单极随钻声波测井换能器感知信号类型的研究

在假定钻铤是光滑的提前下,前人理论模拟了随钻测井的声压波形,但未发表关于理论波形与实验波形的比较的文章。为了认识测量信号所对应的力学类型及相应类型的钻铤波在钻铤内的分布,本文将理论模拟的随钻声波测井波形与实验波形进行对比。与前人单独考虑压电效应或井孔传播效应不同,本文模拟单极随钻声波测井响应时,将发射器、接收器、光滑钻铤和井孔结构作为一个整体,采用有限元法计算模拟了电压源激励下接收器纪录的声压信号和位移信号。将模拟的声压波形与电压信号进行比较,发现二者的钻铤波与斯通利波相对幅值相差较大,而模拟的径向位移波形更接近电压信号。进一步比较理论波形与小模型井内实验测量到的电压信号,证实电压信号更接近位移信号而与声压信号差异明显。这表明当钻铤光滑时,单极随钻声波测井换能器感知的主要是径向位移信号。研究还表明声压信号中的钻铤波能量主要集中在钻铤内壁,径向位移信号中的钻铤波能量主要集中在钻铤外壁。     

Dynamic response of an insonified sonar window interacting with a Tonpilz transducer array

This paper derives and evaluates an analytical model of an insonified sonar window in contact with an array of Tonpilz transducers operating in receive mode. The window is fully elastic so that all wave components are present in the analysis. The output of the model is a transfer function of a transducer element output voltage divided by input pressure versus arrival angle and frequency. This model is intended for analysis of sonar systems that are to be built or modified for broadband processing. The model is validated at low frequency with a comparison to a previously derived thin plate model. Once this is done, an example problem is studied so that the effects of higher order wave interaction with acoustic reception can be understood. It was found that these higher order waves cause multiple nulls in the region where the array detects acoustic energy and that their locations in the arrival angle-frequency plane can be determined. The effects of these nulls in the beam patterns of the array are demonstrated.     

偶极随钻声波测井声压和径向位移响应的差异*

声波测井仪接收到的电信号通常是多个压电片响应的叠加,它主要是由声压还是径向位移响应转化而来,或是两种响应兼有目前未有定论。该文通过实轴积分法和复变函数法计算并对比分析随钻声波测井的声压和径向位移场,发现这两种响应特性有着显著的差异。首先,软地层的偶极随钻测井时,声压信号包含钻铤波和舒尔特波两个波群,而径向位移信号仅有钻铤波波群;其次,单极声源情况下,声压和径向位移信号的钻铤波能量分别集中在钻铤内、外壁,而偶极情况恰好相反,可见,钻铤按照单极情况的分析结果进行刻槽后,高频时的拖尾现象会影响偶极信号中舒尔特波对横波速度的反演。因此,阐明两类信号的差异对横波速度的反演和钻铤波的压制都具有重要意义。     

Signal enhancement in Rayleigh wave interactions using a laser-ultrasound/EMAT imaging system

Enhancement of signal amplitudes from Rayleigh wave interaction at solid surface features has been investigated when signals were detected by an in-plane electromagnetic acoustic transducer (EMAT). A laser-ultrasound system was used to inspect surface-breaking slots, serving as artificial defects. Nd:YAG laser pulses were delivered onto a metal surface via an optical fiber and focused to a line source by a cylindrical lens. An in-plane EMAT receiver detected transient surface acoustic waves. A-scan signals and B-scan images from surface defects revealed increased signal amplitude up to 2.8+/-0.3 depending on the distance of the transducer from a slot. An explanation is based on the interaction of the EMAT sensor with the Rayleigh wave. A supporting computer model was derived to show that experimental signal enhancements were consistent with numerical predictions.     

