Low frequency vibration tests on a floating slab track in an underground laboratory

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.

Simulation and experimental study of fluid induced excitation mechanism for liquid rocket engine immerged rotor

Low frequency vibration has occurred in the turbine pump of one type of liquid-propellant rocket engine,which threatens the safety and reliability of the rockets and their engines seriously.To figure out the mechanism of the low frequency vibration faults,in this paper,a dynamical model of a immersion turbine pump rotor system was established for the consideration of the vibration caused by small gap annual flow excitation which properly happened in immersion turbine pump rotor.The Newmark directly integral method was used to simulate the vibration characteristics of turbine pump,and an experiment was also carried out to investigated this problem.Results showed that,the small gap annual flow excitation could induce large amplitude low frequency vibration on the turbine pump rotor bearing system.The amplitude and frequency of low frequency vibration had relation with the parameters of the turbine pump clearance structure,such as the clearance ratio,length-diameter ratio and the viscosity of the fluid medium.In order to avoid the vibration induced by the small gap annual flow excitation,sealing effect should be improved and length-diameter ratio should be decreased.