ISBN: (纸本)9787030518415

关键词： 臂杆刚度主动控制   空间机械臂   动力学   振动抑制  

摘要： 随着航天科技的迅速发展,空间机械臂需要满足轻量化、高精度及高性能等要求。但空间机械臂的轻量化、大工作半径、高负载能力等特征导致其在运动过程中因臂杆柔性引发结构变形和弹性振动,严重影响机械臂的运动稳定性和末端的定位精度。为解决臂杆柔性带来的动力学问题,本文以基于臂杆刚度主动控制的空间机械臂为研究对象,系统研究了基于臂杆刚度主动控制的空间机械臂动力学建模、实验研究及仿真分析,为空间机械臂的动力学建模和振动抑制提供了理论依据。提出了机械臂的臂杆刚度主动控制方法,建立了空间机械臂的臂杆刚度模型。采用变形耦合法研究机械臂运动过程中臂杆径向弯曲变形对轴向变形的影响,并基于假设模态法对柔性机械臂进行离散化描述,结合Lagrange方程建立了臂杆动力学模型。通过数值求解,随着绳索预紧力的增加,机械臂末端的径向弯曲变形逐渐减小,臂杆刚度逐渐增大,表明本文提出的臂杆刚度主动控制方法可以抑制机械臂运动过程中产生的弹性振动。设计了基于臂杆刚度主动控制方法的平面单自由度实验台,通过调节臂杆内绳索预紧力来调节臂杆刚度,分别研究了机械臂在不同预紧力和不同转速下的机械臂振动特性。研究结果表明,本文提出的臂杆刚度主动控制方法使机械臂发生刚化效应,抑制了臂杆的弹性振动;而在不同转速下,机械臂会随转速的增大发生软化效应,使机械臂的臂杆振动更加剧烈。结合基于臂杆刚度主动控制方法的平面单自由度实验台研究了不同转速下机械臂关节和臂杆的耦合动力学行为,研究发现,机械臂关节在电机和谐波减速器传动过程中产生的非线性摩擦、谐波传动运动滞回以及机械臂反作用于关节的力矩等因素,不仅会引起机械臂关节的动力学响应,还影响机械臂臂杆的动力学响应;此外,机械臂臂杆的动力学响应还受到臂杆刚度和阻尼的影响。通过研究获得了机械臂臂杆振动随绳索预紧力和关节转速的变化规律,并给出了机械臂刚度调节的绳索预紧力最优值。利用ADAMS虚拟样机技术对机械臂的臂杆变刚度模型进行了仿真分析。通过改变仿真参数,研究了材料参数和结构参数对机械臂动力学特性的影响,研究表明材料参数和结构参数对机械臂动力学响应影响较大,合理选择材料参数和结构参数可减小机械臂的动力学响应,这为改善机械臂的动力学性能提供了方法。文章最后推导了漂浮基空间机械臂的动力学模型,结合数值仿真验证了载体与机械臂之间的耦合动力学行为。

摘要： Dukno Yoon是韩国知名的首饰设计师、 艺术家. 他自幼对机械很感兴趣, 机械对他来说是自然的再造甚至替代, 他的首饰作品为人们呈现了一种理解世界的新方式, 对当代艺术首饰的发展具有重要的意义.

关键词： 机械设计制造及其自动化   机械工程专业   材料成型及控制工程   国家特色专业   学院  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院,学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业,其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业,材料成型及控制工程为第三批卓越工程师教育培养计划专业。拥有机械工程一级硕士点、机械工程专业学位点、机械工程领域工程硕士点、工业工程专业学位点,机械制造及其自动化为湖北省重点学科。目前,在校全日制本科学生近2000人,在读研究生160余人,毕业生的一次就业率一直保持在90%以上。学院拥有水电机械设备设计与维护湖北省重点实验室,工程训练中心等,实验室建筑面积1.2万平米,设备仪器总值2000余万元。

摘要： Plug-in hybrid electric vehicles use a powertrain architecture that includes components of traditional powertrains such as internal combustion engines and transmissions, as well as components found in battery electric vehicles. The combination of both technologies enables vehicles to drive emission free, when using the battery as the energy source, while also providing the typical long driving range offered by traditional combustion engines using liquid fuel as the energy source. The goal of this study is to contribute to the design and analysis of machine elements and components used in a series plug-in hybrid vehicle. This vehicle was built for the University of Washington’s team that competes in the EcoCAR 3 Advanced Vehicle Technology Competition. A motorcycle combustion engine was used in the generator system of the vehicle, and a CAE software GT-Power model was used to analyze the engine’s fuel efficiency. Approximations and estimations of model parameters were used to predict the fluid dynamics, combustion process, energy conversion and heat transfer occurring in the engine. Speed and engine load are varied over a broad range to establish a map for brake specific fuel consumption which is data of value for the development of an optimal generator control strategy. The electric drivetrain used in the series hybrid involves single speed reduction gearboxes between motors and drive shafts. Static and fatigue strength analysis is performed to evaluate the strength of an undersized gearbox part for the re-specification of the material and heat treatment used to increase the part’s strength to an acceptable level. The increased number of powertrain components used in hybrid vehicles, particularly the electric battery, lead to an increased vehicle rear mass. This is accommodated for in the analysis of the vehicle’s rear suspension and the design of a new set of coil springs.

