共查询到20条相似文献，搜索用时 640 毫秒
1.
This paper mainly discusses the problem of ground-borne vibrations due to the planned line 8 of Beijing metro which passes under the National Measurement Laboratory. A lot of vibration sensitive equipments are placed in the laboratory. It is therefore necessary to study the impact of vibrations induced by metro trains on sensitive equipments and important to propound a feasible vibration mitigation measure. Based or1 the coupled periodic finite element-boundary element （FE-BE） method, a 3D dynamic track-tunnel-soil interaction model for metro line 8 has been used to predict vibrations in the free field induced by trains running at variable speeds between 30 km/h and 80 km/h. Four types of track structures commonly used on the Beijing metro network have been considered： （1） high resilience direct fixation fasteners, （2） Vanguard fasteners, （3） a floating slab track and （4） a floating ladder track. For each of these track types, the vibration isolation efficiency has been compared. The results of the numerical study can be used to predict vibrations in nearby buildings and to decide upon effective vibration countermeasures. 相似文献
2.
Low frequency vibrations induced by underground railways have attracted increasing attention in recent years. To obtain the
characteristics of low frequency vibrations and the low frequency performance of a floating slab track (FST), low frequency
vibration tests on an FST in an underground laboratory at Beijing Jiaotong University were carried out. The FST and an unbalanced
shaker SBZ30 for dynamic simulation were designed for use in low frequency vibration experiments. Vibration measurements were
performed on the bogie of the unbalanced shaker, the rail, the slab, the tunnel invert, the tunnel wall, the tunnel apex,
and on the ground surface at distances varying from 0 to 80 m from the track. Measurements were also made on several floors
of an adjacent building. Detailed results of low frequency vibration tests were reported. The attenuation of low frequency
vibrations with the distance from the track was presented, as well as the responses of different floors of the building. The
experimental results could be regarded as a reference for developing methods to control low frequency vibrations and for adopting
countermeasures. 相似文献
3.
This paper presents a detailed investigation, via field experiment, into the mechanism of high-order polygonal wear of wheels of a new type of high-speed train. The investigation was carried out during the performance acceptance test of the train and its initial commercial operation. The investigation covered the performance acceptance test of 150 000 km and the commercial operation of about 150 000 km. In the performance acceptance test of the first stage of about 70 000 km, at 200–250 km/h with full loading and sometimes overloading by 30%, the serious polygonal wear of 23-order took place on all the wheels of the train, and was measured and analyzed in detail. All the polygonized wheels were re-profiled because the polygonal wear had caused strong vibration and damage to the train parts. After re-profiling, the vibration of the train and track and the wear status of the wheels were measured and analyzed at different test mileages according to the polygonal wear situation of the wheels. The measured vibration of the train includes the accelerations at different positions of a motor car and a trail car. The vibration modes of the key parts of the bogies of the two cars were calculated. Meanwhile, the track resonant frequencies were investigated at the site. The purpose of the above tests and analysis is try to find the frequency of work mode matching the passing frequency of the high-order wheel polygon. The present investigation shows that one of the working models causes the formation and development of the high-order wheel polygonal wear. The growth of this wear was effectively reduced through the frequent changing of the running speed of the train operating on the way back and forth every day. 相似文献
4.
A 2.5D finite element approach for predicting ground vibrations generated by vertical track irregularities 总被引：1，自引：0，他引：1
Dynamic responses of track structure and wave propagation in nearby ground vibration become significant when train operates
on high speeds. A train-track-ground dynamic interaction analysis model based on the 2.5D finite element method is developed
for the prediction of ground vibrations due to vertical track irregularities. The one-quarter car model is used to represent
the train as lumped masses connected by springs. The embankment and the underlying ground are modeled by the 2.5D finite element
approach to improve the computation efficiency. The Fourier transform is applied in the direction of train’s movement to express
the wave motion with a wave-number. The one-quarter car model is coupled into the global stiffness matrix describing the track-ground
dynamic system with the displacement compatibility condition at the wheel-rail interface, including the irregularities on
the track surface. Dynamic responses of the track and ground due to train’s moving loads are obtained in the wave-number domain
by solving the governing equation, using a conventional finite element procedure. The amplitude and wavelength are identified
as two major parameters describing track irregularities. The irregularity amplitude has a direct impact on the vertical response
for low-speed trains, both for short wavelength and long wavelength irregularities. Track irregularity with shorter wavelength
can generate stronger track vibration both for low-speed and high-speed cases. For low-speed case, vibrations induced by track
irregularities dominate far field responses. For high-speed case, the wavelength of track irregularities has very little effect
on ground vibration at distances far from track center, and train’s wheel axle weights becomes dominant. 相似文献
5.
