涂层表面粗糙性对流体噪声的影响

在铝合金回转体表面涂上一定粗糙度的低表面能涂层，涂层表面的不平度平均高度在６．３～１０．０μｍ时，涂层模型表面为光滑水力壁，这时表面粗糙所引起的那部分流噪声可忽略不计．在光滑（Ｒｚ＝３．２～６．３μｍ）的铝合金模型表面喷涂涂层后，涂层表面较粗糙（Ｒｚ＝１０．０～２０．０μｍ）时，同样在相应的频率范围内涂层模型仍有降噪的效果，而且对不同涂层材料其表面粗糙度对流噪声的影响也不相同．     

多频谐和与噪声作用下Duffing振子的安全盆侵与混沌

研究了软弹簧Duffing振子在多频率确定性谐和外力和有界随机噪声联合作用下,系统安全盆的侵蚀和混沌现象.将Melnikov方法推广到包含有限多个频率外力和随机噪声联合作用的情形,推导出了系统的随机Melnikov过程.根据Melnikov过程在均方意义上出现简单零点的条件给出了系统出现混沌的临界值,然后用数值模拟方法计算了系统的安全盆分叉点.结果表明:由于随机扰动的影响,系统的安全盆分叉点发生了偏移,并且使得混沌容易发生.同时证明:激励频率数目的增加使得系统产生混沌的参数临界值变小,也使得安全盆分叉提前发生,系统变得不安全.     

固体粉末添加剂对主轴承空穴噪声的模拟试验研究

针对汽车发动机主轴承中类似打字机的无规律异常噪声,利用自行研制的平行板挤压油膜试验机模拟发动机主轴承在动态耦合作用下的油膜噪声试验. 在试验机可以实现声音、位移、振动、拉压力和油膜空穴图像同步采集基础上,探究了不同固体粉末添加剂对油膜空穴噪声的影响,其中包括碳粉、多孔质硅铝酸盐、荧光剂(油溶性与非油溶性)和二硫化钼粉末. 结果显示碳粉、多孔质硅铝酸盐粉和非油溶性荧光剂粉有抑制油膜空穴噪声的作用,其平均降噪率分别为50%、70%和75%,这表明后两者具有更优的降噪效果. 随着加入量的增加,碳粉和多孔质硅铝酸盐粉的抑制噪声作用先增强后趋向平稳,而非油溶性荧光剂粉的抑制噪声作用先增强后减弱. 这三者抑制油膜空穴噪声的机理主要是由于其特殊的多孔结构能够增加液体中的成核粒子,形成不易聚集的小空穴,降低了与大气连通的可能性,从而减少了油膜空穴噪声出现的频率.      

The Spirit Is Willing: Nonlinearity, Bifurcations, and Mental Control

In recent years there has been considerable interest in the construction of nonlinear models of the dynamics of human behavior. In this exploratory article we argue that attempts at controlling problematic thoughts, emotions, or behaviors can lead to nonlinearity in mental/behavioral dynamics. We illustrate our model by fitting threshold autoregression models to self-recorded time series of the daily highs in intensity of anxiety and obsessive ruminations, kept by an individual in therapy for this problem. In our discussion, we raise the possibility that bifurcations that occur in this nonlinear model may offer insight into mental control paradoxes.     

Analysis of the Nonstationary Slow Passage of a Cylindrical Vessel Partially Filled with a Liquid Through Resonant Zones

The features of the dynamic behavior of the free liquid surface in a rigid cylindrical body that executes translational quasistationary vibrations are studied. The frequency of these vibrations is a slowly varying function of time. The liquid motion is studied in the resonant zones corresponding to two cases of body excitation — longitudinal and transverse     

用二维FFT滤波消除ESPI条纹中的散斑颗粒噪声

在 ESPI 条纹中,由于存在散斑颗粒,使得条纹对比度极大地下降.并给进一步的分析造成较大的因难.本文用二维 FFT 方法,并配以多种低通滤波函数,有效地消除了条纹图中的散斑颗粒。该方法对原始条纹图质量无任何要求,适用于各种形状的条纹.     

A simple feedback control system: Bifurcations of periodic orbits and chaos

We consider a pendulum subjected to linear feedback control with periodic desired motions. The pendulum is assumed to be driven by a servo-motor with small time constant, so that the feedback control system can be approximated by a periodically forced oscillator. It was previously shown by Melnikov's method that transverse homoclinic and heteroclinic orbits exist and chaos may occur in certain parameter regions. Here we study local bifurcations of harmonics and subharmonics using the second-order averaging method and Melnikov's method. The Melnikov analysis was performed by numerically computing the Melnikov functions. Numerical simulations and experimental measurements are also given and are compared with the previous and present theoretical predictions. Sustained chaotic motions which result from homoclinic and heteroclinic tangles for not only single but also multiple hyperbolic periodic orbits are observed. Fairly good agreement is found between numerical simulation and experimental results.     

