高分子交替多层结构的隔声特性仿真

使用有限元仿真方法对高分子交替多层结构的隔声特性进行了研究,构建了阻抗管测试的平面波声场和高分子多层复合材料模型,使用LMS Virtual. Lab进行了声振耦合计算,得到的隔声量曲线与实验测试结果规律一致。针对聚丙烯(PP)与乙烯-辛烯共聚物(POE)的交替层状样品,探究了在100~5000 Hz的计算范围内,层数、层厚比及两组分材料参数对整体隔声性能规律的影响,结果显示16层结构的隔声性能更优。同时,计算了板与多孔材料交替结构的隔声性能,结果表明,在给定的条件下4层结构有更高的隔声量。

Sound Source Localisation for a High-Speed Train and Its Transfer Path to Interior Noise

Noise is one of the key issues in the operation of high-speed railways, with sound source localisation and its transfer path as the two major aspects. This study investigates both the exterior and interior sound source distribution of a high-speed train and presents a method for performing the contribution analysis of airborne sound with regard to the interior noise. First, both exterior and interior sound source locations of the high-speed train are identified through in-situ measurements. Second, the sound source contribution for di erent regions of the train and the relationships between the exterior and interior noises are analysed. Third, a method for conducting the contribution analysis of airborne sound with regard to the interior noise of the high-speed train is described. Lastly, a case study on the sidewall area is carried out, and the contribution of airborne sound to the interior noise of this area is obtained. The results show that, when the high-speed train runs at 310 km/h, dominant exterior sound sources are located in the bogie and pantograph regions, while main interior sound sources are located at the sidewall and roof. The interior noise, the bogie area noise and the sound source at the middle of the coach exhibit very similar rates of increase with increasing train speed. For the selected sidewall area, structure-borne sound dominates in most of the 1/3 octave bands.

Generalization of the Fourier transform-based method for calculating the response of a periodic railway track subject to a moving harmonic load

A Fourier transform-based method has been developed for calculating the response of a railway track as an infinitely long uniform periodic structure subject to moving or stationary harmonic loads. The track may become a non-uniform periodic structure by, for example, rail dampers which are installed between sleepers to control rolling noise and roughness growth. The period of the structure may become greater than the sleeper spacing. For those new situations, the current version of the method cannot be directly applied; it must be generalized and this is the aim of this paper. Generalization is performed by applying periodic conditions to each type of support and summarizing contributions from all types of support. Responses of the rail, sleeper, and damper are all formulated as an inverse Fourier transform from wavenumber domain to spatial domain. The generalized method is applied to investigate dynamics of a typical track with rail dampers of particular design. It is found that the rail dampers can significantly suppress the pinned-pinned vibration of the original track, widen the stop bands and increase vibration decay rate along the rail. However, it is also found that a new pinned-pinned mode is created by the dampers and between about 450 and 1,300 Hz dampers vibrate stronger than the rail, making noise radiation from the dampers a potential issue. These concerns must be fully investigated in the future. The formulae presented in this paper provide a powerful tool to do that.

Vibration and sound radiation of a rotating train wheel subject to a vertical harmonic wheel–rail force

The rapid development of high-speed railway networks requires advanced methods for analysing vibration and sound radiation characteristics of a fast rotating train wheel subject to a vertical harmonic wheel-rail force. In order to consider the rotation of the wheel and at the same time increase the computational efficiency, a procedure is adapted in this paper taking advantage of the axial symmetry of the wheel. In this procedure, a recently developed 2.5D finite element method, which can consider wheel rotation but only requires a 2D mesh over a cross section containing the wheel axis, is used to calculate the vibration response of the wheel. Then, the vibration response of the wheel is taken as acoustic boundary condition and the 2.5D acoustic boundary element method, which only requires a 1D mesh over the boundary of the above cross section, is utilised to calculate the sound radiation of the wheel. These 2.5D methods and relevant programs are validated by comparing results from this procedure with those from conventional 3D analyses using commercial software. The comparison also demonstrates that these 2.5D methods have a much higher computational efficiency. Using the 2.5D methods, we study the wheel rotation speed influences on the factors including the vertical receptance of the wheel at wheel-rail contact point, sound pressure level at a pre-defined standard measurement point, radiated sound power level, directivity of the radia- tion, and contribution of each part of the wheel. It can be concluded that the wheel rotation speed splits most peaks of the vertical receptance at the wheel-rail contact point, sound pressure levels at the field, and the sound power level of the wheel into two peaks. The directivity and power contribution of the wheel are also significantly changed by the wheel rotation speed. Therefore, the rotation of a train wheel should be taken into account when calculating its vibration and sound radiation.

