机床非线性颤振的分段线性化及其数学模型

通过引入非线性调制环节N(S),本文实现了非线性颤振的分段线性化,建立了统一的切削动力学系统模型。这一模型使线性颤振理论、非线性颤振理论趋于统一,并使超声振动切削抑制颤振的机理从理论上得到解释。     

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正飞机结构气动弹性分析与控制研究(1–27,doi:10.6052/0459-1879-15-423)胡海岩,赵永辉,黄锐评述飞机结构气动弹性研究进展并重点介绍作者的如下研究成果:在亚音速气动弹性研究中,揭示多个控制面间隙、反馈时滞对颤振的影响机理,提出时滞最优控制方法,经风洞实验证明可在较大流速范围内抑制颤振;在跨音速气动弹性研究中,提出非线性气动力的降阶模型,进而有效提高了跨音速颤振分析和颤振主动抑制的效率.     

考虑几何非线性的复合材料机翼气动弹性分析

本文研究结构几何非线性与气动力非平面效应对大展弦比复合材料机翼的气动弹性行为的影响．将非线性有限元法与曲面涡格法结合，计算机翼静气动弹性变形；通过曲面偶极子格网法结合静气动弹性平衡位置处的结构切线刚度，建立气动弹性方程并求解得到机翼颤振速度．针对板模型机翼，分析了迎角对机翼几何非线性气动弹性特性的影响．结果表明：本文复合材料板模型机翼的颤振形式不受水平弯曲模态影响，属于经典弯扭颤振；在几何非线性的影响下，机翼扭转频率随结构变形增大而明显减小，颤振速度随迎角增大而减小．     

适用于几何非线性气动弹性分析的结构动力学降阶模型方法研究

几何非线性是壁板颤振和大展弦比机翼气动弹性等问题的一个主要特征，在进行数值仿真分析时往往需要采用商业非线性有限元求解器，存在计算量大和耦合迭代策略不易控制等问题。本文发展了一种适用于几何非线性的结构动力学降阶模型(CSD-ROM),利用广义坐标的非线性多项式表征非线性内力，采用参数识别方法获取多项式系数，并通过增加额外的线性模态来改善模型预测精度。基于此方法，分别针对壁板颤振、切尖三角翼的CFD/CSD-ROM非线性颤振问题开展了时域响应分析。计算结果表明，通过CSD-ROM计算出的壁板颤振速度为590 m/s,颤振频率为174 Hz,与有限元结果误差分别为0.8%和1.7%。马赫数0.879时切尖三角翼的颤振动压预测结果为2.25 psi,与非线性有限元相比的误差为3.8%。本文采用的非线性和线性模态基底组合方法，在保证计算精度的基础上可有效降低训练样本数量，一定程度上可替代非线性有限元开展气动弹性分析。     

资金项目:国家自然科学基金资助项目

采用能计及非线性结构刚度的颤振方程为控制方程,和非定常N-S方程耦合求解,运用龙格-库塔方法在时域内求解结构响应的时间历程,从而确定颤振临界条件.计算了带结构刚度非线性的跨音速颤振特性.计算结果表明,结构刚度非线性对颤振特性有明显的影响.由于同时具有结构和气动力非线性,导致了具有复杂振荡极限环的特性.     

壁板颤振的分析模型、数值求解方法和研究进展

研究壁板颤振问题需要计及大挠度变形下结构的几何非线性效应,不仅涉及气动弹性稳定性,而且关心结构的非线性颤振响应.该文回顾了飞行器壁板颤振问题的国内外研究情况,评述了在壁板颤振研究中采用的分析模型、数值求解方法以及在理论分析和试验方面的研究成果,并提出了今后壁板颤振问题的4个研究方向.      

切削加工中刀具颤振的迟滞反馈控制

从金属切削加工的实际情况出发，分析了刀具在切削加工中产生颤振的原因．从力学的角度解释了刀具径向非线性颤振的机理，说明这是一种自激振荡，可以通过施加线性迟滞反馈力加以控制．这种反馈力是位移信号的迟滞函数，可以用于抑制振幅，增加刀具的平稳性．数值仿真验证了理论结果．     

切削颤振的研究进展综述

颤振是工件表面质量和尺寸精度的重要影响因素之一,本文全面阐述了切削过程颤振的检测技术、切削颤振的控制技术、颤振的鲁棒和概率分析。探讨了切削颤振的类别以及基于切削过程中的力学特性构建的动力学模型;分析了颤振模型的影响因素,如:切削参数、机床结构、主轴动态特性等,讨论了颤振模型的求解方法。针对切削系统结构和切削过程的非线性动力学特征,提出了时变性的模糊控制、神经网络的智能控制,降低颤振影响和利用颤振发生规律,以改善工件加工质量。随着人工智能、算法优化和智能材料的发展,智能一体化抑振系统将成为未来发展趋势。     

气动耦合扭转非线性振动的稳定性分析

本文在新的非线性气动力模型的基础上，推导出结构与风耦合作用的新非线性扭转气动力项，研究了桥梁的非线性稳定性问题，不仅给出了桥梁发生颤振的临界风速，还在时域内给出了扭转位移与速度的时程曲线，并得到了有益的结论。     

受非线性支承的板状梁结构流致振动研究

研究了受非线性支承的板状梁结构流致振动问题，采用二维不可压缩粘性流体模型，建立了板状梁的运动微分方程；研究非线性支承情况下的流体流速对振幅的影响，并对计算结果进行了分析，结果表明在非线性支承下板状梁结构在流体动压力作用下存在着复杂的动力学行为，像发生极限环颤振和屈曲等。     

叶轮机械叶片颤振研究的进展与评述

颤振一类气动弹性稳定性问题是叶轮机械设计者关心的主要问题之一. 本文对叶轮机械叶片颤振模型研究的进展进行了回顾, 包括非定常气动模型、结构模型以及颤振的预测方法等内容. 通过对颤振模型研究的介绍, 讨论了不同方法处理颤振这类气动弹性稳定性问题的优缺点. 提出了关于颤振研究目前的不足和部分难点, 认为流固耦合模型的研究值得进一步重点关注.      

