受电弓摩擦副载流磨损特性研究

为了解决电气化铁路受电弓网中摩擦副的磨损严重问题,采用自行开发的滑动电接触实验机,基于浸铜碳滑板和纯铜接触线为实验材料,在不同条件下进行了载流磨损实验,分析了受电弓滑板的磨损率与接触压力,接触电流和滑动速度之间的关系。基于方差分析表,采用F检验方法比较接触压力、接触电流、滑动速度3个因素对磨损率的影响程度,通过数据拟合的方法,建立磨损率的数学模型,并通过实验验证了所建立模型的有效性。     

转子突加不平衡的碰摩响应

航空发动机等高速旋转机械在工作时会出现叶片掉块、飞失等突加不平衡情况,突加不平衡引发的碰摩可能导致转子失稳和系统的破坏.本文对一个具有非线性支承刚度的跨中转子在突加不平衡时的碰摩响应进行了数值仿真,计算发现系统在突加不平衡发生后将会出现6种不同的碰摩响应形式,给出了参数-突加不平衡转速平面上不同稳态动力学响应模式的边界曲线,同时针对系统在突加不平衡发生后减速通过临界转速时的失稳现象,给出了失稳边界,研究表明增大转子阻尼,降低转静接触刚度和摩擦系数,可以减小失稳的转速范围.分析了参数对系统瞬态响应的影响,瞬态响应随转速的变化会发生跳跃,而瞬态响应随突加不平衡偏心量的变化,在低于共振转速时是平缓增大的,而在高于共振转速时也会有跳跃发生.     

双电层对纳米流体润滑与摩擦影响的MD模拟 (2.东南大学MEMS教育部重点实验室 南京 210096）

采用分子动力学方法对带电和不带电两硅板之间的水分子润滑薄膜进行模拟研究,通过加双电层的水分子薄膜润滑与未加双电层薄膜润滑摩擦属性的对比,发现摩擦系数在存在双电层的情况下比未加双电层时要小,两板相对滑动速度对摩擦系数的影响与未加双电层时相似,相对滑动速度越大,摩擦系数在一定的速度范围内平稳增大.当速度大于某个数值时,摩擦系数增大变快.两板之间水分子以及离子密度或数目分布在靠近壁面的地方较大,中间密度相对较小.     

分形接触干摩擦模型及在围带叶片受迫响应分析中的应用

为了研究含有围带接触面叶片的非线性振动响应,基于三维干摩擦微滑移模型,发展了一种分形接触干摩擦微滑移模型,用于计算考虑接触面形貌的摩擦力.在该模型中,摩擦接触面被离散成一系列接触单元,每个接触单元由一组接触点对来表征该接触单元的粘滞、滑移、分离的摩擦运动状态.采用分形几何模拟接触表面的形貌,基于分形理论和赫兹接触理论,建立接触面粗糙度、正压力、弹性模量、泊松比等参数与接触刚度和摩擦系数的关系.接触面摩擦力由接触刚度、摩擦系数和接触点对的相对位移确定.采用该发展的模型预测了真实围带叶片的受迫振动响应,研究了接触面形貌和初始正压力对围带叶片共振响应的影响.研究结果表明,本文模型能考虑接触面形貌对围带叶片非线性振动响应的影响;接触面形貌改变时,接触刚度和摩擦系数会发生变化,从而影响接触面摩擦力;在该模型中,接触刚度随着正压力的增加而增加,随着粗糙度的增加而减小;摩擦系数随着正压力增加而增加,随着粗糙度的增加,先增大后减小;接触面形貌和初始正压力对围带叶片受迫振动响应有显著影响.     

基于自适应滑动均值和小波阈值的叶尖间隙信号降噪方法

动叶片与发动机机匣之间的叶尖间隙参数是反映航空发动机工作性能和运行安全的关键状态参数之一.提高叶尖间隙信号信噪比是实现高精度叶尖间隙测量的关键,为此提出基于自适应滑动均值和小波阈值的混合叶尖间隙信号实时降噪方法.首先根据叶片转速等信息,估算叶尖间隙信号带宽大小,然后通过动态改变滑动均值滤波的滑动点数来实现自适应低通滤波...     

航空发动机轮盘参数化结构优化

为降低航空发动机轮盘的质量,提高发动机推质比,对发动机转子轮盘进行参数化结构优化设计.研究辐板不同高度处厚度与轮盘径向破裂裕度的关系,以简化轮盘辐板优化方法.以周向破裂转速裕度为约束条件,体积最小为优化目标函数,利用Isight软件和有限元数值模拟方法研究轮盘盘心优化方法,并通过算例计算验证其正确性.结果表明：在满足约束条件的基础上,轮盘体积减小8.66%,最大等效应力减少10.4%.该方法可为航空发动机轮盘轻量化开发提供参考.     

