End cracking during one-sided submerged-arc welding

Abstract

The mechanical behaviour of end cracking during one-sided SAW was computer-simulated by thermal elastic analysis with the introduction of a dummy element. Experiments on small sized specimens and on-site large specimens have been carried out. The rotational deformation, the mechanism of formation of the end cracking and factors affecting it were investigated. It was concluded that for preventing the formation of end cracks, the end opening displacement and the rate of end opening should be reduced as far as possible. Theoretical analysis and on-site large specimen experiments showed that end cracking can be effectively prevented only if the arrangement of tack welds over the weld end is appropriate, and the stiffness and restraint of slit tab plate are moderate. By the aid of the above mentioned study, end cracking was successfully avoided in over 130 specimens of 12, 14, 16, 18 and 20mm thickness with weld length more than 1000m.     

Detection and analysis of weld penetration in stationary TIG arc welding — a preliminary study

Abstract

A constant voltage microcomputer controlled welding source is used for on-line detection of weld penetration. By adding an instantaneous pulse at regular intervals to the normal welding current the molten pool is excited to oscillate in stationary TIG arc welding. By analysing the signal, the relationship between the frequency of molten pool oscillation and weld penetration is studied and a mathematical model, the weld pool oscillation equation, is established. Using a finite difference equation to solve the eigenvalue problem of the molten pool oscillation, a numerical solution can be obtained. Experimental results obtained from welding 1Cr18Ni9Ti, 20 # and 16Mn steel show good agreement with the theoretical predictions.     

AN ALGORITHM TO IDENTIFY ALL PATHS IN SCHEDULING NETWORKS

The purpose of this paper is to present an algorithm that identifies every path in scheduling networks. The algorithm finds the answer by simulating the way we solve the problem by hand. The result is a list, in sequential order, of all activities involved in each path, the algorithm is divided into forward and backward passes that are repeated until all paths have been identified. Backward passes determine the existence of paths, while forward passes determine the activities involved in the paths. The algorithm has been successfully tested with 31 construction networks, and has been implemented in simulation programs used for construction scheduling and probabilistic analyses.     

我所知道的槇文彦

自二战结束后半个多世纪以来,日本由于战后重建的需要和经济快速发展而提供的可能,产生了大规模的建设过程,也涌现了大批有高度成就的建筑师。在文化方面,日本既保持了原来本土的遗产,又在隋唐以来受中国文化的滋养和明治维新以后受西方列强的影响。特别是二战以后,西方的影响更是在加速扩展。这在建筑方面就表现得尤为清楚。在这50多年来,战前盛极一时的复古风、"帝冠式"逐渐式微。但民族主义     

双非贵金属催化nC_5异构化反应条件探索

考察正戊烷异构化应用双非贵金属丝光沸石催化剂的反应条件,实验在反应温度270～320℃,空速0.2～2.5h~(-1),氢油摩尔比2.0～6.0,反应压力1.4～4.0MPa的范围内进行。首先分析单因素对正戊烷异构化反应的影响,然后应用正交法获取了正戊烷异构化最佳反应条件和结果,即在反应温度300℃,反应压力3.0MPa,空速1.0h~(-1),氢油摩尔比4.0条件下,达到反应转化率0.6754,选择性0.9750;≥C_5异构烷产率0.6382;≥C_5液体收率0.9650。在100mL实验装置上连续进行1000h催化剂活性稳定性试验,证明双非贵金属丝光沸石异构化催化剂性能稳定。     

大型注水系统的运行优化

提出了油田大型注水系统优化运行的２类问题，１类是在注水单耗水于规定值的情况下，确定注水系统各注水站水泵运行台数，使注水系统中各注水站实际水量和分配注水量误差平方和最小；另１类是在注水系统各配水间配注误差不超过值的条件下，使注水系统总的能耗达到最小。