Analysis of ground vibrations due to underground trains by 2.5D finite/infinite element approach   总被引：1，自引：1，他引：0  

Hung Hsiao-Hui  Y. B. Yang 《地震工程与工程振动(英文版)》2010,9(3):327-335

The 2.5D finite/infinite element approach is adopted to study wave propagation problems caused by underground moving trains. The irregularities of the near field, including the tunnel structure and parts of the soil, are modeled by the finite elements, and the wave propagation properties of the far field extending to infinity are modeled by the infinite elements. One particular feature of the 2.5D approach is that it enables the computation of the three-dimensional response of the half-space, taking into account the load-moving effect, using only a two-dimensional profile. Although the 2.5D finite/infinite element approach shows a great advantage in studying the wave propagation caused by moving trains, attention should be given to the calculation aspects, such as the rules for mesh establishment, in order to avoid producing inaccurate or erroneous results. In this paper, some essential points for consideration in analysis are highlighted, along with techniques to enhance the speed of the calculations. All these observations should prove useful in making the 2.5D finite/infinite element approach an effective one.  相似文献   

Contribution of ambient vibration recordings (free-field and buildings) for post-seismic analysis: The case of the Mw 7.3 Martinique (French Lesser Antilles) earthquake,November 29, 2007     

《Soil Dynamics and Earthquake Engineering》2013

Following the Mw 7.3 Martinique earthquake, November 29^th, 2007, a post-seismic survey was conducted by the Bureau Central Sismologique Français (BCSF) for macroseismic intensities assessment. In addition to the inventories, ambient vibration recordings were performed close to the particularly damaged zones in the free-field and the buildings. The objective of the paper is to show the relevancy of performing ambient vibration recordings for post-earthquake surveys. The analyses of the recordings aim at explaining the variability of the damages through site effects, structure vulnerability or resonance phenomena and to help the characterization of the post-seismic building integrity. In three sites prone to site effects, we suspect damage to be related to a concordance between soil fundamental frequency and building resonance frequency. Besides, the recordings of ambient vibrations at La Trinité hospital before and after the earthquake allow us to quantify the damage due to earthquake in terms of stiffness loss.  相似文献   

Delay time optimization in blasting operations for mitigating the vibration-effects on final pit walls' stability     

X.Z. Shi  SH.R Chen 《Soil Dynamics and Earthquake Engineering》2011

Blasting induced vibration is one of the fundamental problems in the open-pit mines and intense vibration can cause critical damage to structures and plants nearby the open-pit mines, especially to the final pit wall's stability. It is very important to study how to control vibration induced by blasting in the mitigation of negative effects of blasting in open-pit mines. This study aims to examine the propagation of blasting induced ground vibrations and find the feasible approaches to reduce the harmful effects of vibrations induced by blasting on the final pit wall's stability. For this purpose, a series of field experiments were conducted in XinQiao Mining Co. Ltd. Sixty-six events and the blasting parameters of these shots were carefully recorded. During the statistical analysis of the collected data, the predictor equation proposed by the United States Bureau of Mines (USBM) was used to establish a relationship between the Peak Particle Velocity (PPV) and the Scaled Distance (SD) factor. The relationship between PPV and SD was determined and proposed to be used in this open-pit mine. Control of maximum charge amount per delay and the selection optimum interval time to reduce the intensity of vibration by waveform interference were applied in practice. Based on the field experiments, we can determine the maximum charge amount per delay and 15 ms delay were proposed to be used in this site, and a decrease in vibration of 24.5% was obtained.  相似文献   

VIV and galloping of single circular cylinder with surface roughness at 3.0×10≤Re≤1.2×10     

