用固体润滑剂改善汽车刮水胶条使用性能的研究

作者将含有MoS_2和石墨的不同配方的固体润滑涂料刷涂在几种国产汽车刮水胶条上,并分别于干摩擦和水润滑的两种刮刷状态下,就固体润滑剂改善刮水胶条的擦拭性能进行了试验研究,指出这是使刮水胶条降低擦拭阻力、提高刮刷效果的可行途径,同时强调配制涂料时应当选用颗粒细小而均匀的固体润滑剂粉末。     

雨刮器非线性摩擦振动的稳定性与分岔特性

针对雨刮器建立2自由度非线性摩擦振动动力学模型,基于复模态理论计算复特征值并进行稳定性及其对刮刷速度的依赖性分析;通过数值计算分析摩擦振动对刮刷速度的分岔特性,并利用相轨迹、庞加莱映射、频谱特性分析不同刮刷速度下的非线性振动现象.研究发现:摩擦-速度特性的负斜率是导致系统不稳定的根本原因,增大刮刷速度有利于提高系统的稳定性;在高、低刮速区,随着刮刷速度的下降,系统振动形态遵循周期→准周期→混沌的演化规律,并会伴随显著的粘滑振动;仅高速区的周期振动和非振动条件下,刮刷时无附加的粘滑振动.     

Bifurcation phenomena of the reversal behavior of an automobile wiper blade

Reducing the noise generated by windshield wipers during reversal is desirable. As a fundamental first step in exploring the cause of this noise, the present study attempts to theoretically and experimentally clarify the dynamics of the behavior of the wiper blade near the reversal point. First, an experiment is conducted to observe the reversal behavior using the cross sectional model of the blade rubber. In order to theoretically explain the experimentally observed phenomena, an analytical link model of the wiper blade is introduced. The reversal behavior of a blade is theoretically investigated through the bifurcation analysis by considering Coulomb??s friction during reversal. Then we show the continuous variation of the angle of blade rubber, and predict a rapid variation of the normal force, which can cause reversal noise, acting to the blade rubber.     

Bulldozer blade control

A simple control system for controlling a bulldozing blade was developed and tested. Both controls of the bulldozing load acting on the bulldozer blade and the blade position control were validated through an operational test. It was observed that the application of this control system could not only reduce the frequent up and down actions of adjusting the bulldozer blade considering the conditions of the load applied and the irregularity of terrain surface, but also could allow the operator to concentrate on the steering during the operation of earth moving.     

A moderate deflection composite helicopter rotor blade model with an improved cross-sectional analysis

The compatibility between a composite beam cross-sectional analysis based on the variational asymptotic approach, and a helicopter rotor blade model which is part of a comprehensive rotorcraft analysis code is examined. It was found that the finite element cross-sectional analysis code VABS can be combined with a moderate deflection rotor blade model in spite of the differences between the formulations. The new YF/VABS rotor blade model accounts for arbitrary cross-sectional warping, in-plane stresses, and moderate deflections. The YF/VABS composite rotor blade model was validated against experimental data and various rotor blade analyses by examining displacements and stresses under static loads, as well as aeroelastic stability of a composite rotor blade in hover, and forward flight vibratory hubloads of a four bladed composite rotor.     

CONTROL OF BLADE FLUTTER USING CASING WITH ACOUSTIC TREATMENT

Control of blade flutter by use of a nonrigid wall may have several advantages compared with the existing method of suppressing blade flutter; but it indeed leads to numerous theoretical problems which have never been clearly elucidated by the existing theories. In the present investigation a new lifting surface model has been suggested based on the application of generalized Green's function theory and double Fourier transformation technique, which is expressed as various upwash integral equations and the corresponding kernel function. In particular, it is found that the change of wall boundary condition not only affects the eigenvalues of the system but also the eigenfunction normalizing factor in comparison with a rigid boundary condition, and it is these variations that finally affect the flow and acoustic field. In addition, the numerical results show that whether a nonrigid wall has positive or negative effect on suppressing blade flutter will mainly depend on what admittance value the wall possesses. It is clear that this conclusion has two implications. One is that there is indeed some possibility for designing a liner for suppressing blade flutter. The second is that modern jet engines using a nonrigid wall or liner to suppress the noise can introduce a detrimental effect on blade flutter stability.     

