Abstract ：

Journal bearing is one of the most important components for supporting high speed rotating machinery such as compressors and turbo machines. In recent trends, non-circular journal bearings (lemon bearing, three-lobe bearing, four-lobe bearing, etc.), for their greater load capacity and better stability, have become a superior choice and found wide spread application. In this paper, the nonlinear oil film force is expressed using the dynamic stiffness and damping of 1st-3rd order. And the film thickness and pressure are analyzed using Fourier method, so that the corresponding harmonic components and their deeper connection can be further explored. The paper shows that the nonlinear dynamic performances are connected closely with the bearings’ profile, and lays the foundation for expressing the precise nonlinear oil film force. Copyright © 2018 ASME.

Keyword ：

Dynamics Fourier analysis Journal bearings Lubricating oils

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Abstract ：

As one of the most important components in a rotor-bearing system, journal bearings provide proper support and damping to the rotor so that it can run both smoothly and efficiently and keep stable under different working conditions. As the rotating speed of the rotor growing faster and load getting heavier, the traditional cylinder journal bearing can no longer meet the demand of stabilizing the rotor, so different kinds of non- circular journal bearings were invented, such as elliptical bearing, multilobe bearing, wave bearing and etc., to provide better stability and greater load capacity. However, these kinds of non- circular bearings were mostly designed by experience of the engineers, and also the current hydrodynamic bearing design methodology still depends on empirical design. There lacks of corresponding theoretical foundation. In order to develop a theoretical method for bearing designing, an innovative analyzing approach needs to be carried out to explore the mechanism of the bearings and its performance. In this paper, a new approach is presented focusing on the profile of each bearing and their film thickness. A universal mathematical expression for different types of noncircular bearings has been put forward based on the Fourier series theory. The influence of periodic harmonics of film thickness on the static performance of non-circular bearings of finite length is studied for incompressible lubricant. The results show that the film thickness can always be expanded into a Fourier series, and the harmonic components of film pressure can be obtained by solving the Reynolds equation. Finally, the relation between the k-th order harmonic component H0,k and the corresponding static pressure component P0,k is established. This new investigation can be used to improve the non-circular bearing designing methodology with theoretical guidance. Copyright © 2018 ASME.

Keyword ：

Harmonic components Hydrodynamic bearings Mathematical expressions Non-circular bearings Rotor-bearing system Static performance Theoretical foundations Theoretical methods

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Abstract ：

In order to achieve high working efficiency, modern gas turbines operate at high temperature which is close to the melting points of metal alloys. However, the support of turbine end suffers the thermal deformation. And the journal center position is also changed due to the effects of high temperature and shaft gravity. Tangential or radial supporting structures, which are composed of supporting struts, diffuser cones, hot and cooling fluid channel, are widely used in gas turbine hot end. Cooling technology is usually used to keep the bearing temperature in a reasonable range to meet requirements of strength and deformation of the supporting struts. In this paper, three major assumptions are proposed: (a) radiation is not considered, (b) cooling flow system is only partially modeled and analysis assumes significantly higher cooling flow that is not typical for current engines, and (c) only steady state heat transfer is considered. And a 3D fluid-solid coupled model based on finite -element method (FEM) is built to analyze the performances of both the tangential and the radial support. The temperature distribution, thermal deformation and stress of supports are obtained from CFD and strength analysis. The results show that either the tangential or radial support is used in a 270MW gas turbine; the thermal stress is about 90.3% of total stress which is produced by both thermal effects and shaft gravity. Comparing to the results from radial supports, it can be seen that the struts stress and position variation of journal center of tangential support are smaller. Due to a rotational effect of the bearing housing caused by the deformation of the tangential struts, the thermal stress in these tangential struts can be relieved to some extent. When both thermal effect and shaft gravity are considered, the stress of each tangential supporting strut is almost uniformly distributed, which is beneficial to the stability of rotor system in the gas turbine.

