供油条件对挤压油膜阻尼器等效阻及周向位置阻尼的影响

为研究供油条件对挤压油膜阻尼器减振特性的影响,利用计算流体力学软件进行阻尼器的建模和数值仿真模拟。为了保证数值模拟的正确性和合理性,借助于双向激励试验器,基于机械阻抗法获得油膜阻尼,与数值仿真结果进行对比验证。通过数值仿真,研究供油孔数量、供油孔横截面积、供油槽尺寸以及供油流量等对阻尼器等效阻尼和周向位置阻尼的影响。结果表明:由于受到供油孔处的供油压力影响,单孔供油阻尼器提供的阻尼随周向位置呈现近似简谐函数曲线的变化规律,多个对称分布的供油孔可以有效地抑制这种影响,含有三个或者四个对称供油孔的阻尼器,不同周向位置的阻尼在一个进动周期内几乎保持不变。对于供油槽较浅的情况,阻尼器的等效阻尼随着偏心率的增加呈现非线性增加的趋势;随着供油槽深度的增加,非线性增加的趋势逐渐减弱;而供油槽较深时,等效阻尼随着偏心率的增加先减小后增加。另外,阻尼器供油槽宽度和供油流量对阻尼器的阻尼特性也有着明显的影响。研究结果将为挤压油膜阻尼器的设计提供依据。     

弹性环式挤压油膜阻尼器的流固耦合建模及动力特性分析

弹性环式挤压油膜阻尼器结合挤压油膜阻尼器和弹性支承的优点,其结构更为紧凑,为能进一步明确其动力学机理,在充分考虑油膜和弹性环之间相互作用的情况下,建立弹性环式挤压油膜阻尼器双向流固耦合模型,通过数值模拟,研究弹性环凸台高度、宽度、数目和在总间隙不变的情况下不同内外层油膜间隙以及弹性环的弹性模量等对该型阻尼器动力学特性的影响。结果表明,外层油膜对刚度的贡献大,内层油膜对阻尼的贡献大,相对较小的内层油膜间隙且较大的外层油膜间隙,有利于增加油膜阻尼而抑制油膜刚度非线性。随着弹性环凸台宽度、高度、数目的减小或弹性模量的增加,内外层油膜刚度和阻尼均增加,其中弹性环的弹性模量对该型阻尼器的动力特性影响相对较小。以上研究将为弹性环式挤压油膜阻尼器的设计、使用和维护提供参考。     

含挤压油膜阻尼器部件的简易传递矩阵

在对转子—轴承系统进行动力学分析时,传递矩阵法目前仍占有主导地位。高速旋转的转子系统为了减振常常采用挤压油膜阻尼器(SFD),但现有的教材与文献没有讲述含有挤压油膜阻尼器部件的传递矩阵。把挤压油膜阻尼器按外力处理,建立了含挤压油膜阻尼器的刚性圆盘质心的运动方程。在对运动方程做进一步的推导与整理过程中,定义一个由油膜刚度与阻尼系数组合形成的等效刚度系数,得到了与线性弹性支撑部件具有相同的形式的传递矩阵,使得含有挤压油膜阻尼器部件的传递矩阵简单明了,便于应用。等效刚度系数是关于油膜轴颈位移的高度非线性函数,同时介绍了一种迭代法求解的具体步骤。并通过与文献中转子系统的实验结果对比验证了该传递矩阵是正确的。     

整体式挤压油膜阻尼器对管道振动抑制试验

针对管道振动现象,设计了一种整体式挤压油膜阻尼器并分析其刚度影响规律。利用SAP2000软件模拟仿真阻尼减振效果。搭建二维门型管道振动试验台,在管道上安装整体式挤压油膜阻尼器,研究整体式挤压油膜阻尼器控制管道振动的影响规律。结果表明：整体式挤压油膜阻尼器安装在激振源处且与激振力平面平行时的减振效果最佳,较原始振动降幅达51.83%;安装在激振源处且与激振力平面垂直时的减振效果最差;安装两个整体式挤压油膜阻尼器减振效果优于安装一个整体式挤压油膜阻尼器;安装在激振源处的减振效果优于安装在远离激振源的效果。     

