Exact solutions for vibration of a vertical heavy string with a tip mass

This technical note considers the free vibration problem of a vertical heavy, inextensible string/chain with a tip mass. The top end is fully restrained from moving in the vertical direction but it is partially restrained in the lateral direction by an elastic spring. The exact frequency characteristic equation for the aforementioned vibration problem is derived and the first five vibration frequencies are presented for various tip mass to string mass ratios and spring constants.     

A numerical and experimental study of crack tip shielding in presence of overloads

The mechanism underlying plasticity-induced shielding of a crack tip under fatigue loading has been already experimentally investigated by means of photoelasticity using a recently-developed mathematical model which considers stress field near the crack tip and along the flanks. Stress intensification factors have also been defined to describe shielding effects on the applied elastic field. In this paper a new application of this model is developed through a numerical simulation of the experimental tests, which were previously performed.The study is aimed to analyze the shielding effect related to constant amplitude cycling loading and a single overload peak, considering numerical simulation. By means of the models developed by XFEM technique, the plastic region is reproduced finding a good agreement with the experimental data, and a systematic procedure is proposed to evaluate the stress intensity factors.A good correspondence is found by comparing the numerical with the experimental parameters, obtained from the mathematical model.     

定向凝固Sn-36%Ni包晶合金凝固组织特征长度的表征

通过对Sn?36%Ni包晶合金在恒定温度梯度(G=20 K/mm)下进行的一定速度范围内(v=2~200μm/s)的定向凝固实验，研究凝固组织特征尺度随生长速度v的变化；测量包括一次与高次枝晶间距及枝晶尖端半径在内的凝固组织特征尺度。通过实验结果与理论模型的对比，发现凝固组织特征尺度随生长速度的变化关系为：对于一次枝晶间距有λ1=335.882v?0.21,且与 Kurz?Fisher 模型吻合；对于二次枝晶间距有λ2=44.957v?0.277,且与 Bouchard?Kirkaldy模型吻合；对于三次枝晶间距有λ3=40.512v?0.274；对于枝晶尖端半径有R=22.7v?0.36。实验结果表明，λ1/λ2随着生长速度的增加而增加，λ1/λ3的变化明显较λ1/λ2的小，表明三次枝晶具有与一次枝晶类似的生长特征；而λ1/R的比值随着生长速度的增加而由2增加到2.3，变化很小。     

轴流压气机叶顶喷气扩稳机理试验研究

轴流压气机叶顶喷气已经被证实能够有效拓宽压气机的失稳裕度。在一台低速单转子轴流压气机上进行叶顶喷气试验研究,采用喷气动量比作为衡量失速裕度改善的指标,并通过改变叶顶间隙和喷气角度对不同喷气量的扩稳效果进行分析,试验中发现随着叶顶喷气动量比的增加,压气机失速裕度的变化会出现两个拐点,即存在两个喷气动量比分界点,并将喷气动量比分界点前后的三个阶段对应的喷气量分别定义为微喷气,大喷气和超大喷气。通过试验测量压气机进出口气动参数以及壁面动态压力信号对喷气动量比分界点前后叶顶喷气扩稳机理进行详细的分析。试验分析结果表明:微喷气扩稳仅仅是因其能够减弱叶顶间隙泄漏涡和叶顶间隙泄漏流非定常性;大喷气则能够同时减小进口气流攻角,推迟叶片吸力面分离和抑制叶顶间隙泄漏涡,推迟叶顶间隙泄漏流非定常性的产生;超大喷气虽能够推迟叶顶间隙泄漏流非定常性的产生,但喷气的影响区域已严重向叶片通道内部转移,甚至影响了压气机的做功能力。     

Intensification of convective heat transfer in a stator–rotor–stator spinning disc reactor

A stator–rotor–stator spinning disc reactor is presented, which aims at intensification of convective heat‐transfer rates for chemical conversion processes. Single phase fluid‐rotor heat‐transfer coefficients h_r are presented for rotor angular velocities rad s^?1 and volumetric throughflow rates m³s^?1. The values of h_r are independent of and increase from 0.95 kWm^?2K^?1 at ω = 0 rad s^?1 to 34 kWm^?2K^?1 at ω = 157 rad s^?1. This is a factor 2–3 higher than values achievable in passively enhanced reactor‐heat exchangers, due to the 1–2 orders of magnitude larger specific energy input achievable in the stator–rotor–stator spinning disc reactor. Moreover, as h_r is independent of , the heat‐transfer rates are independent of residence time. Together with the high mass‐transfer rates reported for rotor–stator spinning disc reactors, this makes the stator–rotor–stator spinning disc reactor a promising tool to intensify heat‐transfer rates for highly exothermal chemical reactions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2307–2318, 2015     

循环气体分析系统在干熄焦中的应用

阐述了干熄焦工艺中对循环气体成分进行实时监测的重要性,结合芜湖干熄焦工程介绍了SERVOMEX公司的循环气体分析系统的构成、原理及系统维护与注意事项。     

新型护肤抗菌型洗手液的试验研究

选用不同抗菌成分和一些温和表面活性剂配制了新型护肤抗菌型洗手液。采用纸片扩散法和悬液定量法,研究了不同抗菌成分的洗手液抑菌效果,并与市场上的某些洗手液和肥皂进行了比较。研究发现,相对于碘伏、过氧化氢、新洁尔灭作为抑菌成分,卡松配制的洗手液抑菌效果较好,对金黄色葡萄球菌和大肠杆菌抑菌环直径分别达到31．7 mm和27．8 mm;作用1 min后,对两种自然菌的去除率都达到100％。结果表明,以2％卡松配制的洗手液稳定且抑菌效果较好。     

城市污水处理厂AmOn工艺曝气系统改造

对采用AmOn工艺的贵州省桐梓县污水处理厂曝气系统进行改造,将原有效率较低、能耗较高的射流式曝气器,改用为中高压型三叶罗茨鼓风机及池底微孔曝气盘。改善了出水水质、提高了出水达标排放率保障,大大降低了运行电耗,且减轻了曝气设备的维护、维修工作量。     

正拱开缝型爆破片爆破性能有限元分析

采用有限元模拟方法,对正拱开缝型爆破片爆破压力进行了研究,探讨了爆破压力与预拱高度、孔间桥长之间的关系。正拱开缝爆破片爆破压力与相对预拱高度成线性关系。正拱开缝型爆破片的承载能力主要由桥长来决定。爆破压力跟桥长在数量上成正比。