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1.
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2.
Matched-field inversion of sound speed profile in shallow water using a parallel genetic algorithm 总被引：1，自引：0，他引：1
A sound speed profile plays an important role in shallow water sound propagation. Concurrent with in-situ measurements, many
inversion methods, such as matched-field inversion, have been put forward to invert the sound speed profile from acoustic
signals. However, the time cost of matched-field inversion may be very high in replica field calculations. We studied the
feasibility and robustness of an acoustic tomography scheme with matched-field processing in shallow water, and described
the sound speed profile by empirical orthogonal functions. We analyzed the acoustic signals from a vertical line array in
ASIAEX2001 in the East China Sea to invert sound speed profiles with estimated empirical orthogonal functions and a parallel
genetic algorithm to speed up the inversion. The results show that the inverted sound speed profiles are in good agreement
with conductivity-temperature-depth measurements. Moreover, a posteriori probability analysis is carried out to verify the inversion results. 相似文献
3.
针对在全三维水力压裂物理模拟实验中,水力裂缝实时扩展形态无法准确描述的问题,利用被动声波监测技术,研究水力裂缝在超大型(762cm×762cm×914cm)天然砂岩岩样中的扩展机理.结果表明:水力压裂裂缝呈经典的径向形态扩展,与实际裂缝形态一致;实验条件下,径向裂缝延伸净压力受断裂韧性的控制,与通常现场裂缝延伸净压力受流体黏性控制有很大区别.为与现场裂缝扩展进行相似对比,建议物模实验参数设计应适当提高液体黏度及排量,同时降低岩样断裂韧性.声波监测技术在超大尺寸水力压裂实验中的应用,可为现场水力压裂裂缝微地震监测技术应用提供指导. 相似文献
4.
KANG Ying PENG LinhuiDepartment of Physics Ocean University of China Qingdao P.R.China 《中国海洋大学学报(英文版)》2003,2(2):218-223
The variations of ocean environmental parameters invariably result in variations of local modal wave numbers of a sound pressure field. The asymptotic Hankel transform with a short sliding window is applied to the complex sound pressure field in the water containing a mesoscale eddy to examine the variation of local modal wave numbers in such a range-dependent environment. The numerical simulation results show that modal wave number spectra obtained by this method can reflect the location and strength of a mesoscale eddy, therefore it can be used to monitor the strength and spatial scale of ocean mesoscale eddies. 相似文献
5.
Because the sound speeds of seawater and seafloor sediment both increase with temperature,the influence of tempera-ture on the bottom reflection characteristics of seafloor sediments needs to be investigated.Based on the calculation of the temperature-controlled experimental measurement data of typical seafloor surface sediment samples,the temperature-dependent acoustic characteristics,including acoustic impedance,acoustic impedance ratio between surface sediment and seawater,and reflection coefficient,were analyzed.The effective density fluid model was used to analyze and explain the reflection coefficient variation of surface sediments with temperature and predict the dispersion characteristics.Results show that the acoustic impedance of the seabed sediment increases with temperature,whereas the acoustic impedance ratio and acoustic reflection coefficient slightly decrease.The acoustic impedance,acoustic impedance ratio,and acoustic reflection coefficient of sandy,silty,and clayey sediments vary similarly with tem-perature variation.Moreover,the influence of temperature on these acoustic characteristics is independent of detection frequencies. 相似文献
6.
We performed a long range acoustic propagation experiment in the South China Sea (SCS) in November 2004. The environment of the experiment was with an isothermal sound speed profile, where influence of water volume fluctuation was small, meaning that bottom parameters can be well estimated from acoustic signals. We inverted the acoustic parameters of sediment by using a hybrid inversion scheme that combines the matched field processing inversion with Hamilton sediment empirical relationship and transmission loss data. The numerical results show excellent agreement with the experiment data, indicating validity of the inverted parameters. 相似文献
7.
Sound propagation in a deep ocean two-axis underwater channel is often complex and difficult to simulate between surface channel and sound fixing and ranging (SOFAR) channel. The beam-displacement ray-mode (BDRM) theory is a normal mode method for propagation modeling in horizontally stratified shallow water. An improved method for computing the upper boundary reflection coefficient in the BDRM is proposed and applied to calculate the acoustic fields of a two-axis underwater channel. Transmission losses in the two-axis underwater channel are calculated in the new BDRM. The corresponding results are in good agreement with those from the Kraken code, and furthermore the computed speed of the new BDRM excels the other methods. 相似文献
8.
We simulated the temporal correlation of sound transmission using a two-dimensional advective frozen-ocean model with temperature
data from a temperature sensor array on a propagation path in the South China Sea (SCS) Experiment 2009, and investigated
the relationships of temporal correlation length, source-receiver range, and maximal sound speed fluctuation mainly caused
by the solitary internal waves. We found that the temporal correlation length is −1.2-power dependent on source-receiver range
and −0.9-power dependent on maximal sound speed fluctuation. The empirical relationship is deduced from one-day environmental
measurements in a limited area, needing more works and verification in the future with more acoustic data. But the relationship
is useful in many applications in the area of SCS Experiment 2009. 相似文献
9.
