Enhanced injection method for synthetically generated turbulence within the flow domain of eddy-resolving simulations

The quality of eddy-resolving turbulence simulations strongly depends on appropriate inflow conditions. In most cases they have to be time-dependent and satisfy certain conditions for the first (mean velocities) and second-order moments (Reynolds stresses) as well as concerning suitable length scales. To mimic a physically realistic incoming flow, synthetically generated turbulent velocity fluctuations superimposed on the mean velocity field are a valuable solution. However, the resolution of the grid near the inlet has to be sufficiently fine to avoid excessive damping of the turbulence intensity. In order to circumvent this problem, the injection of synthetically generated inflow data not at the inlet itself but inside the flow domain near the area of interest, where the grid is typically much finer, is an elegant loophole. In the present study two different injection techniques based on a source-term formulation are analyzed and evaluated. In addition to these techniques the injected data are weighted by a Gaussian distribution defining the influence area. In the recent work the definition of the influence area is enhanced compared to the initial version of Schmidt and Breuer (2017) extending the application range. The case of a rather small influence area in comparison with the grid cell size is now tackled which is often relevant for industrial applications.The flow past a wall-mounted hemisphere is chosen as test case. The bluff body is exposed to a thick turbulent boundary layer at Re $=$ 50,000. The generation of the turbulent velocity fluctuations in the present investigation relies on the digital filter concept, but the injection techniques evaluated are not restricted to this inflow generator. The synthetic turbulent velocity fluctuations are injected about one diameter upstream of the hemisphere. Wall-resolved large-eddy simulations are carried out for two grid resolutions and the corresponding results are analyzed and compared with the reference measurements by Wood et al. (2016). Finally, one injection technique is found to be clearly superior to the other, since it guarantees the correct level of the velocity fluctuations and the reproduction of the autocorrelations.     

基于逆向工程技术的汽车壳体三维扫描系统优化设计

提出基于逆向工程技术的汽车壳体三维扫描系统优化设计,以解决传统三维扫描系统存在的数据捕捉效率低、扫描速率低、壳体扫描精度低等问题。依据汽车壳体三维扫描系统硬件整体结构,对硬件部分的激光线光源、摄像机、数据捕捉卡等设备进行改进设计;优化软件部分的壳体扫描点自校准过程和汽车壳体曲面三维扫描过程,实现基于逆向工程技术的汽车壳体三维扫描系统优化设计。实验结果表明,该系统数据捕捉效率高、扫描速度快、壳体曲面扫描精度高。     

Efficient Infrared Solar Cells Employing Quantum Dot Solids with Strong Inter-Dot Coupling and Efficient Passivation

Lead chalcogenide quantum dot (QD) infrared (IR) solar cells are promising devices for breaking through the theoretical efficiency limit of single-junction solar cells by harvesting the low-energy IR photons that cannot be utilized by common devices. However, the device performance of QD IR photovoltaic is limited by the restrictive relation between open-circuit voltages (V_OC) and short circuit current densities (J_SC), caused by the contradiction between surface passivation and electronic coupling of QD solids. Here, a strategy is developed to decouple this restriction via epitaxially coating a thin PbS shell over the PbSe QDs (PbSe/PbS QDs) combined with in situ halide passivation. The strong electronic coupling from the PbSe core gives rise to significant carrier delocalization, which guarantees effective carrier transport. Benefited from the protection of PbS shell and in situ halide passivation, excellent trap-state control of QDs is eventually achieved after the ligand exchange. By a fine control of the PbS shell thickness, outstanding IR J_SC of 6.38 mA cm⁻² and IR V_OC of 0.347 V are simultaneously achieved under the 1100 nm-filtered solar illumination, providing a new route to unfreeze the trade-off between V_OC and J_SC limited by the photoactive layer with a given bandgap.     

Long-Lived Liquid Marbles for Green Applications

Liquid marbles allow for quantities of various liquids to be encapsulated by hydrophobic particles, thus ensuring isolation from the external environment. The unique properties provided by this soft solid has allowed for use in a wide array of different applications. Liquid marbles do however have certain drawbacks, with lifetime and robustness often being limited. Within this review, particle characteristics that impact liquid marble stability are critically discussed, in addition to other factors, such as internal and external environments, that can be engineered to achieve a robust long-lived liquid marble. New emerging applications, which will benefit from this improvement, are explored such as unconventional computing, cell mimicry, and soft lithography. Incorporation of liquid marbles and liquid crystal technologies shows promise in utilizing structural color for optical display applications, and within green and environmental applications, liquid marble technology is increasingly adapted for use in energy conversion, heavy metal recovery, CO₂ capture, and oil removal.     

