The influence of reflections from the train body and the ground on the sound radiation from a railway rail

Purpose – The vibration of the rails is a significant source of railway rolling noise, often forming the dominantcomponent of noise in the important frequency region between 400 and 2000 Hz. The purpose of the paper is toinvestigate the influence of the ground profile and the presence of the train body on the sound radiation fromthe rail.Design/methodology/approach – Two-dimensional boundary element calculations are used, in which therail vibration is the source. The ground profile and various different shapes of train body are introduced in themodel, and results are observed in terms of sound power and sound pressure. Comparisons are also made withvibro-acoustic measurements performed with and without a train present.Findings – The sound radiated by the rail in the absence of the train body is strongly attenuated by shieldingdue to the ballast shoulder. When the train body is present, the sound from the vertical rail motion is reflectedback down toward the track where it is partly absorbed by the ballast. Nevertheless, the sound pressure at thetrackside is increased by typically 0–5 dB. For the lateral vibration of the rail, the effects are much smaller. Oncethe sound power is known, the sound pressure with the train present can be approximated reasonably well withsimple line source directivities.Originality/value – Numerical models used to predict the sound radiation from railway rails have generallyneglected the influence of the ground profile and reflections from the underside of the train body on the soundpower and directivity of the rail. These effects are studied in a systematic way including comparisons with measurements.

Simplified prediction models for acoustic installation effects of train-mounted equipment

Acoustic models of railway vehicles in standstill and pass-by conditions can be used as part of a virtual certification process for new trains.For each piece of auxiliary equipment,the sound power measured on a test bench is combined with meas-ured or predicted transfer functions.It is important,however,to allow for installation effects due to shielding by fairings or the train body.In the current work,fast-running analytical models are developed to determine these installation effects.The model for roof-mounted sources takes account of diffraction at the corner of the train body or fairing,using a barrier model.For equipment mounted under the train,the acoustic propagation from the sides of the source is based on free-field Green’s functions.The bottom surfaces are assumed to radiate initially into a cavity under the train,which is modelled with a simple diffuse field approach.The sound emitted from the gaps at the side of the cavity is then assumed to propagate to the receivers according to free-field Green’s functions.Results show good agreement with a 2.5D boundary element model and with measurements.Modelling uncertainty and parametric uncertainty are evaluated.The largest variability occurs due to the height and impedance of the ground,especially for a low receiver.This leads to standard deviations of up to 4 dB at low frequencies.For the roof-mounted sources,uncertainty over the location of the corner used in the equivalent barrier model can also lead to large standard deviations.

Exploring the Limits of a Deflection-Based Method for the Estimation of Dynamic Stress in Beams

Estimation of the dynamic stress in structures,such as beams and plates,has previously been made using the relationship between stress and velocity spatial maxima based on far-field assumptions.This paper presents a method for the estimation of dynamic stress in a beam using Euler–Bernoulli beam theory,where deflection data from a grid of measurement points on the surface of the beam is used to estimate the dynamic bending stress in the structure.The limitations of the method are investigated via response data provided by a numerical model of a freefree beam.A nondimensional wavenumber analysis is used to determine the number of points required for an accurate estimate of stress.Beams with a range of material and geometric parameters are modeled in order to explore the limits of the estimation method,and parameters representative of several real-world materials are used to assess the suitability of the method for practical applications.

Field measurement and evaluation of vibration in different areas of a metro depot

This paper presents a study of the characteristics of a railway vibration at three key sections containing different track structures in a metro depot.The results show that the vertical and horizontal vibration acceleration levels are proportional to train speed.The Z-weighted vertical acceleration levels obtained showed that the vibration source strengths at the ballast foot of the testing line and the throat area were very close.The vibration attenuation at the repair line was larger than that of the testing line.In the throat area,the peak frequency of vibration obtained at the ballast foot(2.5 m)could be shifted to a lower frequency band by using polyurethane sleepers instead of standard concrete sleepers.Polyurethane sleepers can help to reduce vertical vibration in a frequency band of 0-10 Hz.The vibration levels would satisfy the limits given in the ISO2631-2-2003(2013)for any location more than 5 m away from the source at the testing line and 2.5 m away from the source at the repair line and throat area.

