The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especi...The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especially the active component of the pressure and horizontal particle velocity cross-spectrum, also called ho- rizontal complex cross acoustic intensity, when only two normal modes are trapped in the waveguide. Both the approximate theo- retic analysis and the numerical results show that the sign of the horizontal complex cross acoustic intensity active component is independent of the range when vertically deployed receiving dual sensors are placed in appropriate depths, the sum of which is equal to the waveguide effective depth, so it can be used to tell whether the sound source is near the surface or underwater; while the range rate is expected to be measured by utilizing the sign distribution characteristic of the reactive component. The further robustness analysis of the depth classification algorithm shows that the existence of shear waves in semi infinite basement and the change of acoustic velocity profiles have few effects on the application of this method, and the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range.展开更多
A lattice Boltzmann (LB) model with overall second-order accuracy is applied to the 1.5-layer shallow water equation for a wind-driven double-gyre ocean circulation. By introducing the second-order integral approximat...A lattice Boltzmann (LB) model with overall second-order accuracy is applied to the 1.5-layer shallow water equation for a wind-driven double-gyre ocean circulation. By introducing the second-order integral approximation for the collision operator, the model becomes fully explicit. In this case, any iterative technique is not needed. The Coriolis force and other external forces are included in the model with second-order accuracy, which is consistent with the discretized accuracy of the LB equation. The numerical results show correct physics of the ocean circulation driven by the double-gyre wind stress with different Reynolds numbers and different spatial resolutions. An intrinsic low-frequency variability of the shallow water model is also found. The wind-driven ocean circulation exhibits subannual and interannual oscillations, which are comparable to those of models in which the conventional numerical methods are used.展开更多
The integral expression for acoustic field due to a point source in shallow waterwhile sediment is either a liquid or a solid is derived. The synthetic full waveforms are simulatedusing real axis integration and FFF m...The integral expression for acoustic field due to a point source in shallow waterwhile sediment is either a liquid or a solid is derived. The synthetic full waveforms are simulatedusing real axis integration and FFF method. The effects of the seabed sediment parametersand center frequency of the source on the low frequency acoustic wave propagation in shallowwater are investigated. The conclusion is that the wave groups received in far field are thoseof the mode waves of the source center frequency. The possibility for inversely deducing thecompressional and shear sound speeds of sediment using the least square optimum through themeasured group velocities of a selected mode at different frequencies is discussed.展开更多
To obtain a universal model solving the uncertain acoustic field in shallow water, a non-intrusive model coupled polynomial chaos expansion （PCE） method with Helmholtz equa- tion is established, in which the polynom...To obtain a universal model solving the uncertain acoustic field in shallow water, a non-intrusive model coupled polynomial chaos expansion （PCE） method with Helmholtz equa- tion is established, in which the polynomial coefficients are solved by probabilistic collocation method （PCM）. For the cases of Pekeris waveguide which have uncertainties in depth of water column, in both sound speed profile and depth of water column, and for the case of thermocline with lower limit depth uncertain, probability density functions （PDF） of transmission loss （TL） are calculated. The results show that the proposed model is universal for the acoustic propa- gation codes with high computational efficiency and accuracy, and can be applied to study the uncertainty of acoustic propagation in the shallow water en^-ironment with multiple parameters uncertain.展开更多
