长高比对隔离段激波串特性的影响研究

隔离段是双模态超燃冲压发动机能够在不同飞行马赫数下以超燃和亚燃模态工作的核心部件。为了研究双模态超燃冲压发动机隔离段设计中长高比对隔离段激波串特性和超音速流动的影响,对以长280 mm、高30 mm的矩形隔离段为基准的一系列隔离段进行数值模拟研究。首先将计算得到的基准隔离段中心壁面压力和第一道激波位置与实验数据进行比较,验证数值模拟的准确性与合理性;进而分析在相同来流条件下,不同长高比对隔离段内激波串的形成位置、压力分布、速度分布等流动特性的影响。研究发现:随着隔离段长高比的增大,隔离段抗反压能力相应增强,激波串位置随之后移,激波强度减弱,激波串结构更加紧密,发生附面层分离及转捩的位置更靠近隔离段的出口位置,隔离段内的空气堵塞程度减小。

Establishment of Dynamic Model for Axle Box Bearing of High-Speed Trains Under Variable Speed Conditions

In this study,a dynamic model for the bearing rotor system of a high-speed train under variable speed conditions is established.In contrast to previous studies,the contact stress is simplifed in the proposed model and the compensation balance excitation caused by the rotor mass eccentricity considered.The angle iteration method is used to overcome the challenge posed by the inability to determine the roller space position during bearing rotation.The simulation results show that the model accurately describes the dynamics of bearings under varying speed profles that contain acceleration,deceleration,and speed oscillation stages.The order ratio spectrum of the bearing vibration signal indicates that both the single and multiple frequencies in the simulation results are consistent with the theoretical results.Experiments on bearings with outer and inner ring faults under various operating conditions are performed to verify the developed model.

Numerical simulation and analysis of aerodynamic drag on a subsonic train in evacuated tube transportation

The aerodynamic drag on a train running in an evacuated tube varies with tube air pressure, train speed and shape, as well as blockage ratio. This paper uses numerical simulations to study the effects of different factors on the aerodynamic drag of a train running at subsonic speed in an evacuated tube. Firstly, we present the assumption of a steady state, two dimensional, incompressible viscous flow with lubricity wall conditions. Subsequently, based on the Navier-Stokes equation and the k-c turbulent models, we calculate the aerodynamic drag imposed on the column train with a 3-meter diameter running under different pressure and blockage ratio conditions in an evacuated tube transporta- tion （ETT） system. The simulation is performed with FLUENT 6.3 software package. An analyses of the simulation re- sults suggest that the blockage ratio for ETT should be in the range of 0.25-0.7, and the tube internal diameter in the range of 2-4 m, with the feasible vacuum pressure in the range of 1-10 000 Pa for the future subsonic ETT trains.

Aerodynamic Design of a Subsonic Evacuated Tube Train System

The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.

Aerodynamic simulation of evacuated tube maglev trains with different streamlined designs

Based on the Navier-Stokes （N-S） equations of incompressible viscous fluids and the standard k-ε turbu- lence model with assumptions of steady state and two dimensional conditions, a simulation of the aerodynamic drag on a maglev train in an evacuated tube was made with ANSYS/FLOTRAN software under different vacuum pressures, blockage ratios, and shapes of train head and tail. The pressure flow fields of the evacuated tube maglev train under different vacuum pressures were analyzed, and then compared under the same blockage ratio condition. The results show that the environmental pressure of 1 000 Pa in the tube is the best to achieve the effect of aerodynamic drag reduction, and there are no obvious differences in the aerodynamic drag reduction among different streamline head shapes. Overall, the blunt-shape tail and the blockage ratio of 0.25 are more efficient for drag reduction of the train at the tube pressure of 1 000 Pa.

