The grain size composition, distribution characteristics and spatial variation of eolian sand soil on distinct positions across two longitudinal dunes and interdune areas were studied by means of conventional grain si...The grain size composition, distribution characteristics and spatial variation of eolian sand soil on distinct positions across two longitudinal dunes and interdune areas were studied by means of conventional grain size analysis and geostatistical methods. In the study, 184 samples of eolian sand soil from the 0-30cm layer were systemically collected and measured from two longitudinal dunes and interdunes in the southern Gurbantunggut Desert. The results show that the dominant grain sizes are fine and very fine sands, and the differences of grain size compositions between the distinct geomorphologic positions are significant. The contents of clay and silt are highest on the interdune areas and lowest on the crests, and higher on the leeward slopes than on the windward slopes. The contents of very fine and fine sands are highest on the windward slopes and lowest on the crests. The contents of medium, coarse and very coarse sands are lowest on the interdune lands, and highest on the crests, and are identical on the two slopes. The coarser sizes (phi(1)) and mean sizes (Mz) for eolian sand soil all have a varying tendency from fine to coarse sizes with interdune area -> leeward slope -> windward slope -> crest, and the sorting (sigma) are poorly to well sorted. The results of geostatistical analysis reveal that phi(1), Mz and a values are moderately to strongly spatially autocorrelated. The values of the spatially correlated ranges are phi(1) < sigma < Mz. The spatial variation for these grain size parameters is significant across the longitudinal dune landscape. From the crests towards the bottom of the slope, there is a varying gradient of zonal distribution, and the gradient values on the leeward slopes are larger than sites on the windward slopes.展开更多
为了解决RRT(Rapidly-exploring random tree)算法在机械臂三维路径规划中采样随机性强、搜索范围大、效率低和路径不平滑的问题,提出了一种基于空间引导点并结合目标偏置采样策略的改进RRT算法。通过在RRT树生成前产生空间引导点,并在...为了解决RRT(Rapidly-exploring random tree)算法在机械臂三维路径规划中采样随机性强、搜索范围大、效率低和路径不平滑的问题,提出了一种基于空间引导点并结合目标偏置采样策略的改进RRT算法。通过在RRT树生成前产生空间引导点,并在采样点选取时,采用目标偏置策略,降低算法搜索的随机性;在生成新节点时,采用自适应调节步长,加快算法在空旷区域搜索的效率,并降低错过障碍物附近更优点的选择;初次生成路径后,通过贪心策略去除路径中多余节点;最后利用Hermite插值对路径进行平滑处理,提升路径质量,并进行了仿真与现场试验。仿真试验结果表明,相比RRT算法,改进后的算法平均搜索时间减少70.83%,平均路径长度减少22.71%。利用6-DOF机械臂进行避障试验,结果表明,改进后的RRT算法相较于RRT算法,平均搜索时间减少79.95%,平均路径长度减少30.93%,路径规划成功率为96.77%。改进后的算法在三维空间中可以快速规划出无碰撞路径,该研究为多关节机械臂运动控制奠定了理论基础。展开更多
基金supported by the National Basic Research Program of China (2009CB825105)
文摘The grain size composition, distribution characteristics and spatial variation of eolian sand soil on distinct positions across two longitudinal dunes and interdune areas were studied by means of conventional grain size analysis and geostatistical methods. In the study, 184 samples of eolian sand soil from the 0-30cm layer were systemically collected and measured from two longitudinal dunes and interdunes in the southern Gurbantunggut Desert. The results show that the dominant grain sizes are fine and very fine sands, and the differences of grain size compositions between the distinct geomorphologic positions are significant. The contents of clay and silt are highest on the interdune areas and lowest on the crests, and higher on the leeward slopes than on the windward slopes. The contents of very fine and fine sands are highest on the windward slopes and lowest on the crests. The contents of medium, coarse and very coarse sands are lowest on the interdune lands, and highest on the crests, and are identical on the two slopes. The coarser sizes (phi(1)) and mean sizes (Mz) for eolian sand soil all have a varying tendency from fine to coarse sizes with interdune area -> leeward slope -> windward slope -> crest, and the sorting (sigma) are poorly to well sorted. The results of geostatistical analysis reveal that phi(1), Mz and a values are moderately to strongly spatially autocorrelated. The values of the spatially correlated ranges are phi(1) < sigma < Mz. The spatial variation for these grain size parameters is significant across the longitudinal dune landscape. From the crests towards the bottom of the slope, there is a varying gradient of zonal distribution, and the gradient values on the leeward slopes are larger than sites on the windward slopes.
文摘为了解决RRT(Rapidly-exploring random tree)算法在机械臂三维路径规划中采样随机性强、搜索范围大、效率低和路径不平滑的问题,提出了一种基于空间引导点并结合目标偏置采样策略的改进RRT算法。通过在RRT树生成前产生空间引导点,并在采样点选取时,采用目标偏置策略,降低算法搜索的随机性;在生成新节点时,采用自适应调节步长,加快算法在空旷区域搜索的效率,并降低错过障碍物附近更优点的选择;初次生成路径后,通过贪心策略去除路径中多余节点;最后利用Hermite插值对路径进行平滑处理,提升路径质量,并进行了仿真与现场试验。仿真试验结果表明,相比RRT算法,改进后的算法平均搜索时间减少70.83%,平均路径长度减少22.71%。利用6-DOF机械臂进行避障试验,结果表明,改进后的RRT算法相较于RRT算法,平均搜索时间减少79.95%,平均路径长度减少30.93%,路径规划成功率为96.77%。改进后的算法在三维空间中可以快速规划出无碰撞路径,该研究为多关节机械臂运动控制奠定了理论基础。