关键词： LD converter slag   Mechanical activation   Oxidation   Isothermal kinetics  

摘要： A thermogravimetric investigation was performed to evaluate the kinetic and thermodynamic parameters and the influence of mechanical activation on oxidation of vanadium-bearing LD (Linz-Donawitz) converter slag. Results indicate that the particle size of d(0.5) significantly decreased from 29 mu m to 0.266 mu m after activation, and the specific surface area based on the BET model increased from 1.324 m(2)/g to 3.289 mm(2)/g. Thermogravimetric investigations were separately performed at 650, 700, 750, 800, 850, 900, 950 and 1000 degrees C. Two distinct stages in the oxidation process were identified. The first stage was controlled by nucleation and growth and the second stage was controlled by 3D diffusion. However, the first stage relatively contributed more to the entire process than the second stage. Kinetic study also reveals that mechanical activation exhibited a significant effect on the oxidation of LD converter slag. Mechanical activation significantly reduced the roasting temperature and shortened the roasting time. The corresponding apparent activation energy Ea and frequency factor A changed from 13.01 kJ/mol to 6.59 kJ/mol and 0.247 min(-1) to 0.141 min(-1) for unmilled and milled slags, respectively.

关键词： 有限元   试验设计方法   近似模型   神经网络   支持向量机   遗传算法   结构动力学优化  

摘要： 针对复杂机械结构动力学优化耗费机时过多的问题,以车载炮炮口扰动为优化目标,车载炮总体结构参数为设计变量,建立了车载炮有限元动力学模型,研究样本点的抽取方法,探索并综合比较多种近似模型的建模方法与预测精度,采用近似模型与遗传算法相结合的方法,优化结构参数,优化效果较好,为复杂非线性机械结构的动力学分析、近似模型建模和优化设计提供了参考与指导。建立了车载炮精细网格模型,研究了车载炮各部分之间的连接关系,探讨了车载炮发射过程中边界条件与载荷的建模,在此基础上建立了车载炮上装部分非线性有限元动力学模型。研究对比了引入三种优化准则的最优拉丁超立方试验设计方法;提出了考虑训练样本点与测试样本点之间距离的遗传拉丁超立方试验设计方法。抽取训练样本与测试样本.并在此基础上进行了车载炮有限元动力学分析,获得了相应车载炮炮口扰动。分别研究了多项式响应面方法、Kriging方法、神经网络方法、支持向量机方法等近似模型技术的建模方法,参数选取方法,及参数的选取对近似模型预测精度的影响。提出了使用10-fold交叉验证法与遗传算法相结合的方法来优化模型参数,有效提高了近似模型的泛化能力。在综合考虑建模复杂程度和模型预测精度的基础上,选择最优的近似方法建立近似模型。提出了采用近似模型与遗传算法相结合的方法进行车载炮结构动力学优化。在所建立近似模型的基础上,构造了炮口扰动优化目标函数,采用遗传算法对目标函数进行求解,实现了车载炮总体结构参数的动力学优化。优化结果表明近似模型与遗传算法相结合的方法应用于复杂机械结构动力学优化设计节省机时并且效果较好。

关键词： Hybrid quantum systems  

摘要： We study the dynamics of a bipartite quantum system in a way such that its formal description keeps holding even if one of its parts becomes macroscopic; the problem is related to the analysis of the quantum-to-classical crossover, but our approach implies that the whole system stays genuinely quantum. The aim of the work is to understand (1) if, (2) to what extent, and possibly (3) how the evolution of a macroscopic environment testifies to the coupling with its microscopic quantum companion. To this purpose we consider a magnetic environment made of a large number of spin-12 particles, coupled with a quantum mechanical oscillator, possibly in the presence of an external magnetic field. We take the value of the total environmental spin S constant and large, which allows us to consider the environment as one single macroscopic system, and further deal with the hurdles of the spin-algebra via approximations that are valid in the large-S limit. We find an insightful expression for the propagator of the whole system, where we identify an effective “back-action” term, i.e., an operator acting on the magnetic environment only, and yet missing in the absence of the quantum principal system. This operator emerges as a time-dependent magnetic anisotropy whose character, whether uniaxial or planar, also depends on the detuning between the frequency of the oscillator and the level splitting in the spectrum of the free magnetic system, induced by the possible presence of the external field. The time dependence of the anisotropy is analyzed, and its effects on the dynamics of the magnet, as well as its relation to the entangling evolution of the overall system, are discussed.

摘要： Minus-one ribosomal frameshifting is a translational recoding mechanism widely utilized by many RNA viruses to generate accurate ratios of structural and catalytic proteins. An RNA pseudoknot structure located in the overlapping region of the gag and pro genes of Simian Retrovirus type 1 (SRV-1) stimulates frameshifting. However, the experimental characterization of SRV-1 pseudoknot (un) folding dynamics and the effect of the base triple formation is lacking. Here, we report the results of our single-molecule nanomanipulation using optical tweezers and theoretical simulation by steered molecular dynamics. Our results directly reveal that the energetic coupling between loop 2 and stem 1 via minor-groove base triple formation enhances the mechanical stability. The terminal base pair in stem 1 (directly in contact with a translating ribosome at the slippery site) also affects the mechanical stability of the pseudoknot. The - 1 frameshifting efficiency is positively correlated with the cooperative one-step unfolding force and inversely correlated with the one-step mechanical unfolding rate at zero force. A significantly improved correlation was observed between - 1 frameshifting efficiency and unfolding rate at forces of 15-35 pN, consistent with the fact that the ribosome is a force-generating molecular motor with helicase activity. No correlation was observed between thermal stability and - 1 frameshifting efficiency.