Dynamics of windscreen wiper blades: Squeal noise,reversal noise and chattering

The motion of a windshield wiper blade is modelled by a mass-spring-damper system on a moving frictional surface. The system dynamics is time-varying, since three different regimes of motion, characterized by different degrees of freedom, are possible. Indeed the system, which schematizes a blade cross-section, can experience stick and slip motions when it is in contact with the glass surface, and free-flight motion when it is detached. The contact between the system and the surface is governed by Stribeck׳s friction law and Poisson׳s impact law, which make the dynamics non-smooth. The model is numerically implemented in an event-driven code, and simulations are performed which reproduce the three basic classes of undesired oscillations observed in the motion of real windscreen wipers, i.e., squeal, reversal and chattering noises. Attention is focused on the causes of these vibrations, and remedies for reducing or avoiding them are proposed.     

A framework for CFD analysis of helicopter rotors in hover and forward flight

A framework is described and demonstrated for CFD analysis of helicopter rotors in hover and forward flight. Starting from the Navier–Stokes equations, the paper describes the periodic rotor blade motions required to trim the rotor in forward flight (blade flapping, blade lead‐lag and blade pitching) as well as the required mesh deformation. Throughout, the rotor blades are assumed to be rigid and the rotor to be fully articulated with separate hinges for each blade. The employed method allows for rotors with different numbers of blades and with various rotor hub layouts to be analysed. This method is then combined with a novel grid deformation strategy which preserves the quality of multi‐block structured, body‐fitted grids around the blades. The coupling of the CFD method with a rotor trimming approach is also described and implemented. The complete framework is validated for hovering and forward flying rotors and comparisons are made against available experimental data. Finally, suggestions for further development are put forward. For all cases, results were in good agreement with experiments and rapid convergence has been obtained. Comparisons between the present grid deformation method and transfinite interpolation were made highlighting the advantages of the current approach. Copyright © 2006 John Wiley & Sons, Ltd.     

Dither signals with particular application to the control of windscreen wiper blades

This study verifies chaotic motion of an automotive wiper system, which consists of two blades driven by a DC motor via the two connected four-bar linkages and then elucidates a system for chaotic control. A bifurcation diagram reveals complex nonlinear behaviors over a range of parameter values. Next, the largest Lyapunov exponent is estimated to identify periodic and chaotic motions. Finally, a method for controlling a chaotic automotive wiper system will be proposed. The method involves applying another external input, called a dither signal, to the system. Some simulation results are presented to demonstrate the feasibility of the proposed method.     

盘-销摩擦系统摩擦接触力测试与特性分析

测量分析动态摩擦接触力是研究摩擦振动与噪声发生机理的关键.本文中建立了盘-销系统摩擦尖叫试验台架,成功再现了摩擦尖叫.采用三向力传感器对有无摩擦尖叫条件下的动态摩擦接触力进行了测量,并利用小波信号分解、概率密度函数、功率谱密度函数、时频分析等方法进行了分析和讨论.研究发现:在发生摩擦尖叫时,动态摩擦力和法向力发生高频波动,是系统噪声的激励源;无摩擦尖叫时的摩擦力和法向力的动态分量为典型的白噪声随机过程,呈非高斯分布;有摩擦尖叫时的摩擦力和法向力为窄带高频类谐波信号,摩擦力呈非高斯分布,而法向力近似为高斯分布;模态耦合是导致盘-销系统发生动态接触力高频波动以及摩擦尖叫的原因.     

