ZERO MODE NATURAL FREQUENCY AND NONLINEAR VIBRATION OF COUPLED LATERAL AND TORSION OF A LARGE TURBINE GENERATOR

Zero mode natural frequency (ZMNF) is found during experiments. The ZMNF andvibrations resulted by it are studied. First, calculating method of the ZMNF excited byelectromagnetic in vibrational system of coupled mechanics and electrics are given from the view ofmagnetic energy. Laws that the ZMNF varies with active power and exciting current are obtained andare verified by experiments. Then, coupled lateral and torsional vibration of rotor shaft system isstudied by considering rest eccentricity, rotating eccentricity and swing eccentricity. UsingLargrange-Maxwell equation when three phases are asymmetric derives differential equation of thecoupled vibration. With energy method of nonlinear vibration, amplitude-frequency characteristics ofresonance are studied when rotating speed of rotor equals to ZMNF. The results show that ZMNF willoccur in turbine generators by the action of electromagnetic. Because ZMNF varies withelectromagnetic parameters, resonance can occur when exciting frequency of the rotor speed is fixedwhereas exciting current change. And also find that a generator is in the state of large amplitudein rated exciting current.

Coupled extension and thickness-twist vibrations of lateral field excited AT-cut quartz plates

In this paper, the coupled extension and thickness- twist vibrations are studied for AT-cut quartz plates under Lateral Field Excitation （LFE） with variations along the x1- direction. Mindlin＇s two-dimensional equations are used for anisotropic crystal plates. Both free and electrically forced vibrations are considered. Important vibration characteristics are obtained, including dispersion relations, frequency spectra, and motional capacitances. It is shown that, to avoid the effects of the couplings between extension and thickness-twist vibrations, a series of discrete values of the length/thickness ratio of the crystal plate need to be excluded. The results are of fundamental significance for the design of LFE resonators and sensors.

Coupled lateral-torsional-axial vibrations of a helical gear-rotor-bearing system

Considering the axial and radial loads, a math- ematical model of angular contact ball bearing is deduced with Hertz contact theory. With the coupling effects of lateral, torsional and axial vibrations taken into account, a lumped-parameter nonlinear dynamic model of helical gearrotor-bearing system （HGRBS） is established to obtain the transmission system dynamic response to the changes of dif- ferent parameters. The vibration differential equations of the drive system are derived through the Lagrange equation, which considers the kinetic and potential energies, the dis- sipative function and the internal/external excitation. Based on the Runge-Kutta numerical method, the dynamics of the HGRBS is investigated, which describes vibration properties of HGRBS more comprehensively. The results show that the vibration amplitudes have obvious fluctuation, and the frequency multiplication and random frequency components become increasingly obvious with changing rotational speed and eccentricity at gear and bearing positions. Axial vibration of the HGRBS also has some fluctuations. The bearing has self-variable stiffness frequency, which should be avoided in engineering design. In addition, the bearing clearance needs little attention due to its slightly discernible effect on vibration response. It is suggested that a careful examination should be made in modelling the nonlinear dynamic behavior of a helical gear-rotor-bearing system.

Random stability for lateral vibration on footbridge based on IEVIE-PDE method

The pedestrian-induced lateral vibration of footbridges is essentially classified as a nonlinear stochastic vibration.Accordingly,bridge vibration stability falls within the field of nonlinear stochastic vibration stability.At present,the Lyapunov method is mainly used to analyze such stability.However,this method is qualitative,and it cannot quantitatively analyze the vibration stability probability.In this study,a new analytical method based on a comparison of the input energy and the variation of intrinsic energy(IEVIE)is used to analyze the nonlinear stochastic vibration stability of the lateral vibration of the footbridge.The improved Nakamura model is used to describe the lateral nonlinear stochastic vibration of the footbridge.A combination of the IEVIE method and the probability density evolution(PDE)method is then proposed,in which the IEVIE method is utilized to determine vibration stability.The PDE method is used to obtain the reliability of vibration stability.The proposed method is successfully applied to the Millennium Bridge,and its effectiveness is verified by comparing the Monte Carlo and Lyapunov methods.The proposed method can obtain the dynamic probability of the vibration as stable or instable and provide a reference for quantitative analysis of lateral nonlinear stochastic vibration stability of footbridges.

