面向360°全景视频的帧内预测编码的快速算法

为了节省360°全景视频的编码时间,对通用视频编码标准中的编码单元划分决策过程进行了研究,提出了一种面向360°全景视频的帧内预测编码的快速算法。通过优化编码树单元(Coding Tree Unit,CTU)的编码深度范围和编码单元的划分模式的选择过程,减少编码时间。实验结果表明,在全帧内模式下,所提算法比原始算法平均可以节省34.33%的时间复杂度,同时带来的BDBR平均增量仅为1.665%,BDPSNR的平均降低量仅为0.076 dB。

基于知识蒸馏的步态识别方法

针对步态识别中网络模型复杂度高、参数量大、训练测试速度慢等问题,提出一种基于知识蒸馏的步态识别方法.通过知识蒸馏方法对ConvNext-KD模型进行训练,在不增加新训练数据集、模型复杂度和模型参数量的前提下,提高ConvNext-KD模型的识别准确率.该方法在中科院CASIA-B和CASIA-C数据库中进行多次仿真实验.结果表明,ConvNext-KD模型在保持较小参数量和较低复杂度的同时,可以显著缩短训练测试的时长并取得较高识别准确率.

八字门滑坡变形与库水位变化动态响应规律分析

为探讨库水位升降作用下水库型滑坡变形动态响应规律,以八字门滑坡为例,结合滑坡地质的特征,分析变形及水位监测资料,并利用ABAQUS有限元软件仿真计算分析库水位升降作用下滑坡变形特征。研究结果表明:八字门滑坡变形机理为库水初始浸泡作用下的滑坡复活变形、库水下降作用下的坡体变形;其整体变形与库水位变化具有显著的阶跃性及间歇性的动态响应规律;在周期性库水位调度的影响下,前缘滑体软化加剧及后缘岩土体相对位移较大时,滑坡体极有可能发生整体性滑塌。

高速铁路钢轨打磨偏差对车辆动力学性能的影响

针对我国高速铁路存在的两种典型的钢轨打磨偏差,建立了我国某型动车组车辆多体动力学模型,仿真分析了轨肩过度打磨和轨头过度打磨对轮轨接触匹配关系、车辆稳定性及车辆运行品质的影响。结果表明:当轨肩过度打磨时,轮轨接触点位置会偏向于踏面外端和轨头部分,导致等效锥度变小,容易诱发一次蛇行(即"晃车")现象,在一次蛇行对应的速度区间,车辆横向加速度增大,平稳性更差;而当轨头过度打磨时,轮轨接触点位置会集中在踏面喉根圆部分和轨肩部分,引起等效锥度异常增大,引发车辆二次蛇行失稳,容易触发动车组构架横向加速度"报警"。因此,为了提高动车组稳定性,改善运营品质,在钢轨打磨过程中,应该严格控制打磨精度,以标准廓形为目标廓形。

轨底坡变化对高速车辆运行行为的影响

现有轨道精调和养护维修过程中往往只针对轨道的高低、方向、水平、扭曲等相关因素进行调整,对轨底坡的相关规定较少.对现有客运专线同一轨道的一段区间进行轨底坡现场测量,发现轨底坡变化较大.通过建立国内某时速250 km动车组车辆模型,考虑LMD车轮型面与标准60 kg/m(CHN60)钢轨匹配,分析了在同一轨道具有标准轨底坡(1∶40)、对称变化轨底坡和非对称变化实测轨底坡条件下的车辆动力学行为.计算结果表明:轨底坡对称变化和非对称变化对车辆直线运行时的平稳性、舒适性影响很大,较标准轨底坡(1∶40)布置时车辆垂向平稳性指标分别增加了32.96%和34.52%,横向平稳性最大值增加了40.65%;直线段的标准、对称变化与非对称变化轨底坡布置对车轮的磨耗影响逐渐增大;直线段非对称、对称变化轨底坡情况较标准轨底坡最大磨耗指数分别增加136.71%和27.65%,最大表面损伤指数分别增加25.14%和15.86%.车辆曲线通过对称变化与非对称变化轨底坡布置时,增大车辆横向晃动;曲线段轨底坡变化对车轮磨耗和疲劳指数相对于标准布置情况影响较小,但曲线段轨底坡变化对车轮磨耗和疲劳指数均大于直线段.最后根据以上结论给出了针对轨底坡的工程化建议.