Effects of pretwist and presetting on coupled bending vibrations of rotating thin-walled composite beams

A refined dynamic theory of rotating blades modeled as anisotropic composite thin-walled beams, experiencing the flapping-lagging-transverse shear coupling is presented. The structural model encompasses a number of non-standard features, such as anisotropy and transverse shear, pretwist and presetting angles, the presence of a rigid hub on which the beam is mounted, and the rotatory inertia. The developed theory and the methodology used to determine the eigenfrequency characteristics are validated against the results available in the literature, and new results emphasizing the influence played by the ply-angle, pretwist and presetting, coupled with that of the rotating speed on blade free vibration characteristics are supplied, and pertinent conclusions are outlined.     

Dynamic Study of a Structure with Flexion-Torsion Coupling in the Presence of Dry Friction

In aero engines, blade vibrations are frequently reduced by centrifugal flyweights, which exert a dry friction force per unit length under blade platforms. The response of this system to a periodic load has been analysed experimentally and theoretically. From a model having mode shapes similar to those of a blade, and a dry friction link per unit length, we show that the presence of the dry friction link is very effective in reducing vibrations for a range of excitation loads. The theoretical analysis is based on the Craig and Bampton mode synthesis, the rigid movement of the platform in its plane and the replacing of the linear dry friction link by several discrete parallel systems. Direct integration of the equations of motion is carried out by using the Newmark method. The comparison with experimental results is good. This method can easily be extended to more complex structures and shows that the dry friction link is effective when stick-slip occurs in the contact zone by limiting the energy provided to the system.     

刮擦线速度对TC4叶片与Ni-G封严涂层磨损行为的影响

利用高速刮擦试验机模拟了压气机叶片与封严涂层的刮擦行为,研究了TC4（钛合金）叶片材料与Ni-G（镍-石墨）封严涂层体系在线速度30~150 m/s范围内的磨损行为.通过对叶片样品端面及涂层样品磨痕的SEM-EDS、XPS分析和涂层样品磨痕表面的显微硬度测试,探讨了对摩体系的磨损机制.结果表明：随着线速度的增大,叶片样品的磨损率呈现先升后降的趋势;在低线速度下涂层样品致密化使叶片样品磨损轻微,中等线速度下叶片样品与涂层样品磨痕中高硬度转移层的刮擦造成叶片样品磨损加剧,高线速度下叶片样品端面较厚氧化膜减轻叶片材料向涂层的转移导致叶片样品磨损下降.     

Application of the integral manifold method to the analysis of the spatial motion of a rigid body fixed to a cable

We analyze the spatial motion of a rigid body fixed to a cable about its center of mass when the orbital cable system is unrolling. The analysis is based on the integral manifold method, which permits separating the rigid body motion into the slow and fast components. The motion of the rigid body is studied in the case of slow variations in the cable tension force and under the action of various disturbances.We estimate the influence of the static and dynamic asymmetry of the rigid body on its spatial motion about the cable fixation point. An example of the analysis of the rigid body motion when the orbital cable system is unrolling is given for a special program of variations in the cable tension force. The conditions of applicability of the integral manifold method are analyzed.     

A contribution to film coefficient estimation in piston cooling galleries

The need to reduce fuel consumption and exhaust emissions in internal combustion engines has been drastically increased during last years. One of the most important processes affecting these parameters is heat transfer from the in-cylinder gas to the surrounding walls, as this mechanism has a direct influence on the combustion process. Regarding the different walls (liner, cylinder head and piston surfaces), heat flow to the piston is especially important, as it is essential to avoid excessively high temperatures that could result in material damage and/or oil cracking. With this purpose different cooling strategies are used, among which the improvement of the piston cooling system by using oil galleries is preferred. In this work, the heat flow through the oil gallery in a Diesel piston was investigated on a dedicated test bench. This bench consists of a controlled heat source and a piston oil cooling system in which different test conditions were evaluated in order to obtain a correlation for the film coefficient associated with piston oil cooling. These experimental results were then incorporated into a lumped model for engine heat transfer. Finally, in order to evaluate the accuracy of this model and the effects of the correlation for oil gallery coefficient on engine heat flows, results obtained on a conventional engine test bench equipped with a Diesel engine, in which two piston temperatures had been measured, were used. The results show an improvement in piston temperature predictions when compared with those obtained using a previously reported expression for the calculation of the oil film coefficient.     

