A 1∶2.5 scale tundish model was set up in laboratory for a six-strand billet continuous casting tundish with different configurations to investigate fluid flow characteristics under different operational conditions b...A 1∶2.5 scale tundish model was set up in laboratory for a six-strand billet continuous casting tundish with different configurations to investigate fluid flow characteristics under different operational conditions by measuring residence time distribution curves.It was found that minimum residence time,maximum concentration time and average residence time of the three strands on the same side of the tundish with the former configuration under normal operation,that is,six strands were open,were small and non-uniform and the tundish had large dead volume fraction.Vortexes easily formed on the liquid surface in the pouring zone of the tundish.The fluid flow characteristics in the tundish with the optimal turbulence inhibitor and baffles were improved and became less non-uniform among the strands.Vortexes were not found on the pouring zone surface in the optimal tundish.For non-normal operation,that is,one strand was close,it was important to choose which strand to be closed for maintaining flow characteristics of the rest two strands.It was found from this investigation that fluid flow characteristics in the optimal configuration tundish with closing strand 2 were better than those with closing strand 3 on the same side.展开更多
Improper flow control devices in a multi-strand tundish can cause some problems, for example, liquid steel cannot reach every nozzle at the same time and the liquid steel in nozzles far away from the entry zone has a ...Improper flow control devices in a multi-strand tundish can cause some problems, for example, liquid steel cannot reach every nozzle at the same time and the liquid steel in nozzles far away from the entry zone has a lower temperature. The water model experiment of a six-strand tundish of Tianjin Iron ＆ Steel Co. Ltd. was performed, a new ＂U＂ type baffle was obtained, and its parameters were defined by perpendicular analysis. The ＂U＂ baffle can not only improve those imperfections, but also prolong the residence time of nonmetallic inclusions, which is good for their flotation and separation.展开更多
Colorado potato beetle(CPB),Leptinotarsa decemlineata,is a notorious destructive pest that mainly feeds on the leaves of potato and several other solanaceous plants.CPB is widely recognized for its adaptation to a rem...Colorado potato beetle(CPB),Leptinotarsa decemlineata,is a notorious destructive pest that mainly feeds on the leaves of potato and several other solanaceous plants.CPB is widely recognized for its adaptation to a remarkable variety of host plants and diverse climates,and its high resistance to insecticides and Bacillus thuringiensis toxins.RNA interference(RNAi)is a sequence-specific,endogenous gene silencing mechanism evoked by small RNA molecules that is used as a robust tool for virus and pest control.RNAi has been extensively tested for CPB management by employing various target genes and delivery methods.This article reviews the screening of RNAi target genes,efficient RNAi delivery systems,and factors affecting RNAi efficiency in CPB,which may help understand the mechanisms of RNAi and its application in CPB control strategy.展开更多
架空输电线路断股修复机器人的作业过程包括线上行走、爬坡、越障等阶段,对机器人动力驱动的同步控制有较高要求。为此本文提出一种基于模型预测控制(model predictive control,MPC)–扩张状态观测器(extended state observer,ESO)的断...架空输电线路断股修复机器人的作业过程包括线上行走、爬坡、越障等阶段,对机器人动力驱动的同步控制有较高要求。为此本文提出一种基于模型预测控制(model predictive control,MPC)–扩张状态观测器(extended state observer,ESO)的断股修复机器人双轮行走同步控制方法。首先,对断股修复机器人挂线行走作业工况进行力学分析,设计挂线行走机械结构,增加作业稳定性与安全性;其次,针对双驱动轮因磨损、轮径不一致导致的线速度同步误差问题,提出一种基于MPC-ESO的主从融合偏差耦合线速度同步控制策略。仿真与实物验证表明,所提出的机器人双驱动轮同步控制方法可有效解决双驱动轮线速度不同步及机器人高空作业受扰问题。展开更多