Jianming Gong Xunhua Zhang Changchun Zou Qiang Chen Lichen Wang Chunfang Yuan Gaowei Hu Yubo Jiang 《中国海洋大学学报(英文版)》2014,13(5):742-746
To revise P-wave velocity and thickness of the hydrate layer in the Shenhu area of the South China Sea, acoustic and resistivity logging curves are reanalyzed. The waterlogging phenomenon is found in the shallow sediments of five drilling wells, which causes P-wave velocity to approximate the propagation velocity of sea water(about 1500 m s-1). This also affects the identification of the hydrate layer and results in the underestimate of its thickness. In addition, because there could be about a 5 m thick velocity ramp above or below the hydrate layer as interpreted by acoustic and resistivity logging curves, the recalibrated thickness of this layer is less than the original estimated thickness. The recalibrated P-wave velocity of the hydrate layer is also higher than the original estimated velocity. For the drilling well with a relatively thin hydrate layer, the velocity ramp plays a more important role in identifying and determining the thickness of the layer. 相似文献
10.
《中国海洋大学学报(英文版)》2021,(5)
In this study, power spectral density and inverse analyses were performed to obtain the frequency characteristics and spatial distribution of temperature in the Qiongzhou Strait using reciprocal sound transmission data obtained in a coastal acoustic tomography experiment conducted in 2013. The results reveal three dominant types of internal tides(diurnal, semidiurnal, and terdiurnal).Spectral analysis of the range-average temperature deviation along the northern and southern transmission paths shows that along the northern path, the energy of the diurnal internal tides was significantly larger than that of the semidiurnal tides. The semidiurnal internal tides, in contrast, were more pronounced along the southern path. A terdiurnal spectrum with an energy level equivalent to that of the semidiurnal internal tide was discernable for both the northern and southern paths. These three types of internal tides can also be recognized in the time variation of the zonal-average temperature deviation. The diurnal internal tides were strengthened along the northern coast, implying their westward propagation and the existence of coastally trapped effects. The other two types of internal tides, which have smaller wavelengths than the diurnal internal tides, were less resolved over the entire tomographic domain due to the insufficient resolution of the inversion. The data quality was verified to be satisfactory by error estimation. 相似文献
11.
A THIRD GENERATION SHALLOW WATER WAVE NUMERICAL MODEL-YE-WAM 总被引：5，自引：0，他引：5
This paper pnesents a third gneration shallow Whter disode spedtal wave nbotal medeIYE-WAM based on the spedtal action balance equation. The mode accounts for all edevan effectsof currents on waves, incuding tmpotally and spatialy varying depth and current inded refraction,sttalning and fequency shift and also explidtly takeS into aanunt all source terms, speclally adePth-limited breaking dheipation. In addition, an energy forcing scheme is propond and applied to themode's open boundaries to areUn for the propagution of sedIs into the study spstem The upwinddiffeIenng scheme and a standard hybrid diffdrencing scheme for the propagaion terrn and a simpleEuler method for the source teme are employed. 相似文献
12.
Achieving reliable underwater communication in shallow water acoustic channels is a difficult because of the random time-varying nature of multipath propagation,severe amplitude fluctuation,and spatial variability of the channel conditions.This paper describes a new signal processing technique-frequency coding and decoding by means of real-time measurement of signal width,jamming and suppressing multipath interference and using redundant coder.The application of the technique to thd model ZTY-1 status monitor for underwater system of seabed is introduced in this paper.The main principle,the technique specifications and the key techniques of the system are discussed here.Theoretical estimations and experimental results proved that the performance of the system is excellent.The method can be used for some other related low-data-rate data transmission detecting in shallow water acoustic channel. 相似文献
13.
In order to investigate the permeability of porous media,it is necessary to figure out the property of wave propagation in this medium. The authors calculated the full waveforms and the 2-dimensional spectrum of fluid saturated porous media,analyzed the wave propagation characteristics of different permeable stratums. From the theoretical acoustic pressure waveform received at the well-axis and the 2-D spectrum it is revealed that longitudinal-,transverse-,Stoneley-,pseudo-Rayleigh-,longitudinal mode-and transverse mode waves are different in characters in various permeable strata. Stoneley wave is sensitive to the change of permeability,and its frequency range and amplitude attenuation are influenced by permeability. 相似文献
14.
