A Method for Identification of Bearing Force Coefficients and Its Application to a Squeeze Film Damper with a Bubbly Lubricant

A general formulation of the instrumental variable filter (IVF) method for parameter identification of a n-DOF (Degrees Of Freedom) mechanical linear system is presented. The IVF is a frequency domain method and an iterative variation of the least-squares approximation to the system flexibilities. Weight functions constructed with the estimated flexibilities are introduced to reduce the effect of noise in the measurements, thus improving the estimation of dynamic force coefficients. The IVF method is applied in conjunction to impact force excitations to estimate the mass, stiffness, and damping coefficients of a test rotor supported on a squeeze film damper (SFD) operating with a bubbly lubricant. The amount of air in the lubricant is varied from nil to 100 percent to simulate increasing degrees of severity of air entrainment into the damper film lands. The experimental results and parameter estimation technique show that the SFD damping force coefficients increase as the air volume fraction in the mixture increases to about 50 percent in volume content. The damping coefficients decrease rapidly for mixtures with larger air concentrations. The unexpected increase in direct damping coefficients indicates the complexity of the SFD bubbly flow field and warrants further experimental verification.     

气油两相流对滑动轴承油膜刚度的影响

本文在引入新型气油两相流粘度模型的基础上，建立了一套管用于气油两相流工况下滑动轴承的数值计算理论，计算研究了气油两相流对滑动轴承油膜刚度的影响，得出了一系列有益的结论。     

油气两相流对滑动轴承油膜破裂位置的影响

滑动轴承油膜破裂位置是滑动轴承静特性之一。本文在引入新型气油两相流流变模型后,组织了一套适用于油气两相流润滑工况下滑动轴承的数值计算理论,用数值计算的方法研究了油气两相流对滑动轴承油膜破裂位置的影响,得出了一组规律性的结论。     

气油两相流对滑动轴承油膜阻尼系数的影响

本文在引入新型气油两相流粘度模型的基础上，组建了一套适用于气油两相润滑工况下，关于滑动承油膜尼系数的数值计算方法，计算研究了气油两相流对滑动轴承油膜阻尼系数的影响，得出了一系列规律性的结论。     

电磁轴承-挤压油膜阻尼器-转子系统的主动控制

转子系统的许多非线性因素由于转子偏心的存在而得到放大 ,至使转子与静件容易出现碰磨现象。本文针对转子系统偏心所引起的离心力提出一种主动控制方法 ,使系统避免出现碰磨 ,同时使挤压油膜阻尼器所产生的非线性不稳定影响最小。本文引入磁轴承理论对转动圆盘进行主动控制 ,并进行了仿真计算。     

故障转子SFD减振特性的实验

针对航空发动机转子常见的两种故障模式碰摩和不对中,实验研究挤压油膜阻尼器分别对上述两种故障引发的振动的抑制效果。在转子实验器上分别模拟碰摩故障和不对中故障,并测试使用挤压油膜阻尼器前后故障转子振动特征的变化。实验结果表明,碰摩故障导致转子振动一阶反进动和一阶进动比增大,不对中故障导致转子振动二倍频增大;对于碰摩故障,挤压油膜阻尼器可以有效减小涡轮盘处振动和弹支辐条的应变,但对压气机盘减振失效;对于不对中故障,挤压油膜阻尼器可以减小转子振动,对于二倍频振动幅值的抑制尤为明显。     

带有阻尼器的滑动轴承转子系统对数衰减率实验特性研究

首先设计了一套试验装置 ,其次就装有不带定心弹簧静压型挤压油膜阻尼器的滑动轴承转子系统的对数衰减率特性进行了试验和测试。结果表明 :装配阻尼器后的转子系统其对数衰减率有了很大提高。     

挤压油膜阻尼器对滑动轴承-转子系统的影响

建立了转子-挤压油膜阻尼器-滑动轴承系统的动力学计算模型,分析了挤压油膜阻尼器对滑动轴承-转子系统的强迫振动的影响、挤压油膜阻尼器的刚度和阻尼搭配关系以及转子-挤压油膜阻尼器-滑动轴承系统的自由振动稳定性问题。研究结果表明,合理的外弹性支承可以使系统的振幅得到有效控制,而且也提高了系统的稳定性;如要减小系统的振幅可以通过一个低的支承刚度和一个合适的阻尼来实现。在小的支撑刚度的情况下,存在一个很宽的支承阻尼域,此域可以获得低幅值的不平衡响应。     

微纳结构形式对镍薄膜超快热化动力学的影响

制备了厚、薄、反点阵结构以及颗粒结构镍薄膜分别作为体、面、线和点结构薄膜样品,利用飞秒激光泵浦探测技术,检测了4种镍薄膜的瞬态反射率变化情况,研究了微纳结构形式对镍薄膜超快热化动力学的影响。结果表明对于微纳结构镍薄膜来说,随着结构维数的减小,量子限域效应对电子热化时间有延缓作用。     

Experimental Study of the Radial and Tangential Forces in a Whirling Squeeze Film Damper

The present work introduces the main results of a detailed experimental program aimed at investigating the influence of the design parameters and of the working conditions on the global characteristics of squeeze film dampers (SFD) for serial aircraft engines. The SFD is sealed at both ends and is executing circular centered orbits. The results are presented for the tangential and the radial global force in the SFD and the leakage flow rate. The pressure field inside the SFD could also be measured and shows the influence of the inertia force, of the cavitation, and probably of the turbulence regime, as well as the interaction of these effects with the feeding groove. The limits of the existing theoretical models are also demonstrated.

