Molecular dynamics simulation of mechanical properties of Ni–Al nanowires

We employed molecular dynamics simulations to study mechanical properties of Ni–Al nanowires by calculating the stress–strain response of the wires under various loading conditions. For this purpose, nanowires were subjected to uniaxial strain at different strain rates and temperatures using embedded atom model potential. The behaviour of the wires at lower and higher strain rates was investigated, and the yield and rupture strain values and also Young’s Modulus were obtained which are essential factors for the ductility of the wires. This work indicates that how the stress–strain response of the nanowires are affected by varying strain rates and temperatures.     

Simulating a conical tuned liquid damper

In recent years, tuned liquid dampers (TLD) have proved a successful control strategy for reducing structural vibrations. The present study focuses on the frustum-conical TLD as an alternative to the traditional cylindrical tank. If compared to the cylindrical reservoir, the cone-shaped TLD allows calibrating its natural frequency through varying liquid depth, which makes it suitable for a semi-active implementation, and attains the same level of performance with a fewer mass, at least for small fluid oscillations. A linear model is presented which can interpret TLD’s behaviour for small excitations. For larger amplitudes, strong nonlinearities occur and the linear model is no longer predictive. Consequently, for a frustum-cone TLD subjected to harmonic excitations, a tuned mass damper (TMD) analogy is established where TMD parameters vary with the excitation amplitude.     

Particle dynamics analysis in bend in a horizontal-vertical pneumatic conveying system with oscillatory flow

The pneumatic system is frequently operated in the high air velocity region, which aggravates the power consumption and erosion of bend, and the intensive study of the particles motion characteristic on a horizontal-vertical pneumatic conveying in various curved 90° bends is necessary. This experimental study focuses on the particles motion characteristic of bend on the horizontal-vertical pneumatic conveying with oscillatory flow (generated by installing the oscillator) in terms of on pressure drop, powder consumption, the evolution of particle velocity and particle fluctuating intensity during flowing through bends. The results indicate that powder consumption can be reduced by using oscillatory flow, which is more obvious with a larger radius ratios bend. Meanwhile, the pressure drop proportion of bend is higher than average pressure drop of the system within the same distance. Otherwise, the total reduction particles velocity through bend is less while using oscillatory flow, which is more obvious using larger radius ratios bend. The particle velocity using oscillatory flow is higher than that of the conventional pneumatic conveying for the cases of larger radius ratios bend, and this effect is less evident while through a smaller radius bend.     

Multi-scale analysis on particle dynamic of vertical curved 90° bend in a horizontal-vertical pneumatic conveying system

To reveal the particle dynamic characteristic in the bend, high-speed particle image velocimetry (PIV) and wavelet transform were used to measure and analyze the particle velocity in a horizontal-vertical pneumatic conveying system. The pressure drop and particle velocity are analyzed to elucidate the macroscopic motion properties of particles in the different radius ratio bend firstly. Then the methods of continuous wavelet transform and one-dimensional discrete orthogonal wavelet transform are used to analyze the particle dynamic characteristic in the different regions of the bend pipe in terms of time–frequency characteristics of particle fluctuation velocity, fluctuation energy distributions of wavelet components, and auto-correlation of various frequencies. The results show that the particles are mainly small-scale motion in the rapidly decreasing region, while the large-scale motion increases in the accelerating region near the inlet and the stable region near the outlet. And the results of the wavelet component show that the acceleration and deceleration of particles in the bend will decrease the proportion of high-frequency fluctuation energy. The auto-correlation coefficient of the high-frequency component decays slower and has a longer period at the critical position of the three regions.     

The spill plume in smoke control design

Using recent data, obtained by Morgan, Poreh and colleagues, we produce correlations for the mass flow of a two-dimensional plume emerging normal to the straight edge of a flat horizontal surface—the balcony—and rising up into a uniform atmosphere (the spill plume). A comparison is made with an earlier correlation of the same data by Poreh et al. which required values of the layer depth, D_B, in addition to those of the layer flow per unit length of line plume, M^′_B. The treatment of Poreh et al. followed others assuming the linear relationship typical of far-field line plumes between the mass flow M^′ and the height z with a correction Δ—the virtual source. This linearity is a theoretical consequence of self-similarity (and a constant entrainment coefficient) in the velocity and temperature profiles across the plume, but recent, as yet unpublished, studies including some by computational fluid dynamics (CFD) cast doubt on the existence of self-similarity for these plumes at the low heights relevant in practice. However, a dimensional analysis of the flow does not require the assumption of self-similarity and we have demonstrated the linearity as a conclusion and not an assumption. The effective entrainment coefficient is, as found by Poreh et al., less than the value 0·16 found by Lee and Emmons and used in early work by Morgan and Marshall. The lower figure of 0·11 is consistent with other recent work on line plumes. The experimental values of D_B, the layer depth reported by Poreh et al., are in reasonable agreement with theoretical values for small increases in temperatures only. Experiments in model atria by Hansell, Morgan and Marshall which are not fully two-dimensional are discussed. Our correlation of them can be reconciled with that obtained by Law and subsequently used by the Chartered Institution of Building Service Engineers (CIBSE).     

