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N. V. Studenichnik 《Acoustical Physics》2003,49(2):207-216
Experimental data are presented on the intensity and space-time characteristics of the sound field generated by explosions in underwater and surface sound channels of the Black Sea. The fine field structure is studied as a function of distance and positions of the source and the receiver. The discreteness of the field structure governed by the deterministic nature of the waveguide is revealed, and the destruction of this structure under the effect of the instability of the waveguide parameters is demonstrated. The effect of the rough sea surface on the sound field in the surface channel is studied, and the diffraction-caused propagation loss is estimated. The mechanism of the forerunner formation is considered. The experimentally observed sound field features are compared with the calculations. A possibility for solving the inverse problem is indicated, and the main parameters that are used in the ray method of determining the source coordinates in the underwater channel (i.e., the method earlier proposed by the author on the basis of the intrinsic structure of the sound field) are pointed out. 相似文献
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利用多物理场耦合有限元法对结构和流体适应性强、抛物方程声场计算高效准确的特点,提出了三维浅海波导下弹性结构声振特性研究的有限元-抛物方程法.该方法采用多物理场耦合有限元理论建立浅海下结构近场声辐射模型,计算局域波导下结构声振信息,并提取深度方向上复声压值作为抛物方程初始值;然后采用隐式差分法求解抛物方程以步进计算结构辐射声场.重点介绍了该方法对浅海下结构声辐射计算的准确性、高效性以及快速收敛性后,对Pekeris波导中有限长弹性圆柱壳的声振特性进行了分析.研究得出,当圆柱壳靠近海面(海底)时,其耦合频率比自由场下的要高(低),当潜深达到一定范围时,与自由场耦合频率基本趋于一致;在低频远场,结构辐射场与同强度点源声场具有一定的等效性,且等效距离随着频率增加而增加;由于辐射声场受结构振动模态、几何尺寸和简正波模式影响,结构辐射场传播的衰减规律按近场声影响区、球面波衰减区、介于球面波和柱面波衰减区、柱面波衰减区四个扩展区依次进行. 相似文献
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A. L. Virovlyansky A. Yu. Kazarova L. Ya. Lyubavin 《Radiophysics and Quantum Electronics》2011,54(5):334-345
We perform theoretical analysis of the method of field focusing in a randomly inhomogeneous waveguide using reradiation of
the received signal with time reversal. The simplest case where point sources and receivers are used for emission and reception
is considered. As an example, the waveguide is chosen which simulates an underwater sound channel with refractive-index fluctuations
caused by random internal waves. In underwater acoustics, the considered method of field focusing is usually applied at relatively
short distances that are shorter than or about 10 km. This work deals with much longer paths, along which sound waves propagate
under conditions of well-developed ray and wave chaos. Main attention is given to studying the width of the focal spot and
the field amplitude at its center. It is shown that the amplitude distribution in the vertical section of the focal spot and
the peak amplitude value at its center can be estimated analytically using the stochastic ray theory. 相似文献
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针对浅海信道下弹性结构声辐射预报尚无高效可靠的研究方法,提出了一种浅海信道下弹性结构声辐射快速预报的联合波叠加法.该方法结合了浅海信道传输函数、多物理场耦合数值计算法和波叠加法理论,运用该方法可对浅海信道下弹性结构辐射声场进行快速预报.经数值法和解析解法验证后,从信道下辐射源、环境影响和辐射声场测量的角度研究分析了浅海信道下弹性圆柱壳的声辐射特性,阐释了进行浅海信道下结构声辐射研究的必要性.研究结果表明,仅在低频浅海信道下弹性结构可近似等效为点源,信道上下边界对声场产生显著的耦合影响,高频段的空间声场指向性分布尤为明显,垂直线列阵进行信道下结构辐射声功率测量时,测量结果受到信道环境边界和潜深的影响较大. 相似文献
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R. A. Vadov 《Acoustical Physics》2002,48(2):142-146
Experimental data on the long-range propagation of explosion-generated sound signals in the shallow-water northern part of the Sea of Okhotsk are analyzed. The propagation conditions in this region are characterized by a fully-developed underwater sound channel that captures the rays crossing the channel axis at angles lower than 3°. The experimental data reveal a small increase in the duration of the sound signal in proportion to the range with the proportionality factor lower than 0.00025 s/km. The frequency dependence of attenuation exhibits a pronounced minimum whose position on the frequency axis is close to the critical frequency of the first “water” mode (about 160 Hz). The increase in the attenuation coefficient at lower frequencies is confirmed by the field calculations performed with the wave-field computer code and is explained by the sound energy loss in the bottom sediments. At frequencies higher than 200 Hz, as in the Baltic Sea, the most probable reason for the attenuation to exceed the absorption in sea water is sound scattering by internal waves. 相似文献
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V. M. Kudryashov 《Acoustical Physics》2000,46(6):700-704
It is shown that, in the Arctic-type deep-water waveguide, the first water mode can be used for acoustic halynometry at frequencies of about 40 Hz and higher. For this task, the stochastic sound scattering by the ice cover and the frequency dispersion of modes are the interfering factors. The data of numerical modeling are presented for the levels of the regular and stochastic components of the pseudo-noise signal and for the impulse response of the waveguide to narrow-band and broadband transmissions. To suppress the stochastically scattered component of the sound field, one can use a horizontal extended array. However, choosing the experimental site in a region with a mainly smooth ice cover may be more advantageous. It is shown that the frequency band of the received signal can be broadened by introducing a frequency-time correction of the propagation time of the first mode as a function of the sound frequency. 相似文献
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R. A. Vadov 《Acoustical Physics》2002,48(1):24-33
