Engineering knowledge formalization and proposition for informatics development towards a CAD-integrated DfX system for product design

Target design methodologies (DfX) were developed to cope with specific engineering design issues such as cost-effectiveness, manufacturability, assemblability, maintainability, among others. However, DfX methodologies are undergoing the lack of real integration with 3D CAD systems. Their principles are currently applied downstream of the 3D modelling by following the well-known rules available from the literature and engineers’ know-how (tacit internal knowledge).This paper provides a method to formalize complex DfX engineering knowledge into explicit knowledge that can be reused for Advanced Engineering Informatics to aid designers and engineers in developing mechanical products. This research work wants to define a general method (ontology) able to couple DfX design guidelines (engineering knowledge) with geometrical product features of a product 3D model (engineering parametric data). A common layer for all DfX methods (horizontal) and dedicated layers for each DfX method (vertical) allow creating the suitable ontology for the systematic collection of the DfX rules considering each target. Moreover, the proposed framework is the first step for developing (future work) a software tool to assist engineers and designers during product development (3D CAD modelling).A design for assembly (DfA) case study shows how to collect assembly rules in the given framework. It demonstrates the applicability of the CAD-integrated DfX system in the mechanical design of a jig-crane. Several benefits are recognized: (i) systematic collection of DfA rules for informatics development, (ii) identification of assembly issues in the product development process, and (iii) reduction of effort and time during the design review.     

An effect of hydrogenation on the photoemission of amorphous SiCN films

The structure, chemical bonding and photoemission of amorphous hydrogenated silicon carbonitride (a-SiCN:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisilazane as a main precursor at different hydrogen flow rates are studied. Film properties are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), absorption optical spectra and photoluminescence (PL). The photoluminescence spectra were presented by four photoemission bands centered at 441–451, 489–496, 530–535 and 577–601 (in nm). To explain structural and photoluminescence properties of the deposited films, first-principles molecular dynamics simulations of un-hydrogenated and hydrogenated silicon carbonitride samples were carried out. Based on experimental and theoretical results a possible explanation of the photoemission of the deposited films and its evolution with increasing hydrogen flow rate was done.     

Mesoscopic particulate system assembled from three-dimensional irregular particles

Particles around us are generally in the form of irregular characteristics in shape and size. Establishing rational mesoscale models that are suitable for different types of particles is of great significance to comprehensively evaluate the mechanical properties of particulate systems assembled from irregular particles. The preponderances of previous works are mainly focused on particle simulations using regular-shaped geometries or simple polyhedrons, and little is known about quantitative characterization for the particles with complex shape characteristics. In this paper, a series of novel and efficient algorithms are presented to generate three-dimensional particulate systems assembled from particles with irregular characteristics in shape and size. According to the developed particle generation algorithm and vector-growth algorithm, the convex- and concave particles with different shape- and size configurations are obtained. Parametric analysis of corresponding algorithm parameters on the shape- and size configurations of particles are quantitatively investigated in terms of different indexes, such as sphericity, angularity and size, which provides an important guidance for the shape- and size control of irregular particles. Based on the generated irregular particles, a series of algorithms are proposed to generate the particulate systems with random spatial characteristics as well. Employing the developed compaction algorithm, mesoscopic particulate systems with different particle gradations and compactness are generated precisely. To sum up, the present particle model provides insights into capturing and studying the meso-structure characteristics and macroscopic mechanical properties of particulate systems.     

Suppression of hydrogen-air explosions by isobutene with special molecular structure

Effects of isobutene (i-C₄H₈) with the unique molecular structure on hydrogen explosions are investigated in a 14 L spherical chamber at 100 kPa and 298 K. The results reveal that for lean hydrogen-air mixtures, the maximum explosion overpressure, maximum pressure rise rate, and de?agration index show a trend from rise to decline. However, for stoichiometric and rich hydrogen-air mixtures, pressure parameters decrease monotonously with increasing i-C₄H₈. The chemical suppression mechanism of i-C₄H₈ on hydrogen explosions is revealed in detail by numerical simulation. The relevant analyses show that i-C₄H₈ can not only change the chain reaction path and cut off the hydrogen-oxygen reaction, but also strengthen the consumption of oxygen and H radicals. This work will provide a novel theoretical foundation for hydrogen explosion prevention and control.     