CPU界面传热过程热接触模型研究

该文设计了CPU与散热器之间界面传热实验装置,研究散热器承受不同压力条件下的界面传热规律,建立了CPU界面传热的热接触模型.研究结果表明该模型误差小于5%;随着接触压力和界面温度的提高,接触界面热阻随着减小;接触压力越高,界面热阻随温度变化越慢.     

滑动电接触磨耗测控系统的研究

为了研究受电弓滑板和接触导线的摩擦磨损性能,研制了一台高性能滑动电接触磨耗试验机;其可以实现导线和滑板的均匀磨耗,可在一定范围内实现电流、载荷和速度等方面的单、多因素控制,实现对接触导线与滑板摩擦系数、滑板往复移动次数、接触导线与滑板磨耗量等的实时在线测量和数据储存,同时设计了基于LabVIEW的监测界面和数据处理系统。通过实验,分析了强电流对浸铜碳滑板摩擦磨损的影响,得出摩擦系数和磨耗率随电流的增大而增大的结论。     

汽车钢板弹簧在不同摩擦系数下疲劳寿命研究

在钢板弹簧的结构设计中,疲劳寿命是评价其可靠性的重要指标.为了更准确地预估钢板弹簧的疲劳寿命,利用AN-SYS的非线性求解模块,建立了某载货汽车钢板弹簧的有限元模型,考虑到簧片间接触摩擦因素,首先分析了不同摩擦系数下板簧的等效应力;考虑到应力与疲劳寿命之间的关系,用Fatigue软件进一步分析摩擦系数对疲劳寿命的影响,并通过试验验证了分析结果的可信性.结果表明,随着摩擦系数的增大,钢板弹簧的等效应力降低,疲劳寿命增大.     

滑动电接触摩擦力的BP与RBF人工神经网络建模

在弓网系统中,受电弓滑板与接触网导线之间的摩擦力受机械、电气以及它们之间的交互作用影响。摩擦力与运行速度、接触电流以及受电弓滑板和接触网导线之间的压力载荷有着密切关系。通过对浸金属碳销（滑板）与铜盘（导线）的载流摩擦实验,得出在不同载流、速度以及载荷条件下的摩擦力特性规律。因摩擦力较难实现数学建模,故采用神经网络中应用最广的BP及RBF算法分别建立了以摩擦力作为输出,以接触压力、滑动速度和接触电流为输入的预测模型,并通过Matlab进行仿真与测试。结果表明：两种算法建立的预测模型均有较高的准确度及良好的泛化能力,为进一步波动载荷下弓网滑动电接触摩擦力预测建模的应用提供参考。     

A numerical study of the dimple/gimbal interface in a hard disk drive

A finite element (FE) model for the dimple/gimbal interface of a hard disk drive is developed as a function of normal load, friction coefficient, material properties and dimple geometry. The air bearing force is approximated as a normal load acting on the slider. A rotational acceleration was applied to the dimple to simulate accessing of a hard disk drive suspension during seeking. Results for the relative displacement between the dimple and the gimbal are determined for a typical suspension as a function of normal load, rotational acceleration, friction coefficient, material properties and geometrical parameters of suspension and flexure.     

The Effect of Adhesion on the Static Friction Properties of Sidewall Contact Interfaces of Microelectromechanical Devices

Static friction between sidewall contact surfaces of polycrystalline silicon micromachines was investigated under different contact pressures, vacuum conditions, relative humidity levels, and temperatures. The static coefficient of friction exhibited a nonlinear dependence on the external contact pressure. A difference between in-contact and pull-out adhesion forces was observed due to the elastic recovery of the deformed asperities at the contact interface. The true static coefficient of friction was determined by considering the effects of the dominant adhesion forces (i.e., van der Waals and capillary forces) on the normal force applied at the sidewall contact interface. The roles of van der Waals and capillary forces in the sidewall friction behavior were analyzed in light of results for the interfacial shear strength and the adhesion force. The major benefits of the present friction micromachine and the developed experimental scheme are discussed in the context of static coefficient of friction and adhesion force results obtained under different environmental and loading conditions     

强电流滑动电接触下的最佳法向载荷研究

弓网系统中滑板磨耗大及电力机车受流不稳定是制约我国电气化铁路向高速、重载、安全、稳定运行方向发展的一个关键问题,亟待采取有效的措施进行解决。在特定的载流、滑动速度条件下,表征滑板磨损快慢的滑板磨耗率随法向载荷增大呈现出先减小后增大的“U”型变化趋势,而表征载流稳定性的载流稳定系数随法向载荷增大而逐渐减小,因此选择合适的法向载荷可使滑板磨耗和载流稳定性均达到相对最佳。通过使用浸金属碳滑板与铜导线进行对磨实验,得到了不同实验条件下滑板磨耗率和载流稳定系数的大量实验数据。以此建立了以法向载荷、载流和滑动速度为输入量,以滑板磨耗率、载流稳定系数为输出量的BP神经网络非线性模型,进而利用遗传算法优化了相关参数,并在特定的载流和滑动速度条件下,采用基于粒子群算法的多目标优化方法,确定了滑板磨耗率最低、载流稳定系数最小的最佳法向载荷对应的非劣解。     

