滚动轴承声信号特征提取和诊断试验研究

为解决振动检测方法不能有效识别低速旋转机械滚动轴承故障问题,利用声发射检测方法,建立了滚动轴承低速声发射信号采集试验装置,对模拟人工缺陷滚动轴承声发射信号进行了采集,进而对滚动轴承声发射信号进行总体平均经验模式分解,结合能量矩及相关系数法综合判断分解后各模态分量的真伪,据此提取出特征信号并做出其局部Hilbert边际谱,最后对滚动轴承各种故障模式进行诊断。试验结果表明该诊断方法能准确识别滚动轴承声发射信号故障频率,依据特征频率及幅值大小可对低速滚动轴承故障进行有效诊断。     

学术期刊学者型编辑的研究方向及发展路径

针对编辑专业发展面临的学术研究瓶颈问题,探讨学术期刊编辑可以选择的研究方向及发展路径。结合学术期刊编辑的工作及自身学术发展的经历,从选择研究方向、开展学术研究、开启学术生涯等方面介绍努力发展成为学者型编辑的路径。学术期刊编辑可以结合自身服务的学术领域选择“科研论文写作”“科学研究方法”“薄弱研究主题”等作为研究方向,实现发展成为学者型编辑的目标。学者型编辑的发展与期刊的发展是相辅相成、密不可分的,学者型编辑可以促进学术期刊的发展,学术期刊也可以滋养编辑的发展。     

弹性箔片动压径向气体轴承动特性的实验研究

建立了新型弹性箔片动压气体轴承性能测试实验台，在静载60N、转速9000r／min条件下进行轴承性能测试试验，通过中心插值法获得轴承中心的扰动速度和加速度，采用时域最小二乘法计算不同激振频率下的8个轴承动态线性刚度和阻尼系数，考察了激振频率对轴承动特性系数的影响．结果表明：轴颈中心扰动轨迹为椭圆形且振幅随动态激振频率增加而增大；刚度和阻尼系数的直接项随动态激振频率增加而减小；交叉刚度和阻尼相对激振频率的变化较小，且其值小于直接项；当激振频率与轴颈转动频率相同时，工频成分的影响较大，轴心扰动幅值明显增大，刚度和阻尼的直接项小于其它频率时的值．     

Nonlinear Dynamics of a Rigid Unbalanced Rotor in Journal Bearings. Part I: Theoretical Analysis

The dynamic behaviour of a rigid rotor supported on plain journal bearings was studied, focusing particular attention on its nonlinear aspects. Under the hypothesis that the motion of the rotor mass center is plane, the rotor has five Lagrangian co-ordinates which are represented by the co-ordinates of the mass center and the three angular co-ordinates needed to express the rotor's rotation with respect to its center of mass. In such conditions, the system is characterised not only by the nonlinearity of the bearings but also by the nonlinearity due to the trigonometric functions of the three assigned angular co-ordinates. However, if two angular co-ordinates have values that are generally quite small because of the small radial clearances in the bearings, the system is de facto linear in these angular co-ordinates. Moreover, if the third angular co-ordinate is assumed to be cyclic [18], the number of degrees of freedom in the system is reduced to four and nonlinearity depends solely on the presence of the journal bearings, whose reactions were predicted with the -film, short bearing model. After writing the equations of motion in this way and determining a numerical routine for a Runge–Kutta integration the most significant aspects of the dynamics of a symmetrical rotor were studied, in the presence of either pure static or pure couple unbalance and also when both types of unbalance were present. Two categories of rotors, whose motion is prevailingly a cylindrical whirl or a conical whirl, were put under investigation.     

Nonlinear Dynamics of a Rigid Unbalanced Rotor in Journal Bearings. Part II: Experimental Analysis