Analysis of torque transmitting behavior and wheel slip prevention control during regenerative braking for high speed EMU trains

The wheel-rail adhesion control for regenerative braking systems of high speed electric multiple unit trains is crucial to maintaining the stability,improving the adhesion utilization,and achieving deep energy recovery.There remain technical challenges mainly because of the nonlinear,uncertain,and varying features of wheel-rail contact conditions.This research analyzes the torque transmitting behavior during regenerative braking,and proposes a novel methodology to detect the wheel-rail adhesion stability.Then,applications to the wheel slip prevention during braking are investigated,and the optimal slip ratio control scheme is proposed,which is based on a novel optimal reference generation of the slip ratio and a robust sliding mode control.The proposed methodology achieves the optimal braking performancewithoutthewheel-railcontactinformation.Numerical simulation results for uncertain slippery rails verify the effectiveness of the proposed methodology.

Configuration Synthesis and Performance Analysis of 9‑Speed Automatic Transmissions

Current research of automatic transmission(AT)mainly focuses on the improvement of driving performance,and configuration innovation is one of the main research directions.However,finding new configurations of ATs is one of the main limitations of configuration innovation.In the present study,epicyclic gear trains(EGTs)are applied to investigate mechanisms of 9-speed ATs.Then four kinematic configurations are proposed for automatic transitions.In order to evaluate the performance of proposed mechanisms,the lever analogy method is applied to conduct kinematic and mechanical analyses.The power flow analysis is conducted,and then transmission efficiencies are calculated based on the torque method.The comparative analysis between the proposed and existing mechanisms is carried out where obtained results show that proposed mechanisms have reasonable performance and can be used in ATs.The prototype of an AT is manufactured and the speed test is conducted,which proves the accuracy of analysis and the feasibility of proposed mechanisms.

Assessment of the curving performance of heavy haul trains under braking conditions

To study the curving performance of trains, 1D and 3D dynamic models of trains were built using nu- merical methods. The 1D model was composed of 210 simple wagons, each allowed only longitudinal motion; whereas the 3D model included three complicated wagons for which longitudinal, lateral, and vertical degrees of freedom were considered. Combined with the calculated results from the 1D model under braking conditions, the behavior of draft gears and brake shoes were added to the 3D model. The assessment of the curving performance of trains was focused on making comparisons between idling and braking conditions. The results indicated the following： when a train brakes on a curved track, the wheel-rail lateral force and derailment factor are greater than under idling conditions. Because the yawing movement of the wheelset is limited by brake shoes, the zone of wheel contact along the wheel tread is wider than under idling conditions. Furthermore, as the curvature becomes tighter, the traction ratio shows a nonlinear increasing trend, whether under idling or braking conditions. By increasing the brake shoe pressure, train steering becomes more difficult.

Impact of train speed on the mechanical behaviours of track-bed materials

For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 'Corail'coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.

A PTS Optimization Scheme with Superimposed Training for PAPR Reduction in OFDM System

Partial Transmit Sequences (PTS) is an efficient scheme for Peak-to-Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) system. It does not bring any signal distortion. However, its remarkable drawback is the high computational complexity. In order to reduce the computational complexity, currently many PTS methods have been proposed but with the cost of the loss of PAPR performance of the system. In this paper, we introduce an improved PTS optimization method with superimposed training. Simulation results show that, compared with conventional PTS, improved PTS scheme can achieve better PAPR performance while be implemented with lower computation complexity of the system.

Inter-carrier Interference Analysis for MIMO-OFDM Systems in High-Speed Train Environment

The orthogonality between the subcarriers of multipleinput multiple-output orthogonal frequency division multiplexing( MIMO-OFDM) systems is destroyed due to the Doppler frequency offset,particularly in the high-speed train( HST) environment,which leads to severe inter-carrier interference( ICI). Therefore,it is necessary to analyze the mechanism and influence factor of ICI in HST environment. In this paper, by using a non-stationary geometry-based stochastic model( GBSM) for MIMO HST channels, ICI is analyzed through investigating the channel coefficients and the carrier-to-interference power ratio( CIR). It is a fact that most of signal energy spreads on itself and its several neighborhood subcarriers. By investigating the amplitude of subcarriers, CIR is used to evaluate the ICI power level. The simulation results show that the biggest impact factor for the CIR is the multipath number L and the minimum impact factor K; when the train speed υR> 400 km / h,the normalized Doppler frequency offset ε > 0. 35,the CIR tends to zero,and the communication quality will be very poor at this condition. Finally,bit error rate( BER) is investigated by simulating a specific channel environment.

