2自由度球形行波型超声波电动机的特性计算模型

理论和试验研究2自由度行波型超声波电动机的机械特性计算问题.分析2自由度行波型超声波电动机空间结构关系和定转子接触面的摩擦力.利用空间位置关系,计算得到了行波定子和球转子接触面上任一点的摩擦驱动力和摩擦阻力.根据运动稳定时行波定子轴向力平衡关系,推导给出2自由度球形行波型超声波电动机的特性计算解析式.通过研制的样机进行理论和试验分析,证实计算模型有效性和准确性,并分析各种电动机参数对输出机械特性的影响.研制的样机实现最大堵转转矩达0.10 N·m,空转转速为90 r/min左右.研究工作为下一步球形行波型超声波电动机的设计、优化和控制提供了理论基础.     

Finite element structural analysis of wind turbine gearbox considering tooth contact of internal gear system

Gearbox for wind turbine must be designed to have the sufficient structural strength to sustain the extreme torque and forces transferred from rotor blades. Traditionally, the structural analysis of gearbox has been made using the simplified FEM models in which the contacts between gear teeth are replaced with the equivalent forces acting on the gear shafts, because the consideration of the detailed internal gear transmission system requires a huge number of degrees of freedom. But, the traditional method can neither accurately reflect the gear transmission forces, nor is it preferable for the dynamic analysis. In order to solve these problems, a structural analysis method considering the tooth contact of internal gear system is introduced in this paper. The actual tooth contact between a pair of gears is modeled with spring elements and the spring constants are determined through the stiffness analysis of gear teeth. The current analysis technique is justified through the comparison with the simplified gear system model and applied to the structural analysis of a 2-stage differentialtype gearbox for wind turbine.     

The rotordynamic analysis of the vibration considering the hydro-electric force supported by rolling elements in 500 kW Francis turbine

A Francis turbine which is one of the reaction water turbine types is mainly used in the multipurpose dam. The purpose of this research is to explain the vibration characteristics due to the various causes generated in Francis-turbines generator system. The hydrodynamic force was determined to use the fluid dynamics analysis considering the exciting force that is transmitted to the shaft from the runner part. Besides, in the generator parts electromagnetic forces can have a severe influence on the rotor dynamics in some situations. Because, the hydro turbine-generator system supported by various types of bearing, mechanical vibration analysis is also necessary. Based on a real small-scale Francis-turbine generators parameter, several analysis were performed the stability at the operating speed of the rotor such as natural frequency analysis and forced response analysis. Through this analysis, aside from the mechanical factor, electromagnetic and hydrodynamic factors have also been found to affect vibration.     

基于气弹耦合特征的风力机叶片优化设计

为提高风力机叶片气动结构性能,基于风力机风轮空气动力学及叶片结构动力学原理,选取叶片所处位置及扭转变形为自由度,在研究叶片摆振、摆振方向各阶振动模态的基础上,提出风力机叶片气动弹性耦合振动变形计算模型。基于风力机整机部件构成及输出功率特征,提出风力机叶片优化设计模型,对某5 MW风力机叶片的进行形状优化设计,通过对比分析优化叶片和原始叶片的输出功率及气弹载荷特性,验证优化叶片气动及结构性能的优越性。     

混流式水轮机转轮动力特性有限元仿真分析

混流式水轮振动现象严重影响水电站的安全运行,为避免共振确定转轮的固有频率是必须的.以转子动力学及有限元法的理论基础,综合应用工程软件Pro/E和ANSYS,可以对混流式水轮机转轮建立实体几何模型和有限元模型,从而分析了转轮自由振动状态下和旋转状态下的固有频率和振型特点、变化规律及差异,结果表明:转轮旋转态的固有频率高于非旋转态固有频率,随着频率的不断升高,转轮由整体振动逐渐变为以叶片局部振动为主.该方法为转轮优化设计和叶片裂纹产生分析进行了有效探索.     

