倾斜层声速简化计算

本文根据地层下边界倾斜角ф较小的情况,对张越等发表的任意倾斜层声速计算方法的研究(1992年第3期182—186)提出的求解方法进行了简化。     

Localisation and phase transition of acoustic waves in a soft medium containing air bubbles

We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are particularly investigated in various cases for distinguishing efficiently the acoustic localisation from the effects of acoustic absorption caused by the viscosity of medium. The numerical results reveal the phenomenon of `phase transition' characterized by an unusual collective oscillation of bubbles, which is an effective criterion to unambiguously identify the acoustic localisation in the presence of viscosity. Within the localisation region, the phenomenon of phase transition persists, and a remarkable decrease in the fluctuation of the oscillation phases of bubbles is observed. The localisation phenomenon will be impaired by the enhancement of the viscosity factors, and the extent to which the acoustic wave is localised may be determined by appropriately analyzing the values of the oscillation phases or the amount of reduction of the phase fluctuation. The results are particularly significant for the practical experiments in an attempt to observe the acoustic localisation in such a medium, which is in general subjected to the interference of the great ambiguity resulting from the effect of acoustic absorption.     

Interaction of acoustic waves with porous layer

Interaction of sound impulse with porous layer is investigated. The presence of a barrier shielded by the layer and the gap between the porous layer and the barrier is possible. Method of calculation in linear approximation of pressures and tensions in the porous layer, gap, and on the barrier has been proposed. The method serves to interpret data on acoustic waves interaction with porous layer obtained experimentally or with the use of finite-difference methods. Specifics of acoustic wave propagation into the porous layer and further reflection from the barrier has been studied. Comparison of calculation data with experimental data of other authors on impulse propagation through the porous plate submerged in water has been carried out.     

Bounds on phase velocities of guided modes in open waveguides

Guiding of waves along cylinders with a surface impedance or along low velocity sound channels lead to eigenvalue problems in unbounded domains. Variational and comparison methods are used to find bounds on the discrete eigenvalues, which are related to the phase velocities of the guided modes. The variational methods yield upper bounds only, but they can be applied systematically to a large class of problems. The comparison methods yield upper and lower bounds, but are restricted to a smaller class of problems.     

Power-mode theorems for guided acoustic waves in piezoelectric media

Relationships between complex power flow pseudo energy, propagation constant and complex frequency are presented for acoustic waves in piezoelectric media. These relationships are essentially energy-power equations which apply to anisotropic, nonconservative, dispersive, linear systems, analogous to those obtained by Chorney and Penfield for guided electromagnetic waves. At vanishing piezoelectric coupling the powermode theorems split into a proper electromagnetic set and a proper mechanical set. By differentiating the power-mode equations with respect to the complex frequency further results are obtained linking the group velocity with power flow and energy storage. Conclusions may be drawn from these expressions regarding the signature of the dispersion (forward or backward waves). The equipartition of pseudo energy is established at cut-off, and the vanishing of the complex power flow at resonance. Examples including wave propagation in lossless and lossy media are included.     

任意倾斜层声速计算方法的研究

通过导出地层下边界倾斜角φ_m和该层声速V_m及其他预先确定的参数之间的关系式,就能在应用迭代法对Shah氏方程式求解的过程中,同时把V_m和φ_m作为迭代变量,从而改进了Zhang S.先前提出的求解方法^[1],提高了地层声速及其边界倾斜角的计算精度。     

Effective tortuosity and different acoustic waves in porous media

Summary A simple method has been suggested to estimate the acoustic characteristics of porous structure from a hybrid model—a hybridisation of Biot's phenomenological model and the microscopic multiple-scattering theory which introduces the idea of an effective tortuosity. Without using any adjustable parameter this model may be used to provide rough estimates of the tortuosity, the fast, the shear and the slow sound speeds. The predictions are compared with observation on water-saturated glass bead samples. The author of this paper has agreed to not receive the proofs for correction.     

Anisotropic propagation of surface acoustic waves on nitride layers

The anisotropic propagation of surface acoustic modes in GaN and AlN induced by the c-sapphire substrate is presented. In the GaN case, the slow acoustic propagation velocity of GaN compared with sapphire leads to guided modes in the overlayer, which propagate at higher velocities but are more attenuated than the Rayleigh mode. Above the transonic state, pseudo-SAW modes are observed, some of them with low insertion losses. In contrast, only the Rayleigh mode is observed in AlN filters due to its higher acoustic propagation velocity with respect to sapphire. The difference in the crystal structure of the sapphire and the nitrides induces a dependence of the sound velocity of all the modes, and hence their frequency, on the propagation direction. The simulations show very good agreement with the experimental data for both nitride/sapphire structures when the anisotropy induced by the substrate is taken into account.     

Near field Rayleigh wave on soft porous layers

Simulations performed for a typical semi-infinite reticulated plastic foam saturated by air show that, at distances less than three Rayleigh wavelengths from the area of mechanical excitation by a circular source, the normal frame velocity is close to the Rayleigh pole contribution. Simulated measurements show that a good order of magnitude estimate of the phase speed and damping can be obtained at small distances from the source. Simulations are also performed for layers of finite thickness, where the phase velocity and damping depend on frequency. They indicate that the normal frame velocity at small distances from the source is always close to the Rayleigh pole contribution and that a good order of magnitude estimate of the phase speed of the Rayleigh wave can be obtained at small distances from the source. Furthermore, simulations show that precise measurements of the damping of the Rayleigh wave need larger distances. Measurements performed on a layer of finite thickness confirm these trends.     

