Effect of the Laying Order of Core Layer Materials on the Sound-Insulation Performance of High-Speed Train Carbody.

The design of sound-insulation schemes requires the development of new materials and structures while also paying attention to their laying order. If the sound-insulation performance of the whole structure can be improved by simply changing the laying order of materials or structures, it will bring great advantages to the implementation of the scheme and cost control. This paper studies this problem. First, taking a simple sandwich composite plate as an example, a sound-insulation prediction model for composite structures was established. The influence of different material laying schemes on the overall sound-insulation characteristics was calculated and analyzed. Then, sound-insulation tests were conducted on different samples in the acoustic laboratory. The accuracy of the simulation model was verified through a comparative analysis of experimental results. Finally, based on the sound-insulation influence law of the sandwich panel core layer materials obtained from simulation analysis, the sound-insulation optimization design of the composite floor of a high-speed train was carried out. The results show that when the sound absorption material is concentrated in the middle, and the sound-insulation material is sandwiched from both sides of the laying scheme, it represents a better effect on medium-frequency sound-insulation performance. When this method is applied to the sound-insulation optimization of a high-speed train carbody, the sound-insulation performance of the middle and low-frequency band of 125-315 Hz can be improved by 1-3 dB, and the overall weighted sound reduction index can be improved by 0.9 dB without changing the type, thickness or weight of the core layer materials.

Highly microporous carbon with nitrogen-doping derived from natural biowaste for high-performance flexible solid-state supercapacitor.

Highly microporous carbon material with nitrogen doping has been synthesized via a facile one-step approach by employing natural biowaste miscellaneous wood fibers derived hydrochar as precursor and melamine as nitrogen source respectively. The added melamine not only results in the incorporation of some nitrogen into the carbon framework but also increases the specific surface area of carbon material. Such resultant N-doped microporous carbon possesses the functionalized nitrogen doping (1.75 at. %), a large specific surface area (∼1807 m2 g-1) and abundant highly interconnected micropores. Benefiting from the synergistic effect of high specific surface area, well-developed pore size distribution and functionalized groups, this carbon material delivers a high specific capacitance of 345 F g-1 at 0.5 A g-1, an excellent capacitance retention with 270 F g-1 at up to 30 A g-1, and a remarkable cycle ability with 91.3% retention after 10,000 cycles at 5.0 A g-1. Based on it, the as-developed flexible symmetric solid-state supercapacitor delivers a high energy density of 7.92 W h kg-1 at the power density of 250 W kg-1. Evidently, this work provides a facile and cost-effective route for functionalized natural biowaste-based carbon materials and further opens up a way for highly value-added recycling of biowaste-like materials.

Boundary integral equations for sound radiation from a harmonically vibrating body moving uniformly in a free space.

In this high-speed transit era, the prediction of sound radiation from a moving and vibrating object is an important research topic. A typical example is a high-speed train wheel that not only moves fast in the railway direction but, due to wheel/rail interaction, also vibrates at high frequency, generating a complex sound field. By making use of sound spectra generated by moving harmonic compact sources, three-dimensional (3D) boundary integral equations are established in this paper for sound radiation from a harmonically vibrating body moving uniformly in a free space. The 3D boundary integral equations are reduced to 2D ones for a special case in which the body is axisymmetric and moves in its axial direction. The 2D boundary element method is applied to solve the 2D boundary integral equations and to produce results for a pulsating and moving sphere. Results show that the moving speed of the pulsating sphere has a significant effect on the generated sound field. This means that, for sounds radiated from a high-speed train wheel vibro-acoustically, the motion of the wheel has to be taken into account.