Finite element modeling of the interaction of laser-generated ultrasound with a surface-breaking notch in an elastic plate

The interaction of surface acoustic waves generated by laser line source in the thermoelastic regime with surface notches are investigated. The finite element method is used to establish the model of the transient displacement field for surface notches with various depths and orientation. The magnitude of the signal enhancement in the near field and the mechanism by which this occurs are explained. The positions of notches were evaluated by the reflected Rayleigh wave. The depths and orientations of the notches were also determined using a shear wave that was generated through mode conversion of a surface acoustic wave at the notch tip. The results agree with previously published experimental measurements.     

Active control of passive acoustic fields: passive synthetic aperture/Doppler beamforming with data from an autonomous vehicle

The maneuverability of autonomous underwater vehicles (AUVs) equipped with hull-mounted arrays provides the opportunity to actively modify received acoustic fields to optimize extraction of information. This paper uses ocean acoustic data collected by an AUV-mounted two-dimensional hydrophone array, with overall dimension one-tenth wavelength at 200-500 Hz, to demonstrate aspects of this control through vehicle motion. Source localization is performed using Doppler shifts measured at a set of receiver velocities by both single elements and a physical array. Results show that a source in the presence of a 10-dB higher-level interferer having exactly the same frequency content (as measured by a stationary receiver) is properly localized and that white-noise-constrained adaptive beamforming applied to the physical aperture data in combination with Doppler beamforming provides greater spatial resolution than physical-aperture-alone beamforming and significantly lower sidelobes than single element Doppler beamforming. A new broadband beamformer that adjusts for variations in vehicle velocity on a sample by sample basis is demonstrated with data collected during a high-acceleration maneuver. The importance of including the cost of energy expenditure in determining optimal vehicle motion is demonstrated through simulation, further illustrating how the vehicle characteristics are an integral part of the signal/array processing structure.     

Source ranging with minimal environmental information using a virtual receiver and waveguide invariant theory

A method is presented for estimating the range of an unknown broadband acoustic source in a waveguide, using a vertical array and a signal sample from another broadband source at a known location relative to the array. The method requires no modeling of the acoustic field, and little to no environmental information for flat bathymetries. Waveguide invariant theory [e.g., D'Spain and Kuperman, J. Acoust. Soc. Am 106, 2454-2468 (1999)] is applied to the "virtual receiver" [Siderius et al., J. Acoust. Soc. Am. 102, 3439-3449 (1997)] to create a "virtual aperture" (VA). In effect, the method effectively converts a source at known range r(g) into a continuum of receivers lying between ranges (1 +/- alpha/beta)*r(g), where beta is a scalar parameter called the acoustic invariant, and alpha approximately 0.1. This effective displacement is achieved by correlating the known source field, measured at frequency component omega, with the unknown source field, measured at frequency component omega + omegas. When the VA output is plotted as a function of omega and omegas, the slope of the resulting correlation contours yields the unknown source range. The concept is illustrated via both simulation and analysis of data collected from a pseudo-random noise source with 75-150-Hz bandwidth during SWellEx-3, a shallow water experiment conducted off the San Diego coast. The virtual aperture can be reformulated for range-dependent environments, if adiabatic propagation assumptions are valid, and if the bathymetry surrounding the array is known.     

不同频段下利用虚拟接收方法的声源测距性能分析

考虑到传统的匹配场处理定位需要复杂的匹配声场计算,并对环境参数和声场模型有很高的依赖,为了克服这种缺点,采用虚拟接收方法对声源进行测距。首先对垂直阵接收到的引导声源和目标声源的信号进行相关处理,得到虚拟接收声场并估计虚拟接收声场干涉条纹的斜率,结合波导不变特征量β对目标声源进行测距。通过数值仿真和2004年南海实验数据处理,讨论了浅海斜坡海域环境中不同频段下利用虚拟接收方法对宽带声源测距的性能。随着频率升高,需要展宽频带以获得完整的干涉条纹和良好的测距结果。在实验数据处理中,选取频段较高的信号时,由于阵列间距偏大不能保证采样的简正波模式的正交归一特性,不能获得正确的测距结果。      

