关键词： Revolute joint clearance   contact forces   multibody dynamics   Kriging metamodel   genetic algorithms  

摘要： Over the past two decades, extensive work has been conducted on the dynamic effect of joint clearances in multibody mechanical systems. In contrast, little work has been devoted to optimizing the performance of these systems. In this study, the analysis of revolute joint clearance is formulated in terms of a Hertzian-based contact force model. For illustration, the classical slider-crank mechanism with a revolute clearance joint at the piston pin is presented and a simulation model is developed using the analysis/design software MSC. ADAMS. The clearance is modeled as a pin-in-a-hole surface-to-surface dry contact, with an appropriate contact force model between the joint and bearing surfaces. Different simulations are performed to demonstrate the influence of the joint clearance size and the input crank speed on the dynamic behavior of the system with the joint clearance. In the modeling and simulation of the experimental setup and in the followed parametric study with a slightly revised system, both the Hertzian normal contact force model and a Coulomb-type friction force model were utilized. The kinetic coefficient of friction was chosen as constant throughout the study. An innovative design-of-experiment (DOE)-based method for optimizing the performance of a mechanical system with the revolute joint clearance for different ranges of design parameters is then proposed. Based on the simulation model results from sample points, which are selected by a Latin hypercube sampling (LHS) method, a polynomial function Kriging meta-model is established instead of the actual simulation model. The reason for the development and use of the meta-model is to bypass computationally intensive simulations of a computer model for different design parameter values in place of a more efficient and cost-effective mathematical model. Finally, numerical results obtained from two application examples with different design parameters, including the joint clearance size, crank speed, and c

关键词： Molecular Dynamic Simulation   Hepatic Encephalopathy   Glutamine Synthetase   Glutamine Synthetase Activity   Mutant R324C  

关键词： Nucleation   High resolution X-ray diffraction   Growth from solutions   Organic compounds   Dielectric materials  

摘要： Single crystals of brucinium 2-carboxy-6-nitrophLhalate clihydraLe (B2C6ND) have been grown by the slow evaporation solution technique at room temperature using water-ethanol (1:1) mixed solvent. The metastable zone width and induction period have been experimentally determined for the growth conditions. Nucleation kinetics and fundamental growth parameters such as surface free energy, critical radius and critical free energy change are also evaluated according to the experimental data. The crystal system and the lattice parameters have been confirmed by single crystal X-ray diffraction. The crystalline perfection of the grown B2C6ND crystals has been characterized by HRXRD method. Optical band gap and Urbach tail width of the sample have been studied employing UV-Vis absorption spectroscopy. The Vickers microhardness number (11,), yield strength (cu) and stiffness constant (C-11) of the grown crystal have been evaluated. The dielectric permittivity and dielectric loss of the grown B2C6ND crystal have been investigated as a function of frequency in the temperature range 313-353 K. The laser damage threshold value of B2C6ND crystal was estimated to be 2.8 GW/cm(2) using a NcLYAG laser. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Amorphous metals   Copper   Nickel   Glass transitions   Activation energies  

摘要： The dynamics of the Johari-Goldstein (JG) beta relaxation and the alpha relaxation in bulk metallic glasses (MGs) has been investigated by using mechanical spectroscopy combined with the Coupling Model. The beta relaxations of MGs exhibit different behaviors such as peaks, humps, and excess wings due to the different fluctuations of the chemical interactions among the constituting atoms. A universal correlation between the beta relaxation and the alpha relaxation is generally found by their activation energies and relaxation times as well as the non-exponentiality parameter of the alpha relaxation, which can be predicted quantitatively from the Coupling Model. Based on the quasi-point defects theory, a correlation factor chi shows a broad peak along with the beta relaxation, suggesting that the concentration and the correlation degree of the string-like configurations involved in the beta relaxation vary with increasing temperature, which challenges the previous view that the system is in an iso-configuration state below T-g and may shed new light on the nature of the JG beta relaxation in metallic glasses. (C) 2014 AIP Publishing LLC.

关键词： 农业机械总动力   灰色预测   背景值  

摘要： 随着现代科技的不断发展，农业机械化程度不断提高，而农业机械总动力是衡量一个国家农业现代化程度的重要指标。传统的灰色预测方法无法更加准确地进行预测，因此，提出了基于背景值优化的GM（1，1）模型预测，并用2003～2012年的数据对模型进行验证对比，解释了此方法相比单纯的灰色预测精度有所提高，可以预测我国未来数年内农业机械总动力的拥有量，便于国家对农机发展的宏观调控。

关键词： Bekker理论   履带   多体接触  

摘要： 对连续采煤机履带建立动力学模型、考虑不同情况对履带行走系统进行了多体接触动力学分析。并以Bekker理论为基础,利用多体动力学软件得到不同工况下履带的受力状态。

关键词： 空间机械臂   关节   辅助对接   关节动力学   力矩控制  

摘要： 针对空间机械臂辅助对接任务中的复杂关节力矩控制问题,建立了含间隙、非线性刚度及啮合阻尼的多级行星齿轮传动复杂关节精细动力学模型,该模型不仅考虑了齿轮啮合刚度,而且考虑了齿轮轴的扭转刚度。提出了一种基于关节动态扭转变形的关节力矩测量方法,并以此建立关节力矩控制系统,利用Runge-Kutta算法对关节精细动力学模型进行了数值计算。计算结果表明,此关节力矩控制方法约有1.7%的稳态误差,能满足关节力矩控制的需要;基于关节动态扭转变形的关节力矩测量方法有效地解决了提高关节力矩测量精度与保持传感器刚度之间的矛盾。

关键词： 螺栓结合面   弹簧阻尼单元   虚拟材料模态分析   准确性  

摘要： 机械结构中螺栓结合面动力学建模的准确性会直接影响其固有频率的准确性。通过计算模态分析与实验模态分析,以某床身螺栓结合面为例,对比分析了弹簧阻尼单元法与虚拟材料法等效螺栓结合面动力学模型,发现运用虚拟材料法等效螺栓结合面动力学模型准确性更高。

关键词： 机械工业信息研究院   自动化   装备制造业   长石   质量效益   增长阶   中国   速度  

摘要： 中国装备制造业已经进入新的历史发展阶段，新世纪以来的十年中，中国装备制造业以每年25％的平均增长速度进行高速增长，但自“十二五”以来我国装备制造业的增长速度持续低迷。已经迈人以转型升级为主基调的中高速增长阶段。现在这个阶段我们认为，整个装备制造业有几个突出的问题，第一，质量效益不高，