Vibration Countermeasures Research Articles

Buffeting Characteristics of a Long-Span Cable-Stayed Bridge Crossing a Deep Canyon during Erection: Response Evaluation and Vibration Control

The stiffness of a long-span cable-stayed bridge under construction may be much lower than that observed in service, making it more susceptible to wind effects, especially for a bridge designed using high piers crossing a deep canyon. To study the buffeting characteristics of such cable-stayed bridges under construction, a long-span cable-stayed bridge (the main span is 575 m) is taken as the engineering background. In this study, the buffeting responses and vibration countermeasures at three different construction states were systematically studied using time-domain analysis. It was found that the buffeting response enlarges with an increase in the wind attack angle. The RMS values of the vertical buffeting of the bridge deck end are relatively greater at the maximum double cantilever construction state and maximum single cantilever state. At maximum double cantilever construction state, the traditional wind-resistant cable connecting the bridge deck end to the bridge pile cap significantly reduces the vertical buffeting response, while the suppression effect on lateral and torsional buffeting is limited. When the bridge deck nears completion, wind-resistant cables installed at both cantilever ending in the ‘soft connection’ method would effectively suppress the vertical, lateral, and torsional buffeting. The suppression effect of cross-arranged wind-resistant cables is superior to that of the parallel arrangement. It is recommended that a reasonable wind-resistant cable layout scheme according to different construction conditions is selected.

Current Performance of Floor Impact Sound Insulation in Wooden Apartment Buildings in Hokkaido

In Hokkaido, Japan, technological developments have been introduced to improve the floor impact sound insulation performance in wooden apartment buildings. However, such technological developments are not widely used, especially in rental properties. To effectively disseminate the required technology, it is vital to report examples of implementation. Therefore, we measured the performance of five types of wooden apartment buildings with high sound insulation performance and analyzed the results. The main results are listed below. (1) A relatively high performance was obtained by installing a floating floor and an independent ceiling. (2) For heavy weight floor impact sound insulation of a car tire source, a floating floor with a surface density of 60 kg/m2 or higher could achieve a performance of Li,Fmax,r,H(1)-60 or higher. However, in the case of a rubber ball source, vibration radiation noise from the wall surface of the lower floor is large, so it is necessary to consider vibration countermeasures. (3) For light weight floor impact sound insulation, sufficient performance cannot be obtained even with a floating floor. Therefore, carpet or wooden soundproof flooring should be used. (4) The light weight floor impact sound pressure level is high when the floor area of the sound receiving room is small.

VIBWAY: A user-friendly computational for the prediction of railway-induced ground-borne vibration and noise

This paper aims to introduce a computationally efficient and user-friendly toolbox, called VIBWAY, able to predict vibration and re-radiated noise levels in two situations. On the one hand, it can predict levels in existing buildings due to new lines or after the application of mitigation measures in existing ones. Thus, it can be used to assess the performance of vibration countermeasures applied at the track, vehicle and/or the building. On the other hand, it can predict levels in new buildings to be constructed close to an existing railway line. The VIBWAY toolbox is based on a non-interface 2.5D FEM-SBM approach for the wave propagation on the soil, on semi-analytical approaches for the track and the building and on multibody modelling of the train vehicle.

Modal contribution index of subsystems for studying vibration countermeasures of a whole structure

Modal contribution index of subsystems for studying vibration countermeasures of a whole structure

Influence of tire-derived aggregates mixed with ballast on ground-borne vibrations

In this paper, the use of recycled tire-derived aggregates (TDA) mixed with ballast material is evaluated in order to reduce the train-induced ground-borne vibrations. For this purpose, a series of field vibration measurements has been carried out at an executed pilot track. The prepared ballast layer was mixed with different percentages of TDA in three sections. Moreover, another test section with pure ballast is considered as a reference. The vibrations generated by a motor-powered draisine at two different speeds are then recorded. Records of vibration data are provided using four seismometers placed once longitudinally and once transversely beside different sections. The outputs are then processed in both velocity–time and velocity–frequency domains. To verify the vibration mitigation performance of TDA in real operation conditions, field measurements under the passage of two planned passenger and freight trains are finally arranged. Results show that the best TDA mixture ratio, i.e., 10% by weight, can reduce the transmitted vibrations up to 12 dB for frequencies above 31.5 Hz. According to the obtained efficiency and the very low cost of the recycled materials, this solution can be considered as a competitive vibration countermeasure.