     

静偏心对挤压油膜阻尼器转子抗振性能的影响及控制方法

研究了静偏心对挤压油膜阻尼器减振与转子抗振性能的影响。结果表明,随着静偏心增大,阻尼器的减振性能先增强再减弱,而转子抗振性能则大幅下降。分析了引起阻尼器静偏心的原因,并根据各因素的特征提出了控制方法。采用预置偏心,合理的结构、工艺设计有利于控制转子自重与设计、加工装配引起的静偏心。采用较小的设计偏心比,有利于提高机动条件下阻尼器转子的抗振性能。     

表面织构的深度影响润滑油膜承载能力的机制研究

采用基于N-S方程的CFD方法,研究最小油膜厚度为4μm时圆弧凹槽表面微织构深度的变化对动压润滑效果的影响,并深入探讨其机制。结果表明,在一定的工况条件下,凹槽深度不同,其承载性能存在一定的差异,当凹槽深度小于4μm时,随织构深度的增加其承载能力逐渐增强,当凹槽深度大于4μm时,随织构深度的增加其承载能力逐渐减弱,即深度值在4μm左右时油膜的承载能力最强。分析发现,织构深度的变化改变了润滑油流场的流动,深度增大到某个值时润滑油开始出现逆流现象,随着凹槽深度的增加,逆流区变大;逆流的存在削弱了织构的承载能力;速度不影响润滑油的流动走向,但会影响承压能力的大小;织构截面形状对润滑油的流动走向有影响,但对织构底部形成漩涡的规模大小影响不大,对润滑油膜承压能力影响不大。     

The Influence of Lubricating Agents on the Formation of a Film of a Styrene/Butadiene Latex

The interactions between paper coating lubricants and a carboxylated styrene/butadiene latex emulsion and their effect on latex film morphology have been studied. Calcium stearate, non-ionic polyethylene emulsion and organic triglyceride lubricants showed different interaction characteristics with the latex emulsion according to viscosity, zeta potential and isothermal calorimetric measurements. Calcium stearate lowered the viscosity of the dilute latex emulsion at low concentration suggesting a strong interaction with the latex particles due to a change in the hydrodynamic dimensions of the latex particles. The exothermic enthalpy change supported the assumption of a dissociative interaction. In contrast, both non-ionic polyethylene and organic triglyceride emulsion showed less pronounced enthalpy changes, indicating lower affinity for the latex particles. The reduction in viscosity showed, however, that at low lubricant concentrations there is an interaction between the latex particles and particularly the organic triglyceride emulsion. This suggests a selective adsorption of stabilizing agents and species from the lubricant emulsion which alters the hydrodynamic radius of the latex particles. The effects of the colloidal interactions on the morphology of the latex films monitored by Atomic Force Microscopy (AFM) indicated that specific surface interaction occurring in aqueous media influenced the topography and the surface chemical heterogeneity of the latex films. Especially in the case of calcium stearate, it seems that the dissolved species arrange themselves around the latex particles inhibiting film formation. The organic triglyceride, on the other hand, showed a lower interaction potential in the aqueous phase and it had a different impact on the film formation.     

Contact Interactions of the Roller in a Planetary Roller Screw and Their Influence on the Load Capacity

Russian Engineering Research - The load capacity of planetary roller screws may be increased, without increase in their size, by decreasing the profile angle of the screw threads. The profile angle...     

Influence of Journal Speed and Load on the Static Operating Characteristics of a Tilting-Pad Journal Bearing with Ball-and-Socket Pivots

Results are described for experiments aimed at determining the effects of increased speed and load on ball-and-socket pivots in tilting-pad journal bearings. Experimental measurements of journal static operating position were made for a 70-mm (2.75-in.), five-pad tilting-pad journal bearing with ball-and-socket pivots. Testing consisted of journal rotational speeds from 1650 to 7840 rpm and bearing static loads as high as 4.45 kN (1000 lbs). These speeds and loads were sufficient to attain a range of heat generation and pivot thermal growths. Results showed that at low speeds substantial cross-coupling effects were present. However, with increased heat generation at elevated speeds and loads, these cross-coupling effects were significantly reduced.