共查询到20条相似文献,搜索用时 125 毫秒
1.
The paper studies the interference structure of low-frequency tonal and wideband signals in shallow water, received by four-component vector-scalar modules. The spatial amplitudes and phase characteristics of the scalar field are analyzed, as well as three components of the vibration velocity vector and the power flux vector. A relationship is established between the zone of interference maxima and minima and the phase gradient in the horizontal and vertical plane, the change in direction of the vertical and horizontal components of the vibration velocity vector, and the change in the depression angle of the power flux vector in the horizontal plane. 相似文献
2.
Spatial attenuation of different sound field components in a water layer and shallow-water sediments
The paper presents the results of an experimental study of spatial attenuation of low-frequency vector-scalar sound fields in shallow water. The experiments employed a towed pneumatic cannon and spatially separated four-component vector-scalar receiver modules. Narrowband analysis of received signals made it possible to estimate the attenuation coefficients of the first three modes in the frequency of range of 26–182 Hz and calculate the frequency dependences of the sound absorption coefficients in the upper part of bottom sediments. We analyze the experimental and calculated (using acoustic calibration of the waveguide) laws of the drop in sound pressure and orthogonal vector projections of the oscillation velocity. It is shown that the vertical projection of the oscillation velocity vector decreases significantly faster than the sound pressure field. 相似文献
3.
We obtain in integral and analytic form the relations for calculating the amplitude and phase characteristics of an interference structure of orthogonal projections of the oscillation velocity vector in shallow water. For different frequencies and receiver depths, we numerically study the source depth dependences of the effective phase velocities of an equivalent plane wave, the orthogonal projections of the sound pressure phase gradient, and the projections of the oscillation velocity vector. We establish that at low frequencies in zones of interference maxima, independently of source depth, weakly varying effective phase velocity values are observed, which exceed the sound velocity in water by 5–12%. We show that the angles of arrival of the equivalent plane wave and the oscillation velocity vector in the general case differ; however, they virtually coincide in the zone of the interference maximum of the sound pressure under the condition that the horizontal projections of the oscillation velocity appreciably exceed the value of the vertical projection. We give recommendations on using the sound field characteristics in zones with maximum values for solving rangefinding and signal-detection problems. 相似文献
4.
The correlation of low-frequency sound signals from towed tonal low-frequency sources at the output of the scalar and vector channels is studied in shallow water. The correlation of the scalar field and signal received by a horizontally oriented vector receiver on average is 0.92–0.99; correlation with the signal received by a vertical vector receiver decreases to 0.66–85. When scalar fields or horizontal projections of the vibration velocity vector with application of the aperture synthesis algorithm are used, 3–5 normal waves are isolated; when the vertical component is used, 7–9 modes. It is demonstrated that the high signal correlation ensures direction-finding accuracy and suppression of strongly noise-emitting moving sources by 20–30 dB or more if the cardioid is directed at the source according to the zone of the minimum. 相似文献
5.
N. N. Komissarova 《Acoustical Physics》2003,49(4):435-443
The noise field anisotropy of surface sources in a coastal region with an arbitrary three-dimensional bottom relief and an arbitrary sound velocity profile is investigated. The results of computations performed by a computer code in two stages are presented. The first stage consists in the computation of horizontal rays, i.e., the projections of the real rays multiply reflected from the bottom and sea surface onto the horizontal plane. The second stage summarizes the contributions of the noise sources lying within the surface elements that are cut out on the sea surface by a narrow ray tube launched from the point of observation in a given direction. The computations show that, in the coastal region, the noise field is essentially anisotropic, and this anisotropy occurs not only in the vertical plane, which is characteristic of the deep ocean, but in the horizontal plane as well. 相似文献
6.
Analytical approximations are derived and a computer simulation is performed in order to study the regularities determining the decay of the components of vibration velocity vectors and low-frequency signal intensity with an increase in distance. It is established that the sound pressure and horizontal components of the vibration velocity and intensity decay similarly, whereas the vertical components decay more rapidly. It is shown that approximating dependences are determined to a great extent by the distance between the source and detectors and are in good agreement with the exact laws describing the decay of the regular field part. 相似文献
7.
We have measured the spectrum of velocity fluctuations in a granular system confined to a vertical plane and driven into a homogeneous, steady state by strong vertical vibration. The distribution of horizontal velocities is not Maxwell-Boltzmann and is given by P(v) = Cexp[-beta(|v|/sigma)(alpha)] where alpha = 1.55+/-0.1 at all frequencies and amplitudes investigated, and also for varying boundary conditions. The deviation from Maxwell-Boltzmann statistics occurs in the absence of spatial clustering and does not result from an inhomogeneous average over regions of varying local density. Surprisingly, P(v) has the same shape over a wide range of densities. 相似文献
8.
