Investigation of the dynamic characteristics of a dual rotor system and its start-up simulation based on finite element method

Recently,the finite element method(FEM) has been commonly applied in the engineering analysis of rotor dynamics.Gyroscopic moments,rotary inertia,transverse shear deformation and gravity can be included in computational models of rotor-bearing systems.In this paper,a finite element model and its solution method are presented for the calculation of the dynamics of dual rotor systems.A typical structure with two rotor shafts is discussed and the procedure for obtaining the coupling motion equations of the subsystems is illustrated.A computer program is developed to solve critical speeds and to simulate the transient motion.The influence of gyroscopic moments on co-rotation and counter-rotation is analyzed,and the effect of the speed ratio on critical speed is studied.The dynamic characteristics under different conditions of increasing speed during start-up are demonstrated by comparison with transient nodal displacements.The presented model provides a complete foundation for further investigation of the dynamics of dual rotor systems.

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.

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.

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.

Bearing loads of dual rotor-bearing system under stationary and transient conditions

Aimed at aeroengine vibration failure, bearing loads of dual rotor-bearing system caused by unbalance are calculated under stationary and transient conditions. The three-dimensional （3-D） finite element method （FEM） model of dual rotor-bearing system was established. Applying the ro- tor dynamics function of Ansys 12.0, bearing loads were calculated under various unbalance force in stationary condition, and the transient vibration characteristics and the effect of acceleration on bearing loads were discussed. On the basis of simulation results, the influence disciplines of unbal- ance on bearing loads and theoretic reference for reducing bearing loads during start-up were ob- tained.

Design, Control and Analysis of Low Cost Archetype Dual Rotor Helicopter for Educational Institution

This paper presents the design and development of low cost archetype dual rotor helicopter (LCADRH) for academic research in an educational institution. The LCADRH is installed with optical pitch encoder and yaw encoder which measure elevation and side to side motion of helicopter. The objective of the project is to design and integrate the helicopter with data acquisition board and sensors to provide hardware features, software support capability for its rapid real time measurement and control. The low cost designed LCADRH facilitates the academic research for students in the institution and is able to provide hands on training to understand the concept of nonlinearity, system modelled and unmodelled dynamics and uncertainty, modelling, simulation and control by doing practical experiments. The mathematical model of the LCADRH is derived using grey box modelling method. The control of LCADRH is challenging due to its nonlinearity and effect of strong coupling between aerodynamic forces and torques generated by the both pitch and yaw actuators. In closed loop position control of LCADRH, pitch and yaw axis motion is regulated using linear quadratic controller (LQR). Encouraging results are obtained both in simulation and hardware.

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。

能量轨道下带碰摩的双转子系统振动特性分析

为提高航空发动机的推重比和燃油效率,调整转子与机壳间的间隙变小,易发生碰摩故障问题,本文针对带碰摩双转子系统的非线性振动特性开展了定性、定量分析。建立了具有非线性弹簧特性和带碰摩故障双转子系统的非线性数学模型,通过仿真与数值分析调查了该模型复杂的碰撞、振动特性。对碰摩故障发生后和即将脱离时该系统的能量交换进行了定量分析,基于振动能量轨道的迁移过程分析了非线性振动特征和诱发机理。使用转子实验验证了数值仿真、理论分析结果和振动能量轨道。本文揭示了带碰摩故障的非线性双转子系统运行时振动变化规律,更好地分析了双转子系统的振动特征。

含中介轴承波纹度的双转子系统振动特性分析

针对双转子系统中存在中介轴承波纹度的问题,以含变截面外转子的双转子-轴承系统为研究对象,考虑中介轴承滚动体和内、外圈滚道波纹度,基于有限元法建立了双转子-轴承系统的动力学模型,采用四阶Runge-Kutta数值解法求解方程,分析了波纹度激励对系统频谱特征和幅频响应曲线的影响。结果表明:内、外圈滚道存在波纹度时系统会出现内、外转子转频和保持架转频的组合频率,滚动体存在波纹度时系统会出现偶数倍的滚动体自转频率;考虑转子不平衡激励,外圈滚道波纹度会增大外转子主激励的共振区域的振动,且随着波纹度幅值的增加,系统的振动会在整个转速范围内增大,而内圈滚道波纹度与不平衡激励两者的振动响应会在内转子主激励的第二次共振区域出现近似同频反相的现象,系统的振动会随着波纹度幅值的增加而降低,在其他区域的振动会增大,相对于高转速区域,滚动体波纹度对低转速区域的振动特性会有较大影响。

