基于拉格朗日的冗余驱动并联机构刚体动力学建模

针对4-UPS-RPU 4自由度冗余驱动并联机构的刚体动力学建模问题,基于拉格朗日方程建立冗余驱动并联机构动力学模型。首先,推导出4-UPS-RPU冗余驱动并联机构系统的动能表达式、势能表达式和作用于并联机构非保守力的等效广义力;然后,应用拉格朗日法建立4-UPS-RPU冗余驱动并联机构的动力学模型,为并联机构驱动力的求解以及整个机构的动力学分析奠定基础;最后结合算例,采用Matlab编程对动力学模型进行数值计算并绘制了机构驱动杆驱动力变化曲线,将上述分析结果与ADAMS虚拟仿真结果对比验证了所建动力学模型的正确性。研究不仅为4-UPS-RPU 4自由度冗余驱动并联机构动力学优化设计和控制等后续研究提供了理论依据,也为其他冗余驱动并联机构的动力学建模提供了可行的方法。     

Adopters,testers or pseudo-adopters? Dynamics of the use of improved tree fallows by farmers in western Kenya

Although there has been increasing research on the adoption of agroforestry technologies over the last decade, few such studies have assessed uptake over a long period and many are based on a single snapshot in time. Furthermore, most of these studies have mainly looked at non-adopters and adopters: only recently have social scientists considered testers. A further category of users neglected in adoption studies has been re-adopters of technologies. Studying this group provides an interesting and more nuanced understanding of adoption and re-adoption. Methodologically, most adoption studies use quantitative methods and fail to link their findings to wider socio-economic, political and institutional settings. This paper presents a study of the dynamics of improved tree fallow use by farmers in Siaya and Vihiga districts of western Kenya over a period of eight years. It uses both qualitative and quantitative data to critically discuss the motivations of adopters, testers/rejecters and re-adopters. The results show that the process of adoption is highly dynamic and variable with farmers planting improved fallows and discontinuing or re-adopting them due to a whole range of factors, of which soil fertility improvement is just one. These factors included incentives from projects, the tying of adoption to credit programmes, prestige, participation in seminars/tours and the availability of a seed market from projects promoting improved fallows. Farmers planting improved fallows for such reasons may be termed ‘pseudo-adopters’. There were significant differences in adoption between the two districts, with more farmers in Siaya planting improved fallows than in Vihiga. A majority of farmers in Vihiga (53%) who were given seed never planted improved fallows, even though they had been exposed to the technology. Some 40% of farmers in Siaya and 38% in Vihiga planted improved fallows but later rejected them. This has some important implications for research and development. For improved fallow technologies to be attractive to farmers, they must provide other tangible economic benefits besides soil fertility improvement. This presents a challenge to researchers who must better attune themselves to the needs and demands of farmers if they wish to see their research findings widely adopted.     

遗传算法在离心泵叶片优化设计中的应用

对遗传算法在流体机械优化设计中的应用现状作了较为全面的总结；提出了将遗传算法应用于离心泵叶片优化设计中，分析了遗传算法在离心泵优化设计中应用的可行性以及存在的问题；对离心泵优化设计的发展提出了一些新建议和尝试。     

悬架橡胶件对汽车平顺性影响的多体动力学分析

应用有限元分析了汽车减振器橡胶支撑件的弹性特性,在此基础上,应用SIM PACK软件建立了整车多体动力学模型,分析了橡胶支撑件的刚度、阻尼对汽车行驶平顺性的影响。分析结果表明：在车身共振区,橡胶件对地板加速度功率谱影响较小,但在4-13Hz中频区,即人体比较敏感的范围内,橡胶件可以使地板加速度功率谱峰值减小6.5%-25.4%,因此悬架橡胶件对汽车行驶平顺性有明显的改善。此外,还得出对于刚度较大的橡胶件应选取较小阻尼,对于较软的橡胶件,可以忽略阻尼影响的结论。     