We obtain, and compare with exact solutions, the approximate analytic relations that determine, for increasing distance, irregularities of attenuation in the regular sound pressure components and orthogonal projections of the oscillation velocity vectors of low-frequency signals formed in a waveguide by various multipoles. We show that the mentioned field characteristics essentially depend on the type of multipole, the distance between the source and receivers, and the specific features of the received scalar or vector field components. It is established that the approximating dependences agree well with the exact laws of attenuation in the field and, despite the variety of dependences, they are divided into three compact groups with uniform characteristics. 相似文献
9.
The results of direction finding of broadband pulses from a pneumatic source, towed along an arc at a distance of 11 to 12 km, using spatial-diversity scalar detectors and vector-scalar modules are compared. The problem of direction finding based on power flux and according to a new method, using artificial vectors constructed from components of only vibration velocity vector, is solved. It is shown that, despite the complicated conditions for sound propagation, the error of direction finding using 100-m-aperture scalar detectors and single (point) vector-scalar detectors is almost the same and does not exceed 1 to 2°. The results of direction finding according to all algorithms are in good agreement. A method for suppressing noise from a local source by a four-component vector-scalar detector has been developed and investigated. A real possibility of increasing the signal-to-noise ratio on scalar detectors to 10?15 dB is established. Application of the developed suppression algorithm is found to increase noise immunity of the detection and direction finding. 相似文献
10.
A combined experimental and theoretical method is proposed for finding the vibration sources in mechanoacoustic systems. The method is similar to the wave front inversion and time reversal focusing methods used in optics and acoustics. The method performs coherent measurements of the vibration field at a set of points and employs the reciprocity principle in its theoretical part. To enhance the stability of the method, modifications are proposed that perform nonlinear processing of vibration fields calculated by the finite element method. Possibilities of using the method in self-testing vibrating systems are discussed. 相似文献
11.
Three different approaches of the equivalent source method for simulating scattered fields are compared: two of them deal with monopole sets, the other with multipole expansions. In the first monopole approach, the sources have fixed positions given by specific rules, while in the second one (ESGA), the optimal positions are determined via a genetic algorithm. The ‘pros and cons’ of each of these approaches are discussed with the aim of providing practical guidelines for the user. It is shown that while both monopole techniques furnish quite good pressure field reconstructions with simple source arrangements, ESGA requires a number of monopoles significantly smaller and, with equal number of sources, yields a better precision. As for the multipole technique, the main advantage is that in principle any precision can be reached, provided the source order is sufficiently high. On the other hand, the results point out that the lack of rules for determining the proper multipole order necessary for a desired precision may constitute a handicap for the user. 相似文献
12.
13.
The reciprocity measurement theory in anomalous reverberant sound fields was investigated.An improved method Was proposed due to the interrelated errors.The source volume velocity Was corrected by spatial average of measurement results and evaluation of the reverberant sound field influence on acoustic energy density.The result was validated in underwater experiment,corrected reciprocity measurement results were almost the same as direct measurement results.It indicates that reverberant sound field does not affect the validitv of the principle,but influences the obtainment of source volume velocity,then influences the measurement of transfer functions with the principle.The proposed method is simple and effective in anomalous reverberant sound fields.The study mav be valuable for the applications which are based on the principle. 相似文献
14.
A. O. Marakulin O. S. Sazhina M. V. Sazhin 《Journal of Experimental and Theoretical Physics》2012,115(1):85-92
The possibility of the influence of adiabatic scalar perturbations on the angular velocity spectrum of extragalactic sources is considered. The multipole expansion coefficients of the angular velocity field in terms of vector spherical harmonics are calculated. We show that there is no contribution from adiabatic perturbations to the angular spectrum for a spatially flat Universe at the dusty stage, while there is a contribution only to the electric multiple coefficients at the stage of ??-term domination. The cases of long-wavelength and short-wavelength perturbations are considered separately. The relationship between the multipole angular velocity spectrum and the primordial scalar perturbation spectrum is discussed. 相似文献
15.
16.
软X射线谱学显微光束线单色器结构设计及精度测试 总被引:2,自引:0,他引:2
针对上海光源谱学显微光束线站的性能要求,对其核心部件单色器进行结构设计。阐述了单色器的扫描运动原理,论述了波长扫描机构的设计方案,具体分析平面镜和光栅的转角重复精度影响因素;描述光栅切换机构,着重分析其水平偏差、垂直偏差、滚角、摆角和投角的精度问题;采用六杆并联机构的方案完成镜箱调节机构的设计,分析其支杆的调节范围和分辨力情况。给出了单色器的结构,并且对其精度进行了测试。测试结果表明,平面镜和光栅的转角重复精度分别为0.166″和0.149″;光栅切换机构的滚角、摆角和投角的重复精度分别为0.08″、0.12″和0.05″。这说明了单色器的结构设计方案和机械精度满足技术要求。 相似文献
17.