Simulink模型接入运行支撑系统的插件式技术

为了提高高层体系结构仿真联邦的开发效率,将Simulink模型接入运行支撑系统,以在高层体系结构分布式仿真中充分利用Simulink强大的数值计算功能,对搭建高层体系结构分布式仿真系统具有很强的实用价值。对现有的3种接入方法进行分析,针对其不足,结合插件技术对基于插件的接入方法进行研究,与现有方法相比,该方法具有更高的模型接入效率。对该方法进行方案设计,并阐述了关键流程,包括接口适配包装、仿真数据绑定与仿真数据更新。采用该方法将Simulink模型接入运行支撑系统,构建了小型固体火箭分布式飞行仿真系统应用实例,证明该方法不但可行,而且高效、易用。

椭圆轨道绳系卫星系统释放的类反步法控制

为解决椭圆轨道上绳系卫星系统的稳定和快速释放问题,在传统反步法的基础上,提出了一种类反步法的非线性控制方法.与传统反步法仅适应于严格反馈系统不同,提出的类反步法非线性控制方法不仅可以应用于非严格反馈系统,并且能够充分地利用系统的非线性模型来改善控制效果.首先,基于拉格朗日力学原理,建立了椭圆轨道上绳系卫星系统释放过程的动力学模型,并通过一种新型的量纲为1的变换对动力学模型进行化简,得到了量纲为1的卫星系统模型;其次,设计了一种类反步非线性控制方法以应对绳系卫星系统模型中的耦合特性,并采用Lyapunov函数验证了各系统状态的渐进稳定性能;最后,设计了绳系卫星系统释放过程的非线性控制和PID控制的数值仿真实验,通过对比验证了所提出的类反步法非线性控制方法的有效性.仿真结果表明,所提出的类反步法控制方案不仅可以稳定、高效地控制椭圆轨道上绳系卫星系统的释放过程;而且相对比传统的PID控制方案所取得的控制效果更优.

轨道参数对轮轨耦合系统固有频率的影响

轮轨系统固有振动特性对车轮失圆和钢轨波磨的形成和发展具有重要影响。建立普通短轨枕整体道床轨道有限元模型和簧下质量-轨道耦合系统有限元模型,分析扣件刚度、地基刚度、簧下质量及轨枕间距对轨道和耦合系统固有频率的影响。结果表明:轨道1阶垂向弯曲频率随扣件刚度的增大而增大,地基刚度对轨道1阶垂向弯曲频率的影响较小;耦合系统1阶垂向弯曲频率(P2共振频率)随扣件刚度的增大而增大,随簧下质量的增大而减小;P2共振频率随地基刚度的增大而增大,当地基刚度大于300MPa/m,地基刚度的变化对P2共振频率影响较小;扣件刚度和地基刚度不变的情况下,轨道1阶垂向弯曲频率和P2共振频率随轨枕间距的增大而减小;轨枕间距随机变化可降低Pinned-Pinned共振响应峰值。通过现场力锤敲击与车辆轨道振动测试结果对模型进行验证,仿真结果与现场测试结果基本一致。

