基于CFD-DEM耦合的揉丝机排料装置内物料运动模拟与试验

为解决传统物理方法难以对揉丝机排料装置内物料运动进行可视化研究的问题,基于CFD-DEM气固耦合法,采用RNG K-ε湍流模型及Euler-Lagrange耦合算法对揉丝机不同主轴转速下排料装置内物料运动过程、内流道气流速度分布、气流对物料的耦合力分布进行了数值模拟,并对风扇主轴转速3 000r/min时物料运动过程进行分区域研究。结果表明:在风扇主轴额定转速3 200r/min范围内,主轴转速2 000、2 500和3 000r/min在模拟结束时分别排出物料数量为6 191、6 669和7 161个;不同区域内物料平均速度形成梯度分布,由大到小依次为物料出口区域(10.00m/s)、风扇转动区域(6.00m/s)、物料入口区域(0.87m/s);风扇转动区域气流速度最大(峰值50.00m/s),对物料耦合力作用最强,物料入口区域则耦合力最小;物料在入口区域内数量最多并在模拟结束时发生少量堆积,在出口区域未见回流现象发生。对模拟结果进行了试验验证,结果表明利用CFD-DEM气固耦合法对揉丝机排料装置内物料运动进行可视化研究是可行的。     

贡嘎山暗针叶林生态系统土壤优先流研究初探

优先流是一种常见的土壤水分运动形式,近年来被应用到不同科学领域,但目前仍然没有国际认可的标准定义。以非饱和带土壤水分运动规律为基础,该文利用自制实验仪器,开展室内土柱实验,与野外实地示踪影像分析相结合对贡嘎山暗针叶林生态系统进行优先流研究。研究采用示踪标定及示踪影像等方法,结合作者前期雷诺数计算分析,判定出研究区域土壤水分流动有优先流现象发生,并初步判定优先流类型是管流。同时采用驻留力矩分析穿透曲线(BTC)的平均穿透时间以及蔓延扩散和拖尾程度,结果表明优先流的穿透曲线具有不对称性。     

Organic agriculture and the conventionalization hypothesis: A case study from West Germany

The recent growth in organic farming has given rise to the so-called “conventionalization hypothesis,” the idea that organic farming is becoming a slightly modified model of conventional agriculture. Using survey data collected from 973 organic farmers in three German regions during the spring of 2004, some implications of the conventionalization hypothesis are tested. Early and late adopters of organic farming are compared concerning farm structure, environmental concern, attitudes to organic farming, and membership in organic-movement organizations. The results indicate that organic farming in the study regions indeed exhibits signs of incipient conventionalization. On average, newer farms are more specialized and slightly larger than established ones and there is a growing proportion of farmers who do not share pro-environmental attitudes. Additionally, a number, albeit small, of very large, highly specialized farms have adopted organic agriculture in the last years. However, the vast majority of organic farmers, new and old ones included, still show a strong pro-environmental orientation. Henning Best holds a MA in Sociology, History, and Ethnology from the University of Cologne, Germany in 2002. He acquired a PhD in Economics and Social Sciences from the University of Cologne in 2006. From 2002 to 2004 he was research associate at the Research Institute for Sociology, University of Cologne. Since 2004 he is researcher and lecturer at the Institute for Applied Social Research, University of Cologne. His research interests include environmental sociology, social inequality, and quantitative methods of social research.     

Dynamics of large wood in an eastern U.S. mountain stream

Large wood (LW) is an important feature in many streams in northeastern North America, yet the dynamics (recruitment, movement, and export) of large wood remain largely undocumented for streams in this region. In this study we quantify the dynamics of LW in 400 m of a second-order, high gradient, boulder-dominated stream in the eastern Adirondack Mountains, NY. Characteristics and location of all LW (>1-m length, >10-cm diameter) in the 400-m study reach were initially recorded and pieces were individually tagged in November 2000. Subsequent surveys were conducted in late summer/fall of 2001, 2003, and 2004. Twenty-six% of the 112 pieces of LW initially tagged moved 5.0 m or more during the 4 years of this study. Mobile wood was, on average, shorter than non-mobile wood. Nearly all mobile wood was shorter than the 8.0-m bankfull width of the stream. From 2000 to 2004, 2.16 m³ (0.54 m³ 100 m⁻¹; 43 pieces) of LW entered the study reach and 0.7 m³ (0.18 m³ 100 m⁻¹; 13 pieces) left the stream. Retention of wood in debris dams was key to reducing potential export. For this stream, located within a second-growth mixed northern hardwood riparian forest that is approaching maturity, the net wood accumulation rate was estimated as ranging from 0.09 to 0.15 m³ 100 m⁻¹ year⁻¹. Our data support previous observations that LW length strongly influences its potential to move in high gradient streams, though debris dams can reduce LW movement rates and movement distances for wood of all sizes.     

