关键词： 拖拉机   自动变速器   换挡   模糊控制  

摘要： 为了改善拖拉机机械式自动变速器的换挡品质,减少驾驶员劳动强度,以换挡过程的冲击度作为换挡品质的主要衡量参数,设计了自动变速器的电-液执行机构,拖拉机自动变速器采用模糊控制的方法。试验结果表明,换挡过程中的冲击度最大值发生在离合器完全接合时刻,为4.76 m/s3,小于我国的推荐值17.64 m/s3,所设计的电-液执行机构及其模糊控制方法能够改善换挡品质,对于拖拉机自动换挡系统是可行的。

关键词： 农业机械化   现代农业   农机购置补贴   水稻插秧机   劳动力转移   小型收割机   注入   柏  

摘要： 河北省柏各庄农场目前年种植面积稳定在25万亩左右。每年到了秋收季节，雇工难、割稻慢，尤其是曹妃甸和冀东油田的开发建设使大量劳动力转移到二三产业，人工割稻成本日益增加，繁重的秋收任务还要借助滦南、丰南等周边县区大量劳动力的加入才能完成。对此，农场抓住国家加大农机购置补贴的机遇，出台鼓励政策，加快推进农业机械化。对购置水稻插秧机、小型收割机的，财政予以30％的购机补贴；购置大型收割机的，每台再补贴2万元。

关键词： U形螺栓   弯曲成形   动力头   机械   应用   展开长度   M30   异形件  

摘要： 我厂生产的各种U形螺栓（见图1）直径不等（M12～M30×1.5）,展开长度有的超过1300mm。此类异形件在一般冲床上压缩成形时,由于受现有的冲床设备行程高度所限,会给生产带来诸多不便。

关键词： locomotion   walking   step length   metabolic cost   exoskeleton   ankle   human   inverse dynamics   joint power   efficiency  

摘要： We examined the metabolic cost of plantar flexor muscle-tendon mechanical work during human walking. Nine healthy subjects walked at constant step frequency on a motorized treadmill at speeds corresponding to 80% (1.00ms(-1)), 100% (1.25ms(-1)), 120% (1.50ms(-1)) and 140% (1.75ms(-1)) of their preferred step length (L*) at 1.25ms(-1). In each condition subjects donned robotic ankle exoskeletons on both legs. The exoskeletons were powered by artificial pneumatic muscles and controlled using soleus electromyography (i.e. proportional myoelectric control). We measured subjects' metabolic energy expenditure and exoskeleton mechanics during both unpowered and powered walking to test the hypothesis that ankle plantarflexion requires more net metabolic power (Wkg(-1)) at longer step lengths for a constant step frequency (i.e. preferred at 1.25ms(-1)). As step length increased from 0.8L* to 1.4L*, exoskeletons delivered similar to 25% more average positive mechanical power (P= 0.01;+0.20 +/- 0.02 Wkg(-1) to + 0.25 +/- 0.02Wkg(-1), respectively). The exoskeletons reduced net metabolic power by more at longer step lengths ( P= 0.002;-0.21 +/- 0.06Wkg(-1) at 0.8L* and -0.70 +/- 0.12Wkg(-1) at 1.4L*). For every 1 J of exoskeleton positive mechanical work subjects saved 0.72 J of metabolic energy ('apparent efficiency'=1.39) at 0.8 L* and 2.6 J of metabolic energy (`apparent efficiency'= 0.38) at 1.4L*. Declining ankle muscle-tendon `apparent efficiency' suggests an increase in ankle plantar flexor muscle work relative to Achilles' tendon elastic energy recoil during walking with longer steps. However, previously stored elastic energy in Achilles' tendon still probably contributes up to 34% of ankle muscle-tendon positive work even at the longest step lengths we tested. Across the range of step lengths we studied, the human ankle muscle-tendon system performed 34-40% of the total lower-limb positive mechanical work but accounted for only 7-26% of the net metabolic cost of walkin

关键词： 农用设备   农业机械   农业   显示器   林业   园艺机具   图形符号   指示装置构件   指示   剪草机   操作元件   机动   符号   拖拉机  

标准号: NF U02-105-2-2009

摘要： La présente partie de l'ISO 3767 établit les symboles à utiliser sur les commandes de l'opérateur et autres indicateurs sur les tracteurs et les machines agricoles tels que définis dans l'ISO *** symboles donnés dans la présente partie de l'ISO 3767 s'appliquent aux commandes et aux indicateurs spécifiques aux tracteurs et aux machines agricoles telles que les moissonneuses-batteuses, les récolteuses de coton et les récolteuses de fourrage.