On bimodal flutter behavior of a flexible airfoil

The dynamic aeroelastic behavior of an elastically supported airfoil is studied in order to investigate the possibilities of increasing critical flutter speed by exploiting its chord-wise flexibility. The flexible airfoil concept is implemented using a rigid airfoil-shaped leading edge, and a flexible thin laminated composite plate conformally attached to its trailing edge. The flutter behavior is studied in terms of the number of laminate plies used in the composite plate for a given aeroelastic system configuration. The flutter behavior is predicted by using an eigenfunction expansion approach which is also used to design a laminated plate in order to attain superior flutter characteristics. Such an airfoil is characterized by two types of flutter responses, the classical airfoil flutter and the plate flutter. Analysis shows that a significant increase in the critical flutter speed can be achieved with high plunge and low pitch stiffness in the region where the aeroelastic system exhibits a bimodal flutter behavior, e.g., where the airfoil flutter and the plate flutter occur simultaneously. The predicted flutter behavior of a flexible airfoil is experimentally verified by conducting a series of systematic aeroelastic system configurations wind tunnel flutter campaigns. The experimental investigations provide, for each type of flutter, a measured flutter response, including the one with indicated bimodal behavior.     

High-frequency plate flutter

Earlier, using the global instability method, the stability of a strip plate in a supersonic gas flow was investigated. In addition to the classical (low-frequency) flutter developing upon the interaction between the plate oscillation modes, a novel (high-frequency) flutter type in which the oscillations are unimodal was detected. In the present study, the effect on the high-frequency flutter of the plate width (earlier only an asymptotic analysis for a width tending to infinity was performed), its damping characteristics, and the presence of a gas at rest on the side opposite the flow is investigated.     

两种湍流模型时域颤振计算方法研究

采用时域计算分析方法进行了机翼跨音速颤振特性研究。在结构运动网格的基础上,采用格点格式有限体积方法进行空间离散和双时间全隐式方法进行时间推进求解雷诺平均N-S方程。针对流动粘性分别应用了SST湍流模型和SSG雷诺应力模型,通过对跨音速标模算例AGARD445.6机翼的计算结果与实验值的对比分析,其中应用SST湍流模型得到的颤振速度与实验值最为接近,特别是在跨音速段平均相对误差在3%以内;并且计算结果整体上反映了跨音速颤振"凹坑"物理特性,验证了方法的有效性。     

Parametric studies on relationships between flutter derivatives of slender bridge (Ⅱ)

Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter deriva-tives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The in-trinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.     

High-frequency flutter of a rectangular plate

In our recent study of strip plate flutter, two flutter types, low-and high-frequency, were revealed. The first arises due to interaction of the oscillation modes and has been investigated in detail in numerous studies using an approximate piston theory. The high-frequency flutter, detected for the first time, is a consequence of the presence of negative aerodynamic damping and cannot be obtained using the piston theory. In the present study, the high-frequency flutter of a rectangular plate is investigated.     

Parametric studies on relationships between flutter derivatives of slender bridge （Ⅱ）

Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter derivatives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The intrinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.     

Transonic limit cycle oscillation behavior of an aeroelastic airfoil with free-play

The limit cycle oscillation (LCO) behaviors of an aeroelastic airfoil with free-play for different Mach numbers are studied. Euler equations are adopted to obtain the unsteady aerodynamic forces. Aerodynamic and structural describing functions are employed to deal with aerodynamic and structural nonlinearities, respectively. Then the flutter speed and flutter frequency are obtained by V-g method. The LCO solutions for the aeroelastic airfoil obtained by using dynamically linear aerodynamics agree well with those obtained directly by using nonlinear aerodynamics. Subsequently, the dynamically linear aerodynamics is assumed, and results show that the LCOs behave variously in different Mach number ranges. A subcritical bifurcation, consisting of both stable and unstable branches, is firstly observed in subsonic and high subsonic regime. Then in a narrow Mach number range, the unstable LCOs with small amplitudes turn to be stable ones dominated by the single degree of freedom flutter. Meanwhile, these LCOs can persist down to very low flutter speeds. When the Mach number is increased further, the stable branch turns back to be unstable. To address the reason of the stability variation for different Mach numbers at small amplitude LCOs, we find that the Mach number freeze phenomenon provides a physics-based explanation and the phase reversal of the aerodynamic forces will trigger the single degree of freedom flutter in the narrow Mach number range between the low and high Mach numbers of the chimney region. The high Mach number can be predicted by the freeze Mach number, and the low one can be estimated by the Mach number at which the aerodynamic center of the airfoil lies near its elastic axis. Influence of angle of attack and viscous effects on the LCO behavior is also discussed.     

飞行器跨声速气动弹性数值分析

将流体和结构运动方程分别构造为含子迭代的计算格式,发展了一种紧耦合气动弹性分析方法.其中流体计算的空间离散采用改进的HLLEW(Harten—Lax-van Leer-Einfeldt-Wada)格式. TFI(transfinite inter- polation)方法用于生成随结构变形的自适应多块动网格.利用所发展的方法,对-翼-身-尾气动外形,数值预测了马赫数在0.3-1.3范围内的气动颤振边界.并详细研究了时间步长、子迭代步数、初始流场、耦合方法、疏密网格对颤振计算结果的影响.