转子-滚动轴承-机匣耦合系统中滚动轴承故障的动力学分析

针对实际的航空发动机转子系统,建立了含滚动轴承故障的转子-滚动轴承-机匣耦合模型.在模型中,考虑了机匣运动,弹性支承与挤压油膜阻尼的作用,同时,充分考虑了轴承间隙、滚珠与滚道的非线性赫兹接触力以及由滚动轴承支撵刚度变化而产生的变柔性(Varying Cbmpliance)VC振动.在此基础上,建立了耦合系统中滚动轴承外圈、内圈及滚动体的损伤动力学模型,并运用数值积分方法进行了动力学仿真与分析.结果充分表明了本文提出的转子-滚动轴承-机匣耦合系统及滚动轴承故障动力学模型的正确有效性.     

带碰摩耦合故障的转子-滚动轴承-机匣耦合动力学模型

建立了含转子不平衡-松动-碰摩耦合故障的转子-滚动轴承-机匣耦合动力学模型.在模型中,充分考虑了转子系统的不平衡、基础松动及转静碰摩故障的耦合;对滚动轴承模型,充分考虑了轴承间隙、轴承滚珠与滚道的非线性赫兹接触力以及由轴承支撑刚度变化而产生的VC（varying compliance）振动.运用数值积分方法获取了系统响应,并利用振幅-转速曲线图、分叉图、相平面图、频谱图、Poincaré截面图和轴心轨迹图研究了系统的分叉与混沌运动,分析了旋转速度、碰摩刚度、转子偏心量、轴承座质量、轴承座与机匣间的连接刚度以及机匣与基础间的连接刚度对系统响应的影响,得到了在不平衡-松动-碰摩故障耦合下的转子-滚动轴承-机匣耦合系统动力响应规律.     

磁浮车辆辅助变流器的风机轴承振动失效分析

针对磁浮列车辅助变流器的外转子风机轴承短期内失效问题,首先开展风机装车线路运行和台架安装变频运行的振动测试和频响测试,结合外转子风机双质量振子系统的分析,揭示风机轴承过度磨损故障的原因为耦合共振,耦合共振是由风机4倍电磁激振力波及4倍电流谐波激励与其定转子同向运动轴向振动模态产生的.然后提出基于故障振动形态和实测载荷谱...     

具有不平衡-碰摩耦合故障的转子-滚动轴承系统非线性动力学研究

建立了滚动轴承支承下的转子系统的不平衡-碰摩耦合故障动力学模型.在滚动轴承模型中,充分考虑了滚动轴承间隙、滚动轴承的滚珠与滚道的非线性赫兹接触力以及由滚动轴承支撑刚度变化而产生的VC(Varying compliance)振动,在转子系统中,考虑了不平衡和转静碰摩耦合故障.运用数值积分方法获取了系统的非线性动力响应,分析了转子旋转速度、滚动轴承间隙、碰摩刚度、转子偏心量对系统动力响应的影响,研究了系统分叉与混沌特征分析,发现了通往混沌的倍周期分叉和阵发性分叉途径.     

含不平衡-碰摩-基础松动耦合故障的转子-滚动轴承系统非线性动力响应分析

建立了滚动轴承支承下的转子系统的不平衡-碰摩-基础松动耦合故障动力学模型.充分考虑了滚动轴承的间隙、非线性赫兹接触力以及由变柔性VC(Varying compliance)振动,综合考虑了转子不平衡、转静碰摩以及基础松动故障的耦合振动.运用数值积分方法分析了转子旋转速度、滚动轴承间隙、碰摩刚度、转子偏心量及轴承座质量对系统动力响应的影响,并运用分叉图、相平面图、频谱图以及Poincar橛成溲芯苛讼低撤植嬗牖煦缣卣?发现了含不平衡、碰摩及基础松动耦合故障的转子-滚动轴承系统的非线性动力响应规律.     