车轮多边形激励下的滚动接触疲劳裂纹瞬态扩展行为研究

利用ANSYS/LS-DYNA建立带车轮多边形的三维轮轨滚动接触疲劳裂纹扩展模型,将真实轮轨间瞬态滚滑和高频动力作用考虑在内,分析车轮多边形和连续钢轨裂纹造成的瞬态接触载荷对钢轨裂纹动态扩展行为的影响。速度250 km/h牵引工况的结果表明:零间隙多裂纹对法向轮轨力的影响甚微,但会造成切向轮轨力不可忽略的波动;车轮多边形会造成法向和切向轮轨力显著的周期性波动,如0.1 mm波深23阶多边形会使得各裂纹面最大法向和切向接触力较圆顺工况分别增长19.6%、34.1%;任一裂纹面内法向和切向接触应力在接触斑滚过的0.22 ms内发生了复杂的瞬态变化,进一步导致各裂纹的最大裂尖应力场强度因子的周期性波动,影响裂纹动态扩展行为;随着车轮多边形波深和阶数的增加,上述各种波动的幅度均会变大,加速裂纹扩展。

基于粒子群优化算法的云数据均衡放置策略

在拥有多个存储节点的云数据存储系统中,保持云存储系统的负载均衡水平为一个合理的值和最小化数据检索的时间是一个值得研究的问题。本文提出一种基于粒子群优化算法的云数据均衡放置策略(balanced placement strategy of cloud data based on particle swarm optimization algorithm,BPCD),首先,给出一种云存储系统模型;其次,引入基尼系数作为衡量该系统负载均衡水平的指标,结合数据检索时间目标函数构建多目标约束优化模型;再次,采用粒子群优化算法对问题进行求解,主要包括数据节点编码与参数设置、种群初始化、粒子群空间搜索、算法迭代4个过程;最后,将本文算法与传统云数据放置算法进行对比分析。仿真实验表明,本文提出的云数据均衡放置策略在优化云存储系统的负载水平和数据检索时间方面具有良好的效果。

医学工程保障中除颤监护仪质量检测分析研究

目的通过质量控制,检测两种除颤监护仪的精神科医院临床应用效能。方法采用FLUKE除颤分析仪对本院同时采购的两个品牌共16台除颤监护器进行包括外观和正常性检测、释放能量准确性、充电时间、同步延时时间、心率示值等5个项目的质控检测。结果除1台美国A除颤器释放能量检测不合格,其他合格率均为100%。结论上海B除颤仪在释放能量准确性、充电时间等两个方面都要比美国A除颤监护仪稳定、有效、安全,更适合精神专科医院临床使用。

眼动仪在精神分裂症诊断方面的发展和研究

本文主要介绍了精神科用医用眼动仪的发展历程。阐述了眼电法眼动仪、角膜反光法眼动仪以及瞳孔-角膜反射向量法医用眼动仪的工作原理和眼动仪在精神分裂症诊断方面的临床应用效果,介绍了国内外眼动仪研究现状,且结合实际工作提出了未来医用眼动仪的设计发展趋势。

Investigation into the Vibration of Metro Bogies Induced by Rail Corrugation

The current research of rail corrugation mainly focuses on the mechanisms of its formation and development. Compared with the root causes and development mechanisms, the wheel-rail impacts, the fatigue failure of vehicle-track parts, and the loss of ride comfort due to rail corrugation should also be taken into account. However, the influences of rail corrugation on vehicle and track vibration, and failure of vehicle and track structural parts are barely discussed in the literature. This paper presents an experimental and numerical investigation of the structural vibration of metro bogies caused by rail corrugation. Extensive experiments are conducted to investigate the effects of short-pitch rail corrugation on the vibration accelerations of metro bogies. A dynamic model of a metro vehicle coupled with a concrete track is established to study the influence of rail corrugation on the structural vibration of metro bogies. The field test results indicate that the short-pitch rail corrugation generates strong vibrations on the axle-boxes and the bogie frames, therefore, accelerates the fatigue failure of the bogie components. The numerical results show that short-pitch rail corrugation may largely reduce the fatigue life of the coil spring, and improving the damping value of the primary vertical dampers is likely to reduce the strong vibration induced by short-pitch rail corrugation. This research systematically studies the effect of rail corrugation on the vibration of metro bogies and proposes some remedies for mitigating strong vibrations of metro bogies and reducing the incidence of failure in primary coil springs, which would be helpful in developing new metro bogies and track maintenance procedures.

