Optimal design of lightweight acoustic metamaterials for low-frequency noise and vibration control of high-speed train composite floor

Low-frequency noise and vibration are new challenges faced in high-speed trains. Conventional sound insulation and absorption materials or structures have insufficient efficiency for low-frequencies. This paper studies how to design lightweight acoustic metamaterials and apply them to high-speed train composite floors, for low-frequency noise and vibration control. First, through in-situ experiments, the interior noise characteristics and sound source distributions of a high-speed train were measured and analysed, including the sound transmission characteristics of the composite floor. Second, based on the finite element method, a vibration analysis model of the composite floor was established and validated. The target frequency of noise and vibration control was determined. Third, based on the multi-parametric optimisation method, a lightweight and low-frequency acoustic metamaterial (beam-like resonator) for the low-frequency noise and vibration control was designed, and the band gap properties of the beam-like resonator were obtained. Finally, the noise reduction effects of the beam-like resonator installed on different positions of the high-speed train composite floor were analysed, including vibration transfer ratio, vibration response and radiated sound power. The results demonstrate that the weight of the optimal beam-like resonator could be reduced by 60.7 %, compared to the initial solution prior to optimisation design. When the beam-like resonators are installed on the wooden floor, the vibration transfer ratio of the target frequency is reduced drastically, the overall acceleration level is reduced by 2.9 dB, and the overall radiated sound power level is reduced by 3.9 dB. The lightweight acoustic metamaterial designed in this paper has an obvious effect on the low-frequency noise and vibration control of composite structures.