Diffusion tensor imaging of spinal microstructure in healthy adults： improved resolution with the readout segmentation of long variable echo-trains

Diffusion tensor imaging plays an important role in the accurate diagnosis and prognosis of spinal cord diseases. However, because of technical limitations, the imaging sequences used in this technique cannot reveal the fine structure of the spinal cord with precision. We used the readout segmentation of long variable echo-trains（RESOLVE） sequence in this cross-sectional study of 45 healthy volunteers aged 20 to 63 years. We found that the RESOLVE sequence significantly increased the resolution of the diffusion images and improved the median signal-to-noise ratio of the middle（C4–6） and lower（C7–T1） cervical segments to the level of the upper cervical segment. In addition, the values of fractional anisotropy and radial diffusivity were significantly higher in white matter than in gray matter. Our study verified that the RESOLVE sequence could improve resolution of diffusion tensor imaging in clinical applications and provide accurate baseline data for the diagnosis and treatment of cervical spinal cord diseases.

不同运动时间和间歇模式的大强度间歇运动对愉悦情绪和享受感的影响

探讨4种不同运动时间和间歇模式的大强度间歇运动(HIIT)诱发愉悦情绪和享受感的效果差异。方法:将75名大学生随机分配至运动30 s间歇30 s组、运动1 min间歇1 min组、运动30 s间歇1min组和运动1 min间歇2 min组,分别于运动前、运动后即刻和20 min测量其享受感,并对运动中的疲劳感、愉悦情绪和享受感进行测试。结果:1)运动30 s间歇1 min HIIT相比运动1 min间歇2 min,运动30 s间歇30 s HIIT相比运动1 min间歇1 min HIIT均可诱发更积极的愉悦情绪。运动30 s间歇1 min HIIT诱发的愉悦情绪最高,运动1 min间歇1 min HIIT诱发的愉悦情绪最低。2)1:1间歇模式HIIT诱发的享受感水平低于1:2间歇模式,并且与运动30 s间歇30 s、运动1 min间歇1 min HIIT相比,运动1min间歇2 min HIIT诱发的享受感水平更高。3)运动30 s间歇1 min HIIT诱发的享受感水平显著高于运动1 min间歇1 min,相同间歇模式HIIT诱发的享受感水平没有显著差异。结论:1)运动时间和间歇时间等量时,运动时间越长,愉悦情绪越低,运动时间小于间歇时间的HIIT诱发的愉悦情绪更高。2)间歇期长的HIIT诱发的享受感水平更高,相同间歇模式的运动时间长短不影响运动后产生的享受感。3)短时间多组数HIIT是诱发愉悦情绪的最佳方案,长时间的间歇期HIIT是诱发享受感的最佳方案。

低真空管道磁浮列车交会激波流场特性分析

为了解决管道列车高速运行时产生的激波等气动效应问题,通过建立三维仿真模型,针对不同阻塞比、线间距和列车外形,基于DES湍流模型,开展非稳态数值模拟研究,分析列车在低真空管道内交会时的激波流场结构、管道壁面压力、列车表面压力。研究结果表明:随阻塞比的增大,列车前端壅塞长度增加,且正压区域压力增大,激波反射更加剧烈,尾流激波反射强度增大,激波串长度加长;阻塞比增大有助于增大激波和膨胀波的入射角,从而增大激波和膨胀波的反射次数。随线间距的增大,管道内压力波动幅度相对增大,但改变线间距对管道内激波流场结构、管道壁面压力、列车表面压力的影响不大。列车头部压力和尾部激波强度与流线型长度存在一定的关系,随着列车流线型长度的增加,列车前端壅塞长度缩短,车头前端高压区壅塞强度和车尾末端尾流区域激波反射强度均减小。

