Evolution of long-span bridge response to wind-numerical simulation and discussion

Flutter and buffeting are two important phenomena of long-span bridges susceptible to wind actions. When the wind velocity increases to the bridge flutter velocity, an initial or self-excited multi-frequency vibration in laminar flow becomes single-frequency flutter instability. Similarly, in turbulent flow, the multi-frequency buffeting vibration develops into a single-frequency dominated divergent vibration that can also be interpreted as flutter instability. Even though this transition from buffeting to flutter was observed in wind tunnel tests, the mechanism of transition from multi-frequency type of buffeting to single-frequency type of flutter has not been well demonstrated numerically. Some existent explanations on the occurrence of flutter are very generic and even somewhat confusing. An attempt to reinvestigate numerically the transition of these two phenomena was made in the present study. The established procedure demonstrates numerically how a pre-flutter multi-frequency free vibration and a multi-frequency buffeting vibration merge into a single-frequency dominated flutter at the flutter critical wind velocity. It is concluded that the modal coupling effect forces all modes to vibrate mainly in a frequency close to the oscillation frequency of the critical flutter mode. The oscillation frequency of each mode itself does not merge to that of the critical mode. As a result, some confusing concepts in flutter vibrations are clarified and the mechanisms of the vibration transition process are better understood. Numerical analyses of the Humen suspension bridge with a main span of 888 m were conducted to facilitate the discussions.     

Buffet suppression in long-span suspension bridges

We study the aerodynamic control of long-span suspension bridges and seek to raise the critical flutter wind speeds, while simultaneously suppressing buffeting. The control system design study is based on a simple flexible bridge section model that interacts with a constant-velocity air stream. A streamlined bridge deck is assumed and non-steady thin aerofoil theory is used to describe the interactions between the bridge deck and the air stream. Classical turbulence models, first developed in the aircraft industry, are used to model the buffet forces acting on the deck. While a wide variety of control systems is possible, we focus on a compensation scheme that can be implemented using passive mechanical components such as springs, dampers and a rack and pinion mechanism. A single-loop control system is investigated that controls a trailing-edge flap by sensing movements of the bridge deck; several such mechanisms are contemplated. The first finding is that the critical wind speed for flutter can be greatly increased, with good robustness characteristics, through passive feedback control. It is also possible simultaneously to suppress flutter using the same passive mechanical controller by solving a passive mixed H₂/H_∞ control problem. The effect of flexible controller mounting arrangements are considered briefly.     

碳纤维缆索悬索桥竖向非线性自由振动研究

在把碳纤维缆索悬索桥与钢缆索悬索桥比较的基础上，研究了悬索桥的竖向非线性自振问题，利用Galerkin原理及L-P法求出了悬索桥竖向非线性自振的近似解，讨论分析了温度、振幅等因素对悬索桥竖向非线性自振的影响．得到了温度升高使悬索桥非线性自振频率降低，且对钢缆索悬索桥振动时程曲线影响较大，而温度变化对碳纤维缆索悬索桥振动时程曲线几乎无影响，振幅增大将使悬索桥非线性自振频率增大的结论．     

履带车辆半主动悬挂计算机仿真研究

基于可调式半主动悬挂系统,以保持车辆悬挂性能最优或次优,可改善车辆振动环境。用动力学分析软件RecurDyn和控制分析软件Matlab／Simulink联合仿真,通过实体建模方法对高速履带车辆整车进行了被动和半主动悬挂对比仿真分析,研究结果表明,半主动控制通过悬挂阻尼力的变化改善车体振动效果明显,在高速履带车辆上采用可调阻尼式的半主动悬挂控制是可行和有效的。     

激光雷达风速模拟系统设计

多普勒测风激光雷达是大气风场探测的重要手段。本文以光纤Mach-Zehnder干涉仪作为测风激光雷达系统的鉴频器,设计并建立了风速模拟探测激光雷达的自校正式实验系统,采用可控转速机械转轮产生的线速度引起激光多普勒频移的方法模拟大气风场。其主要由激光发射系统、模拟风场系统和光电探测系统组成。初步利用种子激光器的可调节波长实现了系统输出强度变化,通过能量探测方式验证了光纤Mach-Zehnder干涉仪透过率谱强度曲线,实验分析结果验证了鉴频系统的可靠性,并进一步实现了鉴频系统光程差精确校正。     

Series method for analyzing 3D nonlinear torsional divergence of suspension bridges

A simplified method for analyzing 3D nonlinear torsional divergence of suspension bridges is proposed in this paper. The geometric nonlinearity in the deflection theory and the three components of displacement-dependent wind loads are taken into account in the method. This method is a two-step process: the calculation of deflection response under the displacement-dependent wind loads, and the calculation of the critical wind velocity. The response under the displacement-dependent wind loads is calculated from Fourier series. The critical wind velocity is calculated by means of an iterative method. It is found that a small number of iteration cycles and Fourier coefficients are sufficient enough for convergence. The advantages of the proposed method are showed by a comparing the numerical results of this method with those obtained from the linear method and nonlinear finite element methods.     