Remarkable hydrogen properties of MgH2 via combination of an in-situ formed amorphous carbon

Carbon-based materials have been proposed as an ideal medium to reduce the reaction energy barriers and improve the (de)hydrogenation kinetics of magnesium-based hydrogen storage material (MgH₂) in term of their excellent dispersion. However, tedious preparation process and uneven distribution of carbon restrict the application. Therefore, in this paper, we cover MgH₂ by in-situ formed amorphous carbon via a facile approach of co-sintering Mg with fluorene followed by hydriding combustion and ball milling processes, named as MgH₂-carbonization product of fluorene (MgH₂-CPF). As a result, the MgH₂-CPF composite prepared at 823 K initially dehydrogenates at 557 K, 94 K lower than the as-milled MgH₂ (651 K). Meanwhile, the composite can release 5.67 wt% H₂ within 1000 s at 623 K. Even at a lower temperature of 423 K, the MgH₂-CPF composite still reabsorbs 5.62 wt% H₂ within 3600 s, while the as-milled Mg can hardly absorb hydrogen under a same condition. Furthermore, by addition of CPF, the apparent activation energy of the system is decreased from 161.2 kJ/mol to 87.2 kJ/mol. Our finding suggests that the carbon layer can keep the MgH₂ from aggregation, promote hydrogen transport and improve the efficiency of hydrogen absorption and desorption.     

Heterofullerene C48B12-impregnated MOF-5 and IRMOF-10 for hydrogen storage: A combined DFT and GCMC simulations study

The H₂ storage properties of isoreticular metal-organic framework materials (IRMOFs), MOF-5 and IRMOF-10, impregnated with different numbers and types of heterogeneous C₄₈B₁₂ molecules were investigated using density functional theory and grand canonical Monte Carlo (GCMC) calculations. The excess hydrogen adsorption isotherms of IRMOFs at 77 K within 20 bar indicate that suitable number and type of C₄₈B₁₂ molecules play a crucial role in improving the H₂ storage properties of IRMOFs. Among the studied pure and nC₄₈B₁₂ (n = 1, 2, 4, 8) in Ci symmetry impregnating into MOF-5, at 77 K under 6 bar, MOF-5-4C₄₈B₁₂ with a 3.5 wt% and 29.9 g/L hydrogen storage density, and at 77 K under 12 bar, the pure MOF-5 with a 4.9 wt% and 31.0 g/L hydrogen storage density has the best hydrogen storage properties. Whereas, among the studied pure and nC₄₈B₁₂ (n = 1, 2, 4, 8) in S6 symmetry impregnating into IRMOF-10, IRMOF-10-8C₄₈B₁₂ always shows the best hydrogen storage properties among the pure and C₄₈B₁₂-impregnated IRMOF-10 at 77 K within 20 bar. IRMOF-10-8C₄₈B₁₂ has a 6.0 wt% and 34.6 g/L hydrogen storage density at 77 K under 6 bar, and has a 7.1 wt% and 41.4 g/L hydrogen storage density at 77 K under 12 bar. The confinement effect of IRMOFs on C₄₈B₁₂ molecules, and steric hindrance effect of C₄₈B₁₂ molecules on IRMOFs mainly affects the H₂ uptake capacity by comparing the absolute H₂ molecules in individual IRMOFs units, C₄₈B₁₂ molecules, and IRMOFs-nC₄₈B₁₂ compounds. The absolute hydrogen adsorption profiles show that eight C₄₈B₁₂ molecules impregnating into MOF-5 can exert obvious steric effects for H₂ adsorption. The saturated gravimetric and volumetric H₂ densities of IRMOF-10-8C₄₈B₁₂ higher than those of MOF-5-8C₄₈B₁₂ due to with larger free volume.     

