塑料大棚结构的脉动风速与风压时程模拟

作用在塑料大棚结构上的主要动力荷载是风荷载,考虑脉动风作用的塑料大棚结构风振响应能真实地反映结构的受力特点。为了对塑料大棚结构进行时域内风振响应分析,必须解决脉动风速时程模拟问题。为此,采用谐波叠加法对塑料大棚结构表面的脉动风速进行模拟,获得不同空间点的风速时程曲线,对比了模拟功率谱与目标功率谱的变化趋势,分析了不同空间位置的相干性随两点距离增加的变化规律,模拟了不同点的脉动风压,从而为研究塑料大棚结构风振响应提供了荷载条件。     

基于双峰分布的风胁迫雾滴沉积分布模型研究

为研究因风胁迫产生的雾滴飘移对雾滴沉积分布的影响规律,设计了三因素三水平的喷雾飘移沉积试验,测定了不同条件下的雾滴沉积量分布。为更好描述雾滴飘移沉积分布情况,建立了基于正态分布概率密度函数的双峰分布式数学模型,系统地表达了沉积范围与沉积量的关系,分析了各水平因素对双峰分布式中各参数的影响。结果表明,沉积量参数k1与k2变化规律相反,随着喷雾高度、喷雾压力和横风风速的增加,k1减小而k2增大,质量由第1峰值分布向第2峰值分布转移;双峰分布的2个位置参数μ1、μ2具有相同的变化趋势,均随着风速、高度的升高而增大,随喷雾压力的升高而减小,因此增大喷雾压力可以减小中心飘移距离;第1和第2峰值分布的范围（尺度参数σ1、σ2）均随着喷雾高度和风速的增加而增加,沉积量分布更加分散;增大喷雾压力可以有效减少第一峰值的质量分散,但对第2峰值分布无影响。本文探究了不同强度横风作用、喷雾高度和喷雾压力对雾滴飘移沉积分布的影响,可为优化农药喷雾技术和增强雾滴抗飘移能力提供参考。     

天然地形和人工沙棘风障对排土场平台植被恢复的影响

以霍林河露天煤矿为例 ,通过对排土场不同地段植被的观察、野外小区实验和室内分析的方法 ,调查研究了天然地形风障以及人工沙棘风障对半干旱地区露天煤矿排土场平台植被恢复状况的影响。研究结果表明 ,地形与人工沙棘风障不仅起到防风作用 ,还可以改善土壤理化性质 ,促进其它植物的生长 ,防治水土流失 ,加速排土场的植被恢复与生态重建的进程。     

影响沙棘生长主要生态因子的灰色优势分析

在黄土高原沟壑区，影响沙棘生长的主要生态因子中，地形、土壤因子的影响集中表现为土壤水分的影响，而土壤水分主要受气象因子的影响。气象因子对沙棘生长的影响很大，其中水分类子出于对沙棘总体生长的影响大于热量类子因子；４～６月降雨为影响沙棘生长的优势气象因子。在土壤水分条件较好的阴沟坡，沙棘生长与气象因子的关联度最小，在水分条件较差的它立地，沙棘生长与气象因子的关联度较大。由此可见，生长在阴沟议的沙棘基本上能达到“旱涝保收”，而在干旱立地上，沙棘生长对水分类气象子因子的依赖性很大。     

Wind tunnel simulation of ridge-tillage effects on soil erosion from cropland

In the arid and semi-arid regions, ridge tillage was often used as an alternative practice for wind erosion control on the croplands without sufficient crop residues left during the fallow period. Through wind tunnel experiments, wind erosion rate and vertical mass flux profile of blown sand under the simulated conditions of ridge tillage and flat tillage were studied in 15, 10, 10, 5, 3 min exposures at the wind velocities of 8, 10, 15, 20, 24 m s⁻¹, respectively. The results for the soil tested indicate that the mean rate of wind erosion under flat tillage was 129.89 g m⁻² min⁻¹, while that under ridge tillage were 20–60% less. Under ridge tillage with different structures, average wind erosion rate had a positive correlation with the spacing between adjacent ridges. For the same ridge height, average wind erosion rate decreased with increasing ratio between the height of ridge and the width of furrow. For the same ratio between the height of ridge and the width of furrow, average wind erosion rate increased with increasing height of ridge. Power function relationships were found between wind erosion rate and wind velocity on all the simulated tillage conditions. A wind velocity of 15 m s⁻¹ was the critical velocity, above which wind erosion rate increased rapidly for the soil and simulated tillage conditions tested. Compared with flat tillage, ridge tillage remarkably decreased wind erosion rates when wind velocities were beyond 15 m s⁻¹. Under ridge tillage, the total mass of sand transported at a height of 0–20 cm above soil surface (Q_0–20), and the fraction of that travelling at a height of 0–4 cm (Q_0–4/Q_0–20), were less man mat under flat tillage. For the same ridge height, Q_0–4/Q_0–20 increased with increasing ratio between the height of ridge and the width of furrow. For the same ratio between the height of ridge and the width of furrow, Q_0–4/Q_0–20 decreased with increasing height of the ridge. Sand transport rate under flat tillage decreased with increasing height by a negative exponential function, while negative linear functions were found under ridge tillage. Thus ridge tillage decreased the rate of wind erosion and sand transportation near soil surface, reduced the loss of soil nutrient caused by wind erosion and plant damage caused by blown sand abrasion, which make it an effective agricultural technology for wind erosion control in the arid and semi-arid regions.     