小孔内表面磁力研磨加工技术研究进展

磁力研磨加工是提高小孔内表面质量的一种重要光整技术,利用该技术能高效提升小孔类零部件在极端环境下的使役性能。针对小孔内表面的磁力研磨光整加工,按其发展历程对磁力研磨加工技术进行总结,归纳了磁性磨粒研磨、磁针磁力研磨、液体磁性磨具研磨、超声辅助磁力研磨和电解磁力复合研磨等加工方法的技术特点,并分析评述了其局限性。对磁力研磨加工过程中材料去除机理进行了研究,材料主要以微量切削与挤压、塑性变形磨损、腐蚀磨损、电化学磨损等方式去除,材料种类不同,去除机理也不同。其中,硬脆性材料主要以脆性断裂、塑性变形和粉末化的形式去除;塑性材料在经历滑擦阶段、耕犁阶段和材料去除阶段后主要以切屑的形式去除。此外,还对磁力研磨加工过程中的材料去除模型进行了研究,对单颗磁性磨粒材料去除模型和“磁力刷”材料去除模型进行了分析讨论。最后,对磁力研磨加工技术今后的研究发展给出了建议并进行了展望。     

W6Mo5Cr4V2/A100复合材料的制备及摩擦性能

为了提高A100钢的摩擦学性能,采用气雾化法制备纯A100钢粉末及分别添加10%、17%、23% W6Mo5Cr4V2高速钢的W6Mo5Cr4V2/A100合金粉末,再利用粉末冶金工艺制备W6Mo5Cr4V2/A100复合材料。研究不同含量W6Mo5Cr4V2钢对复合材料力学性能和摩擦性能的影响,并探讨其磨损机理。结果表明,随着W6Mo5Cr4V2钢含量的增加,复合材料的硬度先上升后下降,且摩擦因数和磨损率都有不同程度的降低,但是材料的密度和韧性都略微下降。当W6Mo5Cr4V2钢含量为17%时,复合材料的摩擦性能最优,这与其优异的微观结构和力学性能有着密不可分的关系。     

面向多目标透镜的连通域标记检测算法

文中提出了一种适合FPGA实现的多目标连通域标记算法。该算法通过初次扫描时在图像的边框处做特殊的标记值,提取出环形具有内外双层轮廓的目标内部区域,进而将紧挨在一起的目标分离开以实现多目标的检测。该方案采用单次逐像素扫描的方法,对图像进行一次逐像素扫描即可完成连通域的标记和等价表的整理。实验结果表明,对一幅大小为M×N的图像,在不计算等价表递归时间的情况下,经过M×N×2个时钟周期后可识别出多个目标,且得到了每个目标对应区域的面积和外接矩形等参数。     

适用于LED阵列光源的新型双层TIR透镜设计

针对贴片LED阵列光源,文中提出了一种新型双层全内反射透镜结构,并利用LightTools -SolidWorks桥对其进行设计与优化,光斑的芯片成像与黄斑问题得到了解决。透镜最大外径为40 mm,透镜总高为12 mm,实现了照明系统的紧凑小型化,实际的软件模拟和测量结果表明,透镜匹配3×3阵列的贴片3030LED光源后,光学效率高达85%以上,光斑均匀,无明显黄斑现象。此款透镜被用于实际射灯灯具中。     

Synthesis and characterisation of hydrophilic and organophilic graphene nanosheets

Hydrophilic graphene nanosheets were rapidly synthesized by reacting graphene oxide nanosheets with poly(sodium 4-styrene sulfonate) and simultaneously reducing by hydrazine hydrate under hydrothermal conditions. Organophilic graphene nanosheets were prepared by reacting with octadecylamine and reduction by hydroquinone through a reflux process. Ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy measurements confirmed the attachment of organic molecules to the graphene nanosheets to achieve hydrophilic and organophilic affinity. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy analysis indicated that the crystal structure of the graphene nanosheets was maintained intact after chemical functionalisation.