Experimental investigation on tunnel sonic boom

Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu _p ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements.     

EXPERIMENTAL 3-D SIMULATION OF THE COMPRESSION WAVE,DUE TO TRAIN–TUNNEL ENTRY

The work presented in this paper concerns the first compression wave generated in a tunnel when a high-speed train enters it. This wave is the first of successive compression and expansion waves which propagate back and forth in the tunnel. Once generated at the tunnel entrance, its amplitude and gradient vary according to the train and tunnel characteristics. These waves provoke: (a) an aural discomfort for train passengers, (b) mechanical stresses on train and tunnel structures, and (c) emission of impulsive noises outside the tunnel. A reduced-scale test method, using low-sound-speed gas mixtures, has been developed and validated by using newly available European full-scale test-results. It can reproduce quite well the three-dimensional effects due to the train geometry and its position in the tunnel. The study also clearly points out that three-dimensional effects on the front of the first compression wave are attenuated with distance from the tunnel entrance and that the wave front can be considered well established and planar for distances larger than four times the tunnel diameter. Characteristics of the planar wave are in good agreement with Japanese results. The reduced-scale train Mach number has been extended up to 0.34 to determine its test domain. Our study clearly shows that, as far as the characteristics of the wave front of well-established planar first compression wave are concerned, axially symmetrical models can advantageously replace three-dimensional models, provided that the longitudinal cross-sectional area profile is the same for both configurations. This feature yields the following train nose design procedure: first determine the cross-sectional profile of a train nose against train–tunnel interactions by means of axially symmetrical configuration, then give a three-dimensional shape for drag and stability optimisation.     

基于传质现象的高速铁路隧道入口压缩波数值分析

基于一维可压缩非定常不等熵流动理论,认为隧道内空气流通截面是流动时间和流动距离的二元函数,考虑了空气与隧道壁和列车壁之间的摩擦和传热效应,采用广义黎曼特征线法,对高速列车进入存在传质现象的等截面缓冲罩隧道引起的入口压缩波进行了数值计算。另外进行了不同缓冲罩参数的计算,并且对计算结果进行了定性与定量分析,结果说明了相关的空气动力学效应。     

Attenuation of weak shock waves along pseudo-perforated walls

In order to attenuate weak shock waves in ducts, effects of pseudo-perforated walls were investigated. Pseudo-perforated walls are defined as wall perforations having a closed cavity behind it. Shock wave diffraction and reflection created by these perforations were visualized in a shock tube by using holographic interferometer, and also by numerical simulation. Along the pseudo-perforated wall, an incident shock wave attenuates and eventually turns into a sound wave. Due to complex interactions of the incident shock wave with the perforations, the overpressure behind it becomes non-uniform and its peak value can locally exceed that behind the undisturbed incident shock wave. However, its pressure gradient monotonically decreases with the shock wave propagation. Effects of these pseudo-perforated walls on the attenuation of weak shock waves generated in high speed train tunnels were studied in a 1/250-scaled train tunnel simulator. It is concluded that in order to achieve a practically effective suppression of the tunnel sonic boom the length of the pseudo-perforation section should be sufficiently long. Received 23 June 1997 / Accepted 16 September 1997     

高速铁路长隧道压缩波波前变形规律分析

高速列车进入隧道时产生的压缩波在长隧道中传播时会产生波前变形,即波前压力梯度发生变化。线路测量和学者的研究表明,隧道出口处微气压波的强度与压缩波波前压力梯度最大值成正比,而微气压波的大小又与隧道出口的爆破音直接相关,因此有必要研究压缩波在长隧道中传播时的波前变形规律。采用计算流体力学三维动态仿真计算方法,对长隧道内压缩波的生成和传播过程进行研究。证明了压缩波的波前变形不仅与初始压缩波生成时的惯性运动和气体摩擦相关,而且与列车在隧道中的运动相关,即列车运动产生的能量输入会影响压缩波波前的变形。通过多工况计算,获得了隧道内压力梯度的最大值及其出现位置与列车速度和隧道阻塞比之间的变化规律。     

Stability of bichromatic gravity waves on deep water

The stability of bichromatic gravity waves with small but finite amplitudes propagating in two directions on deep water is considered. Starting from the Zakharov equation, elementary quartet interactions are isolated and stability criteria are formulated. Results are illustrated for various combinations of bichromatic wave trains, from long-crested to standing waves. Two generic mechanisms operate: the first one is a modulational instability of one of the two components of the bichromatic wave train; the second mechanism is a modulation which couples both components of the wave train. However a third mechanism eventually comes into play: the resonant interaction of Phillips and Longuet-Higgins which leads initially to the linear growth of a third wave. When this latter is active, in particular for wave trains with wave vectors close together, it is shown by numerical integration that the long-time recurrence is destroyed.     

