Research on the radiation characteristics of aerodynamic noises of a simplified bogie of the high-speed train

This paper built a simplified bogie model including 2 axles, 2 wheel-sets and frames, and it was then installed on the high-speed train to compute the aerodynamic noise. The computational result showed that bogies made the noise of the high-speed train obviously serious, the noise near the bogie increased obviously, and the maximum sound pressure level increased by 1.3dBA. Based on Lighthill acoustic theories, this paper adopted large eddy simulation (LES) and FW-H (Ffowcs Williams-Hawking) acoustic model to compute numerical solution for the aerodynamic noise of the bogie. The aerodynamic flow behavior of the bogie and the distribution of aerodynamic noises in the far field were analyzed. Fluctuating pressure at the surface of the bogie was obtained and then combined with boundary element method (BEM) to study the aerodynamic noise sources and acoustic propagation characteristics of the bogie. Computational results showed that large eddies were in axles and wheel-sets, and axles mainly caused the phenomenon of Karman Vortex Street. When the bogie ran at the speed of 30 m/s, main frequencies were 278 Hz and 556 Hz, and the main frequency of aerodynamic drag was twice that of aerodynamic lift. In the vertical plane, longitudinal plane and lateral plane, the aerodynamic noise of the bogie had the characteristics of dipole noises. The main directions of radiation were 90° and 270°. The maximum sound pressure level was 57.3 dBA. The main direction of propagation for the aerodynamic noise of the bogie was right above and below the bogie rather than the left side and the right side of the bogie. The aerodynamic noise sources of the bogie were mainly at the second end axle and the surface of wheel-sets close to axles

Barrier-Free Wheelchair with a Mechanical Transmission

Wheelchairs are an important means of transportation for the elderly and disabled. However, the movement of wheelchairs on long curbs and stairs is restricted. In this study, a wheelchair for climbing stairs was developed based on a mechanical transmission system that rotates the entire driving part through a link structure and an actuator to change the speed. The first mode drives the caterpillar, and the second mode drives the wheels. When driving on flat ground, it uses landing gears and wheels, and when climbing stairs, it uses the caterpillar; accordingly, a stable driving is possible. The stability of the transmission is confirmed through stress analysis. The method used in our study makes it is possible to manufacture lightweight wheelchairs because a single motor drives both the wheel and caterpillar through the transmission system