秸秆覆盖对季节性冻融期土壤水分特征的影响

以北方高寒区典型城市哈尔滨市为研究区域,通过冬季大田试验(试验周期2013-11-01—2014-04-30),设置自然无覆盖、覆盖秸秆厚度5、10、15 cm 4个处理,分别测定不同处理下20、40、60、100、140、180 cm深度土壤液态含水率以及气象数据,分析季节性冻融期秸秆覆盖对土壤水分变化特征的影响。研究结果表明:秸秆覆盖使0~60cm土层内液态含水率增加或减小的时间拐点发生延迟,随着秸秆覆盖厚度的增加其延迟效果越明显,但土壤冻结期的延迟效果比冻土融化期明显;秸秆覆盖阻碍了冻土融化初期融雪水入渗,使自然无覆盖处理液态含水率在20、40、60 cm土壤深度出现短暂的峰值,而在冻土融化末期秸秆覆盖抑制了土壤水蒸发,使各秸秆覆盖处理液态含水率在20、40、60 cm土壤深度又高于自然无覆盖。秸秆覆盖可有效平抑冻融期0~60 cm土层土壤液态含水率的变化幅度,且随着土壤深度的增加其平抑效果具有减弱趋势;积雪融水和秸秆覆盖的双重作用能够有效增加土壤墒情,但其增墒能力随着土壤深度的增加而降低,不同秸秆覆盖处理对0~60 cm土层的平均增墒能力由大到小排序依次为:15、10、5 cm。     

复配剂中霜脲氰在马铃薯和土壤中残留动态研究

采用田间试验方法，研究了霜脲氰在马铃薯及土壤中的残留动态，应用液相色谱法测定了霜脲氰在马铃薯和土壤中的残留量。结果表明，霜脲氰在马铃薯和土壤中消解较快，半衰期分别为2．26d和5．75d，施药3240g ai·hm^-23次时，末次施药距收获间隔28d，霜脲氰的残留量在马铃薯中低于0．0098mg·kg^-1，在土壤中为ND-0．0100mg·kg^-1。该药属易分解农药（％〈30d），按推荐使用剂量使用是安全的。     

高黎贡山百花岭瓢虫群落结构及多样性研究Ⅱ——物种多样性的季节变化趋势

[目的]初步探明季节变化对高黎贡山百花岭瓢虫群落多样性的影响。[方法]2008年4月至2009年2月对高黎贡山百花岭瓢虫群落物种多样性的季节变化规律进行了研究。[结果]2008年4～6月瓢虫物种多样性逐渐上升,6、9月达到高峰,10月以后逐渐下降。气温和降雨量差异较小的月份瓢虫群落相似性较高。[结论]为进一步研究瓢虫多样性提供了理论依据。     

深井离心泵的水力设计和二次回归正交试验

根据研发新型井泵节能节材的要求,将水力设计与计算流体动力学技术和二次回归正交试验方法相结合,进行提高井泵效率的试验研究.试验选择深井离心泵的叶轮出口安放角和出口宽度两个几何因素,按二次回归正交试验方案,设计了10副叶轮.通过计算流体动力学技术对包含叶轮、导叶在内的两级新型深井离心泵的全流场进行了设计工况下的三维流场数值模拟,得到了10组设计方案额定点的效率值.通过二次回归正交试验法研究了叶轮出口安放角、出口宽度对效率的影响规律,根据计算结果对新型深井离心泵效率提出了二次回归约束方程.结果表明,采用叶轮极大直径设计法对提高新型深井离心泵的水力效率具有一定的参考价值.     

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.     

Legume–barley intercropping stimulates soil N supply and crop yield in the succeeding durum wheat in a rotation under rainfed conditions

Legume–cereal intercropping is increasingly being appreciated in dryland areas, where severe climatic conditions and intensive agricultural practices, generally dominated by continuous cereal cultivation, determine depletion of soil nutrient resources and decline of soil fertility. This research aimed to assess whether and to what extent a newly introduced legume-based intercropping system is able to ameliorate the biological fertility status of an arable soil in a way that is still noticeable during the succeeding durum wheat cropping season in terms of changes in bacterial community structure, soil C and N pools, and crop yield. A field experiment was carried out under rainfed conditions in Southern Italy on a sandy clay loam soil cultivated with durum wheat following in the rotation a recently established grain legume (pea, faba bean)–barley intercropping. Soil chemical, biochemical and eco-physiological variables together with compositional shifts in the bacterial community structure by LH-PCR fingerprinting were determined at four sampling times during the durum wheat cropping season. Soil fertility was estimated by using a revised version of the biological fertility index. Results showed that even though the microbial biomass was significantly altered, the preceding legume intercrops stimulated C-related functional variables thus leading to an increased release of mineral N, which was larger in crop treatments succeeding pea-based than faba bean-based intercropping. The increased N made available in soil enabled the succeeding durum wheat to achieve an adequate grain yield with a reduced N-fertilizer use. Soil type and environmental conditions rather than crop treatments were major determinants of bacterial community structure. The biological fertility status was not varied, suggesting that in intensively managed rainfed areas long-term crop rotations with intercropped legumes are needed to consistently ameliorate it.