The band structures of flexural waves in a phononic crystal thin plate with straight, bending or branching linear defects are theoretically investigated using the supercell technique based on the improved plane wave expansion method. We show the existence of an absolute band gap of the perfect phononic crystal and linear defect modes inside the gap caused by localization of flexural waves at or near the defects. The displacement distributions show that flexural waves can transmit well along the straight linear defect created by removing one row of cylinders from the perfect phononic crystals for almost all the frequencies falling in the band gap, which indicates that this structure can act as a high efficiency waveguide. However, for bending or branching linear defects, there exist both guided and localized modes, and therefore the phononic crystals could be served as waveguides or filters. 相似文献
6.
In this study, ground vibrations due to dynamic loadings from trains moving in subway tunnels were investigated using a 2.5D finite element model of an underground tunnel and surrounding soil interactions. In our model, wave propagation in the infinitely extended ground is dealt with using a simple, yet efficient gradually damped artificial boundary. Based on the assumption of invariant geometry and material distribution in the tunnel??s direction, the Fourier transform of the spatial dimension in this direction is applied to represent the waves in terms of the wave-number. Finite element discretization is employed in the cross-section perpendicular to the tunnel direction and the governing equations are solved for every discrete wave-number. The 3D ground responses are calculated from the wave-number expansion by employing the inverse Fourier transform. The accuracy of the proposed analysis method is verified by a semi-analytical solution of a rectangular load moving inside a soil stratum. A case study of subway train induced ground vibration is presented and the dependency of wave attenuation at the ground surface on the vibration frequency of the moving load is discussed. 相似文献
7.
研究平底平面闸门在不稳定淹没泄流作用下垂向振动、水平平移振动、水平弯曲振动的非线性响应．建立一个非线性振子模型来模拟不稳定漩涡与闸门运动的耦合激励机制．推导出这３类振动的运动方程,并通过模型实验确定振动方程中的参数,解决了非线性振动稳态响应的求解问题．计算结果与前人关于不同折减流速和不同闸门系统参数的实验结果吻合较好． 相似文献
8.
《浙江大学学报(A卷英文版)》2021,(1)
To improve the low-frequency vibration reduction effect of a steel spring floating slab track(FST), nonlinear quasizero-stiffness(QZS) vibration isolators composed of positive stiffness elements(PSEs) and negative stiffness elements(NSEs) were used to support the FST. First, considering the mechanical characteristics of the nonlinear QZS vibration isolators and the dynamic displacement limit(3 mm) of the FST, the feasible parameter groups were studied with the nonlinear stiffness variation range and bearing capacity as evaluation indices. A vertical vehicle quasi-zero-stiffness floating slab track(QZS-FST) coupled dynamic model was then established. To obtain a reasonable nonlinear stiffness within a few millimeters, the original length of the NSEs must be analyzed first, because it chiefly determines the stiffness nonlinearity level. The compression length of the NSEs at the equilibrium position must be determined to obtain the low stiffness of the floating slab without vehicle load. Meanwhile, to meet the dynamic displacement limit of the FST, the PSE stiffness must be increased to obtain a higher stiffness at the critical dynamic displacement. Various stiffness groups for the PSEs and NSEs can provide the same dynamic bearing capacity and yet have a significantly different vibration reduction effect. Excessive stiffness nonlinearity levels cannot effectively improve the vibration reduction effect at the natural frequency. Furthermore, they also significantly amplify the vibrations above the natural frequency. In this paper, the vertical vibration acceleration level(VAL) of the floating slab and the supporting force of the FST can be decreased by 6.9 dB and 55%, respectively, at the resonance frequency. 相似文献
9.
10.
为研究边界摩擦对碟簧隔振器力学性能的影响,基于能量守恒定律推导了在考虑边界摩擦时碟簧隔振器的载荷位移迟滞曲线公式.通过有限元分析与静载试验验证了该公式的正确性.在此基础上研究了边界摩擦对碟簧隔振器承载能力的影响,并通过动载试验研究了边界摩擦对碟簧隔振器的动态性能的影响.试验结果表明:边界摩擦可提供较大的阻尼,使得碟簧隔振器具有良好的阻尼特性,其阻尼比可达0.23;隔振器的耗能、动刚度和阻尼特性对加载幅值更为敏感,而对加载频率敏感度较小.该研究成果对碟簧隔振器设计具有重要的指导意义. 相似文献
11.
