主动格栅紊流场对典型主梁颤振导数影响的研究

为研究紊流积分尺度对桥梁颤振导数的影响,选取了理想平板、流线型箱梁以及高宽比1∶6矩形断面三种气动外形渐变的典型断面,采用主动格栅模拟了二维大积分尺度紊流场,利用强迫振动装置测试了主动格栅紊流场中三种断面节段模型的颤振导数,并与均匀流场试验值进行了对比。试验结果表明,紊流积分尺度对颤振导数的影响随断面钝化逐渐减弱;主动格栅二维紊流对流线型断面颤振导数影响较小,无明显趋势性变化;对钝体矩形断面影响显著,并且随折减风速增加而加剧,其气动阻尼项导数由正向负衰减显著,有利于改善结构颤振性能。     

桥梁节段模型气弹振动的非线性判别方法研究

在ERA(Eigensystem Realization Algorithm)的理论框架内建立了误差因子,评估桥梁节段模型风洞实验中气动导数的辨识质量。通过子空间能量分解,分别计算辨识过程中有效识别信号成分能量和未被识别信号成分能量与总信号能量的比值,并以此构造误差因子。将相同实验环境下自由衰减振动和尾流激励随机振动两组实验的误差因子相互比对,判断桥梁节段模型的气弹振动非线性是否对气动导数辨识结果产生影响。依据误差因子判断,在本文所使用的两种节段模型中,部分流线型箱梁断面具有较强的耦合非线性;而槽形开口型断面的模型具有较低的耦合非线性。     

不同交通流状态下桥梁气动导数的风洞试验研究

为了考虑实际运营车辆对桥梁气动导数的影响,根据车辆密度模拟了三种交通流状态,基于强迫振动装置,分别对每个交通流和无车状态下的桥梁气动导数进行风洞试验研究,讨论了不同攻角下不同车流的车辆对桥梁气动导数的影响,探究了车辆对气动导数影响的百分比以及气动导数变化量的变化规律。研究结果表明:不同攻角下不同车流的车辆均对直接导数A*2、H*4和交叉导数A*4、H*2影响显著,A*2、A*3变化量随着折减风速有一定的变化规律。虽然不同攻角下不同车流的车辆对气动导数的影响程度及影响规律不同,并且车流的繁忙程度对大多数气动导数的影响规律不明显,但是车辆对桥梁气动导数的影响不容忽略。     

基于流场定常化的桥梁颤振分析简化数值方法

基于数值方法实现快速有效地分析评价大跨桥梁颤振稳定性.针对强迫振动法识别颤振导数试验中的大跨桥梁二维节段模型.利用RNG κ-ε湍流模型并采用有限体积法求解桥梁模型绕流二维不可压缩流体Navier-Stokes方程.通过计算桥梁断面模型在周期运动中少数离散时刻的气动力,利用最小二乘法计算颤振导数,采用SCANLAN方法求解颤振临界风速,最终进行颤振稳定性分析.通过该方法计算出了丹麦Great Belt East桥和我国虎门大桥的颠振临界风速.计算结果与已有试验结果十分接近,进而验证了该数值方法的有效性和可靠性.     

主动控制翼板抑制悬索桥颤振的研究

主动控制翼板是一种新型桥梁气动措施。本文基于非定常气动力理论，推演了安装主动控制翼板后作用在整个桥梁主梁单位长度上气动力表达式，从增加系统扭转阻尼的角度，研究了翼板主动扭转振动参数的选取。在此基础上，对某大跨悬索桥方案进行了二自由度颤振分析，结果表明：合理选取翼板的主动扭转振动参数，主动控制翼板能够有效地提高该桥的颤振稳定性。     

主动约束层阻尼对超声速梁结构颤振特性的影响

本文采用主动约束层阻尼技术研究超声速梁的颤振特性,利用Hamilton原理和假设模态方法建立结构的运动方程,采用活塞理论模拟超声速梁的气动压力,采用速度负反馈控制获得主动阻尼,求解本征值问题得到复特征值,进而得到结构的固有频率和损耗因子.计算结构的固有频率随无量纲气动压力的变化曲线,得到颤振点,分析了主动阻尼和被动阻尼对颤振速度的影响.计算结果表明主动阻尼可以影响梁的气动弹性特性,并增大超声速梁的颤振速度.本文研究结果对超声速飞行器结构的颤振分析和气动设计具有重要意义.     