关键词： Molecular dynamics  

摘要： Carbon nanotube (CNT) polymer-matrix composites exhibit promising properties as structural materials for which appropriate constitutive models are sought, to predict their macroscale behavior. The reliability of determining the homogenized response of such materials depends upon the ability to accurately capture the interfacial behavior between the nanotubes and the polymer matrix. In this work, molecular dynamics simulations, using the Consistent Valence Force Field (CVFF) to describe the atomistic interactions, are used to study nanoscale load transfer between polyethylene and a graphene sheet, a model system chosen to characterize the force-separation behavior between CNTs and the polymer matrix. Separation studies are conducted for both opening as well as sliding modes and cohesive zone parameters such as peak traction and energy of separation are evaluated for each mode. Studies are also carried out to investigate the effect of tension and compression on sliding mode separation. Size dependence studies are conducted utilizing different sizes of the computational domain and different boundary conditions, to obtain the representative volume element and connect to continuum level properties. These results set the stage for continuum length-scale micromechanical models which may be used in determining the overall material response, incorporating interfacial phenomena.

关键词： Aluminum Matrix Nanocomposite   Silicon-Carbide Nanoparticle   Interface   Molecular Dynamics Simulation   Modified Embedded Atom Method   Elastic Modulus   Yield Stress   Finite Element Analysis   Interatomic Potential  

摘要： Mechanical properties and interfacial structure of an aluminum (AI) matrix nanocomposite reinforced by nanometer-sized beta-SiC particles are studied through molecular dynamics (MID) simulations. The modified embedded atom method (MEAM) is used to describe the atomic interactions, and the simulated annealing technique is employed to locate the global minimum of the total system energy. Tension tests at constant strain rates are simulated using both displacement and periodic boundary conditions. The stress-strain curves of the AI/SiC nanocomposite are obtained from the simulated tension tests using the average virial stress and true strain, from which the effective elastic modulus and yield stress are determined. The numerical results indicate that the MD model employing the periodic boundary conditions can better describe the macroscopic properties of the nanocomposite. For comparison, a finite element (FE) analysis is performed by considering that the nanocomposite consists of only two phases (i.e., Al matrix and beta-SiC particle, with the interfacial zone neglected). The MID simulation results reveal that both the effective elastic modulus and yield stress are much higher than those predicted by the two-phase FE model which ignores the interphase near the SiC particle surface. Also, the MID model predicts that the yield stress of the nanocomposite with 1.0 vol% beta-SiC nanoparticles is significantly higher than that of aluminum alloy A356. In addition, the MD simulations show that the Al atoms tend to aggregate around the SiC particle surface to form an interfacial layer. These findings agree with what was reported in existing atomistic and experimental studies.

关键词： Kinetic parameters   Transition states   Reaction mechanisms   Imidazoles   Gases  

摘要： The primary and secondary deuterium kinetic isotope effects as well as leaving-group fluorine kinetic isotope effects have been calculated for the base-promoted elimination of hydrogen fluoride from 4-fluoro-4-(4'-nitrophenyl)butane-2-one in 75% aqueous methanol solution. The elimination was studied for both formate and imidazole as the catalytic base;and reactant and transition state structures and vibrational frequencies have been calculated by including the base explicitly and by including the solvent by an implicit solvation model that includes both electrostatics by class IV charges and first-solvation-shell effects by atomic surface tensions. We used the M06-L density functional for all calculations. The optimized stationary points, the geometry changes along the solution-phase minimum free energy path, and the solution-phase free energy profile indicate that the elimination reaction occurs concertedly but asynchronously via an E1 cb-like transition state. Reaction rates were calculated by the equilibrium solvation path method, using variational transition state theory with multidimensional tunneling. The primary deuterium kinetic isotope effects are calculated to be large: 1.67 and 5.13 for formate and imidazole, respectively. The corresponding C-4-secondary deuterium kinetic isotope effects are 1.044 and 1.044, and the leaving group fluorine kinetic isotope effects are respectively 1.020 and 1.015.

