回转角对AZ31镁合金管材冷轧成形过程的影响

回转角是三辊式冷轧无缝管材过程中的关键工艺参数,本文以冷轧AZ31镁合金管材为研究对象,通过对不同回转角下的冷轧过程进行了完整的仿真,对比分析了不同回转角在各特征变形段对等效应力、等效塑性应变及节点温度的影响规律,结果表明随着回转角的增大,等效应力、等效塑性应变以及节点温度均增大。借助元胞自动机模型以及实验等手段,通过实验与数值仿真结果对比分析,探明了晶粒在轧制过程中产生连续再结晶并细化的初步组织演变规律,获得了50°的回转角可以更好的满足工艺要求,为镁合金管材冷轧成形回转角的选择提供依据。     

超亲水防雾表面研究进展

透明玻璃和树脂材料应用广泛，是未来世界重要的构成元素。但这些材料表面常易发生水蒸气凝结起雾现象，不但降低了材料本身的透明度，影响相关产品的使用，还会给设备的运行安全带来隐患。因此，如何防雾逐渐引起研究人员和产业届的关注。常见的防雾技术有自动擦拭、热力防雾、表面涂层等。其中，具有主动防雾性能的超亲水表面涂层技术在施工简便性、持续防护性及运行维护成本的经济性等方面具有独特优势，是最有发展潜力的防雾技术。详细介绍了超亲水防雾表面的设计和制造技术的最新进展，从起雾现象的机制出发，介绍了水滴的形核和生长，并由此引出超亲水表面的防雾机理。分类介绍了由不同制备方法所得到的超亲水防雾表面，重点综述了近年来超亲水防雾涂层技术的研究进展，包括有机超亲水涂层、无机超亲水涂层与有机无机杂化超亲水涂层。针对各种形式的超亲水涂层技术，分别从涂层的亲水性、防雾性、耐久性及制备膜层的结构与性能之间的关系等方面进行了归纳。最后，根据超亲水防雾表面在不同领域的实际应用，对其未来的发展进行了展望。     

发电柴油机选择性催化还原系统尿素喷雾锥角的仿真及试验研究

对大功率发电柴油机选择性催化还原(selective catalytic reduction,SCR)尿素喷雾锥角进行研究。运用计算流体动力学(computational fluid dynamics,CFD)软件模拟了4种不同喷雾锥角尿素混合管内的结晶风险和NH_3分布均匀性,通过分析仿真结果,优选出60°和70°两种喷雾锥角的尿素喷嘴。使用选定的喷雾锥角进行结晶对比试验和性能对比试验。结晶对比试验结果显示,60°喷雾锥角的结晶风险明显低于70°喷雾锥角的结晶风险。性能对比试验结果显示,两种喷雾锥角的NOx转化效率基本一致。综合分析仿真结果与试验结果,最终将SCR系统的尿素喷雾锥角优化为60°。     

汽油/柴油掺混燃油两段喷射喷雾特性试验研究

基于定容燃烧弹与超高速数码相机搭建的LED-Mie散射喷雾试验台,研究了不同参数对柴油、汽油质量占比20%的柴汽混合油(记为G20)单段与两段喷射主喷液相喷雾特性的影响。结果表明,单段喷射喷雾贯穿距与喷雾锥角随喷射压力的增大而增大,G20喷雾贯穿距略小于柴油喷雾贯穿距,G20喷雾锥角略大于柴油喷雾锥角。将环境温度由300K升高到850K,喷雾贯穿距变小且喷雾很快达到稳定。冷态环境下(300K),两段喷射主喷喷雾贯穿距起始阶段与单段喷射喷雾贯穿距基本一致,但随着喷雾发展200μs左右后,两段喷射主喷喷雾贯穿距变得略小于单段喷射喷雾贯穿距。两段喷射主喷喷雾锥角略大于单段喷射喷雾锥角,预主喷间隔时间对喷雾锥角影响较小。     

不同相对湿度下亲疏水纳米纤维膜空气过滤性能实验研究

利用静电纺丝法制备了表面静态接触角为23.6°的具有亲水功能的PAN/PVP复合纳米纤维膜、接触角为81.2°的PAN纳米纤维膜、接触角为131.9°的具有疏水功能的PAN/PVDF复合纳米纤维膜。利用自行搭建的空气过滤实验台，在40%、55%、70%三种相对湿度下对三种纳米纤维膜进行空气过滤实验，对纳米纤维膜的过滤效率、阻力损失及品质因子进行分析。结果表明：三种纳米纤维膜的过滤效率随着相对湿度的增大而升高，PAN/PVP膜和PAN膜的阻力损失随着相对湿度的增大而增加，PAN/PVDF的阻力损失随着相对湿度的增大而减小；PAN/PVP膜和PAN膜的品质因子随着相对湿度的增大而减小，PAN/PVDF膜的品质因子随着相对湿度的增大而增大，湿度越大，PAN/PVDF纳米纤维膜的过滤性能越显著。     

