基于改进萤火虫算法的移动车辆参数识别

提出了一种基于萤火虫优化算法的移动车辆参数直接识别方法。采用四自由度双轴十二参数车辆模型和欧拉梁有限元模型建立了车桥耦合系统的动力方程,并利用Newmark直接积分法求解了系统的动力响应。通过引入一种局部搜索策略和末位淘汰机制改进了萤火虫优化算法的收敛速率,并提高了识别结果的精度。本文方法仅利用车辆振动的竖向加速度响应测量就能进行移动车辆参数的识别。数值算例表明,改进的萤火虫优化算法可以准确地识别出车辆的质量、悬挂刚度和阻尼等参数,并且对测量噪声不敏感。     

基于虚拟变形法的车-桥耦合系统移动质量识别

利用双自由度质量-弹簧阻尼模型模拟移动车辆, 并基于虚拟变形(VDM)方法的结构快速重分 析思想, 提出一种车-桥耦合系统的移动质量快速识别的有效方法. 该方法以双自由度车体模 型的质量为变量, 通过最小化桥体结构实测响应和计算响应的平方距离来识别移动质量 (载荷), 避免了识别载荷时常遇到的病态问题, 对噪声鲁棒性强, 且需要传感器信息少. 每步优化 中, 利用在VDM方法基础上提出的移动动态影响矩阵概念, 无需时时重构车-桥耦合系统的时 变系统参数矩阵, 显著提高了计算效率. 利用数值框架梁模型, 通过比较不同车辆简化模型 对移动体质量及等效移动载荷的识别效果, 验证了该方法的可行性和有效性, 即使在5% 的噪声影响下, 利用一个传感器可以准确地识别多个移动体的质量.     

基于移动车载响应的连续梁损伤识别

应用有限元法将连续桥梁结构离散为两跨耦合欧拉-伯努利梁模型.利用Newmark直接积分法求出在移动车载作用下桥梁的动态响应,并进一步推导出动态响应桥梁对物理参数(如杨氏模量)的时域灵敏度.在反问题中利用基于响应灵敏度的有限元模型修正法识别出桥梁的局部损伤,并讨论了人工测量噪声对损伤识别结果的影响.算例表明本文方法能够快速有效地识别出耦合梁系统的局部损伤,并具有精度高、对测量噪声不敏感等特点.     

基于移动载荷响应的多跨连续桥梁损伤检测

应用有限元法将连续桥梁结构离散为两跨弱耦合欧拉-伯努利梁模型,研究了该弱耦合梁系统由于局部损伤而引起的振动模态局部化现象.利用Newmark直接积分法求出在移动车载作用下桥梁的动态响应,并进一步推导出动态响应桥梁对物理参数(如杨氏模量)的时域灵敏度.在反问题中利用基于响应灵敏度的有限元模型修正法识别出桥梁的局部损伤,并讨论了人工测量噪声对损伤识别结果的影响.算例表明该方法能够快速有效地检测具有相重频率的弱耦合系统的局部损伤,并具有精度高、对测量噪声不敏感等特点.     

复杂承载钢结构模态参数识别与综合性能评价

提出了根据动力特性试验识别结构的模态参数,运用优化算法修改动力有限元模型,进而评价复杂承载钢结构练合性能的方法.针对复杂承载钢结构的结构特点和激振形式,推导了模态参数识别公式;介绍了有限元模型动力修正的一阶搜索优化算法.利用近似平稳随机激励,对井架钢结构进行了现场模态试验,识别出前三阶固有频率和前二阶振型,分析了该结构的实际运行状况.仅依据前二阶固有频率,应用一阶搜索的优化算法,对动力有限元模型进行了修正,重分析表明:该修正模型实现了前三阶固有频率和应力特征的精确反演,能够用于进一步的静、动力分析和综合性能评价.     

