Damping oscillations in a wire bending process

This paper presents an approach to modify CAD/CAM generated motion profiles for wire bending machines, in order to damp wire oscillations without decreasing machine throughput. Two different methodologies are presented, both leveraging on a simple and easily identifiable model of wire oscillations, the first one based on a filtering approach, the second one on an optimisation approach. The two methodologies are both characterised by a low computational complexity, allowing them to be integrated directly in the bending machine user interface, and can rely on a standard camera to identify wire oscillation parameters. A thorough experimental validation of the approaches is also presented, showing promising results in damping oscillations with wires of different materials.     

如何选用振动压路机振动轴用轴承

分析了振动压路机振动轴用轴承的受力及选用轴承的类型、游隙、保持架、配合等问题。     

"摇摆"的教堂——象山丹城基督教堂设计札记

教堂作为特定文化内涵下的西方传统建筑类型,在国内的建设必然面对文化、传统、地域、情感等诸多问题.该文结合丹城基督教堂的设计实践,从传统与现代、神性与人性、独立与交融、形制与创作这四个方面来探讨其创作思路和设计方法.     

化学振荡指纹图谱用于凉茶表征的研究

运用非线性分析方法,探讨了B-Z化学振荡系统的复杂现象及机理。研究了以凉茶（潘高寿）、8%的硫酸、5%的丙酮、1.67%的硫酸锰、1.07%的溴酸钠形成的反应振荡体系。通过只改变凉茶的量（其他条件均不变）,温度为（37.5±0.1）℃,测定离子选择性电极上的电势U随时间（t）变化的U-t曲线。由B-Z振荡曲线可以了解其反应随时间作周期性的变化,即可得到以下振荡参数：振荡诱导期、振荡周期、振荡寿命、振荡△E等等。结果表明：随着凉茶的量的增加,其振荡的时间逐渐缩短,诱导期缩短,周期也逐渐缩短且趋于稳定。但振幅的改变率不明显。初步说明了反应物与电极电势之间存在良好的线性关系。当加入氧化剂溴酸钠时,振荡图形整体向上漂移。     

Effect of mold oscillation on the metallurgical characterization and mechanical properties of A319 aluminum alloy casting

Effect of mold oscillation on metallurgical characterization and mechanical properties of the A319 alloy was investigated. Experimental results show that the microstructure of A319 alloy was significantly refined regarding α-Al grain refinement along with improved silicon particle morphology due to mold oscillations. Mechanical properties of casting such as tensile strength, yield strength, percentage elongation and micro-hardness improved by 39.05, 28.05%, 2.67 times and 27.02% respectively as compared to that of stationary casting. This investigation is an attempt to study the effect of mold frequency on mechanical and metallurgical properties of aluminum alloys.     

北极涛动对华北沙尘暴频次的影响

This study has investigated the influence of Arctic Oscillation (AO) on dust storm frequency in North China in spring seasons during 1961-2007. There is a significant linkagebetween dust storm frequency and AO; a negative (positive) AO phase is related to an in-creased (decreased) dust storm frequency in North China. This relationship is closely related to changes in the cold air activity in Mongolia. The cold air activity exerts large impacts on the dust storm frequency; the frequency of cold air activity over Mongolia not only positively cor-relates with the dust storm frequency in North China, but also shows a long-term decreasing trend that is an important reason for the long-term decreasing of dust storm frequency in North China. The AO has large influence on the frequency of cold air activity over Mongolia; a negative (positive) AO phase is highly related to an increased (decreased) frequency of cold air activity over Mongolia, which results in an increased (decreased) dust storm frequency in North China.     

Influence of Bubble Evolution on the Effective Kinetics of Heterogeneously Catalyzed Gas/Liquid Reactions. Part I: Reactions with Gaseous Products

For heterogeneously catalyzed multiphase reactions the formation of bubbles may have an influence on mass and heat transfer as well as on the effective reaction rate. This first of two contributions deals with the Ni‐catalyzed decomposition of H₂O₂, which was used as a model system for an (almost) isothermal reaction with a gaseous product. (In part II the strongly exothermic hydrogenation of hexene will be analyzed, where gas/vapor bubbles may be generated by overheating of the catalyst.) The discharge of O₂ bubbles formed by decomposition of H₂O₂ enhances the external mass and heat transfer up to one order of magnitude. This is in analogy to the well‐known phenomena during nucleate boiling. The experiments and theoretical considerations also show that the internal mass transfer depends on the intensity of the reaction and thus on the H₂O₂ concentration, which is in contradiction to the classical Thiele approach. This discrepancy could be explained by a modified model that takes the formation of bubbles into account.     

Effect of plate position and size for self-induced flow oscillation of underexpanded supersonic jet impinging on perpendicular plate

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of t...     

Mechanism analysis of non-sinusoidal oscillation of continuous casting mold synchronously driven by double servomotors

Due to the disadvantages of complexity,high maintenance and vast investment of the electro-hydraulic servo oscillator,a new mechanical device synchronously driven by double servomotors was proposed.The working principle of the non-sinusoidal oscillator was analyzed and the model of the oscillator was validated via simulation software.Then,taking advantage of resonance technology,the hinging force and moment were calculated.The results showed that the hinging force and driving moment reduced,which was useful in reducing the impact of the hinge and prolonging the service life of the bearing.Besides,the best initial spring pressure was 0.9 times the mold gravity,which improved the oscillation system stability and reduced the load fluctuation and servomotor driving power.     

5MW低温供热反应堆微沸腾运行启动可行性研究

文章用RETRAN-02程序,对清华大学核能技术研究所设计和建造的5MW低温供热堆的微沸运行启动方式进行了较为系统的研究;分析了控制反应性引入速率、主回路蒸汽冷凝量大小及主回路对外总传热量的大小对启动稳定性的影响。结果表明,在一种新颖的启动方式下,只要对反应堆的某些特定参数作适当的实时控制,反应堆就能从单相向两相微沸运行方式稳定过渡。