Bifurcations and synchronization of singularly perturbed oscillators: an application case study

We present numerically obtained bifurcations of two dual singularly perturbed nonlinear oscillating circuits. Each of the circuits comprises two coupled sections: a nonlinear section with dissipation and a linear one with a small constant biasing source. The two dual oscillators show an interesting pattern of hierarchical oscillations that follow the Stern?CBrocot tree with intervals of synchronization yielding Arnold??s tongues and their corresponding devil??s-like staircases. Several numerical results are included.     

Bifurcations in the Mean Angle of a Horizontally Shaken Pendulum: Analysis and Experiment

A pendulum excited by high-frequency horizontal displacement of its pivot point will vibrate with small amplitude about a mean position. The mean value is zero for small excitation amplitudes, but if the excitation is large enough the mean angle can take on non-zero values. This behavior is analyzed using the method of multiple time scales. The change in the mean angle is shown to be the result of a pitchfork bifurcation, or a saddle-node bifurcation if the system is imperfect. Analytical predictions of the mean angle as a function of frequency and amplitude are confirmed by physical experiment and numerical simulation.     

Effect of Vertical Modulation on the Onset of Filtration Convection

The present paper examines the effect of vertical harmonic vibration on the onset of convection in an infinite horizontal layer of fluid saturating a porous medium. A constant temperature distribution is assigned on the rigid boundaries, so that there exists a vertical temperature gradient. The mathematical model is described by equations of filtration convection in the Darcy–Oberbeck–Boussinesq approximation. The linear stability analysis for the quasi-equilibrium solution is performed using Floquet theory. Employment of the method of continued fractions allows derivation of the dispersion equation for the Floquet exponent σ in an explicit form. The neutral curves of the Rayleigh number Ra versus horizontal wave number α for the synchronous and subharmonic resonant modes are constructed for different values of frequency Ω and amplitude A of vibration. Asymptotic formulas for these curves are derived for large values of Ω using the method of averaging, and, for small values of Ω, using the WKB method. It is shown that, at some finite frequencies of vibration, there exist regions of parametric instability. Investigations carried out in the paper demonstrate that, depending on the governing parameters of the problem, vertical vibration can significantly affect the stability of the system by increasing or decreasing its susceptibility to convection.      

The Slow Erosion Limit in a Model of Granular Flow

We study a 2 × 2 system of balance laws that describes the evolution of a granular material (avalanche) flowing downhill. The original model was proposed by Hadeler and Kuttler (Granul Matter 2:9–18, 1999). The Cauchy problem for this system has been studied by the authors in recent papers (Amadori and Shen in Commun Partial Differ Equ 34:1003–1040, 2009; Shen in J Math Anal Appl 339:828–838, 2008). In this paper, we first consider an initial-boundary value problem. The boundary condition is given by the flow of the incoming material. For this problem we prove the global existence of BV solutions for a suitable class of data, with bounded but possibly large total variations. We then study the “slow erosion (or deposition) limit”. We show that, if the thickness of the moving layer remains small, then the profile of the standing layer depends only on the total mass of the avalanche flowing downhill, not on the time-law describing the rate at which the material slides down. More precisely, in the limit as the thickness of the moving layer tends to zero, the slope of the mountain is provided by an entropy solution to a scalar integro-differential conservation law.     

Bifurcations of Poiseuille flow between parallel plates: Three-dimensional solutions with large spanwise wavelength

The spatial dynamics approach is applied to the analysis of bifurcations of the three-dimensional Poiseuille flow between parallel plates. In contrast to the classical studies, we impose time periodicity as well as spatial periodicity with period 2/ in the streamwise direction. However, we make no assumptions on the behavior in the spanwise direction, except the uniform closeness of the bifurcating solution to the basic flow. In an abstract setting it is shown how the dimension of the critical eigenspace of the spatial dynamics analysis can be uniquely determined from the classical linear stability problem. For the three-dimensional Poiseuille problem we are able to find all relevant coefficients from the analysis of the purely two-dimensional problem. Moreover, we are able to analyze precisely the influence of a spanwise pressure gradient and the associated spanwise mass flux. The study of the reduced problem shows that there are two different kinds of solutions (spirals and ribbons) which are 2p/ periodic in the spanwise direction, as in the Couette-Taylor problem, and both of them bifurcate in the same direction.     

汽车制动噪声的研究

近年来,随着人们环保意识的增强,汽车制动产生的噪声污染备受关注.本文分析了汽车制动噪声产生的特点,并从实验和理论两方面系统回顾了制动噪声的研究工作,重点对各种制动噪声的机理进行了分析和评述.最后,指出目前制动噪声研究工作的不足,并对未来的研究工作提出了一些展望和建议.     

Effect of Confining Wall on Properties of Gas Flow Through Metal Foam: An Experimental Study

While the Darcy and Forchheimer relations are widely applied to determine the permeability and the form drag coefficient of open-cell metal foam, they both assume that the porous medium is infinite in all directions, i.e., large enough so that the effect of any confining walls is negligible. Many researchers, however, pay little or no attention to the size of metal foam samples in pressure-drop studies. The size of a foam sample perpendicular to the flow direction may be small enough such that wall effects are significant. This article experimentally investigates the wall effect on the permeability and form drag coefficient for two types of open-cell aluminum foam subjected to airflow entering the foam in the Forchheimer regime. The Forchheimer equation was recast in two different manners, which resulted in new non-dimensional numbers that correlated very well with the diameter of the foam samples measured in cells. The correlations are valid for a confining-tube-diameter-based Reynolds number ranging from approximately 13,000 to 105,000, and for diameters ranging from 12 to 36 cells and 24 to 60 cells for 10- and 20-pore per inch foam, respectively. The obtained correlations allow for determining pressure drop given only the velocity and the diameter of an aluminum foam sample.     