对挤压油膜阻尼器轴承和旋转机械转子—挤压油膜阻尼器轴承系统动力特性研究的回顾与展望

简要介绍挤压油膜阻尼器轴承及其基本分类，介绍各种挤压油膜阻尼器轴承的动力学特性研究和建立阻尼器流体动力模型与挤压油膜力的进展情况，总结了支承在挤压油膜阻尼器轴承上的旋转机械转子系统的动态响应特性和稳定性的研究结果及对这类强非线性的转子－阻尼器支承系统的非线性响应特性研究的进展情况，并对该类减振结构的未来发展进行了展望。     

挤压油膜阻尼器非线性特性实验研究

针对挤压油膜阻尼器转子系统的动力学特点,实验研究了大不平衡量条件下转子的非线性振动特性;同时研究了转子变速过程角加速度、滑油温度以及阻尼器静偏心对转子非线性振动的影响。结果表明:大不平衡量条件下转子系统可能出现非线性振动跳跃;增大转子变速过程角加速度,降低油温,可抑制非线性振动跳跃;提高阻尼器内外环同心度,减小阻尼器静偏心,可提高阻尼器减振性能,同时抑制非线性振动跳跃;阻尼器设计时必须考虑重力影响,为转子设计预置偏心。     

可控挤压油膜阻尼器—转子系统主动控制试验

通过调节可控挤压油膜阻尼器（ＣＳＦＤＢ）的结构参数（油膜间隙、油膜承载长度）,使其产生的非线性油膜力逼近线性转子系统所需的控制力,可以有效地控制转子系统的不平衡响应。试验研究了可控挤压油膜阻尼器（ＣＳＦＤＢ）对转子系统振动的主动控制,并取得了良好的控制效果。     

转子挤压油膜阻尼器减振效率的理论研究

针对如何有效降低滚动轴承-转子系统振动幅值的问题,将挤压油膜阻尼器-滚动轴承-双盘转子系统作为研究对象,以雷诺方程、动压润滑理论、短轴承假设、油膜力周向边界条件、非线性赫兹接触理论等为基础,建立转子系统动力学方程,运用Newmark-β迭代数值求解方法结合Newton-Raphson迭代来求解转子系统相应节点的激励响应结果,分析该转子系统非线性动力学特性,从轴心轨迹图和时域曲线图两个方面对比有无挤压油膜阻尼器转子系统的位移响应,从理论角度对转轴振动能量被鼠笼支撑及挤压油膜部分有效吸收的程度进行研究,并对转子系统0～10 000 r/min转速区间下不同阻尼器参数情况下的减振效率进行考量,研究发现转子系统在转速相对较低时减振效果不佳,并分析其原因,研究结果可为转子系统挤压油膜阻尼器的结构参数设计提供理论依据。     

挤压油膜阻尼器非线性振动机理 及结构创新综述

针对带有挤压油膜阻尼器(SFD)的转子系统在恶劣工况下出现的非线性振动问题,阐述了挤压油膜阻尼器的锁死、双稳态响应及非协调进动等因素,导致减振失效的一系列非线性振动现象,归纳了其发生的原因;对通过优化系统参数来改善其工作特性的思路进行了阐述,指出了挤压油膜阻尼器技术今后的改进方向;重点介绍了一种新型的整体式挤压油膜阻尼器(ISFD)结构,对其提高稳定性的机理进行了分析,列举了其在工程上的应用实例。研究结果表明:与传统的挤压油膜阻尼器相比,整体式挤压油膜阻尼器具有良好的动力特性,能显著提高转子系统的稳定性,有效避免非线性振动的发生。     

浮环式挤压油膜阻尼器减振机理研究

从广义雷诺方程出发,推导了浮环式挤压油膜阻尼器(FSFD)内、外层油膜的稳态雷诺方程。根据文中的理论模型,基于有限差分法编写了计算程序,研究分析了结构参数对FSFD动力特性的影响。研究表明:与传统SFD比较,FSFD改善了油膜力的非线性;相同条件下,FSFD内层油膜力要大于外层油膜力,内、外层油膜力都随油膜宽度的增大而增大,随油膜间隙的增大而减小;在结构参数一定的情况下,FSFD抑制突加不平衡的能力要强于传统SFD。     

Sine Sweep Load vs. Impact Excitations and Their Influence on the Damping Coefficients of a Bubbly Oil Squeeze Film Damper

