Laser-TIG hybrid welding of ultra-fine grained steel

For improving the weldability of ultra-fine grained (UFG) steel, detailed experiments of laser-tungsten inert gas (TIG) hybrid welding were carried out on this material to investigate the effects of welding parameters on weld shape, microstructure, grain growth in heat-affected zone (HAZ) and mechanical performance. For the hybrid welds, increasing energy ratio of laser to arc (ER_LA) can narrow weld width, reduce the tendency of grain growth and ferrite grain coarsening in HAZ and also make the microstructure of fusion zone gradually change from coarse pearlite to fine martensite and bainite. The hybrid weld with low ER_LA has obvious softening zone in HAZ; while that with high ER_LA has no softening zone because of the low line energy. Compared to laser weld, under appropriate welding parameters hybrid weld with high ER_LA can obtain higher welding speed, better weld shape and more sound mechanical performance including similar tensile strength and higher toughness. These results demonstrated that laser-TIG hybrid welding is an effective process for UFG steel.     

Prediction of laser beam welding-induced distortions and residual stresses by numerical simulation for aeronautic application

This paper focuses on the prediction of laser beam welding-induced distortions and residual stresses through numerical simulation. Fabrication of fuselage panels of latest generation civil aircraft involves welding of stringers on thin sheets of 6056T4 aluminium alloy. The efforts are made to exercise better control over the excessive out-of-plane distortions. A series of experiments have so far been performed using small specimens. One of the test cases that include single-pass fusion welding on a 6056T4 thin sheet with the industrially used thermal and mechanical boundary and loading conditions is being studied in this work. Laser beam welding in the keyhole regime is employed. The test plate is maintained in position with the help of an air suction table made of aluminium. Although a pressure of 1 bar is used experimentally, yet the possibility of leakage cannot be overruled. Various magnitudes of pressures are, therefore, introduced during numerical simulation to study the effect of each. The effect of contact between test plate and support over thermal and mechanical results is also integrated. A 3D symmetric model of test plate and support is incorporated and the comparison between simulation and experimental results is developed. Finally, a good correlation is found between experimental and simulation results, on the basis of which residual stress state in the test plate is predicted.     

Perceived control and gender difference on the relationship between trialability and intent to play new online games

With the growing number of online game players and the increasing of new online games development, it is imperative for marketers to develop a better understanding of players’ new game adoption decisions. This study examines perceived control as a mediator of trialability-product adoption relationship, and gender difference as a moderator of the relationship between trialability-product adoptions. A field survey was conducted to test the hypotheses of the study. Respondents were graduate students from Taiwan universities. A total of 411 undergraduate students with massively multiplayer online gaming (MMOGs) experience participated in this study. The structural equation model (SEM) method was employed to analyze the data. The findings indicate that perceived product trialability has a direct influence on intent to play new games, and indirect effects through perceived process control. Gender differences also moderate the trialability effects on the adoption of new online games. Perceived trialability had more of an effect on intention to play new online games for female players than for male players. To develop an effective product development and communication strategy, the finding suggests that online game firms should focus on new product characteristics and consider consumer gender differences.     

Analysis of H2 and CO production via solar thermochemical reacting system of NiFe2O4 redox cycles combined with CH4 partial oxidation

Thermal reduction of the partial oxidation of CH₄NiFe₂O₄ followed by oxidation with H₂O and CO₂ was numerically investigated for H₂ and CO production. P1 radiation model was used to account for radiative heat transfer. The synergistic effect of the reactivity of Fe/Ni exhibited a very promising strategy for producing 45% of syngas with 2.54 ratios of H₂:CO at the first step and 55% of syngas with 2.34 ratios of H₂:CO at the second step. The increase in incident radiation heat flux to 437.69 kW/m² resulted in higher reduction kinetics of species conversion until the formation of oxygen carriers consisting of 65% of FeO, 35% of NiFe and 2.6% of carbon deposition. However, during the reduction process, the decrease in total pressure to 0.05 MPa enhanced the species reactivity and the production of H₂ and CO while minimizing carbon deposition. Moreover, the oxidation temperature, operating pressure and the concentration of oxidizing species have strong impacts on the oxidation kinetics. Unlike high thermal reduction process, increasing the total pressure to 1 MPa has favorable effects on syngas production at oxidation step.     

