Identification of low productivity sites for European larch (Larix decidua Miller) in Maine,USA

As silvicultural capital becomes limited, allocation of funds to high quality sites becomes critical and sites with low productivity potential should be avoided. Data collected from 31 plots located in 12 plantations established between 1930 and 1982 throughout central Maine were used to develop a soil-based rule to identify sites having a low productivity potential for European larch in Maine, thereby removing them from consideration for plantation establishment. Stepwise regression and discriminant analyses identified several variables that were associated with site index at an index age of 20 years breast height (SI₂₀): solum thickness, B horizon clay content, and B horizon exchangeable K. Using these variables, a classification rule was developed to classify sites into 2 categories (poor, average SI₂₀=14.7 m; and good, average SI₂₀=17.7 m). Cross-validation demonstrated that the classification functions correctly identified 88% of the poor sites and 81% of the good sites.     

尼尔基水利枢纽工程隧道的防排水技术分析

通过对尼尔基灌溉输水洞隧道防排水设计原则、洞门段防排水、初期支护、结构自防水、施工缝的防水等方面的设计与探讨,详细介绍了隧道工程防排水技术。     

浅谈循环流化床锅炉在运行中的若干问题及其防止

本文简单介绍了循环流化床锅炉在运行中极易出现的飞灰含碳量高、流化床结渣、冷渣管堵塞等问题,进行原因分析以及采取的相应防止措施。     

Subsurface discharge and suspended sediment yield interactions in a valley head of a small forested watershed

Sediment hield caused by hydraulic agents is believed to be one of the most important geomorphic processes in headwaters. Observations of shallow groundwater levels and suspended sediment yield were used to develop relationships between subsurface discharge and sediment movement in a valley head of a small forested watershed in Hokkaido, northern Japan. Drainage capacity of the soil was closely correlated with subsurface soil movement in the valley head. An increase in subsurface discharge associated with an increase in the drainage capacity of the soil depended heavily on the discharge of fine-grained particles originating from the soil. Clogging created by the fine-grained particles in the soil caused a decrease in subsurface discharge associated with the decline in the drainage capacity. In addition, neither the drainage capacity of the soil nor subsurface discharge changed because of the sediment unavailability within the subsurface flow system. Accordingly, as shown by the changes in the drainage capacity of the sedimentary soil, subsurface discharge and suspended sediment yield from the valley head showed strong interactions.     

谈低温热水地板辐射采暖

分析低温热水地板辐射采暖技术的优越性,叙述了在管材选用以及设计和施工中应当注意的 一些问题。     

中国长江三峡地区花岗岩坡面管流运动特性

人们早就认识到土体内的水分运动 ,在很多时候并不都遵从达西定律所描述的呈层流流态 ,只有当雷诺数Re≤ 10时 ,土壤水分运动才遵从达西定律 .该文通过观察位于中国长江三峡地区湖北省秭归县花岗岩坡面下部开挖的一长度为 2 9m、深度为 2 13 2 6 0m的土壤剖面 ,发现土管主要分布在B层 (花岗岩风化程度较高的层次 )和C层 (花岗岩风化程度较低的层次 )的过渡带附近 .在坡面下部坡脚部位垂直于坡长方向上 ,每米宽度大约分布有土管 5 7个 .通过连续观测实验坡面的土管在多场降雨过程中的管流现象 ,发现管流流速与沿程水力坡降呈现非线性关系 ,而呈一定的抛物线关系 .结合土壤、地质和土地利用状况等调查结果 ,经对多场降雨及管流观测数据进行整理分析 ,建立了研究地点的管流模型 .由管流模型计算的管流流速VP、流量QP 和土管半径r,与 4个管流的实测值具有较好的相似性 .尤其是依据模型模拟的土管长度X ,反映出不同土管由于所处剖面位置的差异 ,其长度差别较大 ,所模拟的 4条土管长度分别为研究集水区最长距离的 98 1%、2 7 6 %、11 0 %和 3 0 % .管流模型建立过程及模拟结果均反映出管流是土壤水分运动的一种特殊形式 ,它遵从Darcy Weisbach定律所描述的土壤水分运动 .其水分通量远大于一般意义上的土壤     

过路管道顶管施工方法

本文结合具体工程 ,详细阐述了过路管道顶管施工方法及质量保证措施。在特定情况下使用该方法具有较好的适用性。     

工厂化对虾养殖池管式射流集污水力特性

工厂化养殖池内水体的流场分布特性直接决定了其对残饵、粪便等的排污性能。本实验研究了管式射流驱动模式下,射流角度与射流流速对养殖池内水体流场与污物聚集特性的影响。养殖池流场特性采用点式流速仪进行布点测量,利用MATLAB软件对流场特性进行分析。采用相机采集的养殖池集污效果图像,并利用Photoshop软件与自行开发的不规则图形面积分析软件对图像进行分析。研究表明,流速从池心向外呈"V"型变化,在射流角度固定的情况下,射流速度越大,池心低流速区域越小,污物向池心的聚集效果越好;在流速固定的情况下,存在一个最佳的射流角度,本实验在24 cm/s流速条件下,射流角度为40°时,池内污物聚集效果最优。结论认为在保证养殖对象生长的前提下,可尽量提高射流流速;在24 cm/s流速条件下,最佳射流角度在40°左右。本研究成果可为工厂化养鱼池、养虾池等管式射流水力驱动系统的优化设计提供参考依据。     

改善多层住宅供暖设计的几项措施

提出了将水平干管敷设于屋面以解决上供下回系统在建筑层高较低时 ,水平干管影响室内美观及排气阀浮球不易检修等矛盾的几种设计方案 ;介绍了几项改善管网运行效果的措施。     

轴流泵出水管内部流动水力特性研究

用五孔探针测定轴流泵出水管内部三维流场,揭示其流动规律,分析流场形成机理,利用流场数值模拟方法计算出水管水力损失.结果表明,后导叶出流环量较大,由于出流环量和出水弯管二次流的共同作用,出水管内为复杂的螺旋流,断面轴向流速和周向流速分布不均匀、不对称,与常规轴向均匀流和对称流的假定不符.过大的环量增大了出水管内水力损失,减小环量可减小水力损失,提高泵装置效率4%～8%.