关键词： 动力总成   悬置系统   正向开发   隔振率  

摘要： 为减少工程机械整机开发过程中的设计成本,提出一种动力总成悬置系统正向设计方法。基于某型新开发的工程机械产品,应用正向设计流程,确定悬置系统的位置、刚度及支架方案。通过动力总成悬置系统装配后的实车测试,分析发动机怠速和最高转速工况的隔振率,验证结果表明该正向设计方法能够正确指导悬置系统的设计。

关键词： Persulfate activation   Carbon nanotubes   Non-radical oxidation   Quantitative structure-activity relationships   Polyparameter linear free energy relationships  

摘要： There is increasing interest in persulfate (peroxydisulfate (PDS) and peroxymonosulfate (PMS)) activation by (non-toxic) metal-free catalysts for advanced oxidation of organic contaminants. Nevertheless, the non-radical reaction mechanisms of these catalytic reactions are not well understood. Herein, we provide mechanistic inference on the non-radical reaction pathway of the carbon nanotubes (CNTs)/persulfate system and the associated kinetics. We determined the initial degradation rates of 18 phenols and 4 anilines at various initial concentrations by commercial multiwalled carbon nanotubes (MWCNTs) and peroxydisulfate (PDS), which followed binary Langmuir-Hinshelwood kinetics. Polyparameter linear free energy relationships (pp-LFERs) and quantitative structure-activity relationships (QSARs) were developed for the equilibrium adsorption constant (K) and the surface reaction rate constant (k(r)). QSAR analyses for logK suggested that affinity interactions between organics and MWCNTs are mainly related to pi-pi interactions. The molecular volume term (V) in the pp-LEFRs contributes the most to the interaction, indicating hydrophobic interactions are also significant. QSAR analyses for log k(r) indicated one-electron oxidation potential (E-ox, representing single-electron transfer ability) and polarizability (alpha) are predominant factors affecting the reactivity of aromatic organics towards MWCNTs/PDS. Additionally, non-radical reactions occur between adsorbed aromatic compounds and adsorbed PDS, indicating that surface interactions and reactions with MWCNTs dominate the overall reaction rates.

关键词： 机械手臂   移动末端执行器   轴向运动   旋转运动   动力学分析  

摘要： 为了分析带有移动末端执行器的柔性机械臂的振动特性,将该系统建模成一个带有移动质量的在竖向平面内作伸缩和旋转运动的柔性悬臂梁。为了方便研究,引入了两个坐标系:随悬臂梁旋转的局部坐标系和固定不动的整体坐标系;结构在局部坐标系下的物理量转化到整体坐标系中,并给出总动能和总势能,利用拉格朗日方程和假设模态法导出了结构的动力学方程;当机械臂以匀速旋转时,系统动力学方程为线性;当机械臂变速旋转时,系统动力学方程为非线性;通过数值算例分析了机械臂和移动末端执行器在不同运动状态下的动力响应;此外还讨论了移动末端执行器和机械臂间的摩擦力对机械臂振动特性的影响。所得结论为相关机器人及其装备的设计提供了理论依据。

关键词： 农业劳动力   农业机械化   错配  

摘要： 在农业资源中,农业劳动力是其中重要的一部分,优化并改进农业劳动力错配,深入探讨农业劳动力错配与农业机械化的关系,具有重要的意义。以29个省市面板数据(2003-2017年)为基础,结合固定效应模型以及差分GMM计量方法开展研究,探讨时空因素与农业劳动力错配程度的关系,并阐述农业劳动力错配、地域与农业机械化的关系。

关键词： 振动与波   惯容-橡胶复合隔振器   柴油发电机组   试验分析   隔振  

摘要： 建立柴油发电机组隔振系统简化模型,介绍含惯容器的柴油发电机组隔振系统的动力学方程,对6L23/30H型柴油发电机组进行数值分析及台架试验。结果表明,使用惯容-橡胶复合隔振器后,柴油发电机组积极隔振系统的最低共振频率降低;柴油发电机组的振动加速度以及位移响应降低;基座结构的垂向振动减弱,同时发现惯容-橡胶复合隔振器能够实现更大的振级落差。分析试验数据可知,惯容-橡胶复合隔振器拥有良好的减振隔振效果,在低频隔振场景中有广泛应用前景。

关键词： 贵州省   农业机械总动力   拥有量  

摘要： 利用贵州省2000-2018年农业机械总动力及拥有量指标数据,运用线性趋势分析法、空间插值法、SPSS相关性分析法对农业机械总动力及拥有量变化进行研究。结果表明:(1)贵州省农业机械总动力、大中型拖拉机、小型拖拉机、农用水泵年际变化呈上升趋势;(2)贵州各地农业机械总动力、大中型拖拉机、小型拖拉机、农用水泵变化差异性突出;(3)农业人口、乡村从业人员数量、经济作物播种面积及第一产业GDP对农业机械总动力、大中型拖拉机、小型拖拉机、农用水泵均呈正相关关系,且相关性显著。