It is shown that scalar, horizontal, and vertical vector receivers efficiently split modes of different numbers, which makes it possible to analyze the mode structure and estimate the characteristics of surface layers of a shallow sea bottom. To analyze the mode structure of propagating pulses from a towed pneumatic source, Winger transform was applied, with which seven modes were isolated by vertical vector receivers, whereas the scalar receivers and horizontal vector receivers isolated only three modes. It is established that the use of four-component vector-scalar receivers makes it possible to increase the accuracy in estimating the parameters of a layered bottom model. 相似文献
18.
采用湍流统计理论、谱分析和快速畸变理论研究稳定分层二层流非湍流/湍流层无平均剪切密度界面处的湍流.分别在密度界面厚度(h)可忽略和很薄两种情况下,推导出任意理查森数(Ri)Ri→∞时,湍流层中水平、垂直方向速度的欧拉频谱和水平、垂直方向均方根速度的积分表达式.在h可忽略情况下:(1)任意Ri,Ri→∞时,密度界面对大尺度涡的影响显著,而对小尺度涡几乎无影响;距离密度界面越近,湍流层中水平方向均方根速度增大而垂直方向均方根速度减小;(2)任意Ri且在无量纲频率较大时,密度界面处、湍流层中水平、垂直方向速度的欧拉频谱满足-5/3幂次律,但是,它们不收敛于同一直线,表明密度界面处部分湍流转化为内波.在h很薄的情况下:(1)在水平方向上密度界面对湍流无显著的影响;湍流层中垂直方向速度的欧拉频谱出现过渡区,不满足-5/3幂次律,其幂次律增大,表明湍流过渡区的能量减少,但是,密度界面对线性小尺度涡仍几乎无影响;(2)距离密度界面越远,密度界面厚度对湍流的影响减弱并且偏向于线性中尺度涡;当远离密度界面时,过渡区消失,表明考虑密度界面厚度后密度界面对湍流的影响范围有限;(3)密度界面处垂直方向速度的欧拉频谱的幂次律减小,表明密度界面处线性内波的能量向线性低频区集中;(4)随着密度界面厚度增加,密度界面处垂直方向速度的欧拉频谱在整个线性内波频域里等幅度减小,湍流层中垂直方向速度的欧拉频谱只在线性低频区域减小且减小的幅度随着频率增大而减小;密度界面对湍流层中水平、垂直方向均方根速度影响的垂向范围随Ri增大而减小. 相似文献
19.
Auditory resolution of moving sound sources was determined in a simulated motion paradigm for sources traveling along horizontal, vertical, or oblique orientations in the subjects's frontal plane. With motion restricted to the horizontal orientation, minimum audible movement angles (MAMA) ranged from about 1.7 degrees at the lowest velocity (1.8 degrees/s) to roughly 10 degrees at the highest velocity (320 degrees/s). With the sound moving along an oblique orientation (rotated 45 degrees relative to the horizontal) MAMAs generally matched those of the horizontal condition. When motion was restricted to the vertical, MAMAs were substantially larger at all velocities (often exceeding 8 degrees). Subsequent tests indicated that MAMAs are a U-shaped function of velocity, with optimum resolution obtained at about 2 degrees/s for the horizontal (and oblique) and 7-11 degrees/s for the vertical orientation. Additional tests conducted at a fixed velocity of 1.8 degrees/s along oblique orientations of 80 degrees and 87 degrees indicated that even a small deviation from the vertical had a significant impact on MAMAs. A displacement of 10 degrees from the vertical orientation (a slope of 80 degrees) was sufficient to reduce thresholds (obtained at a velocity of 1.8 degrees/s) from about 11 degrees to approximately 2 degrees (a fivefold increase in acuity). These results are in good agreement with our previous study of minimum audible angles long oblique planes [Perrott and Saberi, J. Acoust. Soc. Am. 87, 1728-1731 (1990)].(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
20.
V. M. Kuz’kin G. N. Kuznetsov S. A. Pereselkov V. A. Grigor’ev 《Physics of Wave Phenomena》2018,26(2):150-159
Results of a computer simulation of the resolution of three noise sources with different intensities against the background of isotropic noise in an oceanic waveguide are presented. A comparative analysis of the error in determining their coordinates (bearing, radial velocity, distance, depth) is performed. A computational experiment is implemented based on the interferometric method of source localization using vector-scalar receivers. 相似文献