Rubbing-Induced Vibration Response Analysis of Dual-Rotor-Casing System

Considering gyroscopic effects caused by rotational speed,torsional vibration as well as coupling effects among inner rotor,out rotor and casing,a dynamic model of the dual-rotor-casing system is established using finite element(FE)method.By comparing the natural characteristics obtained from MATLAB and ANSYS,the developed model is verified.Then rubbing-induced vibration responses in dual-rotor-casing system are analyzed.The effects of rotational speed and speed ratio on rubbing vibration responses of the system are discussed.Results show that different combined frequency components will appear in the spectrum except two unbalanced excitation frequencies and their multiple frequency components,and these frequencies can be used as the dual-rotor aero-engine rubbing failure diagnosis frequencies when rubbing occurs.Besides,the amplitude of torsional vibration is larger than that of lateral vibration under the same working condition,and speed ratio has a great impact on the periodicity of the system rubbing-induced motion trajectory.The amplitude of rubbing-induced responses under counter-rotation is less than that under co-rotation with the same parameters.

Analysis on Nonlinear Dynamic Properties of Dual-Rotor System

In order to clarify the effects of support structure on a dual-rotor machine,a dynamic model is established which takes into consideration the contact force of ball bearing and the cubic stiffness of elastic support. Bearing clearance,Hertz contact between the ball and race and the varying compliance effect are included in the model of ball bearing. The system response is obtained through numerical integration method,and the vibration due to the periodic change of bearing stiffness is investigated. The motions of periodic,quasiperiodic and even chaotic are found when bearing clearance is used as control parameter to simulate the response of rotor system. The results reveal two typical routes to chaos: quasi-periodic bifurcation and intermittent bifurcation. Large cubic stiffness of elastic support may cause jump and hysteresis phenomena in resonance curve when rotors run at the critical-speed region. The modeling results acquired by numerical simulation will contribute to understanding and controlling of the nonlinear behaviors of the dual-rotor system.

Effect of Hub-Ratio on Performance of Asymmetric Dual-Rotor Small Axial Fan

Currently, domestic and abroad scholars put more attention on contra-rotating dual-rotor axial fan. But there is less scholars study on asymmetric dual-rotor small axial fan, which is one of the contra-rotating dual-rotor axial fans. Like axial fan, many factors have influence on the performance of the asymmetric dual-rotor small axial flow fan, such as the wheel hub ratio, blade shape, blade number, stagger angle and the tip clearance. Because wheel hub ratio has great impact on the performance of the fan, we choose the size of wheel hub ratio as a variable factor to study the model change. There is a different wheel hub ratio between front stage impeller and rear stage of asymmetric dual-rotor small axial fan, so it is very beneficial to select the greater wind area that the fan area of external diameter minuses the area occupied by the blades and the hub as front stage impeller. In this paper, the hub-ratio of front stage impeller is 0.72, and that of rear stage is 0.72, 0.67 and 0.62 respectively along with the front stage impeller. Three kinds of models with different hub ratio of rear stage are simulated using the CFD software and the static characteristics are obtained. Based on the experimental test results, the internal flow field of the asymmetric dual-rotor small axial fan is analyzed in detail, the impact trends of different hub-ratio on the performance of asymmetric dual-rotor small axial fan are obtained and the argument of structure optimization for dual-rotor small axial fan is provided.

Dynamic balancing of dual-rotor system with very little rotating speed difference

Unbalanced vibration in dual-rotor rotating machinery was studied with numerical simulations and experiments. A new method is proposed to separate vibration signals of inner and outer rotors for a system with very little difference in rotating speeds. Magnitudes and phase values of unbalance defects can be obtained directly by sampling the vibration signal synchronized with reference signal. The balancing process is completed by the reciprocity influence coefficients of inner and outer rotors method. Results showed the advantage of such method for a dual-rotor system as compared with conventional balancing.

