表征漫射体反射特性的一个重要物理参数——双向反射分布函数

本文着重介绍了双向反射分布函数f_b(θ_i,φ_i,θ_r,φ_r)及其在漫射测量中的主要作用,给出了f_b(θ_i,φ_i,θ_r,φ_r)与九种反射比和九种反射比系数之间的关系,同时介绍了f_b(θ_i,φ_i,θ_r,φ_r)的几种测试方法,有关测试仪器的设计准则以及我所研制和使用这种仪器的简单情况.     

激光斑点的衍射和斑点强度测量

做了激光斑点衍射和斑点强度测量的实验,并对激光斑点衍射作了理论分析.实验说明,当斑点平均直径与测量孔直径之比d_r/d_o≥1时,可以观察到孔的夫琅和弗衍射图或“准”夫在琅和弗衍射图.给出在不同d_r/d_o值时的斑点强度几率密度函数.在d_r/d_o》1和较粗糙的散射面的情况下,得到了负指数形式的几率密度函数.实验说明在d_r/d_o》1时,可以用对比度来表征散射面的粗糙度.     

全息凹面光栅的点列图

为了评价全息凹面光栅的成象质量,我们同时采用了两种方法:一是通过光线追迹,求出它的点列图,在理论上进行分析和评价;二是采用拍照该光栅的谱线,在实际上进行核对和最后评价.在设计全息凹面光栅时,得出不同的仪器结构参数(r_A、r_B、ρ、α、β)和记录参数(r_O、r_D、γ、δ),我们根据它们的点列图,在制造之前,就能判断出那些结果使用效果最佳,还能利用它修正记录参数,选定最佳值.然后在制造时实测谱线,并改正各种参数,使它达到优良的谱线质量.本文参照文献着重讨论点列图.     

光学系统的杂光计算分析

探讨了光学系统杂光分析方法,[提出了鬼像判别依据,在修改小镜面散射理论中几何遮挡因子(Geometrical Masking-shadowing Factor)基础上,抽象出光学系统中表面粗糙度σ_m/λ≥1.0,的表面双向反射分布函数(BRDF)模型,同时应用矢量微扰理论给出表面粗糙度σ_m/λ<<1.0的 BRDF 模型,并编制杂光分析程序     

H2O/CO2污染对煤油燃料超声速燃烧影响数值研究

在纯净空气与H₂O/ CO₂污染空气来流对比试验结果基础上,采用数值计算方法和化学动力学方法,研究了H₂O和CO₂污染组分对煤油燃料超声速燃烧的影响,获得了试验手段难以得到的燃烧室流场参数和性能数据。完成了相应的煤油燃料超声速燃烧室二维数值计算,其中匹配了进口总温、总压、马赫数、氧气摩尔分数和工作当量油气比。将数值计算结果与相应试验测量值进行了对比分析,并结合燃烧室流场数据、性能参数分析了H₂O和CO₂污染的动力学影响、以及对燃烧室性能的影响。研究表明:(1)数值计算结果与实验测量值总体上吻合,两种手段均体现了纯净空气来流时不同煤油当量油气比的燃烧室性能,并反映了一致的“污染效应”影响趋势;(2) H₂O污染、H₂O+ CO₂污染的存在降低了煤油燃料超声速燃烧室性能,体现在燃烧诱导压升、燃烧效率、流向冲量增量的下降,而且随着污染组分含量的增加,燃烧室性能下降越加显著。      

采用 CCD 器件的半导体材料应力测试仪的研制

研究和实现了采用面阵CCD器件的半导体材料应力测试仪。介绍了测量原理,设计完成了相应的光学测量系统、硬件控制系统和控制测量所需的软件。最后介绍了对硅上SiO₂、Si₃N_{4膜应力实际测量的结果。}     