Prediction of curved oil–water interface in horizontal pipes using modified model with dynamic contact angle

In this study, interface shapes of horizontal oil–water two-phase flow are predicted by using Young-Laplace equation model and minimum energy model. Meanwhile, the interface shapes of horizontal oil–water twophase flow in a 20 mm inner diameter pipe are measured by a novel conductance parallel-wire array probe(CPAP). It is found that, for flow conditions with low water holdup, there is a large deviation between the model-predicted interface shape and the experimentally measured one. Since the variation of pipe wetting characteristics in the process of fluid flow can lead to the changes of the contact angle between the fluid and the pipe wall, the models mentioned above are modified by considering dynamic contact angle. The results indicate that the interface shapes predicted by the modified models present a good consistence with the ones measured by CPAP.     

Surface wettability and flow properties of non-metallic pipes in laminar flow

In this paper, three liquids flowing in five pipes with the same inner diameter of 14 mm were studied to determine the relationship between the surface wettability and flow properties in laminar flow(Re b 2000). This was motivated by oilfield observations of increased pressure drops in non-metallic pipes compared to those in metal pipes,which was contrary to expectations. A new expression for the frictional coefficient that considers the Reynolds number and contact angle θ in laminar flow for non-metallic pipes was proposed based on the experimental results of single-phase flow using dimension and regression analyses. The solutions of the anomalous phenomenon were proposed from the perspectives of the pipe diameter, contact-angle difference, and the compatibility between flexible composite pipe and JLHW105 oil according to the new formula. The surprising finding was that the surface wettability could control the frictional resistance by the critical contact angle(39.9°) obtained at the same Reynolds number. If 0° b θ≤ 39.9°, the frictional coefficient increased as the contact angle increased. In contrast, if 39.9° b θ b 180°,the frictional coefficient decreased with increasing contact angle. The influences of the pipe diameter and contactangle difference on the pressure drop difference of JLHW105 oil showed an inversely proportional relation. A series of materials and liquids were tested. The selection of pipe material for transporting a given fluid can be based on the contact angle, surface tension, and critical limit of the contact angle obtained. The research results are expected to provide some guidelines for the selection of the appropriate pipe material for a given set of fluids.     

滚筒采煤机截齿安装角的角位特性分析

截齿截割安装角直接影响着滚筒采煤机工作时的截割阻力,因此准确安装截齿方位非常重要。介绍了该安装角在滚筒上的空间位置,建立了安装角与滚筒以及截齿空间参数之间的数学模型,分析了截齿安装时的几何约束特性。     

帮坡角变化对露天矿采剥量以及经济效益的影响

露天矿最终帮坡角是影响露天矿安全生产的主要因素之一,也对露天经济效益产生重要影响,特别是对大型深凹露天矿的影响尤为突出。在保障露天矿安全生产条件下,本文通过优化矿区不同帮坡角条件下的最终境界,研究帮坡角变化对矿山岩石剥离量、矿石采出量以及经济效益的影响。结果表明,随着帮坡角的增加,最终境界内的岩石剥离量、矿石采出量可能增多也可能减少,但经济效益呈现增加趋势。     

AHRS 的老人跌倒检测算法

独居老人如在室内或室外发生意外摔倒时,没有得到及时医疗救助治疗,将给老年人造成巨大的心理与身体的伤害。 将航姿参考系统(attitude and heading reference system,AHRS)应用在跌倒检测中,将跌倒的过程转变成姿态的变化,从而来判断 跌倒的程度。 AHRS 航姿系统比过去原有实验方案 3 种姿态角度均有所提升,俯仰角( pitch)提升 2. 371%,滚转角( roll)提升 9. 238%,偏航角(yaw)提升 4. 682%,加速度计最大值精确了 0. 171g,AHRS 航姿系统融合扩展卡尔曼滤波器在检测老年人跌倒 姿态中比过去原有实验方案在检测时间计算上提升了 1 s。 综上实验验证 AHRS 航姿融合在检测老年人跌倒上可以数据更精 确,计算时间更少,在研究人体真实跌倒姿态中更贴近了一步。