Squeeze Film Dampers (SFD) suppress excessive vibrations and rotordynamic instabilities in turbomachinery. However, air ingestion into the oil film is a pervasive phenomenon that affects their performance, complicating their analysis and design, and demanding careful experimentation. The type of force excitation affects the damping coefficients since the ensuing dynamic journal motions may lead to a rapid expulsion or to coalescence and entrapment of the air within the lubricant matrix. Experimental force coefficients from a small rotor-SFD apparatus operating with controlled mixtures of air and oil, i.e. emulating degrees of air entrainment, are obtatined from the dynamic response to sine sweep forces and impact loads. The parameter identification procedure renders damping coefficients that are sensitive to the type of force excitation. For impact tests, damping coefficients steadily increase for lubricant mixtures up to 50 % in air volume content. For unidirectional sine sweep load excitations, the damping coefficients are nearly constant even for mixtures with larger air volume fractions. The larger and sustained amplitudes of periodic journal motion induced in the sweep sine tests expel rapidly the air from the mixture, thus leaving a lubricant film that generates invariant dumping coefficients. Conversely, in the impact tests, the journal motions are of small amplitude and short duration thus providing larger damping values; the mixture behaves as a nearly incompressible fluid of larger viscosity.     

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.     

An experimental study on oil-film dynamic coefficients

The oil-film force of hydrodynamic bearing is often characterized by a set of linear stiffness and damping coefficients. This paper presents an experimental method to recognize these coefficients and establishes their characteristics under varieties of operating conditions. The fundamental test model is obtained from a Taylor series expansion of bearing reaction force. A delicate test rig is constructed and experimental data are acquired under various testing conditions. The coefficients are evaluated by means of least mean square in time domain. The experiments indicate that the linear oil-film dynamic coefficients are sensitive to the excitation force. The sensitivity is varied for the different coefficients. From the investigation, it can be seen that the linear model is invalid under condition of high excitation force. That is to say, the nonlinear components, which are ignored in traditional linear model, should be considered in those conditions.     

舰船尾轴承变形对其阻尼特性的影响研究

舰船推进轴系受多个载荷的作用，导致船体、螺旋桨轴和尾轴承发生变形，并在尾轴承中心线与螺旋桨轴颈中心线之间形成一个变形角。研究了变形夹角对轴承油膜动态阻尼参数的影响关系，用数值计算的方法计算得到了轴承油膜阻尼参数与变形角之间的变化关系。结果表明：轴承中线与轴颈轴线之间的变形夹角对轴承润滑阻尼参数的影响关系为强的非线性关系；变形角对轴承阻尼特性影响较大，随着变形角的增大，油膜阻尼Dxx和Dyy会增大，而阻尼Dyz和Dxy会减小；轴颈中线与轴承中线之间夹角对油膜阻尼参数的影响局限在一定的弯曲变形范围内，当变形继续增大时，螺旋桨轴与尾轴承发生刚性接触，此时轴与轴承的刚性接触摩擦作用增大，阻尼作用急剧改变。     

Force coefficients for a large clearance open ends squeeze film damper with a central feed groove: Experiments and predictions

The paper describes a large load squeeze film damper (SFD) test rig, details measurements of dynamic loads inducing circular orbits conducted on a large clearance (c=0.250 mm) open ends centrally grooved SFD, and presents the identified experimental SFD force coefficients for operation at three static eccentricities. The rig has a bearing cartridge supported atop four elastic rods and a stationary journal, 0.127 mm in diameter. The damper consists of two parallel film lands, 12.7 mm in length, separated by a central groove, 6.35 mm 9.5 mm in depth. In the journal, three equally spaced holes, 120° apart, supply a light lubricant into the central groove and squeeze film lands. The experimental SFD force coefficients are compared to test results obtained earlier for a damper with the same film land lengths but with a smaller clearance (c=0.140 mm) and against predictions obtained from an advanced physical model that accounts for the flow field in the central groove and the interaction with the adjacent film lands. Dynamic pressures in the film lands and in the central groove are (not) surprisingly of the same order of magnitude. The central groove affects the dynamic forced response of the test damper to generate large direct damping coefficients, ~3.5 times those derived from classical lubrication formulas. Experimental added mass coefficients are ~7.4 times the predictive classical values. Predictions from an advanced model correlate well with the test data when using a shallow groove depth. The measurements and analysis advance knowledge on the dynamic forced performance of SFDs, point out to the limited value of simplistic predictive formulas, and validate the accuracy of a modern predictive tool.     