Influence of Vehicle Parameters on Critical Hunting Speed Based on Ruzicka Model

While introducing foreign advanced technology and cooperating with Chinese famous research institutes,the high-speed vehicles are designed and take the major task of passenger transport in China.In high-speed vehicle,the characteristic of shock absorber is an important parameter which determines overall behavior of the vehicle.The most existing researches neglect the influence of the series stiffness of the shock absorber on the vehicle dynamic behavior and have one-sided views on the equivalent conicity of wheel tread.In this paper,a high speed passenger vehicle in China is modeled to investigate the effect of the parameters taking series hydraulic shock absorber stiffness into consideration on Ruzicka model.Using the vehicle dynamic model,the effect of main suspension parameters on critical speed is studied.In order to verify the reasonableness of shock absorber parameter settings,vibration isolation characteristics are calculated and the relationship between suspension parameters and the vehicle critical hunting speed is studied.To study the influence of equivalent conicity on vehicle dynamic behavior,a series of wheel treads with different conicities are set and the vehicle critical hunting speeds with different wheel treads are calculated.The discipline between the equivalent conicity of wheel tread and critical speed are obtained in vehicle nonlinear system.The research results show that the critical speed of vehicle much depends on wheelset positioning stiffness and anti-hunting motion damper,and the series stiffness produces notable effect on the vehicle dynamic behavior.The critical speed has a peak value with the equivalent conicity increasing,which is different from the traditional opinion in which the critical speed will decrease with the conicity increasing.The relationship between critical speed and conicity of wheel tread is effected by the suspension parameters of the vehicle.The study results obtained offer a method and useful data to designing the parameters of the high speed vehicle and simulation study.

Wheel-rail Profiles Matching Design Considering Railway Track Parameters

The profile of wheel/rail has great concern with the vehicle running safety, the wheel/rail wear and the rolling contact fatigue between wheel and rail, due to its severer impact on the dynamic behavior of both the railway vehicle/track, and the wheel/rail rolling contact status. However, recent studies in this respect are mainly explored in reverse methods, where track parameters are predetermined and invariable during the optimizing process. This paper attempts to propose a wheel-rail profiles matching design method considering multi-parameter, through optimizing wheel/rail profile under different rail cants and track gauges, based on the existed optimization technology for the normal gap of wheel/rail. The method presented in this paper can also, compared with the prior reverse methods, be called ＂forward solution method＂ in which the riding comfort, wheel unloading rate and wheel/rail contact stress of the speed-up railway passenger car are calculated by means of a vehicle-track coupling dynamic model, with the range of the rail cant varying from 1/20 to 1/40 and the rail gauge from 1 433 mm to 1 441 mm. These results show that the distribution status of the pairs of contact points can be obviously improved and the contact stress can be reduced significantly; a great influence is exposed by the rail cant and track gauge on the dynamic behavior of the high speed passenger car, and an optimal vehicle dynamics behavior are obtained with the optimized wheel/rail profile when the rail cant is 1/30 and the track gauge is 1 435 mm. This research can provide important references for the investigation of the wheel-rail profiles matching design method considering multi-parameter.

Effect of Wheel Load on Wheel Vibration and Sound Radiation

The current researches of wheel vibration and sound radiation mainly focus on the low noise damped wheel. Compared with the traditional research, the relationship between the sound and wheel/rail contact is difficulty and worth studying. However, there are few studies on the effect of wheel load on wheel vibration and sound radiation. In this paper, laboratory test carried out in a semi-anechoic room investigates the effect of wheel load on wheel natural frequencies, damping ratios, wheel vibration and its sound radiation, The laboratory test results show that the vibration of the wheel and total sound radiation decrease significantly with the increase of the wheel load from 0 t to 1 t. The sound energy level of the wheel decreases by 3.7 dB. When the wheel load exceeds 1 t. the attenuation trend of the vibration and sound radiation of the wheel becomes slow. And the increase of the wheel load causes the growth of the wheel natural frequencies and the mode damping ratios. Based on the finite element method （FEM） and boundary element method （BEM）, a rolling noise prediction model is developed to calculate the influence of wheel load on the wheel vibration and sound radiation. In the calculation, the used wheel/rail excitation is the measured wheel/rail roughness. The calculated results show that the sound power level of the wheel decreases by about 0.4 dB when the wheel load increases by 0.5 t. The sound radiation of the wheel decreases slowly with wheel load increase, and this conclusion is verified by the field test. This research systematically studies the cffcct of wheel load on wheel vibration and sound radiation, gives the relationship between the sound and wheel/rail contact and analyzes the reasons, therefore, it provides a reference for further research.