大跨度悬索桥颤振控制的研究状况与进展

当悬索桥主跨跨径超过2 000 m后, 气动稳定性已经成为悬索桥面临的最重要的安全问题,选择合适的装置避免桥梁在施工及运营阶段发生颤振势在必行.综述了国内外大跨度悬索桥颤振控制方法、措施及发展现状,系统介绍了大跨度悬索桥颤振控制的结构措施、耗能措施及气动措施的装置与应用,并讨论了各种措施的优缺点及其适用性.      

基于主动控制策略的机翼颤振特性模拟

航空航天飞行器舵翼类结构的气动颤振是一种灾难性的动力学行为.在基于偶极子理论的气动弹性动力学模型中,气动载荷可表达为基于结构动力学响应的一种状态反馈的闭环控制力,控制律取决于翼型的几何参数、材料参数、结构动力学特性以及来流速度等多种条件,通常需通过实际飞行或风洞实验进行辨识与检验.在实验室条件下,以系统动力学响应的模态特征等效为前提,提出了一种基于人工主动控制的方式进行气动载荷下舵翼类结构自激颤振的特征值跟踪策略.建立并讨论了等效系统的非自伴随动力学微分方程及其特征方程的求解过程,并与通用软件的计算结果进行了对比,二者具有较好的一致性.通过优化搜索分别获得了位移和速度的最优反馈点、最优作动点位置及最优反馈增益系数,经对比计算拟合得到风速-位移增益曲线和风速-速度增益曲线,从而实现了由单点反馈、单点作动的集中力的闭环控制等效系统的真实气动力分布控制.仿真算例表明,由此预示的实验过程无需辨识和重构非定常气动力的时域波形,无需其他干预即可实现地面模拟实验,主动控制的效果满足预期,初步实现了自激颤振的特征值跟踪,为进一步推动主动控制模拟实验及颤振参数辨识提供了基础.      

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.      

基于主动控制策略的机翼颤振特性模拟

航空航天飞行器舵翼类结构的气动颤振是一种灾难性的动力学行为.在基于偶极子理论的气动弹性动力学模型中,气动载荷可表达为基于结构动力学响应的一种状态反馈的闭环控制力,控制律取决于翼型的几何参数、材料参数、结构动力学特性以及来流速度等多种条件,通常需通过实际飞行或风洞实验进行辨识与检验.在实验室条件下,以系统动力学响应的模态特征等效为前提,提出了一种基于人工主动控制的方式进行气动载荷下舵翼类结构自激颤振的特征值跟踪策略.建立并讨论了等效系统的非自伴随动力学微分方程及其特征方程的求解过程,并与通用软件的计算结果进行了对比,二者具有较好的一致性.通过优化搜索分别获得了位移和速度的最优反馈点、最优作动点位置及最优反馈增益系数,经对比计算拟合得到风速–位移增益曲线和风速–速度增益曲线,从而实现了由单点反馈、单点作动的集中力的闭环控制等效系统的真实气动力分布控制.仿真算例表明,由此预示的实验过程无需辨识和重构非定常气动力的时域波形,无需其他干预即可实现地面模拟实验,主动控制的效果满足预期,初步实现了自激颤振的特征值跟踪,为进一步推动主动控制模拟实验及颤振参数辨识提供了基础.     

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

Relationships between flutter derivatives of slender bridge are investigated based on our previously proposed semi-analytical flutter derivatives of flexible structure. The intrinsic relations are validated with test data of flutter derivatives of two bridges. Changes in flutter derivatives with the aerodynamic center, rotation speed, and angle variation are also studied by using a parametric method. The results show correctness of the proposed expressions of flutter derivatives given by authors in Ref. [1], and indicate that certain relations exist between these derivatives. It is also shown that semi-analytical flutter derivatives are applicable to bridges with a streamlined cross-section.     

离心泵叶轮内密相液固两相湍流的数值模拟

利用作者建立的描述密相液固两相湍流的 KET模型和推导的基本控制方程组 ,在处理壁面边界条件时考虑了颗粒和叶片的相互碰撞作用 ,对离心泵叶轮内密相液固两相流动进行了数值模拟 ,得到了泵叶轮内两相流动的一些规律 ,为液固两相流泵的设计提供了一定的理论依据。     

大跨度桥梁多模态耦合颤振DTMD控制研究

DTMD是一种具有双频率的调谐质量阻尼器,与普通TMD相比,可以同时实现对主梁竖向和扭转运动的控制,具有较高的控制效率。本文基于多模态耦合颠振理论,导出带有DTMD的桥梁颠振系统运动微分方程,采用PK—F法求解系统颠振运动微分方程,并编制了多模态耦合颠振DTMD控制和参效分析程序,以崖门斜拉桥为算例,分析了DTMD对桥梁颤振控制的有效性并与普通TMD进行了对比,计算结果表明与传统TMD相比,DTMD对桥梁颠振具有更高的控制效率。     