基于相似原理，建立了八流连铸中间包的1：2物理模型，通过水模实验测定了1#～4#控流方案下中间包内的停留时间分布（Residence time distribution，简称RTD）。通过推导提出了多流连铸中间包的RTD曲线分析方法，并以此分析了中间包内...基于相似原理，建立了八流连铸中间包的1：2物理模型，通过水模实验测定了1#～4#控流方案下中间包内的停留时间分布（Residence time distribution，简称RTD）。通过推导提出了多流连铸中间包的RTD曲线分析方法，并以此分析了中间包内的流体平均停留时间、流动模式和各流流动一致性，进而对控流装置进行优化选择。研究结果表明，3#控流方案能较好地改善中间包内的流动特征。展开更多
基金Item Sponsored by National High Technology Research and Development Plan of China(2007AA04Z194)
文摘A 1∶2.5 scale tundish model was set up in laboratory for a six-strand billet continuous casting tundish with different configurations to investigate fluid flow characteristics under different operational conditions by measuring residence time distribution curves.It was found that minimum residence time,maximum concentration time and average residence time of the three strands on the same side of the tundish with the former configuration under normal operation,that is,six strands were open,were small and non-uniform and the tundish had large dead volume fraction.Vortexes easily formed on the liquid surface in the pouring zone of the tundish.The fluid flow characteristics in the tundish with the optimal turbulence inhibitor and baffles were improved and became less non-uniform among the strands.Vortexes were not found on the pouring zone surface in the optimal tundish.For non-normal operation,that is,one strand was close,it was important to choose which strand to be closed for maintaining flow characteristics of the rest two strands.It was found from this investigation that fluid flow characteristics in the optimal configuration tundish with closing strand 2 were better than those with closing strand 3 on the same side.
文摘Improper flow control devices in a multi-strand tundish can cause some problems, for example, liquid steel cannot reach every nozzle at the same time and the liquid steel in nozzles far away from the entry zone has a lower temperature. The water model experiment of a six-strand tundish of Tianjin Iron ＆ Steel Co. Ltd. was performed, a new ＂U＂ type baffle was obtained, and its parameters were defined by perpendicular analysis. The ＂U＂ baffle can not only improve those imperfections, but also prolong the residence time of nonmetallic inclusions, which is good for their flotation and separation.
基金funded by the National Natural Science Foundation of China (31572071)
文摘Colorado potato beetle(CPB),Leptinotarsa decemlineata,is a notorious destructive pest that mainly feeds on the leaves of potato and several other solanaceous plants.CPB is widely recognized for its adaptation to a remarkable variety of host plants and diverse climates,and its high resistance to insecticides and Bacillus thuringiensis toxins.RNA interference(RNAi)is a sequence-specific,endogenous gene silencing mechanism evoked by small RNA molecules that is used as a robust tool for virus and pest control.RNAi has been extensively tested for CPB management by employing various target genes and delivery methods.This article reviews the screening of RNAi target genes,efficient RNAi delivery systems,and factors affecting RNAi efficiency in CPB,which may help understand the mechanisms of RNAi and its application in CPB control strategy.
文摘架空输电线路断股修复机器人的作业过程包括线上行走、爬坡、越障等阶段,对机器人动力驱动的同步控制有较高要求。为此本文提出一种基于模型预测控制(model predictive control,MPC)–扩张状态观测器(extended state observer,ESO)的断股修复机器人双轮行走同步控制方法。首先,对断股修复机器人挂线行走作业工况进行力学分析,设计挂线行走机械结构,增加作业稳定性与安全性;其次,针对双驱动轮因磨损、轮径不一致导致的线速度同步误差问题,提出一种基于MPC-ESO的主从融合偏差耦合线速度同步控制策略。仿真与实物验证表明,所提出的机器人双驱动轮同步控制方法可有效解决双驱动轮线速度不同步及机器人高空作业受扰问题。
文摘基于相似原理，建立了八流连铸中间包的1：2物理模型，通过水模实验测定了1#～4#控流方案下中间包内的停留时间分布（Residence time distribution，简称RTD）。通过推导提出了多流连铸中间包的RTD曲线分析方法，并以此分析了中间包内的流体平均停留时间、流动模式和各流流动一致性，进而对控流装置进行优化选择。研究结果表明，3#控流方案能较好地改善中间包内的流动特征。