Che-Chun Chang  Michael M. Bernitsas 《Ocean Engineering》2011,38(16):1713-1732

Passive Turbulence Control (PTC) in the form of selectively distributed surface roughness is used to alter Flow Induced Motion (FIM) of a circular cylinder in a steady flow. The objective is to enhance FIM's synchronization range and amplitude, thus maximizing conversion of hydrokinetic energy into mechanical energy by oscillator in vortex-induced vibration and/or galloping. Through additional viscous damping, mechanical energy is converted to electrical harnessing clean and renewable energy from ocean/river currents. High Reynolds numbers (Re) are required to reach the high-lift TrSL3 (Transition-Shear-Layer-3) flow regime. PTC trips flow separation and energizes the boundary layer, thus inducing higher vorticity and consequently lift. Roughness location, surface coverage, and size are studied using systematic model tests with broad-field laser visualization at 3.0×10⁴<Re<1.2×10⁵ in the low-turbulence free-surface water-channel of the Marine Renewable Energy Laboratory of the University of Michigan. Test results show that 16° roughness coverage is effective in the range (10°-80°) inducing reduced vortex-induced vibration (VIV), enhanced VIV, or galloping. Range of synchronization may increase or decrease, galloping amplitude of oscillation reaches three diameters; wake structures change dramatically reaching up to ten vortices per cycle. Conversion of hydrokinetic energy to mechanical is enhanced strongly with proper PTC.  相似文献   

Building vibrations and dynamic pavement loads induced by transit buses     

O. Hunaidi  W. Guan  J. Nicks 《Soil Dynamics and Earthquake Engineering》2000,19(6):547

The purpose of this study was to investigate the effect of bus suspension systems on building vibrations and dynamic pavement loads. Building vibrations and pavement loads induced by two instrumented buses having different characteristics were measured simultaneously under controlled field conditions. Field tests were performed at several vehicle speeds, normal and reduced tire pressures, and with roads having good surface condition as well as abrupt surface irregularities. Tests were carried out at two vibration complaint sites in Montréal. The level and frequency content of vibrations and loads induced by the two buses were evaluated and compared. The results show that the dynamic component of pavement loads induced by the two buses were significantly different but the difference in building vibration levels was not as significant.  相似文献   

Ground vibrations from sheetpile driving in urban environment: measurements, analysis and effects on buildings and occupants     

G. A. Athanasopoulos  P. C. Pelekis 《Soil Dynamics and Earthquake Engineering》2000,19(5)

Following a comprehensive review of the subject of man-made ground vibrations, measurements of ground vibration caused by vibratory sheetpile driving in recent soil deposits are reported in terms of particle velocities vs. distance from the source of vibration. The measurements were conducted on paved surfaces and sidewalks in the inner urban environment. Reconstructed particle displacement paths indicated, predominantly, vertical vibrations of the Rayleigh type. The attenuation rate of vibrations with distance was compared to published results of other studies and satisfactory agreement was found to exist. Values of particle velocity measured in this study, however, were lower than corresponding values of other studies under comparable values of rated vibratory kinetic energy. This is possibly due to different soil conditions. Average and upper bound linear log–log attenuation relationships are proposed, which fit the results of measurements and are representative of the conditions likely to be encountered in the urban environment. Measurement of vibrations on higher floors of multistory reinforced concrete buildings indicated a significant amplification of vertical vibration and an average curve for amplification magnitude vs. floor level was fitted to the results of measurements. A comparison of measured values of vibration with the observed performance of buildings and with damage threshold values suggested by existing codes and standards indicated that the latter do not provide safety against damage caused by vibratory densification of loose sandy soils. On the other hand, the existing criteria for human exposure to vibrations in buildings, according to the results of this study, seem to adequately define the degrees of human discomfort.  相似文献   

Free vibrations of three-dimensional extensible marine cables with specified top tension via a variational method   总被引：1，自引：0，他引：1  

Somchai Chucheepsakul  Narakorn Srinil 《Ocean Engineering》2002,29(9)

