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On the Interaction of Resonance And Bragg Scattering Effects for the Locally Resonant Phononic Crystal with Alternating Elastic and Fluid Matrices

Yuan B., Chen Y., Jiang M., Tang S., He M., Tu M.

Archives of Acoustics

2017

Vol. 42, No. 4

725--733

Three-dimensional (3D) locally resonant phononic crystals (LRPCs) are studied with the aim of optimising the sub-wavelength band gaps of such composites. By analysing their effective acoustic properties, it has been found that the effective acoustic speed of the composite will drop to zero when local resonance arise, and will increase monotonically when Bragg scattering effects occur. Moreover, if the matrix is a low-shear-speed medium, local resonators can significantly reduce the effective acoustic speed of the composite and, therefore, lower the frequency where Bragg scattering effects occur. Hence, a specific LRPC with alternating elastic and fluid matrices is proposed, whose resonance and Bragg gaps are already close in frequency. The fluid matrix behaves as a wave filter, which prevents the shear waves from propagating in the composite. By using the layer-multiple-scattering theory, the coupling behaviour of local resonance and Bragg scattering band gaps has been investigated. Both gaps are enhanced when they move closer to each other. Finally, a gap-coupled case is obtained that displays a broad sub-wavelength band gap. Such proposal excels at the application of underwater acoustic materials since the arrangement of structure can be handily adjusted for tuning the frequency of coupled gap.

The research of characteristic for mining coal seam deformation and seepage flow after the protective layer was mined

Tu M., Fu B. J.

AGH Journal of Mining and Geoengineering

2012

Vol. 36, no. 3

367-376

Based on (RFPA2D-Gasflow) numerical software, the characteristic of mining strata damage and fracture distribution after the mining of protective layer has been analyzed and the coal seam by discharging pressure level and vertical displacement change rule has been studied. Finally the coal seam gas pressure and permeability evolution characteristics after the discharging pressure mining has been concluded. Research results show that as the range of stope expand, the discharged pressure coal seam gas pressure is reduced, and the permeability of coal seam is increased signiificantly. The research result has been applied by the engineering. A lane is arranged in a group of inclined to wear on the length of drilling, extraction discharging pressure gas effect is remarkable, which ensure the safety and efficiency of mining, research results for discharging pressure gas extraction and extraction drilling provides theoretical basis for designing.

Za pomocą oprogramowania numerycznego (RFPA2D-Gasflow) przeprowadzono analizę charakterystyki szczelinowania pokładów węgla oraz zeszczelinowania po eksploatacji warstwy ochronnej, a także zbadano złoże węgla kamiennego na podstawie ciśnienia odprowadzanego gazu i zasady przesunięcia pionowego. Następnie opracowano charakterystykę zmienności ciśnienia i gazoprzepuszczalności złoża węglowego po odprowadzeniu gazu z pokładu. Wyniki badania pokazują, obniżenie ciśnienia gazu odprowadzanego ze złoża węglowego oraz znaczne zwiększenie gazoprzepuszczalności złoża węglowego. Wyniki badania zostały zastosowane w technice inżynierskiej. W pochylni wykonano wyrobisko dla skrócenia wiercenia, co pozwoliło na skuteczniejsze zmniejszenie ciśnienia gazu odprowadzanego podczas wiercenia, a przez to na zapewnienie bezpieczeństwa i wydajności procesu wydobycia gazu. Wyniki badania ujmowania gazu podczas wiercenia stanowią podstawę teoretyczną do tworzenia nowych projektów.