离心场中双自由度振动系统的动频和极化运动性质

双自由度的弹簧-质量振动系统在离心场中存在两阶动频和两阶复模态。振动离心系统的动频关联于旋转系统的转速,并受到离心软化和科氏力的影响。科氏项导致系统出现复模态矢量,质量点形成极化的圆周运动轨迹,反映了旋转系统的运动耦和而非物理阻尼,它不引起系统自由振动的衰减,单一复模态对应的质量点的圆周运动轨迹保持不变     

轴流式压缩机叶片固有频率及动应力分析

以某轴流式压缩机的一级动叶片为研究对象,建立叶片的三维有限元模型,研究轴流式压缩机叶片的频率特性。从理论方面分析了影响频率的旋转软化和应力刚化效应,分析了旋转软化和应力刚化效应对叶片固有频率的影响。应用完全法瞬态分析,计算了叶片的动应力,分析结果为叶片的调频和振动特性的改善提供了依据。     

弹性体作定轴转动的耦合动力学模型与数值分析

应用含偶应力的弹性理论建立弹性力学模型,应变和曲率张量分别描述弹性体的平动变形和旋转变形,且分别对应于应力和偶应力两种内力。对已知定轴变转速刚体转动的情况,采用哈密尔顿原理建立了含偶应力弹性体作定轴刚体转动的运动与变形耦合动力学模型,模型计及了相对惯性力、离心力、科氏力和切向惯性力。考虑以弹性体的位移和变形转角为独立变量,利用约束变分原理建立了含偶应力弹性体作定轴刚体转动的有限元方程,其中单元离散采用8个节点48个自由度的三维六面体实体等参元。以绕定轴旋转的悬臂梁为例,数值分析了旋转悬臂梁的动力学特性和动力学响应。当幅值变化但刚体转速恒定时,旋转方梁的一阶特征频率出现随转速增加保持不变和下降两种情况。当刚体变转速时,考察了旋转悬臂梁位移、变形转角、动态应力以及偶应力的时变规律。该研究可为作定轴旋转系统的结构部件的动力学分析提供理论模型和数值分析方法。     

晃动的流体对渡槽结构振动的抑制与放大效应

本文对渡槽结构横向流-固耦合动力特性及其幅频响应特性进行了较为详尽的分析,分析表明：1)结构体系存在二个横向振动固有振动频率 、 , 当系统以较小的频率 （同相位频率）振动时,结构振动的方向与流体的晃动方向一致;当系统以较大的频率 （异相位频率）振动时,结构振动的方向与流体的晃动方向相反。2) 当外动力荷载的频率（或卓越频率）与 （或 ）接近时,结构体系会发生共振反应,流体对结构振动会产生放大效应。3)渡槽结构体系还存在一个特殊的振动频率 ,当外动力荷载的频率（或卓越频率）与 接近时,晃动的流体对结构起到减振的作用。4)渡槽内的流体质量可以分为固定质量与晃动质量两部分,其中固定质量会加大结构顶端的动力惯性反应,可能会对结构安全构成不利影响。     

燃料电池车用离心压缩机窄带啸叫噪声实验测试与分析

以某燃料电池车用离心压缩机为研究对象,测试并分析其在不同工况下的气动性能及气动噪声。试验结果表明:当离心压缩机工作在高效率的额定工况区时,进口处气动噪声最小,总声压级峰值出现在轻度喘振线附近;额定工况和阻塞工况的主要噪声源为旋转基频噪声;轻度喘振工况的主要噪声源为窄带啸叫噪声,其频率约为转频的3.9倍;深度喘振工况时550~2 000 Hz的宽频噪声明显上升;叶片通过频率噪声与流量无明显关系,且对总体噪声贡献量不大。应用商业软件CFX对轻度喘振工况下离心压缩机窄带啸叫噪声的产生机理进行分析。仿真结果表明:当离心压缩机流量低于额定流量时,进口冲角增大,导致主叶片、分流叶片前缘及扩压器内靠近轮罩面出现严重的二次流,叶片前缘和扩压器的同时失速是造成轻度喘振工况下窄带啸叫噪声的主要原因。     