Influence of Shear Effects on the Characteristics of Axisymmetric Wave Propagation in a Buried Fluid‑Filled Pipe

The acoustic propagation characteristics of axisymmetric waves have been widely used in leak detection of fluid-filled pipes.The related acoustic methods and equipment are gradually coming to the market,but their theoretical research obviously lags behind the field practice,which seriously restricts the breakthrough and innovation of this technology.Based on the fully three-dimensional effect of the surrounding medium,a coupled motion equation of axisymmetric wave of buried liquid-filled pipes is derived in detail,a contact coefficient is used to express the coupling strength between surrounding medium and pipe,then,a general equation of motion was derived which contain the pipe soil lubrication contact,pipe soil compact contact and pipe in water and air.Finally,the corresponding numerical calculation model is established and solved used numerical method.The shear effects of the surrounding medium and the shear effects at the interface between surrounding medium and pipe are discussed in detail.The output indicates that the surrounding medium is to add mass to the pipe wall,but the shear effect is to add stiffness.With the consideration of the contact strength between the pipe and the medium,the additional mass and the pipe wall will resonate at a specific frequency,resulting in a significant increase in the radiation wave to the surrounding medium.The research contents have great guiding effect on the theory of acoustic wave propagation and the engineering application of leak detection technology in the buried pipe.

Numerical Investigation on the Aerodynamic Noise Generated by a Simplified Double-Strip Pantograph

In order to understand the mechanism by which a pantograph can generate aerodynamic noise and grasp its farfield characteristics,a simplified double-strip pantograph is analyzed numerically.Firstly,the unsteady flow field around the pantograph is simulated in the frame of a large eddy simulation(LES)technique.Then the location of the main noise source is determined using surface fluctuating pressure data and the vortex structures in the pantograph flow field are analyzed by means of the Q-criterion.Based on this,the relationship between the wake vortex and the intensity of the aerodynamic sound source on the pantograph surface is discussed.Finally,the far-field aerodynamic noise is calculated by means of the Ffowcs Williams-Hawkings(FW-H)equation,and the contribution of each component to total noise and the frequency spectrum characteristics are analyzed.The results show that on the pantograph surface where vortex shedding or interaction with the wake of upstream components occurs,the pressure fluctuation is more intense,resulting in strong dipole sources.The far-field aerodynamic noise energy of the pantograph is mainly concentrated in the frequency band below 1500 Hz.The peaks in the frequency spectrum are mainly generated by the base frame,balance arm and the rear strip,which are also the main contributors to the aerodynamic noise.

A review of mid-frequency vibro-acoustic modelling for highspeed train extruded aluminium panels as well as the most recent developments in hybrid modelling techniques

The present paper reviews the vibro-acoustic modelling of extruded aluminium train floor structures including the state-of-the-art of its industrial applications, as well as the most recent developments on mid-frequency mod- elling techniques in general. With the common purpose to predict mid-frequency vibro-acoustic responses of stiffened panel structures to an acceptable accuracy at a reasonable computational cost, relevant techniques are mainly based on one of the following three types of mid-frequency vibro- acoustic modelling principles： （1） enhanced deterministic methods, （2） enhanced statistical methods, and （3） hybrid deterministic/statistical methods. It is shown that, although recent developments have led to a significant step forward in industrial applicability, mature and adequate prediction tech- niques, however, are still very much required for solving sound transmission through, and radiation from, extruded aluminium panels used on high-speed trains. Due to their great potentials for predicting mid-frequency vibro-acoustics of stiffened panel structures, two of recently developed mid-frequency modelling approaches, i.e. the so-called hybrid finite element-statistical energy analysis （FE-SEA） and hybrid wave-based method- statistical energy analysis （WBM-SEA）, are then recapitulated.

An investigation into high-speed train interior noise with operational transfer path analysis method

Passengers’demands for riding comfort have been getting higher and higher as the high-speed railway develops.Scientific methods to analyze the interior noise of the high-speed train are needed and the operational transfer path analysis(OTPA)method provides a theoretical basis and guidance for the noise control of the train and overcomes the shortcomings of the traditional method,which has high test efficiency and can be carried out during the working state of the targeted machine.The OTPA model is established from the aspects of“path reference point-target point”and“sound source reference point-target point”.As for the mechanism of the noise transmission path,an assumption is made that the direct sound propagation is ignored,and the symmetric sound source and the symmetric path are merged.Using the operational test data and the OTPA method,combined with the results of spherical array sound source identification,the path contribution and sound source contribution of the interior noise are analyzed,respectively,from aspects of the total value and spectrum.The results show that the OTPA conforms to the calculation results of the spherical array sound source identification.At low speed,the contribution of the floor path and the contribution of the bogie sources are dominant.When the speed is greater than 300 km/h,the contribution of the roof path is dominant.Moreover,for the carriage with a pantograph,the lifted pantograph is an obvious source.The noise from the exterior sources of the train transfer into the interior mainly through the form of structural excitation,and the contribution of air excitation is non-significant.Certain analyses of train parts provide guides for the interior noise control.