Theoretical and experimental research on characteristics of lateral vibration for a pre-stress bolt supporting system

According to the structure and stress trait of bearing bolts,a lateral-vibrationmechanics model was established for them,and the relation between lateral-vibration frequencyand axial load was analyzed;then,lateral-vibration trait of bearing bolts was studiedthrough laboratory simulation test.The results indicate that vibration frequency of boltsupport system increases as well as axial force,the detection on axial load of bolts can bemade by generating lateral vibration of bearing bolts.Theoretical and experimental researchresults show that frequency method is effective for detecting the axial force of boltsupport system.

Coupled bending-torsion vibration of a homogeneous beam with a single delamination subjected to axial loads and static end moments

Delaminations in structures may significantly reduce the stiffness and strength of the structures and may affect their vibration characteristics. As structural components, beams have been used for various purposes, in many of which beams are often subjected to axial loads and static end moments. In the present study, an analytical solution is developed to study the coupled bending-torsion vibration of a homogeneous beam with a single delamination subjected to axial loads and static end moments. Euler-Bernoulli beam theory and the ＂free mode＂ assumption in delamination vibration are adopted. This is the first study of the influences of static end moments upon the effects of delaminations on natural frequencies, critical buckling loads and critical moments for lateral instability. The results show that the effects of delamination on reducing natural frequencies, critical buckling load and critical moment for lateral instability are aggravated by the presence of static end moment. In turn, the effects of static end moments on vibration and instability characteristics are affected by the presence of delamination. The analytical results of this study can serve as a benchmark for finite element method and other numerical solutions.

INFLUENCE OF UNBALANCE ON LOW-FREQUENCY VIBRATION OF ROTOR-BEARING SYSTEM

The influence of unbalance on low-frequency vibration exists whenthere are nonlinear factors in oil film force. Based on the Muszpeka oil film mod-el , a theoretical proof is presented. Some new results are obtained based on the im-proved simulation meth

BTA深孔加工镗杆的横向随机振动

采用随机方法分析了蕴含轴向流动流体的BTA(boring and trepanning association)深孔镗杆在随机力下的横向随机动力行为。建模时考察了流固耦合镗杆承受的弯曲、拉伸和扭转变形;经Galerkin Method离散化处理,分析了BTA镗杆在有、无随机激励两种情况的特征值和特征频率对振动特性的影响;利用响应方差最大值和谱密度解析了BTA镗杆横向振动的临界转速与临界失稳频率;明确了镗杆随转速、刚度、初始轴向总力和剪切模量等参数变化对系统振动特性的影响机制:镗杆转速变化对系统稳定性不再具有单调性,随BTA镗杆转速持续增加,系统可历经两次转速的临界失稳,相继出现二次失稳和二次稳定;增加系统等效刚度和等效剪切模量会促进工作过程的稳定,改变轴向力对工作过程稳定的影响不明显;并以随机振动物理试验信号的功率谱分析,验证了理论仿真结果与试验结果的一致性。该研究在一定程度上揭示了BTA深孔工艺系统运动状态的复杂性,这种研究模式为进一步分析在复杂状态下的运动演化提供了更多的可能。研究结论为更好地理解BTA深孔镗杆工作时的随机动力行为提供了依据,也为BTA深孔工艺过程的振动控制和参数优化奠定了理论基础。