Plane strain sliding contact of multilayer magnetic storage thin-films using the finite element method

The sliding contact or scratch behavior of multi-layer thin-films such as those found in magnetic storage disks has been studied using the finite element method. A rigid cylinder sliding over a multilayered thin-film half-space was implemented to simulate the contact between a feature of the recording slider (such as the protrusion on the trailing edge of the slider, which is part of the thermal flying-height control, TFC) and the magnetic storage multilayer disk. The effects of different parameters such as normal load, friction coefficient and TFC radius on the von Mises, shear and principal stresses in the multilayer system were analyzed. Results showed that under sliding conditions, for a given normal load, the friction coefficient influences the location and magnitude of the plastic strain in the multilayer system. Repeated sliding contact was also performed to characterize its effect on the stress and strain behavior under various loading conditions and investigate shakedown behavior.     

Investigation of non-kinematic conical roll bending process with conical rolls

Although high quality cones can be produced with kinematic conical roll bending due to the non-slide condition between the conical rolls and the plate, the process flexibility is limited because the conical rolls cannot be reused to produce cones of different cone angles. In this paper, a non-kinematic three-roll bending process is proposed to reduce manufacture costs by reusing existing conical rolls. In this process, an attachment is added to the top edge of the plate to obtain required circumferential velocity as the top/bottom radius ratio of the desired cone is smaller than the rolls. The top sides of the conical rolls slide on the plate to reduce the local velocity near the top edge and an appropriate velocity near the top edge of the plate can be obtained by adjusting the friction coefficients between the rolls and the plate. This flexible process can provide performance similar to the kinematic conical roll bending process. The process modeling is based on the finite element method under ANSYS/LS-DYNA environment. A relation between the gap size of the bent cone and the friction at the plate/attachment contact interface has been investigated by using numerical simulations. The simulation results give a well bent cone compared with an ideal cone.     

Measurements of particle size distribution and average particle charge in operating a hard disk drive

As the flying height of a slider in a hard disk drive decreases, the slider and disk are more likely to come into contact and generate contamination particles. Since particle contamination can cause serious problems including thermal asperity, it must be prevented to increase storage capacity. In this work, first we measured the size distribution of the particles according to the disk rotational speed by using an APS (aerodynamic particle sizer) and DMA (differential mobility analyzer)–CPC (condensation particle counter). The results showed that mainly submicron particles were generated and particle generation rate increased as the disk rotational speed increased. Then, the electrical current due to particle charge was measured by a Faraday cup. Calculated from experimental data, the average number of elementary charges per particle was from 1.9 to 5.2, and it decreased as the disk rotational speed increased. Finally, SEM (scanning electron microscopy) images of particles were obtained by using a particle sampler designed in our laboratory. With these images, we were able to verify the relation between particle generation rate and disk rotational speed.     

改进型双馈风力发电机最大功率点跟踪策略

针对传统双馈风力发电机最大功率点跟踪极值搜索策略将正弦信号作为搜索信号而很难将正弦信号从总的输出信号中区分出来的问题,提出了一种利用风湍流作为极值搜索信号的改进型最大功率点跟踪策略。该改进策略对叠加风湍流的叶尖速比和功率系数进行傅里叶变换,获得相位差信息,从而确定叶尖速比变化方向,使双馈风力发电机达到最佳运行工作点。仿真结果表明,该改进策略可控制风力发电机转速较好地跟踪风速变化,实现了额定风速以下运行区域的最大风能捕获。     

The effect of surface roughness and contaminant on the dynamic friction of porcelain tile

Surface roughness affects friction, but it is not clear what surface roughness characteristics are better correlated with friction. The average of the maximum height above the mean line in each cut-off length (Rpm) and the arithmetical average of surface slope (deltaa) had the highest correlation with dynamic friction coefficient in a previous study. The previous study was expanded to two different footwear materials and four different contaminants on a porcelain tile in the current investigation. The results showed that dynamic friction decreased as the interface speed and glycerol content in the contaminant were increased due to the hydrodynamic lubrication effect. Deltaa had the highest correlation with friction for most of the test conditions with neolite. For Four S rubber, friction coefficient appeared to have the highest correlation with the parameters related to the surface void volume at 30% glycerol content, related to the surface slope at 70 and 85% glycerol contents, and related to the peak to valley distance at 99% glycerol content. A good indicator of surface slip resistance probably should consist of the surface parameters representing the surface slope, the surface void volume and the surface peak-to-valley distance with the coefficients determined by the system parameters.