In order to improve the underwater acoustic target strength of comer reflectors,according to the principle of acoustic impedance mismatch of the boundary layer,the method of using air cavity to increase the underwater...In order to improve the underwater acoustic target strength of comer reflectors,according to the principle of acoustic impedance mismatch of the boundary layer,the method of using air cavity to increase the underwater acoustic target strength of corner reflectors is proposed.The acoustic reflection coefficients of underwater air layer and single layer metal sheet are calculated and compared.The results show that the reflection coefficient of single layer metal sheet is greatly affected by frequency and incidence angle,and the reflection coefficient of air layer in water is large and little affected by frequency and incidence angle.On this basis,a new kind of airfilled cavity corner reflector is designed.The acoustic scattering characteristics of underwater airfilled cavity comer reflector are calculated cumulatively,and the results are compared with the monolayer metal sheet corner reflector.The simulation results show that the acoustic reflection effect of the airfilled cavity corner reflector is better.In order to verify the correctness of the method,the test was carried out in the silencing tank.The experimental results show that the simulation results are in good agreement with the experimental results,and the airfilled cavity can improve on acoustic reflection performance of the underwater corner reflector.展开更多
In this paper, the microstructures and mechanical properties of underwater laser welds of Type 304 stainless steel were investigated. JISY308L type filler wire was used as filler wire during welding. A gas-shielding n...In this paper, the microstructures and mechanical properties of underwater laser welds of Type 304 stainless steel were investigated. JISY308L type filler wire was used as filler wire during welding. A gas-shielding nozzle was used to form a local dry cavity surrounding the welding zone. The main results are summarized as follows: (1) The shielding condition of the local dry cavity severely affects the oxygen content of the weld, the worst shielding condition leading to the oxygen content of 800×10-6, which largely increases the oxide inclusions and somewhat reduces the ferrite content. (2) The increase of oxygen content reduces the elongation rate and reduction of area in tensile test, but has no influence on the tensile strength. (3) In appropriate shielding condition, the mechanical properties of the underwater laser welds can be as same as that in the air.展开更多
The outer cavity Janus-Helmholtz with sound insulation layer is presented for ob- taining the capacity of high-power non-directional transmitting. The radiation efficiency and directivity in the 0 degrees direction ca...The outer cavity Janus-Helmholtz with sound insulation layer is presented for ob- taining the capacity of high-power non-directional transmitting. The radiation efficiency and directivity in the 0 degrees direction can be improved when the radiation mode is changed by laying sound insulation layer. The operating bandwidth can be expanded effectively by the dual mode coupling between the cavity vibration and longitudinal vibration of Janus transducer. A prototype is designed by finite element method. Test results show that the results are in good agreement with the design results. Compared with inner cavity Janus-Helmholtz transducer, acoustic radiation performance of outer cavity Janus-Helmholtz underwater acoustic transducer in the 0 degrees direction has been significantly improved.展开更多
文摘In order to improve the underwater acoustic target strength of comer reflectors,according to the principle of acoustic impedance mismatch of the boundary layer,the method of using air cavity to increase the underwater acoustic target strength of corner reflectors is proposed.The acoustic reflection coefficients of underwater air layer and single layer metal sheet are calculated and compared.The results show that the reflection coefficient of single layer metal sheet is greatly affected by frequency and incidence angle,and the reflection coefficient of air layer in water is large and little affected by frequency and incidence angle.On this basis,a new kind of airfilled cavity corner reflector is designed.The acoustic scattering characteristics of underwater airfilled cavity comer reflector are calculated cumulatively,and the results are compared with the monolayer metal sheet corner reflector.The simulation results show that the acoustic reflection effect of the airfilled cavity corner reflector is better.In order to verify the correctness of the method,the test was carried out in the silencing tank.The experimental results show that the simulation results are in good agreement with the experimental results,and the airfilled cavity can improve on acoustic reflection performance of the underwater corner reflector.
基金supported by the Natural Science Foundation of Tsinghua University
文摘In this paper, the microstructures and mechanical properties of underwater laser welds of Type 304 stainless steel were investigated. JISY308L type filler wire was used as filler wire during welding. A gas-shielding nozzle was used to form a local dry cavity surrounding the welding zone. The main results are summarized as follows: (1) The shielding condition of the local dry cavity severely affects the oxygen content of the weld, the worst shielding condition leading to the oxygen content of 800×10-6, which largely increases the oxide inclusions and somewhat reduces the ferrite content. (2) The increase of oxygen content reduces the elongation rate and reduction of area in tensile test, but has no influence on the tensile strength. (3) In appropriate shielding condition, the mechanical properties of the underwater laser welds can be as same as that in the air.
基金supported by the National Natural Science Foundation of China(11304057)the Opening Fund of Acoustics Science and Technology Laboratory(SSKF2015001)
文摘The outer cavity Janus-Helmholtz with sound insulation layer is presented for ob- taining the capacity of high-power non-directional transmitting. The radiation efficiency and directivity in the 0 degrees direction can be improved when the radiation mode is changed by laying sound insulation layer. The operating bandwidth can be expanded effectively by the dual mode coupling between the cavity vibration and longitudinal vibration of Janus transducer. A prototype is designed by finite element method. Test results show that the results are in good agreement with the design results. Compared with inner cavity Janus-Helmholtz transducer, acoustic radiation performance of outer cavity Janus-Helmholtz underwater acoustic transducer in the 0 degrees direction has been significantly improved.
