Influence of fastener stiffness mutation in ballastless track on dynamic characteristics of high-speed trainsEI北大核心

Research purposes: The elasticity for the ballastless track structure is mainly provided by the fastening system. During the construction and maintenance of ballastless track on high-speed railway, the incorrect installation and the unreasonable transition between the old and new rail-pads may occur to the fasteners, which will cause a stiffness mutation for the fasteners. Even though this problem can hardly be found under the static condition, it can have a great effect on the stability and safety for the high-speed vehicle operation. Here different conditions for the fastener stiffness mutation are considered, according to the actually measured data. And the influence of fastener stiffness mutation on the dynamic performance of high-speed vehicle and track is calculated and analyzed by using the vertically coupled vehicle-ballastless track-subgrade vibration spatial model and the finite element software ANSYS/LS-DYNA. Research conclusions: The calculation and analysis results show that: (1) When there is a local mutation for the stiffness of fasteners, the maximum and minimum of vehicle acceleration basically keep the same. That is to say, the fastener stiffness mutation has few influence on the stability of vehicle operation. (2) The fastener stiffness mutation has much obvious effect on the wheel load reduction rate, which is related to the safety of vehicle operation. Further, when the train speed is larger than 300 km/h, the fastener stiffness mutation will directly cause the wheel load reduction rate to exceed the standard. (3) This research results can be used to provide a theoretical basis for monitoring the fastener stiffness in construction or repairing and establishing the strict control standards in high-speed railway.     

中国城市网约车服务对公交使用量的影响

城市网约车服务的蓬勃发展对包括公共交通在内的传统出行方式将产生影响.本文针对公交使用量的影响问题，运用109个城市数据做实证分析，并从网约车进入时长和城市类别做异质性检验.研究结果表明：网约车服务进入城市对城市公交使用量有明显的负向影响，且负向影响在超大型城市中更为严重；随着时间推移，网约车服务对公交使用量的负向影响呈现先增强后减弱的规律.研究结论揭示了中国城市网约车对公交的影响规律，对交通管理者制定相关政策具有参考意义.     

区域性阴极保护在集输站场中的应用

结合区域性阴极保护技术在集输站场中的应用,介绍了区域性阴极保护的技术特点、方案设计及运行调试方法,提出了区域阴极保护技术实施中需要关注的问题,对于站场区域阴极保护技术的应用具有借鉴作用。     

Cooperative path following control of UAV and USV cluster for maritime search and rescue北大核心CSCD

［Objectives ］ This paper studies a three-dimensional (3D) cooperative path-following control problem in the process of maritime search and rescue for a heterogeneous unmanned cluster system composed of unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs).［Methods ］ First, kinematic models of the UAVs and USVs are established under a fixed coordinate system and body coordinate system. In order to design a 3D path-following controller suitable for motion control, an air coordinate system is established, and the path tracking error models of the UAVs and USVs are established in the Serret-Frenet coordinate system. Next, a 3D line-of-sight (LOS) guidance law is designed at the kinematic level, and a cooperative path-following control method suitable for heterogeneous clusters of marine vehicles is proposed, allowing the UAVs and USVs to track the preset parameterized path. Finally, the stability of the control system is analyzed based on the Lyapunov stability theory.［Results］The simulation results verify the effectiveness of the proposed cooperative path-following control method for heterogeneous clusters of marine vehicles.［Conclusions］The results of this study can provide references for maritime search and rescue by using the proposed cooperative path-following control method. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Visual analysis semantic label method based on navigation logic division北大核心CSCD

[目的]旨在探索处理内河实船数据、提高其可理解性和辅助研究识别船舶行为的新方法。[方法]通过构建航行逻辑层级和划分时序数据获得船舶行为的语义标签,设计航行逻辑可视化分析系统,将船舶航行状态与数据可视化相结合,辅助分析数据及研究船舶行为特征。最后,依托数字航道,选择船舶行为复杂的内河航道工作船的数据进行实例检验,利用所提系统分析异常数据并研究船舶行为。[结果]通过航行逻辑的交互可视化,可有效确定无规律的位置跳动异常数据产生的原因及特点,帮助进行异常数据处理,并经过定性分析特征和定量分析阈值,划分出了靠泊与直航状态数据,进一步丰富了船舶行为语义标签。[结论]结合船舶行为语义标签设计的可视化分析系统,通过人机自由交互,提高了数据的可理解性,可辅助异常数据分析处理及船舶行为研究,为数据分析人员提供研究工具。     