兆瓦级风电机组变桨距过程动态仿真

在分析风电机组变桨距调节原理的基础上,建立了包含风力机、变桨距执行系统、变桨距控制算法、变桨速率、动态尾流、塔架动态、传感器响应的变桨距风电机组整体动态数学模型。以此为基础,运用MATLAB/SIMULINK仿真模拟平台搭建了变桨距风电机组动态仿真模型。以阵风为例,运用该模型对一台1.5 MW的风电机组进行了变桨距过程动态特性仿真。仿真结果与简化模型仿真结果对比表明：建立的模型能很好地描述变桨距过程中的机械转矩过冲、桨距角滞后等动态特性,弥补了现有各种模型过于简化的不足。     

基于ANSYS的大跨预应力混凝土桥梁空间仿真方法

针对大跨预应力混凝土(Prestressed Concrete,PC)桥梁经常发生梁体开裂的问题,对ANSYS进行二次开发,实现大跨PC桥梁参数化实体建模,解决大跨PC桥梁空间仿真中变截面箱梁参数化建模、复杂预应力钢束参数化建模、高精度单元网格划分和施工过程仿真等几个关键技术问题,提出基于ANSYS的桥梁空间分析整套技术流程.利用所提出的技术路线对某大跨PC连续梁进行施工过程仿真分析,验证该技术的可行性.     

一类非线性船舶在随机波上的倾覆概率仿真

研究一类非线性船舶在随机波上的倾覆概率仿真。船舶在给定随机波上的、直到颠覆的大幅度横摇可用一个四元非线性方程表示;假定噪声为白噪声的情况下,该方程通过转化可被改写成对应的二阶随机微分方程;基于半离散数值解法,设计了一类非线性船舶在随机波上的倾覆概率仿真算法,该方法简单,易于工程应用;给出实例演示了方法的应用,验证了算法的有效性。     

风洞试验绳牵引并联支撑系统自适应滑模控制

针对绳牵引并联支撑系统在风洞试验中的应用,提出一种自适应滑模控制方法以提高飞行器模型动态试验的运动精度.首先,详细分析了系统不确定因素,并重点考虑了气动力与绳弹性变形的影响,重构了系统动力学方程;基于奇异摄动理论,提出一种复合控制律,其中对慢变状态量采用自适应连续非奇异终端滑模控制,对快变状态量采用微分控制;通过李雅普诺夫函数法对系统的稳定性进行了分析,确定了控制律中微分增益项的影响.最后,以两种典型的动态轨迹为例,考虑气动力建模,对所设计控制律进行多参数仿真分析.结果表明该复合控制律可以减小绳弹性以及气动力等不确定性参数对跟踪误差的影响,提高运动控制精度,因此该控制方法有效可行,可为绳牵引并联支撑的动态试验应用提供理论指导.     

喷射器内液—液湍流反应过程的数值模拟

利用两环境矩直接积分模型(DQMOM)对喷射器内液液平行-竞争反应体系进行了研究,结果表明:在固定引射流速的情况下,随着喷嘴速度的增加,平行-竞争反应的选择性越来越高, 副反应的转化率越来越低;在固定喷嘴流速的情况下,随着引射流体速度的增加,平行-竞争反应的选择性越来越低,副反应的转化率越来越高;速度比一定时,喷嘴绝对速度值越大,副反应的转化率越低.     

风场作用下大规模草地场景动态模拟*

草体作为自然场景的一种重要元素,其数量众多、覆盖范围广,很难实现实时动态模拟。针对已有方法存在的问题,提出了一种风场作用下大规模草地场景动态模拟方法,首先利用混合式表达方法构建出大规模静态草地场景,通过二维向量建立风场模型,采用混合动力学方程以及移动布告板上端顶点的方法,分别模拟出离视点不同距离的草体在风场作用下的形变。实验结果表明,该方法不仅能绘制出风场中草体随风摆动的逼真效果,同时对可变风场有很好的支持。     

15自由度重型汽车乘坐舒适性计算机仿真

重型汽车驾驶室的乘坐舒适性直接影响驾驶员的驾驶疲劳,从而影响汽车的行驶安全性。在重型汽车垂直振动固有特性中有几个固有频率对乘坐舒适性具有较大影响,车架的弯曲弹性振动就是其中之一。该文建立了包含车架弹性振动的15自由度整车振动模型,通过计算机仿真模拟了路面随机输入响应;通过改进驾驶室悬架参数,显著改善了驾驶室的乘坐舒适性。     