深井超深井大尺寸井眼钻具疲劳失效分析与防控

地球深部蕴藏着丰富的油气资源,随着深井超深井钻井数量的递增,钻具失效(断钻具、钻具刺漏)事故呈现逐年递增趋势。为进一步明确深井超深井大尺寸井眼钻具失效原因、减少钻具失效事故,梳理了近年来中国石油西部三大油田钻具失效情况及特征,并以西部油田某口典型超深井?444.50 mm井眼连续5次断钻具事故为对象开展原因分析。首先基于弹性动力学密哈顿原理(Hamilton’s principle)和纽马克方法(Newmark-β)建立了钻具动力学模型,结合雨流法和Miner疲劳损伤累积理论实现对钻具运动、受力及疲劳寿命的定量评价,并验证了模型的准确性,最后提出了大尺寸井眼预防断钻具配套工艺措施。研究结果表明:(1)深井超深井中钻具失效主要发生在上部大尺寸井段,失效位置多集中在下部钻具接头或本体尺寸较小的薄弱位置;(2)因钻具横向振动诱发高频弯曲应力是导致钻具疲劳失效的主要因素,持续剧烈的横向振动在数小时内会导致钻具疲劳失效;(3)提高下部钻具组合刚度、使用“高钻压+低转速”参数钻进有助于降低钻具横振强度;(4)因钻具组合刚度偏小、钻井参数不合理导致下部钻具剧烈横向振动,叠加“中性点”在钻具接头及本体尺寸较小等薄弱位置反复交替,是典型案例井连续断钻具的直接原因。结论认为,建立的模型可以定量评估钻具疲劳失效情况,提出的预防措施可为深井超深井大尺寸井眼预防钻具失效提供技术参考。

离散侧向平移支撑圆弧拱的自由振动分析

拱通常采用离散侧向平移支撑增加其面外稳定性,而离散侧向平移支撑会产生振型耦合效应,显著影响拱的振动特性。为研究等间距离散侧向平移支撑对两铰圆弧拱自由振动的影响,通过假定拱的耦合振型,基于Hamilton原理求解离散侧向平移支撑圆弧拱的自振频率,并与有限元数值结果比较。同时,还探究了拱的面外长细比、圆心角以及侧向支撑的数量和位置对拱的临界刚度及最大基频的影响。研究结果表明:假定的耦合振型可以描述复杂的离散侧向平移支撑拱的弯扭振型,并能准确预测拱的自振频率和支撑临界刚度。侧向平移支撑拱的基频随支撑刚度的增加呈现多种增长模式,根据振型变化情况将其划分为第1类、过渡和第2类增长模式,不同增长模式之间的转换取决于拱的面外长细比、拱的圆心角、支撑数量以及支撑位置。当拱的面外长细比和拱的圆心角的组合靠近第1类增长模式和其他增长模式的分界线时,拱的支撑临界刚度和最大基频显著增大。支撑位置靠近两端翼缘时可能会改变拱的基频振型,但支撑位置在剪切中心附近时,拱的基频最大。拱基频在第1类增长模式时,支撑数量的增加显著提高拱的最大基频,在过渡增长模式时,支撑数量的增加对最大基频的影响减弱,而在第2类增长模式下,拱的最大基频随支撑数量的增加基本不发生变化。

基于凸轮-滚子结构的多自由度准零刚度系统设计

基于凸轮-滚子结构设计一种多自由度非线性准零刚度低频隔振装置。通过静力学特性计算,结合横向刚度计算理论,得到系统在多个自由度上实现准零刚度的参数条件。利用谐波平衡法分析了系统动力学特性,得出系统力传递率,并分析了预压、阻尼比及激励力对系统振动传递率的影响。为验证准零刚度系统隔振性能,搭建隔振测试系统,试验结果表明,相较于传统线性隔振系统,多自由度隔振系统在竖直方向上起始隔振频率从6.7 Hz降低至3.5 Hz,隔振效率最大提升约84.3%;水平方向上起始隔振频率从6.0 Hz降低至4.0 Hz,隔振效率最大提升约45.0%;在10.0 Hz以下,多自由度隔振系统的振动传递率远小于线性隔振系统。