润滑油添加剂——偏硼酸钠抗磨特性的研究

作者利用四球试验机和Timken试验机研究了白油中所含偏硼酸钠的抗磨特性,以及分散剂和结晶水对偏硼酸钠的抗磨性能的影响,并且利用X—光电子能谱仪(XPS)和俄歇电子能谱仪(AES)考察了摩擦表面的组成及硼的价态。结果表明,含偏硼酸钠的白油能在摩擦表面形成含偏硼酸钠的表面膜而具有较好的抗磨性,硼在摩擦表面膜中以偏硼酸钠的形式存在,钠和钙的石油磺酸盐型分散剂会降低偏硼酸钠的抗磨性,而丁二酰亚胺类分散剂则能提高其抗磨性。     

Effect of Slow and Fast Moving Liquid Zones on Solute Transport in Porous Media

A conceptual model is developed in this article that accounts for the effect of slow and fast moving liquid zones on solute transport in porous media. The liquid phase within the porous media is divided into three zones—immobile, slow moving, and fast moving. Slow moving liquids surround the solid particles in thin layers and have lower velocity in flow. Fast moving liquids have higher velocity and are not in contact with the solid particles. Solute mass transfer occurs between the slow and fast liquids, and the slow and immobile liquids. The immobile and slow moving liquids interact with the solid matrix in the media through the mechanism of sorption and desorption. Implicit finite-difference methods are used to solve the partial differential equations that describe the slow and fast movement of solute in the porous medium. The model was validated for a laboratory column experimental data. Sensitivity analyses were conducted to ascertain the effects of the model parameters on solute movement. The effect of each parameter on retardation of the solute movement was analyzed. It was observed that the maximum retardation of solute occurs when there is high adsorption coefficient, high mass transfer rates, and high volume of slow moving liquid in the porous media.     

离子液体添加剂对硬脂酸钾固体润滑薄膜摩擦磨损性能的影响

采用浸渍-提拉方法在单晶硅片上制备硬脂酸钾以及添加离子液体的硬脂酸钾复合薄膜,采用DF-PM型静-动摩擦磨损试验机考察薄膜在低速滑动条件下的摩擦磨损性能,采用扫描电子显微镜和X射线能量散射谱仪观察分析薄膜及其偶件表面的磨损形貌及典型元素面分布.结果表明:在相对低速滑动条件下,在羟基化硅基底上制备的复合薄膜的摩擦磨损性能优于硬脂酸钾薄膜;在载荷为1.0 N条件下,含离子液体质量分数40.0%的复合薄膜的耐磨寿命超过5 000次,而硬脂酸钾薄膜仅为100次左右;随着复合薄膜中离子液体含量增加,复合薄膜更容易在偶件钢球表面形成有效转移薄膜,使复合薄膜摩擦磨损性能得以提高.     

摩擦副材料对二烷基二硫代氨基甲酸钼添加剂摩擦学特性的影响

选择等离子喷涂钼合金层、渗氮层以及镀铬层为摩擦副材料 ,以全配方矿物基发动机油 SJ/ 5 W- 30作为基础润滑油 ,研究了上述 3种摩擦副材料对油溶性二烷基二硫代氨基甲酸钼 (Mo DTC)添加剂摩擦学特性的影响 .结果表明 :Mo DTC的摩擦学特性与摩擦副材料类型有关 ;采用喷钼层、渗氮层及镀铬层作为摩擦副材料 ,Mo DTC均表现出减摩和抗磨作用 ,对渗氮层的减摩抗磨效果最佳 .X射线光电子能谱分析表明 :摩擦副材料类型对添加剂中的 Mo和 S的化学状态和相对含量均有影响 ;摩擦副材料类型不同时 ,Mo DTC摩擦学行为的差异与其在磨损表面形成的 Mo S2 以及 Mo O3 、Fe S和磷酸盐等物质的含量有关     

硫代钼酸镍作为油品添加剂的尺寸效应和摩擦学性能

用水溶液法、高能球磨法和乳状液相转移法制备出颗粒尺寸分别为微米和纳米量级的硫代钼酸镍粉末,研究了粉末粒径大小与其在润滑油中分散稳定性的关系和作为油品添加剂从室温到高温的摩擦学性能,结果表明：硫代钼酸镍粉末粒径对其在油品中的分散稳定性和摩擦学性能有明显影响,当粉末粒径变小时,其分散稳定性可提高48倍,在四球试验机上测定的pB值提高约3.3倍,磨斑直径WSD值降低三分之二,在室温到高温的销《盘摩擦磨损试验中,摩擦系数最多可降低70%左右;其降低程度与摩擦副配副及其表面粗糙度有关。