关键词： 自动榴弹发射器   动力学仿真   ADAMS   架座   有限元分析  

摘要： 本文简要地介绍了目前自动榴弹发射器在国内外的发展现状及研究方向,在现有的自动榴弹发射器的基础上确定了某高初速35mm自动榴弹发射器的总体方案布置及主要零部件设计方案。 提出了刚性固连式、弹簧枪身后坐缓冲器式、驻锄缓冲式、组合缓冲式和机架一体驻锄缓冲式五种不同的架座安装方案,为解决发射初速与后坐力之间的矛盾提供了方案支持。 运用经典内弹道学和武器气体动力学的相关理论建立了榴弹发射器火药气体压力计算的数学模型,通过调整不同参数对榴弹初速与火药气体压力之间进行了合理的匹配,给出了初速分别为300m/s、350m/s和400m/s时武器系统较为合理的膛压和导气室压力值。 运用多刚体系统动力学的相关理论和仿真软件ADAMS建立了武器系统五种不同方案下的虚拟样机模型,通过对不同方案进行动力学仿真分析,得到了不同初速时武器系统各特征参数的运动规律,并进行了方案分析和对比,得出了解决武器初速与后坐力之间矛盾的最佳方案。 运用有限元分析软件Patran和Nastran对现有的QLZ87式35mm自动榴弹发射器的架座进行静强度分析,校核现有架座是否满足高初速发射的强度要求。如不满足要求,则在现有架座的基础上确定高初速武器系统架座的修改方案。 对改进后的架座模型进行静态和瞬态分析,反求架座承受的最大应力,校核架座的强度。对武器系统进行模态分析,研究其固有频率对武器系统射击稳定性和射击精度的影响。

关键词： 机械臂   运动学   动力学   工作空间   ADAMS  

摘要： 由于核电高压容器的特殊性,对其进行磨削加工的机械臂就有着更高的要求。为了提高国内企业的竞争力,探索高压容器高效磨削的机理,填补国内在高压容器高效智能磨削方面的空白,利用“万能磨削”之称的砂带磨削技术开发核电高压容器砂带磨削机械臂已变得十分紧迫。论文以开发核电高压容器砂带磨削机械臂为契机,进行了六自由度机械臂的运动学与动力学研究。 建立了六自由度的核电高压容器砂带磨削机械臂的简化模型,利用D-H法建立该机械臂的各杆件坐标系,并计算出了数学模型。在一定运动轨迹下,求出了各关节的运动参数以及末端执行器的运动轨迹,为该机械臂的静力学、运动学、动力学分析做好了准备。由于该机械臂体型较大,工作空间对于各组成杆件的设计很重要,论文采用了蒙特卡罗概率算法对该机械臂工作空间进行了求解,在MATLAB中输出机械臂的工作空间图,为确定各杆件尺寸建立了很直观的依据。基于第二类拉格朗日方程建立了该机械臂的动力学方程,并结合ADAMS及MATLAB求解出各关节驱动力矩(或力)。论文运用三维建模软件Pro/E建立了核电高压容器砂带磨削机械臂三维模型,通过Pro/E与ADAMS之间无缝接口软件MECHANISM/Pro把该模型数据导入ADAMS。以一定运动轨迹下的各关节的速度函数作为各关节的驱动,通过仿真可以清楚地观察到该机械臂运动情况,利用ADAMS强大的测量功能测得该机械臂运动的一系列运动特性参数,如关节位移、速度、加速度、驱动力矩(或力)、杆件动能的大小,从而可以为各关节的驱动电机的选择提供依据。最后将理论计算得到的驱动力矩(或力)与模型中测量得到的驱动力矩(或力)相比较,从而验证了该机械臂动力学方程的正确性。 论文为核电高压容器砂带磨削机械臂的下一步研究奠定了一定的基础,完成了该机械臂的前期开发工作。