非对称入流工况下钟形进水流道数

结合南水北调某大型泵站钟形进水流道的设计,采用雷诺平均纳维—斯托克斯方程(RANS)和标准 湍流模型,运用SIMPLEC算法,模拟了钟形进水流道两种设计方案在对称进水工况和偏流进水工况下的三维流场。结果表明：原设计方案在偏流进水工况下流道中易产生旋涡,而加设隔板后流道中则无旋涡产生。用泵装置模型试验对计算结果进行了验证,试验结果表明,加设隔板方案的泵装置性能较原设计方案的泵装置性能有了较大的提高,装置最高效率提高可达15%。说明在进行大型泵站钟形进水流道的优化设计时,应充分考虑到偏流进水对流态的影响。     

A new apparatus for measuring the gas diffusion coefficient in soil using a large sample and controlling soil water suction

A new apparatus that determines the gas diffusion coefficient in soil after establishing steady state gas conditions was developed. The CO₂ concentration is kept constant above and below the soil sample to establish the steady state conditions. The sample column is 60 cm long with an inner diameter of 20 cm. The gas diffusion coefficients of sandy soil were measured at 10 cm intervals using this apparatus while controlling the soil water content. The ratios of gas diffusion coefficients in soil and air,D _s/D₀, with different soil water conditions were determined. A part of this paper was presented at the 110th Annual Meeting of the Japanese Forestry Society (1999).     

气吸式水稻播种机泥浆铺土装置的设计研究

研究了采用泥浆铺土方法实现秧盘连续铺浆的机理,设计了泥浆铺土装置。试验结果表明,采用泥浆铺土方法,能简化播种工序,改善作业环境,提高根系土坨硬度,为实现机械抛秧提供了一种实用的方法。     

滤纸法测非饱和黄土土水特征曲线试验及拟合研究

土—水特征曲线是非饱和土力学研究的重要曲线,其拟合参数对于分析非饱和土的各种性质具有重要意义。基于滤纸法试验,测定了庆阳非饱和黄土土—水特征。以Gardner模型为基础,采用计算机语言MATLAB中的Lsqcurvefit、Nlinfit、Fminunc函数对试验结果进行拟合,同时对基质吸力与土体微观平面孔隙率及体积含水率间关系进行综合研究,结果表明:Nlinfit函数拟合效果较好,参数相近,曲线整体形状符合土水特征曲线(SWCC)的特征,且Nlinfit函数拟合的SWCC误差小于10%,具有较好的精度和稳定性。     

气力滚筒式排种器种子吸附边界模型及验证

为了探索气力滚筒式播种机对不同规格小粒蔬菜种子吸附性能的影响,该文对种子在吸种孔外部气流场中处于临界运动时与吸种孔的位置关系进行了理论分析。通过分析吸种孔外部气流场的气体的流动状态以及种子在气流场中的绕流阻力与其到吸种孔距离的关系,并对种子在气流场中运动临界状态进行受力分析,从而推导出种子吸附边界的数学模型。分析吸附边界大小对种子吸附性能的影响,以菜心种子、芥兰种子、辣椒种子为试验对象,排种器真空度在1 k Pa~12 k Pa变化,吸种孔半径为0.25 mm,导种板为无振动和振幅为0.4 mm。试验结果与模型分析结果一致:种子吸附的前提条件是种子持续不断的进入吸附边界内,种子的吸附性能与种子边界的大小和种子形状和大小有关;对于小粒蔬菜种子,扁平种子的单粒率低于球形种子,球形种子的直径越小,越难获得高的单粒率。对于小粒扁平种子和直径较小的小粒球形种子,合理的供种方法和增大排种器真空度使吸种孔不空种,再清除吸种孔上的多余种子,是实现排种器精密播种的一种途径。研究结果为气力滚筒式播种机的精密播种研究提供参考。     

Peat Substrate Reuse in Lilium “Helvetia” Crop

The reuse of substrates for more than one growing season is an excellent alternative to reduce production costs and to improve the sustainability of the ornamental plant production system. The objectives of the present trial were to study the effects of substrate reuse on Lilium var. Helvetia plants cultivated in shipping crates in a polyethylene greenhouse, as well as possible changes in the physical and physical–chemical properties of the substrates employed. Peats used during two and three cultivation cycles and new unused peat were tested. The reused substrate reduces the particle fraction with higher diameter size, porosity, and organic matter and increases particle bulk and substrate carbon (C)?/?nitrogen (N) ratio, due to the substrate decomposition. However, it does not affect flowers, flower stems and leaves, and dry and fresh matter. The level of phosphorus (P) and magnesium (Mg) in leaf, as well as nitrate, potassium (K), and Mg in the substrate solution are similar among the three kinds of substrates studied. Nevertheless, the substrate used for three cultivation cycles leads to increases in organic N and K and decrease of calcium in leaves.     

气吸式排种器带式导种装置的设计与试验

针对免耕播种机双圆盘式开沟器投种点高,种子播入土壤中粒距变异系数大,合格指数低的缺陷,该文在对气吸式排种器成穴时间平衡分析的基础上,设计开发了一种与取种盘转速、播种机行走速度相关,且传动与投种机构一体的带式导种装置,并确定了该气吸式排种器带式导种装置的主要结构参数。在综合试验因素对株距合格率,重播率和漏播率影响不同的基础上,确定影响排种质量的主次顺序为投种点高度、取种盘转速和负压室压力,较优参数组合为投种点高度100mm,取种盘转速30r/min和负压室压力3.5kPa。此时粒距合格率为98.50%、漏播率为0.48%、重播率为1.02%。通过试验验证,试验值与理论值误差分别为0.11%、0.17%和0.08%,符合试验要求。该文为气吸式排种器的参数优化与排种质量进一步提升提供了理论依据。     

Matric Suction Effect on Shear Strength of Roadbed Unsaturated Soil

A study which focuses on the role of matric suction in the stress strength of roadbed unsaturated soil was presented. Two types of tests were described, namely, the suction controlled shear test and microstructure scanned test. For the former, four sub tests were conducted under different suction and net normal stress conditions. And two unsaturated soil samples that belong to the same type but with different water contents were scanned. In contrast with clay soil, the corresponding results show that the strength of silty sand soil does not always increase as matric suction increases or soil water content decreases; there exists a peak contributed by matric suction that acts on soil stress strength. The main reason for this kind of phenomenon is due to the typical microstructure of this type of soil and the various types of pore water retention. Additionally, the state of stress in which soil sample meets can also exerts important influence on soil strength.     

小麦吸浆虫的发生与防治

小麦吸浆虫是小麦生产上的一种毁灭性害虫。由于耕作制度、栽培方式、管理水平的原因,致使小麦吸浆虫的发生逐年加重,面积逐年增加。一般受害田块减产10%～30%,严重的达70%,甚至绝收。     

万吨级反渗透海水淡化高压泵的优化设计

结合反渗透海水淡化高压泵的能耗状况,合理选择了万吨级反渗透海水淡化高压泵的泵型,提出了一种轴向吸入节段式高压多级泵的新型结构型式.在已有高效水力模型的基础上,对影响效率的几个关键水力尺寸进行不同的优化组合,设计了6种叶轮模型和2种导叶模型,组合成6组水力模型.应用CFD方法对6组水力模型进行了性能预测,挑选出2组效率高（预测）的水力模型制作成2台单级模型泵进行试验研究.2组水力模型试验表明,泵的流量、扬程满足高压泵的要求,其中最优模型的效率达到了79.72%.