考虑摩擦动力学特性的渐开线齿轮润滑分析

以渐开线齿轮为研究对象,综合考虑齿面摩擦、油膜刚度和阻尼的影响,将摩擦动力学特性和齿面形貌考虑到有限长线接触弹流润滑理论(EHL)中,采用多重网格数值求解法获得了渐开线齿轮在不同啮合位置处的动载荷分布,压力与膜厚分布,并对比分析了干摩擦与润滑条件下压力分布的不同特征以及动载荷对油膜分布的影响.计算结果表明:低速时,动载荷接近稳态分布,在单双齿交替点有明显的高频冲击,随着转速的增加,动载荷变化趋于平缓;与干摩擦相比,润滑油膜可以减小最大压力峰值以及入口区和出口区的压力,但对粗糙峰凹谷处压力有所增加.沿啮合线方向,压力在节点位置附近达到最大值,膜厚受动载荷的影响较小,近似呈线性增加趋势.     

外电场作用下三元环状水分子团簇的特性研究

The influence of an external field on the ground states energy and dipole moment of the cyclic water trimer is investigated. Employing the Hartree-Fork method with basis sets 3-21G. The field-induced H-F force including the internal and external forces and clusters equilibrium structures under balance of this force are analyzed. The external field is varied in the 0.001~0.01 a.u. range. It is shown that the magnitude of the external electric field has important effects on these characteristics of the cyclic water trimer. The energy was found to decrease and the dipole moment to increase with the increasing external field. The change of the electronic population of every atom leads the electrostatic field to vary accordingly.     

弹性接触问题的一种新的力学模型

从机械系统的角度出发,描述了系统中构件间局部接触与构件弹性变形间的耦合关系;用多组坐标系描述机械系统中物体的位形;用分离接触边界法描述物体接触边界间的约束;通过接触虚功原理建立了更加广泛意义上的接触系统静力学模型．作为算例,将该力学模型应用于内啮合少齿差行星齿轮多齿啮合问题的研究,揭示了行星齿轮传动中有多对轮齿相互接触,获得了其接触应力分布状态．通过实验验证了力学模型、计算方法和计算结果的正确性．     

渐开线直齿轮弹流润滑条件下的多轴疲劳寿命预估

本文中基于弹流润滑分析和次表面应力建立了渐开线直齿轮多轴疲劳寿命计算模型.相对于传统的单轴疲劳模型,考虑了齿轮固定点的应力历史和材料属性对疲劳寿命的影响,并可以得到齿轮在完整啮合过程中的寿命分布.首先建立齿轮的有限长弹流计算模型,得到齿轮啮合过程中的油膜压力和油膜厚度,再根据油膜压力计算出次表面的应力分布;通过分析齿轮计算区域随啮合过程移动的关系,得到固定点的应力历史,再根据基于应力历史的多轴疲劳寿命模型对齿轮的完整啮合过程进行寿命预估.计算分析了不同粗糙度幅值对轮齿各点寿命大小和分布的影响.研究表明:齿面粗糙度对疲劳寿命的影响显著,随着粗糙度幅值的增大,表层下最大应力向齿面移动,导致低疲劳寿命区向齿面发展且逐步扩展到整个单齿啮合区;而表面粗糙度降低到一定程度则对疲劳寿命的影响变得不明显.     

基于LabWindows/CVI的导弹舵机测控系统设计

舵机是导弹控制系统的重要执行机构,为实现对电动及气动多种型号导弹舵机性能的测试,设计开发了一种基于LabWindows/CVI虚拟仪器的测控系统。介绍了该测控系统硬件组成和软件结构流程,软件设计过程中充分利用多线程、数据库等技术,准确快速完成舵机自动化性能测试。应用结果表明:该舵机测控系统工作稳定,测试精度和自动化程度高,满足舵机试验测试精度和技术指标要求,为舵机的性能研究和维修维护提供了良好的测试环境。     

On the design of external excitations in order to make nonlinear oscillators respond as free oscillators of the same or different type

This study deals with nonlinear oscillators whose restoring force has a polynomial nonlinearity of the cubic or quadratic type. Conservative unforced oscillators with such a restoring force have closed-form exact solutions in terms of Jacobi elliptic functions. This fact can be used to design the form of the external elliptic-type excitation so that the resulting forced oscillators also have closed-form exact steady-state solutions in terms of these functions. It is shown how one can use the amplitude of such excitations to change the way in which oscillators behave, making them respond as free oscillators of the same or different type. Thus, in cubic oscillators, a supercritical or subcritical pitchfork bifurcation can appear, whilst in quadratic oscillators, a transcritical bifurcation can take place.     

Post-divergence and post-flutter analysis of sub-tangentially loaded and damped Beck column using a nonlinear FE procedure

Both post-divergence and post-flutter behaviors of damped Beck columns subjected to a sub-tangentially follower force are rigorously explored using an exact co-rotational frame element. First a linear stability theory of the damped Beck column is summarized using a stability map. A geometrically nonlinear frame element based on the co-rotational formulation is then formulated including mass matrix, Rayleigh damping matrix, and load-correction stiffness matrix due to circulatory forces. The dynamic FE analysis is performed using Newmark integration method. Finally a Beck column model is parametrically analyzed in order to investigate non-linear stability characteristics of the internally and externally damped non-conservative system. In particular, interesting nonlinear behaviors of Beck column quite different from those predicted by the linear theory are reported through static and dynamic nonlinear analysis with variation of sub-tangentiality of the follower force.     

Development of picosecond time‐resolved X‐ray absorption spectroscopy by high‐repetition‐rate laser pump/X‐ray probe at Beijing Synchrotron Radiation Facility

A new setup and commissioning of transient X‐ray absorption spectroscopy are described, based on the high‐repetition‐rate laser pump/X‐ray probe method, at the 1W2B wiggler beamline at the Beijing Synchrotron Radiation Facility. A high‐repetition‐rate and high‐power laser is incorporated into the setup with in‐house‐built avalanche photodiodes as detectors. A simple acquisition scheme was applied to obtain laser‐on and laser‐off signals simultaneously. The capability of picosecond transient X‐ray absorption spectroscopy measurement was demonstrated for a photo‐induced spin‐crossover iron complex in 6 mM solution with 155 kHz repetition rate.     

电动流动分析系统测定纯净水中的硝酸根

提出一种电渗驱动，电泳富集和离子选择电极检测相结合的流动分析方法。电渗泵驱动具有流量稳定，流量调节范围大，流向可逆，流动压强较大和驱动电压安全等优点。电泳的电堆积富集法具有设备简单，富集倍数大和可同时分离异种电荷离子等优点。因而该流动分析系统设备简单，电源通用，操作方便，功能多样且检出限低，可用于超低浓度离子的定量分析。文章还进一步探讨了电泳的电堆积原理，以及各种实验条件对富集的影响，并应用此系统