Numerical Analysis of Rolling-sliding Contact with the Frictional Heat in Rail

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.

Vibro-acoustic Radiation Characteristics Analysis of Railway Vehicle Wheel with Damping Ridges Based on Modal Strain Energy

The existing researches on the damping wheel mainly focus on investigating the influence of damping structure change on the vibro-acoustic control.The changes include the geometric size of the damping structure,the damping material parameters,and the placement,and so on.In order to further understand the mechanism in reducing the acoustic radiation of railway wheel with layer damping treatment,in this paper,the wheel is simply modified by a full-sized circular plate.The circle plate side has stuck circumference constrained damping ridges and radial constrained damping ridges on it.Based on a hybrid finite element method-boundary element method（FEM-BEM）,the paper develops a vibro-acoustic radiation model for such a distributed constrained damping structure.The vibration and acoustic radiation of the circular plate is analyzed.In the analysis,the dynamic response of the system is obtained by using the 3D finite model superposition method.The obtained vibration response is used as the initial boundary condition in solving Helmholtz boundary integral equation for the sound radiation analysis.In the procedure,firstly,the modal analysis of the circular plate is performed to get the distribution of the system modal strain energy.Secondly,the vibro-acoustic radiation characteristics of the plate with different kinds of circumference damping ridges and radial damping ridges are compared in order to try to find the best effective damping ridge structure.Thirdly,using the distribution of the plate modal strain energy investigates the effect of the ridge distribution locations on the circular plate on its vibro-acoustic radiation.The calculation and analysis research results show that,the sticking circumference and radial damping ridges on the plate can control the vibro-acoustic radiation of the plate effectively in different frequency range.The distribution of the constrained damping ridge has an effect on reduction in vibro-acoustic radiation of the circular plate.The present research is very useful in the design of railway wheel with low noise level.

ANALYSIS OF CREEP FORCES OF WHEEL/RAIL

The effects of structure elastic deformations of wheelset and track on creep forces of wheel and rail are investigated.Finite element method is used to calculate the influence coefficients expressing the relations between structure elastic deformations of wheelset and track and the corresponding loads in the rolling direction and the lateral direction of wheelset,respectively.The influence coefficients of wheelset and track are used to revise some of the influence coefficients obtained with the formula of Bossinesq and Cerruti in Kalker's theory of three dimensional elastic bodies in rolling contact with non Hertzian form.The theory of Kalker and the modified theory of Kalker are respectively employed to analyze creep forces of wheelset and track.The numerical results obtained show a great influence of structure elastic deformations of wheelset and track on the creep forces.Therfore it is not reasonable that wheel and rail are treated as elastic half space in the analysis of wheel and rail in rolling contact,and the present theories of rolling contact based on the assumption of elastic half space need to be further improved

永定河北京段生态补水回顾与思考

生态补水是退化河流生态系统保护与修复的重要举措,永定河自2019年以来连续6年实施生态补水,河道有水河长、流动时间不断增加,生态环境持续改善。梳理了生态补水工作开展情况、补水成效,分析了存在的问题,提出了河道水系连通、提升供水管线防洪标准、协调大宁水库防洪与供水矛盾以及改造宛平泵站等方面建议,可为进一步做好永定河生态补水工作提供借鉴和参考。