压气机试验件转子对试验台转子横振不平衡响应的影响

重型燃气轮机压气机试验台系统的动力学性能由试验台转子与试验件转子共同决定。对于已经建成的试验台,在实际运转过程中,需要满足不同试验件的实验需求。因此,在设计试验件转子时,需要考虑其对试验台转子横振不平衡响应的影响。将未知试验件转子的动力学特性模化为试验台转子和试验件转子交界面上的机械阻抗,在交界面处利用机械阻抗综合法的阻抗匹配原理来确定试验件转子对试验台转子横振不平衡响应的影响,得出未知试验件转子的设计限制范围。最后,建立了某一试验台转子和试验件转子的动力学模型,分析了该系统的横向振动不平衡响应,验证了试验件转子不平衡响应的设计限制范围的有效性。研究结论为压气机试验件转子的设计提供了指导意见。

中速磁浮列车-轨道梁-桥墩横向耦合振动分析

为研究桥墩参与作用的中速磁浮横向耦合振动,基于车辆动力学、结构动力学和PD控制算法原理,建立了考虑桥墩参与振动的车-桥横向动力分析模型。基于Mathematica编写的仿真程序分析了中速磁浮系统横向耦合振动的动力响应,研究了桥墩高度变化对系统振动的影响规律。研究结果表明,风荷载是中速磁浮系统横向耦合振动的主要激振源;是否考虑桥墩受风荷载作用对车辆系统动力响应的影响有限,桥墩高度变化对车辆系统的动力响应影响较小;是否考虑桥墩受风荷载作用对轨道梁位移响应的影响较大,差异值可达20%,桥墩高度与轨道梁位移不是单一线性关系,存在一个临界桥墩高度值,小于临界值时桥墩高度与轨道梁位移呈正相关,大于临界值时呈负相关。

横向振动作用下螺栓连接节点松动规律数值模拟

输电铁塔螺栓连接节点因常常受到横向往复荷载作用发生松动,从而导致输电铁塔的损害。目前许多在紧固件振动试验机上进行的单个螺栓试验与有限元研究因螺栓约束条件问题并不适用于角钢-螺栓群节点的实际工作情况,针对这一问题在ABAQUS软件中建立考虑螺纹升角的精细化螺栓模型,根据紧固件试验结果验证有限元模型的适用性,再将螺栓模型推广到复杂的单肢、单包及双包的角钢-螺栓群节点模型,分析螺栓群节点在横向振动荷载下松动机理与预紧力变化过程。分析结果表明:在横向循环载荷作用下,预紧力出现交替的上升与下降;螺纹接触面先于螺头承压面进入滑移状态;螺栓预紧力随摩擦因数、预紧扭矩的增大而降低,随着振动幅值的增大而增大,振动频率对螺栓松动影响不显著;单包与双包节点螺栓松动程度从外侧到内侧逐渐递减,施加预压力在一定程度上可降低螺栓的松动趋势,双肢单包节点螺栓松动程度下降了16.00%~23.24%,双肢双包节点下降了2.63%~3.80%。因此在实际工程要做好对易松动部位螺栓的监测,保证节点的承载能力。

时速400 km高速列车通过隧道诱发车体横向振动的气动机制研究

为研究列车以更高速度通过双线隧道时,由于列车和隧道形成的几何空间为非对称空间,列车两侧空气非对称流动,隧道内复杂的压力环境作用至车体两侧和列车尾涡引起的车厢两侧压力变化、列车车体表面压力波动与气动力相互关系和车体振动频谱特征,采用三维非定常可压缩流动N-S方程和IDDES湍流模型,建立时速400 km高速列车1∶1的8节编组空气动力学仿真模型,使用重叠网格技术模拟列车与隧道之间的相对运动方法。研究结果表明:1)隧道内行驶的列车在隧道压力波作用下会使车厢两侧出现压差和侧向力幅值的大范围变化,且变化程度由头车向尾车逐渐增大;2)列车在隧道内运行时的尾流区存在1对反向涡旋;3)尾车明线段涡脱落主频率为2.002 Hz,隧道内运行时,涡脱落频率为3.003 Hz;4)列车在明线或隧道内运行,车体气动侧向力和摇头力矩引起的车体振动频率为2.002 Hz。