Generation of narrowband Lamb waves based on the Michelson interference technique

An optical method of generating narrowband Lamb waves is presented. It is carried out with a laser line array in a thermoelastic regime implemented by the Michelson interference technique, where the formed array element spacing can be flexibly and conveniently changed to achieve selective mode excitation. In order to simulate the displacement response generated by this array, its intensity distribution function is presented to build a theoretical analysis model and to derive the integral representation of the displacement response. The experimental device and measuring system are built to generate and detect the Lamb waves on a steel plate. Numerical calculation results of narrowband Lamb wave displacement signals based on the theoretical model show good agreement with experimental results.     

Turboprop and rotary-wing aircraft flight parameter estimation using both narrow-band and broadband passive acoustic signal-processing methods

Flight parameter estimation methods for an airborne acoustic source can be divided into two categories, depending on whether the narrow-band lines or the broadband component of the received signal spectrum is processed to estimate the flight parameters. This paper provides a common framework for the formulation and test of two flight parameter estimation methods: one narrow band, the other broadband. The performances of the two methods are evaluated by applying them to the same acoustic data set, which is recorded by a planar array of passive acoustic sensors during multiple transits of a turboprop fixed-wing aircraft and two types of rotary-wing aircraft. The narrow-band method, which is based on a kinematic model that assumes the source travels in a straight line at constant speed and altitude, requires time-frequency analysis of the acoustic signal received by a single sensor during each aircraft transit. The broadband method is based on the same kinematic model, but requires observing the temporal variation of the differential time of arrival of the acoustic signal at each pair of sensors that comprises the planar array. Generalized cross correlation of each pair of sensor outputs using a cross-spectral phase transform prefilter provides instantaneous estimates of the differential times of arrival of the signal as the acoustic wavefront traverses the array.     

Analysis of acoustic channels with a time-evolving sinusoidal surface

Sea-surface movement in the ocean induces a time-varying acoustic channel which affects underwater system including acoustic communication. For an investigation of surface movement effects on communication channel parameters (delay time, amplitude, etc.), acoustic transmission and reception experiments were conducted in the water tank. The delay time and amplitude of single surface bounce path from the measurement data show periodic time dependence, which is caused by a travelling periodic sinusoidal surface. A ray-based propagation model is applied to the experimental environment to estimate communication channel parameters. A comparison between measurement data and model result permit a physical interpretation of the communication channel parameters. The difference of single surface bounce path delay times from the model and measurement data are within small error bound. The delay times oscillate around the delay time of single surface bounce path when the surface is flat and show the periodic sine function. The amplitudes from the model are in agreement with those from the measurement data except at low amplitude region. Slight angle and frequency dependencies of source and receiver and noise in the water tank account for the disagreement in this region. Since the crest and trough of surface wave respectively make the acoustic energy emitted from the source converge and diverge, the amplitudes have high fluctuation and same phase with the delay time. The ray model is applied to an environment in the ocean. A striation pattern appears in surface reflected signal due to shadow zone on the surface.     

Dispersion of the signal of a parametric array in shallow water

Results of an experimental study of shallow-water propagation are presented for a broadband acoustic signal produced by a parametric array. The narrow-beam character of the signal provides single-mode excitation of the oceanic waveguide. The possibility of compression of the broadband signal in the course of its propagation in shallow water is discussed for the case of a specially adjusted frequency modulation. The use of waveguide dispersion leads to an increase in the efficiency of parametric radiation in shallow water.     