微传感器和执行器的计算机模拟技术

介绍了计算机模拟技术在微传感器和微执行器设计中的应用 ,通过对多晶硅压力传感器和微泵膜片的计算机模拟分析 ,优化了器件的结构设计。研究工作表明计算机模拟是微传感器和微执行器设计的有效工具     

悬索桥主缆初应力对桥梁动力特性的影响

为掌握主缆初应力对桥梁动力特性的影响,以悬索桥为例,采用静力非线性分析方法计算应力变化过程中悬索桥的跨中挠度、缆索轴力及加劲梁的轴力变化;将得到的内力作为结构的预加应力进行有预应力的模态分析. 应用ANSYS软件进行分析,其中有限元建模时采用4种单元类型:空间梁单元BEAM4用于模拟加劲梁和塔;空间杆单元LINK10用于模拟主缆及吊杆;通过设定BEAM4和LINK10单元初应变进行有预应力的模态分析;采用MASS21单元模拟横隔板、吊杆锚固装置和桥面上的栏杆,并分别考虑质量和质量惯性矩的作用. 分析表明,悬索桥主梁竖弯振动频率受主缆初应力的影响较大,而侧弯振动频率和扭转振动频率受此影响较小. 该结果为同类桥梁的动力特性分析提供参考.     

湍流燃烧反应数值模拟的研究与实现

基于开源计算流体力学平台OpenFOAM和化学动力反应模型库Cantera设计出定常可压缩的湍流燃烧反应解算器,使用该解算器对Sydney钝体驻定火焰HM1进行数值模拟,模拟采用煤气和空气的详细反应机理,并根据计算结果得到燃烧流动组分浓度分布图和温度曲线变化图.通过计算结果与实验数据对比分析表明,模拟效果较好的符合燃烧组分变化的研究要求,这说明设计的解算器对定长可压缩燃烧流动问题有很好的计算仿真效果,体现了其可行性.湍流燃烧流动解算器的设计对于燃烧室性能预估有一定的参考价值.     

模拟投资过程的计算机游戏系统

介绍了一种计算机游戏的设计思想与设计过程。该游戏的基本设计思想是根据投资的收益与风险,最终确定一个企业的真正收益。通过人机互动过程模拟现实企业的投资过程,可以在此基础上收集企业投资的辅助决策信息,为真正的投资过程积累必要的经验。     

Vibrations of an aramid anchor cable subjected to turbulent wind

The vibration response of an initially pre-stressed anchor cable made of parallel-lay aramid fibres excited by a measured and artificially simulated spatial turbulent wind field is presented in the paper. Results of the analyses of in situ measured wind records are described. For selected data set statistical characteristics and power spectral density functions of the measured wind velocity components are calculated. The wind stochastic velocity fluctuation is modelled as a one-variate bi-dimensional random field. Cross-power spectral density functions, at different point locations are introduced. The combination of the weighted amplitude wave superposition method (WAWS) with the Shinozuka–Deodatis method is used for the analyzed problem. A time-dependent behaviour of the synthetic cable is investigated which is subjected to turbulent wind with large expected oscillations that arise as a result of slackening due to the relaxation effects. A nonlinear transient dynamic analysis is used in conjunction with the finite element method to determine the dynamic response of the cable subjected to turbulent wind at its initially prestressed state and in the selected times after the relaxation effect. The constitutive equation of the relaxation of the aramid cable follows an experimentally obtained law of the logarithmic type. To monitor the dependences of the individual quantities of cable vibration in the phase space, attractors and Poincaré maps are created by sampling the cable’s displacement and velocity at periods of relevant frequencies. Interesting findings based on the response of the cable with rheological properties to turbulent wind are presented.     

风力发电机输出信号仿真检测和分析系统

建立了一种基于LabVIEW软件平台的风机信号仿真检测和分析系统。系统使用LabVIEW的信号发生器仿真风机的输出信号,在软件中设置FIR滤波器对风机输出信号进行调理,并通过离散傅里叶变换和自相关函数分别对信号做频域和时域分析。结果表明,本系统可以准确的仿真风机信号的发生、检测和分析过程。     

机电作动器悬架硬件在环仿真测试平台研究

为了提高汽车的平顺性,提出一种机电作动器悬架,设计了机电作动器悬架硬件在环仿真测试平台。建立基于机电作动器的主动悬架数学模型与仿真模型,以嵌入式系统单片机为主处理器设计机电作动器悬架的控制器;在此基础上,以dSPACE为模型运行载体搭建机电作动器悬架硬件在环仿真测试平台;利用该测试平台进行了仿真试验。结果表明所研究的硬件在环仿真测试平台具备较好的硬件在环仿真功能,能够对机电作动器悬架性能、主动悬架控制算法进行验证与评价。