Attractive fixed-point solution study of shell model for homogeneous isotropic turbulence

The attractive fixed-point solution of a nonlinear cascade model is stud- ied for the homogeneous isotropic turbulence containing a parameter C, introduced by Desnyansky and Novikov. With a traditional constant positive external force added on the first shell equation, it can be found that the attractive fixed-point solution of the model depends on both the parameter C and the external force. Thus, an explicit force is introduced to remove the effects of the external force on the attractive fixed-point solu- tion. F^arthermore, two groups of attractive fixed-point solutions are derived theoretically and studied numerically. One of the groups has the same scaling behavior of the velocity in the whole inertial range and agrees well with those observed by Bell and Nelkin for the nonnegative parameters. The other is found to have different scaling behaviors of the velocity at the odd and even number shells for the negative parameters. This special characteristic may be used to study the anomalous scaling behavior of the turbulence.

A Phase-Dependent Hypothesis for Locomotor Functions of Human Foot Complex

The human foot is a very complex structure comprising numerous bones, muscles, ligaments and synovial joints. As the only component in contact with the ground, the foot complex delivers a variety of biomechanical functions during human locomotion, e.g. body support and propulsion, stability maintenance and impact absorption. These need the human foot to be rigid and damped to transmit ground reaction forces to the upper body and maintain body stability, and also to be compliant and resilient to moderate risky impacts and save energy. How does the human foot achieve these apparent conflicting functions？ In this study, we propose a phase-dependent hypothesis for the overall locomotor functions of the human foot complex based on in-vivo measurements of human natural gait and simulation results of a mathematical foot model. We propse that foot functions are highly dependent on gait phase, which is a major characteristics of human locomotion. In early stance just after heel strike, the foot mainly works as a shock absorber by moderating high impacts using the viscouselastic heel pad in both vertical and horizontal directions. In mid-stance phase （-80% of stance phase）, the foot complex can be considered as a springy rocker, reserving external mechanical work using the foot arch whilst moving ground contact point forward along a curved path to maintain body stability. In late stance after heel off, the foot complex mainly serves as a force modulator like a gear box, modulating effective mechanical advantages of ankle plantiflexor muscles using metatarsal-phalangeal joints. A sound under- standing of how diverse functions are implemented in a simple foot segment during human locomotion might be useful to gain insight into the overall foot locomotor functions and hence to facilitate clinical diagnosis, rehabilitation product design and humanoid robot development.

Applications of optimal mathematic-physical models in metallurgical manufacture scheduling system at Baosteel

The transfer of mass flow between ironmaking and steelmaking process atBaoshan Iron and Steel Co. Ltd. has been analyzed. The mathematic-physical models of transportscheduling for hot metal manufacturing have been researched combined with the practical problem inthe metallurgical manufacture procedure. Taking into account these models, the scheduling softwarehas been designed, programmed and tested on-line. The new automation system of production schedulinghas been implemented successfully at Baosteel, which produces a great economic benefit.

A Secure and Effective Energy-Aware Fixed-Point Quantization Scheme for Asynchronous Federated Learning

Asynchronous federated learning(AsynFL)can effectivelymitigate the impact of heterogeneity of edge nodes on joint training while satisfying participant user privacy protection and data security.However,the frequent exchange of massive data can lead to excess communication overhead between edge and central nodes regardless of whether the federated learning(FL)algorithm uses synchronous or asynchronous aggregation.Therefore,there is an urgent need for a method that can simultaneously take into account device heterogeneity and edge node energy consumption reduction.This paper proposes a novel Fixed-point Asynchronous Federated Learning(FixedAsynFL)algorithm,which could mitigate the resource consumption caused by frequent data communication while alleviating the effect of device heterogeneity.FixedAsynFL uses fixed-point quantization to compress the local and global models in AsynFL.In order to balance energy consumption and learning accuracy,this paper proposed a quantization scale selection mechanism.This paper examines the mathematical relationship between the quantization scale and energy consumption of the computation/communication process in the FixedAsynFL.Based on considering the upper bound of quantization noise,this paper optimizes the quantization scale by minimizing communication and computation consumption.This paper performs pertinent experiments on the MNIST dataset with several edge nodes of different computing efficiency.The results show that the FixedAsynFL algorithm with an 8-bit quantization can significantly reduce the communication data size by 81.3%and save the computation energy in the training phase by 74.9%without significant loss of accuracy.According to the experimental results,we can see that the proposed AsynFixedFL algorithm can effectively solve the problem of device heterogeneity and energy consumption limitation of edge nodes.

