Vehicle-seat-passenger system dynamics on high-speed train

Abstract

As the increase of train speed and the adoption of lightweight technology, the vibration induced by wheel-rail interaction transmitted to the passengers via suspensions, bogies, carbody and seat becomes intensified, which worsens ride comfort. The human-seat system is always ignored in the study of ride comfort. And the existing studies of the biodynamics of human body and the dynamic characteristics of human-seat system are mainly focused on single-axis vibrations, which shows their limitations when applied to typical multi-axis vibration environment of rail vehicles. Further comprehensive research needs to be carried out to advance the understanding under typical multiaxis vibrations and apply to the study of ride comfort of rail vehicles. Firstly, a vertical train model incorporated with calibrated human-seat systems was developed for studying ride comfort. The relationship between the ride comfort and geometry filter effect of vehicle was analyzed, and the influencing factors of ride comfort were revealed and discussed. In addition, the contribution of different modes of carbody to ride comfort was defined and analyzed. A field measurement was carried out on a high-speed train for the vibration transmission of the seat, and the data were analyzed with a proposed new multi-input and single-output (MISO) system. The new method has the advantage of evaluating the contribution of inputs and their coherent part to the output independently of the sequences of inputs compared with the original method. It was found three inputs (vertical, lateral and roll accelerations) from the carbody floor could well account for the vertical, lateral or roll vibrations at the seat pan or backrest. An experimental study of the biodynamics of seated human body exposed to vertical, lateral and roll vibration was carried out. The principal resonance frequencies of the apparent masses generally had a negative correlation with the weighted root-sum-square (r.s.s.) value of the lateral, vertical and roll excitation magnitudes, which was more significant under low r.s.s value or significant only under low r.s.s value. A seated human model exposed to combined vertical, lateral and roll vibration was developed and calibrated by the experimental data. Three modes of the seated human body were observed by modal analysis to be correlated with the resonances in the measured apparent masses. The first mode (1.01 Hz) was found to be associated with the lateral and roll motions of the upper body, the second (2.53 Hz) with lateral motion of the lower body in addition to these motions, and the third mode (5.54 Hz) was dominated by the vertical motion of the whole body. The experimental study of the dynamics of the train seat with subjects exposed to vertical, lateral and roll vibration was carried out. There was a decrease in the principal resonance frequencies of the seat transmissibilities as the increase of the weighted r.s.s. value of lateral, vertical and roll magntides, which was more significant at low r.s.s. value or significant only at low r.s.s. value. Models of the double-unit train seat, the seat with one and two subjects were developed and calibrated. It was found the primary peak around 5 Hz in the vertical transmissibility on the seat pan arose from a whole-body vertical mode of human body with slightly higher modal frequency. Two modes around 15 and 27 Hz of the seat contributed to the peaks with approximate frequencies in the seat transmissibilities. What is more, human body had a tendency of increasing the modal damping of the seat modes. Finally, a 3D rigid-flexible coupled track-train-seat-human model was developed with the developed human-seat model. The influence of train speed, carbody damping, suspension parameters and seat position on ride comfort as well as the proportion of different vibration positions and directions in the overall ride comfort index were studied with this model. In addition, the contribution of the rigid and flexible modes of carbody to the ride comfort was also defined and studied. This study gives a useful guide for the design of rail vehicles and the matching of the human-seat system with the vehicle.

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