中心刚体-旋转悬臂板耦合系统碰摩动力特性解析法研究

针对大型旋转机械叶片与机壳间发生的碰摩故障,建立了中心刚体-旋转悬臂板耦合系统碰摩动力学模型,考虑了离心刚化效应,利用Hamilton原理推导出运动微分方程。基于实验和有限元分析碰摩力的结果,给出了碰摩力的近似数学表达式,得到了系统振动响应解析解,通过与文献中实验结果的对比,验证了模型及方法的准确性,讨论了叶片梁模型和薄板模型在不同点碰摩及线碰摩情况下各自的适用范围,分析了转速对碰摩动力响应的影响。结果表明：论文解析解具有较高精度;薄板模型能够更全面地反映叶片各种不同碰摩情况下的动力特性,比梁模型更准确、可靠;随着转速的增大,碰摩力导致薄板自由端幅值突变,这是引发工程中叶片掉角,甚至折断的重要原因。     

Some experiments on the effect of isolated protuberances on flow through tubes

At various locations in the arterial system, plaques, or small relatively isolated protuberances, can develop on the inner wall of the vessel and project into the lumen. A number of investigators have suggested that the development and growth of these protuberances is related to the flow in the vicinity of the protuberance. In this study, the conditions under which the flow separates from an isolated protuberance located in a cylindrical tube were investigated. The critical Reynolds number at which separation first takes place for a given protuberance was determined. A series of tests was performed for steady flow of a Newtonian fluid through a rigid tube in which protuberances of various sizes were inserted. The results of the tests show the effect of the protuberance height and shape on the separation characteristics. In general, the results indicate that separation takes place at relatively small values of the Reynolds number; values that commonly occur in the arterial system, so that this phenomenon may be important in the study of the “coupling” between blood flow and arterial lesions.     

Calibration of granular material parameters for DEM modelling and numerical verification by blade-granular material interaction

The discrete element method (DEM) is a promising approach to model blade-granular material interactions. The accuracy of DEM models depends on the model parameters. In this study, a calibration process was developed to determine the parameter values. The particle size was the same as the real material and the particle shape was modelled using two spherical particles rigidly clumped together to form a single grain. Laboratory shear tests and compressions tests were used to determine the material internal friction angle and stiffness, respectively. These tests were replicated numerically using DEM models with different sets of particle friction coefficients and particle stiffness values. The shear test results are found to be dependent on both the particle friction coefficient and the particle stiffness. The compression test results show that it is only dependent on the particle stiffness. The combination of shear test and compression test results can be used to determine a unique set of particle friction and particle stiffness values. The calibration process was validated experimentally and numerically by modelling a blade moving through granular material. Results show that the forces acting on the blade can be accurately modelled with DEM and the maximum error is found to be 26%. The relative particle-blade displacements were used to predict the position and shape of the shear lines in front of the blade. A good qualitative correlation was achieved between the experiments and the DEM simulations.     

Non-linear dynamics of a mechanical system with a frictional unilateral constraint

We analyze the dynamics of a two-dimensional system constituted by two masses subjected to elastic, gravitational and viscous forces and constrained by a moving frictional mono-lateral surface. The model exhibits a time-varying dynamics capable of reproducing the hopping phenomenon, an unwanted phenomenon observed in many applications such as the motion of a robotic arm on a surface or that of a wiper on a windscreen. The system dynamics, besides being affected by geometrical non-linearities, has a non-smooth nature due to the impact and friction laws involved in the model. The complexity of the resulting equations and of the transition conditions require the problem to be solved numerically. Various periodic motions are found and the effect of varying the system parameters, in particular the friction coefficient, is investigated. Finally, simulations are used to gain some insight the behavior of the windscreen wiper.