支管射流三通结构优化与试验

为了提高支管射流三通水力性能,改善滴灌的灌水均匀性,基于CFX数值模拟技术,对进口宽度为15 mm的支管射流三通进行结构优化.选取位差、劈距、劈尖半径和侧壁倾角为影响因素,通过四因素三水平正交设计了9组模型,边界条件设定为进口压力100 kPa.选取支管射流三通出口设计流量为评价标准,支管射流三通最优结构尺寸为位差5.5 mm、劈距113 mm、劈尖半径13 mm、侧壁倾角10°.此结构尺寸参数下的支管射流三通水力性能试验结果表明:在进口水压为100 kPa时,支管射流三通脉冲频率为148次/min,水头压力振幅为37.9 kPa,水头压力损失为16.7 kPa,出口流量为0.698 L/s;支管射流三通所接滴灌带长度为60 m时,与普通支管三通相比,支管射流三通的灌水均匀系数提高了2.78%,流量偏差率降低了4.72%.该研究可为射流技术在脉冲滴灌系统的研究、开发与应用提供理论依据.     

利用盘式吸渗仪确定土壤水力学参数研究进展

各种农业措施显著影响土壤的物理性质,特别是土壤水力学参数。随着计算机模型广泛用于土壤物质迁移的预测预报,准确确定土壤水力学参数成为一项重要的研究任务。盘式吸渗仪作为一种简便实用的仪器正被广泛用于田间土壤水力学参数的测定。国内外学者研究了稳态、瞬态和反推等方法,利用盘式吸渗仪来确定土壤近饱和导水率、吸渗率和水分特征曲线。同时该仪器可以用于田间测定土壤孔隙分布状况,以及两区模型中的参数。笔者对国内外有关盘式吸渗仪研究从相关理论和应用方面进展进行了综述,并对田间测定操作中注意的问题进行评述,指导田间试验以获得准确的测定数据。盘式吸渗仪在田间测定土壤孔隙,特别是大孔隙流方面有独特的优点,但是其并未在中国不同质地土壤上得以广泛应用。     

Impact on soil physical properties of using large-grain legumes for catch crop cultivation under different tillage conditions

In Central Europe, various plant species including large-grain legumes and their mixtures are grown as catch crops, particularly between grains harvested early and subsequent summer crops. This article investigates the question of how soil structure in the topsoil is influenced when catch cropping with large-grain legumes (experimental factor A: without catch crop, with catch crop) under different ploughless tillage conditions during catch crop seeding (experimental factor B: deep tillage/25–30 cm, shallow tillage/8–10 cm). Five one-year trials were performed using standard machinery at various sites in Germany. Soil core samples extracted from the topsoil in the spring after catch crop cultivation served to identify air capacity, saturated hydraulic conductivity and precompression stress. The above-ground and below-ground biomass yields of the catch crops were also determined at most of the sites. In addition, the soil compaction risk for the working steps in the experiments was calculated using the REPRO model.The dry matter yield of the catch crops varied considerably between the individual trial sites and years. In particular, high levels of dry matter were able to form in the case of early seeding and a sufficient supply of precipitation. The soil structure was only rarely affected positively by catch crop cultivation, and catch crops did not contribute in the short term to loosening already compacted topsoils. In contrast, mechanical soil stresses caused by driving over the ground and additional working steps used in cultivating catch crops often led to lower air capacity in these treatments. This is consistent with the soil compaction risks calculated using the REPRO model, which were higher in the treatments with catch cropping. Catch crop cultivation also only resulted in improved mechanical stability at one location. The positive effect of deep ploughless tillage on air capacity and saturated hydraulic conductivity, however, became more clearly evident regardless of catch crop cultivation. In order for catch crop cultivation with large-grain legumes to be able to have a favourable impact on soil structure, it is therefore important that cultivating them does not result in any new soil compaction. In the conditions evaluated, deep tillage was more effective at loosening compacted topsoil than growing catch crops.     

地表火对宝天曼栎类森林生态系统服务功能的影响研究

2008年4月至2010年6月采用时间序列代替空间序列的方法,对宝天曼栎类森林生态系统服务功能受地表火影响在不同时间的涵养水源、保育土壤、固碳释氧、生物保育、积累营养物质、负离子提供和森林病虫害防治等7个方面进行了初步评估。结果表明,地表火干扰造成宝天曼栎类森林生态系统服务功能损失的价值在时间序列上依次为1年是24.95万元.hm-2,5年是11.68万元.hm-2,10年是4.91万元.hm-2,15年是0.68万元.hm-2;各项服务功能价值量损失排序为保育土壤>涵养水源>病虫害防治>固碳释氧>积累营养物质>净化大气>生物保育,其中保育土壤和涵养水源两项的损失占总损失量的70%左右,这表明地表火主要影响宝天曼栎类森林生态系统中的保育土壤和涵养水源功能。     

全液压山地手扶式苜蓿刈割压扁机设计与试验

为适应我国山坡、丘陵地带苜蓿收获特殊需求,提高苜蓿收获机械作业操作灵活性和安全性,提出了一款山地手扶式苜蓿刈割压扁机。该机采用全液压驱动,整机液压系统由行走驱动回路、工作装置升降控制回路及工作装置驱动回路3部分组成,可实现自走、工作装置升降和刈割压扁作业;工作装置升降机构采用平行四连杆机构,以保证工作装置升降过程中割刀刀盘倾角不变。同时,进行了样机试制与田间性能试验,试验表明:整机能够有效地实现苜蓿的刈割、压扁作业,爬坡度可达30%,行驶速度可达5km/h,能够实现单边制动转向及原地转向等功能,满足山坡、丘陵地带苜蓿收获的需求。     