关键词： Reactor coolant pump   Hydrodynamic mechanical seal   Wavy-tilt-dam   OpenFOAM  

摘要： This work analyzes the operation conditions of the wavy-tilt-dam (WTD) mechanical seal under different structural parameters using the DNS method. The pressure difference within the liquid film is considered due to the complicated constructor of the WTD mechanical seal. The effects of the main structural parameters on the mechanical seal are studied, including the film thickness, taper, dam-width ratio, and waviness amplitude. Numerical results show that the increase of base film thickness will increase the leakage rate and decrease the opening force. The larger taper will lead to a higher leakage rate and opening force. As the taper increases, the stiffness increases first and then decreases. As the dam-width ratio increases, the leakage rate, the opening force, and the stiffness will increase correspondingly. The waviness amplitude has a small effect on these three performance parameters. Besides, the comparisons between the Reynolds approximation and the DNS technique show that the Reynolds approximation can be applied to analyze the leakage rate under different thicknesses, small tapers, and large dam-width ratios. The opening force under small thickness, different tapers, and different dam-width ratios can also be considered using the Reynolds approximation. To ensure the safe and stable operation of RCP, the optimal structural parameters can be set as taper beta = 600 grad, dam-width ratio 6 = 0.2, waviness amplitude alpha = 0.8, and wavenumber omega = 9. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Bulk metallic glass   Glass forming ability   Crystallization kinetics   Rare-earth elements  

摘要： Investigations were carried out to explore the consequences of Er adding on the glass forming ability (GFA), mechanical properties, and crystallization kinetics of Cu50Zr43Al7 bulk metallic glass (BMG). It is found that the (Cu50Zr43Al7)(100-x)Er-x (x = 0, 2, 4, 6 at %) BMGs reflects its best GFA at x = 2 and correlate well with GFA indicator (gamma and K) and thermal stability parameter (AT). The Er-containing BMGs showed high compressive strength and Young module in the range of 1816-1890 Mpa and 116-120 GPa, respectively, but no plastic deformation observed in them. The crystallization kinetics lagged with 2 at % Er addition. The large atomic radius of Er and large negative mixing enthalpy of Er with the other constituent elements causes the significant atomic size mismatch and the formation of short-range order in the melt which restrict the long-range diffusion and ordering of atoms that lead to improving GFA and lagging the crystallization kinetics of (Cu50Zr43Al7)(98)Er-2.

关键词： Coupling rub-impact   Double translational joints   Subsidence   Chaos   Time-varying load  

摘要： In this paper, a novel dynamic model of coupling translation joints with subsidence for time-varying load in a planar mechanical system is established. One translational joint has four working scenarios, which are free motion, one corner rub-impact, two adjacent corners rub-impact and two opposite corners rub-impact. However, the rub-impact of double coupling translation joints are not a simple superposition of these scenarios, but rather a more complex rub-impact configuration that should be considered in this model. An adaptive fourth-order Runge-Kutta method is utilized to solve the dynamic differential equations. After that, we discuss the dynamic behavior of the rub-impact coupling by taking a triplex member of the crosshead slider, piston rod and piston slider as an example in the reciprocating compressor system. The results show that the double coupling translation joints experience free motion, continuous contact motion and rub-impact motion. The difference is that, in the rub-impact motion, for the crosshead slider there only appears one single corner and two adjacent corners impacting the guide, while the coupling piston slider experiences multiple rub-impact situations including one single corner, two adjacent corners and two opposite corners impacting the guide. Moreover, the results reveal that the subsidence has a significant influence on the rub-impact behavior of the coupling translation joints, and the greater the subsidence, the more severe the vibration response of the slider impacting the guide. Finally, in this rub-impact coupling system, the existence of chaotic behavior is confirmed by the Poincare section and the largest Lyapunov exponent approaches.

关键词： Aminated graphene   Nanocomposites   MD simulation   Covalent bond  

摘要： This paper is devoted to studying the thermal and mechanical properties of aminated graphene (AG)/epoxy nanocomposites connected by covalent bond using molecular dynamics (MD) simulation. The effects of crosslinking degree, mass fraction and functionalized graphene (FG) type on AG/epoxy nanocomposites are considered. The elasticity modulus (E), the glass transition temperature (T-g), the coefficient of thermal expansion (CTE) and the interfacial energy (E-int) are also investigated. The MD simulation results indicate that, when the mass fraction of AG is between 1.2% and 3.1% and crosslinking degree reaches about 70%, the E, T-g, E-int and CTE of AG/epoxy nanocomposites are significantly improved compared with those of pure epoxy and graphene/epoxy nanocomposites. The reason is that AG not only possesses some excellent thermodynamic properties of graphene, but also has the function of curing agent to crosslink with epoxy monomer to form the carbon-nitrogen (C-N) covalent bond. A better interfacial interaction between nanoparticles and epoxy is essential in enhancing the thermal and mechanical properties of nanocomposite materials, which will provide a microscopic theoretical basis for the study of epoxy nanocomposites.