Synchronous impact phenomenon of a high-dimension complex nonlinear dual-rotor system subjected to multi-frequency excitations

The“synchronous impact”is a phenomenon that increases the dynamic load of the inter-shaft bearing,when the frequency of the aerodynamic excitation is close to the contact frequency of the inter-shaft bearing.This work addresses the“synchronous impact”phenomenon of an aero-engine.The 104 degree-of-freedom dynamical model of an aero-engine is established by the finite element method,in which the complex nonlinearity of the Hertzian contact force of the inter-shaft bearing with clearance is included,and the multi-frequency excitations such as the unbalanced excitations of the high-and low-pressure rotors and the aerodynamic excitation are considered.A harmonic balance method combined with the alternating frequency time-domain method(HB-AFT)is introduced to obtain periodic responses of the high-dimension complex nonlinear dual-rotor system.The results show that there emerges a peak value of the amplitude-frequency response for the contact frequency harmonic component of the outer ring of the inter-shaft bearing,when the aerodynamic excitation frequency is close to the contact frequency.In addition,the dynamic load of the inter-shaft bearing increases significantly.Moreover,the parametric analysis shows that the“synchronous impact”phenomenon is sensitive to the change of the speed ratio of the high-and low-pressure rotors.The dynamic load of inter-shaft bearing can be significantly reduced by changing the speed ratio by 1%.The results obtained in this paper not only provide more insight into the mechanism of the“synchronous impact”phenomenon but also demonstrate the HBAFT method as a potential semi-analytical tool to explore the high-dimension complex nonlinear system.

某型航空发动机振动值波动故障诊断和排除

针对某型航空发动机试车过程中的稳态振动波动问题,开展了时域和频域分析,指出振动波动是由于低压2倍频和高压基频振动拍振所引起。推导了航空发动机拍振引起的振动响应,建立了某型航空发动机双转子动力学模型,并进行了仿真分析。仿真结果表明,当发动机两个激振力频率相近时,会产生拍振引起振动波动,仿真结果与试验结果相吻合。结合发动机结构和其工作特点,分析了发动机形成低压倍频-高压基频耦合拍振的条件,给出了拍振排除方法,并通过试验验证了方法的正确性。工程上可以通过调整高压和低压转子转差关系,将转速比调整到合理范围内即可消除拍振。

双并列转子永磁直驱电机转子不平衡力分析与优化

双并列转子永磁直驱电机受轴间距限制,设计时会切掉部分定子铁心和绕组,造成转子电磁力不平衡。为最大限度地抑制转子所受的不平衡电磁力,该文从双并列转子结构出发,分析了电机绕组电感参数不对称的原因,提出通过合理设计线圈跨距和分布平衡三相电感。在此基础上,构建转子所受总电磁力的数学模型,理论分析各个分力的来源及影响因素,研究各个分力对转子所受总电磁力的影响,提出了优化占空角、优化耦合间距、采用定子端部不对称结构、采用转子偏心结构和切除部分单元电机五种优化方法,实现对转子所受电磁力的优化,探讨了不同方法的优化效果,以及其对转矩脉动的影响,总结了不同优化方法的优缺点。

双转子-中介轴承系统动力学仿真与实验研究

针对双转子系统复杂的动力学特性以及总是存在的质量不平衡现象,建立内外双转子系统动力学模型,通过轴心轨迹图、时域图、频谱图、庞加莱截面图和分岔图分析其振动特性,并通过双转子系统实验台升速和不平衡实验验证了理论和仿真结果。结果表明:双转子系统在升速过程中会发生2次振幅突然加剧的现象,2次主共振分别由内、外转子转速达到系统固有频率引起;双转子系统在不同的转速下会呈现出不同的振动特性;增大内转子的不平衡量,不仅会影响内转子系统振动响应,还会影响外转子系统振动响应,并且对前者的影响更显著。

微速差双转子信号分离方法精度研究

针对提取频率相近信号特征的经典算法Zoom-FFT(ZFFT)在分离差频1 Hz以内的微速差信号时,需要足够的数据长度才能达到良好的信号分离效果的问题,为了在不增加数据长度的基础上提高信号频率分辨率,在ZFFT算法的基础上产生了ZFFT+FT算法。通过LabVIEW软件仿真试验研究了该算法对频率差1 Hz和0.5 Hz的微速差信号提取精度,并与chirp Z transform(CZT)算法、ZFFT算法以及FFT算法的提取精度作了对比,通过提取结果的相对误差及方差来衡量提取精度。在同轴微速差双转子试验台进行现场试验,利用FFT对微速差信号28 s数据集的提取结果与CZT,ZFFT及ZFFT+FT算法对4 s数据集的提取结果作对比,ZFFT+FT与FFT算法的提取结果最大相差0.56 μm,验证了ZFFT+FT的实时性和精确性。结果表明,ZFFT+FT算法能够实时精准提取频率差1 Hz以内的微速差信号。研究结果可为旋转机械微速差信号的提取提供参考。