基于SHAP-RF框架的越野车辆路面识别算法研究

根据越野车辆在不同路面上行驶时的动力学响应特征,可以实现路面类型的在线识别,为面向路面特征调整底盘控制子系统参数从而获取更好的行驶性能奠定基础.但越野环境地面特征复杂,车辆响应机理分析困难,给基于车辆动力学响应进行路面准确识别带来挑战.提出了一种SHAP-RF路面识别算法设计框架,通过SHAP (Shapley additive explanations)模型解释方法实现高维随机森林(random forest, RF)路面识别模型的降维化:首先采集了试验车在压实土路、沙地、良好沥青路与冰雪路4种路面上的行驶数据并计算了3个次级行驶特征;进一步计算了行驶数据的共计105个时域特征和频域特征,并以此为输入特征建立了高维随机森林路面识别模型;利用SHAP解释法分析高维模型输入特征对识别结果的影响从而提炼出各个特征与路面类型的关联性,完成特征筛选;最后,利用筛选后的特征设计降维随机森林路面分类器.基于实车数据的算法验证试验表明,设计的降维路面识别模型对4种路面的识别精确率在94%以上,召回率在93%以上,相比高维的随机森林路面识别模型,各种路面上的精确率和召回率最大降幅不超过3.2%,证明本...     

结构动力模型修正方法的比较研究及评估

在实际工程中,由结构动力模型得到的计算值与通过试验获得的测量值间往往存在偏差,为了能够精确预测结构的动力响应,依据测量信息修正存在的动力模型是非常必要的.对现有几种有效的用于结构动力模型修正的理论方法(包括基于敏感性分析的矩阵型法、基于神经网络算法的参数型法和基于遗传优化算法的方法)做了详细的综述;介绍了这些方法的步骤和研究进展;并分析了这些动力模型修正方法在工程运用中存在的一些实际问题,如不完整的模态测量值、模型修正的鲁棒性、模型修正的计算效率和收敛性等.最后,通过对一实际的五层钢框架的动力模型修正,比较了这几种方法的优缺点,提出了今后需要解决的问题.      

不确定动力系统平稳随机响应分析

由于设计、建造以及测量等诸多不确定因素的影响,通常的有限元力学分析模型只是原型结构的一种均值近似,采用随机结构模型是更为合理的.本文应用随机矩阵模拟不确定线性动力系统有限元模型中质量阵、阻尼阵和刚度阵的随机不确定性,并进一步建立此类非参数概率系统在平稳随机外载作用下动力响应的虚拟激励高效求解算法.数值结果表明,均值有限元模型和随机矩阵模型的动力响应具有很大的差异.对于精细制造,模型的随机性是不能忽略的,本文提出的算法为此类问题求解提供了一条有效途径.     

基于LS -DYNA公路桥车桥耦合的车辆模型研究

研究公路桥梁在移动车辆荷载作用下的动力响应,建立合理的车辆模型非常重要。为更真实地体现桥梁在车载作用下的动力响应,基于LS-DYNA程序,结合常用重型车辆的结构特性及参数,对车辆的橡胶轮胎、轮胎内气体压力、车轮转动和车辆悬架系统进行模拟,使车辆模型更接近实际车辆。通过车辆轴重和动力特性初步验证车辆有限元模型的有效性;同时,以一座混凝土简支空心板梁桥为算例,验证车轮转动和车桥相互接触力,并将LS-DYNA计算结果与桥梁实测结果进行对比,进一步验证车辆有限元模型的有效性。研究结果表明,基于LS-DYNA建立的三维车辆有限元模型是可行的,可以用于研究车桥相互作用。     

物理参数直接识别法对于分布系统的应用

本文将物理参数直接识别法用于均匀分布系统等效离散模型的物理参数识别，数值模拟结果表明，识别得到的离散模型的动力特性较好地接近分布系统的动力特性，离散系统物理参数识别的有关结论对分布系统仍然成立，数值模拟与实验结果还表明，均匀分布系统时域响应测量点应等距离布置。     

A hybrid multi-objective imperialist competitive algorithm and Monte Carlo method for robust safety design of a rail vehicle

This paper deals with the robust safety design optimization of a rail vehicle system moving in short radius curved tracks. A combined multi-objective imperialist competitive algorithm and Monte Carlo method is developed and used for the robust multi-objective optimization of the rail vehicle system. This robust optimization of rail vehicle safety considers simultaneously the derailment angle and its standard deviation where the design parameters uncertainties are considered. The obtained results showed that the robust design reduces significantly the sensitivity of the rail vehicle safety to the design parameters uncertainties compared to the determinist one and to the literature results.     