高速铁路工程中若干典型力学问题

高速铁路是一个复杂的系统工程,涉及一系列关键力学问题.本文讨论高速铁路工程中的3个关键固体力学问题:高速铁路轮轨滚动接触力学问题、高速列车关键结构部件疲劳问题和高速列车与线路结构动态相互作用问题;概述了其研究进展与工程应用;提出了今后进一步结合高速铁路工程需求的研究方向.     

高速移动荷载下黏弹性半空间体的动力响应

分别以移动荷载和黏弹性半空间体模拟运动列车荷载和地基,分析了地基在运动列车作用下的动力响应.首先采用Green函数法求解黏弹性半空间体在各种移动荷载模式作用下的动力响应的解析解,包括恒常和简谐移动点源、线源和面源荷载.然后采用IFFT算法和自适应数值积分算法计算解析解中的二维积分,得到了包括低音速、跨音速和超音速移动荷载作用下位移的数值结果.最后分析了速度对位移的分布和最大值的影响,发现当速度大于Rayleigh波速时,位移发生显著变化.     

A non-hydrostatic numerical scheme for dispersive waves generated by bottom motion

A numerical scheme based on the staggered finite volume method is presented at the aim of studying surface waves generated by a bottom motion. We address the 2D Euler equations in which the vertical domain is resolved only by one layer. The resulting non-hydrostatic scheme is used to simulate surface waves generated by bottom motion in a water tank. Here we mimic Hammack experiments numerically, in which a bed section is moved upwards or downwards, resulting in transient dispersive waves. For an impulsive downward bottom thrust, free surface responds in terms of a negative leading wave, followed with dispersive train of waves. For an upward bottom thrust, amplitude of the leading wave decays as the wave propagates, and no wave of permanent form evolves— instead, there appears a train of solitons. In this article, we show that our numerical scheme can produce the correct wave profiles, comparable with the analytical and experimental results of Hammack. Simulations using intermediate and slow bottom motions are also presented. In addition, we perform a simulation of a wave generated by submerged landslide, that compares well against previous numerical simulations. Via this simulation, we demonstrate that our scheme can incorporate a moving wet–dry boundary algorithm in the run-up simulation.     

高速列车服役模拟建模与计算方法研究

高速铁路的出现,使得轮轨交通技术达到更高的层次.速度提升不仅对列车的牵引动力与动力学性能提出更高要求.而且,列车与线路、气流等运行环境的耦合作用加剧,并直接影响到了列车的运行品质和安全性.在高速列车发展初期,研究关注的是如何保证高速列车能高速、平稳和安全运行.随着运行速度的提高,系统间耦合加强,服役模拟也越来越受到重视...     

Vibration suppression for high-speed railway bridges using tuned mass dampers

This paper deals with the applicability of passive tuned mass dampers (PTMDs) to suppress train-induced vibration on bridges. A railway bridge is modeled as an Euler–Bernouli beam and a train is simulated as series of moving forces, moving masses or moving suspension masses to investigate the influence of various vehicle models on the bridge features with or without PTMD. According to the train load frequency analysis, the resonant effects will occur as the modal frequencies of the bridges are close to the multiple of the impact frequency of the train load to the bridge. A single PTMD system is then designed to alter the bridge dynamic characteristics to avoid excessive vibrations. Numerical results from simply supported bridges of Taiwan High-Speed Railway (THSR) under German I.C.E., Japanese S.K.S. and French T.G.V. trains show that the proposed PTMD is a useful vibration control device in reducing bridge vertical displacements, absolute accelerations, end rotations and train accelerations during resonant speeds, as the train axle arrangement is regular. It is also found that the inner space of bridge box girder of THSR is wide and deep enough for the installation and movement of PTMD.     