In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of acoustic amplitudes at different ranges in typical shallow water are presented. Record...In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of acoustic amplitudes at different ranges in typical shallow water are presented. Recorded time is 48.96 h. Thickness of the thermocline is about 2 m-4 m. The deviation of temperature recorded at a fixed depth is 10℃-15℃. The vertical displacement of isotherm curves is about 5 m-6 m, which is mainly dominated by the lowest model. The measured spectrums of vertical displacement have obvious spectral packet within the range of 0.05 cpm (20 min) and 0. 143 cpm (7 min) besides the diurnal and semidiurnal tide frequency bands. Spectrum attenuation coefficients are between -1.5 and -1.7. Numerical calculation shows that phase velocity and group velocity of internal waves are equal to 0.329 m/s at lower frequencies. And with the increasing of frequency, the group velocity differs from phase velocity at about 0.03 cpm (33.33 min) and drops more quickly. The measured fluctuation of acoustic amplitude is about 8 dB-10 dB. With the increasing of range, the fluctuation trends to be faster and acoustic signals are declining. Spectrum attenuation coefficients are between -1.45 and -2.0. At last, PE method is used to simulate the acoustic amplitude fluctuation, in which internal waves are the important element.展开更多
Based on the piezo-optic effect of medium, the refractive index of medium is the function of its density, and so it's also the function of acoustic pressure. Therefore, acoustic pressure in the optical path everyw...Based on the piezo-optic effect of medium, the refractive index of medium is the function of its density, and so it's also the function of acoustic pressure. Therefore, acoustic pressure in the optical path everywhere can be determined absolutely by laser-interferometric technique and relative distribution of pressure in the middle and far acoustic field, which can be obtained from theory or experiment respectively. Theory and experiment of measurement of pressure in acoustic field with laser-interferometer are introduced. Distribution of pressure radiated by a power ultrasonic transducer is determined by laser interferometric technique. The theoretical and experimental results are in good agreement. The receiving sensitivity of a PVDF (Polyvinylidene fluoride) transducer in free field is also calibrated absolutely due to above results and its sensitivity is -118.5 dB.展开更多
A new method to obtain numerical solution of Acoustic Transfer Function (ATF) by BEM is presented. For a simply supported panel backed by a rectangular cavity at low frequency band (0-200 Hz), the frequency property o...A new method to obtain numerical solution of Acoustic Transfer Function (ATF) by BEM is presented. For a simply supported panel backed by a rectangular cavity at low frequency band (0-200 Hz), the frequency property of ATF is analyzed. The relation between the accuracy of the rapid evaluation of sound field and the discretization schemes of the vibrational panel is discussed. The result shows that the method to obtain ATF and the rapid evaluation of sound field using the ATF is suitable to low frequency band. If an appropriate discretization scheme is choosed based on the frequency involved and the effort to obtain ATF, the accuracy of the rapid evaluation of sound field is acceptable.展开更多
Background As the widespread use of electric devices in modern life, human are exposed to extremely low frequency magnetic fields （ELF MF） much more frequently than ever. Over the past decades, a substantial number ...Background As the widespread use of electric devices in modern life, human are exposed to extremely low frequency magnetic fields （ELF MF） much more frequently than ever. Over the past decades, a substantial number of epidemiological and experimental studies have demonstrated that ELF MF （50 Hz） exposure is associated with increased risk of various health effects. The present study examined the effects of chronic exposure to ELF MF on anxiety level and spatial memory of adult rats. Methods The 50-Hz ELF MF was used during the whole experimental procedures and the value of magnetic field （MF） was set to 2 mT. Adult rats were divided randomly to control, MF 1 hour and MF 4 hours group. Anxiety-related behaviors were examined in the open field test and the elevated plus maze; changes in spatial learning and memory were determined in Morris water maze aRer 4 weeks of daily exposure. Results Rats in MF 4 hours group had increased anxiety-like behaviors with unaltered locomotor activity. In the Morris water maze test, rats had reduced latency to find the hidden platform and improved long-term memory of former location of platform without changes in short-term memory and locomotor activity. Conclusion Chronic ELF MF exposure has anxiogenic effect on rats, and the promoting effects on spatial learning and long-term retention of spatial memory.展开更多
