压力室测定根系导水率方法探讨

用压力室连续测定了玉米根系升压和降压过程的导水率。结果表明 ,降压过程测得的根系导水率显著大于用升压过程的 ,并且前者的相关系数大于后者。这种差异是由于这两个过程中质外体途径细胞壁空间充水量不同造成的。开始升压时 ,由于细胞壁空间含水量低 ,质外体途径阻力大 ,导致非结构阻力 ;随着压力的升高 ,细胞壁空间含水量增大 ,质外体途径导度增大 ,减小甚至可以消除非结构阻力。降压法可以使根系快速复水 ,消除传统方法因长时间复水所致根结构的改变。建议用降压法测定根系导水率

根输水机理研究进展

概述了从根的结构出发开展根运输水分机理的研究进展 ,包括输水阻力的分布、水孔蛋白和根的复合运输模型等 ,并就其可能的生理意义加以评述。

土石混合介质饱和导水率的研究

采用恒定水头法对土石混合介质的饱和导水率进行测定,分析不同碎石含量及碎石直径对饱和导水率的影响,同时利用实测值对Peck-W atson及Bouw er-R ice两个传统估算方程的估测精度进行比较。结果表明:(1)饱和导水率随碎石含量先增大后减小,且两者呈二项式关系;(2)饱和导水率随碎石直径增大而减小,两者呈幂函数关系;(3)碎石直径介于1.0~5.0 cm时,Bouw er-R ice和Peck-W atson方程对饱和导水率的估算结果均大于实测值。

Modeling of Hillslope Runoff and Soil Erosion at Rainfall Events Using Cellular Automata Approach

National Science Fund for Distinguished Young Scholars of China [40225004]; National Natural Science Foundation of China [40471048]

Impacts of socio-economic factors on sediment yield in the Upper Yangtze River

In recent years, the role of human activities in changing sediment yield has become more apparent for the construction of hydraulic engineering and water conservation projections in the Upper Yangtze River, but it has not been evaluated at the macro scale. Taking Sichuan Province and Chongqing City as an example, this paper studies the relationship between socio-economic factors and sediment yield in the Upper Yangtze River based on section data in 1989 and 2007. The results show that sediment yield is significantly correlated with population density and cultivated area, in which the former appears to be more closely related to sediment yield. Moreover, in the relation of sediment yield vs. population density, a critical value of population density exists, below which the sediment yield increases with the increase of population density and over which the sediment yield increases with the decrease of population density. The phenomenon essentially reflects the influence of natural factors, such as topography, precipitation and soil property, and some human activities on sediment yield. The region with a higher population density than critical value is located in the east of the study area and is characterized by plains, hills and low mountains, whereas the opposite is located in the west and characterized by middle and high mountains. In the eastern region, more people live on the lands with a low slope where regional soil erosion is slight; therefore, sediment yield is negatively related with population density. In contrast, in the western region, the population tends to aggregate in the areas with abundant soil and water resources which usually lead to a higher intensity of natural erosion, and in turn, high-intensity agricultural practices in these areas may further strengthen local soil erosion. It is also found that population tends to move from the areas with bad environment and high sediment yield to the areas with more comfortable environment and less sediment yield. The natural factors have greater influence on sediment yield of western region than that of eastern region. Generally, the natural factors play a dominant role on sediment yield in the Upper Yangtze River.

运动解耦机理分析与解耦关节设计

分析了运动解耦机理,提出了只有结构解耦才能方便地做到运动解耦,给出了结构解耦的条件:所有回转轴线交于一点,前面的转动使得有关回转轴线的位姿发生变化,后面的转动按照已经发生变化的回转轴线转动,即保证杆的长度不发生变化和杆的回转中心不发生平移。在此基础上,设计了一种三自由度运动解耦液压伺服关节。

液压绞车主动升沉补偿控制研究

对水下机器人铠缆收放绞车进行主动升沉补偿控制,可以提高水下机器人作业和收放的安全性能。该文建立了液压绞车的主动升沉补偿控制模型,通过测量母船升沉运动进行主动升沉补偿控制,并采用了前馈控制器以提高液压绞车的响应速度。试验表明,液压绞车主动升沉补偿前馈控制可以得到较高的水下机器人升沉补偿效率。

有缆水下机器人主动升沉补偿控制研究

针对母船的升沉运动影响有缆水下机器人的释放与回收的工程实际需求,提出了利用液压绞车降低中继器的升沉速度来实现水下机器人主动升沉补偿控制的方法,来提高水下机器人释放与回收的安全性能。建立液压绞车的数学模型并设计主动升沉补偿前馈控制器。水下机器人主动升沉补偿实验表明液压系统的非线性降低了液压绞车主动升沉补偿前馈控制的升沉补偿效率。针对液压绞车的非线性特性,设计了液压绞车主动升沉补偿预测控制算法,仿真实验表明基于液压系统参数辨识的液压绞车主动升沉补偿预测控制可以得到较高的升沉补偿效率。

水下机器人主动升沉补偿系统研究

介绍一种基于水下机器人常规液压收放绞车的主动升沉补偿系统,利用加速度传感器获得母船的升沉运动信号,控制绞车的运转来降低母船的升沉运动对水下机器人的影响。通过理论计算建立主动升沉补偿系统的数学模型,仿真分析绞车运动对水下机器人升沉运动的补偿效果,并利用主动升沉补偿系统实验台验证基于常规液压收放绞车的主动升沉补偿方案的可行性。

潜水器恒张力收放绞车系统的建模与仿真

在潜水器收放过程中,要求收放绞车具有恒张力控制功能,减小由于波浪起伏对潜水器的冲击。本文根据液压系统的流量连续性方程,建立恒张力收放绞车泵控液压马达系统的数学模型,并对该系统进行了仿真分析,仿真结果表明:该系统能够满足实际的作业工况,且具有良好的动态和稳态工作性能。仿真结果为收放系统的设计提供了依据。

用于AUV收放装置的变幅机构研究

这里主要介绍了变幅机构的理论分析及AUV载体的收放方法,并简要介绍了收放机构的组成情况。

液压系统在水下机器人中的应用

结合典型的缆控水下机器人 ,介绍了缆控水下机器人液压系统的发展状况、特点和已取得的一些研究成果 ,并指出了发展大功率液压推进系统的重要意义。

液压系统在水下机器人的应用

本文结合在中型、大型水下机器人液压系统的设计、安装、调试的经验和体会,阐述液压系统在水下机器人应用的技术特点和技术措施,为水下液压系统设计提供借鉴.

锻压机导套对立柱作用反力的分析研究

讨论了锻压机工作时偏心载荷对机架下横梁和立柱应力变化的影响程度，验证了下横梁的断裂原因；详细地讨论了导套筒对立柱作用反力的影响，指出了传统液压机设计方法中假设条件的不足，为该类机械的结构设计和改进提出了新的见解。