轨道车辆一系螺旋弹簧振动疲劳失效分析

轨道车辆服役工况下一系悬挂系统中的金属螺旋弹簧疲劳断裂时有发生,影响列车运行安全性。针对某一系螺旋弹簧疲劳失效故障,考虑轮轨激励与弹簧结构动态特性耦合关系,建立准确提取弹簧载荷的模型,通过结构频域疲劳分析法计算弹簧动应力响应与疲劳寿命。首先考虑螺旋弹簧结构的动态特性,建立包含一系动刚度特性的车辆-轨道耦合精细化动力学模型,然后在轮轨激励下提取服役工况弹簧两端动载荷,最后采用结构频域疲劳分析法计算弹簧动应力响应与疲劳寿命,并与实测动应力结果进行对比验证。结果表明:螺旋弹簧自身动态特性体现在:多阶模态频率下弹簧中部的最大模态变形与簧条1~2圈间的最大模态应力;基于耦合动力学模型,计算得到内簧动应力响应与实测结果一致,在58 Hz的动应力峰值是其它频率动应力峰值的3倍以上;由于内簧一阶固有频率与轮轨系统P2共振频率接近,弹簧内部共振引起簧条1.2圈内侧高应力,该处疲劳寿命最短的分析结果与现场断裂位置吻合,而外簧的最短疲劳寿命约为内簧的3.6倍。因此,同时考虑轮轨激励与螺旋弹簧自身动态特性,使得一系螺旋弹簧固有频率远离轮轨共振频率,可提高弹簧结构的抗疲劳特性。

船舶辅机浮筏半主动非线性隔振系统振动特性分析

磁流变阻尼器因其低耗能、响应迅速等特点而被广泛应用。文章采用一种改进的Bingham模型对船舶辅机浮筏隔振装置中的非线性磁流变阻尼力进行建模。该模型简单且含滞后特性,便于理论分析。对建立的船舶辅机浮筏隔振系统的非线性动力学模型,通过平均法求解船舶辅机浮筏半主动隔振系统的理论解,并运用Matlab对理论解进行数值仿真验证。以力传递率作为评价指标,分析了磁流变阻尼器各参数对隔振效果的影响规律。研究结果可为非线性船舶辅机浮筏隔振系统的设计提供理论依据,从而能更有效地控制船舶辅机的振动。

An improved subspace weighting method using random matrix theory

The weighting subspace fitting(WSF)algorithm performs better than the multi-signal classification(MUSIC)algorithm in the case of low signal-to-noise ratio(SNR)and when signals are correlated.In this study,we use the random matrix theory(RMT)to improve WSF.RMT focuses on the asymptotic behavior of eigenvalues and eigenvectors of random matrices with dimensions of matrices increasing at the same rate.The approximative first-order perturbation is applied in WSF when calculating statistics of the eigenvectors of sample covariance.Using the asymptotic results of the norm of the projection from the sample covariance matrix signal subspace onto the real signal in the random matrix theory,the method of calculating WSF is obtained.Numerical results are shown to prove the superiority of RMT in scenarios with few snapshots and a low SNR.

不对中故障下带挤压油膜阻尼器的滚动轴承转子系统的动力学分析（英文）

目的:工业的不断发展对航空发动机、泵、燃气轮机等旋转机械的动力性能提出了更高的要求。转子系统是旋转机械的重要组成部分。复杂的转子系统在高速运转时会产生故障和非线性振动,从而影响系统的可靠性。因此,开展转子系统的非线性动力性研究,研究转子系统在高速运转时的非线性响应及其抑制作用对转子系统的设计和故障诊断具有重要的意义。创新点:1.在建模的时候考虑转子系统的实际结构,在不对中模型中引入齿式联轴器啮合力,在滚动轴承模型中考虑弹流润滑影响;2.探究挤压油膜阻尼器参数对转子系统非线性特性抑制的影响,总结其变化规律。方法:1.基于Hertz接触和弹流润滑理论,建立滚动轴承动力学模型,同时考虑齿式联轴器齿之间的啮合力,建立不对中故障下的齿式联轴器啮合力模型,并在此基础上,根据转子系统的支撑形式,建立0-2-1支撑的转子动力学模型;2.开展转子动力学实验,验证模型的准确性并分析不对中量对系统频谱特性的影响;3.在分析不对中故障非线性特性的基础上,研究挤压油膜阻尼器参数对于非线性特性抑制的作用。结论:1.齿式联轴器啮合作用和滚动轴承的弹流润滑对不对中故障下转子系统的失稳产生一定的影响,润滑会导致系统发生分岔的窗口推迟;2.对于转子系统的弹性支撑,其一阶临界转速和振幅随着刚度的增大而增大,选择合适的刚度有利于转子系统的稳定运行;3.挤压油膜阻尼器的参数对转子系统故障引起的非线性具有较好的抑制作用,其作用的大小取决于不对中量和挤压油膜阻尼器的油膜间隙的耦合,合理地调节油膜间隙有助于增大系统的稳定区间范围。

H_∞ Autopilot Design for Autonomous Underwater Vehicles

The design approach of H∞ autopilot for autonomous underwater vehicles (AUVs) is proposed. Comprised by the three sub-controllers,i.e. speed,heading and depth controllers,the designed autopilot has advantage over existing H∞ control of AUVs. The overshoot in speed,heading and depth control systems under step commands is restricted by refining the weighting function for robust stability. The dynamic performance of heading and depth control systems is improved by feeding back yaw rate and pitch angle,respectively. To evaluate the design approach,it is then utilized to synthesize the autopilot for flight control of Subzero Ⅲ,a low cost test-bed for AUV control techniques. Both simulations and water trails verify the effectiveness of the design approach.