碳酸盐岩声波传播特征具有重要的应用价值,系统性地分析流体类型、流体压力、温度及围压对碳酸盐岩声波速度与频谱特性影响的研究仍需加强。选取四川盆地合川-潼南地区灯影组缝洞碳酸盐岩,开展了不同条件下的声波透射实验,分析了围压、孔隙压力、压力差、温度及流体类型对碳酸盐岩样品声波速度的影响及不同条件下透射声波的主频特征。研究结果表明:饱和地层水时声波速度对压力变化的敏感度较饱和氮气时低。压力变化过程中,声波速度变化幅度与岩样孔隙度为正相关关系。实验温度范围内,随着温度逐渐升高,饱和地层水、氮气岩心纵波速度、横波速度均小幅降低。当差应力较低时,通过改变孔隙压力来改变差应力的方式对应的声波速度大于通过改变围压来改变差应力方式对应的声波速度,当差应力较高时,结论相反。相同差应力条件下,声波速度对围压变化较孔隙压力变化更为敏感。定围压变孔隙压力与定孔压变围压曲线所对应的2条声波速度-差应力关系曲线的夹角及斜率差可定性反映岩样动态Biot有效应力系数相对大小。随着差应力增大,孔隙压力对有效应力的贡献逐渐降低。随着孔隙压力增大,纵波主频幅值、横波主频幅值均逐渐下降,随着围压增大,纵波主频幅值、横波主频幅值均逐渐增大,随着温度逐渐升高,纵波主频幅值、横波主频幅值均逐渐增大。研究结果有助于基于测井声波信息开展碳酸盐岩地层孔隙压力预测相关理论研究及工程应用。 相似文献
15.
Harmful algal blooms(HABs),caused by the overgrowth of certain phytoplankton species,have negative effects on marine environments and coastal fisheries.In addition to cell-counting methods using phytoplankton nets,a hydroacoustic technique based on acoustic backscattering has been proposed for the detection of phytoplankton blooms.However,little is known of the acoustic properties of HAB species.In this study,as essential data to support this technique,we measured the acoustic properties of two HAB species,Akashiwo sanguinea and Alexandrium affine,which occur in the South Sea off the coast of Korea.Due to the small size of the target,we used ultrasound for the measurements.Experiments were conducted under laboratory and field conditions.In the laboratory experiment,the acoustic signal received from each species was directly proportional to the cell abundance.We derived a relationship between the cell abundance and acoustic signal received for each species.The measured signals were compared to predictions of a fluid sphere scattering model.When A.sanguinea blooms appeared at an abundance greater than 3 500 cells/mL,the acoustic signals varied with cell abundance,showing a good correlation.These results confirm that acoustic measurements can be used to detect HAB species. 相似文献
16.
The sound velocity of seafloor sediments from shallow seas can provide important information for harbor design, and ocean and seacoast engineering projects. In this study, in situ measurements were used to obtain accurate sediment sound velocities at 45 stations offshore of Qingdao. The relationships between the sound velocity and granular properties of the seafloor sediments were analyzed. Sound velocity showed an increase with the sand content, sand-clay ratio, and sorting coefficient; and a nonlinear decreasing trend with increasing mean grain size and clay content. We plotted a sound velocity distribution map, which shows that the sound velocity was closely related to the geological environment. Previous empirical equations suggested by Hamilton, Anderson, and Liu were used to calculate the velocity with grain size. A comparison between the measured and calculated velocities indicates that the empirical equations have territorial limitations, and extensive data are essential to establish global empirical equations. Future work includes the calibration of the laboratory acoustic measurements with an in situ technique. 相似文献
17.
证明了流体力学边界层理论中著名的Blasius方程的一个新性质,它在二维平板流的研究中具有重要的作用,由此建立它的积分形式,并给出方程中的临界值βc的分析估计。 相似文献
18.
证明了流体力学边界层理论中著名的Blasius方程的一个新性质,它在二维平板流的研究中具有重要的作用,由此建立它的积分形式,并给出方程中的临界值βc的分析估计。 相似文献
19.
X.H.Wang 《中国海洋大学学报(英文版)》2004,3(2):115-122
Floc breakup dynamics are studied by a sediment transport numerical model in an idealized tidal estuary that has a constant water depth and rapid flocculation of cohesive sediments. The focus is placed on the effects of boundary layer stratification induced by a bottom nepheloid layer on floc breakup and size distribution in the water column. In a neutrally stratified estuary, the floc size distribution follows a parabolic function with maximum values at the surface and bottom. The sediment-induced stratification in the bottom boundary layer increases the median floc sizes. Furthermore, sediment-voided convection caused by the settling lutocline generates significant turbulent kinetic energy dissipation and reduces floc size at the depth where the convective mixing happens. Below that depth, a weak local maxima in the floc size is predicted due to presence of the lutocline. The effect of sediment-stratified bottom boundary layer on the floc breakup can be consistently approximated by a linear regression between the maximal floc size and flux Richardson number. 相似文献
20.
X. H. Wang 《中国海洋大学学报(英文版)》2004,3(2):115-122
Floe breakup dynamics are studied by a sediment transport numerical model in an idealized tidal estuary that has a constant
water depth and rapid flocculation of cohesive sediments. The focus is placed on the effects of boundary layer stratification
induced by a bottom nepheloid layer on floe breakup and size distribution in the water column. In a neutrally stratified estuary,
the floe size distribution follows a parabolic function with maximum values at the surface and bottom. The sediment-induced
stratification in the bottom boundary layer increases the median floe sizes. Furthermore, sediment-voided convection caused
by the settling lutocline generates significant turbulent kinetic energy dissipation and reduces floe size at the depth where
the convective mixing happens. Below that depth, a weak local maxima in the floe size is predicted due to presence of the
lutocline. The effect of sediment-stratified bottom boundary layer on the floe breakup can be consistently approximated by
a linear regression between the maximal floe size and flux Richardson number. 相似文献