Influence of joint models on lower-limb musculo-tendon forces and three-dimensional joint reaction forces during gait

Several three-dimensional (3D) lower-limb musculo-skeletal models have been developed for gait analysis and different hip, knee and ankle joint models have been considered in the literature. Conversely to the influence of the musculo-tendon geometry, the influence of the joint models--i.e. number of degrees of freedom and passive joint moments--on the estimated musculo-tendon forces and 3D joint reaction forces has not been extensively examined. In this paper musculo-tendon forces and 3D joint reaction forces have been estimated for one subject and one gait cycle with nine variations of a musculoskeletal model and outputs have been compared to measured electromyographic signals and knee joint contact forces. The model outputs are generally in line with the measured signals. However, the 3D joint reaction forces were higher than published values and the contact forces measured for the subject. The results of this study show that, with more degrees of freedom in the model, the musculo-tendon forces and the 3D joint reaction forces tend to increase but with some redistribution between the muscles. In addition, when taking into account passive joint moments, the 3D joint reaction forces tend to decrease during the stance phase and increase during the swing phase. Although further investigations are needed, a five-degree-of-freedom lower-limb musculo-skeletal model with some angle-dependent joint coupling and stiffness seems to provide satisfactory musculo-tendon forces and 3D joint reaction forces.     

Thermohydrodynamic Performance of a Plain Journal Bearing

The brush seal, with superior leakage performance, is emerging as a new sealing technology to effectively control cooling and leakage flows in gas turbine engines. Because the bristles slide against the rotor surface, wear at the contact becomes a major concern as it determines the life and efficiency of the seal. To optimize seal life and efficiency, an in-depth study of the factors causing the seal stiffness is needed, and a good choice of materials must be made. This work investigates some of the past research on brush seal wear. Although considerable research has been done on material selection and tribopairs, the brief survey reveals the lack of reliable analyses to evaluate contact loads and to address heat transfer issues. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study the details that may not be available through analytical formulations. In an effort to meet this need, the present work includes a preliminary computational model of a brush seal. The model consists of a 3-D finite element model of a representative brush seal segment with a mating rotor surface. Preliminary results from the model show reasonable agreement with actual seal behavior.     

Effect of teeth bending and mushrooming damages on leakage performance of a labyrinth seal

To achieve higher aerodynamic performance, turbine usually works at tight clearance, which results in inevitable rub between the rotor and stator parts of labyrinth seal due to vibrations, misalignment, mechanical force, thermal stress, etc. In the rubbing events, contact between labyrinth fin and rotor part will commonly induce the teeth bending and mushrooming damages, which significantly affect the discharge performance of a labyrinth seal. To account for the influence of teeth bending and mushrooming on leakage performance of a straight-through labyrinth seal, the leakage rates and flow fields in the worn labyrinth seal are measured and also compared with the original design cases. With numerical methods, the discharge behaviors of the labyrinth seal with different degrees of bending and mushroom damages are analyzed. It shows that the predicted leakage performance and flow fields in the labyrinth seals match well with the experimental tests. For the bending cases, the leakage rates and flow patterns in labyrinth seals are dependent on the effective clearance and bending angle. The leakage ratio of forward bending case is smaller than that of backward bending case with the same geometrical dimensions. However, for the mushroomed labyrinth seals, the leakage rates and flow patterns are much dependent on the effective clearance but slightly dependent on the mushroom radius.     

The contact forces of lip seals for a ball bearing

Simplified equations are derived for the evaluation of the axial contact forces for a special design of lip seal for bearings. The contact forces of the lip seals for a ball bearing are analysed as a function of the ratio of real contact length, the thickness of the seal lip, the inclined angle of the seal lip, and the deflected interference between the edge of the seal lip and the rotating inner ring. An experimental apparatus is developed for testing the seal lip contact forces. Using a non-linear FEM program, the contact force of the seal lip was analysed for various values of the deflected interference. The calculated results show that the deflected interference and the circumferential stress cause considerable change of contact forces for the low sealed lubricant pressure. The results of contact forces obtained from the derived equation for the contact force are in good agreement with experimental and numerical results.     

Analysis and measurement of lateral elliptic motion effect for an asymmetric disc-type ultrasonic motor

This paper presents an analysis and measurement method for studying lateral elliptic motion effect of an asymmetric disc-type ultrasonic motor whose stator is a circular disc with a bonded PZT plate serving as a drive. At the edge of the stator with a simple, fixed three-point support of a 120°–90°–150° configuration, there exists a coupled vibration wave with lateral elliptical motion so as to generate a driving force between the stator and the rotor. The equations of the lateral elliptic motion and the driving force are analytically formulated based on the wave equation on the circular plate, thereby obtaining the driving frequency and the revolution speed of the motor. The relationship between the ultrasonic stator and its boundary condition is investigated as well. The analysis shows that the circumferential edge with a 90° included angle is an optimal contact section for the placement of the rotor. Experiments using the laser vibrometer and photodetector are used to show the validity of the proposed analysis method.     