液粘传动界面间油膜态数值模拟研究

为了研究在软启动过程中,液粘调速离合器摩擦副间隙内油膜形态的演变机理,基于计算流体动力学理论,建立流体油膜的计算模型,并考虑油膜的粘温特性,采用Fluent软件对摩擦副间隙内的油膜流场进行求解,获得了油膜的多物理场分布。研究结果表明：界面间油膜的最大温升从油膜出口位置转移至油膜入口位置附近;油膜在中间位置及出口位置的温度和径向速度呈现出抛物线状分布;影响摩擦副间隙内油膜最大动压的主要因素是油膜厚度与主、被动片相对转速;油膜的粘性扭矩输出呈现先增加后减小的趋势,粘性扭矩峰值出现在启动初期。     

挤压条件下弹流油膜的摩擦学现象研究

纯挤压条件下弹流油膜的研究已证实了油膜的中央凹陷。研究利用常载荷下的钢球在较小的初始间隙下冲击附有润滑油的玻璃盘,在接触区外围出现了外围凹陷,而不是熟知的中央凹陷。研究结果表明当初始的冲击间隙较大时,油膜的压力分布和厚度以及中心压力-时间曲线中的峰值和接近结束时的中央凹陷都与以前的自由落球问题相似。随着初始的冲击间隙减小,最大压力从接触区中心转换到圆周外围区,相应地,中央凹陷变得越来越不明显而在外围区出现了圆周凹陷,进一步的数值分析,发现当油膜足够厚时在小的初始间隙条件下也出现了外围凹陷。这主要是当初始的冲击间隙变小时,中央油膜厚度比大冲击间隙条件下润滑油被"冰冻"时薄很多,中央凹陷不明显;在外围区域,表面间隙很小,局部挤压效应变强,因此形成了外围凹陷。     

挤压油膜阻尼器油膜阻尼系数识别及分析

为了进行挤压油膜阻尼器油膜阻尼系数识别的实验研究,首先,利用信号发生器和功率放大器对双向激励实验器进行激振;然后,借助阻抗头获得激励和响应数据;最后,基于机械阻抗原理,通过最小二乘法拟合,得到挤压油膜阻尼器的油膜阻尼系数。通过改变油膜宽度和油膜间隙,研究不同挤压油膜阻尼器参数对油膜阻尼的影响。研究结果表明,随着油膜宽度的线性增大,油膜阻尼呈现非线性增大的趋势。可以通过增大油膜宽度和油膜阻尼,来提高阻尼器的减振性能。随着油膜间隙的线性增大,油膜阻尼呈现非线性减小的趋势,减振性能下降。     

精密多油楔动压轴系的楔形间隙参数与油膜运动稳定特性

针对精密仪器轴系的研制和精度分析,研究了立式三油楔动压轴系的结构、轴承轮廓结构,建立数学模型、分析模型,对轴系动压油膜的动力特性做了分析.对于主轴在动压油膜反力与外载荷作用下处于某一平衡位置(e,θb)运转时,能否经得起任意微扰动的干扰而失稳,建立了油膜运动稳定性的判据.应用数值模拟和计算机编程,深入研究了关键设计参数楔形间隙bm、cm相应的油膜运动稳定特性,揭示了楔形间隙值与轴系失稳的对应关系,给出了油膜稳定性因数Log(Sp)与偏心率ε(ε=e/c)之间的变化曲线图,并指出了楔形间隙参数最佳的取值范围.研究结果指出:楔形间隙是轴系设计和制造的重要敏感参数;最大楔形间隙bm和最小间隙cm值之间应保持一定的比例,否则油膜运动发散,轴系平衡失稳,导致主轴转动中产生较大的晃动.对于低速立式三油楔动压轴系,则bm-cm≥0.8 μm.比较研究结果与成功轴系实例,表明实例中bm、cm取得符合轴系的油膜稳定条件.证明研究结果对该类轴系的设计具有实用性.     

基于多物理场耦合的可倾瓦滑动轴承性能优化分析

针对大型可倾瓦滑动轴承的湍流效应和瓦块变形,基于COMSOL和MATLAB的联合仿真构建三维热弹流体动力润滑模型.模型中,考虑湍流的修正雷诺方程、能量方程和热传导方程的计算采用COMSOL偏微分方程物理场模块实现,瓦块变形计算采用COMSOL中热应力物理场模块实现,多物理场耦合和计算过程控制利用MATLAB实现.基于所...     