列车荷载作用下轨道和地基的动响应分析

分析了列车运动荷载引起的应力波在轨道结构和周围地基中的传播,用动力子结构方法求解了铁路轨道和多层地基的相互作用问题,特别是在模型中考虑了轨枕离散支撑的作用.研究的对象结构包括列车运动荷载和受轨枕支撑的钢轨,以及下面的无限分层黏弹性地基.通过傅里叶变换求解微分形式的支配方程,得到了在频域和波数领域中的钢轨以及周围地基的振动准解析解,而响应时程则通过傅里叶逆变换得到.利用结果可以评估高速铁路列车运行时产生的轨道与周围地基的振动强度;同时提出了一种直观的方法来确定轨道与地基中产生共振时列车运行的临界速度.     

Aerodynamic design on high-speed trains

Compared with the traditional train, the operational speed of the high-speed train has largely improved, and the dynamic environment of the train has changed from one of mechanical domination to one of aerodynamic domination. The aerodynamic problem has become the key technological challenge of high-speed trains and significantly affects the economy, environment, safety, and comfort. In this paper, the relationships among the aerodynamic design principle, aerodynamic performance indexes, and design variables are first studied, and the research methods of train aerodynamics are proposed, including numerical simulation, a reduced-scale test, and a full-scale test. Technological schemes of train aerodynamics involve the optimization design of the streamlined head and the smooth design of the body surface. Optimization design of the streamlined head includes conception design, project design, numerical simulation, and a reduced-scale test. Smooth design of the body surface is mainly used for the key parts, such as electric-current collecting system, wheel truck compartment, and windshield. The aerodynamic design method established in this paper has been successfully applied to various high-speed trains (CRH380A, CRH380AM, CRH6, CRH2G, and the Standard electric multiple unit (EMU)) that have met expected design objectives. The research results can provide an effective guideline for the aerodynamic design of high-speed trains.     

高速磁浮列车气动噪声分布规律研究

本文基于上海线高速磁浮列车现场噪声测试，结合数值仿真分析了磁浮列车行驶时的噪声特性以及气动噪声分布规律．数值仿真采用延时分离涡结合声比拟的方法，并对比现场测试噪声数据，给出了高速列车气动噪声特性以及噪声源分布规律．研究结果表明：列车行驶时噪声时程呈现很强脉冲性，频率小于100 Hz噪声主要来源于与高架桥梁结构振动相关的二次辐射噪声，特别是次声频段内，桥梁自振会产生显著的噪声．磁浮列车表面气动噪声分布规律与噪声频率相关，低频噪声与列车的车尾涡脱相关，高频噪声由车头边界层分离以及再附着、车身边界层流动等引起，而中频噪声主要产生于列车底部、抱轨与轨道梁表面相对运动作用．因此，高速磁浮列车除了要重点考虑车头、车尾的气动外形对气动噪声的影响外，还应考虑轨道间隙处气动噪声及其分布规律．     

The genetically optimized tunnel-entrance hood

A numerical procedure is investigated for optimizing the design of tunnel-entrance hoods used for controlling the compression wave generated when a high-speed train enters a tunnel. Long hoods are required for long tunnels and train speeds exceeding about 350 km/h. The hood must minimize the maximum pressure gradient across the compression wave-front by taking advantage of the pressure-release provided by open windows distributed along one or both of its walls. The compression wave produced by the train can be evaluated by means of a rapid computational scheme devised and validated against experiment. Optimization is achieved by representing a possible distribution of windows by a binary string. The individuals in an initial, random population of such strings are allowed to ‘mate’ and evolve by ‘natural selection’ through several generations towards an optimal configuration by application of a genetic algorithm. The genetically fittest hood is associated with the minimum possible maximum pressure gradient for prescribed values of the train speed and hood dimensions. The algorithm yields an optimal design from among a theoretically unlimited number of possibilities; it can also supply near-optimal, smoothly varying window distributions (or optimize the variation in width of a long slit-like window in the hood wall) satisfying additional constraints imposed by the designer.     

