关键词： 七连杆双自由度并联机构   虚拟样机   运动仿真   结构参数优化  

摘要： 由于汽车驾驶机器人换挡机械手结构的复杂性,使得机械手运动学与动力学分析的具体数学描述较为困难,而计算机虚拟仿真技术,为换挡机械手的特性分析提供了依据。为解决原换挡机械手驱动机构的横摆问题,通过增设选挡推杆及挂挡推杆,改进原七连杆二自由度并联机构。在ADAMS/View中建立了改进后换挡机械手机构的虚拟样机模型并进行了运动仿真,仿真结果验证了改进后的换挡机械手解决原换挡机械手驱动机构横摆问题的有效性。在上述基础上,以选挡推杆及挂挡推杆的长度为设计变量,以换挡机械手的最大驱动力最小为优化目标,利用ADAMS/View中Design Evaluation模块对挡机械手进行了结构参数优化,取得了较好的优化效果,为实际工程运用提供了依据。

关键词： 中外合作办学   教学管理   高校  

摘要： 截至目前，全国经审批机关批准设立或举办的中外合作办学机构有2545家，已经成为我国教育对外开放事业的重要组成部分，但也面临着一些新的挑战。中外合作办学项目的基层教学管理，是高校教学管理的新课题。文章以河南理工大学机械与动力工程学院为例，首先分析了中外合作办学模式下基层教学管理存在的问题，随后提出了解决此类问题的思路和办法。

关键词： MMET   Capture mathematical model   Ideal velocity for capture   Capture velocity error   Dynamics  

摘要： The dynamics of motorized momentum exchange tether (MMET) during and after payloads capture is studied. The ideal velocities of payloads with same mass for capture are analyzed, and a mathematical model of capture is proposed. If the MMET captures the payloads at the ideal velocity, the MMET's orbit and motion state are unchanged. However, considering that capture velocity error exists in practice, and analyzing the velocity error in relation to the payload approaching from the earth as an example, the impact on the MMET's orbital parameters and state motion are investigated during payload capture for different capture velocity errors, including errors in magnitude and direction. The simulation results show that if the payload velocity has only magnitude error, the perigees remain overlapping and the semi-major axes of the changed orbits also continue to coincide after capture;however, the changes in other orbital parameters are approximately proportional to the error. If the payload velocity has both magnitude and direction errors, then all of the orbital parameters change, including the perigee and the direction of the semi-major axis. However, the normal velocity increment caused by the capture's normal velocity error changes the orbital parameters far less than the tangential velocity increment. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.

关键词： 混合动力   工程机械   动力系统   机电一体化  

摘要： 文章从力学的角度分析了曲轴两种耦合振动产生的机理,根据牛顿定律得到轴系耦合振动相互作用的关系表达式,然后针对混合动力工程机械系统的结构特殊性,通过对混合动力系统轴系的简化。对于实际的混合动力系统,由于存在多动力元件给系统主轴结构带来更多的复杂性,轴系因此而产生的振动情况要复杂的多,而且针对上述建立的耦合方程的求解也十分不便。由此,建立实际轴系的几何模型,运用有限元技术和多体动力学方法具体分析混合动力轴系的振动性。

关键词： 多体动力学   机械工程领域   运用  

摘要： 多体系统属于一门综合性课程,涵盖的学科较多,包括计算力学、工程力学等,是机械领域发展的新型课程。近年来,互联网技术也与其良好融合。通过实践证明显示,多动体力学对机械工程领域的推动作用较大,引起了社会的广泛重视。

关键词： 电动汽车   上海交通大学   博士生导师   工程学院   机械   “十五”时期   新能源汽车   产业竞争力  

摘要： 从第一个五年建设计划到“十五”时期，我国走过了近50年的历程。如今，新能源汽车特别是电动汽车已被确立为我国“十三五”规划的重点支持方向之一，而发展电动汽车也早已被确定为提高我国汽车产业竞争力、保障能源安全和发展低碳经济的重要途径。

关键词： Biomechanics   Elastic exoskeleton   Muscle-tendon mechanics   Unconstrained work loops   Biorobotics  