In the first part of the present investigation [9], the dynamic behaviour of a rigid rotor supported on plain journal bearings was studied, focusing particular attention on its nonlinear aspects. In the present paper an experimental confirmation of the theoretical results is sought. The steel rotor of the experimental rig was given a constant circular cross section in order to fix in an easy way the two distances between supports corresponding, respectively, to the values of the parameter assigned in [9]. Two steel rings, each one with a series of holes and a clamping screw, were mounted onto the rotor with a small clearance. This arrangement made it possible to fix the positions of the rings and their holes respect to the rotor, so as to realize a pre-estabilished unbalance. The two bronze journal bearings were characterised by a relatively low length/diameter ratio, and a relatively high value of the radial clearance and were lubricated with oil delivered from a thermostatic tank. In this way, despite the relative lightness of the rotor, the dimensionless static eccentricity _s was given the high values that were apt to realize the operating conditions assumed in the theoretical analysis. The rotor was driven by means of a d.c. motor connected to a toothed belt-drive. Varying the rotor speed in the range 1000 ÷ 10000 r.p.m., made it possible to assign the values of the modified Sommerfeld number assumed in the theoretical analysis. Three pairs of eddy-current probes were mounted in order to detect the trajectories of three points (C₁, C and C₂) suitably fixed along the rotor axis. These orbits were finally put in comparison with the corresponding ones previously obtained through numerical analysis. The comparison pointed out that the experimental data were in good agreement with the theoretical predictions, despite the approximations that characterise the theoretical model and the unavoidable errors affecting measures in the course of the experimental test.     

Modulation of Energy Conversion Processes in Carbonaceous Molecular Bearings

The energetics and photodynamics of carbonaceous molecular bearings with discrete molecular structures were investigated. A series of supramolecular bearings comprising belt‐persistent tubular cycloarylene and fullerene molecules accepted photonic stimuli to afford charge‐separated species via a photoinduced electron transfer process. The energy conversion processes associated with the photoexcitation, however, differed depending on the molecular structure. A π‐lengthened tubular molecule allowed for the emergence of an intermediary triplet excited state at the bearing, which should lead to an energy conversion to thermal energy. On the other hand, low‐lying charge‐separated species induced by an endohedral lithium ion in fullerene enabled back electron transfer processes to occur without involving triplet excited species. The structure–photodynamics relationship was analyzed in terms of the Marcus theory to reveal a large electronic coupling in this dynamic supramolecular system.     

小孔节流气体静压润滑的离散化和计算收敛

通过在雷诺方程式中增加一流量项,以避免求解雷诺方程时,为满足流量条件而求解压力梯度所带来的噪声和误差,并将不同坐标系内的雷诺方程式变换成为相同形式,以简化数值计算;对加权余量法和变分求极值法这2种将微分方程离散化的方法进行了分析;探讨了小气膜时出现发散的原因并提出了应对措施。     

Rotordynamic analysis of systems with a non-linear model of tilting pad bearings including turbulence effects

An analytical model of a tilting pad bearing was developed based on the short bearing assumption with the turbulence effect included. In order to determine its influence on the dynamic behavior of the rotor, this model was compared against one without the turbulence effect through a simulation of a Jeffcott/Laval rotor supported by a couple of bearings. Both models were also used to determine the influence of geometric parameters on tilting pad bearing making use of the aforementioned system at different rotor speeds. When analyzing the results, the parameters which presented the largest influence were: pad preload, number of segments, radial clearance, pad position, and pad pivoting angle. As the pad moment of inertia and the pivoting distance have changed the shaft motion only a few microns, their effects can be neglected. The bearing model with turbulent flow effect has generated higher hydrodynamic forces when compared to the one without this effect, which remarks the importance of considering such phenomenon during the analysis of the high speed hydrodynamic bearings.     

High-speed electrospindle running on air bearings: design and experimental verification

In high-speed machining there are a number of applications in which the spindle is supported by air bearings. This type of bearings has very low friction and wear, resulting in virtually unlimited life. If the system is designed correctly the radial stiffness on the tool is comparable to that of ceramic ball bearings. A mathematical model of rotor-air bearing system and experimental work on high-speed spindle for machining applications are presented. The model is numerically solved paying special attention to boundary condition of supply ports. The discharge coefficient c _d is considered on the basis of experimental findings. The influence of clearance and supply port diameter is discussed for radial bearings and axial thrust bearings. The aim is to find an optimum solution representing the compromise between high stiffness, supply flow and stability. The prototype of a high-speed electrospindle running on air bearings is described. The rotor, 50 mm in dia. and weighing 7 kg, is designed for 100 krpm. The spindle is driven by a high frequency asynchronous motor featuring closed loop speed control. Experimental stiffness curves are shown at different supply pressure ratings.