Sound radiation attenuation by circular total-reflection elastic metasurface composed of subunits with cubic profiles

Utilizing metamaterials or acoustic black holes(ABHs)to control wave propagation and then to realize vibration control and sound radiation attenuation is a hot topic in recent years.However,using elastic metasurfaces that possess similar wave manipulation abilities with metamaterials and ABHs to attenuate sound radiation has not been reported yet.In this paper,a circular total-reflection elastic metasurface(CTREM)composed of subunits with cubic profiles similar with ABHs is proposed to realize vibration isolation and achieve broadband sound radiation attenuation of a plate below the cut-on frequency of the ABH.Compared with the corresponding bare plate and the plate containing a single ABH with a conventional design,the sound radiation efficiencies of the CTREM plate within and outside the vibration isolation band are both substantially attenuated.This phenomenon can be attributed to two distinct mechanisms:the total reflection of flexural waves caused by vibration isolation,and the local resonances of subunits.Analyses of the wavenumber spectra obtained from normal vibration velocities of the CTREM plate,both experimentally and numerically,along with the supersonic intensity patterns,reveal that the confined vibration energies are subsonic components localized within ineffective sound radiation areas.This,in turn,reduces the coupling strength of sound and vibration,thereby significantly attenuating sound radiation efficiency.The proposed CTREM provides a lossless and lightweight method for sound radiation attenuation.

Calculations of Radiations Attenuation and Dose Assessments of Tunnels Passing under Water Canals

Most of the developed countries have used their tunnels as protective structures （public nuclear shelters） in case of nuclear emergencies to protect their citizens from the dangerous effects of nuclear weapons. The research aims to explain how to use tunnels to protect some people from neutrons and gamma rays and account the required safe depth. The computer code （MCNP5） is used at this model for such tunnel to account attenuation of both neutrons and gamma rays passing through the canal water, sand, soil and reinforced concrete wall layers. The last one （thickness 105 cm） constructed the tunnel construction. Also, the computer code is used to account the dose inside the tunnel, and account （neutron） dose, （neutron, gamma） dose, prompt （gamma） dose, total （gamma） dose and total （neutron ＋ gamma） dose estimated by μsv/h, at different depths from the water surface level （depths 200 cm, 500 cm, 1,000 cm, 1,600 cm, 2,200 cm, 2,600 cm, 2,800 cm, 3,400 cm, 3,700 cm, 4,000 cm and 4,600 cm）. Then, account these doses for three bombs （its intensity 20 KT, 100 KT and 1,000 KT）.