基于频域分析垂直轴风力发电机组旋转主轴的风致动力疲劳

使用ANSYS有限元软件研究在风荷载作用下垂直轴风力发电机组(Vertical-axis wind turbine,VAWT)主轴在旋转状态下的风致动力疲劳问题.首先,在频域内,研究在脉动风作用下机组旋转主轴(转速为15.5 m/s)三个关键位置处的风动力响应特性.然后,基于机组旋转主轴风动力响应的计算与分析,对机组旋转主轴进行风致动力疲劳分析,计算其疲劳寿命耗用系数,以评价该机组旋转主轴的工作状况.     

呼吸裂纹梁非线性动力特性研究

疲劳裂纹是结构损伤的重要形式,是引起结构破坏的主要因素之一。建立了含非对称疲劳裂纹梁的非线性数值分析模型,采用奇异单元模拟裂纹尖端的效应,使用无摩擦的接触单元模拟疲劳裂纹的张开闭合特性,研究了结构在简谐荷载激励下的非线性动力特性。以悬臂梁为例分别分析了外部激励频率、裂纹深度以及裂纹位置等参数的变化对系统非线性行为的影响,重点讨论了系统的亚谐、超谐等共振现象,并且提出了系统频率的相对幅值用于辨识裂纹深度的方法。研究结果为裂纹结构的损伤识别提供了一定的理论基础和参考。     

建筑物对爆破振动中不同频率能量成分的响应特征

爆破地震对建筑物的影响实质上是一种能量的传递与转化过程,这种传递与转化的过程受到建筑物动力特性的影响。利用结构动力学理论,结合典型工程实例,研究了建筑物对爆破地震中不同频率能量成分的响应特征,结果表明:建(构)筑物对于爆破振动中的不同频率能量成分存在明显的选择放大效应。在爆破地震中,与结构固有频率相一致的能量成分将被最大程度的放大。在制定爆破振动安全判据时,要将爆破地震自身特征和建筑物动力特性更好的结合起来,重视爆破振动中与建筑物固有频率相对应的能量大小。     

基于PD结合输入整形控制的含有刚性模态弹性机构的力及能耗分析

高速轻型机构在大幅度刚性运动的同时弹性构件存在着弹性变形,从而产生残留振动,导致刚性体运动与弹性体运动相互耦合,使整个系统难以精确定位。在研究含有刚性模态弹性机构的动力学特性的基础上,将时滞环节引入控制系统中,提出PD结合输入整形控制策略,研究在阶跃输入信号作用下PD结合输入整形控制系统的振动特性,分析输入整形对系统控制力和能耗的作用规律。在相同反馈增益的情况下,与PD反馈控制相比较,PD结合输入整形控制系统控制力降低56%,能耗降低47%,同时提高了系统的响应速度。     

体外预应力梁动力特性的能量法分析

不引入解析法中体外筋预拉力增量与梁中点振动位移成正比的假设,提出用能量法分析体外预应力梁动力特性。由于不引入解析法中的假设,梁自振频率也更准确,与数值解吻合良好。计算结果表明：解析法低估了体外筋对第1自振频率效应;高估了对第2自振频率效应;体外预应力筋对第1自振频率影响较大,对高阶的频率影响很小,可以不考虑其影响;随着体外筋面积和偏心距的增加,梁的第1自振频率也随之增加。在理论上,体外预应力能减小梁的自振频率,而体内预应力对梁的自振频率没有影响     

Structural optimization of rotating tapered laminated thick composite plates with ply drop-offs

In this study, structural optimization of rotating tapered thick laminated composite plates with ply drop-offs has been investigated numerically. The governing differential equations of motion of the tapered composite plate have been presented including the energy associated with the inertia force, coriolis force, displacement dependent centrifugal force and initial stress resultants due to steady state rotation. Four noded quadrilateral finite element has been formulated based on the first order shear deformation theory. Finite element analysis results are validated with experimental results for natural frequencies of the tapered plate with various configurations. Various cases of optimization problems are formulated with different objective functions in terms of maximization of natural frequencies and damping factors (individually and combined) and solved using genetic algorithm in order to obtain optimal ply sequence and ply orientation. It is shown that the optimization problem with maximization of fundamental modal damping factor without rotating condition yields the optimal layout as 90° for all the layers in the plate. It is also observed that maximization of the fundamental modal damping factor yields identical optimal orientation for uniform and all the configurations of a tapered composite plate.     