微转速差双转子系统对自动液力变速器车型怠速抽动的影响研究

为分析液力变矩器与曲轴组成的微转速差双转子系统对自动液力变速器(AT)车型怠速抽动的影响,通过对双转子系统动不平衡耦合激励力进行希尔伯特变换(Hilbert Transform),揭示出部件拍振是导致有规律怠速抽动的根本原因,其抽动激励幅值最大值为激励力之和,抽动间隔频率为激励力频率之差。建立包括发动机、变速器、悬置等系统的机械系统动力学自动分析(ADAMS)模型并进行仿真,结果表明,动力总成垂向刚体模态频率与激励频率越接近,液压悬置垂向一阶动刚度越大,振动幅值越大。因此,可通过动力总成Z向模态频率与曲轴动不平衡激励频率间的避频设计、降低液压悬置垂向动刚度、提高悬置系统的隔振性能等方式改善怠速抽动。

基于联轴器不对中的磁悬浮双转子系统不平衡响应分析

为探讨联轴器不对中故障对磁悬浮双转子系统振动响应的影响,基于有限元法构建包含不对中故障的磁悬浮双转子系统动力学模型,利用Newmark-β法求解其运动方程,通过时域和频域分析不对中情况下转子系统的振动响应。研究结果表明:在不对中引起的附加力作用下,磁悬浮双转子系统的响应会呈现显著的二倍频分量,且随着不对中程度的增加,二倍频分量的幅值也相应增大;内转子由于不对中故障引起的二倍频分量会通过中介轴承传递到外转子上;在不同控制参数下不对中故障对系统的影响有所不同,通过选取合适的比例系数和较大的微分系数,可以有效降低不对中故障对系统振动响应的影响。

支承刚度各向异性对双转子系统进动状态的影响

为提高航空发动机的推重比,航空发动机静子系统的工程解决方案常引起转子系统支承刚度各向异性,进而对转子系统的动力学特性产生显著影响。针对支承刚度各向异性的双转子系统,建立动力学特性计算模型,在验证计算模型准确性的基础上,研究支承刚度各向同性和各向异性对双转子系统固有频率、进动状态和不平衡响应的影响。研究结果表明:支承刚度各向同性时,双转子系统Campbell图中的低阶固有频率线出现交叉,而支承刚度各向异性使低阶固有频率线具有相互分离的趋势。支承刚度各向同性时,不平衡力仅触发转子系统的正进动运动,转子进动轨迹为圆形;而支承刚度各向异性时,转子系统的反/正进动均被不平衡力触发,转子进动轨迹为椭圆形。支承刚度各向异性时,在某些转速下转子系统不同位置处的进动方向可能不同。支承阻尼减小转子系统反/正进动的振幅及反进动的转速区间,降低支承刚度各向异性对双转子系统动力学特性的不利影响。

在能量空间中实现非线性双转子系统的碰摩振动机理表征

碰摩是转子系统发生失稳的一个重要原因。在碰摩故障发生时,转子与机壳随时间的推移在碰撞和脱离等状态间变化,容易产生能量交换,并引发复杂的振动现象。通过构建带碰摩故障的非线性双转子系统模型及动力学方程,采用龙格-库塔法进行数值仿真,在相空间中分析系统的非线性振动特性。在振动能量空间中使用非线性能量供给函数模拟碰摩故障发生后系统的转子振动能量变化,利用振动能量轨道的迁移表征碰摩振动机理。研究结果更好地揭示了非线性双转子系统发生碰摩故障后的碰摩振动机理,提出的方法为双转子系统的振动机理分析提供了新的视角。

内外激励下双转子系统非线性动力学特性研究

针对含中介轴承的双转子系统,在考虑转子不平衡和中介轴承非线性因素的基础上,推导并建立了双转子系统的非线性动力学模型,研究了内外激励下双转子系统的非线性动力学特性。首先,针对建立的双转子-中介轴承系统非线性动力学模型,研究了双转子系统的幅频响应,获得了高低压转子的主共振特性;其次,考虑双转子系统非线性参数的影响,分析了内外激励下双转子系统的非线性动力学响应,通过分岔图、轴心轨迹图、庞加莱截面图、时域波形图和频谱图等,获得了不平衡影响下高低压转子在激励频率变化下的运动状态和频率特征;最后,分析了不平衡量对双转子系统非线性响应特性的影响,研究了不平衡量变化下高低压转子动力学特性的演变规律。研究结果可为双转子系统动力学特性设计和高低压转子故障诊断提供参考。