Research developments in numerical methods of fluid-structure interactions in naval architecture and ocean engineering北大核心CSCD

流固耦合问题较为复杂,通常难以通过理论推导求得,而数值模拟则能提供一种有效的解决方案,并被广泛用于船舶与海洋工程领域。流固耦合数值方法根据其网格离散方式,可以分为贴体网格方法、非贴体网格方法、重叠网格方法和粒子类方法 4类,对这4类方法的特点及研究进展进行概述并总结得出:贴体网格方法和重叠网格方法均能精确捕捉界面的变形和演化,适合高雷诺数流动问题,在考虑结构变形时一般采用贴体网格方法,而考虑复杂几何形状的刚体运动时则常采用重叠网格方法;非贴体网格方法能够避免网格的更新操作,使计算较为简单,目前多用于模拟流动控制、水下柔性仿生航行器的研发以及多体运动干扰等问题;粒子类方法因其固有的拉格朗日属性,在模拟涉及自由液面剧烈变形、砰击、爆炸等强非线性流固耦合问题中发挥着重要作用。不同的流固耦合问题属性决定了不同方法的适用性,如何选取适合的数值方法,同时结合各类方法的优势开发新的计算方法以应对更为复杂的问题,是流固耦合算法开发的重要发展方向。     

Feedback-feedforward variable gain iterative learning method adopted in electro-hydraulic position servo system北大核心CSCD

[目的]为了实现电液位置伺服系统的精确控制,提出一种反馈-前馈变增益迭代学习法。[方法]首先建立电液位置伺服系统的简化模型,然后对迭代学习控制算法进行改进,采用带遗忘因子的变增益学习律,最后开展Matlab仿真对比验证。[结果]仿真结果表明:相较于传统的迭代学习和传统PID控制,改进后的迭代学习算法具有更好的收敛性和更小的跟踪误差,可以使电液位置伺服系统快速精确地跟踪位置曲线,从而提高系统动态特性。[结论]研究成果可为电液位置伺服系统的控制性能优化及实际工程应用提供参考。     

Analysis on acoustic performance of floating raft vibration isolation system with liquid tank北大核心CSCD

［Objective］This paper aims to establish a dynamic model of a floating raft vibration isolation system with a liquid tank in order to study the mass effect of the liquid medium, tank form, structural stiffness and loading rate on acoustic performance. ［Methods］A floating raft system with a cuboidal or cylindrical liquid tank is taken as the research object, and a fluid-structure coupling finite element dynamic model is established. The dynamic force transmission rate and power flow are then used to evaluate the acoustic performance of the system. The influence of the mass effect of the liquid medium, tank form, structural stiffness and loading rate of tank volume on the acoustic performance of the floating raft system are analyzed.［Results］The results show similar laws obtained through the calculation and analysis of the floating raft system with two types of tanks. The structural stiffness of the tank affects the mass effect of the liquid medium in the tank to a certain extent. ［Conclusions］If full advantage is to be taken of the liquid mass effect in the tank with a large loading rate to improve the acoustic performance of the floating raft system, the design of the liquid tank and raft structure must have sufficient stiffness. In addition, under the condition that the floating raft structure has sufficient stiffness, its acoustic performance will improve significantly as the tank loading rate increases in the relevant low frequency range. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Parametric study of a free piston linear alternator

This work presents the modeling and simulation of a novel free piston linear alternator. The modeling consists of two parts, a thermodynamic model and dynamic model, and these are combined and solved by matlab/simulink. The effects of various intake pressures, moving masses, ignition positions, and resistance loads are studied. The simulation results show that the free piston motion is different from that of the traditional internal combustion engine (ICE). The free piston accelerates and decelerates more quickly at the end of the stroke and additionally, the top dead center is free and changes accordingly with the studied parameters. Thus, a high compression ratio can be easily achieved.     

基于改进蚁群算法的多物流中转站选址规划

根据多物流中转站选址问题的特点,应用遗传算法和分配算法将大规模客户点划分为不同的配送单元,建立了包含配送中心和中转站的运营成本以及配送中心和中转站的大小车维护费用的数学模型,其中,运营成本包括车辆的运输成本和中转站的建造成本.提出了一种解决多物流中转站选址问题的改进蚁群算法,由于该算法在评价函数中隐含加入了约束条件,并...