Thrust bearing design for high-speed composite air spindles

The air spindles whose shafts are made of carbon fiber composite are appropriate for high-speed and high-precision machining such as small hole drilling of printed circuit board (PCB) or wafer cutting for manufacturing semiconductors because the carbon fiber composite shaft has low rotational inertia, high damping ratio and high fundamental natural frequency.

The axial load capability and stiffness of air spindles for drilling operation are dependent on thrust bearings that are composed of air supply part mounted on the housing and rotating part mounted on the rotating shaft of spindle.

Since the stresses induced in the rotating part of thrust bearing by centrifugal force are very high at high-speed rotation, the axial stiffness and load capability of an air spindle should be designed considering the stresses induced by the centrifugal force as well as the natural frequency of rotating shaft to avoid the resonant whip vibration of the spindle.

In this work, the air supply part of a thrust air bearing for a high-speed composite air spindle was designed considering its axial stiffness and load capability. The rotating part of the thin thrust bearing was designed through finite element analysis considering the static and dynamic characteristics under axial load and the centrifugal force during high-speed rotation.     

变截面功能梯度旋转轴的自由振动特性

基于微分求积有限元(DQFEM)和铁木辛柯梁理论研究轴向变截面功能梯度旋转轴自由振动特性。首先利用上述理论和方法建立理论分析模型;然后将基于该模型所得的计算结果与已有文献和有限元软件ANSYS进行对比验证,结果表明该模型具有准确性、稳定性和通用性;最后采用上述模型分别研究变截面锥度系数和梯度系数对转轴固有频率和临界转速的影响,结果表明变截面锥度系数和梯度系数均会对转轴的固有频率和临界转速产生不同程度影响。同时发现转轴涡动频率(固有频率)会随转速增加发生分岔现象。     

强离心场下旋转型行波超声电机定子动力学分析与试验

研究了强离心场下旋转型行波超声电机定子的动力学特性,分析了离心刚化效应对定子的影响。通过计算离心力做的功(或称为离心势能)推导出因离心刚化效应引起的附加刚度矩阵,进而得到强离心场下定子的特性矩阵(包括质量矩阵和刚度矩阵),求解得到定子的模态参数;并根据压电陶瓷的孤极区反馈的电压信号,确定了高旋环境下定子的固有频率;总结了强离心场下超声电机定子动力学特性变化规律,给出了高旋环境下超声电机的驱动控制应对策略,为高旋环境下超声电机的应用奠定基础。     

Behavior of a Light Solid in a Rotating Horizontal Cylinder with Liquid Under Vibration

Dynamics of a cylindrical body in a rotating cavity is experimentally studied under transversal translational vibrations of the cavity rotation axis. Experiments are run at high rotation rate, when under the action of centrifugal force the body shifts to the rotation axis (the centrifuged state). In the absence of vibrations, the lagging rotation of the body is observed, due to the body radial shift from the axis of rotation caused by gravity. The body average rotation regime depends on the cavity rotation rate. The vibrations lead to the excitation of different regimes of body differential rotation (leading or lagging) associated with the excitation of its inertial oscillations. The dependence of the differential speed of the body rotation on the vibration frequency is investigated. The body dynamics has a complex character depending on the dimensionless vibration frequency. The analysis of body oscillation trajectory revealed that the body oscillatory motion consists of several modes, which contribute to the averaged dynamics of the body and the flows in the cavity.     

