Search Results (3)

Although crucial transport equipment in coal mining enterprises, tubular belt conveyors cause serious noise pollution. In this paper, the sound absorption and isolation performance of three kinds of highly efficient sound-absorbing and -insulating materials were studied by finite element multiphysics field software COMSOL and acoustic tests, and the structure of highly efficient sound-absorbing and -insulating materials was optimized and designed. The results show that the acoustic superstructure plate has an excellent sound insulation effect of 36 dB, and achieves an excellent sound absorption coefficient of 0.95 at 210 Hz on the acoustic simulation test. The simulated weighted sound insulation of acoustic metamaterial plate is 37 dB, and the simulated weighted sound insulation of acoustic metamaterial plate filled with particle material is 42 dB, which improves the sound insulation effect by 4~7 dB after filling with particle material, and the comprehensive absorption coefficient of the high-frequency noise of more than 800 Hz reaches 0.94, and it can effectively absorb and block the low-frequency noise as well; rock wool acoustic panels in the 500 Hz to achieve a better acoustic capacity, the absorption coefficient of 0.8 or more, but the low-frequency noise acoustic capacity is still lacking, and can not be a good solution to the full-frequency band of the acoustic problem. It can be seen that the acoustic metamaterial plate has the best sound absorption and insulation effect. At the same time, the acoustic metamaterials based on the honeycomb structure are optimized, and the sound absorption and insulation structure with the angle of 60° of the inclined plate and the length of 693 mm of the inclined plate is the optimal structure. It provides a solution to the noise pollution caused by tubular belt conveyors. Full article

This article presents a new analysis to determine the variation in modal dynamic characteristics of bridge superstructures caused by hydrodynamic added mass (HAM) during progressive flooding. The natural frequency variations were numerically and experimentally extracted in various artificial flood stages that included dry conditions, semi-wet conditions, and fully wet conditions. Three-dimensional finite element modeling of both subscale and full-scale models were simulated through a coupled acoustic structural technique using Abaqus^®. Experiments were performed exclusively on a subscale model at a flume laboratory to confirm the numerical simulations. Finally, an approach to quantify the directional HAM in the dominant axes of vibration was pursued using the concept of effective modal mass. It is shown that specific vibrating modes with the largest effective mass are strongly affected during artificial flood events and are identified as the dominant modes. Numerical simulation shows that large directional HAM is introduced on those dominant modes during flood events. For the full-scale representative bridge, the magnitude of the HAM along the first structural mode was estimated to be over 5.8 times the bridge’s structural modal effective mass. It is suggested that directional HAM should be included during the design of bridges over streamways that are prone to flooding in order to potentially be appended to the AASHTO code. Full article

The one-dimensional extended Hubbard model with lattice dimerization and alternated site potentials is analyzed using the renormalization group method. The coupling of electrons to structural degrees of freedom such as the anion lattice and acoustic phonons is investigated to obtain the possible instabilities against the formation of lattice superstructures. Applications of the theory to anionic and spin-Peierls instabilities in the Fabre and Bechgaard salts series of organic conductors and ordered alloys are presented and discussed. Full article