带横向裂纹的拉杆转子非线性动力学特性研究

以拉杆转子为对象,对具有横向裂纹的拉杆转子非线性动力学响应特性进行研究。基于达朗贝尔原理建立考虑轮盘之间非线性接触特性的裂纹拉杆转子系统运动方程。采用数值积分方法对运动方程进行求解,得到轮盘振幅随转速变化的曲线。分析裂纹刚度减小量、轮盘质量偏心矢量夹角、接触面阻尼系数、裂纹角等系统参数对轮盘幅频特性的影响。同整体转子相比,裂纹拉杆转子除在1/2阶、1/3阶临界转速附近发生1/2阶、1/3阶亚谐共振外,在超临界转速区域存在超谐共振。系统参数对裂纹拉杆转子幅频特性曲线影响较大。分析结果可为认识裂纹转子系统的响应特性、开展裂纹转子的故障诊断提供理论指导。     

滚动轴承-JEFFCOTT转子系统非线性动力响应分析

分析了滚动轴承运动时的非线性轴承力,建立了考虑非线性轴承力的滚动轴承-Jeffcott刚性转子系统的动力学方程,并用数值方法对其求解.利用分岔图和poincaré映射图,分析了滚动轴承-Jeffcott转子系统的非线性动力响应行为.结果表明:转子系统具有丰富的周期和非周期(拟周期或混沌)响应形式,转子系统进入混沌的主要途径是倍周期分岔,合理的选择转子系统的结构和工作参数,如转速,游隙和阻尼,可降低系统的不稳定性.     

非线性转子—密封系统的亚谐共振失稳机理研究

研究单圆盘转子－密封系统的亚谐共振失稳机理，密封力采用Ｍｕｓｚｙｎｓｋａ模型。文［１］曾研究了平衡系统的Ｈｏｐｆ分岔，表明转子平衡态失稳后进入周期涡动状态，本文研究不平衡质量对失稳运动的影响，即周期扰动的Ｈｏｐｆ分岔问题。研究得到了转子在分岔点附近的１／２亚谐共振情况下的振动性态，为转子亚谐共振故障的识别和预防提供了一些新的理论依据。     

基础激励下转子-轴承-支座系统动力学特性研究

针对基础激励影响转子轴承系统动力学特性问题,提出基于有限元和集中质量法的转子系统耦合动力学模型,分析基础激励对系统动力学特性的影响规律。模型中,转子采用梁单元离散建立有限元模型,滚动轴承考虑非线性接触力和间隙影响,支承阻尼环采用Kelvin-Voigt线性力学模型表征其力学特征。通过Runge-Kutta数值方法研究基础位移激励对系统动力学行为的影响规律;在此基础上,基于遗传算法对支承阻尼环的动力学参数进行优化设计。结果表明：基础在水平或垂直方向上的位移激励不仅对该方向转子振动有影响,对其他方向振动也存在一定影响;基础激励频率不等于滚动轴承VC(Varying Compliance)频率或其谐波频率时,系统中出现了组合共振现象;同时,经优化设计后,基础激励对系统动力学行为的影响显著降低。研究结果为基础振动下转子轴承系统的动力学分析提供了理论支撑。     

某航空发动机整机系统非线性振动特性分析

以某型号航空发动机整机振动试验台为研究对象,建立了简化的整机动力学模型,考虑中介轴承的非线性弹性恢复力,运用Newmark-β与Newton-Raphoson法结合进行数值求解,通过对比整机系统中高低压转子处与机匣测点处的非线性振动响应,分析了中介轴承间隙对整机系统非线性振动响应的影响规律。结果表明,随着中介轴承间隙的增大,可能导致整机系统出现振动突跳、双稳态、高低压转子耦合程度降低以及组合共振等现象,其中机匣能够反映内部转子的振动特性,但机匣不同位置测点的情况不同,总体上中后测点在转子出现非线性振动特性时也能观测到相应的非线性振动特性,特别是在出现组合共振时能够表现出更为丰富的组合频率信息。研究结果有助于认识中介轴承非线性对航空发动机整机系统尤其是机匣的非线性振动特性影响规律,对航空发动机机匣上测点位置的选择能提供一定的指导。     