基于改进LADRC的矢量推力双旋翼飞行器姿态控制

针对矢量推力双旋翼无人机姿态控制过程中存在强耦合、模型不精确的问题,提出了一种改进型的线性自抗扰姿态控制(linear active disturbance rejection controller,LADRC)方法。该方法利用改进线性扩张状态观测器(linear extended state observer,LESO)提高对总扰动的实时观测精度,根据姿态角的误差及其变化率引入模糊控制思想对线性状态误差反馈控制律进行在线参数整定,最后以矢量推力双旋翼飞行器为研究对象,对比PID和常规LADRC对外界扰动的抗扰效果,仿真试验验证了该方法能够较好估计补偿系统的总扰动,具有更好的抗扰性能和收敛速度。

A 5-DOF Model for Aeroengine Spindle Dual-rotor System Analysis

This paper develops a five degrees of freedom（5-DOF） model for aeroengine spindle dual-rotor system dynamic analysis.In this system,the dual rotors are supported on two angular contact ball bearings and two deep groove ball bearings,one of the latter-mentioned bearings works as the inter-shaft bearing.Driven by respective motors,the dual rotors have different co-rotating speeds.The proposed model mathematically formulates the nonlinear displacements,elastic deflections and contact forces of bearings with consideration of 5-DOF and coupling of dual rotors.The nonlinear equations of motions of dual rotors with 5-DOF are solved using Runge-Kutta-Fehlberg algorithm.In order to investigate the effect of the introduced 5-DOF and nonlinear dy-namic bearing model,we compare the proposed model with two models：the 3-DOF model of this system only considering three translational degrees of freedom（Gupta,1993,rotational freedom is neglected）;the 5-DOF model where the deep groove ball bearings are simplified as linear elastic spring（Guskov,2007）.The simulation results verify Gupta＇s prediction（1993） and show that the rotational freedom of rotors and nonlinear dynamic model of bearings have great effect on the system dynamic simula-tion.The quantitative results are given as well.

混合转子永磁电机双风道冷却系统设计

混合转子永磁电机具有高功率密度的优势,但也导致电机散热空间和散热能力不足等问题。为此,根据其特有的转子结构提出一种双风道冷却系统,并采用计算流体力学(Computational fluid dynamics,CFD)的方法对电机温度场进行验证。首先,根据电机损耗和尺寸设计一个适合双风道的轴流风扇。其次,对不同进、出风口的结构参数进行仿真,对比和分析仿真结果,选出冷却性能较好的参数组合。最后对单风道和该参数组合下的双风道进行数值模拟,仿真结果表明,使用双风道冷却结构后电机散热能力显著提升。

新型双转子双定子永磁同步发电机的磁场及耦合效应分析

为了解决目前海上风力发电机存在的成本高、体积大等问题,提出一种新型双转子双定子永磁同步发电机(DRDS-PMSG).建立了发电机的等效磁路模型,采用有限元分析方法评估了发电机的电磁特性及内外电机的耦合效应,部分仿真结果得到了实验验证.仿真结果表明:随着内、外永磁体相对位置的改变,电机等效磁路存在3种典型情况,并可通过耦合系数对耦合区域的等效磁阻进行描述;内、外电机的耦合效应体现在齿槽转矩、电磁转矩等电磁特性上,内、外电机的齿槽转矩峰峰值分别为0.52和1.64 kN·m,电磁转矩平均值分别为11.65和27.09 kN·m,转矩脉动分别为6.02%和4.12%;总体来看,内、外电机之间存在一定程度的耦合,但该耦合效应被隔磁环有效削弱.