摘要： We present a novel biorobotic framework comprised of a biological muscle-tendon unit (MTU) mechanically coupled to a feedback controlled robotic environment simulation that mimics in vivo inertial/gravitational loading and mechanical assistance from a parallel elastic exoskeleton. Using this system, we applied select combinations of biological muscle activation (modulated with rate-coded direct neural stimulation) and parallel elastic assistance (applied via closed-loop mechanical environment simulation) hypothesized to mimic human behavior based on previously published modeling studies. These conditions resulted in constant system-level force-length dynamics (i.e., stiffness), reduced biological loads, increased muscle excursion, and constant muscle average positive power output all consistent with laboratory experiments on intact humans during exoskeleton assisted hopping. Mechanical assistance led to reduced estimated metabolic cost and MTU apparent efficiency, but increased apparent efficiency for the MTU + Exo system as a whole. Findings from this study suggest that the increased natural resonant frequency of the artificially stiffened MTU + Exo system, along with invariant movement frequencies, may underlie observed limits on the benefits of exoskeleton assistance. Our novel approach demonstrates that it is possible to capture the salient features of human locomotion with exoskeleton assistance in an isolated muscle-tendon preparation, and introduces a powerful new tool for detailed, direct examination of how assistive devices affect muscle-level neuromechanics and energetics. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Contact mechanics   Dry friction   Painleve paradox   Contact regularization   Impact without collision  

摘要： We investigate the dynamics of finite degree-of-freedom, planar mechanical systems with multiple sliding, unilateral frictional point contacts. A complete classification of systems with 2 sliding contacts is given. The contact-mode-based approach of rigid body mechanics is combined with linear stability analysis using a compliant contact model to determine the feasibility and the stability of every possible contact mode in each class. Special forms of non-stationary contact dynamics including "impact without collision" and "reverse chattering" are also investigated. Many types of solution inconsistency and indeterminacy are identified and new phenomena related to Painlev,'s non-existence and non-uniqueness paradoxes are discovered. Among other results, we show that the non-existence paradox is not fully resolvable by considering impulsive contact forces. These findings contribute to a growing body of evidence that rigid body mechanics cannot be developed into a complete and self-consistent theory in the presence of contacts and friction.

关键词： microbial interactions   methane emission   permafrost thawing   water table   soil aggregate  

摘要： The sensitivity of polar regions to raising global temperatures is reflected in rapidly changing hydrological processes associated with pronounced seasonal thawing of permafrost soil and increased biological activity. Of particular concern is the potential release of large amounts of soil carbon and stimulation of other soil-borne greenhouse gas emissions such as methane. Soil methanotrophic and methanogenic microbial communities rapidly adjust their activity and spatial organization in response to permafrost thawing and other environmental factors. Soil structural elements such as aggregates and layering affect oxygen and nutrient diffusion processes thereby contributing to methanogenic activity within temporal anoxic niches (hot spots). We developed a mechanistic individual-based model to quantify microbial activity dynamics in soil pore networks considering transport processes and enzymatic activity associated with methane production in soil. The model was upscaled from single aggregates to the soil profile where freezing/thawing provides macroscopic boundary conditions for microbial activity at different soil depths. The model distinguishes microbial activity in aerate bulk soil from aggregates (or submerged profile) for resolving methane production and oxidation rates. Methane transport pathways by diffusion and ebullition of bubbles vary with hydration dynamics. The model links seasonal thermal and hydrologic dynamics with evolution of microbial community composition and function affecting net methane emissions in good agreement with experimental data. The mechanistic model enables systematic evaluation of key controlling factors in thawing permafrost and microbial response (e.g., nutrient availability and enzyme activity) on long-term methane emissions and carbon decomposition rates in the rapidly changing polar regions.

关键词： Polyoxymethylene   CNT   composites   reinforcement   mechanical properties  

摘要： Carbon nanotube (CNT) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composite film through a simple melting extrusion. An effective approach was developed to clean and modify the surface of as-received CNT with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/CNT composites due to the improved interfacial adhesion between CNT and the matrix. The thermal stabilities of the composites were also improved in the presence of CNT. The studies on crystallization behaviors showed that CNT acted as a nucleation agent for the crystallization of POM domain in composites, and therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of CNT.