双稳系统的振动共振及特性分析

基于非线性双稳系统受高、低两种不同频率作用的双时间尺度特性和谐波平衡法，解析地分析了双稳系统对低频信号响应的幅值与高频信号参数、系统参数之间的关系，表明系统响应的幅值随高频信号或系统参数的变化并非单调，而是存在着称之为振动共振的极大值。基于这些参数与共振曲线的关系，提出了共振状态下的频率特性。理论近似解析分析的结论与数值仿真计算的结果基本一致。     

Electron spin resonance studies of some cuprate(II)systems

The electron spin resonance (ESR) of a number of ternary oxides of copper (II) has been studied at both 77 K and 300 K. Materials investigated include those which might be considered 1-dimensional analogues of La₂CuO₄, namely A₂CuO₃ (A=Ca,Sr, Ba) plus the related material SrCuO₂. The two oxygen rich derivatives of Ba₂CuO₃ have also been studied in view of their different oxygen environments around copper. Also other alkaline earth cuprates such as the recently described Sr₁₄Cu₂₄O_41-x and Bi₂Cu₂O₅, both pure and doped with Sr²⁺ are included. Compounds containing extended Cu-O chains are found to be essentially ESR silent both at room temperature and 77 K, regardless of whether the chains are one-dimensional or form two-dimensional sheets as in Ca(Sr)CuO₂. In Sr₁₄Cu₂₄O_41−x , which contains both Cu-O chains and chains of edge-shared CuO₄ square-planar units there is an asymmetric signal which sharpens on cooling.     

Feshbach Shape Resonance in Multiband Superconductivity in Heterostructures

We report experimental data showing the Feshbach shape resonance in the electron doped MgB₂ where the chemical potential is tuned by Al, Sc, and C substitutions. The scaling of the critical temperature T _c as a function of the Lifshitz parameter z = E _Γ−E _F, where E _F is the chemical potential and E _Γ is the energy of the Γ critical point where the σ Fermi surface changes from the 3D to a 2D topology, is reported. The resonant amplification of T _c(z) driven by the interband pairing is assigned to a Feshbach shape resonance characterized by quantum superposition of pairs in states corresponding to different spatial location and different parity. It is centered at z = 0 where the chemical potential is tuned to a Van Hove-Lifshits feature for the change of Fermi surface dimensionality in the electronic energy spectrum in one of the subbands. In this heterostructure at atomic limit the multiband superconductivity is in the clean limit because the disparity and negligible overlap between electron wavefunctions in different subbands suppresses the single electron interband impurity scattering rate. The emerging scenario from these experimental data suggests that the Feshbach shape resonance could be the mechanism for high T _c in particular nanostructured architectures.     

Excitation techniques for resonance analysis of packages

This paper discusses the advantages and drawbacks of various excitation techniques used to detect the vibration transmissibility characteristics of packaging systems, such as resonant frequencies and damping properties. Historical and background information on the commonly used sweep sine excitation technique is presented. In addition, more recent and sophisticated techniques, such as broad‐band random excitation, random burst, pulse and chirp excitation are discussed and their usefulness highlighted. More specifically, the suitability of these excitation techniques in stimulating and detecting the non‐linear characteristics of packaging systems are considered. Some of the advantages of using low‐level and low‐duration excitation techniques to minimize potential damage to the test prototype are also expounded. Copyright © 2002 John Wiley & Sons, Ltd.     

结构-地基相互作用水平与扭转的超亚谐振动

基于多线性随动强化模型求得了基础和地基土之间的水平刚度与摇摆刚度，在此基础上建立了结构，地基非线性相互作用体系模型，利用能量法得到了结构水平侧移和扭转相耦合的振动方程，采用多尺度法研究了结构，地基相互作用体系的超谐和亚谐共振，比较了结构与地基非线性因素给体系反应带来的影响，揭示了发生超谐和亚谐振动时水平振动和扭转振动耦合的不同规律，为工程抗震提供了理论依据。     

The interaction of seasonal forcing and immunity and the resonance dynamics of malaria

