红松林冠对降水的截留特征

通过野外测定与统计分析,系统研究了红松(Pinus koraiensis)林冠对降水的截留特征。在观测期间(2003年5-9月),红松林分林冠截留量为103.48mm,占同期降水量的26.19%;降水按以下比例被再次分配:穿透降水68.16%,林冠截留26.19%,树干径流5.65%。利用Horton改进模型进行模拟分析,结果表明:红松林分表征林冠吸附容量的参数Ic*m=2.387mm,大于该地区针叶树种樟子松和落叶松的吸附容量;表征区域降雨蒸发能力的参数α=13.9%。2个参数较好的解释了红松林冠截留吸附、湿润与蒸发机理;红松林冠截留率随降水的变化曲线可分为快变期(截留率>30%,降水量<15mm)、渐变期(截留率30%~18.67%,降水15~50mm)和稳定期(截留率<18.67%,降水>50mm)3个阶段,红松林冠稳定截留率为18.67%。红松林冠截留构成中吸附截留量较大。     

景谷县森林蓄积量遥感估测及其动态变化分析

以云南省景谷县为研究区,基于Landsat5和Landsat8遥感数据,利用2012年和2017年两期全国森林资源连续清查实地调查数据,建立多元逐步回归和随机森林模型对景谷县森林蓄积量进行遥感估测对比研究.结果显示:综合建模精度来看,随机森林法在相同样地数量条件下具有更好的估测效果;从估测结果与林地保护利用规划和林地变...     

大网目底拖网在稳定流场中的数值模拟

通过有限单元法构建大网目底拖网渔具的数学模型,以计算在定常流条件下底拖网渔具的受力情况、网口扩张和渔具的形态变化.为了提高计算效率,提出了适用于拖网的网目群化方法.群化后的拖网模型为单元数6513的model-1模型和单元数1787的model-2模型两种规格,分别进行数值计算,并与水槽物理模型试验结果进行比较.结果表...     

The role of geomorphology in substratum patch selection by freshwater mussels in the Hawkesbury–Nepean River (New South Wales) Australia

• 1. Microhabitat preferences of freshwater mussels and associated substrate characteristics were investigated across a range of geomorphic reaches in the Hawkesbury–Nepean River, Australia.
• 2. The structure of substratum patches available was strongly influenced by geomorphic reach type. In each reach type, mussel distribution was most frequently correlated with coarse sand and a roughness element characteristic for that reach. Roughness elements such as boulders and cobbles create a flow refuge and were linked with mussel size.
• 3. Small mussels tended to be associated with boulder‐stabilized habitats and medium sized mussels with cobble habitats. Large mussels rarely co‐occurred with any particular roughness element. Individual species were strongly linked to geomorphic reach type. This association may be due to species' differences in ability to colonize available microhabitat types.
• 4. The highly tolerant Velesunio ambiguus dominated shale reaches, characterized by fine sediments and human impacts. In contrast, Hyridella depressa dominated in gorges, utilizing small flow refuges among boulders, while H. australis were present in low densities across a range of substrate conditions.
• 5. The persistence of multispecies assemblages in mussel beds throughout the Hawkesbury–Nepean River implies similar niche utilization among species. Partitioning of habitats across species on the basis of size suggests some degree of habitat selection, or differential survival. At the local scale, microhabitat characteristics influenced the size distribution and densities of mussel assemblages. Continuing declines in mussel densities are likely to result from ongoing channel modification and increased siltation resulting from changes to riparian vegetation.

Copyright © 2008 John Wiley & Sons, Ltd.     

Estimation of irrigation return flow from paddy fields considering the soil moisture

The objective of this study was to estimate irrigation return flow in irrigated paddy fields considering the soil moisture. The proposed model was applied to examine its feasibility with regard to the growing period of rice. Simulation results showed a good agreement between the observed and simulated values: root mean square error (RMSE) of 6.05-7.27 mm day⁻¹, coefficient of determination (R²) of 0.72-0.73, and coefficient of efficiency (E) of 0.54-0.55. The estimated average annual irrigation return flow during the period from 1998 to 2001 was 306.2 mm, which was approximately 25.7% of the annual irrigation amounts. Of this annual irrigation return flow, 14.1% was attributable to quick and 11.6% to delayed return flow. These results indicate that considerable amounts of irrigation water in the paddy fields were returned to streams and canals by surface runoff and groundwater discharge. The modeling assessment method proposed in this study can be used to manage agriculture water and estimate irrigation return flow under different hydrological and water management conditions.     

滑阀节流槽阀口的流量控制特性

提出以节流槽内节流面的串并联效应确定二节矩形节流槽阀口面积的原则,推导出阀口面积的计算公式并编制了阀口面积的计算程序;在此基础上对二节矩形节流槽的流量特性进行了试验,试验表明二节矩形节流槽阀口的流量系数是单节矩形槽阀口流量系数的组合,流量系数在阀口开度较小或接近全开时流量系数快速增大,在阀口开度中间区段流量系数较小,在二节节流槽的交界处流量系数增大,流出节流槽方向的流量系数比流入方向约大0.1;提出了反映节流槽阀口流量控制特性的参数阀口流量面积Aq,阀口流量面积为阀口面积和流量系数的耦合函数,与阀口面积及流量系数传统概念相比,阀口流量面积更加合理地表征了阀口几何面积和阀口形状对流量的控制作用.     

液力偶合器部分充液流场数值模拟与特性计

利用CFD平台的滑动网格法与混合模型模拟液力偶合器流场的瞬态流动,得到偶合器内部速度与压力分布.总结了不同充液率下流场结构的变化及两相分布情况.基于速度、压力数值解计算了液力偶合器叶轮转矩,并计算出不同充液率下液力偶合器的原始特性.将性能预测结果与实验进行了对比分析,结果表明,数值模拟计算结果与实验结果吻合较好,基本反映了流道内部流动的基本特征.     

双流道泵内非定常固液两相流的数值分析

采用Mixture多相流模型、标准的k-ε湍流模型与SIMPLEC算法,应用FLUENT软件对双流道泵内固液两相湍流进行了非定常数值模拟.研究结果表明:不同时刻,泵流道内的压力分布明显不同,呈现周期性变化规律;在叶轮流道内,固相体积浓度分布极不均匀,颗粒主要集中于叶轮出口处的工作面和后盖板上,而在蜗壳流道内,固相颗粒多集中于离叶轮半径较大的蜗壳壁面上.     

添加剂湍流减阻流动的传热特性数值计算

采用雷诺应力模型和Cross粘度方程,对二维轴对称圆管内湍流流动的聚丙烯酰胺稀溶液（PAM）的流场和温度场进行了数值模拟.在数值计算结果的基础上,系统研究了流速对减阻流体的减阻性能和传热特性的影响.结果表明,减阻流体的减阻率和传热降低率随流速的增大逐渐增大到渐进值,而且传热降低率恒大于减阻率.减阻流体柯尔本（Colburn）因子与摩擦系数的对比结果表明柯尔本比拟,特别是在较低流动雷诺数下有较大偏差.     

PASSAT领驭2.0自动变速箱偶尔出现紧急运行状况检修分析

结合PASSAT领驭2.0轿车偶尔出现自动变速箱Ⅲ挡运行的紧急运行状况故障,分析了故障码、有关传感器电路,以及故障产生的原因,据此找出了故障点,并排除了故障。