Temporal changes of soil physical quality under two residue management systems

Although crop residue management is known to affect near‐surface soil physical quality, little is known about the temporal variability of these indicators over short time intervals. This study evaluates the temporal changes of nine indicators of soil physical quality. These are organic carbon content, structural stability index, bulk density, macroporosity, air capacity, relative field capacity, plant available water capacity, Dexter's S‐index and saturated hydraulic conductivity. A second set of soil physical indicators, based on the distribution of soil pore volume, was also evaluated. The indicators were determined in three different times during the growing cycle of winter durum wheat cultivated within a long‐term field research carrying out in Southern Italy and comparing two types of crop residue management, that is, burning (B) and soil incorporation (I). Only the bulk density changed over time for both treatments, although the air capacity also changed for the incorporation of wheat residues. Residual effects of the autumnal soil tillage and soil compaction were a common source of variability, irrespective of which treatment was used. Based on the existing guidelines for evaluating the physical quality of these agricultural soils, optimal or near‐optimal values were detected in about half of the cases under consideration. This suggests that both B and I create sufficiently good conditions for crop growth during the crop cycle. The comparison between observed and optimal soil pore distribution function was always poor. The pore volume distributions showed lower densities of small pores and relatively higher densities of large pores than the proposed optimal distribution. This study also suggests that the considered optimal or references curves probably cannot be applied successfully to a wide range of agricultural soils.     

抛物线形混凝土衬砌渠道标准化结构形式研究

通过实例比较了2种常用的抛物线形渠道水力最佳断面参数,得出二次抛物线渠道的水力性能优于半立方抛物线形渠道,并推导出了二次抛物线渠道实用经济断面的计算公式,提出了详细的计算步骤,给出了二次抛物线渠道实用经济断面水力计算表以供设计人员使用。同时,根据渠道工程实际应用情况和现行规范要求,提出了抛物线形混凝土衬砌渠道标准化结构形式,计算得出了常用抛物线形混凝土渠道结构尺寸、不同比降流量表,在实际工程应用中可根据设计渠道的具体情况进行选用。     

Developing a reliable strategy to infer the effective soil hydraulic properties from field evaporation experiments for agro-hydrological models

The Richards equation has been widely used for simulating soil water movement. However, the take-up of agro-hydrological models using the basic theory of soil water flow for optimizing irrigation, fertilizer and pesticide practices is still low. This is partly due to the difficulties in obtaining accurate values for soil hydraulic properties at a field scale. Here, we use an inverse technique to deduce the effective soil hydraulic properties, based on measuring the changes in the distribution of soil water with depth in a fallow field over a long period, subject to natural rainfall and evaporation using a robust micro Genetic Algorithm. A new optimized function was constructed from the soil water contents at different depths, and the soil water at field capacity. The deduced soil water retention curve was approximately parallel but higher than that derived from published pedo-tranfer functions for a given soil pressure head. The water contents calculated from the deduced soil hydraulic properties were in good agreement with the measured values. The reliability of the deduced soil hydraulic properties was tested in reproducing data measured from an independent experiment on the same soil cropped with leek. The calculation of root water uptake took account for both soil water potential and root density distribution. Results show that the predictions of soil water contents at various depths agree fairly well with the measurements, indicating that the inverse analysis is an effective and reliable approach to estimate soil hydraulic properties, and thus permits the simulation of soil water dynamics in both cropped and fallow soils in the field accurately.     

高阶椭圆锥齿轮泵的流量特性

针对齿轮泵的变量功能及非圆锥齿轮的应用,提出了一种新型相交轴变量齿轮泵——高阶椭圆锥齿轮泵.该齿轮泵是以高阶椭圆锥齿轮为工作转子的非圆锥齿轮泵.根据齿轮的空间啮合原理,给出了其工作转子高阶椭圆锥齿轮副的齿形生成方法.基于该种齿轮特殊的运动学特性,分析了高阶椭圆锥齿轮泵的传动特性,并对其工作结构进行了设计.依据球面微分理论,推导出了高阶椭圆锥齿轮泵的平均理论流量公式、瞬时流量公式以及流量脉动公式,同时分析了高阶椭圆锥齿轮的偏心率、阶数等参数对其流量特性的影响.在同等参数模型及工况条件下,将对高阶椭圆锥齿轮泵的平均理论流量、瞬时流量及其变量范围与圆柱齿轮泵和非圆柱齿轮泵的流量特性进行了对比分析,获得了该锥齿轮泵在同等条件下排量最大、变量范围最大的特点.     

涌泉根灌灌水器螺纹流道水力特性研究

针对涌泉根灌灌水原理,提出了一种新型的螺纹式涌泉根灌灌水器,并运用Pro／E三维造型、CFD数值模拟、快速成形及试验验证等方法对该新型灌水器的水力性能进行了研究,得到了不同长度流道的压力流量关系曲线和内部压力、速度分布图。结果表明,该流道水力性能良好,流态指数约为0．5,处于紊流状态,消能形式以局部水头损失为主,试验验...