Dynamics of trains and train-like articulated systems travelling in confined fluid—Part 2: Wave propagation and flow-excited vibration

Wave propagation and response of a train of flexibly interconnected rigid cars travelling in a confined cylindrical “tunnel” subjected to fluid dynamic forces are studied theoretically. For the wave propagation analysis, an infinite-length train represented by a lumped-parameter Timoshenko-beam (LTB) model is employed. The train response is simulated using a travelling sinusoidal aerodynamic force that mimics the features obtained during running experiments on real trains. In addition, the response of the system is examined when the velocity of the force approaches the minimum phase velocity of a travelling wave in the train. The principal aim of this study is to investigate the effect of aerodynamic forces on the dynamics of a high-speed train running in a tunnel, or more generally of a train-like system travelling in a coaxial cylindrical tube. The results of this study show that: (a) when aerodynamic forces act on a train, the frequency bands of the dispersion relation of wave propagation shift, and thus no classical normal modes (standing wave solutions) exist in the system; (b) the wavelength of the travelling sinusoidal force controls the phase differences between cars in the train; and (c) the response of the train can be considerably amplified when the speed of the travelling force coincides with the minimum phase velocity of travelling waves in the train.     

Impact of vacuum degree on the aerodynamics of a high-speed train capsule running in a tube

Motivated by the growing scientific and engineering interest in evacuated tube railway transportation systems, in this paper we numerically study the influence of the vacuum degree on the flow field around a train capsule running in an evacuated tube with circular section. The vacuum degree is increased by lowering the nominal pressure inside the tube. The numerical simulations are fully verified by wind-tunnel experimental data of supersonic flows around a blunt body and in a scramjet combustion chamber, as well as by several numerical results in other related studies. The flow around the train capsule is characterized by a compression region in front of the train, a chocked flow near the train, and a complex highly unsteady region behind the train, where expansions waves and reflecting oblique shock waves exist. The total aerodynamic drag and the vacuum degree are found to be linearly related, revealing that lowering the nominal pressure can have a significantly beneficial effect on the aerodynamic performance of the train capsule. The aerodynamic heating due to compressibility effects and the increased pressure are more prominent along the centreline of the tube than on the tube wall. As the vacuum degree increases, the temperature and pressure differences between the front and the tail of the train and the intensity of the reflected shock waves become less significant, so that the extension of the expansion region in the train wake shortens.     

MOVING MODEL ANALYSIS OF THE INITIAL COMPRESSION WAVE IN TUNNEL FOR HIGH-SPEED TRAINS1)

利用动模型实验方法,主要研究列车头型横截面变化对初始压缩波的影响。结果表明,在列车最大横截面积和流线型部分长度相同的情况下,列车头部流线型部分的平均横截面积和截面变化率均会对初始压缩波的压力峰值产生影响,平均横截面积决定了初始压缩波形成时的强度大小,截面变化率则通过影响初始压缩波的压力梯度,决定在隧道传播过程中初始压缩波压力峰值的衰减程度。     

轴向应力波作用下圆柱壳塑性轴对称动力屈曲

运用有限元特征值分析方法对应力波作用下圆柱壳塑性轴对称动力失稳问题进行了研究。基于应力波理论和相邻平衡准则导出了圆柱壳轴对称动力失稳时的特征方程,在分析中同时考虑了应力波效应及横向惯性效应,把圆柱壳塑性动力失稳问题归结为特征值问题。通过引入圆柱壳动力失稳时的波前约束条件实现了此类问题的有限元特征值解法。计算结果揭示了圆柱壳塑性轴对称动力屈曲变形发展的机理,以及轴向应力波和屈曲变形的相互作用规律。     

高速铁路连续箱型梁桥的动力响应与减振分析

根据列车具体的轴距和轴重,建立了和谐号动车组CRH380AL型列车简化模型;对高速铁路两跨连续梁桥采用多自由度欧拉伯努利梁单元进行主梁的模拟,并将液体黏滞阻尼器模拟为有限元阻尼单元;采用Newmark直接积分方法求解了高速列车作用下的连续梁桥运动方程,数值分析了列车车速以及液体黏滞阻尼器的阻尼系数对于高速铁路连续梁桥振动响应的影响。结果表明:黏滞阻尼器对于桥梁具有明显的减振效果,阻尼力不仅与阻尼系数有关还与列车时速有关;同一黏滞阻尼器条件下,桥梁的最大加速度并不随列车速度的增加而单调增加,而是在某些特定列车车速下桥梁的最大加速度出现了峰值,且随着黏滞阻尼器的阻尼系数增大,桥梁振动响应峰值处的最大加速度减幅不同;同一列车时速的条件下,桥梁的减振效果并不是随着阻尼系数的递增呈正比递增,而是随着阻尼系数的增大,阻尼器的减振效果增幅在减小。