Large-Deflection Effect on Thermoelastic Dissipation of Microbeam Resonators

In real applications, beam resonators in MEMS/NEMS often vibrate beyond the linear regime. The present paper aims to study the effect of large-deflection on thermoelastic dissipation of doubly-clamped microbeam resonators. Detailed formulas are derived for quality (Q-) factor due to thermoelastic dissipation which depends on the amplitude of vibration deflection. Under adiabatic or isothermal surface thermal conditions, the nonlinear effect of large-deflection on thermoelastic dissipation is demonstrated with a comparison to the results based on linearized small deflection vibration. Our results show that thermoelastic dissipation is reduced monotonically with increasing amplitude of vibration deflection under adiabatic surface condition, while thermoelastic dissipation is increased monotonically with increasing amplitude under isothermal surface condition. Under both adiabatic and isothermal surface conditions, the large-deflection effect on thermoelastic dissipation becomes more significant for higher vibration frequencies than lower ones. For the first time to the best of our knowledge, these results reveal that large deflection has a significant effect on thermoelastic dissipation of microbeam resonators and surface thermal condition plays an important role in the large-deflection effect.     

旋转轴系弯-扭振动耦合的数值分析

介绍了一种可以同时计算出旋转轴系的弯曲振动及扭转振动的瞬态响应的数值计算方法,该方法所依据的模型是一种分段的连续质量模型,具有比较好的计算精度,而与有限元方法比较,该方法的计算工作量及比较小。作者用该方法对旋转轴系弯曲振动与扭转振动的耦合问题进行了一些分析     

Effects of Thermoelastic Damping on The Operation of The Ring Shape Anchored Contour Mode Disk Resonators

Thermoelastic damping is one of the most important energy loss mechanisms in MEMS resonators especially when the resonator is miniaturized to achieve higher frequencies. Based on thermal energy produced as the result of the resonator expansion and contraction, by considering the thermoelastic coupled equation, this article presents a solution to thermoelastic damping for previously demonstrated ring shape anchored contour mode disk RF MEMS resonator. This research proves that the thermoelastic damping has a negligible effect on the quality factor of the resonator. In addition the results mention that this effect becomes stronger when the surface to volume ratio is decreased for achieving higher frequency resonators. Obtained results reveal that the resonator could be utilized for ultra-low far-from-carrier phase noise oscillators.     

300MW汽轮机低压缸末级长叶片与轴系扭振的耦合振动

计算分析了３００ＭＷ汽轮机低压缸末级长叶片Ａ０振型弯曲振动与轴系扭振耦合对叶片安全性的影响。末级长叶片与轴系扭振耦合将使该叶片振动的实际频率避开率低于计算值,当发生严重的两相短路故障时在叶片根部的最大动弯矩远远高出其额定值;如果电网频率偏离５０Ｈｚ,会对叶片安全性产生更为不利的影响。     

Control of Thermally Induced Vibration in a Composite Beam with Damping Effect

ABSTRACT

This article deals with control of thermally induced vibration in a composite beam with damping effect. The beam consists of a central thermoelastic structural layer and two outer piezothermoelastic layers. The thermoelastic vibration in the beam is suppressed by the superposition of electroelastic vibration. The electroelastic vibration is repeatedly excited through application of electric potential differences across the piezoelectric layers. The initiation and termination times of the applied electric pulses are determined by a method similar to the optimization procedure developed previously by the authors. The amplitudes of the applied electric pulses are determined using a control method based on speed feedback. Numerical results for an aluminum/PZT ceramic beam are illustrated graphically.     

基于发动机三维流动模拟与一维动力性能模拟的气道参数化设计研究

模拟了CG150型发动机进气道-气缸-排气道的三维流动特性,分析得到其进、排气道的流量系数和缸内涡流比;并进一步将三维模拟的结果作为一维模拟的输入参数,通过模拟一维发动机的整机工作循环,得到发动机的外特性曲线,与试验台中得到的外特性结果进行对比,验证了数值试验平台的可靠性;最后,利用参数化设计方法改进发动机的气道参数,并利用上述数值试验平台,验证改进后的方案,提高了气道的流通能力。本文提出的参数化设计方法可以指导一般气道设计。     

考虑流固耦合效应的输电导线风振响应分析

针对传统输电导线风振响应分析方法不能分析导线在强风中的振动问题,基于流固耦合的基本理论和方法,采用ANSYS软件分析了稳态风场及导线轴向与风向之间存在风攻角时导线流固耦合风振响应,通过与不考虑流固耦合效应的情况进行对比,验证了考虑流固耦合效应的必要性。     

750 kV强耦合并行单回架设线路感应电压和电流研究

交流输电线路采取同塔双回架设方式时,必须对由于回路间电气耦合而产生的感应电压、电流问题进行关注,并对线路的接地开关参数进行合理选择,以确保运行安全。对于2条并行架设的单回线路,当回路间距较近时,其回路问的电磁耦合作用也较强,使得感应电压、电流问题也较为突出,需要采取措施加以限制。目前该问题尚未引起关注,也未开展限制措施研究。依托西北地区某在建的750kV并行单回架设线路,采用EMTP电磁暂态仿真工具对其感应电压和电流问题进行研究,针对其静电感应电压高且超过现有接地开关技术参数的突出问题,提出一种新的线路换位及相序布置方式,可以明显降低感应电压、电流水平,解决接地开关设备选型问题。研究成果为限制超／特高压强耦合并行单回架设线路的感应电压、电流问题提供了一种新的思路,对解决工程实际问题具有借鉴意义。     

高弹橡胶联轴器对变频风机轴系扭振特性影响研究

以某台1 000 MW超超临界机组的轴流式引风机为例,在MATLAB/SIMULINK环境下建立了矢量变频模式运行的轴系机电耦合模型。分析了高弹橡胶联轴器对于轴系扭矩脉动幅值与频谱特性的影响,并进行了联轴器更换前后的扭矩现场测试。结果表明:高弹橡胶联轴器能够降低风机变频运行时的轴系扭矩脉动幅值,减少轴系扭振对于设备的危害。     

弯曲和质量失衡对转子弯扭耦合振动影响的探讨

建立基于单质量柔性转子模型的弯扭耦合振动数学模型,模型中考虑了质量失衡及转子弯曲等因素,对数学模型进行的数值计算结果表明质量失衡和弯曲对转子的弯扭耦合振动具有重要的影响,一定程度的转子质量失衡是转子发生弯扭耦合振动的必要条件,仿真计算表明当偏心率及弯曲度大到一定程度时,转子转速会出现两个耦合区,质量偏心与转子弯曲的相位差会影响耦合区的大小及耦合区内的耦合振动,转子扭转刚度较大时的耦合效应较弱。     

固结灌浆深度对丹巴水电站深厚覆盖层坝基中流固耦合的影响

中国西南地区水利工程多建于有明显强弱相间结构的河谷深厚覆盖层上,此类大坝通常采用垂直防渗墙或帷幕灌浆等防渗措施,但这些措施不能有效提高坝基承载力,坝基不均匀沉降反而会造成防渗体的破坏和失效。因此,引入多孔介质存储系数S_α,采用有限元软件Comsol Multiphysics建立双场耦合模型,探寻固结灌浆联合垂直防渗墙条件下深厚覆盖层渗流场和应力场演化规律。研究发现,层状深厚覆盖层中,上部弱透水层、弹性模量较小而厚度较大的强透水层是固结灌浆的控制层。当上部关键层固结灌浆后,且灌浆深度达到总坝基深度50%以上时,再增加灌浆深度意义不大。研究成果可为类似工程提供参考。