Dynamic Respons Analysis And Prediction Of Ground Vibration Of The Semi-active Vibration-reduce Of Floating Slab Track By Using Magneto-rheological Dampers

With the rapid development of the urban rail transit in China, the ground vibration problem has a increasingly remarkable effect on people’s production and life. A mass of engineering practices show that the anti-vibration measures adopted at the vibration source is a relatively economical and effective method to control the ground vibration. Among these methods, the spring floating slab track which has the best damping effect can isolate vibration within a relatively wide frequency range, but its effect on the soil vibration with a long wavelength and strong penetrability at low frequencies (<20 Hz) is not favorable. Referring to the application of magnetorheology damping semi-active control technology on the other engineering domains, there is a new way to promote the effect of the spring floating slab track on reducing the vibration at low frequencies. In this thesis, the dynamic responses of the vertically coupled metro vehicle-spring floating slab track was analyzed systematically so as to determine the reasonable values of the main design parameters of the spring floating slab track. Based on the analysis above, with consideration of the nonlinear dynamic characteristics of the magnetorheology damper, the vertically coupled metro vehicle-magnetorheology damping semi-active anti-vibration floating slab track model was established to analyze its dynamic responses, and determine the strategies and key design parameters for the magnetorheology damping semi-active control. Finally, the control effect on the ground vibration along the metro lines was predicted. The main research outcomes and conclusions are as follows.(1) Based on the analysis of the dynamic responses in the time/frequency domain for the coupled metro vehicle-track system, the design process for the main parameters of the spring floating slab track was proposed. Firstly, according to the engineering application cases, the fastener stiffness, the dimension of the floating slab (thickness and length), the stiffness and supporting spacing of vibration isolator were determined initially. Then the transient dynamic analytical method in the time domain for the coupled metro vehicle-spring floating slab track system was applied to determine the adjustable range of the fastener parameters, the dimension of the floating slab track and the vibration isolator parameters by taking the vertical displacement of rail and floating slab track and the rate of wheel load reduction as the limiting value from the angle of construction conditions and wheel-rail safety. Finally, the steady dynamic analytical method in the frequency domain for the coupled metro vehicle-spring floating slab track system was applied to determine the fastener parameters, the dimension of the floating slab track and the vibration isolator parameters from the angle of reducing the metro vibration.(2) Integrated with the intelligent controllable characteristics of the magnetorheology damper, the traveling time window based feedback control algorithm was designed to authentically simulate the operation process of the magnetorheology damper under the floating slab.(3) In the wheel-rail coupling vibration system with large nonlinearity and randomness, with the overall consideration of wheel-rail safety and anti-metro vibration effect, the groundhook control strategy was suggested to control the vertical vibration of the floating slab track. For the districts under the general anti-vibration requirement, the magnetorheology damping force taking as 6 kN is reasonable, while for the districts under the higher anti-vibration requirement, the magnetorheology damping force can be larger but limit to 12 kN. In order to prevent the high-frequency vibration of rail and floating slab track in the vertical direction, the firing threshold value of the magnetorheology damper sets as about 0.5 mm. The response lag is closely related to the track irregularity condition. With consideration of the short wave irregularity, the response lag of the magnetorheology damper was designed as 0.15s. Under the groundhook control strategy, because the magnetorheology damping can inhibit the vertical vibration displacement of the rail and floating slab remarkably, the stiffness of the spring can decrease by 20% to have the support reaction force reduced by 4.9% within the frequency range of 1 Hz-20 Hz in favor of further promoting the anti-vibration effect of the floating slab track at low frequencies.(4) According to the tunnel-soil finite element model transient simulation analysis, in the range of 40m-60m from the center line, the vertical vibration acceleration of ground soil amplifies partly during the pass of subway train. This phenomenon is strongly related to the reflection, refraction and transmission of the vibration wave in the stratum structure along the subway. A decline appears in ground vertical vibration acceleration once the distance to center line is more than 80m, due to damping and radiation attenuation in vibration wave when spreading in the earth. Under the condition of a certain geological condition along the subway tunnel, the vibration attenuation rate of ground soil is closely related to the vibration frequency as well as propagation distance. That means, when spreads in soil, the high frequency vibration attenuates faster with increasing propagation distance, while the low frequency vibration attenuates more slowly as propagation distance increases. Hence the low frequency vibration is of farther propagation distance and wider influence range. On the basis of the study, based on the theoretical simulation analysis of the tunnel-soil transient finite element analytical model, compared with the traditional spring floating slab track, the magnetorheology damping semi-active anti-vibration floating slab track within the frequency range of 0-80 Hz can promote the anti-vibration effect along the metro lines to varying degrees. The anti-vibration effect on the vertical vibration of the ground soil along the metro lines within the frequency range of 0-20 Hz is the most remarkable. Within this frequency range, the larger magnetorheology damping force leads to the stronger attenuation of the environmental vibration. When the magnetorheology damping force takes as 12 kN, the maximum attenuation reaches to 8.7 dB. The burial depth of the tunnel ranging within 10 m-20 m has almost no effect on the vibration control for the magnetorheology damping semi-active anti-vibration spring floating slab track.