Abstract: A comprehensive geological-engineering classification evaluation method for low-permeability reservoirs, includes: constructing geological classification evaluation indexes of a reservoir: adopting gray correlation method to obtain main controlling factors of reservoir geology of the low-permeability reservoirs that affects fracturing effects; based on the main controlling factors of the reservoir geology, constructing the geological classification evaluation indexes of low-permeability reservoirs by principal component analysis; constructing engineering classification evaluation indexes of the reservoir: adopting gray correlation method to obtain main controlling factors of geomechanics of the low-permeability reservoirs that affects fracturing effects; based on the main controlling factors of geomechanics, constructing the engineering classification evaluation indexes of low-permeability reservoirs by an analytic hierarchy process; and according to classification limit values of the geological classificatio

Abstract: Low-frequency duct noise is relatively difficult to deal with by passive methods such as porous duct lining. Reactive methods like expansion chamber are rather bulky, while compact resonators are to narrow-banded. This invention shows that a suitably stetched thin membrane backed by a slender cavity can achieve a satisfactory performance from low to medium frequencies over an octave band.

Abstract: Low-frequency duct noise is relatively difficult to deli with by passive methods such as porous duct lining. Reactive methods like expansion chamber are rather bulky, while compact resonators are too narrow-banded. This invention shows that a suitably stretched thin membrane backed by a slender cavity can achieve a satisfactory performance from low to medium frequencies over an octave band.