传统的观点认为,波就是周期性振动的传播.而实际上,物体的基本运动形式有平动、转动和振动三类,它们的传播过程都能形成波.文章根据运动的基本形式和规律,提出了波的全新分类及＂转动波＂的概念,得出了转动波的数学表示. 相似文献
12.
The dynamic response of a flexible spinning vehicle with the varying thrust was investigated. The varying thrustwas modeled as a series of simple harmonic components superimposed on a constant thrust. The analytical solutions forlongitudinal motion were obtained by combining the motion equations and boundary conditions, and then, the transversebending of rocket was examined solved by considering a coupled forcing vibration with varying parameters. Numericalsolutions for a rocket with end-varying thrust were studied. It is shown that the lateral vibrations and motion attitudes ofrocket depend on the frequencies of varying thrust to great extent, and an important phenomenon, beating, maybe take place.The proposed approach is more accurate and efficient in comparison to those standard numerical techniques. 相似文献
13.
张志良 《上海大学学报(英文版)》2007,11(2):193-194
An overview of the research conducted in the area of linear and nonlinear vibrations of loudspeakers and revolution shells was given in the turning-point frequency range in Chapter 1. It shows that some problems concerning vibrations of shells in the turning-point range have to be further studied. 相似文献
14.
用试验方法研究了阀门的开启程度、支撑位置变化和管道内液体脉动对管道系统振动特性的影响．结果表明：由阀门开启程度引起的振动频率随着阀门开启程度的减小而增大;由可移动支撑位置改变引起的两个振动频率随着可移动支撑向中间的靠近而逐渐远离;由管道内液体脉动引起的振动频率随着可移动支撑向中间靠近和阀门开启程度的减小而减小． 相似文献
15.
Floods result in many problems, which may include damage to cross-river tunnels. The cross-river tunnel, as a new style of transportation, deserves a large amount of attention. In this paper, a large-scale cross-river tunnel model is proposed based on discrete element method (DEM). Micro parameters used in the model are calibrated by proposing a triaxial numerical model. Different in situ strata, high water pressures of normal flood-water levels and random vibration levels induced by running trains are taken into account to evaluate the dynamic characteristics of a high-stress tunnel in deformation and stress analysis. The results show that the upper half of the tunnel, including the concrete lining and the surroundings, is at higher risk than the lower half. Vibration waves transferring into the surroundings undergo an amplification process. The particles of the surroundings at the vault of the tunnel separate and move downward and then reassemble during the dynamic vibrations. The vibration levels, represented by particle accelerations, are lower under flood conditions than those under normal conditions. As train speed increases, the acceleration of the track and particles in the foundation increases, accompanied by a decrease in deformation. 相似文献
16.
运用非均匀有理B样条方法描述赛道内外边界以及赛车行驶线,并运用序列二次规划算法对赛车行驶线曲率进行优化.该方法能帮助赛道工程师在比赛前分析赛道特性. 相似文献
17.
18.
研究结果表明:对于一维更键（alternatingbond）铁磁链海森堡摸型，在一级近似下：（1）存在磁间隙孤子（振动频率位于磁频谱间隙内）和响应纽结（振动频率位于磁频谱内）．（2）内禀局域模（振动频率位于所有磁频谱带上方）是不可能存在的． 相似文献
19.
用多尺度方法对－土－平台系统进行了摄动分析，发现此系统存在多种组合共振现象，其固有振动频率与模型平台实测结果一致．在主参数共振条件下，文章讨论了在不同振动类型（自激，锁定，强迫）下的非线性动力学特性，这与现场观察到的冰激平台共振现象一致，本文还解释了冰激振动的机理，为海洋平台系统的非线性分析建立了一个合理的力学模型． 相似文献
20.
A Novel Electromagnetic Bandgap Structure for Filter 总被引：1，自引：0，他引：1
Electromagnetic bandgap (EBG) materials are periodic structures capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic of EBG has wide application. The structures to be studied here are mainly planar EBG materials of two dimensions, which are periodic arrays of holes etched in the ground plane of a conventional microstrip line. EBG structures are calculated with finite-difference time-domain (FDTD) method in this paper. Technique of the perfectly matched layer is used for the absorption of electromagnetic waves in FDTD. The FDTD method is programmed with the blend of C^ and Matlab languages, which makes the program both simple and fast computing. A kind of new EBG structure is brought out through a lot of experiments and analyses. A filter with wide stop-band and another filter with two stop-bands are designed. 相似文献