基于圆周排列的Helmholtz共振腔单元,设计并实现了一种具有低频宽禁带的声人工结构,可以在结构中心处实现二维隔声效果.针对实际模型,搭建了二维声场测量平台,进行了相应的实验研究,实验结果与有限元仿真结果符合较好.该结构在较宽的频...基于圆周排列的Helmholtz共振腔单元,设计并实现了一种具有低频宽禁带的声人工结构,可以在结构中心处实现二维隔声效果.针对实际模型,搭建了二维声场测量平台,进行了相应的实验研究,实验结果与有限元仿真结果符合较好.该结构在较宽的频带内(680—1050 Hz)可以实现较好的隔声效果,最大隔声量可达41 d B.实验中还研究了单元参数及共振状态对隔声效果的影响.隔声区的大小与共振单元的分布形式有直接关系,而良好的共振状态将对提高隔声量有一定帮助.研究结果对设计新型声防护结构具有理论与应用价值.展开更多
基金supported by the National Natural Science Foundation of China(1140440611374072)
文摘The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especially the active component of the pressure and horizontal particle velocity cross-spectrum, also called ho- rizontal complex cross acoustic intensity, when only two normal modes are trapped in the waveguide. Both the approximate theo- retic analysis and the numerical results show that the sign of the horizontal complex cross acoustic intensity active component is independent of the range when vertically deployed receiving dual sensors are placed in appropriate depths, the sum of which is equal to the waveguide effective depth, so it can be used to tell whether the sound source is near the surface or underwater; while the range rate is expected to be measured by utilizing the sign distribution characteristic of the reactive component. The further robustness analysis of the depth classification algorithm shows that the existence of shear waves in semi infinite basement and the change of acoustic velocity profiles have few effects on the application of this method, and the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range.
基金The work was supported by the One Hundred Talents Project of the Chinese Academy of Sciences(Grant No.KCL14014)the Impacts of Ocean-Land-Atmosphere Interactions over the East Asian Mon soon Region on the Climate in China(EAMOLA)(Grant No:ZKCX2-SW-210)the National Outstanding Youth Science Foundation of China(Grant No.40325016).
文摘A lattice Boltzmann (LB) model with overall second-order accuracy is applied to the 1.5-layer shallow water equation for a wind-driven double-gyre ocean circulation. By introducing the second-order integral approximation for the collision operator, the model becomes fully explicit. In this case, any iterative technique is not needed. The Coriolis force and other external forces are included in the model with second-order accuracy, which is consistent with the discretized accuracy of the LB equation. The numerical results show correct physics of the ocean circulation driven by the double-gyre wind stress with different Reynolds numbers and different spatial resolutions. An intrinsic low-frequency variability of the shallow water model is also found. The wind-driven ocean circulation exhibits subannual and interannual oscillations, which are comparable to those of models in which the conventional numerical methods are used.
文摘The integral expression for acoustic field due to a point source in shallow waterwhile sediment is either a liquid or a solid is derived. The synthetic full waveforms are simulatedusing real axis integration and FFF method. The effects of the seabed sediment parametersand center frequency of the source on the low frequency acoustic wave propagation in shallowwater are investigated. The conclusion is that the wave groups received in far field are thoseof the mode waves of the source center frequency. The possibility for inversely deducing thecompressional and shear sound speeds of sediment using the least square optimum through themeasured group velocities of a selected mode at different frequencies is discussed.
文摘To obtain a universal model solving the uncertain acoustic field in shallow water, a non-intrusive model coupled polynomial chaos expansion （PCE） method with Helmholtz equa- tion is established, in which the polynomial coefficients are solved by probabilistic collocation method （PCM）. For the cases of Pekeris waveguide which have uncertainties in depth of water column, in both sound speed profile and depth of water column, and for the case of thermocline with lower limit depth uncertain, probability density functions （PDF） of transmission loss （TL） are calculated. The results show that the proposed model is universal for the acoustic propa- gation codes with high computational efficiency and accuracy, and can be applied to study the uncertainty of acoustic propagation in the shallow water en^-ironment with multiple parameters uncertain.