含呼吸裂纹的多盘双转子系统振动特性探究

由于材料、工作环境等因素影响,以航空发动机为代表的旋转机械在工作过程中可能会产生裂纹故障,常见的裂纹类型为呼吸裂纹。为分析该故障对轴系振动特性的影响,基于某型双转子涡扇航空发动机,建立了包含风扇和多个轮盘在内的双转子—支承动力学数值仿真模型,使用Newmark-β法分别对不同裂纹相对深度和不同转速下的系统工况进行了数值仿真求解。结果发现:随着裂纹逐渐加深,转子高频分量愈加明显,系统稳定性下降;随着转速升高,系统出现了2X,3X分量,工频分量在一阶临界转速前后先增大后减小,轴心轨迹由不规则形状逐渐转变为圆形。

Modal analysis strategy and nonlinear dynamic characteristics of complicated aero-engine dual-rotor system with rub-impact

This paper aims to gain insight into the nonlinear modal characteristics and the possible influence of the modes on the responses for the practical dual-rotor system with rub-impact in aero-engine.The finite solid element method combined with a constraint stiffness model produced by rub-impact is introduced to build the governing equation of the complicated nonlinear dual-rotor system.In order to deal with the efficiency and numerical divergence in the process of solving the nonlinear modes of this large-scale nonlinear system,an analysis strategy is proposed by integrating a two-layer reduction technique into the harmonic balance method.The effectiveness of the analysis strategy is validated by applying to a simple rotor system,which can easily obtain the theoretical result.Based on the modeling method and analysis strategy,the modal characteristics of an aero-engine dual-rotor system with rub-impact are revealed.The results show that the modal frequency of the dual-rotor system increases when rub-impact occurs and has the feature of interval,which allows us to obtain the critical speeds of the rubbing system by traditional Campbell diagram.The rotation direction is an important factor since it can not only affect the gyroscopic effect but also change the friction effect of the rub-impact.It is found that the modal frequencies of the counter-rotation dual-rotor are less than those of co-rotation condition.More importantly,the forward modes of the counter-rotation dual-rotor may be instable when rub-impact occurs at a certain rotor,while the corresponding modes under the co-rotation condition are always stable.Furthermore,by analyzing the rubbing response of the dual-rotor,it is found that the modal characteristics have an important influence on rotor’s response.The instable forward modes existing in the counter-rotation dual-rotor may lead to the divergence of the response when passing the corresponding critical speed.

Nonlinear vibration response characteristics of a dual-rotor-bearing system with squeeze film damper

Rolling bearing and Squeeze Film Damper(SFD)are used in rotor support structures,and most researches on the nonlinear rotor-bearing system are focused on the simple rotor-bearing systems.This work emphasizes the comparative analysis of the influence of SFD on the nonlinear dynamic behavior of the dual-rotor system supported by rolling bearings.Firstly,a reduced dynamic model is established by combining the Finite Element(FE)method and the freeinterface method of component mode synthesis.The proposed model is verified by comparing the natural characteristics obtained from an FE model with those from the experiment.Then,the steady-state vibration responses of the system with or without SFD are solved by the numerical integration method.The influences of the ball bearing clearance,unbalance,centralizing spring stiffness and oil film clearance of SFD on the nonlinear steady-state vibration responses of the dual-rotor system are analyzed.Results show that SFD can effectively suppress the amplitude jump of the dual rotor system sustaining two rotors unbalance excitations.As the ball bearing clearance or unbalance increases,the amplitude jump phenomenon becomes more obvious,the resonance hysteresis phenomenon strengthens or weakens,the resonant peaks shift to the left or the right,respectively.SFD with unreasonable parameters will aggravate the system vibration,the smaller the oil film clearance,the better the damping performance of the SFD,the larger the centralizing spring stiffness is,the larger resonance amplitudes are.

Nonlinear resonance characteristics of a dual-rotor system with a local defect on the inner ring of the inter-shaft bearing

In this paper,the nonlinear resonance characteristics of a dual-rotor system are investigated with the consideration of a local defect on the inter-shaft bearing of the system.A simplified model of the dual-rotor system is proposed by considering that there is a local defect on the inner ring of inter-shaft bearing.The local defect is modelled as an inverted isosceles trapezoidal groove,which can make great influence on the inter-shaft bearing force due to the change of radial clearance of the inter-shaft bearing.The motion equations of the dual-rotor system are formulated by using the Lagrange equation.The Runge-Kutta method is employed to solve the motion equation.The amplitude-frequency response curve of the dual-rotor system is obtained,the abnormal resonance characteristics are analyzed.In addition,the influence of defect parameters,rotors and support parameters and inter-shaft bearing parameters on the amplitude-frequency characteristics of the system are discussed.The results show that there are two main resonance peaks and four abnormal resonance peaks on the amplitude-frequency response curve of the dual-rotor with a local defect on the inner ring of the inter-shaft bearing.Through analyzing the vibration response of the abnormal resonance peaks,it is found that the first two abnormal resonances are caused by the combined resonance,which are related to the inner ring fault and the rotational speed of high or low pressure rotors,and the last two resonances are caused by the induced resonance of the inner ring fault.At the same time,when the parameters of defect,rotors and support and inter-shaft bearing change,the resonance of the system also shows the corresponding change law.