升力翼对高速列车通过隧道时气动效应的影响

在高速列车上安装升力翼可以为高速列车提供升力,降低列车对轨道的压力,从而有效减少轮轨磨损,但安装升力翼对列车在隧道内行驶时的气动性能产生较大影响,为此,基于三维非定常可压缩RNG k−ε两方程湍流模型,对升力翼列车通过隧道时的气动效应进行数值模拟研究。研究结果表明:在列车进入隧道过程中,升力翼尾流结构增大,对列车表面压力产生一定的影响;升力翼尾流使列车表面压力下降,同时升力翼增加车隧阻塞比,使列车表面的压力上升,两者共同影响列车表面压力,导致列车表面压力分布复杂;安装升力翼使列车表面与隧道壁面的压力幅值均增加,列车表面压力幅值最大增加5.4%,隧道壁面压力幅值最大增加14.1%;同时,对隧道出口的微气压波产生不利影响,在距离隧道出口20 m处的微气压波幅值上升4.1%。研究结果可为升力翼的参数优化设计提供指导。

奥美沙坦酯联合利拉鲁肽注射液治疗糖尿病肾病对氧化应激损伤和尿白蛋白肌酐比值的影响

目的分析奥美沙坦酯联合利拉鲁肽注射液治疗糖尿病肾病对氧化应激损伤以及尿白蛋白肌酐比值的影响。方法在2019年7月~2023年2月诊治的糖尿病肾病患者中选取80例作为研究对象,采用随机数字表法将其分为对照组和观察组,各40例。两组均进行基础治疗,对照组在基础治疗基础上使用奥美沙坦酯治疗,观察组在基础治疗的基础上使用奥美沙坦酯联合利拉鲁肽注射液治疗,比较两组治疗效果、氧化应激水平[丙二醛(MDA)、超氧化物歧化酶(SOD)、总抗氧化能力(T-AOC)]、肾功能指标[血肌酐(Scr)、尿素氮(BUN)、尿白蛋白排泄率(UAER)]和尿白蛋白肌酐比值(UACR)。结果观察组治疗有效率90.00%(36/40)高于对照组60.00%(24/40)(P<0.05);两组治疗后MDA水平均降低,且观察组水平较低,两组SOD、T-TOC水平均升高,且观察组水平均较高(P<0.05);两组治疗后Scr、BUN、UAER、UACR水平均降低,且观察组水平较低(P<0.05)。结论奥美沙坦酯联合利拉鲁肽注射液治疗糖尿病肾病具有较好的临床效果,能够减轻患者氧化应激损伤,降低尿白蛋白肌酐比值,改善肾功能。

风载作用下高速列车曲线通过性能研究

在风载和曲线欠超高叠加的不利工况下,高速列车的运行安全性表现出复杂的变化规律,因此需要针对风载作用下高速列车的曲线通过安全性进行深入研究。采用空气动力学和车辆动力学相结合的分析方法,考虑车速和风速变化、实际轮轨匹配及线路激励情况,建立瞬态风载模型、横风作用下高速列车空气动力学模型及车辆动力学模型;对高速列车在不同车速和风速作用下的气动载荷变化规律进行分析,并对其以不同速度通过不同欠超高曲线线路时的脱轨系数、轮重减载率和轮轴横向力等车辆关键动力学参数的变化规律进行分析,研究风载和曲线欠超高对高速列车脱轨和倾覆的影响。结果表明:风速变化引起的侧向力系数变化幅度大于车速;在风载和曲线欠超高叠加的不利工况下,除轮重减载率安全裕量明显降低外,轮轴横向力的安全裕量也降低,且车辆关键悬挂部件工作状态恶化,其中二系横向止档的位移迅速增大且工作状态接近压并,左右两侧空气弹簧压力差也迅速增大,车辆动力学性能的安全裕量明显下降。

具有抗高过载能力的大传爆比传爆序列

针对超音速巡航导弹抗高过载、飞行速度快,安全性、可靠性的新要求,提出并设计了一种具有抗高过载能力的大传爆比传爆序列,该序列由电子雷管、导爆管、传爆管、水平转子和垫片组成。其中,水平转子的转轴与弹轴不重合,使得导爆管与电子雷管和传爆管错位,使之平时处于隔离状态。发射后,在离心力的作用下解除保险,水平转子开始运动,转子旋转一定角度后使导爆管与电子雷管对正,解除隔离使之处于待发状态。该序列中的垫片包括平台和凸台两部分,它可以起到双重的缓冲作用,同时保护位于上部的水平转子和底部的传爆管,具有优异的抗高过载能力。该序列具有大传爆比的特点,传爆管药量的增加为战斗部节省了空间,提高了战斗部的装药量,增强了武器的毁伤能力。