小麦-蚕豆间作对土壤水势的影响

通过小麦-蚕豆间作盆栽试验,研究了小麦-蚕豆间作中小麦和蚕豆、间作与单作在土壤水势变化方面的差异。研究结果表明,在小麦-蚕豆间作中,除小麦苗期外,其它生育期小麦土壤水势下降速度都快于蚕豆,而且在小麦孕穗期下降速度最快,这证明土壤水分除小麦苗期外,其它生育期都由蚕豆向小麦迁移,而且迁移速度在小麦孕穗期最快。间作小麦和单作小麦相比,除小麦苗期前期,间作小麦与蚕豆对土壤水分的竞争较弱,其它生育期间作小麦与蚕豆对土壤水分的竞争都比较激烈。     

黄河河口地区微咸水灌溉的水土环境效应研究

以河口地区土壤水文均有差别的2个典型灌区作为研究对象,在2个灌区内各选取一个典型取样点,对灌区水样、土壤进行采样分析,研究灌区土壤水质特征。运用HYDRUS-1D 4.15软件,在实验数据的基础上,确定边界条件并率定参数,建立了2个灌区的一维饱和-非饱和水盐运移模型。对灌区设计了3种不同灌溉制度,灌溉后进行水盐运移模拟,分析了微咸水灌溉对当地水土环境的影响。结果表明咸淡轮灌的方式有利于灌区盐渍化改善。     

脱硫石膏施用下宁夏龟裂碱土水盐运移特征

通过室内土柱淋洗试验,开展了脱硫石膏施用下不同淋洗水量对宁夏龟裂碱土水盐运移影响的研究,结果表明：脱硫石膏施用下龟裂碱土随着入渗时间的增加,湿润锋深度和累积入渗水量呈先急剧增加再缓慢增加的趋势;0~20 cm土层土壤pH值、碱化度和全盐量均有较大幅度的降低;连续淋洗条件下,最大脱盐深度位于40~60 cm土层;0~40 cm土层,随入渗水量的增加土壤脱盐率缓慢增加,其中0~20 cm土层处理1到处理4土壤脱盐率分别为79.72％、89.88％、91.93％和92.22％;随淋洗水量的增加,0~20 cm土层主要盐分离子易于溶脱的顺序为Mg2＋>Cl－>SO2－4>Na＋> HCO3－, Mg2＋溶脱率最大,可达到100％,20~40 cm土层主要盐分离子易于溶脱的顺序为Na＋>Cl－>Mg2＋, Na＋溶脱率最大,可达到91.42％, HCO3－和SO2－4含量则先增加后降低,0~40 cm土层Na＋、 Cl－、 Mg2＋随淋洗水量的增加淋洗效果更为明显。     

基于离散元的排种器排种室内玉米种群运动规律

高寒干旱地区免耕地表播种作业时,排种器振动与种群运动状态对气吸式排种器的吸种性能有较大影响。为研究气吸式免耕播种机在免耕地表作业时排种器振动参数及振动对排种器内玉米种群运动的影响规律,该文采用BK加速度传感器和Pulse LAN-XI振动测试系统,对2BM-5型气吸式免耕播种机在免耕地表作业时排种器振动特性进行了测试,并应用Matlab软件对振动信号进行了分析。在此基础上基于离散元法模拟了在田间作业振动条件下玉米种群运动规律,并基于室内台架试验进行了验证。播种机田间作业振动信号分析结果表明:播种机前进速度为2、3、4、5、6、7 km/h时,排种器振动的位移功率谱密度较大值的频率为5、6、7 Hz,排种器振动的幅值由2.4到7.9 mm线性增加。由离散元方法仿真得到了种子室内玉米种群最大速度、种群平均速度与播种机作业速度的拟合曲线。台架验证结果表明:气吸式排种器排种性能较好的作业速度为3~5 km/h,较好的振动幅值为6 mm;种群最大速度范围为0.120 3~0.224 3 m/s,种群平均速度范围为0.080 7~0.141 3 m/s,吸种区种群最大速度范围为0.127~0.26 m/s时,气吸式排种器吸种性能较好。该研究可为免耕播种机气吸式排种器吸种性能的提高提供参考。     

基于离散元法的旋耕过程土壤运动行为分析

土壤与耕作部件间的相互作用规律是设计和选用土壤耕作部件的基础。研究土壤和耕作部件间的相互作用规律就是要研究耕作部件对土壤产生的作用和它们之间的作用力,首先必须探讨耕作部件工作时土壤运动规律和施加于土壤的作用力。为此本文建立基于离散元方法的旋耕工作模型;对比分析实验与仿真的土壤位移:在土槽实验中采用示踪块方法测量土壤位移,仿真中通过追踪表层土壤颗粒的运动获得仿真位移;利用实验和仿真数据对土壤位移和运动机理进行分析。结果表明:土壤水平和侧向位移都随着转速增加呈现增加的趋势;土壤的水平运动位移总是大于同转速下的侧向位移。浅层土壤颗粒的运动位移最大,中层土壤次之,深层土壤最小。较深位置的土壤,距离旋转中心越近的土壤颗粒水平位移和侧向位移越大。在旋耕刀切土范围内的土壤,有向相反方向运动趋势的浅、中、深层颗粒比例分别为26.2%、72.1%、48.4%。在水平力作用下,大部分土壤颗粒随着旋耕刀切土有向后运动的行为;土壤在开始时刻的侧向受力和侧向运动方向,由颗粒的侧向位置是否偏离侧切刃轴线决定,位于侧切刃轴线左侧的颗粒,则其侧向力向左,反之亦然;土壤在垂直方向先随着刀具入土向下运动,然后滑出刀刃边界被抛起。本文建立的仿真模型得到的土壤水平位移和侧向位移与相应实验值的误差为24.9%和15.3%。本文运用离散元法进行旋耕过程中土壤宏观和细观运动行为的分析,有助于理解旋耕刀与土壤的相互作用机理,为旋耕机械的设计与优化提供理论依据。