基于波纹箔片刚度试验的气体箔片轴承动力学特性

为了研究波纹刚度特性以及其对箔片轴承动力学特性的影响,设计了波纹箔片刚度测试试验台。分别对两端固定和一端固定一端自由两种约束条件下的波纹箔片刚度进行了测试,并将试验结果与仿真结果进行了对比分析。最后基于轴承波纹结构刚度特性,利用小扰动法求解了轴承动力学特性系数,研究了波纹箔片刚度特性对轴承动力学特性系数的影响。结果表明：两端固定波纹箔片刚度较一端固定一端自由波纹箔片单位宽度刚度大5倍以上,并且随着波纹变形量的增加,两端固定约束使其波纹箔片刚度比一端固定一端自由波纹箔片更具有非线性,而刚度仿真结果并没有体现出非线性,只是模型中引入的结构摩擦因数使得刚度值随摩擦因数有所增大。最后轴承载荷增加会使得轴承刚度系数以及主阻尼增加,其他阻尼系数减小,并且鉴于波纹箔片刚度非线性的原因,采用刚度试验值计算得到的轴承动力学系数增加幅度要明显大于文献仿真模型。     

Identification of the dynamic performance of a gas foil journal bearing operating at high temperatures

This paper presents an experimental investigation of the dynamic force performance of gas foil bearings (GFBs) at high temperatures. A dynamic performance test rig with a GFB mounted on a rotating hollow shaft, heated by a cartridge heater inside the hollow shaft, and excited by two orthogonally positioned electromagnetic shakers determines the frequency dependent stiffness and damping coefficients of the test GFB for increasing shaft temperatures. The test heater temperatures are 21°C (room temperature without heating), 100°C, 200°C, 300°C, and 400°C, and the excitation frequencies are 120 Hz, 140 Hz, 160 Hz, and 180 Hz. The test rotating speed and static load are 12 krpm and 30 N, respectively. The vibration amplitude of the test GFB is adjusted to approximately 30 μm by controlling the power amplifier connected to the electromagnetic shakers throughout the series of experiments. The test results show that both the direct stiffness and damping coefficients of the test GFB increase with increasing excitation frequencies. As the shaft temperature increases, the direct stiffness coefficients decrease by ～ 8%, and the direct damping coefficients decrease by approximately 30%. A model prediction benchmarked against the test data reveals that the cross-coupled stiffness coefficients are smaller than the direct stiffness coefficients for the test GFB.     

A Three-Dimensional Navier-Stokes-Based Numerical Model for Squeeze Film Dampers. Part 2—Effects of Gaseous Cavitation on the Behavior of the Squeeze Film Damper

The damping coefficients for a squeeze film damper (SFD) were determined and discussed in Part 1 using the full Navier-Stokes equations (NSE) coupled with a homogeneous cavitation model. In this continuation, Part 2, article these coefficients are introduced into the governing equations of motion to determine the trajectory of the rotor and its stability. The nonlinear response of the damper predicted by the NSE model is compared to results obtained from the application of the Reynolds equation. The influences of gas mass concentration as well as that of the amount of imbalance on transmissibility and eccentricity of the damper are also investigated.     

An experimental identification model of rotordynamic coefficients of seals using unbalanced synchronous excitation method

This study presents an improved impedance method based on unbalanced synchronous excitation to identify the rotordynamic coefficients of labyrinth seals. The rotordynamic coefficient test is implemented near the cylinder resonance frequency to enlarge the influence of seal force. The force generated by the rotor unbalance is used to provide synchronous frequency excitation for the rotordynamic coefficient test. Four unique equations are set up under two sets of different rotor unbalance conditions to obtain four unknown complex rotordynamic coefficients. The factors that influence the rotordynamic coefficients of seals, namely, unbalance mass, inlet/outlet pressure ratio, and rotating speed, are considered. The dynamic coefficients are minimally affected by different rotor unbalances. The direct items are nearly equal with same signs, whereas the cross-coupled items are nearly equal with opposite signs. All coefficients increase with increasing inlet/outlet pressure ratio and rotating speed. The direct stiffness coefficients increase more quickly than the cross-coupled items. In addition, the effect stiffness and effect damping coefficients are analyzed; results indicate that both coefficients increase with increasing rotating speed.