排序:
共找到3条结果
  • 天然河道糙率计算及取值方法

    在洪水计算中,河道糙率是一个重要参数.通过对河道糙率影响因素分析,利用李营水文试验站的实测资料,阐述了河道糙率的计算方法.糙率确定时影响因素较多,不同的水深、植被、河床等因素,都会对糙率值产生影响.在实际计算中,大部分设计河段没有实测糙率资料,在实际应用中要借助相似河道的参数代替,对计算精度影响较大.收集了国内外不同情况下的河道糙率实验资料,可供河道糙率计算参考.
    张秉文 - 南水北调与水利科技
    文章来源: 万方数据
  • As the two most important indexes of bearing raceway,surface roughness and roundness have significant influence on bearing noise.Some researchers have carried out studies in this field,however,reason and extent of the influence of raceway surface geometric characteristics on bearing running noise are not perfectly clear up to now.In this paper,the raceway of 6309 type bearing's inner and outer ring is machined by floating abrasive polishing adopting soft abrasive pad.Surface roughness parameters,arithmetical mean deviation of the profile Ra,the point height of irregularities Rz,maximum height of the profile Rmax and roundness f of raceways,are measured before and after machining,and the change rules of the measured results are studied.The study results show that the floating abrasive polishing can reduce the surface geometric errors of bearing raceway evidently.The roundness error is reduced by 25%,Rmax value is reduced by 35.5%,Rz value is reduced by 22%and Ra value is reduced by 5%.By analyzing the change of the geometrical parameters and the shape difference of the raceway before and after machining,it is found that the floating abrasive polishing method can affect the roundness error mainly by modifying the local deviation of the raceway's surface profile.Bearings with different raceway surface geometrical parameter value are assembled and the running noise is tested.The test results show that Ra has a little,Rmax and Rz have a measurable,and the roundness error has a significant influence on the running noise.From the viewpoint of controlling bearings'running noise,raceway roundness error should be strictly controlled,and for the surface roughness parameters,Rmax and Rz should be mainly controlled.This paper proposes an effective method to obtain the low noise bearing by machining the raceway with floating abrasive polishing after super finishing.
     - 中国机械工程学报
    文章来源: 万方数据
  • 运用因次分析法比较中国能源通道

    近年来,中国能源运输通道问题日益显现,以马六甲海峡及南海等区域最为突出.为解决我国能源通道安全受到严重制约的困局,利用因次分析法,依据评价指标体系建立的各项基本原则,针对出现的不同情况分别对传统运输通道与新路线做简要对比分析.在保证国内石油安全充足供应,尽可能降低物流成本的前提下,提出较为有效合理的对策和建议,对我国能源安全运输具有现实意义.
    刘传铎,王海灵 - 物流技术
    文章来源: 万方数据
共1页 转到