文摘In this paper, the results of experiments concerning the fluctuations of internal waves on the thermocline and the fluctuations of acoustic amplitudes at different ranges in typical shallow water are presented. Recorded time is 48.96 h. Thickness of the thermocline is about 2 m-4 m. The deviation of temperature recorded at a fixed depth is 10℃-15℃. The vertical displacement of isotherm curves is about 5 m-6 m, which is mainly dominated by the lowest model. The measured spectrums of vertical displacement have obvious spectral packet within the range of 0.05 cpm (20 min) and 0. 143 cpm (7 min) besides the diurnal and semidiurnal tide frequency bands. Spectrum attenuation coefficients are between -1.5 and -1.7. Numerical calculation shows that phase velocity and group velocity of internal waves are equal to 0.329 m/s at lower frequencies. And with the increasing of frequency, the group velocity differs from phase velocity at about 0.03 cpm (33.33 min) and drops more quickly. The measured fluctuation of acoustic amplitude is about 8 dB-10 dB. With the increasing of range, the fluctuation trends to be faster and acoustic signals are declining. Spectrum attenuation coefficients are between -1.45 and -2.0. At last, PE method is used to simulate the acoustic amplitude fluctuation, in which internal waves are the important element.
基金National Natural Science Foundation of China!(No.59738150)
文摘Based on the piezo-optic effect of medium, the refractive index of medium is the function of its density, and so it's also the function of acoustic pressure. Therefore, acoustic pressure in the optical path everywhere can be determined absolutely by laser-interferometric technique and relative distribution of pressure in the middle and far acoustic field, which can be obtained from theory or experiment respectively. Theory and experiment of measurement of pressure in acoustic field with laser-interferometer are introduced. Distribution of pressure radiated by a power ultrasonic transducer is determined by laser interferometric technique. The theoretical and experimental results are in good agreement. The receiving sensitivity of a PVDF (Polyvinylidene fluoride) transducer in free field is also calibrated absolutely due to above results and its sensitivity is -118.5 dB.
基金This work is supported by the National Natural Science Foundation of China (No.59875069).
文摘A new method to obtain numerical solution of Acoustic Transfer Function (ATF) by BEM is presented. For a simply supported panel backed by a rectangular cavity at low frequency band (0-200 Hz), the frequency property of ATF is analyzed. The relation between the accuracy of the rapid evaluation of sound field and the discretization schemes of the vibrational panel is discussed. The result shows that the method to obtain ATF and the rapid evaluation of sound field using the ATF is suitable to low frequency band. If an appropriate discretization scheme is choosed based on the frequency involved and the effort to obtain ATF, the accuracy of the rapid evaluation of sound field is acceptable.
文摘Background As the widespread use of electric devices in modern life, human are exposed to extremely low frequency magnetic fields （ELF MF） much more frequently than ever. Over the past decades, a substantial number of epidemiological and experimental studies have demonstrated that ELF MF （50 Hz） exposure is associated with increased risk of various health effects. The present study examined the effects of chronic exposure to ELF MF on anxiety level and spatial memory of adult rats. Methods The 50-Hz ELF MF was used during the whole experimental procedures and the value of magnetic field （MF） was set to 2 mT. Adult rats were divided randomly to control, MF 1 hour and MF 4 hours group. Anxiety-related behaviors were examined in the open field test and the elevated plus maze; changes in spatial learning and memory were determined in Morris water maze aRer 4 weeks of daily exposure. Results Rats in MF 4 hours group had increased anxiety-like behaviors with unaltered locomotor activity. In the Morris water maze test, rats had reduced latency to find the hidden platform and improved long-term memory of former location of platform without changes in short-term memory and locomotor activity. Conclusion Chronic ELF MF exposure has anxiogenic effect on rats, and the promoting effects on spatial learning and long-term retention of spatial memory.
文摘基于圆周排列的Helmholtz共振腔单元,设计并实现了一种具有低频宽禁带的声人工结构,可以在结构中心处实现二维隔声效果.针对实际模型,搭建了二维声场测量平台,进行了相应的实验研究,实验结果与有限元仿真结果符合较好.该结构在较宽的频带内(680—1050 Hz)可以实现较好的隔声效果,最大隔声量可达41 d B.实验中还研究了单元参数及共振状态对隔声效果的影响.隔声区的大小与共振单元的分布形式有直接关系,而良好的共振状态将对提高隔声量有一定帮助.研究结果对设计新型声防护结构具有理论与应用价值.
