Analysis And Research On The Characteristics And Mechanisms Of Interior Noise Of A 250 Km/h High Speed Train

In this thesis, we conducts field measurements for interior noise, bogie noise and vibration, and noise source identification for two frequently-used 250 km/h EMUs, and based on these measurements, analyses the characteristics and tramsmmission paths of the interior noise. We get the noise specta and A-weighted noise levels at the noise measurement points, and we also get a clear sense of the frequency components contributing highly to train interior noise. By comparing the measured noise and vibration data of two different types of EMUs, measures for noise reduction are proposed.Firstly, from the noise and vibration experimental data, we find the phenomenon that when train runs at 250 km/h and Coach 1 works as the head car, the A-weighted noise level inside Coach 1 of the first type EMU (Train Ⅰ) are 74.6 dB(A) in the front area,74.0 dB(A) in the middle area and 74.9 dB(A) in the rear area. The predominant noise frequencies range from 500 to 800 Hz. While for the second type EMU (Train Ⅱ), the A-weighted noise level in the front area, middle are and rear area are 71.4 dB(A),67.7 dB(A), and 73.5 dB(A) respectively. The most remarkable noise frequency is about 117Hz.Then, we seek train interior noise sources using microphone arrays. In principle, acoustic leakage at the inter-coach region probably plays a great role for the high levels of train interior noise. To decrease train interior noise, we need to enhance the sound insulation at the inter-coach region, as well as the train roof and train floor.Subsequently, byanalyzing bogie noise and vibration transmission, we find that high-order rotational excitation from the wheels influences highly on Train Ⅰ’s bogies, mainly because excitation frequencies are close to Train Ⅰ bogie’s natural frequencies (550～650 Hz), and further, influences highly on train interior noise. While passing sleeper effect influences highly on Train Ⅱ’s bogies, which is due to the sleeper-passing frequencies are close to the Train Ⅱ bogie’s natural frequency,117Hz. Noise and vibration transmission anlysis at the bogie region shows that vibration energy flows from the axle box and gear box to bogie framw mainly through the primary springs, and secondly through the tumblers.Finally, we find that the head car shape of Train Ⅰ, as well as its air conditioning system mounted at the roof of the front area of Coach 1, cause Train Ⅰ to suffer from higher aerodynamic excitation than Train Ⅱ. Thus, noise level inside the front area of Coach 1 of Train Ⅰ is higher than the figure for Train Ⅱ. Besides, Train Ⅰ has a better traction motor than Train Ⅱ as far as low noise design is concerned.We believe that inforrmation documented in this thesis will be helpful for low noise design and maintenance for 250 km/h EMUs.