推力轴承支承方式及间隙影响研究

研究了推力轴承支承方式及油膜间隙对推力轴承性能的影响,利用Newton-Raphson法编制差分计算程序,求得了推力轴承Reynolds方程和二维能量方程的数值解,得到了不同支撑方式下瓦块的油膜厚度、压力分布和温度分布。计算结果表明,点支承扇形瓦推力轴承的热力学性能要好于线支承扇形瓦推力轴承,同时支承处的油膜厚度对瓦块的承载能力影响很大。可以通过控制每个瓦块支承处的油膜厚度,避免推力轴承内部偏载的发生,降低推力瓦块的最大温升。     

Theoretical investigations on the performance of an externally adjustable fluid-film bearing including misalignment and turbulence effects

An externally adjustable fluid-film bearing has been devised whereby the hydrodynamic conditions can be changed as required in a continuously controlled manner. Principal feature of the externally adjustable pad bearing is the facility to control the bearing clearance and film thickness gradient in circumferential direction, irrespective of the operating conditions. Unlike a tilting pad bearing, this bearing can have both radial and tilt adjustments. A single pad externally adjustable pad bearing will perform as a conventional partial arc bearing when the adjustments are set to zero.The paper deals with the effect of turbulence and misalignment on steady state characteristics of a centrally loaded 120° single pad externally adjustable bearing. The bearing has an aspect ratio of one and operates over a wide range of eccentricity ratios with adjustments and degrees of misalignment. Reynolds equation incorporated with linearized turbulent lubrication model of Ng and Pan is solved using a finite difference method. Static performance characteristics calculated are presented in terms of attitude angle, Sommerfeld number, friction variable, misalignment moment and oil flow. A study with various adjustments predicts that negative radial and negative tilt adjustment configuration results in superior static characteristics as compared to a conventional fluid-film bearing.     

液黏离合器油槽结构参数对油膜剪切转矩的影响分析

合理确定油槽的结构参数能有效地改善摩擦副间流体的流场特性和油膜剪切摩擦转矩性能。为了揭示摩擦副油槽结构对油膜剪切转矩的影响,以双圆弧油槽为研究对象,建立了集油槽结构参数化设计、流场数值模拟与试验设计方法(DOE)为一体的油槽结构参数影响分析平台。重点分析了液黏离合器摩擦副双圆弧油槽宽度、油槽对数、偏心距与内圈偏心圆直径对油膜剪切转矩的影响,并探究了各个参数的敏感性。结果表明,液黏离合器油膜剪切转矩随着摩擦副油槽宽度、油槽对数及内圈偏心圆直径的增大而增大,随着偏心距的增大而减小。摩擦副油槽宽度与内圈偏心圆直径是影响液黏离合器油膜剪切转矩的敏感参数。     

轴瓦弹性变形对固定瓦-可倾瓦组合径向滑动轴承润滑特性的影响

采用一种新型耦合算法,将有限差分法和3D有限元法综合应用于求解油膜压力和轴瓦弹性变形过程中。与其他算法相比,该算法更为科学、合理,同时具有收敛快、精度高的特点。通过对固定瓦-可倾瓦组合径向滑动轴承的研究,分析轴瓦弹性变形对油膜厚度、油膜压力、油膜承载力、摩擦阻力及轴承端泄量等润滑性能的影响。研究结果表明,在大偏心率的情况下,轴瓦弹性变形对轴承润滑性能影响较大。     

Role of smoke from combustion of oil in tribological applications to ceramics

The influence of smoke from combustion of light oil on friction properties was investigated with various ceramic specimens (Al₂O₃, Si₃N₄ and SiC) at a normal load of 58.8 N, a circumferential velocity of the rotating ring of 0.1 m/s. The variation of friction torque with sliding distance was measured with these specimens over a range of testing temperatures from 100°C to 400°C. It was found that a stable sliding condition was characterized by the formation of a smooth carbon film on the surface. The carbon films thus formed were investigated in relation to the change in friction coefficient with film thickness. The result showed that the optimum film thickness for minimizing the friction coefficient is 0.2–0.3 μm, almost irrespective of the kind of ceramic samples. It was deduced that an effective amount of soot as a lubricant is about 10–40 g/m²/h depending on the kinds of ceramic couple.     