中国土壤风蚀灾害发生的范围

从大尺度讨论土壤风蚀灾害,认为风蚀是侵蚀因子（风力、可蚀表面等）和抑制因子（植被、水分等）斗争的结果,风蚀灾害发生在侵蚀风和干燥无覆被土壤共同出现的时段,所以说气候决定风蚀灾害的范围。依据李世奎等的《中国农业气候区划》诊断各个农业气候区发生风蚀灾害的时间和强度,农业土壤和非农业土壤采用的方法相似,但指标体系不同,确定了中国土壤风蚀灾害发生的范围。结果表明中国土壤风蚀灾害主要发生在温带,范围涉及国土面积60.9%的广大地区,其中,东部季风农业气候大区和青藏高寒农业气候大区,土壤风蚀灾害以农业土壤为主;西北干旱农业气候大区,农业和非农业土壤均遭受风蚀灾害,而且风蚀程度也大于其他气候大区。     

阴山北麓不同用地土壤有机质含量对抗风蚀的作用研究

随着人类对土地利用的强度不断增大,改变了自然土壤表层原有的性质,并对风产生不同的抗蚀效果。不同的土地利用方式下,土壤的有机质含量是不同的。土壤有机质影响土粒间微结构的胶结力和土壤结构体间的抵抗离散力,从而影响土壤的抵抗风蚀能力。通过对阴山北麓不同土地利用方式下的土地进行野外调查取样和室内理化分析,分析了土壤有机质含量变化过程,研究了土壤有机质含量对抗风蚀的影响。结果表明：土壤有机质含量与土壤抗风蚀强度成正相关关系,也就是随着土壤有机质含量的增加,土壤的抗风蚀强度增强,凡是有机质含量较高的土地利用类型,其土壤的抗风蚀强度较强,例如：人造林地的土壤有机质含量为3.904%,其土壤风蚀相对强弱指数是1.726;未成林林地的土壤有机质含量为2.775%,其土壤风蚀相对强弱指数是23.409;人造林地的土壤有机质含量高于未成林林地,而人造林地的土壤风蚀相对强弱指数小于未成林林地,也就是人造林地的抗风蚀强度大于未成林林地。因此,应当针对阴山北麓处于西北风主风向地带、风速大、土壤风蚀易发生的实际情况,合理保护和利用有限的土地资源,使土壤资源得以保护。     

Wind tunnel test and Cs tracing study on wind erosion of several soils in Tibet

The soils of alpine meadows and alpine grassland steppes, aeolian soils, coarse-grained soils, and farm soils cultivated from alpine grasslands in Tibet are typical soils that are suffering from different degrees of soil erosion by wind. Based on field investigations, wind tunnel experiments, and a ¹³⁷Cs trace study, this work tested the erodibility of these soils by wind, simulated the protective functions of natural vegetation and the accelerative effects of damage by livestock, woodcutting, and cultivation on erosion, and estimated erosion rates from 1963 to 2001. The results indicated that alpine meadows have the strongest resistance to wind erosion, and that undamaged alpine meadow soils generally sustain only weak or no wind erosion. Alpine grassland steppes with good vegetation cover and little damage by humans exhibit good resistance to wind erosion and suffered from only slight erosion. However, soil erodibility increased remarkably in response to serious disturbance by livestock and woodcutting; wind erosion reached 33.03 t ha⁻¹ year⁻¹. The erodibility of semi-stabilized aeolian soil and mobile aeolian soil was highest, at 52.17 and 56.4 t ha⁻¹ year⁻¹, respectively. The mean erosion rates of coarse-grained soil with various levels of vegetation coverage and of farm soil were intermediate, at 45.85 and 51.33 t ha⁻¹ year⁻¹, respectively. Restricting livestock, woodcutting, and excessive grassland cultivation are the keys to controlling wind erosion in Tibet. In agricultural regions, taking protective cultivation and management to enhance surface roughness is a useful way to control wind erosion.     

土壤风蚀物中沙粒的动力学特性分析

该文以内蒙古阴山北部的典型农牧交错带耕地为试验区,采用SC-I型沙尘采集器收集跃移沙粒,对收集到的土壤风蚀物进行分析整理,得出了沙粒动力学计算的各重要参数,并从单颗粒土壤在气流中所受的作用力出发,紧密联系野外实验测得的数据,采用4/5阶RKF算法,对沙粒不同受力状况下的运动轨迹和运动特征进行分析。研究表明沙粒粒径愈小发生漂浮所需要的条件愈低,随粒径的增大要求达到的旋转角速度ω、垂直起跳初速度v0越来越大,而小于0.075 mm的颗粒容易在脱离地面后,浮在空中从而成为悬移的主体;同时得到了沙粒最大跃移高度Hm关于风蚀物粒径D和垂直起跳初速度v0的通用双因子预测模型。研究为今后风沙运动力学理论的深入研究及土地荒漠化的防治提供依据。     

NK-1型可移动式风蚀风洞洞体设计

针对土壤风蚀研究的需求,依据空气动力学要求设计了NK-1型可移动式风蚀风洞。该风洞由进气段、动力段、过渡段、转角段、稳定段、收缩段、实验段和扩散段组成,总高2456mm,全长15900mm,能量比0.41。该风洞主要特点为:进气口为双扭线形唇口;转角段为20°仰角设计;稳定段采用六角形蜂窝器和两层阻尼网组合设计;实验段风速为0.3～20m/s连续可调;尾部扩散段扩散角为20°。最后运用Fluent6.3流体模拟软件,对空风洞实验段纵截面的气流速率分布、静压分布进行了模拟,满足设计要求。