关键词： 船舶动力   机械螺旋桨   湍流动力   性能仿真  

摘要： 不同动力机械螺旋桨在湍流环境下进行动力性能仿真过程中,存在量化误差较大的问题,为此提出船舶动力机械螺旋桨在不同湍流的动力性能仿真。分别设计螺旋桨动力性能仿真平台硬件结构和软件系统,实现螺旋桨动力性能仿真平台构建;基于仿真平台对船舶动力机械螺旋桨湍流流体动力学进行分析,通过平台大数据技术,实现船舶动力机械螺旋桨在不同湍流的动力性能仿真分析。试验数据表明,本文系统仿真效果与常规仿真方法相比,量化准确率提升10.25%,适合不同环境下的船舶螺旋桨动力性能分析。

关键词： 船舶动力机械   空蚀现象   粒子群算法   优化控制方法  

摘要： 空蚀直接影响船舶动力机械的寿命,为了解决当前船舶动力机械空蚀控制精度低的难题,提出了基于粒子群算法的船舶动力机械空蚀优化控制方法,首先对当前船舶动力机械空蚀优化控制研究现状进行分析,并采集船舶动力机械空蚀的历史数据,然后采用神经网络对船舶动力机械空蚀的历史数据进行学习,找到船舶动力机械空蚀变化特点,并引入粒子群算法对神经网络的参数进行优化,最后进行船舶动力机械空蚀优化控制的仿真测试。结果表明,本文方法可以描述船舶动力机械空蚀变化的特点,可以提高船舶动力机械空蚀预测精度,有利于制定船舶动力机械空蚀优化控制方案。

关键词： beta-Type Ti alloys   Ti-45Nb   Powder-pack boriding   Growth kinetics   Solid-state diffusion  

摘要： In this study, beta-type Ti-45Nb alloy was borided by solid-state diffusion process in order to achieve a hard and adhered boride layer. Boriding was carried out in a solid medium consisting of amorphous boron, anhydrous borax and active carbon at temperatures between 850 and 1100 degrees C for time intervals of 3-24 h in order to determine boron diffusion kinetic and to achieve an optimum adhered layer thickness. Microstructure, mechanical properties, adhesion characteristic and growth kinetic of borided layers were investigated in detail by X-ray diffraction, GDOES and SEM-EDS analysis, microhardness and Rockwell-C adhesion tests. A layer consisting of monolithic TiB2 center dot NbB2 phase with the hardness of about 34.3 GPa on the top and TiB whisker with the hardness of about 14.7 GPa beneath it was formed by boriding using optimum processing parameters. A diffusion model based on mass balance equations was used to estimate boron diffusion coefficients and activation energies in the boride layers. Activation energies in TiB2 center dot NbB2 and TiB layers were determined to be 203.96 +/- 2.4 kJ/mol and 138.33 +/- 24.5 kJ/mol, respectively. Fracture toughness of the borided layer formed at 1000 degrees C for 24 h was found to be 2.84 +/- 0.8 MPa m(1/2). Multiple concentric cracks occurred at the peripheral zone of indent by Rockwell-C adhesion test. But no or very limited delamination or spalling occurred due to the result of deeper penetration of TiB whiskers.

标准号: YS/T 5222-2018

摘要： 本标准规定了机械基础地基动力特性测试工作所采用的仪器设备的性能参数、测试方法、参数计算及测试成果报告编制的要求。本标准适用于有色金属工业建设中动力机械基础的地基动力特性测试。

关键词： microtubule   dynamic instability   C. elegans   cryo-EM   single molecule   catastrophe  

摘要： The dynamic instability of microtubules is a conserved and fundamental mechanism in eukaryotes. Yet microtubules from different species diverge in their growth rates, lattice structures, and responses to GTP hydrolysis. Therefore, we do not know what limits microtubule growth, what determines microtubule structure, or whether the mechanisms of dynamic instability are universal. Here, we studied microtubules from the nematode C. elegans, which have strikingly fast growth rates and non-canonical lattices in vivo. Using a reconstitution approach, we discovered that C. elegans microtubules combine intrinsically fast growth with very frequent catastrophes. We solved the structure of C. elegans microtubules to 4.8 angstrom and discovered sequence divergence in the lateral contact loops, one of which is ordered in C. elegans but unresolved in other species. We provide direct evidence that C. elegans tubulin has a higher free energy in solution and propose a model wherein the ordering of lateral contact loops activates tubulin for growth.