Kinematic modeling and analysis of novel eight-wheel lunar rover

A new kind of eight-wheel lunar rover is developed, which is a complex closed-chain system and has good capabilities of climbing slope, surmounting obstacles and adapting to uneven terrain. In this paper, the mechanical structure of the novel eight-wheel lunar rover is introduced, forward and inverse kinematic models of the rover are established according to the closed-chain coordinate transformation and instantaneous coincidence coordinate. Based on structural characteristics, its kinetic characteristics are analyzed. Wheel slippages are separated and calculated, and a method for closed-loop control modification using wheel slip estimation during the model establishment is proposed. The results can be applied to the motion control of lunar rover.

基于失效演化模拟的电力机车用IGBT模块解析剩余寿命建模研究

牵引变流器作为电力机车系统中最关键且故障率最高的设备,影响系统的安全运行,其中绝缘栅双极晶体管(insulated gate bipolar transistor,IGBT)模块是导致牵引变流器失效的主要部件。开展IGBT模块剩余寿命准确评估,对降低运维成本和系统故障率具有重要的战略价值和经济意义。目前采用“里程修”的运维方式,未考虑机车运行线路、工况、负载差异等因素对寿命的影响,导致一些线路过早更换的高昂运维成本和一些线路过晚替换的系统停运风险。因此,在牵引系统IGBT模块故障率高、运行线路间可靠性差异大且采用不合理的“里程修”方式背景下,目前业界普遍关心的问题是各线路基于固定里程修更换的IGBT模块剩余寿命是多少。该文针对电力机车用IGBT模块剩余寿命准确评估的问题,以IGBT模块焊料层不同服役里程空洞尺寸分布规律为基础,建立考虑焊料层空洞空间分布规律的精细化多物理场模型,开展多芯片并联IGBT模块失效演化物理过程模拟,提出以焊料层空洞分布统计规律为老化状态的电力机车用IGBT模块解析剩余寿命预测模拟,并通过功率循环试验验证改进模型准确性。研究成果丰富功率器件的寿命预测和可靠性评估理论,为系统从“里程修”向“状态修”转变提供科学依据。

复杂地形下轮腿复合机动平台动态运动控制

复杂地形环境下质心参考轨迹的动态精确跟踪是保障轮腿复合机动平台稳定执行各项任务的关键。为提升平台的地形适应能力与位姿跟踪能力,提出一种动态运动控制策略。综合地形因素,建立包含车轮动力学的单刚体动力学模型,并通过近似简化将系统动力学模型转化为状态空间方程的标准形式。考虑车轮与腿部耦合运动,提出一种基于前馈力矩与反馈力矩的混合运动控制方法。通过二次规划算法求解最优地面反作用力,利用雅克比矩阵将作用力映射至关节以获取前馈力矩。为避免由环境引起的外部扰动造成系统无法在较短时间内完成优化计算,引入关节力矩反馈控制及时修正位姿跟踪误差,使系统能够快速准确地响应外部扰动,有效提高系统的鲁棒性和稳定性。仿真结果表明,新方法可有效提升平台在复杂地形下位姿动态跟踪精度,保障平台平稳运行,为复杂地形下轮腿复合机动平台的工程应用提供有力支撑。

重载机车无模型黏着预测控制研究

重载机车牵引动力的有效发挥依赖于轮对和钢轨接触时形成的黏着力,然而,由于重载机车黏着过程动力学非线性强、变量耦合多、最优蠕滑速度检测难,导致传统控制方法难以对黏着进行高效控制。针对该问题,提出一种无模型黏着集成预测控制方法。首先,分析传统无模型方法存在的问题,建立重载机车蠕滑速度新型扩张超局部模型。其次,设计扩展滑模观测器估计超局部模型中的不确定部分,不同于传统观测方法,该观测器能够“一步式”估算机车当前的黏着系数和蠕滑速度;同时引入一种改进的后调制无稳态振荡极值搜索方法并进行收敛性分析,在有效黏着系数观测的基础上实时寻优期望蠕滑速度。再次,基于最优蠕滑速度极值搜索设计一种离散蠕滑速度预测控制器,避免传统的控制律设计中引入蠕滑速度微分导致的噪声放大问题,并证明闭环控制下的系统稳定性。最后,与传统滑模黏着控制策略进行仿真对比,印证本文所提控制框架能有效降低黏着控制策略设计的复杂度,提升控制转矩的平滑度。在轨面条件突变的情况下,改进无稳态极值搜索方法能够准确搜索适合的最优蠕滑速度,在3种预设工况下都能够准确锁定最优值;离散黏着控制律能够更为精确地控制驱动转矩,与传统的带有蠕滑速度微分的黏着控制律相比极大地降低了转矩抖振。由此可知,该重载机车无模型黏着预测控制方法能够充分发挥黏着系统效能,实现多工况瞬变下的高效黏着控制。

