用PID控制弧焊逆变电源的试验研究

本文介绍了对逆变电源进行数字PID控制的原理和方法,分析了采样周期、PID参数及不同的焊接工况对控制特性的影响。试验表明,只要恰当地选择PID(或PI)参数,不仅能实现高精度的恒流控制,而且能使系统的动态性能显著提高。     

高职现代办公设备课程的教学体会

"现代办公设备"是一门操作性、实用性和应用性极强的课程,是高职计算机专业和计算机相关专业学生必修的一门课程。如何使学生掌握现代办公设备的操作技能启发学生的创造性思维,引导学生掌握核心的操作技巧。该文根据自己近几年的教学实践经验,谈谈在该课程教学过程中的几点体会。     

基于J2EE的多媒体设备管理系统的设计与实现

该文介绍了多媒体设备管理系统的设计与实现,阐述了J2EE开发该系统的关键技术,重点说明了该系统的功能与特点。     

双同心椭圆弧的几何拟合方法

提出一种带有同心条件的双椭圆弧拟合方法。该方法利用椭圆几何定义得到的残差来衡量误差,建立关于误差的最小二乘方程,进而采用迭代方法求出描述双椭圆弧的8个参数。算法仿真实验研究了椭圆弧度、长短轴比率以及样本噪声对算法的影响,研究表明弧度越大、长短轴比率较接近1.1、样本噪声较小的时候,算法较稳定、准确。该方法也可以扩展处理多个同心椭圆弧的拟合问题。     

基于Agent的虚拟抢修任务系统的设计与实现

针对复杂装备抢修现实问题,提出了构建虚拟抢修任务系统概念模型,建立了其系统框架,并搭建了基于多Agent的系统结构,分析确定了系统运行的事件驱动机制.在完成该Agent系统实现方法、系统行为及Agent行为推理的Petri网模型研究之后,设计实现了该虚拟抢修任务系统.该系统对于优化复杂装备的抢修性设计,提高装备使用单位抢修水平都有一定的借鉴和指导意义,可以有效地解决复杂装备现实抢修面临的诸多问题.     

Advantage综合录井仪数据采集系统国产化设计

在分析研究Advantage综合录井仪数据采集系统功能与原理的基础上,提出了一种数据采集系统国产化的思路。设计并研制了国产化数据采集系统。新系统从软、硬件两方面着手进行开发,研制了全新的系统软件和设备组成．使Advantage综合录井仪的使用和维护更加稳定、便捷,实现了对原进口设备的替代。     

基于贝叶斯网络的复杂装备D-S诊断

利用D-S证据理论进行故障诊断时,首先需要确定出故障识别框架和基本置信分配.但在导弹武器等复杂装备中,存在着故障原因与故障征兆之间关联关系不确定的现象,增加了求取故障识别框架和基本置信分配的困难.文中提出了利用贝叶斯网络理论来解决难题的方法,使D-S证据理论能在复杂装备故障诊断中得到应用.文中首先给出了诊断贝叶斯网络的适应度函数,并利用改进的粒子群优化算法求解了诊断贝叶斯网络.然后分析了诊断贝叶斯网络中故障原因与故障征兆间的关联关系,给出了征兆集合、异因征兆集合概念.提出了求解故障识别框架和基本置信分配的方法.最后,通过实例的D-S诊断,验证了所提方法的正确性.     

最小通路法在通信保密装备可靠性建模中的应用

针对通信保密装备可靠性建模难度大的问题,提出了一种新的适用于复杂系统的可靠性建模方法一最小通路法。通过在系统拓扑结构图上搜索出所有能够使系统正常工作的最小通路,建立系统的可靠性模型。该方法基于广义的网络拓扑结构,因此网络的源节点和目标节点不必局限于严格的定义,可以随意指定,具有很大的灵活性。实例证明,该方法可行有效。     

Fabrication of Titanium Aluminides via Powder-Cored Wire Arc Additive Manufacturing: Microstructural and Mechanical Characterization

Herein, an innovative powder-cored wire arc additive manufacturing (PC-WAAM) process is proposed to fabricate γ-TiAl thin-walled intermetallic alloy. The metallography, phase composition, and mechanical properties at different thin-wall locations are characterized. The results show that the alternatively distributed layer-like microstructure composed of α₂ (Ti₃Al) and γ (TiAl) phases is obtained along the building direction. The content of α₂ phase exhibits the tendency of decreasing from the bottom to top region. This unique microstructure characteristic is closely related to the typical thermal cycling history during deposition. Moreover, the tensile strength and microhardness of the top region are lower than the middle and bottom region. In general, the current PC-WAAM technique shows promising capability of fabricating γ-TiAl intermetallic alloy with low cost. This work becomes a valuable reference for understanding the evolution mechanism of microstructure and paves the way for the flexible and customized additive manufacturing of γ-TiAl alloy.     

Thermal and cardiovascular strain imposed by motorcycle protective clothing under Australian summer conditions

Motorcycle protective clothing can be uncomfortably hot during summer, and this experiment was designed to evaluate the physiological significance of that burden. Twelve males participated in four, 90-min trials (cycling 30 W) across three environments (25, 30, 35 °C [all 40% relative humidity]). Clothing was modified between full and minimal injury protection. Both ensembles were tested at 25 °C, with only the more protective ensemble investigated at 30 and 35 °C. At 35 °C, auditory canal temperature rose at 0.02 °C min^?1 (SD 0.005), deviating from all other trials (p < 0.05). The thresholds for moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 min (SD 20.6) and 180 min (SD 33.0), respectively. Profound hyperthermia might eventuate in ~10 h at 30 °C, but should not occur at 25 °C. These outcomes demonstrate a need to enhance the heat dissipation capabilities of motorcycle clothing designed for summer use in hot climates, but without compromising impact protection.

Practitioner’s Summary:

Motorcycle protective clothing can be uncomfortably hot during summer. This experiment was designed to evaluate the physiological significance of this burden across climatic states. In the heat, moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 and 180 min, respectively.