The data of repeated experiments on the long-range propagation of explosion-generated and cw signals in the Norwegian Sea in summer conditions (with a fully-developed underwater sound channel) are presented. These data are used to analyze the spatial and time structures of the sound field, as well as to estimate the attenuation coefficient at frequencies within 63–630 Hz and to determine its frequency dependence. The spatial variability of the propagation conditions is analyzed on the basis of the experimental data obtained for the propagation of explosion-generated signals along a 815-km-long path crossing the Norwegian and Lofoten Hollows. 相似文献
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N. V. Studenichnik 《Acoustical Physics》2003,49(4):455-462
The space-time and frequency-phase stability of the acoustic field is studied for the case of long-range propagation in the underwater sound channel. The possibility of splitting the field components produced by the Doppler effect in the total interference structure of a monochromatic signal is revealed for different ranges, parameters of the channel inhomogeneities, and frequencies. The experiments are performed in summertime in the northwestern part of the Pacific Ocean, near the Kamchatka Peninsula, on a path of 2100 km. Highly stable sound sources with resonant frequencies of 230 and 380 Hz are used for the measurements. The sources are towed at a depth of 70 m with a speed of 5–6 knots. To receive the signal near the channel axis, a bottom-moored (at a depth of 200 m) stationary system is used. The width of the sound beams is studied, and the broadening limits of the frequency spectra are estimated for the coherent and incoherent field components in the case of super-long-range sound propagation. The phase velocities of the split components are determined. 相似文献
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本文介绍近30年来水声信号处理领域理论研究的新进展和在声纳设计中的应用。包括水声信号建模、声场匹配、海洋波导和内波现象的探索和研究、声矢量场信息获取和处理,低频水声信道的时/空相关特性,水下目标辐射噪声的不变特征量提取和检测技术,水下语音、图像传输和抗干扰技术。同时概述,声纳设计的前沿领域:大孔径拖曳线列阵声纳、高分辨力合成孔径声纳、深海传呼机等的发展情况。 相似文献
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Experiments on long-range propagation of low-frequency sound that were conducted starting from the mid-1980s indicate a complex
character of propagation in an underwater sound channel, in which a source and a receiver are located close to the channel
axis. A burst of energy propagating along the axis follows early arrivals, which are well described by the formulas of geometrical
acoustics, in plots of acoustic intensity as a function of propagation time and hydrophone depth. This energy burst cannot
be described using geometrical acoustics because of caustics with caustic beaks located near the channel axis. Very complex
interference processes occur near these caustics. As the distance from the source grows, the dimensions of the interference
vicinity increase and start to overlap producing a peculiar “axial wave.” For an arbitrary two-dimensional underwater sound
channel, the axial wave can be represented as a sum of the first normal modes and a residue. This conclusion is based on the
use of two representations for an acoustic field. The first of them includes the sum of ray components and an axial wave.
The second representation consists of ray addends, the sum of the first normal modes, and a residue. Numerical results are
obtained for a canonical profile of sound velocity at the frequency of 200 Hz for the distances of 1600–1650 km. 相似文献
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When bulk acoustic waves are applied to an optical waveguide, several modulation effects are observed, depending on the type of wave (longitudinal or shear). Longitudinal sound waves frequency-shift the guided light, thus providing a means of modulating light in a wide variety of waveguide materials. Using thin-film mosaic acoustic transducer technology, we have demonstrated such modulation at frequencies in the gigahertz region. By segmenting the acoustic transducer electrodes, the same arrangement can be used for deflecting the light since, with this arrangement, the acoustic field sets up a time-varying grating whose spatial frequency is set by the segment spacing. Theoretical frequency limitations on these devices do not appear to be important until approximately 30 GHz is reached. Thus, they are potentially useful for extremely wide-band data links. Experiments at 1.5 GHz show 30% bandwidth of acoustic modulation using optical heterodyne detection. 相似文献
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从理论上提出一种由局域共振单元组成的声子晶体低频多通道滤波模型.在二维三组元局域共振声子晶体中引入不同填充率的共振单元构成波导结构,通过有限元法计算出其能带结构、透射曲线和透射场图.结果显示:这种设计能够在低频带隙范围内不同填充率散射体的共振频率附近产生新的分立模,且这些分立模能够使相应的声波在声子晶体中沿波导方向传播;这些分立模只与相应的共振单元相关,抗干扰能力强.所得结果为低频多通道滤波器的设计提供了一种新的理论依据. 相似文献
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K. Murawski 《Waves in Random and Complex Media》2004,14(3):467-477
The effect of space- and time-dependent random mass density, velocity, and pressure fields on frequencies and amplitudes of acoustic waves is considered by means of the analytical perturbative method. The analytical results, which are valid for weak fluctuations and long wavelength sound waves, reveal frequency and amplitude alteration, the effect of which depends on the type of random field. In particular, the effect of a random mass density field is to increase wave frequencies. Space-dependent random velocity and pressure fields reduce wave frequencies. While space-dependent random fields attenuate wave amplitudes, their time-dependent counterparts lead to wave amplification. In another example, sound waves that are trapped in the vertical direction but are free to propagate horizontally are affected by a space-dependent random mass density field. This effect depends on the direction along which the field is varying. A random field, which varies along the horizontal direction, does not couple vertically standing modes but increases their frequencies and attenuates amplitudes. These modes are coupled by a random field which depends on the vertical coordinate, but the dispersion relation remains the same as in the case of the deterministic medium. 相似文献