不平衡电压下双笼转子无刷双馈发电机的多目标控制

该文以双笼转子无刷双馈感应发电机为主要研究对象。为了解决不平衡电网电压带来的功率绕组(power winding,PW)定子绕组功率脉动和电流不平衡的问题,设计了简化矢量控制策略,对PW侧谐波功率和负序电流进行抑制。此外,通过建立控制绕组(control winding,CW)电流统一表达式,对各个控制目标之间的关系进行了数学推导和理论分析。在此基础上,建立了PW电流不平衡度约束条件下,针对PW有功功率脉动幅值和无功功率脉动幅值的多目标控制数学模型。并采用粒子群算法进行求解,对CW统一电流表达式中的系数进行优化,计算CW参考电流值从而实现多目标控制。最后在双笼转子无刷双馈感应发电机实验平台上,对所提出的控制策略的有效性和理论推导的正确性进行了验证。

双分梳转杯纺花色牛仔纱设计及产品开发

为了解决传统牛仔纱颜色单调、织物风格单一,且存在染色污染的问题,从牛仔纱线花色设计出发,详述选用黑白粘胶纤维、通过改变不同颜色纤维组分比例,在双分梳转杯纺单头试验机上纺制5种双节花色变化牛仔纱的方案设计;选取颜色风格为灰黑的牛仔纱,以分梳辊转速、转杯转速及成纱捻度3因素设计正交试验,对比不同试验水平所纺的纱线性能,优选出最佳纺纱工艺组合及其织物织造工艺。指出:在分梳辊转速为7.5 kr/min、转杯转速为50 kr/min、纱线捻度为65捻/(10 cm)的条件下,纺制的牛仔纱质量较好,织物具有明显的灰黑牛仔风格;采用双分梳转杯纺技术、改变原料组分及交替比例的纺纱模式,能直接进行牛仔纱色彩设计,生产方便高效且过程环保;增加有色原料组分变化比例及变化次数,可纺制出多节渐变的花色牛仔纱。

面向全色域转杯纺纱的Kubelka-Munk双常数理论模型构建及颜色预测

为了能在色纺纱的纺纱阶段即时调控纱线颜色,减少混色成本,缩短工艺流程,结合三通道数控转杯纺纱的特点构建了全色域网格化混色模型,该模型可在纺纱过程中进行全色域范围内的色相调控、明度调控和彩度调控。为了解决色纺纱的测配色问题,得到与之相匹配的测配色系统,根据来样快速进行计算机测配色,节约成本,结合传统Kubelka-Munk双常数理论模型的特点,从构建的全色域网格化混色模型中选取混合样来进行颜色预测。从传统Kubelka-Munk双常数理论模型颜色预测的结果发现,部分混合样的预测反射率明显低于实际的反射率,针对这个问题,重新构建了新的Kubelka-Munk双常数理论模型来进行颜色预测得到新的预测反射率,并用插值替换的方法,把传统Kubelka-Munk双常数理论模型预测结果中明显低于实际反射率的部分用新的预测反射率替换,得到最终的混合样预测反射率。结果表明:与传统的Kubelka-Munk双常数理论模型预测混合样颜色结果相比,新的Kubelka-Munk双常数理论模型预测颜色并用插值替换法替换后得到的最终的混合样的颜色,色差平均值从1.48降低到1.04,且所有混合样的色差均能控制在2.0以内。该预测方法较传统Kubelka-Munk双常数理论模型具有更好的预测精度,所构建的全色域网格化混色模型和新的Kubelka-Munk双常数理论模型可应用于多基色纤维混色色彩和混合比的预测。