Acoustic normal mode fluctuation statistics in the 1995 SWARM internal wave scattering experiment

In order to understand the fluctuations imposed upon low frequency (50 to 500 Hz) acoustic signals due to coastal internal waves, a large multilaboratory, multidisciplinary experiment was performed in the Mid-Atlantic Bight in the summer of 1995. This experiment featured the most complete set of environmental measurements (especially physical oceanography and geology) made to date in support of a coastal acoustics study. This support enabled the correlation of acoustic fluctuations to clearly observed ocean processes, especially those associated with the internal wave field. More specifically, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. Tomography sources of 224 Hz and 400 Hz were moored 32 km directly shoreward of this array, such that an acoustic path was constructed that was anti-parallel to the primary, onshore propagation direction for shelf generated internal wave solitons. These nonlinear internal waves, produced in packets as the tide shifts from ebb to flood, produce strong semidiurnal effects on the acoustic signals at our measurement location. Specifically, the internal waves in the acoustic waveguide cause significant coupling of energy between the propagating acoustic modes, resulting in broadband fluctuations in modal intensity, travel-time, and temporal coherence. The strong correlations between the environmental parameters and the internal wave field include an interesting sensitivity of the spread of an acoustic pulse to solitons near the receiver.     

Noise immunity of a combined hydroacoustic receiver

A statistical analysis of the noise immunity of a combined receiver is performed for the observation of a fluctuating tone signal against the background of underwater dynamic noise. The analysis is based on the experimental data obtained in deep ocean with the use of two four-component combined hydroacoustic receivers positioned at depths of 150 and 300 m. Theoretical expressions are obtained for the signal-to-noise ratio of a combined receiver, for reciprocal spectral levels of the signal and noise in both narrow and wide frequency bands. The definition of the combined receiver gain is introduced in terms of the functions of a common single-point coherence for the acoustic pressure and the particle velocity in an acoustic wave. According to the experimental data obtained, in the case of multiplicative processing, the maximal gain in the signal-to-noise ratio of a combined receiver, as compared to a hydrophone-based square-law detector, can reach 15–16 dB for the horizontal channel and 30 dB for the vertical channel of the combined receiver in the case of the compensation of opposing flows of the signal and noise energy.     

Anomalous sea surface reverberation scale model experiments

Low frequency sea surface sound backscattering from approximately 100 Hz to a few kHz observed from the 1960s broadband measurements using explosive charges to the Critical Sea Test measurements conducted in the 1990 s is substantially higher than explained by rough sea surface scattering theory. Alternative theories for explaining this difference range from scattering by bubble plumes/clouds formed by breaking waves to stochastic scattering from fluctuating bubble layers near the sea surface. In each case, theories focus on reverberation in the absence of the large-scale surface wave height fluctuations that are characteristic of a sea that produces bubble clouds and plumes. At shallow grazing angles, shadowing of bubble plumes and clouds caused by surface wave height fluctuations may induce first order changes in the backscattered signal strength. To understand the magnitude of shadowing effects under controlled and repeatable conditions, scale model experiments were performed in a 3 m x 1.5 m x 1.5 m tank at the Technical University of Denmark. The experiments used a 1 MHz transducer as the source and receiver, a computer controlled data acquisition system, a scale model target, and a surface wave generator. The scattered signal strength fluctuations observed at shallow angles are characteristic of the predicted ocean environment. These experiments demonstrate that shadowing has a first order impact on bubble plume and cloud scattering strength and emphasize the usefulness of model scale experiments for studying underwater acoustic events under controlled conditions.     

Investigation of the phase velocities of guided acoustic waves in soft porous layers

A new experimental method for measuring the phase velocities of guided acoustic waves in soft poroelastic or poroviscoelastic plates is proposed. The method is based on the generation of standing waves in the material and on the spatial Fourier transform of the displacement profile of the upper surface. The plate is glued on a rigid substrate so that it has a free upper surface and a nonmoving lower surface. The displacement is measured with a laser Doppler vibrometer along a line corresponding to the direction of propagation of plane surface waves. A continuous sine with varying frequencies was chosen as excitation signal to maximize the precision of the measurements. The spatial Fourier transform provides the wave numbers, and the phase velocities are obtained from the relationship between wave number and frequency. The phase velocities of several guided modes could be measured in a highly porous foam saturated by air. The modes were also studied theoretically and, from the theoretical results, the experimental results, and a fitting procedure, it was possible to determine the frequency behavior of the complex shear modulus and of the complex Poisson ratio from 200 Hz to 1.4 kHz, in a frequency range higher than the traditional methods.     