Nonlinear Dynamic Response of Cylindrical Roller Bearing–Rotor System with 9 Degree of Freedom Model Having a Combined Localized Defect at Inner–Outer Races of Bearing

This article presents a nonlinear dynamic model for a cylindrical roller bearing–rotor system with interaction forces between the inner race, outer race, and roller. Roller–race contacts are modeled predicting nonlinear stiffness (Hertz contact theory) and nonlinear damping for a rotor–cylindrical roller bearing system. Here a shaft–rotor bearing system is modeled with 9 degrees of freedom with one defect on the inner race and one defect on the outer race for a case of combined localized defects. In the mathematical formulation, contacts between rolling elements and inner and outer races are considered as nonlinear springs and nonlinear damping is taken into consideration. Contact force calculations with nonlinearity are solved using the Newton-Raphson method for n unknown nonlinear simultaneous equation. The Newmark-β implicit integration technique coupled with the Newton-Raphson method is used to solve the differential equations. The results are obtained in the form of a time domain plot, frequency domain plot, and phase plot/Poincare map. The validity of the proposed model is compared with experimental results. A bifurcation graph of speed versus peak amplitude predicts the behavior of the system.     

大型轴流式水轮机转轮体刚强度对比分析

应用有限元法建立了轴流式水轮机转轮体的力学模型,对比分析了几个典型的大型轴流式水轮机转轮体的应力水平和变形情况,对今后转轮体的刚强度分析及大尺寸转轮体的优化设计具有重要参考价值。     

基于接触有限元的齿轮-转子系统动态特性分析

考虑齿轮-转子系统各部件的弹性,基于接触有限元理论提出一种能够高保真模拟齿轮副连续啮合过程的动态特性分析方法。该方法利用实体有限元进行系统建模,可体现各部件的结构特征;基于接触有限元进行啮合过程仿真,可模拟系统的时变刚度、啮合冲击等真实激励进而得到全面准确的响应信息。以一直齿轮-转子系统为例进行啮合过程的数值仿真,利用中心差分法求得系统各动力学参量在时域上的响应,通过中心距偏差、动态传递误差、动态接触力等参数分析系统的弯曲振动、扭转振动、齿轮副的啮合特性及其耦合关系。研究结果表明：考虑各部件尤其是转子的弹性后,系统的非线性振动特性显著,齿轮副啮合存在明显的双边冲击及脱啮现象。     

VIBRATION ANALYSIS OF TURBINE BASED ON FLUID-STRUCTURE COUPLING

The vibration of a Francis turbine is analyzed with the additional quality matrix method based on fluid-structure coupling （FSC）. Firstly, the vibration frequency and mode of blade and runner in air and water are calculated. Secondly, the influences to runner frequency domain by large flow, small flow and design flow working conditions are compared. Finally the influences to runner modes by centrifugal forces under three rotating speeds of 400 r/rain, 500 r/min and 600 r/rain are compared. The centrifugal force and small flow working condition have greatly influence on the vibration of small runner. With the increase of centrifugal force, the vibration frequency of the runner is sharply increased. Some order frequencies are even close to the runner natural frequency in the air. Because the low frequency vibration will severely damage the stability of the turbine, low frequency vibration of units should be avoided as soon as possible.     

汽轮机转子结构强度理论研究现状与展望

对目前汽轮机转子结构强度理论的研究现状进行了综述,分析了汽轮机转子结构强度理论的局限性和存在的问题,并对当前的损伤力学理论进行了简要的介绍,阐述了将损伤力学理论应用于转子结构强度分析的优越性,并就汽轮机转子结构强度的损伤力学研究进行了展望。     

Kinematics of motions in rotor system during contact between rotor and floating elements

The contact regimes in the rotor system when the contact of the rotor with light movable elements of the system have been considered The vibrations of an imbalanced rotor–floating ring system when rotating the rotor inside the floating ring when permanent contact with them have been investigated. Furthermore, the ring vibrations occur, during of which it runs the rotor when permanent contact with it in the direct precession regime (the precession direction coincides with the rotation direction) (hula hoop-type vibration). This article considers the kinematics of ring motion. The trajectories of ring motion in both absolute and relative motion at different ratios between the radii of the ring and rotor have been plotted. It has been revealed that the ring vibrations are a direct asynchronous precession; furthermore, the ring points circumscribe epitrochoids and the trajectory shape depends significantly on the ratio between the radii of the rotor and the ring.     