南水北调中线水源区浮游植物群落结构 及其生物多样性

为探究南水北调中线水源区丹江口水库浮游植物群落结构变化及其生物多样性，于 2014—2015 年对丹江 口水库进行为期 1 年的调查和分析。发现浮游植物共 8 门 76 属 101 种，其中，绿藻门、蓝藻门及硅藻门占总种数 90.10%，绿藻门种类数最多（45 种），其次是蓝藻门（26 种）和硅藻门（20 种）。浮游植物群落结构随季节变化有所 不同：夏秋季节生物量明显高于冬春季节；优势种在冬季以颗粒直链藻、颗粒直链藻极狭变种、铜绿微囊藻和小 环藻为主，春季以球衣藻、薄甲藻属及小环藻为主，夏季以简单颤藻、单胞衣藻原变种和球衣藻为主，秋季以类颤 藻鱼腥藻、简单颤藻、球衣藻和小环藻为主。应用 Shannon-Wiener 多样性指数 H′、Pielou 均匀度指数 J′、Margalef 丰富度指数 Dm评价水质结果表明：丹江口水库夏秋季水体营养化程度更高。典型对应分析表明：水温、透明度、 总氮、总磷等是影响浮游植物群落结构的主要环境因子，夏秋季受温度影响蓝藻、绿藻数量逐渐增多，一定程度 上增加了受水区生态变化风险。本研究可为南水北调中线水源区丹江口水库生态环境变化及生物迁移风险提供 数据支持。     

Synthesis,structure identification and linear/nonlinear optics of hydrothermally grown WO3 nanostructured thin film/FTO: Novel approach

Thin film of WO₃ has been deposited on conductive fluorine tin oxide substrate using the hydrothermal technique. The film's microstructural, morphological and optical properties have been identified using X-ray diffraction, atomic force microscope, and spectrophotometer. The obtained results have confirmed the nanocrystalline structure of the as-received WO₃ thin film with crystallite size ≈63.4 nm. Analysis of the absorption coefficient using Tauc's model shows the possibility of direct and/or indirect allowed transition with energy gaps 3.95 and/or 3.45 eV, respectively. The refractive index has been determined by different methods showing the average value (2.2 and 2.3 corresponding to the direct and indirect transitions, respectively). The nonlinear refractive index and third-order nonlinear optical susceptibility have been determined, showing the high polarizability of WO₃/FTO with radiation to be promising for different optical devices and applications.     

Tribological performance of UV picosecond laser multi-scale composite textures for C/SiC mechanical seals: Theoretical analysis and experimental verification

The performance of mechanical seals can be improved by using multi-scale composite textures with spiral grooves and micro-dimples, but without a clear texture function mechanism, it is difficult to optimize the textures on the sealing surface. This research established a mathematical model based on the mass-conservative JFO cavitation boundary to analyze the mechanical seal performance of multi-scale composite micro-textures. We use the multi-grid method for numerical solutions, investigate the hydrodynamic lubrication characteristics of composite-textured mechanical seals, and inspect the coupling effect of micro-dimples and spiral grooves. We also analyzed the influence of the geometrical parameters of composite textures on the sealing performance and optimized the sealing surface textures using theoretical analysis. The numerical analysis showed that the multi-scale composite-textured mechanical seal produced a coupling effect between the micro-dimples and spiral grooves, which improved the lubrication of the sealing pair. Eventually, C/SiC mechanical seal bench tests confirmed the tribological improvement of composite textures compared with the un-textured seal under various sealing liquid pressures and rotation speeds. Through comparing the Stribeck curve, the multi-scale composite textured C/SiC mechanical seals have a lower and more stable friction torque than the un-textured.     

富芳烃重油组分结构调变对中间相沥青形成的影响机制

对重油富芳烃组分转化为次生沥青及其氢化改性沥青的热转化行为进行了比较，并对热转化过程中体系化学结构组成特征对中间相形成的影响进行了研究。采用红外光谱及氢核磁共振波谱，对比分析了次生沥青及其氢化改性沥青的化学结构组成特征；借助偏光显微镜、X射线衍射，考察了两体系中间相沥青的形成过程。结果表明：控制体系短烷基侧链含量可有效抑制过度炭化的发生，提高炭化产物的微观有序度；短烷基侧链可以持续稳定释放出小分子自由基，对大分子自由基反应进行调控，显著提升炭化产物微观结构的均一性。