小口径超空泡子弹头部外形的优化设计

在水下高速运动时,小口径射弹周围的水会发生空化现象,阻力系数最优的弹头几何外形对应着射弹被空泡全包裹的超空泡状态。针对一种小口径射弹,可以利用计算流体力学（CFD）数值方法模拟含空化现象的气液两相流动,探究空泡形态和阻力系数与射弹头部几何外形的关系。选取三段锥形为基本射弹头形,采用分步优化方式对射弹头部外形进行了优化。同时,结合神经网络与序列二次规划（SQP）算法减少优化过程中的计算量,缩短了优化工作所需的总时间。优化后的射弹阻力系数比优化前的减小约30%,且能够形成包裹全弹体的超空泡。     

Performances of dynamic vibration absorbers for beams subjected to moving loads

The goal of this work is a general assessment regarding the performances of linear and nonlinear dynamic vibration absorbers (DVAs) applied to the specific problem of moving loads or vehicles. The problem consists of a simply supported linear Euler–Bernoulli beam excited with a moving load/vehicle; a DVA is connected to the beam in order to reduce the vibrations. The moving vehicle is modeled by a single degree of freedom mass spring system. The partial differential equations governing the beam dynamics is reduced to a set of ordinary differential equations by means of the Bubnov–Galerkin method. A parametric analysis is carried out to find the optimal parameters of the DVA that minimize the maximum vibration amplitude of the beam. For the case of a moving vehicle, the energy absorbed by the DVA is evaluated. Comparisons among the performances of different types of linear and DVAs are carried out. The goal is to clarify if the use of nonlinearities in the DVAs can effectively improve their performances. The study shows that the most effective type of DVA for the test cases considered is the piecewise linear elastic restoring force.     

Interaction of subway LIM vehicle with ballasted track in polygonal wheel wear development

This paper develops a coupled dynamics model for a linear induction motor (LIM) vehicle and a subway track to investigate the influence of polygonal wheels of the vehicle on the dynamic behavior of the system. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom. A Timoshenko beam is used to model the rails which are discretely supported by sleepers. The sleepers are modeled as rigid bodies with their vertical, lateral, and rolling motions being considered. In order to simulate the vehicle running along the track, a moving sleeper support model is introduced to simulate the excitation by the discrete sleeper supporters, in which the sleepers are assumed to move backward at a constant speed that is the same as the train speed. The Hertzian contact theory and the Shen- Hedrick-Elkins’ model are utilized to deal with the normal dynamic forces and the tangential forces between wheels and rails, respectively. In order to better characterize the linear metro system (LMS), Euler beam theory based on modal superposition method is used to model LIM and RP. The vertical electric magnetic force and the lateral restoring force between the LIM and RP are also taken into consideration. The former has gap-varying nonlinear characteristics, whilst the latter is considered as a constant restoring force of 1 kN. The numerical analysis considers the effect of the excitation due to polygonal wheels on the dynamic behavior of the system at different wear stages, in which the used data regarding the polygonal wear on the wheel tread are directly measured at the subway site.     

人行荷载下梁式结构振动分析的DQ-IQ混合法

为了评估人行荷载作用下梁式结构的振动舒适度,利用微分求积-积分求积,即DQ-IQ混合法求解移动荷载作用下梁的振动响应。人行荷载作用下梁式结构的振动控制方程是含Dirac函数的偏微分方程,首先利用IQ法离散与时间相关的Dirac函数,再利用DQ法把控制方程转化为二阶常系数微分方程,最后利用Newmark算法求解微分方程。以某钢结构连廊为例,利用DQ法计算结构自振频率并与解析解进行对比,结果验证了节点选取和边界条件施加的合理性,再利用DQ-IQ混合法和振型叠加法分别计算了不同行走步频下连廊的响应,计算结果表明,DQ-IQ混合法具有较高的可靠性和精确性。DQ-IQ混合法也可以推广到诸如车辆荷载作用下路面或桥梁的动力响应等其他移动荷载下结构的振动分析。     

Dynamic response of plates due to moving vehicles using finite strip method

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A preconditioned dual time-stepping procedure coupled with matrix-free LU-SGS scheme for unsteady low speed viscous flows with moving objects