人行桥人致横向振动及横向锁定分析

为了研究人群荷载下人行桥的人致振动特性,采用Duhamel积分求解了行人上下桥过程中简支梁桥的人致横向振动理论解,分析了横向锁定条件和临界人数。结果表明:与原地踏步相比,行人上下桥过程中,桥梁横向振动响应增大;频率比为1.0时,跨中横向加速度最大,产生横向锁定的同步临界人数最少;随着桥上总人数增加,跨中横向加速度最大值线性增加,但超过临界人数后由于同步概率的增加使增长幅度提高;在临界人数附近桥梁发生横向锁定,行人舒适性接近“较差”等级下限值。

横向振动条件下防振锤螺栓松动关键影响因素

线夹螺栓松动导致的防振锤滑移问题普遍存在于架空输电线路中。为研究影响防振锤线夹螺栓松动的关键因素,分析了螺栓松动的主要原因,建立了横向振动条件下导线对防振锤线夹的激振力模型,在理论分析的基础上结合工程实际确定了影响螺栓松动的主要参数。通过正交试验获得各因素不同水平组合条件下螺栓紧固力矩的衰减值,并对其进行极差分析和方差分析,明确了各因素对螺栓松动影响的主次顺序、显著性及显著水平。结果表明,防振锤振动频率越高、振幅越大螺拴越容易松动,与工程实际相符,从而验证了所确定因素的关键性和合理性,可为工程实践提供理论和技术方面的支撑。

固体发动机振动试验典型工况下的螺栓连接计算模型及验证

固体发动机振动试验卧式工况下,连接振动试验工装的螺栓主要承受横向振动载荷而难免出现松动现象。为解决这一影响试验有效性的工艺问题,采用斜面滑块模型分析螺栓松动机理,并通过电磁振动台在固体发动机振动试验典型卧式工况下进行试验验证,给出常用的M16螺栓的连接安装预紧力与试验横向载荷幅值的建议比值。研究结果表明,固体发动机振动试验典型卧式工况下,要保证发动机在振动试验过程中(通常不超过10 min)的螺栓连接可靠,螺栓连接安装预紧力与横向振动载荷幅值的建议比值为12。该研究结果可为固体发动机振动试验工装设计过程中螺栓孔径大小及数量的选取提供参考,为试验工艺技术改进提供支撑。

城际铁路曲线地段梯形轨枕有砟轨道动力性能分析

围绕梯形轨枕有砟轨道在城际铁路中适应性问题,测试城际列车以80~176 km/h通过半径为1432 m曲线地段时梯形轨枕有砟轨道系统动力性能指标,对比梯形轨枕有砟轨道和普通Ⅲ型枕动力性能。运用车辆与轨道动力相互作用原理和有限元方法建立曲线地段梯形轨枕有砟轨道动力学模型,进一步评估城际列车以不同速度通过时的行车安全性及舒适性。研究结果表明:(1)列车实际通过曲线地段梯形轨枕有砟轨道时的安全性和轨道结构稳定性均满足规范要求;(2)梯形轨枕有砟轨道较普通Ⅲ型枕有更良好的减振性能,车速从80提高至176 km/h时,减振效果从8.3降低至6.2 dB;(3)考虑道床横向阻力非线性特性的车辆与轨道动力相互作用分析表明,随着车速增大,梯形轨枕有砟轨道动力响应增大,列车运行安全性和舒适性均降低,但仍满足规范要求,其中车辆与轨道的横向动力响应受车速影响更为明显。

桥墩横向位移对车-轨-桥耦合系统动力响应的影响分析

为了提高列车运营的安全性和舒适性,基于SIMPACK-ANSYS联合仿真平台,以某4跨32 m简支箱梁桥、8节列车为框架,建立了列车-轨道-桥梁的耦合系统动力分析模型,开展了桥墩横向位移量对列车动力响应的仿真计算与影响分析。结果表明:桥墩横向位移对列车振动响应影响尤为明显,对桥梁振动响应影响并不显著;当桥墩横向位移超过26.4 mm时,列车的轮轴横向力超过了安全限值(62 kN)。因此,桥墩横向位移值应控制在26.4 mm以内。