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Abstract ：

随着滚动轴承向着高速化和重载化的方向发展，在轴承设计需要考虑“偏载效应”和轴承润滑的影响。以圆弧修型滚子为研究对象，建立偏载工况下的有限长线接触等温弹流润滑模型，研究滚子倾斜角度和卷吸速度对滚子次表面应力的影响。计算结果表明，当滚子发生倾斜后，滚子轴向的压力分布不均，受载端的油膜压力和von Mises应力明显增大，并随着倾斜角变大而增大；当滚子载荷不变，卷吸速度增大时，油膜出口区的二次压力峰逐渐增加，导致次表面最大von Mises应力增大，最大von Mises 应力的位置向滚子表层移动。研究结果表明，滚子倾斜及卷吸速度对滚子的次表面应力有较大的影响。

Keyword ：

次表面应力 偏载工况 弹流润滑

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Abstract ：

分析了电磁式动平衡头励磁线圈的工作特点,提出了一种“BUCK调压+H桥调相”复合式励磁线圈驱动电路.BUCK调压电路产生幅值可变电压,H桥调相电路在励磁线圈中产生间断的、方向交错的电流.调压和调相结合,满足励磁线圈初始电磁力大、电磁力方向交错变化的特殊要求.仿真及实验验证了驱动电路的有效性,该电路在实际的电磁式动平衡系统中得到了很好的应用,具有工作稳定、通用性强的特点.

Keyword ：

电磁式动平衡 励磁线圈 驱动电路

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Abstract ：

电磁平衡头是近十几年出现并发展起来的一种新型在线动平衡装置.由于其磁性盘为一内齿轮结构,其与永磁体之间因此存在齿槽转矩,影响平衡头运动的平稳性.本文设计了一款电磁平衡头,分析了其运行原理,同时基于Ansoft-MaxweU软件计算了其齿槽转矩和电磁运行转矩.借鉴永磁电机的齿槽转矩抑制方法,采用在磁性盘端面开设矩形槽的方法,研究了不同开槽方案对平衡头电磁转矩即运行平稳性的影响.研究表明,当励磁电流较小时,在齿状磁性盘上开一个或多个一定尺寸的矩形槽时,可一定程度上提高平衡头运行平稳性.

Keyword ：

齿槽转矩 齿状磁性盘 电磁平衡头 辅助槽 运行平稳性

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Abstract ：

In order to investigate the cause of the typical bush rupture and wear damages in the journal bearing of the steam turbine generator set, the lubrication turbulence and thermo-hydrodynamic effects were studied. The generalized Reynolds equation, energy equation and heat conduction equations were solved with the finite difference method, and the pressure, temperature, thickness distribution of the oil film were obtained. Analysis results can be well explains the bearing bush burst in bearings maximum pressure place because of heavy load running. The bearing bush burst made friction intensified that caused oil temperature increasing and the viscosity reduce, which led to the rotor eccentricity increase, the minimum film thickness smaller and bearing static working point down, thus causing the wear damages until shutdown.

Keyword ：

journal bearing thermo-hydrodynamic effect turbulence wear

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Abstract ：

Based on the nonlinear theory, the unbalanced response behavior of the rotor dynamic system supported by gas journal bearings is investigated. A time-dependent mathematical model is established to describe the pressure distribution of gas journal bearing with nonlinearity. The rigid Jeffcott rotor with self-acting gas journal bearing supports is modeled. The differential transformation method is employed to solve the time-dependent Reynolds equation of gas bearings. The unbalanced responses of the rotor system supported by finite width gas journal bearings with three axial grooves are analyzed by bifurcation diagram, orbit diagram, Poincare´ map diagram and frequency diagram. The numerical results reveal periodic, period-doubling, period-4, period-8 and chaotic motion of nonlinear behaviors of the system.

Keyword ：

Differential transformation methods Gas journal bearings Nonlinear Nonlinear dynamic behaviors Rotor dynamic systems Self-acting gas journal bearings Time-dependent reynolds equation Unbalanced response

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Keyword ：

电磁轴承 高速电机 滚动轴承 挤压油膜阻尼器 临界转速 弹性支撑

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Abstract ：

基于非线性理论,分析了气体动压轴承-转子非线性动力系统的不平衡响应.建立了与时间相关的非线性气体动压轴承的压力分布模型和气体动压轴承-刚性Jeffcott转子系统的动力学模型.运用微分变换法求解了动压气体润滑的Reynolds方程,得到了非线性气膜压力分布.运用分岔图、轨迹图、Poincaré映射图及频谱图研究了三轴向槽有限宽气体轴承支承的非线性转子系统的不平衡响应.数值结果表明,系统的非线性行为包括周期运动、周期二运动、周期四运动、周期八运动及混沌运动等.

Keyword ：

动压气体轴承 非线性 微分变换法 转子

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