Broadband Forward Light Scattering by Architectural Design of Core–Shell Silicon Particles

A goal in the field of nanoscale optics is the fabrication of nanostructures with strong directional light scattering at visible frequencies. Here, the synthesis of Mie-resonant core–shell particles with overlapping electric and magnetic dipole resonances in the visible spectrum is demonstrated. The core consists of silicon surrounded by a lower index silicon oxynitride (SiO_xN_y) shell of an adjustable thickness. Optical spectroscopies coupled to Mie theory calculations give the first experimental evidence that the relative position and intensity of the magnetic and electric dipole resonances are tuned by changing the core–shell architecture. Specifically, coating a high-index particle with a low-index shell coalesces the dipoles, while maintaining a high scattering efficiency, thus generating broadband forward scattering. This synthetic strategy opens a route toward metamaterial fabrication with unprecedented control over visible light manipulation.     

Weakening Intermediate Bindings on CuPd/Pd Core/shell Nanoparticles to Achieve Pt-Like Bifunctional Activity for Hydrogen Evolution and Oxygen Reduction Reactions

Although Pd is a potential substitution of Pt-based catalysts for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), the binding of *H and oxygenated (*O, *OOH, *OH) intermediates on Pd are stronger than on Pt, leading to its inferior activity for HER and ORR. In this work, CuPd/Pd core/shell nanoparticles with an ultrathin Pd shell (0.5 nm) are developed, which demonstrate the Pt-like bifunctional activity for HER and ORR in acid electrolytes. The overpotential at 350 mA cm⁻² for HER and the half-wave potential for ORR on the optimal CuPd/Pd core/shell NPs are 76 mV and 0.854 V versus reversible hydrogen electrode (RHE), respectively, which are comparable to that of Pt and among the best of the reported Pd-based catalysts. Density functional theory calculations indicate that the significantly enhanced HER/ORR activity on CuPd/Pd core/shell NPs with 0.5 nm Pd shell stem from the compressive strain induced downshift of d-band center for Pd (by 2.0%), which weakens the binding strength of *H and oxygenated intermediates and promotes the reaction kinetics.     

压电纤维复合材料层合壳的非线性动力学研究

本文对横向激励作用下的1-3型压电纤维复合材料层合壳进行了非线性动力学分析,并研究了压电特性对结构振动响应的影响.首先建立了压电纤维复合材料层合壳的非线性动力学方程,并且在已知的几何结构和材料特性基础上考虑了电场属性.然后根据位移边界条件,选择合适的振型函数,通过Galerkin方法将运动控制方程转化成两自由度的非线性常微分方程.通过数值模拟方法分析了横向激励和压电系数对压电纤维复合材料层合壳非线性振动特性的影响.通过波形图、三维相图、庞加莱图和分叉图等来研究壳体不同类型的周期和混沌运动.结果表明,外激励作用下结构存在复杂的非线性振动响应,同时压电参数对层合壳结构振动响应具有很强的调节作用.     

基于ANN的复合材料变厚度壳体固化变形预测

研究目的是建立基于人工神经网络的复合材料固化变形预测模型。复合材料固化变形的多因素性致使很难得到精确的解析解。应用人工神经网络方法结合实验实测数据,模拟复合材料各项参数与变形间的非线性关系,对相同材料(玻璃钢)在相近固化条件下的固化变形进行预测,计算速度快,精度高,为固化变形的预测控制提供了一种新方法。     

单分散核壳结构SiO2磁性微球的制备及性能

采用溶胶-凝胶法、酸碱两步催化法和乳液成球法制备单分散核壳结构的SiO2磁性微球,利用Leitz光学显微镜、场发射扫描电镜、X射线衍射仪、能谱仪和振动样品磁强计分别对微球的形貌、粒度分布、物相组成、化学成分和磁性能进行了表征.结果显示:采用酸碱二步催化乳液成球法制备的SiO2磁性微球显示出良好的核壳结构,粒径分布在20 μm左右,主要物相是无定形的SiO2和尖晶石型的FegO4,保持了Fe3O4磁性粒子的超顺磁性,是一种优异的生物磁性材料.     

固体发动机纤维缠绕壳体的成型工艺设计及试验

采用网格理论对缠绕壳体进行了工艺参数的设计计算,计算出缠绕工艺参数,结合微机控制缠绕软件编制程序,提出了强度设计、线型控制、变形校核三位一体的设计思想,确定了缠绕工艺设计的内容、计算方法及所需和所应产生的参数结构,对包络线轨迹进行平滑处理,控制缠绕线型,用实验进行壳体筒身段的强度设计和变形(强度)校核,结果表明理论分析与实验结果能够较好地相互吻合,壳体的爆破压强误差较小,其值小于5%.