基于CoppeliaSim的蛇形机器人建模与运动仿真

在进行蛇形机器人的结构设计及控制算法研究时,需要建立合理的仿真模型和良好的测试环境,便于研究人员有效评估。以课题组自主研发的蛇形机器人为例,基于CoppeliaSim和ROS设计了仿真模型及其运动控制系统,并进行了虚拟仿真,测试了蛇形机器人的蜿蜒运动和侧移运动。结果表明,仿真环境中模型的运动状态良好,机器人与环境交互正常,为蛇形机器人结构和控制算法的测试提供了理想的评估环境。

Multi-locomotion transition of tensegrity mobile robot under different terrains

Knowing how to make a multi-locomotion robot achieve locomotion transition under different terrains is a challenging problem,especially for tensegrity robots with multi-locomotion modes.In this study,a motion planning method for the transition of a multi-locomotion tensegrity robot(hereafter TJUBot)under different terrains is proposed.The robot can achieve four locomotion modes:earthworm-like,inchworm-like,tumbling,and sliding locomotion with only two motors.Kinematic models of the four locomotion modes under five typical terrains,including flat ground,confined space,obstacle,gap,and descending slope,are established using the energy method.Meanwhile,the kinematic characteristics(driving law and initial position)of the robot under these terrains are obtained.On this basis,motion planning for the locomotion transition of TJUBot is conducted,which includes a perception strategy based on three laser sensors and a transition strategy under different terrains.The driving laws of the two motors that can ensure the effective locomotion transition of TJUBot under different terrains are naturally obtained.Finally,experiments are conducted.Results demonstrate that the robot can achieve effective locomotion transition when the motion planning method is used.

基于MTSP的机车运用分析与优化

不固定牵引区段机车交路极大地提高了机车运用效率,是机车运用工作的发展方向。基于多旅行商问题模型(MTSP)分析武汉局集团公司江岸机务段机车运用情况,并提出优化方案。武汉局集团公司地处全国铁路网中部和地理位置中心,是全国铁路的重要枢纽,也是华中地区综合交通体系的重要组成部分,对于疏解全路车流起到了至关重要的作用。通过结合江岸机务段不同机车交路,针对不固定机车交路牵引方式建立数学模型,在满足列车开行和机车整备约束的条件下,以机车使用台数最少为目标,给出目标函数的具体求解。最后,结合不同分界口机车交路的MTSP模型,给出武汉局集团公司机车运用优化建议,对其他地区的机车运用工作也具有一定指导意义。

某型电力机车动力学仿真分析

文章以国内主力货运机车为研究对象,在对该型机车进行拓扑分析的基础上,依据该产品的实际结构,重点考虑了一系轴箱弹簧、二系橡胶堆和横向油压减震器等力学参数并对其进行了多体动力学建模。根据相关标准确定了多个工况,并对该型重载电力机车进行动力学性能评估,利用Sperling法进行了机车的平稳性分析以及机车非线性临界速度、脱轨系数、轮重减载率、轮轨横向力的稳定性和安全性分析。结果表明,在曲线的工况下,曲线半径对机车安全性的影响较小;在50~70 km/h的速度范围内,机车的运行速度与机车运行平稳性密切相关,所研究内容对国内机车产品的设计具有一定的指导意义。

机车车辆橡胶元件动态建模及其应用

橡胶的动态特性依赖于外界激扰的幅值和频率。为充分体现铁道车辆橡胶部件的真实物理特性,兼顾动力学仿真计算的精度和时间,基于弹塑性理论建立橡胶元件动态模型。分别用摩擦力和黏滞力表征橡胶的振幅相关性和频率相关性;计算分析简谐激励下橡胶元件的等效刚度和阻尼;将橡胶元件模型结合车辆-轨道耦合动力学模型,分析车辆通过曲线时一系定位节点力的动态特性。研究结果表明:摩擦力提供的等效刚度随激扰幅值的增大而减小,阻尼随激扰幅值的增大而增大;黏滞力提供的等效刚度和阻尼都随激扰频率的增大而增大;橡胶元件在车辆曲线通过的不同阶段可反映不同的动态特性。

快速客运机车踏面磨耗状态下的悬挂参数多目标优化

针对快速客运机车在磨耗轮状态下的动力学性能退化问题,开展了机车转向架悬挂参数多目标优化,以提升机车的动力学性能。首先,建立了快速客运机车动力学仿真模型并验证了准确性;然后通过相关性分析选取关键悬挂参数,并建立与动力学性能指标之间的代理模型;最后基于代理模型采用遗传算法对悬挂参数进行动力学多目标优化。优化结果表明:选取合适的悬挂参数可提升磨耗轮状态下的机车运行安全性、稳定性及平稳性,转向架二次蛇行稳定性得到了较好的提升,其中脱轨系数及轮重减载率降低20%以上,轮轴横向力及构架横向加速度降低30%以上。

