RUSLE侵蚀模型及其应用(综述)

在对RUSLE和USLE进行分析和比较的基础上,探讨了RUSLE对USLE的改进内容和形式:RUSLE模型所用的数据量比USLE大得多,并纠正了USLE分析中的错误,填补了原始数据的空白,且增加了其灵活性,使能模拟不同的系统和替代方法和侵蚀量,对RUSLE模型的应用前景作了展望。     

Determination of nuclear magnetic resonance T2 cutoff in remoulded loess by the freezing point

Proton nuclear magnetic resonance (NMR) is widely applied to characterize the microscopic properties of hydrogen-containing porous media. The transverse relaxation time cutoff (T_2c) value is the crucial parameter for the quantitative analysis of NMR data. Currently, there is no universal method for the determination of the T_2c in clayey soils. This study aimed to develop a laboratory method for determining the T_2c of remoulded loess by the freezing point of loosely bound water. Malan loess, a kind of typical clayey silt, was used as test material. Based on the soil freezing characteristic, NMR measurements were performed on remoulded loess with different macro-parameter controls during the cooling process to obtain the T₂ spectrum at each target temperature. By analysing the variation of unfrozen water content with temperature reduction, the freezing point of loosely bound water and the T_2c value within the freezing-point range was determined. The freezing point of loosely bound water in remoulded loess is about −3 to −5°C and that of firmly bound water is less than −5°C. Accordingly, the T_2c value of remoulded loess is determined to be 1.5–1.8 ms. The assessment of heating and cooling process and different methods for determining the T_2c shows that the laboratory method by the freezing point is effective and reliable, and the T_2c determined by statistical methods is worthy of further study and improvement. The saturated permeability of remoulded loess is evaluated according to the determined T_2c, and two NMR-based permeability equations can well reflect pore water distribution in remoulded loess, but to a certain extent, both equations ignore soil microstructure, pore connectivity and chemical effects of pore solution. The laboratory method by the freezing point and the determined T_2c value of remoulded loess fill the gap of NMR measurement in loess analysis and are of great significance for low-plastic clays and clay types.     

汾河源头地区土壤侵蚀时空变化及其空间自相关分析

[目的]汾河源头地区是山西省重要的水源涵养地和供水区,土壤流失严重。研究该区域土壤侵蚀时空变化的目的在于为该流域的水土保持工作提出科学依据。[方法]采用2004和2009年9月的SPOT影像作为数据源,将GIS和USLE结合对汾河源头地区土壤侵蚀的时空变化进行研究,并借助GeoDa软件分析了研究区2009年土壤侵蚀的空间自相关性。[结果](1)从时间变化来看,2009年汾河源头地区土壤侵蚀模数较2004年有所增加,中度以上侵蚀的面积占总侵蚀面积的比例也相应增大,且以极强度侵蚀和剧烈侵蚀增加为主;(2)从空间上看,土壤侵蚀程度高的区域分布在流域的东南部,土壤侵蚀程度低的区域分布在流域的西北部;(3)降雨和植被覆盖是影响汾河源头地区土壤侵蚀的2个主要因子;(4)除了微度侵蚀和剧烈侵蚀外,其他侵蚀强度类型向更高程度的侵蚀强度类型转移的面积都远大于向低程度的侵蚀强度类型转移的面积;(5)空间自相关分析表明,研究区土壤侵蚀存在一定的正相关和空间集聚,主要表现为高值与高值集聚,低值与低值集聚。[结论]研究区内土壤侵蚀现象不断加剧,应加强土壤侵蚀治理力度。     

滑移型三叉式联轴器运动学建模

为了解滑移型三叉式联轴器的运动学特性,建立了其运动学模型:应用坐标变换技术,建立输入输出轴转角之间的关系及滑杆对于输入轴和三叉的相对位移表达式;运用输入输出轴两轴线的向量叉积求出了联轴器夹角方程式.结果表明:输出角误差、输出轴角速度误差、滑杆相对于输入轴和三叉的相对位移及联轴器夹角都具有周期性并相似于正弦曲线;输出角误差、输出轴角速度误差和联轴器夹角都3倍于输入轴频率,而滑杆对输入轴和三叉的相对位移则分别等于和2倍于输入轴频率.数值结果与相关文献一致性较好证明了所建模型的有效性.     

旋耕—碎茬通用刀片结构参数优化试

以L型碎茬刀及宽型旋耕刀为基础,设计了9种旋耕-碎茬通用刀片.通过土槽单刀功率消耗(扭矩)试验确定了通用刀片的结构参数为:弯折角67°、弯曲半径20 mm、正切刃滑切角12°、单刀作业幅宽60 mm.并分别进行了通用刀片与国标旋耕刀的旋耕对比试验及通用刀片与批量生产的碎茬刀切断对比试验.试验结果表明,通用刀片单位幅宽功率消耗小于国标旋耕刀,但大于常用碎茬刀;单刀幅宽相同条件下,通用刀片功率消耗低于旋耕刀及碎茬刀,表明通用刀片结构参数选择合理可行.     

驱动轴三阶激励下的某纯电动车低频抖动研究

针对某纯电动全油门加速行驶过程地板产生的低频抖动问题,经主观评价及试验诊断分析后,排查出电机转速在3000~4200 r/min,地板出现明显0.33阶次振动。通过传递路径分析阶次激励源产生的原因,并进行路试试验、理论分析、动力总成及传动系统试验模态等分析方法,排查出整车急加速过程中地板低频抖动激励源为驱动轴内三轴销万向节产生的附加弯矩激励源与动力总成Y向平动模态耦合,因而产生共振。结合开发车型设计情况,提出通过降低悬架高度来降低万向节附加弯矩,然后对调整的方案进行试验验证。试验后,地板0.33阶次抖动由0.065 g降为0.025 g,提高了乘坐舒适性。