针灸联合康复训练对脑卒中后偏瘫并腰椎间盘突出症患者患肢运动功能及生存质量的影响

目的探讨针灸联合偏瘫肢体综合训练对脑卒中后偏瘫并腰椎间盘突出症(LDH)患者患肢运动功能及生存质量的影响。方法选取2019年6月至2021年6月收治的脑卒中后偏瘫并LDH患者68例,采用随机数字表法分为观察组和对照组各34例。2组均给予常规治疗及偏瘫肢体综合训练,观察组在偏瘫肢体综合训练前采用针灸进行治疗。比较2组治疗前后患肢运动功能[脑卒中康复运动功能评定量表(STREAM)]、痉挛程度[改良的Ashworth量表法(MAS)]、神经功能缺损[美国国立卫生研究院卒中量表(NIHSS)]、生活自理能力[日常生活活动能力评定(ADL)]、疼痛程度[视觉模拟评分法(VAS)]、腰椎功能[日本骨科协会评估治疗分数量表(JOA)]、腰背肌力学[屈伸松弛比(FRR)、肌张力、压痛阈]、足底压力、生活质量[脑卒中生活质量量表(SS-QOL)]。结果治疗后,2组STREAM各项评分、JOA各项评分、压痛阈、SS-QOL评分、患足静态压力占比、患足中部动态压力峰值均较治疗前升高,且观察组高于对照组(P<0.05)。治疗后,2组MAS评分、NIHSS评分、ADL各项评分、VAS评分、健足中部动态压力峰值、FRR、肌张力均较治疗前显著下降,且观察组低于对照组(P<0.05)。结论针灸联合偏瘫肢体综合训练用于脑卒中后偏瘫并LDH患者治疗,可显著改善患者患肢运动功能,缓解痉挛、疼痛和神经功能缺损程度,同时改善腰椎功能、腰背肌力学和足底压力相关指标,促进患者生活自理能力恢复,提升生活质量。

高速铁路无砟轨道斜拉桥刚度理论分析与设计参数研究

为研究高速铁路无砟轨道斜拉桥的刚度特征以及合理结构设计参数,采用理论公式推导、数值分析等手段,得到结构设计参数刚度影响解析公式及其影响规律,用于指导桥梁设计。首先引入索梁活载刚度比的概念,通过建立斜拉桥主梁多点支承连续梁的三弯矩方程得到主梁刚度,通过考虑主塔变形和拉索伸长量得到斜拉索等效刚度,进而给出斜拉桥整体刚度、索梁活载刚度比和主梁跨中挠度的理论公式,并基于理论公式得出主梁惯性矩、斜拉索倾角、塔高以及拉索面积对斜拉桥整体刚度的影响。以广湛铁路东平水道特大桥主桥(67.5+60+60+350+60+60+67.5)m钢箱混合组合梁无砟轨道斜拉桥为例,通过对比跨中活载位移理论解与数值解验证本文理论公式的准确性,进而采用理论公式分析结构设计参数对桥梁刚度的影响。研究结果表明:随拉索倾角增大或者塔高增加,主梁的跨中位移先减小后增大,索梁活载刚度比先增大再减小,拉索倾角为29.2°~73.9°时主梁跨中位移达到最小值36.4 cm,此时索梁活载刚度比为15.4。随着主梁的梁高增加,主梁跨中位移减小,索梁活载刚度比减小,但是减小幅度较为缓慢。拉索面积增大,主梁跨中活载位移减小,索梁活载刚度比增加。提出了桥梁合理梁高、塔高和斜拉索规格及拉索面积。桥梁结构静动力检算、桥上轨道静态高低不平顺验算以及无砟轨道受力与层间压缩量等检算结果均表明,该桥具有良好的安全性和行车平稳性。