Theory has emphasized the importance of both intrinsic factors such as host immunity and extrinsic drivers such as climate in determining disease dynamics. In particular, seasonality may lead to multi-annual cycles in prevalence, but the likelihood of this depends on the role of acquired immunity. Some diseases including malaria have immunity that falls between the classic susceptible–infectious–removed and susceptible–infectious–susceptible models. Here, we investigate the general conditions promoting the subharmonic resonance behaviour that may lead to multi-annual cycles in a general malaria dynamical model. Utilizing two complementary approaches to bifurcation analyses, we show that resonance is promoted by processes shortening the length of the infectious period and that subharmonic cycles are favoured in situations with strong seasonality in transmission but at intermediate levels of endemicity. We discuss the implications of our results for understanding prevalence patterns in long-term malaria datasets from Kenya that show multi-annual cycles and one from Thailand that does not and discuss the possible implications of treatment.     

压电-磁致伸缩双层磁电复合材料的机电谐振

基于压电相和磁致伸缩相的本构方程以及弹性体的运动方程,简要推导了一维机电谐振模式下压电-磁致伸缩双层磁电复合材料横向磁电电压系数的表达式。采用相应的材料参数计算分析了Tb_1-x Dy_x Fe_2-y (TDF)-Pb(Zr,Ti)O₃(PZT)双层磁电复合材料的横向磁电电压系数与交流磁场频率的关系,以及复合材料的长度和压电相体积分数对机电谐振频率的影响。计算与分析结果表明,双层磁电复合材料在机电谐振频率处具有明显的磁电 响应特性。当有效机械品质因数为50,在谐振频率55.2 kHz处横向磁电电压系数达到峰值11.2 V·cm^-1·Oe^-1,是低频下峰值(281.9 mV·cm^-1·Oe^-1)的40倍。机电谐振频率随复合材料长度的减小和压电相体积分数的增加而上升。实验结果说明TDF-PZT双层磁电复合材料在机电谐振频率处具有显著增强的磁电效应,实际有效机械品质因数约为48。     

粗细端截面比对阶梯形变幅杆谐振频率的影响

文章研究了粗细端截面比对阶梯形变幅杆谐振频率的影响．通过对粗细端等长和不等长阶梯形变幅杆谐振频率的测量，找出了两组变幅杆谐振频率的降低系数β随粗细端面积比N^2的时数lnN^2的变化规律，分析了不同阶数振动的频率变化特点，为阶梯形变幅杆的研究和具体设计提供了一定依据。     

三层结构模型的内共振和组合共振

主要对三层结构模型的内共振和组合共振实验进行了研究。通过模态设计使得结构一、二阶模态频率之比接近1:3。经振动台水平基础激励实验发现：以一阶模态频率、二阶模态频率激励,都可激发出一、二阶模态间的内共振行为,同时该结构中还存在多种组合共振行为。为下一步非线性振动实验装置的改进奠定了基础。     

Observation of Fano Resonances in All‐Dielectric Nanoparticle Oligomers

It is well‐known that oligomers made of metallic nanoparticles are able to support sharp Fano resonances originating from the interference of two plasmonic resonant modes with different spectral width. While such plasmonic oligomers suffer from high dissipative losses, a new route for achieving Fano resonances in nanoparticle oligomers has opened up after the recent experimental observations of electric and magnetic resonances in low‐loss dielectric nanoparticles. Here, light scattering by all‐dielectric oligomers composed of silicon nanoparticles is studied experimentally for the first time. Pronounced Fano resonances are observed for a variety of lithographically‐fabricated heptamer nanostructures consisting of a central particle of varying size, encircled by six nanoparticles of constant size. Based on a full collective mode analysis, the origin of the observed Fano resonances is revealed as a result of interference of the optically‐induced magnetic dipole mode of the central particle with the collective mode of the nanoparticle structure. This allows for effective tuning of the Fano resonance to a desired spectral position by a controlled size variation of the central particle. Such optically‐induced magnetic Fano resonances in all‐dielectric oligomers offer new opportunities for sensing and nonlinear applications.