Numerical investigation on the effects of reaction orders on the flame propagation dynamic behaviors for premixed gas in a closed tube

In this paper, the premixed flame propagation in a closed tube is surveyed using Computational Fluid Dynamics. The propagation characteristics of premixed flame are obtained coupling a single-step reaction mechanism with a laminar flame model. Three single-step reaction mechanisms are established with different reaction orders for hydrocarbon fuels. This study is to establish a wider range of reaction mechanisms and represent actual experimental conditions better. The numerical simulation results demonstrate that reaction orders can affect the tulip flame development. As the flame spreads, the tulip flame fronts become wrinkled. When the reaction order is 2, there are more wrinkles in the flame front and the degree of wrinkles is more obvious. Reaction orders also affect the flame tip velocity and the flame skirt velocity. The main reason is that laminar flame speeds are significantly different. When the reaction orders are 1.5 and 2, laminar flame speeds are mainly affected by temperature, which respectively increase by about 25% and 75%. When the reaction order is 1, the pressure is crucial for the variation of laminar flame speed. The laminar flame speed decreases by about 33%.     

Pb~(2+)在掺硼金刚石膜电极上的电化学行为

为了充分发挥掺硼金刚石膜(BDD)电极在分析检测工业废水中重金属离子的优势,利用BDD电极作为工作电极,采用线性扫描阳极溶出伏安法测定水溶液中的铅离子,考察了硝酸、硫酸、高氯酸、盐酸4种酸体系对铅离子分析测试的影响。结果发现,在实验室条件下检测铅离子最优的支持电解质体系是硫酸,并且与其他3种酸(硝酸、盐酸、高氯酸)相比,硫酸更加稳定,不具挥发性。     

倾斜可液化场地中矩形闭合型地下连续墙桥梁基础动力特性研究

矩形闭合型地下连续墙作为一种新型桥梁基础,在倾斜可液化场地中的动力响应特性还不清楚。基于离心机振动台试验结果,研究在倾斜可液化场地中的不同地震动工况下,矩形闭合型地下连续墙桥梁基础抵抗土体液化的性能及其位移(沉降、转角和水平位移)特征。通过对比在三种地震动(小震峰值为0.05g、中震峰值为0.13g、大震峰值为0.50g)作用下,远场土体与墙内土芯的动力响应特征,证实了矩形闭合型地下连续墙基础的抗液化性能。综合分析在3种地震动工况下,矩形闭合型地下连续墙基础的位移特征,讨论了其在倾斜可液化场地中作为桥梁基础的优劣性;分析发现在中震工况下,在可液化场地中矩形闭合型地下连续墙基础作为桥梁基础的性能最为显著。此外,通过对比有、无承台的两组矩形闭合型地下连续墙基础的位移特征,分析了矩形闭合型地下连续墙基础顶部承台的作用。     

基于STM32的可遥控智能跟随小车设计

针对物品搬运时人类双手仍无法完全解放的现状,设计并实现了一种基于STM32、超声波测距以及比例控制算法的可遥控智能跟随小车。小车以STM32为控制核心,有智能跟随和红外遥控2个模式可选。跟随模式下用2个安装在前端的超声波模块分别实时测量小车与目标之间的距离,单片机采用比例控制算法,根据实测距离控制左右电机转速;遥控模式下单片机根据接收到的红外遥控信号控制小车的运动方向。试验结果表明：小车在2m以内准确跟随几率大于95％、响应时间小于250 m s。该设计实现了小车对目标的360°智能跟随以及在必要情况下对小车的遥控操作,系统可靠,较人性化。     

Electrical and thermal conductivity in Mg–5Sn Alloy at different aging status

The electrical conductivity, thermal conductivity and its relationship with the microstructure in Mg–5Sn alloy aged at 513 K for different aging times were investigated systematically in this paper. The results show that the electrical conductivity and thermal conductivity obviously increase with the increasing aging time, and its values increase from 10.25 × 10⁶ S·m^− 1 to 13.7 × 10⁶ S·m^− 1, 87.5 W·m^− 1·K^− 1 to 122 W·m^− 1·K^− 1 after aging treatment for 120 h, respectively. Meanwhile, it is found that there exist quite different relationships between unit cell volume and thermal conductivity in early and later aging stages.     

Influence of market structures on concession pricing in Public-Private-Partnership utilities with asymmetric information

This study investigates the influence of market structures on Public-Private-Partnership (PPP) utility concession pricing. The private firm's cost and the government's public-management cost, and redundancy risk in the separation scenario, are considered by modeling concession pricing. The results suggest that the effect of the firm's cost is similar under the integrated and separated structures. Redundancy risk increases service prices and may decrease government subsidies. The findings suggest that vertical separation may help control public-management costs under PPPs.     

低温氢泄漏及射流火传播特性研究现状

阐述了低温氢的应用前景及泄漏危险性,从气体扩散特性和射流火点火、传播行为两方面介绍了低温氢泄漏的研究现状,对低温氢泄漏气体扩散及射流火传播特性的研究方法、手段及结论进行了总结分析。目前,低温氢泄漏研究方法包括实验研究和数值模拟,多数研究集中在气体扩散特性,对射流火的点火、传播行为的产生条件及影响因素尚不明确。未来应完善低温氢泄漏气体扩散预测模型,以建立有效的低温氢泄漏气体扩散过程及射流火点火、传播预测模型。     

Back calculation and hazard prediction of a debris flow in Wenchuan meizoseismal area,China

Bulletin of Engineering Geology and the Environment - On August 20, 2019, many catastrophic debris flows broke out in meizoseismal area of Wenchuan M s 8.0 earthquake in China under the influence...     

Influence of acid rain on slope instability mechanism—a case study in Sichuan provincial highway,China

Bulletin of Engineering Geology and the Environment - Acid rain has important influences on the physical and mechanical properties of rock as a result of mineral conversion and dissolution of...     

基于机器视觉的航空铆钉尺寸检测技术

航空铆钉的尺寸偏差会增加航空事故发生的可能性。为了实现航空铆钉尺寸检测的高精度与智能化,提出一种基于机器视觉的航空铆钉尺寸检测方法。通过边缘检测算法对铆钉进行自动识别与检测,可减少航空铆钉尺寸的误差。基于航空铆钉产品规范,分析得出各项尺寸参数要求与事件流程,使用OpenCV作为开发平台,采用阈值分割算法与分水岭算法进行图像分割;同时,通过平滑处理、形态学、轮廓提取算法完成图像处理。实测结果表明,在±0.005mm精度下,铆钉尺寸检测结果与实际值的吻合度达到90%以上。