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： Mechanical activation   DTA   Raman spectroscopy   Sintering kinetics   Spinel  

摘要： Solid-state mechanical activation of MgO and alpha-Al2O3 powders was used to produce MgAl2O4. The cation site occupancy in the resulting MgAl2O4 spinel was investigated using different methods. Differential thermal analysis and thermal gravimetry showed that mechanical activation reduced the spinel formation temperature by around 200 degrees C, and the corresponding activation energy by about 25%. In addition, characteristic temperatures for evaporation of physisorbed water and decomposition of Mg(OH)(2) shifted to lower values, and peaks were more pronounced. Raman spectra were used to characterize the degree of inversion as a function of the sintering temperature for all of the sintered specimens, indicating that the breaking point for ordering of the crystal structure was around 1500 degrees C for non-activated samples, and 1400 degrees C for activated samples.

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.

关键词： Grain boundaries  

摘要： Molecular dynamics simulations are performed to study the mechanical behaviors and microstructural evolution in nanocrystalline Cu films created by the phase field model under different strain rates and temperatures. The results indicate that grain boundaries' (GBs) migration caused by shear stress difference of GBs is found in the initial deformation stage. The migration on the site with a small curvature radius of curved GBs is large due to the high stress difference. The migration process of curved GBs in the initial stage is that atoms migrate from FCC structures to GBs along the (111) surface, which is different from the mechanism of atomic shuffling for the flat GBs. Meanwhile, the initial GBs migration can make curved GBs become flat. In addition to temperature and stress difference, the hexagonal-close-packed (HCP) structures including stacking faults and twin boundaries can accelerate GBs' migration. The influence of initial GB migration on mechanical properties is achieved by changing the fraction and distribution of HCP structures. Larger initial GB migration at a higher temperature significantly reduces stress concentration on GBs, which leads to the distribution of HCP changing from the grains with large initial GB migration to other grains. Therefore, the sites of crack nucleation at conditions of low and high temperatures are different due to different magnitudes of initial GB migration.

关键词： Boron  

摘要： We report the determination of diffusion paths and potential barriers of boron point defects in TiB2 calculated using the climbing image nudged elastic band method at T = 0 K, and ab initio molecular dynamics studies on the structural stabilities, diffusion behavior of boron point defects and mechanical strengths of TiB2 at elevated temperatures. In contrast to the previous conjecture that TiB2 with boron vacancies are thermodynamically unstable based on the calculations at T = 0 K that boron vacancies have positive formation energies and shift electronic Fermi energies from the pseudogap valleys to the bonding states, our results show that boron vacancies in TiB2 are very robust and they have negligible effects on the structural stabilities and mechanical strengths of TiB2 at least up to 2000 K within the vacancy concentration we studied (<2.5 at%). On the other hand, our results reveal that the boron interstitials can diffuse easily in TiB2 at a moderately high temperature (1000 K) or under large shear and tensile deformations, which give rise to significant deteriorations (more than 50% reduction) in the mechanical strength of TiB2 at a high temperature (2000 K) with a boron interstitial density below 2.5 at%. Under all the shear and tensile deformations we applied, the boron interstitials in TiB2 eventually diffuse into the boron layers, causing deformations of these boron layers, which weakens their interactions with metal layers nearby and consequently reduces the mechanical strengths of the materials as temperature and boron interstitial density increase. The present findings expand our understandings on the material strength of TiB2 at high temperatures with boron point defects, and offer new insights for its applications as a high-strength ultra-high temperature ceramic.

关键词： alternative splicing   molecular modeling   evolution   transcript phylogeny   kinase  

摘要： Alternative splicing and alternative initiation/termination transcription sites have the potential to greatly expand the proteome in eukaryotes by producing several transcript isoforms from the same gene. Although these mechanisms are well described at the genomic level, little is known about their contribution to protein evolution and their impact at the protein structure level. Here, we address both issues by reconstructing the evolutionary history of transcripts and by modeling the tertiary structures of the corresponding protein isoforms. We reconstruct phylogenetic forests relating 60 protein-coding transcripts from the c-Jun N-terminal kinase (JNK) family observed in seven species. We identify two alternative splicing events of ancient origin and show that they induce subtle changes in the protein's structural dynamics. We highlight a previously uncharacterized transcript whose predicted structure seems stable in solution. We further demonstrate that orphan transcripts, for which no phylogeny could be reconstructed, display peculiar sequence and structural properties. Our approach is implemented in PhyloSofS (Phylogenies of Splicing Isoforms Structures), a fully automated computational tool freely available at https://***/PhyloSofS-Team/PhyloSofS. (C) 2020 Elsevier Ltd. All rights reserved.