重载列车模糊自适应模型预测控制方法研究

机车自动驾驶系统本身是一个非线性、时变系统。列车在运行过程中,会遇到各种不同的线路情况,因此控制器不仅要具备预测控制功能,控制器的参数也需要根据实际的运行线路情况进行动态调整。为此,文章提出了一种重载列车模糊自适应模型预测控制方法。该方法在建立非线性多质点模型的基础上,构造了考虑多优化目标及多运行约束条件的优化问题,搭建了基于重载列车多质点模型的模型预测控制系统框架,对列车运行状态进行预测和动态调节;针对固定的控制器参数无法适应不同线路情况的问题,文章利用模糊控制与模型预测控制方法相结合的方法,通过对模型预测控制器的权重系数进行自适应整定,从而实现列车在不同运行线路上自适应优化控制。仿真结果表明,模糊自适应模型预测控制器具有良好的控制性能,不仅能够实现对列车的精确控制,将速度误差控制在±1km/h范围内,而且能够保证列车运行的平稳性。

机车检修数据标准化用特制大语言模型

机车检修数据标准化是确保机车检修数据进行以可靠性为中心的维修(RCM)数据分析的关键步骤之一,但目前存在样本数量少、数据格式不规范、分析难、人工成本高等问题,导致使用传统的人工方式进行数据标准化的工作难度大。大语言模型在理解自然语言处理和处理复杂任务方面具有强大的性能,近几年来在学术界和工业界取得了很大的发展。文章首先研究了大语言模型在机车检修数据上进行信息抽取的应用性能,发现统一信息抽取大语言模型(UIE)适用于机车检修领域进行信息抽取,扩大机车数据数量可以提升UIE对机车检修数据信息抽取的性能,平衡故障标签种类对UIE进行机车检修数据信息抽取的性能提升不大;然后,针对数据标注困难的问题,通过采用编写脚本方式,实现数据标注自动化,并利用ChatGLM对机车检修数据进行标准化处理,Bleu-4、Rouge-1、Rouge-2、Rouge-L指标分别达到86.87%、89.60%、87.54%、94.26%,满足工程应用要求;最后,开发了一个封装大语言模型的辅助数据标准化预处理工具,简化了数据标准化流程。

非固定区段运用的双机牵引机车周转优化模型

对于不成对机车周转图,多基于固定的机车运转区段且为单机牵引进行研究,传统机车周转图的勾划方法难以适应非固定区段机车周转图编制的需求.机车的非固定区段运用有利于缩短机车周转时间,优化机车周转方案,对提高机车运用效率意义重大.本文在充分考虑部分双机牵引不成对机车周转图中可能出现的情况:到达单机牵引列车数与出发单机牵引列车数不同,到达双机牵引列车数与出发双机牵引列车数不同.综合分析铁路运输运营效益、列车运行图均衡性等具体要求,以机车在站停留时间、机车周转图均衡性、机车周转距离、机车运用数量等4个目标函数为求解目标的基础上,建立了机车周转图的01多目标规划模型,并给出求解的方法.最后以西宁西—西宁货区段进行实例验证,得出了对应的最少机车总消耗时间,最优附挂方案和机车周转图.

韶山Ⅳ型电力机车谐波电流的分析计算

谐波污染是当前电力系统中的一大问题。为了定量地分析电力机车产生的谐波电流对电力系统的影响，根据国产韶山Ⅳ（ＳＳ４）型电力机车的电路，建立了一种适用于电力机车在牵引工况下的数学模型，利用牛顿－拉夫逊法进行迭代求解，得出ＳＳ４型电力机车的谐波电流，为进一步研究ＳＳ４型电力机车对电力系统的影响提供了可靠的依据。

应用Simpack对复杂机车多体系统建模与分析方法的研究

结合实例,对复杂多体系统动力学建模的基本方法进行了研究,建立了一种机车整车虚拟动力学模型。结合机车动力学建模系统中的体之间的铰接、约束和力元等建模技术的难点,说明如何正确进行复杂机车多体系统的动力学建模。实例中对机车动力学模型输入标准轨道谱,分析其在标准轨道谱的随机激励下车体结构的响应特征,并对动力学平稳性结果进行部分评价。

机车-轨道空间耦合动力学模型及其验证

基于车辆 -轨道耦合动力学理论 ,以六轴机车为例 ,建立了机车 -轨道空间耦合动力学模型 ,并编制了相应的计算机仿真软件。通过与实车线路试验结果进行比较 ,表明该模型及其仿真软件是正确可靠的 ,可以用于分析研究机车与轨道的动态相互作用问题 。