In this paper an effective method is developed to solve unsteady low speed viscous flow problems with moving objects by using the governing equations of compressible fluids. The method is based on a dual time-stepping scheme, combined with low Mach number preconditioning and an implicit matrix-free Lower-Upper Symmetric Gauss-Seidel iteration on unstructured dynamic meshes. Because preconditioning modifies the governing equations, that induces the change of system's eigenvalues and eigenvectors, characteristic boundary conditions are also modified to suit the preconditioned characteristic system. Several test cases are simulated, including an in-line oscillating cylinder in a fluid at rest, flow over a flapping NACA0014 airfoil and low speed flow past a flapping-wing micro-air vehicle. Compared with experimental results whenever possible, the computed results indicate that this algorithm shows satisfactory improvement of solution efficiency and accuracy for low speed flow problems.     

轮对非线性动力学系统蛇行运动的解析解

在对铁路车辆系统的极限环幅值和非线性临界速度进行分析时通常采用数值方法, 不便于研究其随系统参数的变化规律. 轮对系统保留了影响车辆系统动力学性能的几个关键要素: 如轮轨几何非线性约束、轮轨接触蠕滑关系和悬挂系统等, 可以反映铁路车辆系统蛇行运动的本质特性. 轮对系统自由度少、参数少, 可以采用解析方法进行分析. 本文选取合适的特征量把轮对非线性动力学方程无量纲化, 得到了带有小参数的两自由度微分方程; 采用多尺度方法对该方程进行了解析求解; 给出了轮对系统极限环幅值的解析表达式并对其稳定性进行了判定; 给出了轮对系统的分岔速度解析表达式, 并进而获得系统的非线性临界速度的解析表达式. 在对得到的解析解用数值结果进行验证后, 用得到的解析解进行了系统参数影响分析. 传统的分岔图计算方法(如降速法、路径跟踪法等)需对微分方程进行大量数值积分计算方可求解系统的非线性临界速度值, 而通过本文获得的解析表达式可直接给出系统的非线性临界速度值和极限环幅值, 便于研究轮对系统动力学特性随参数的变化规律,进行快速方案比对和筛选, 为转向架结构优化设计提供参考.      

An image processing method for feature extraction and dynamic tracking of particle clusters in CFBs

A new image processing method based on the high-speed camera is proposed to identify, locate, and track clusters. The instantaneous characteristic parameters of particle clusters in the riser of the circulating fluidized bed (CFB) can be acquired, such as solids holdup, vertical velocity, lateral displacement, aspect ratio and near-circularity. Experiments were carried out with glass bead particles, river sand particles and FCC particles. The time series of images of gas–solid flow in a CFB riser with a 100 mm × 25 mm cross-section and 3.2 m in length were obtained using high-speed cameras. The k-means++ clustering algorithm is utilized to identify the clusters, centroid is applied to locate the clusters, and the cross-correlation algorithm is employed to track the specific clusters and number them to get the instantaneous characteristic parameters. The results illustrate that the shapes of clusters in the center area are closest to circle, moving upwards at a uniform speed, while the clusters in the side-wall area are mostly elongated or long chain-like, moving slowly downwards. In the transition area, the clusters are more complex, moving upwards at a constant speed, and having large lateral displacement. The results show that the image processing method used in this study is successful in acquiring the dynamic and structural parameters of the clusters simultaneously.     

Investigation of aerodynamic effects on the high-speed train exposed to longitudinal and lateral wind velocities

The wind stability of the high-speed train has gained an increasing interest in the last few years. In this paper, an investigation of the effects of stochastic winds with longitudinal and lateral components on the high-speed train is described. The longitudinal and lateral wind time histories at the position of a moving vehicle, for a variety of wind directions, are first simulated. An algorithm for computing the unsteady aerodynamic load time histories is then derived for a moving vehicle. A typical railway vehicle has been modeled using the vehicle dynamic simulation package ‘Simpack’, and the unsteady wind loads of the same vehicle are applied to the vehicle model to investigate the dynamic response behavior. The simulated vehicle behavior is assessed against the indicator of load reduction factor, which indicates wheel unloading and therefore potential roll over. The characteristic wind curves (CWC) and its spread range are then obtained to evaluate the operational safety of the high-speed train. The results demonstrate that the operational safety of the high-speed train will be overestimated if the lateral wind velocity is not considered, especially for the small angles between vehicle and wind.