速度对扇形可倾瓦推力轴承润滑性能的影响研究

采用数值分析方法研究速度对扇形可倾瓦推力轴承润滑性能的影响,分析速度对最小油膜厚度、最大油膜压力、最高油膜温度、功率损失和流量等参数的影响规律,得到了速度与扇形可倾瓦推力轴润滑参数的关系。结果表明:最小油膜厚度在一定的速度范围内随速度呈线性变化,且随着速度的增加而增加;最大油膜压力随速度的增大产生波动性变化,但最终逐渐稳定到某一具体值;随着速度的增加温度升高;瓦功耗和瓦流量随速度的增加基本上呈线性增加变化。     

基于CFD的齿轮泵实际最优端面间隙确定方法

齿轮泵端面间隙是内泄漏和黏性摩擦损失最重要的影响因素,其大小主要由浮动侧板背面高压油压紧力与其所受端面油膜反推力平衡状态确定。针对某型号齿轮泵,考虑了端面间隙、油液含气量和油液蒸发等因素对反推力压力分布的影响,采用CFD方法计算获得常用工况下5组给定端面间隙对应的端面油膜反推力,由最小二乘法拟合得到间隙小范围变化时的端面油膜平均反推力线性化方程,求解现有总功率损失最小条件下最优端面间隙值,将其代入端面油膜平均反推力方程,反解出浮动侧板背面所需高压油压紧力。据此,通过调整浮动侧板背面高压区形状,使齿轮泵的实际端面间隙在常用工况下处于最优值。对实际工程中确定齿轮泵最优端面间隙具有重要的参考价值。     

Influence of a ring flat zone in the point contact surface on thermal elastohydrodynamic lubrication

This paper describes a geometrical profile, an elastohydrodynamically lubricated point contact surface with a ring flat zone, aimed at building up local line contact elastohydrodynamic lubrication (EHL) in point contact conjunctions to reduce the influence of side-leakage on the central film thickness. Effects of the ring flat zone on the thermal EHL characteristics are studied. A dimensionless coefficient, r_W, is defined to represent the relative half width of the ring flat zone in a point contact EHL surface. Thermal EHL numerical simulations have been performed to investigate the influence of r_W on the film thickness as well as pressure, temperature and friction coefficients under different operating conditions. In the range of 0≤r_W≤1.0 results show that the minimum film thickness decreases with increasing r_W and the central film thickness increases with increasing r_W, and the influence of r_W on the film thickness is more pronounced than those on the maximum pressure, the maximum temperature and the friction coefficients. It is revealed that the proposed ring flat zone with appropriate width is beneficial to the thermal lubrication.     

Theoretical and Experimental Study on the Axial Oil Film Stiffness of Tilting Pad Thrust Bearings

Tilting pad thrust bearings are a key component of marine propulsion shaft systems. The dynamic performance of thrust bearings has a significant influence on the propeller vibration. To investigate the axial oil film stiffness of tilting pad thrust bearings, a two-dimensional thermohydrodynamic model incorporating the vibration frequency is developed. The test apparatus and experimental identification model are also constructed. The axial oil film stiffness is experimentally identified at different speeds, loads, and temperature employing the hammer impulse excitation. The axial oil film stiffness between theoretical and experimental results is compared. The discrepancies are not more than 7% for 30 kN operation cases but increase with axial static load. This is partially because the influence of the pivot stiffness becomes obvious with the axial static load increase and cannot be ignored. The results indicate that axial oil film stiffness is at a magnitude of 10⁹ N·m^?1. Compared to foundation stiffness of the thrust bearing system, the influence of axial oil film stiffness needs to be considered for bearing–rotor system design of marine propulsion systems in engineering practice.