Flow field analysis of a turbulent boundary layer over a riblet surface

The near-wall flow structures of a turbulent boundary layer over a riblet surface with semi-circular grooves were investigated experimentally for the cases of drag decreasing (s ⁺=25.2) and drag increasing (s ⁺=40.6). One thousand instantaneous velocity fields over riblets were measured using the velocity field measurement technique and compared with those above a smooth flat plate. The field of view was 6.75 × 6.75 mm² in physical dimension, containing two grooves. Those instantaneous velocity fields were ensemble averaged to get turbulent statistics including turbulent intensities and turbulent kinetic energy. To see the global flow structure qualitatively, flow visualization was also carried out using the synchronized smoke-wire technique under the same experimental conditions. For the case of drag decreasing (s ⁺=25.2), most of the streamwise vortices stay above the riblets, interacting with the riblet tips frequently. The riblet tips impede the spanwise movement of the streamwise vortices and induce secondary vortices. The normalized rms velocity fluctuations and turbulent kinetic energy are small near the riblet surface, compared with those over a smooth flat plate. Inside the riblet valleys, these are sufficiently small that the increased wetted surface area of the riblets can be compensated. In addition, in the outer region (y ⁺ > 30), these values are almost equal to or slightly smaller than those for the smooth plate. For the case of drag increasing (s ⁺=40.6), however, most of the streamwise vortices stay inside the riblet valleys and contact directly with the riblet surface. The high-speed down-wash flow penetrating into the riblet valley interacts actively with the wetted riblet surface and increases the skin friction. The rms velocity fluctuations and turbulent kinetic energy have larger values compared with those over a smooth flat plate. Received: 24 March 1999/Accepted: 10 March 2000     

Method of Lines for Transient Flow Fields

A computational fluid dynamics (CFD) code based on the method of lines (MOL) approach was developed for the solution of transient, two-dimensional Navier-Stokes equations for incompressible separated internal flows in complex rectangular geometries. The predictive accuracy of the code was tested by applying it to the prediction of flow fields in both laminar and turbulent channel flows with and without sudden expansion, and comparing its predictions with either measured data or numerical results available in the literature. The predicted flow fields were found to be in favorable agreement with those available in the literature for laminar channel flow with sudden expansion and turbulent channel flow with Re=6600. The code was then applied to the prediction of the highly turbulent flow field in the inlet flue of a heat recovery steam generator (HRSG). The predicted flow field was found to display the same trend with the experimental findings and numerical solutions reported previously for a turbulent diverging duct. As the code uses the MOL approach in conjunction with (i) an intelligent higher-order spatial discretization scheme, (ii) a parabolic algorithm for pressure, and (iii) an elliptic grid generator using a body-fitted coordinate system for complex geometries, it provides an efficient algorithm for future direct numerical simulation (DNS) applications in complex rectangular geometries.     

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.     

CHAOTIC MOTIONS AND LIMIT CYCLE FLUTTER OF TWO-DIMENSIONAL WING IN SUPERSONIC FLOW

Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.     

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.     

超音速气流中受热曲壁板的非线性颤振特性

基于von Karman 大变形理论及带有曲率修正的一阶活塞理论, 用Galerkin方法建立了超音速气流中受热二维曲壁板的非线性气动弹性运动方程; 采用牛顿迭代法计算得到由静气动载荷和热载荷引起的静气动弹性变形; 根据李雅谱诺夫间接法分析了壁板初始曲率与温升对颤振边界的影响; 对二维曲壁板的非线性气动弹性方程组进行数值积分求解,分析了动压参数对受热二维曲壁板分岔特性的影响, 给出了典型状态下曲壁板非线性颤振响应的时程图与相图. 分析结果表明对小初始曲率的曲壁板, 温升对其静气动弹性变形影响较大, 且随着温升的增加其颤振临界动压急剧减小; 对具有较大初始曲率的曲壁板, 温升对其静气动弹性变形的影响较弱, 且随着温升的增加颤振临界动压基本保持不变. 初始几何曲率与气动热效应使得曲壁板具有复杂的动力学特性, 不再像平壁板一样, 经过倍周期分岔进入混沌, 而会出现由静变形状态直接进入混沌运动的现象, 且在混沌运动区域中还会出现静态稳定点或谐波运动, 在大曲率情况下, 曲壁板不会产生混沌运动, 而是幅值在一定范围内的极限带振荡.