电磁轴承-无轴承电机系统在转子主动控制的应用研究

主动磁轴承借助电磁力来控制转子的振动,无轴承电机在实现转矩控制的同时实现电机的悬浮控制。本文在对永磁偏置三自由度电磁轴承和两自由度无轴承电机的磁悬浮机理一般性描述的基础上,分析了其产生的悬浮控制力。并以转子电磁振动为研究对象,结合电磁轴承和无轴承电机的特点,提出利用一种新型的五自由度磁悬浮异步电机作为执行机构对转子电磁振动进行主动控制,实现了转子系统稳定工作。此系统可以有两方面的应用,既可以用做转子的支承,也可以用做转子振动主动控制的增稳。     

一种锥形定转子交直流磁轴承建模与耦合特性研究

为简化三自由度轴向-径向磁轴承结构,减小轴向长度和提高系统临界转速,设计了一种新型三自由度交直流轴向-径向混合磁轴承。该磁轴承定子采用两片式六极结构,分隔式锥形磁极与圆锥形转子均有30°锥角,磁场对圆锥形转子产生的磁吸力在轴向和径向方向上均有分量,实现了利用同一工作气隙同时控制圆锥形转子在轴向和径向3个自由度的悬浮。论文介绍了三自由度锥形定转子交直流混合磁轴承基本结构及悬浮力产生的工作原理,用等效磁路法对永磁和励磁混合磁轴承的磁路进行了分析,推导出了悬浮力数学模型。利用Matlab工具对磁轴承各变量之间的非线性关系和各自由度之间运动、磁路之间的耦合特性进行了计算和分析,并对各自由度之间的电磁耦合特性及各变量之间的非线性关系用ANSOFT软件进行了有限元分析验证。理论分析和仿真结果表明:该磁轴承各自由度在平衡位置附近时运动和磁路之间没有耦合,各变量之间具有良好的线性关系,对各自由度可采用分散独立的PID控制实现磁轴承的稳定悬浮。     

不平衡量对转子碰摩振动的影响

建立了与限位器碰摩的转子动力学方程 ,用数值积分方法得到了碰摩非线性动力响应。分析中考虑了陀螺效应 ,采用分段线弹性和库仑摩擦模型描述碰摩力。研究双频进动、局部碰摩、拟整圈碰摩和整圈碰摩的振动特征。讨论了不平衡量和激振力幅度变化对碰摩振动形式和特征的影响 ,并给出碰摩振动试验结果 ,以验证数值分析结论。     

Mechanics of the passive knee joint. Part 2: interaction between the ligaments and the articular surfaces in guiding the joint motion

The aim of this study was to examine how the interaction between ligament tensions and contact forces guides the knee joint through its specific pattern of passive motion. A computer model was built based on cadaver data. The passive motion and the ligament lengthening and force patterns predicted by the model were verified with data from the literature. The contribution of each ligament and contact force was measured in terms of the rotational moment that it produced about the tibial medial plateau and the anterior-posterior (AP) force that it exerted on the tibia. The high tension of the anterior cruciate ligament (ACL) and the geometric constraints of the anterior horns of the menisci were found to be key features that stabilized the knee at full extension. The mutual effect of the cruciates was found as the reason for the screw-home mechanism at early flexion. Past 300, the AP component of contact force on the convex geometry of the lateral tibial plateau and tension of the lateral collateral ligament (LCL) were identified as elements that control the joint motion. From 60 degrees to 90 degrees, reduction in the tension of the ACL was determined as a reason for continuation of the tibial anterior translation. From 90 degrees to 120 degrees, increase in the tension of the posterior cruciate ligament and the AP component of the contact force on the convex geometry of the lateral tibial plateau pushed the tibia more anteriorly. This anterior translation was limited by the constraining effects of the ACL tension and the AP component of the contact force on the medial meniscus. The important guiding role observed for the LCL suggests that it should not be overlooked in knee models.