CZ法砷化镓单晶生长中熔体流动状态转换

考虑浮力、热毛细力、离心力和科里奥利力的情况下, 对CZ法砷化镓单晶生长中熔体流动和传热建立了三维时相关紊流数学模型. 通过数值求解预测到了熔体中流动状态的转变. 结果表明, 熔体中温度梯度驱动的浮力与热毛细力的联合作用和晶体旋转产生的离心力与科里奥利力的联合作用相匹配时, 熔体流动为非轴对称流动; 当其中一方占优势时, 熔体流动为轴对称流动. 流动为非轴对称流动时, 熔体中出现斜压热流体波. 由轴对称流动转变为非轴对称流动的机制为斜压不稳定性. 得到了能描述不同条件下熔体流动状态的流动区域图. 数值结果对优质砷化镓单晶生长具有重要的参考价值.     

Vibration analysis of rotating cantilever plates

A finite element technique is used to determine the natural frequencies and the mode shapes of a cantilever plate mounted on the periphery of a rotating disc. The plane of the plate is assumed to make any arbitrary angle with the plane of rotation of the disc. The distributed centrifugal force is resolved into two components—one acting in the plane of the plate and the other normal to the plate. The stresses produced in the middle surface of the plate due to the in-plane forces are first determined. The increase in the bending stiffness of the plate elements due to these in-plane stresses is obtained in a manner similar to that used in the stability analysis of plates. The component of the distributed centrifugal force normal to the plate surface is added to the inertia force. From the results of computations carried out for various values of the aspect ratio, the speed of rotation, the disc radius and the setting angle, empirical formulae are derived giving the effect of these parameters on the natural frequencies. These empirical formulae are observed to be in agreement with the corresponding known formulae for rotating cantilever beams, when the aspect ratio is high.     

考虑温升梯度影响的表贴式高速永磁电机转子强度分析

针对非导磁金属护套表贴式高速永磁电机的转子强度分析问题,基于弹性力学的平面应力模型,采用极坐标下的位移法,推导了考虑静态过盈量、转速以及转子温升梯度影响的转子强度解析解,并通过有限元仿真和试验验证了解析解的有效性。在转子强度解析解的基础上,进一步研究了护套厚度、静态过盈量、转速及转子温度等参数对转子应力的影响。仿真及试验结果表明:解析解能够准确计算考虑温升梯度影响的表贴式高速永磁电机转子的径向应力、环向应力及等效Mises应力。高速离心力和转子发热使永磁体内的拉应力大幅增加,同时也增加了护套所承受的Mises等效应力。适当增加静态过盈量和护套厚度可增强永磁体内的预压力,使永磁体免受高速离心力及转子发热产生的拉应力所破坏。     

Oscillatory thermo capillary convection in a spinning cylindrical liquid bridge under micro-gravity condition

In a viscous liquid column thermocapillary convection arises under the action of an axial temperature gradient. If this temperature gradient is oscillatory it induces surface oscillations and may lead to large amplitudes, if the frequency of the temperature fluctuation is in resonance with that of the liquid column. The response of the liquid column (non-rotating and rotating) has been determined and the effect of changing aspect ratio, Prandtl number, thermal expansion coefficient and rotational speed of the column in the case of steady temperature gradient may deteriorate for fluctuating temperatures, especially, if the fluctuating frequency is in reasonance with one of the lower natural frequencies of the liquid. The streamlines for the rotating and non-rotating liquid bridge are also presented and show the complex morphology of the convectional flow field, which is due to rotation and temperature oscillations of the liquid system.     

离心泵空化下的转速瞬变特性试验研究

通过安装轴编码器获取了离心泵空化过程的转速瞬变信号,利用时域和频域分析手段进一步探索在不同空化程度下转速瞬变的特点和规律。分析结果表明:当离心泵内刚发生空化时,离心泵的转速变化范围最大,以标准差衡量转速的波动程度也最大,严重空化时转速的波动程度高于未空化时的波动程度;在频域上,试验用离心泵—电机系统的转速的固有频率为2.9 Hz,空化条件下泵转速的主频也是轴频,不随流量和空化程度的改变而改变,但是同一流量下,空化初生时主频的幅值最高,严重空化时次之,未空化时最小;而不同流量下空化初生主频处的幅值则随着流量的增加先增大后减小,在设计流量下空化初生时主频处的幅值达到最大;在时频域上,通过小波分析的方法对转速的特征进行了分析,发现在空化下转速的能量主要集中在39~46.9 Hz,并且在空化初生时转速的能量最大。