基于协同仿真的柔性机翼动力学建模及应用*

利用多领域协同仿真技术,应用气动弹性分析理论和方法,对柔性机翼进行结构有限元建模、动力学特性分析、固有振动分析,并针对垂直阵风载荷减缓进行讨论.仿真结果验证了该方法在工程中是有效的.     

外流作用下管道流固耦合非线性动力学研究进展

管道广泛应用于海洋、核电以及航空航天等重大工程中,是采油平台、蒸汽发生器等重要工程装备的关键结构之一.当有外部流体经过时,管道会发生流固耦合振动行为,是导致重大装备振动破坏和失效的重要原因之一,已成为重大工程设计必须解决的关键问题.本文针对外流作用下柔性管道流固耦合非线性动力学机理这一科学问题,梳理了国内外学者的重要研究成果,重点分析了柔性管道分别在横向外流和轴向外流作用下的流固耦合非线性振动行为.从实验研究、仿真分析和理论建模等方面进行了深入地探讨,揭示了外部流体对管道动力学行为的影响机制.最后,对当前国内外研究现状进行了简要的总结,并给出了这一研究仍存在的难点与挑战.     

Parametric study of the aeroelastic response of mistuned bladed disks

Mistuning, imperfections in the cyclical symmetry of bladed disks, is unavoidable due to many factors, including manufacturing tolerances and in-service wear and tear. Even small mistuning levels can cause large changes in the dynamics of bladed disks because mistuning destroys cyclic symmetry. In particular, mistuning can cause mode localization and a drastic increase of the maximum forced response level. To study mistuning, classical finite element analyses (FEA) approaches become computationally expensive because mistuning requires the analysis of the full disk model. Recently, compact and accurate reduced order models (ROMs) of mistuned bladed disks considering only structural coupling between sectors have been developed. However, the incorporation of unsteady aerodynamic effects into these ROMs is limited despite the fact that accurately accounting for the aerodynamic blade-to-blade coupling is essential for predicting mistuning effects in turbomachinery. Previous studies by the authors have shown that aerodynamic coupling can have important effects on the dynamics of bladed disks for subsonic flows. In particular, differences in the aerodynamic damping affect significantly the forced response amplification factor, and aeroelastic mistuned mode shapes differ significantly from the structural ones. These phenomena are accentuated in the transonic regime, where the presence of the shock creates a stronger blade-to-blade coupling than in the subsonic regime, as demonstrated herein. Parametric studies are conducted for various inflow Mach numbers and incidence angles. It is shown that the effect of aerodynamic coupling diminishes when the inflow Mach number is smaller, while the differences in the aerodynamic damping values still affect significantly the dynamics of mistuned bladed disks. Also, severe mistuned mode localizations are observed for modes having separated frequencies due to frequency veering.     

车削加工中的振动原因分析及消振措施探讨

受机床床身、主轴结构、刀具安装、工件装夹等组成的工艺系统的影响,在机械加工过程中无可避免的会产生受迫振动和自激振动。本文从现有机械加工过程中产生了哪几种振动,这些振动为什么会产生,以及振动产生的影响这三方面人手,提出通过改善机械工艺来解决振动问题。     

弹性预紧约束非线性对结构振动的影响

针对大型空间可展开结构中存在的关节非线性间隙约束问题,研究弹性预紧约束非线性对结构动态特性的影响.首先,基于轴向拉伸力学模型,构造了轴向拉伸关节三维梁单元.其次,使用Kelvin-Voigt接触及Coulomb摩擦模型,建立了粘弹性预紧约束下整体结构非线性动力学方程,继而分析了不同预紧约束下关节对结构非线性振动的影响.结果表明,在关节非线性约束下,结构振动传递特性的高频响应增加,低阶振动能量传递到高阶振动上.     

Frequency- and time-domain methods for the numerical modeling of full-bridge aeroelasticity

A numerical framework for full-bridge aeroelasticity is presented, based on unsteady cross-sectional load models and on the finite-element modeling of the structure. A frequency-domain approach based on aeroelastic derivatives and nonlinear complex eigenvalue analysis is compared to its equivalent time-domain counterpart based on indicial functions and direct integration of the equations of motion. A version of the time-domain load model consistent with the quasi-steady limit behavior is developed and a procedure for the numerical identification of the indicial functions from measured aeroelastic derivatives is presented. The aeroelastic stability analysis is chosen as benchmark. A numerical example is offered where the equivalency of the two approaches is proved for a full-bridge model. Advantages and disadvantages of the two techniques are discussed.     

An application of adaptive techniques to vibration rejection in adaptive optics systems

In modern Adaptive Optics (AO) systems, lightly damped sinusoidal oscillations resulting from telescope structural vibrations have a significant deleterious impact on the quality of the image collected at the detector plane. These oscillations can be observed in any mode of a generic modal representation of the AO wave-front sensor. A technique for the rejection of periodic disturbances recently presented in the literature has been adapted to the problem of rejecting vibrations in AO loops. The proposed methodology aims at estimating the harmonic disturbance together with the response of the plant at the vibration frequency. The algorithm has been tested in simulation on realistic scenarios and at the telescope.     

Vibrational control of nonlinear systems: Vibrational stabilizability

In this work, the theory of vibrational control for nonlinear systems is developed. The present paper gives criteria for stabilizability of nonlinear systems by linear multiplicative vibrations, by almost periodic forcing and by vector additive vibrations. Illustrative examples are also considered. In a subsequent paper, the problem of vibrational controllability and transient behavior will be addressed.     

Command shaping control for micro-milling operations

Micro milling requires both high speed and high accuracy in order to economically produce parts with features on the scale of 1 μm. Micro mills are smaller and more flexible than traditional large-scale machines. Therefore, vibration of the machine structure is a significant problem. Given that micro milling requires high positioning precision, even small vibrations in the controller dynamics are problematic. The small-scale operation has considerably lower tool/workpiece interaction forces than traditional-scale milling. These low cutting forces have minimal effect on the machine structural response. Therefore, the dominant dynamic factor in exciting vibration can be the machine tool motion, rather than the workpiece/tool interaction. Given this realization, properly shaping the motions of the micro mill is a promising approach to reduce vibration. This paper presents a nonlinear command-shaping technique to reduce the vibrations of a micro mill that can be implemented with a standard CNC controller. The robustness of this technique to modeling errors and disturbances is investigated. Theoretical proofs and experimental demonstrations of the command-shaping technique are presented. The improved performance from the command shaping enables higher throughput and improved accuracy of the micro mill.     

Dynamic modeling and fuzzy logic control of vibrations of a railway vehicle for different track irregularities

Safe and comfortable transportation of passengers and goods on railways can be achieved by solving the vibration problem. In this study, the dynamic modeling of the full railway vehicle is used to perform vibration analysis in order to observe displacements and accelerations. The full railway vehicle model consists of 54 degrees of freedom which are defined by differential equations. Additionally, wheel–rail contact problem (i.e. creepage factors and hertzian spring stiffness of rails) is analyzed by finite element method. Dynamic modeling and vibration analysis are carried out using Matlab–Simulink software. Using the developed model, the car body vibrations, caused by a lateral and two vertical sinusoidal track irregularities, are controlled by fuzzy logic controllers placed between the car body and bogies. The fuzzy logic algorithm herein is used for realizing the active control of car body vibrations. The simulations of vibration analysis are obtained in time and frequency domains and compared with passive controlled status. The robustness of the designed controller is verified by simulations, carried out for the cases of car body mass variations. The results show the effectiveness of the proposed algorithm.