可听声频段的声学超材料

制作了一维周期排列的亥姆霍兹共振器超材料,在空气环境下测试了其在可听声频段声学透射行为.实验结果表明,在2.1—3.5 kHz附近该材料具有透射衰减的吸收峰,利用声传输线理论（ATLM）计算的透射率和实验结果一致,同时由计算的等效阻抗分析可知,实验中出现的吸收峰是由HRs共振的回波反射引起的.另外,实验测试的样品中透射信号分布进一步验证了材料的共振效应,也就是会出现与外加激励反相响应.基于前述的共振模型计算出该材料的等效弹性模量为负. 关键词： 亥姆霍兹共振器 声传输线 吸收峰 等效弹性模量     

The effect of anisotropy of a rough sea surface on the generation of acoustic radiation

A model that relates the frequency-angular characteristics of wind waves on the sea surface to the frequency spectrum of acoustic radiation generated by them is constructed. Based on empirical wave energy distribution functions, it is shown that, in the vicinity of the peak of the wind wave spectrum, the intensity of acoustic radiation strongly depends on the model chosen for the angular distribution function ?(α) and on its parameters. At high frequencies, four to five times higher than the dominant wave frequency, it is possible to assume that, to a first approximation, ?(α) = const. In the intermediate frequency range, between the dominant frequency and the high frequencies, the predominant contribution to the sound radiation is made by the waves that travel in the direction close to orthogonal with respect to the wind.     

具有单相单向换能器的水平剪切声表面波压力传感器插入损耗特性

为实现水平剪切声表面波压力传感器低损耗设计,系统研究了均匀叉指换能器(IDT)和单相单向换能器(SPUDT)器件的声波能量损耗性能。在确定最优反射系数的SPUDT结构的基础上,建立3D周期性有限元仿真模型,计算器件表面振动位移和双向输出电压瞬态响应。通过对电压信号进行傅里叶变换获得器件模型的插入损耗,并制备两种不同换能器的声学传感器,测试其频率特性和灵敏度。与均匀IDT相比,基于SPUDT器件插入损耗的仿真和实验结果分别降低了5.2 dB和5.6 dB,SPUDT器件灵敏度约为均匀IDT器件的两倍。结果表明,SPUDT能有效降低SH-SAW压力传感器声波能量的单向损耗,提高检测灵敏度,且构建的3D周期性有限元仿真模型有助于声学传感器的声波损耗分析,实现高精度和小型化的声学测量系统。      

方位偶极声波远探测技术研究与应用

偶极横波远探测测井技术是当前缝洞型和复杂储层油气勘探开发和评价不可缺少的技术手段。常规偶极远探测技术受限于180?方位的不确定性,难以判别缝洞等地质体的真实方位。采用双偶极错位发射多分量阵列接收研究偶极方位识别方法。首先以传统正交偶极模式获得地质体方位探测结果,再以45?错位角发射偶极声波信号,通过多个邻近接收器的波形差的组合以及反射波在仪器孔径上的时间延迟来区分方位,进一步压制伪像干扰获得地质体真实的方位成像结果。针对弱反射信号,在硬件上,研究了多分量有源接收器阵列声系,有效提升了偶极声波信号信噪比,结合动态增益控制提升反射波幅度;研究了双偶极宽频发射器与多模式发射技术,提高偶极发射功率,保证了偶极声波信号在地层中的远距离传播与反射。数值仿真与实际测井数据表明,双偶极方位识别方法可行,有助于偶极横波远探测技术的进一步发展和应用。