基于MATLAB/GUI的船舶发电系统仿真软件设计的研究

本软件旨在为从事燃气轮机发电系统设计及性能优化的工程设计人员提供一个集中设计和管理的软件平台。本文利用系统仿真技术,基于模块化的建模思想,对船舶发电系统进行模块化建模,建立了一套船舶燃气轮机发电系统仿真模型。利用Matlab/GUI技术建立船舶燃气轮机发电系统仿真界面,通过人机界面实现控制仿真模型,并实现后处理等功能,使整个仿真系统操作更为人性化,减轻使用者的操作需求。     

基于夹心弯振换能器的双向驻波超声波直线电动机

一种利用夹心式弯振换能器的激励弯曲驻波的驻波超声波直线电动机。运用振动理论分析了电机的致动原理,通过激励两种不同谐振频率的弯曲驻波,并结合驱动齿的合理分布,可实现双向运动。采用有限元法确定其具体结构尺寸,验证了各驱动齿端部振动轨迹为倾向一致的斜线。制作了样机并测定了其机械输出特性。     

Critical dwell time of switched linear systems

In this paper, we consider the relation between the switching dwell time and the stabilization of switched linear control systems. First of all, a concept of critical dwell time is given for switched linear systems without control inputs, and the critical dwell time is taken as an arbitrary given positive constant for a switched linear control systems with controllable switching models. Secondly, when a switched linear system has many stabilizable switching models, the problem of stabilization of the overall system is considered. An on-line feedback control is designed such that the overall system is asymptotically stabilizable under switching laws which depend only on those of uncontrollable subsystems of the switching models. Finally, when a switched system is partially controllable （While some switching models are probably unstabilizable）, an on-line feedback control and a cyclic switching strategy are designed such that the overall system is asymptotically stabilizable if all switching models of this uncontrollable subsystems are asymptotically stable. In addition, algorithms for designing switching laws and controls are presented.     

一种基于支持向量回归机的经验模态分解方法

经典经验模态分解中采用基于曲线参数插值拟合局部均值曲线,该类方法对参加拟合的极值点很敏感,若出现干扰的异常极值点或得不到真实的极值点,将导致分解结果失真或产生模态混叠.提出一种基于支持向量回归机拟合局部均值曲线的经验模态分解方法,即利用序列的极值点训练支持向量回归机拟合局部均值曲线代替传统的曲线参数插值.实验表明,与经典算法相比,该方法具有更好的频率分辨率,对采样频率不敏感且能克服微弱高频间断信号的干扰,有效解决Hilbert-Huang变换中存在的模态混叠问题.     

原子力显微镜在分子自组装研究中的应用

原子力显微镜(AFM)以其分辨率高、样品无需特殊制备、实验可在大气环境中进行等优点被广泛应用于分子自组装这种自下而上的微细加工技术的研究中。近年来,随着对自组装行为研究的深入,其应用已由对自组装分子表面几何形貌的观测发展到制备纳米级结构和表征表面其它性能的研究领域。文中在简单介绍AFM及分子自组装优势的基础上,总结了AFM在自组装研究方面的若干新应用,并对其应用前景作出展望。     

特种车辆小底架结构分析

小底架是特种车辆中的主要承载部件。其设计的优劣将直接影响特种车辆的性能。文中对特种车辆小底架进行了结构分析及稳定性计算。采用有限单元法对小底架结构的强度、刚度、挠跨比进行了分析计算,为小底架设计提供了参考依据。