Vibration Failure Analysis and Countermeasures of the Inlet Pipelines at a Gas Compressor Station

A gas compressor station only had its about 35% design processing capacity as a result of the abnormal piping vibrations on the inlet pipelines. Characterization, diagnostics, analysis, and elimination of piping vibration were performed. The root causes and sources of the abnormal vibration were investigated by on‐site measurements and analysis of vibration and pulsation under various load conditions of compressors. The results revealed that it was not mechanical resonance, but the high pressure pulsation and acoustic resonance occurred on the inlet pipelines, which resulted in the severe vibration. Three different modification models against vibration were proposed by shortening the length of the pipe to avoid acoustic resonance, enlarging the volume of the gathering manifold to buffer pressure pulsation, and adding supports to increase the stiffness. A better modification model was applied by performing modal analysis and fluid‐structure interaction (FSI) vibration analysis using the finite element method. The effect of countermeasures was evaluated by vibration and pulsation measurements during operation after modifications, which results showed the level of piping vibration and pressure pulsation was within the allowable limits. The processing capacity of the gas station has reached its design requirement as a result of the desired reduction in vibrations.

Changes of perceived unevenness caused by in-track vibration countermeasures in slab track

Abstract This paper investigates the relation between unevenness at different locations in a railway track and the unevenness perceived by a train, for the particular case of a slab track. The different types of unevenness considered are: slab and track bed unevenness, bent rail and bent slab, variation of rail pad stiffness, variation of slab bearing stiffness, and variation of rail and slab bending stiffness. The unevenness perceived by the wheels of a moving train is the result of all these types of unevenness. When vibration countermeasures, such as resilient elements (e.g. soft rail pads), are introduced in a track, the perceived unevenness is modified. The slab track is modelled as a double beam supported on a rigid foundation. Analytical expressions are derived to relate the input and perceived unevenness. It is shown that in-track vibration countermeasures always introduce a change in perceived unevenness, which may turn out to be an increase or decrease and, consequently, result in a change of the performance of vibration countermeasures. This is illustrated for the particular case of a slab track on elastic supports on metro line M1 of ATM in Milan (Italy). This paper shows that prediction of vibration insertion loss based on conventional models may lead to inaccuracies in absence of information about different sources of unevenness. After the installation of vibration countermeasures, it is advised to measure the perceived unevenness in order to interpret differences between predicted and measured insertion loss.

Prediction and mitigation analysis of ground vibration caused by running high-speed trains on rigid-frame viaducts

In this study a 3D numerical analysis approach is developed to predict the ground vibration around rigid-frame viaducts induced by running high-speed trains. The train-bridge-ground interaction system is divided into two subsystems: the train-bridge interaction and the soil-structure interaction. First, the analytical program to simulate bridge vibration with consideration of train-bridge interaction is developed to obtain the vibration reaction forces at the pier bottoms. The highspeed train is described by a multi-DOFs vibration system and the rigid-frame viaduct is modeled with 3D beam elements. Second, applying these vibration reaction forces as input external excitations, the ground vibration is simulated by using a general-purpose program that includes soil-structure interaction effects. The validity of the analytical procedure is confirmed by comparing analytical and experimental results. The characteristics of high-speed train-induced vibrations, including the location of predominant vibration, are clarified. Based on this information a proposed vibration countermeasure using steel strut and new barrier is found effective in reducing train-induced vibrations and it satisfies environmental vibration requirements. The vibration screening efficiency is evaluated by reduction VAL based on 1/3 octave band spectral analysis.

MAN B&W ME機関の振動の特徴およびその対策

MAN B&W ME機関の振動の特徴およびその対策

The fictitious force method for efficient calculation of vibration from a tunnel embedded in a multi-layered half-space

This paper presents an extension of the Pipe-in-Pipe (PiP) model for calculating vibrations from underground railways that allows for the incorporation of a multi-layered half-space geometry. The model is based on the assumption that the tunnel displacement is not influenced by the existence of a free surface or ground layers. The displacement at the tunnel–soil interface is calculated using a model of a tunnel embedded in a full space with soil properties corresponding to the soil in contact with the tunnel. Next, a full space model is used to determine the equivalent loads that produce the same displacements at the tunnel–soil interface. The soil displacements are calculated by multiplying these equivalent loads by Green׳s functions for a layered half-space. The results and the computation time of the proposed model are compared with those of an alternative coupled finite element–boundary element model that accounts for a tunnel embedded in a multi-layered half-space. While the overall response of the multi-layered half-space is well predicted, spatial shifts in the interference patterns are observed that result from the superposition of direct waves and waves reflected on the free surface and layer interfaces. The proposed model is much faster and can be run on a personal computer with much less use of memory. Therefore, it is a promising design tool to predict vibration from underground tunnels and to assess the performance of vibration countermeasures in an early design stage.