关键词： Physical and chemical processes   Hematite   Natural organic matter   Minerals   Kinetics  

摘要： In natural environments, kinetics of As(V) sequestration/release is usually coupled with dynamic Fe mineral transformation, which is further influenced by the presence of natural organic matter (NOM). Previous work mainly focused on the interactions between As(V) and Fe minerals. However, there is a lack of both mechanistic and quantitative understanding on the coupled kinetic processes in the As(V) Fe mineral NOM system. In this study, we investigated the effect of humic acids (HA) on the coupled kinetics of ferrihydrite transformation into hematite/goethite and sequestration of As(V) on Fe minerals. Time-resolved As(V) and HA interactions with Fe minerals during the kinetic processes were studied using aberration-corrected scanning transmission electron microscopy, chemical extractions, stirred-flow kinetic experiments, and X-ray absorption spectroscopy. Based on the experimental results, we developed a mechanistic kinetics model for As(V) fate during Fe mineral transformation. Our results demonstrated that the rates of As(V) speciation changes within Fe minerals were coupled with ferrihydrite transformation rates, and the overall reactions were slowed down by the presence of HA that sorbed on Fe minerals. Our kinetics model is able to account for variations of Fe mineral compositions, solution chemistry, and As(V) speciation, which has significant environmental implications for predicting As(V) behavior in the environment.

关键词： Cooling rate   Free volume   Icosahedra-like   Cu50Zr50  

摘要： In this paper, the molecular dynamics simulations are utilized to study the cooling rate effect and to understand the relationship among the local atomic structure, free volume, and mechanical property in Cu50Zr50 metallic glass. The radial distribution function, bond pair analysis technique, and Voronoi tessellation are performed to characterize the structure evolution and local atomic configurations during the cooling process. The results demonstrate that a faster cooling rate results in a higher glass transition temperature and less amount of icosahedra-like clusters. It has been recognized that the concentration of free volumes presents a strong evidence of upward trends as the cooling rate increases. The analyses for the free volume and Voronoi polyhedron indicate that icosahedral-like clusters show a lower free volumes as compared with the rest clusters, revealing that well-developed icosahedra-like clusters in Cu50Zr50 make the system densely packed and lower free volume structure. In addition, the simulated alloy obtained at a lower cooling rate exhibits a higher yield strength and elastic modulus, all of which may attribute to the structure with more densely icosahedral-like clusters and less free volumes.

关键词： Physiology   Stress   Organic compounds   Probes   Polymers  

摘要： Optical probe reorientation experiments and mechanical stress relaxation measurements in the linear response regime were performed on a polymer glass. Segmental dynamics of lightly cross-linked poly(methyl methacrylate) (PMMA) were monitored via both methods at temperatures between 9 and 24 K below the glass transition temperature (T-g) and over the course of 8 h of aging. Relaxation times from the two methods cover a range of similar to 1.7 decades. Similar results were obtained from the two experiments other than a slight difference in the aging rate. A difference of similar to 0.3 decades (a factor of similar to 2) is observed between the optically and mechanically obtained relaxation times, related primarily to the size of the probe. Both experiments give a value near 0.3 for the Kohlrausch-Williams-Watts (KWW) beta parameter. These results provide an important baseline for the interpretation of optical probe reorientation experiments during nonlinear deformation.

关键词： Reaction rates  

摘要： Electrochemical reactions are a critical class of processes strongly influenced by atomic scale effects, where the relationships between local chemical composition, stress, strain, and reactivity are not well understood. Here we investigate the relationship between applied stress and reaction rates for the oxygen evolution reaction on multi-layered graphene using conductive atomic force microscopy. During the reaction, oxygen groups accumulate on the surface and the oxygenation rate increases with applied load. The results also show that the rate is not uniform across the surface, where local edges and defects are more reactive than the basal plane. The results presented here are interpreted in the context of transition state theory, where applied load over the reaction coordinate linearly modifies the energy landscape. This work motivates the general efficacy of atomic force microscopy as a tool to study relationships between local mechanical surface effects and electrochemical reactivity.

关键词： Mechanical Bull Riding   Ferromagnetic resonance   magnetic field   RESONANCE   Mechanical   magnetization   resonant frequencies   direct current   Linear dependence   MICROWAVE   MECHANICAL DAMPING   absorption of shock  

摘要： Mechanical resonance properties of a microcantilever made of a magnetic insulator have been investigated by laser-doppler vibrometry under DC magnetic fields and microwaves. At ferromagnetic resonance conditions, reduction of magnetization along the DC field was detected as a change in the mechanical resonance frequency. Above a microwave power threshold at which the change in the mechanical resonance frequency deviates from the linear dependence on the power, the mechanical damping was found to be enhanced steeply. The result suggests that the non-linear magnetization dynamics gives rise to additional dissipation in the mechanical motion. Published by AIP Publishing.