This paper presents a model formulation that can be used for analyzing the three-dimensional vibration behaviours of an inclined extensible marine cable. The virtual work-energy functional, which involves strain energy due to axial stretching of the cable and virtual work done by external hydrostatic forces is formulated. The coupled equations of motion in the Cartesian coordinates of global systems are obtained by taking into account the difference between Euler’s equations and equilibrium equations. The method of Galerkin finite element is used to obtain the mass and stiffness matrices which are transformed into the local coordinate systems. Then the eigenvalue problem is solved to determine its natural frequencies and corresponding mode shapes. The model formulation developed herein is conveniently applied for the cases of specified top tension. The numerical investigations are carried out to demonstrate the validity of the model and to explore in details the influence of various parameters on the behaviours of marine cables. Results for the frequency avoidance phenomenon, maximum dynamic tension and coupled transverse mode shapes are presented and discussed.  相似文献   

Effect of fluid column dynamics on longitudinal vibrations of an ultra deepwater riser covered by an orifice plug     

Vadim S. Tikhonov  Alexander I. Safronov 《Ocean Engineering》2002,29(1):99-112

The paper studies longitudinal vibrations of an ultra-deepwater drilling riser whose bottom end is disconnected from the sea floor and covered by a plug (a blind one or the one with a hole). An elastic shell is used as a model of a riser pipe. The fluid column motion in the riser is described by the Navier–Stokes equation for a compressible fluid. Losses of fluid pressure during its flowing through a hole in the plug are taken into account. Solution of the riser equations is carried out in the frequency domain. Analysis of the effect which the riser length, wave period and height, and the plug-hole diameter on the amplitude of the riser's tension vibrations is conducted. A riser manufactured of strong aluminium alloys, some of prospective materials for ultra deepwater drilling, was considered as a prototype. It has been shown that risers 2000–4000 m long, plug-hole, and a riser 6000 m long with plug-hole of 0.087 m in diameter can withstand wave height of >15 m throughout the frequency range.  相似文献   

On the response of a free span pipeline subjected to ocean currents   总被引：5，自引：0，他引：5  

G. K. Furnes  J. Berntsen 《Ocean Engineering》2003,30(12):1553-1577

A mechanistic study is performed to examine the coupling between the in-line and the cross-flow motion of a cylindrical structure subjected to current forces. The structure represents a free span pipeline but concerns marine risers as well.A time domain model is formulated in which the in-line and cross-flow deflections are coupled through the axial tension which in turn is computed from the pipeline prolongation at any time. This formulation introduces time dependent tensions and non-linearity into the problem.Preliminary validation of the model simulations vs. physical test data are carried out for one specific case to ensure that the sag and the in-line deflection are correctly resolved by the model. Using this as the initial condition a series of calculations are carried out to examine cross-flow induced deflections induced by an in-line prescribed deflection and vice versa. Finally, an idealistic simulation of flow induced vibration is presented.The model simulations demonstrate that the coupling varies with the mode shape and with which component it is initially introduced into. However, it is evident that the coupling effects may be significant and not negligible.  相似文献   

A Novel Wake Oscillator Model for Vortex-Induced Vibrations Prediction of A Cylinder Considering the Influence of Reynolds Number     

GAO Xi-feng  XIE Wu-de  XU Wan-hai  BAI Yu-chuan  ZHU Hai-tao 《海洋工程》2018,32(2):132-143

It is well known that the Reynolds number has a significant effect on the vortex-induced vibrations (VIV) of cylinders. In this paper, a novel in-line (IL) and cross-flow (CF) coupling VIV prediction model for circular cylinders has been proposed, in which the influence of the Reynolds number was comprehensively considered. The Strouhal number linked with the vortex shedding frequency was calculated through a function of the Reynolds number. The coefficient of the mean drag force was fitted as a new piecewise function of the Reynolds number, and its amplification resulted from the CF VIV was also taken into account. The oscillating drag and lift forces were modelled with classical van der Pol wake oscillators and their empirical parameters were determined based on the lock-in boundaries and the peak-amplitude formulas. A new peak-amplitude formula for the IL VIV was developed under the resonance condition with respect to the mass-damping ratio and the Reynolds number. When compared with the results from the experiments and some other prediction models, the present model could give good estimations on the vibration amplitudes and frequencies of the VIV both for elastically-mounted rigid and long flexible cylinders. The present model considering the influence of the Reynolds number could generally provide better results than that neglecting the effect of the Reynolds number.  相似文献