽然它只是无数低速带速度模型中的一个,但它给整个上地幔速度结构的反演计算带来方便。作为一个算例,作者计算了北京——台湾地区剖面的上地幔顶部速度结构。      

鄱阳湖典型湿地沉积物粒度分布及其动力解释

通过对沉积物粒度分析,揭示出翻阳湖典型湿地现代沉积物主要由含泥细粉砂至泥质极细粉砂组成,反映出三角洲前缘低能沉积环境,控制湿地粒度分布的动力,主要为重力型湖流,但波浪和风的作用也参与了沉积物的搬运与沉积,汛期,重力型湖流不仅控制了粒度分布的区域特征,而且决定了由草滩顶部－草滩下部－过滤带－泥滩沉积断面上粒度特征递变规律,枯水期,波浪作用的改造,使得沉积断面上的过滤带沉积物粗化,并使各粒度参数相应变化,特别是面积较大洼地的迎风岸,在过滤带地面坡度转折处,出现了粒度突变或跃变,风蚀“沙山”物质的搬运,使得“沙山”附近的湿地含砂量猛增,粒径变粗,这些动力作用,还控制着湿地的演化,即湿地范围增大,草滩扩张,过滤带以及泥滩下移,枯水期洼地水面缩小趋于消亡,严重影响湿地的生态环境,但可通过造造人工坝加以控制。     

于桥水库风季流埸的计算与分析

本文依据水流运动的基本理论,并考虑风对水体的剪切作用,应用改进的移步ADI法,建立了风作用下流场的数值模似系统,其结果与连续四年的实测资料验证相吻合。计算预报了于桥水库三个典型水文年定常风不同风速、风向的流场,并由计算机绘制出彩色流场图。文中还针对计算应用成果进行了分析。     

于桥水库风季流场的计算与分析

本文依据水流运动的基本理论,并考虑风对水体的剪切作用,应用改进的移步ADI法,建立了风作用下流场的数值模似系统,其结果与连续四年的实测资料验证相吻合。计算预报了于桥水库三个典型水文年定常风不同风速、风向的流场,并由计算机绘制出彩色流场图。文中还针对计算应用成果进行了分析。     

Mean wind speed profiles in the surface layer above wavy water surface

Analysis of field and laboratory measurements and theoretical studies was used to establish that the generally adopted logarithmic shape of wind speed profile near the ocean surface does not hold in the presence of waves. It was shown that, under the conditions of developing or developed waves at high wind speed, this profile assumes the form of two logarithmic branches, which join at a large height where wave-induced pulsations of wind speed decay. A model of wind speed profile under these conditions was constructed.Translated from Vodnye Resursy, Vol. 32, No. 2, 2005, pp. 165–170.Original Russian Text Copyright © 2005 by Matushevskii.