Pedestrian-induced torsional vibrations of suspended footbridges: Proposal and evaluation of vibration countermeasures

The aim of the paper is to propose and evaluate different design arrangements addressed to mitigate the in-service pedestrian-induced torsional vibrations of lightweight suspended footbridges. All the proposed structural countermeasures are characterised by the addition of few elements to the original structure, i.e. punctual masses and/or additional cables located in specific sections to reduce vertical and longitudinal relative displacements of the suspension cables, in order to preserve the bridge lightness and slenderness. An application to a test case footbridge is provided. Its structural nonlinear analysis is carried out by means of numerical simulations. On the basis of a preliminary modal analysis, a criterion for the localization of the vibration countermeasures along the span is proposed. The effectiveness of the localization criterion and of the proposed design arrangements is evaluated by comparing the structural responses obtained through step-by-step dynamic analyses with and without the countermeasures. The analysis of the results allows the design arrangements to be discussed and the best suited ones to be selected.

Prediction of vibrations induced by trains on line 8 of Beijing metro

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 on 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.

Vibrations of probe used for the defect detection of helical heating tubes in a fast breeder reactor: Part 3. The mechanism of the vibration and the countermeasures

An eddy current testing (ECT) probe is used for the diagnosis of helical heating tubes installed in the Japanese fast breeder reactor “Monju”. Vibrations of the ECT probe occur and make the diagnosis difficult. In our previous study, several characteristics of the vibrations were elucidated through some experiments, and we took some empirical countermeasures against the vibrations. Further, we showed that the vibrations were caused by Coulomb friction through some numerical simulations. In this paper, firstly, the return process of the ECT probe out of the heating tube is considered since only the insertion process of the ECT probe was considered in our previous study. Following this, the efficacy of the proposed vibration countermeasures is evaluated by way of numerical simulation. The mechanism of the vibration and the countermeasures are discussed on the basis of the entire behavior of the probe, which was obtained by a numerical simulation. Lastly, an improvement in the countermeasure is proposed. The validity of the improvement is demonstrated through a numerical simulation both in the insertion and the return processes.

Prediction of vibrations induced by underground railway traffic in Beijing

This paper examines the problem of subway induced vibrations on line 4 of Beijing metro, which is currently under construction and is planned to pass in close proximity of the Physics Laboratory of Beijing University. The laboratory has a lot of equipment that is very sensitive to traffic induced vibrations and future operation of metro line 4 is a matter of concern. Hence, it is important to study the influence of subway induced vibrations inside the laboratory and to propose a viable solution to mitigate the vibrations. In this paper, the tunnel north of Chengfulu station is modelled using a coupled periodic FE–BE model and the free-field response due to moving trains is predicted. In addition, vibration measurements have been performed on the site of the Physics Laboratory to estimate the existing vibration levels due to road traffic. The predicted and measured vibrations are superimposed to assess the vibrations due to the combined effect of road and railway traffic in the vicinity of the Physics Laboratory. Apart from the numerical investigations, vibration measurements have also been performed on a similar site at line 1 of Beijing metro to substantiate the estimated results on metro line 4. Finally, it is studied how the vibrations can be controlled using a floating slab track, which is widely used as an effective measure of vibration isolation in tunnels. The efficiency of a 7.9 Hz floating slab track as a vibration countermeasure is assessed in this paper. This study demonstrates the applicability of the numerical model for the relevant assessment of subway induced vibrations and its use to study the performance of different track structures in the tunnel.

A numerical model for calculating vibration from a railway tunnel embedded in a full-space

Vibration generated by underground railways transmits to nearby buildings causing annoyance to inhabitants and malfunctioning to sensitive equipment. Vibration can be isolated through countermeasures by reducing the stiffness of railpads, using floating-slab tracks and/or supporting buildings on springs. Modelling of vibration from underground railways has recently gained more importance on account of the need to evaluate accurately the performance of vibration countermeasures before these are implemented. This paper develops an existing model, reported by Forrest and Hunt, for calculating vibration from underground railways. The model, known as the Pipe-in-Pipe model, has been developed in this paper to account for anti-symmetrical inputs and therefore to model tangential forces at the tunnel wall. Moreover, three different arrangements of supports are considered for floating-slab tracks, one which can be used to model directly-fixed slabs. The paper also investigates the wave-guided solution of the track, the tunnel, the surrounding soil and the coupled system. It is shown that the dynamics of the track have significant effect on the results calculated in the wavenumber–frequency domain and therefore an important role on controlling vibration from underground railways.