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G. L. Komissarova 《Acoustical Physics》2009,55(3):319-328
The properties of harmonic surface waves in an elastic cylinder filled with a liquid are studied. The case of elastic material for which the shear wave velocity is higher than the sound velocity in a liquid is considered. The wave motion is described based on the complete system of equations of the dynamic theory of elasticity and the equation of motion of an ideal compressible liquid. The asymptotic analysis of the dispersion equation in the region of large wave numbers and qualitative analysis of the dispersion spectrum showed that in such a waveguiding system there exist two surface waves, the Stoneley and the Rayleigh waves. The lowest normal wave forms the Stoneley wave on the internal surface of the cylinder. In this waveguide phase, velocities of all normal waves, except for the lowest one, have the velocity of sound in the liquid as their limit. Therefore, the Rayleigh wave on the external surface of the cylinder is formed by all normal waves in the range of frequencies and wave numbers in which phase velocities of normal waves of the composite waveguide and the lowest normal wave of the elastic hollow cylinder coincide. 相似文献
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The frequency shifts of sound field maxima that are caused by the variability of the medium in an oceanic waveguide are described. The condition under which the time spectrum of the frequency shifts of interference maxima is proportional to the time spectrum of fluctuations in the dispersion characteristic of the waveguide is determined. 相似文献
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Abstract When bulk acoustic waves are applied to an optical waveguide, several modulation effects are observed, depending on the type of wave (longitudinal or shear). Longitudinal sound waves frequency-shift the guided light, thus providing a means of modulating light in a wide variety of waveguide materials. Using thin-film mosaic acoustic transducer technology, we have demonstrated such modulation at frequencies in the gigahertz region. By segmenting the acoustic transducer electrodes, the same arrangement can be used for deflecting the light since, with this arrangement, the acoustic field sets up a time-varying grating whose spatial frequency is set by the segment spacing. Theoretical frequency limitations on these devices do not appear to be important until approximately 30 GHz is reached. Thus, they are potentially useful for extremely wide-band data links. Experiments at 1.5 GHz show 30% bandwidth of acoustic modulation using optical heterodyne detection. 相似文献
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O. P. Galkin V. S. Gostev O. E. Popov L. V. Shvachko R. F. Shvachko 《Acoustical Physics》2006,52(3):252-258
The experimental data on the sound field structure, which were obtained by emitting a continuous pseudonoise signal (a midfrequency of 3.2 kHz) in a two-channel oceanic waveguide, are compared with the calculations performed by the wave program with allowance for the fine structure of the sound speed inhomogeneities. A considerable increase in the intensity of the sound field with a definite angular spectrum is observed in the upper channel in the first shadow zone, and, in the experiment, the increase begins nearer to the sound source than predicted by the wave and ray calculations for a smooth sound speed profile. These features of the field structure are explained by the illumination of the shadow zone by the regular scattering of signals from highly anisotropic fine-structure inhomogeneities of the sound speed profile, which are clearly pronounced in the region of the given oceanic experiment. 相似文献
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Joint statistical moments of mode amplitudes at different frequencies in a random acoustic waveguide
《Waves in Random and Complex Media》2013,23(4):564-580
This paper considers an approximate ray-based analytical approach for evaluating the joint statistical moments of mode amplitudes in an acoustic waveguide with large-scale sound speed fluctuations. Explicit analytic expressions for the statistical moments are derived from an approximate analytical solution of the mode-coupling equations. The analytic solution allows one to deduce a scaling law establishing the connection between amplitudes of modes with the same ratio of the mode number to frequency. The applicability of the ray-based approach for evaluating the joint statistical moments of modes amplitudes including the moments at different frequencies is demonstrated using the Monte Carlo simulation of sound fields in a model of the underwater acoustic waveguide in a deep ocean. Numerical simulation also shows different manifestations of the scaling law. In particular, it is shown how this law manifests itself in the acoustic energy distribution between normal modes, in the jump-like range variations of statistical moments, and in the shape of the correlation function between amplitudes of different modes at different frequencies. 相似文献