Bistable Piezoelectric Flutter Energy Harvesting with Uncertainty

The analytical formulation of piezoelectric flutter energy harvesting using a bistable material, while considering uncertainties in the model is presented in this paper. Bistable laminates provide the advantage of large deflection due to the nonlinear snap-through characteristics when exposed to external loading, and can therefore provide a suitable base for piezoelectric material in energy harvesting applications. A piezoelectric material that is bounded on the surface of bistable laminates, subjected to external loading, generates large strains and hence relatively higher electrical output energy, in comparison with the case where piezoelectric material is bonded on a regular surface, with analogous loading conditions. Although information regarding the external loading, material characteristics of the bistable laminate and the piezoelectric material, boundary conditions, and overall electrical circuit efficiency can be defined for analytical purposes, the exact model of the system is not readily accessible. The unavoidable uncertainties in the material, loading, and efficiency of a complex system call for a probabilistic approach. Hence, this paper provides a formulation that considers uncertainty bounds in obtaining a realistic model. Optimal Uncertainty Quantification (OUQ) is used in this paper, which takes into account uncertainty measures with optimal bounds and incomplete information about the system, as a well-defined optimization problem according to maximum probabilities, subjected to the imposed constraints. The OUQ allows the inspection of the solution for a span of uncertain input parameters, as a reliable and realistic model.     

基于磁流变液减振器的抑制深孔钻削颤振研究

深孔机床在钻削加工中出现颤振,会导致加工精度和效率降低、刀具与机床寿命缩短和有害噪声的产生。因此对颤振和其抑制技术的研究至关重要。通过对磁流变液效应机理以及工作原理的研究,设计出基于挤压模式的自适应磁流变液减振器,将其安装在深孔机床上。建立动力学模型并求得动力学方程,通过MATLAB的Simulink平台对动力学模型进行仿真,对比分析在不同转速下安装减振器的系统与未安装减振器系统的振动图形。结果表明:磁流变液减振器可以大幅、迅速地衰减振幅并缩短振动周期,因此自适应磁流变液减振器对机床切削颤振具有很好的抑制作用。     

风雨共同作用下平板模型的气动导数试验研究

气动导数是大跨桥梁结构颤振和抖振分析中确定颤振临界风速和抖振响应的重要依据。在实际中 ,强风(特别是台风 )一般总伴随着暴雨。但遗憾的是 ,目前所有的研究均是在均匀风场或紊流风场中识别气动导数 ,而没有考虑暴雨的作用。本文采用随机系统识别方法 ,在模拟的风雨共同作用条件下识别了薄平板模型的气动导数。初步研究结果表明 ,风雨共同作用下平板结构的气动导数明显不同于仅有风作用的结果。这一新发现值得研究人员和工程技术人员的重视     

悬索桥跨径的空气动力极限

桥梁建设已经进入了一个建造跨海大桥的新时代。在跨海大桥工程的可行性研究中存在许多技术方面的挑战 ,对于桥梁设计者来说 ,超大跨径悬索桥的气动稳定问题始终是必须十分关注的问题。本文首先研究超大跨径悬索桥的技术可行性及潜在的要求 ,然后讨论各种气动措施的性能 ,其中包括缆索系统的调整、中央开槽方案、垂直及水平稳定板以及振动控制措施等。从技术及航运要求出发 ,设计了一个接近极限跨径的主跨为5 0 0 0m的悬索桥方案 ,以此为基础研究并阐述解决其空气静动力稳定性的方法     

提高大跨悬索桥颤振临界风速的气动措施研究

指出了提高大跨悬索桥颤振临界风速的措施有很多,而气动措施常为研究考虑的重点.通过对一主跨1 280 m的悬索桥的风洞模型抗风试验,对此进行了研究探索,结果表明,在主梁上增加风嘴可作为一种有效措施加以实施.     

大跨度桥梁多模态耦合颤振二分法全自动搜索

在分析和评价国内外对大跨度桥梁风致颤振研究的成果和目前各种常用颤振分析方法优缺点的基础上,基于结构的固有模态坐标,进一步完善了大跨度桥梁多模态耦合颤振的双参数搜索状态空间法。通过将结构和气流作为一个动态系统,最后将颤振问题归结为数学上一个非对称实矩阵的广义特性值问题。在求解中,风速搜索采用了二分法加速收敛技术,频率采用搜索迭代法,该方法可以按指定的搜索精度,迅速搜索到颤振临界风速和颤振频率,无须设定步长,且能真实地给出各阶模态频率和阻尼比随风速的全过程。最后对具有理想平板截面的悬臂梁进行颤振分析验证了本文方法的正确性,同时对总跨度1177m的香港汀九大桥进行颤振分析,计算得到的颤振临界风速基本与风洞试验结果基本一致,进一步表明本文方法的可靠性和高效性。     

竖扭耦合的大跨度桥梁颤抖风振响应分析

以 Scanlan的颤抖振分析理论为基础 ,推导了桥梁截面偏心时大跨度桥梁竖弯、扭转相互耦合的颤抖风振基本方程及响应均方值表达式 ,以金门大桥为算例 ,证明了求解方法的正确性 .     

Flutter control effect and mechanism of central-slotting for long-span bridges

The flutter control effect and mechanism of central-slotting, which have gradually been adopted in the design and construction of long-span bridges as an effective flutter controlling measure, were investigated with theoretical analysis and wind tunnel test. Five basic girder cross-sections representing five typical aerodynamic configurations were selected and central-slotted with two different slot widths. Then, a series of sectional model tests and theoretical analyses based on the two-dimensional three-degrees-of-freedom coupling flutter analysis method (2 dimension-3 degrees of freedom method, 2d-3DOF method) were carried out to investigate the aerody namic performance, flutter mechanism and flutter modality of the five basic sections and their corresponding central-slotted sections. The results show that central-slotting can not always improve the aerodynamic stability of bridge structure. The control effect of central-slotting depends on the aerodynamic configuration of the original girder section and the corresponding central-slotting width. If the original section is inappropriate or the slot width is unsuitable, central-slotting will even deteriorate the structural flutter performance. Theoretical investigations indicated that the differences in flutter control effects come from the different formation and evolution of aerodynamic damping, and flutter modality especially the participation level of heaving motion also has a significant influence on the control effect of central-slotting. __________ Translated from China Civil Engineering Journal, 2006, 39(7): 74–80 [译自: 土木工程学报]     

影响大跨径悬索桥颤振的非线性因素研究

随着桥梁跨径的增大 ,各种非线性因素对大跨径悬索桥颤振特性的影响将不容忽视。在线性颤振分析方法的基础上 ,考虑风速的空间非均匀分布、结构以及作用于结构上的气动力随结构变形的非线性变化影响因素 ,建立了大跨径桥梁的三维非线性颤振分析方法。以某悬索桥为例 ,进行了考虑风速空间非均匀分布、结构动力特性以及气动力随结构变形的非线性变化等因素的颤振分析 ,揭示了各种非线性因素对大跨径悬索桥颤振影响的机理和规律     

斜拉-悬吊协作体系桥的颤振稳定性研究

运用多模态颤振有限元分析方法 ,分别从悬索的矢跨比、吊跨比、斜拉索索面布置形式、边跨辅助墩的设置以及桥面主梁构成等设计参数着手 ,对主跨 14 0 0m的斜拉 -悬吊协作体系桥进行了颤振稳定性分析 ,指出了影响斜拉 -悬吊协作体系桥颤振稳定性的关键设计参数 ,并从抗风性能角度探讨了斜拉 -悬吊协作体系桥的合理结构型式。