Finite element calculations of rail vibration countermeasures

Elastic waves may constitute a nuisance for people living close to high-speed lines. In order to decrease the spread of vibrations, it is common to reinforce the ground with lime cement columns. This article presents the results of simulations of three different ways to install the columns. The calculations have been done with an integrated rigid body—finite element model. Equations from various physical domains are merged into one big system. The results indicate that the straight configuration works best to protect the track. When attention is focused on preventing vibrations from the soil, the leaning column method is more effective. The chosen technique would depend on the aims of the countermeasure.

Numerical modelling of ground-borne noise and vibration in buildings due to surface rail traffic

This paper deals with the numerical computation of the structural and acoustic response of a building to an incoming wave field generated by high-speed surface railway traffic. The source model consists of a moving vehicle on a longitudinally invariant track, coupled to a layered ground modelled with a boundary element formulation. The receiver model is based on a substructuring formulation and consists of a boundary element model of the soil and a finite element model of the structure. The acoustic response of the building's rooms is computed by means of a spectral finite element formulation. The paper investigates the structural and acoustic response of a multi-story portal frame office building up to a frequency of 150 Hz to the passage of a Thalys high-speed train at constant velocity. The isolation performance of three different vibration countermeasures: a floating-floor, a room-in-room, and base-isolation, are examined.

A power flow method for evaluating vibration from underground railways

One of the major sources of ground-borne vibration is the running of trains in underground railway tunnels. Vibration is generated at the wheel–rail interface, from where it propagates through the tunnel and surrounding soil into nearby buildings. An understanding of the dynamic interfaces between track, tunnel and soil is essential before engineering solutions to the vibration problem can be found. A new method has been developed to evaluate the effectiveness of vibration countermeasures. The method is based on calculating the mean power flow from the tunnel, paying attention to that part of the power which radiates upwards to places where buildings’ foundations are expected to be found. The mean power is calculated for an infinite train moving through the tunnel with a constant velocity. An elegant mathematical expression for the mean power flow is derived, which can be used with any underground-tunnel model. To evaluate the effect of vibration countermeasures and track properties on power flow, a comprehensive three-dimensional analytical model is used. It consists of Euler–Bernoulli beams to account for the rails and the track slab. These are coupled in the wavenumber–frequency domain to a thin shell representing the tunnel embedded within an infinite continuum, with a cylindrical cavity representing the surrounding soil.

Wave Barriers for Reduction of Train-Induced Vibrations in Soils

This paper is aimed at studying the effectiveness of different vibration countermeasures in isolating the ground vibrations induced by trains moving at sub- and supercritical speeds, with respect to the Rayleigh wave speed of the supporting soils. The vibration countermeasures considered herein include the installation of open trenches, in-filled trenches, and wave impeding blocks. The 2.5D finite/infinite element approach developed previously by the authors is employed in this study. This approach allows us to consider the load-moving effect of the train in the direction normal to the two-dimensional profile considered, and therefore to obtain three-dimensional results using only two-dimensional elements. The moving train is simulated as a sequence of moving wheel loads that may vibrate at some specific frequencies. The performance of the three types of wave barriers in isolating soil vibrations for trains moving at sub- and supercritical speeds with various excitation frequencies is evaluated with respect to some key parameters, along with suggestions made for enhancing the isolation efficiency.

Countermeasure of Vibration for Improving Availability of Laser Machine (Effect of Powder Composite Damper)

Recently, some kinds of laser machines have often been used for a special machining. Generally, it has been thought that static stiffness is unnecessary for these machines, because laser machining never generate relative machining force between a laser torch and a work, and the laser elements are very light. Therefore, dynamic stiffness in these machines also became low, and waiting time after the movement of the table is long. Hence, some countermeasures of the structural vibration are necessary for improving availability of the laser machine. In this paper, a vibration countermeasure has been proposed. At first, vibration properties of conventional laser machine was investigated using FEM simulation. Next, damping ratio of the structure was improved by the powder composite damper. It is concluded from the results that ; (1) The number of natural frequency on low frequency territory decreased and the compliance became small. (2) The logarithmic decrement of the structure became big.