航空发动机双转子轴间碰摩非线性动力学特性

航空发动机双转子之间通常采用封严结构,容易导致双转子发生轴间碰摩。针对双转子轴间碰摩问题,推导了轴间碰摩力模型,结合实体有限元法建立了双转子轴间碰摩动力学模型,并将固定模态界面综合法和数值方法结合,提出了此类高维转子轴间碰摩响应的一般计算流程。基于该计算流程,详细研究了轴间碰摩导致的双转子复杂非线性动力学特性。结果表明:双转子发生轴间碰摩时,主要存在持续碰摩、间歇碰摩和自激振动三种碰摩状态。持续碰摩主要引起双转子间振动耦合;间歇碰摩对转子产生较明显冲击特征,导致转子频域响应中出现多阶模态频率成分及组合频率成分;自激振动则是由切向摩擦诱发的、转子正进动模态频率成分主导的一种运动状态,此时转子呈正向涡动,但振动幅值很高,对转子危害极大。通过减小摩擦系数或碰摩刚度,能显著减小自激振动发生的转速范围,提升转子运行稳定性。

带中介轴承双转子系统“可容模态”优化设计及实验

为解决航空发动机双转子系统无法避开临界转速的问题,提高双转子系统容忍振动的能力,根据带中介轴承双转子系统的“可容模态”优化设计方法,以某型带中介轴承双转子发动机相似模型为初始模型进行优化设计,并以此搭建一套双转子实验器系统。通过模态测试、响应测试、连续变转速以及长时间“共振”实验,先后验证了带中介轴承双转子系统的“可容模态”优化设计方法的准确性、有效性、稳定性和可靠性。研究发现,双转子实验器测试结果与计算结果临界转速误差最高3.06%、模态振型误差最高9.6%;工作范围内任意转速下,即使频繁穿越临界转速,振动幅值均不超过50µm;在6阶临界转速处各完成了不少于3790s的“共振”实验,所容忍的不平衡量最大为设计不平衡量的5.2倍,振幅平稳,且可容度评价函数值越高,容忍共振能力越强。实验结果充分验证了带中介轴承双转子系统的“可容模态”优化设计方法是可行的。

含中介轴承的双转子系统动力学建模及振动分析

为了深入研究复杂工况下燃气轮机双转子系统的动力学特征,根据中介轴承对双转子系统的耦合作用,基于Ansys建立中介轴承-双转子系统三维实体有限元模型,进行仿真模拟。考虑内外转子转速、负载、偏心、接触及摩擦等因素,计算整个系统的固有振动特性及临界转速,并与试验结果进行对比验证。计算双转子系统在不同转速下的振动响应,分析其不平衡振动耦合特性规律,为工程实际中转子系统的设计提供参考。

永磁/磁阻混合转子双定子低速大转矩同步电机冷却及热管理技术研究

低速大转矩同步电机(LSHTSM)在诸多领域有着广泛应用,针对现有低速大转矩永磁电机内部空间未得到充分利用,转矩密度较低且永磁体成本高、易发生高温退磁等问题,研究了一种永磁/磁阻混合转子双定子低速大转矩同步电机。首先,介绍了电机的拓扑结构及机械结构,针对电机结构复杂、温度难以快速准确计算问题,建立了电机精确热网络温度计算模型,详细推导了电机各特殊结构件之间的热阻数学模型,解析计算了电机各部件稳态温度,总结了电机温度分布特点。其次,针对电机结构特殊、散热困难问题,设计了一种双水冷方式的冷却系统,研究分析了冷却系统结构参数对电机冷却效果的影响,总结了特殊结构电机冷却系统设计原则。最后,分别采用有限元仿真与实验方法验证了所建立热网络温度计算模型的准确性以及冷却系统的有效性。

用于河道洪水预警的双转子型摩擦纳米发电机及其电源管理电路

针对摩擦纳米发电机在采集环境中的低频能量时,面临能量利用效率低和输出电能不稳定等问题,设计了一种双转子型摩擦纳米发电机。在有限的空间内装配两个发电单元提高能量利用率,并且双转子结构可以让每个发电单元中的两种摩擦材料向相反的方向运动,通过相对运动增加频率可进一步提高发电机的发电量。同时设定了双发电单元信号叠加效果的判定标准,通过理论计算指导信号叠加方式。所设计的电源管理电路包含整流、电荷积累和滤波三个模块,能够提升负载电压,稳定电路后端输出,经处理后的负载纹波电压为0.03 V,纹波系数为0.9%。触发摩擦纳米发电机点亮LED灯,为供电环境监测警示系统提供了新思路。

双转子系统碰摩有限元接触分析模型及故障诊断

针对常用碰摩力模型的不足,应用AN SY S软件在求解转静子之间的碰摩力与法向相对位移之间的关系的基础上得到了碰摩力模型,并与整体传递系数法相结合建立转静件碰摩的动力学方程。采用整体传递系数法计算转子系统的动力特性,进而求解双转子系统的瞬态响应。利用时域波形、频谱分析和小波变换对响应进行了分析,得出并分析了相关的故障特征。