海底薄地层和硬地层声速测量方法的研究(射线参数法和折射法分析)

应用T²-X²法测量海底薄地层和硬地层的声速常常不能得到满意的结果。为此,有必要在一个由声源和拖曳水听器阵组成的声速测量系统中设置接射线参数法和折射法测量海底地层声速的处理功能。本文从这两种方法的测量原理出发,着重研究了地层回波时距数据的处理方法,以及由各种因素(如回波时间随机抖动和地层界面倾斜角不确定性等)所引起的声速测量误差等问题。射线参数法和折射法测量声速的数据处理和运算过程已经用TURBO-PASCAL语言编程,并通过对典型实例的模拟计算作了验证。     

Investigation of transient acoustic waves in KDP electrooptic modulators

Piezoelectrically generated acoustic transients in longitudinal KDP modulator crystals were investigated, using a photographic method developed for visualizing the acoustic waves. The method gives the possiblity of following the processes of acoustic wave propagation, the reflections of waves at the side faces of the crystal and the wave diffusion caused by crystal imperfections.     

Reflection and transmission of acoustic waves on multilayered porous media

Based on the Boit theory of acoustic wave propagation in fluid-satu-rated porous medium we have studied in this paper the acoustic reflection andtransmission on multilayered porous media,in which the adequate boundaryconditions across the interfaces are taken into account.Numerical calculationsof the reflection and transmission coefficients at different incident angles andfrequencies of the fast compressional wave incident on porous media with threeor four layers are presented.The results indicate that the maximum or mini-mum reflection and transmission coefficients appear at certain ratios of thewavelength to the thickness.The acoustic incident angle and porous mediumproperties are shown to affect significantly these coefficients.As an example,the measured transmission coefficients in a water-saturated fused glass beadsample are in good agreement with theoretical prediction.     

含有孔隙的层状材料中声表面波传播特性的理论研究

研究含有孔隙的层状材料中Rayleigh波的传播特性。采用本征函数展开法,并利用孔隙率与材料的弹性常数和密度之间的关系,模拟了不同孔隙率情况下铁基氧化铝层状材料中Rayleigh波的相速度色散曲线,分析了孔隙率对铁基氧化铝层状材料中Rayleigh波相速度的影响。Rayleigh波色散曲线的变化规律能同时反映层状材料中弹性模量、泊松比、密度和孔隙率的信息,为含有孔隙的层状材料参数的反演提供了理论依据。     

Borehole guided waves in a non-Newtonian (Maxwell) fluid-saturated porous medium

<正>The property of acoustic guided waves generated in a fluid-filled borehole surrounded by a non-Newtonian (Maxwell) fluid-saturated porous formation with a permeable wall is investigated.The influence of non-Newtonian effects on acoustic guided waves such as Stoneley waves,pseudo-Rayleigh waves,flexural waves,and screw waves propagations in a fluid-filled borehole is demonstrated based on the generalized Biot-Tsiklauri model by calculating their velocity dispersion and attenuation coefficients.The corresponding acoustic waveforms illustrate their properties in time domain.The results are also compared with those based on generalized Biot's theory.The results show that the influence of non-Newtonian effect on acoustic guided wave,especially on the attenuation coefficient of guided wave propagation in borehole is noticeable.     

Theories of elastic properties and elastic waves of equal phase velocities in crystals

A survey is made of pairs of heteronormal planar elastic waves, which can propagate in an unlimited crystal medium and have equal theoretical values of the phase velocity, using Voigt elastic moduli. Such pairs are chosen for which it is possible that the theoretical equality of velocities will be disturbed when using another theory of the elastic properties of crystals with generally different tensors of material constants (for example Kuvshinskij J. V., Aero E. L.: Fiz. tv. tela5 (1963), 2591). In such a case, a comparison of the measured velocities of a suitable pair of waves can help to decide between the two theories. Pairs of waves are found for 12 non-piezoelectric crystal classes. Among such pairs it is easy to find pairs of waves of the same properties for piezoelectric crystal classes.     

Combined spectral estimator for phase velocities of multimode Lamb waves in multilayer plates

A novel combined spectral estimate (CSE) method for differentiation and estimation the phase velocities of multimode Lamb waves whose wave numbers are much close or overlap one another in multiplayer plates is presented in this paper, which based on auto-regressive (AR) model and 2-D FFT. Simulated signals in brass plate were processed by 2-D FFT and CSE. And experiments are performed by using two conventional angle probes as emitter and receiver on the same surface of three-layered aluminum/xpoxy/aluminum plates, which include symmetrical and unsymmetrical plates. The multimode Lamb waves are excited in these laminates, and the received signal is processed by 2-D FFT and CSE, respectively. The results showed that the phase velocities of multimode signals whose wave numbers are much closed cannot be differentiated by 2-D FFT, but CSE has strong spatial resolution. Compared the measured phase velocities with the theoretical values, the error is smaller than 2% on the whole. It promises to be a useful method in experimental signals processing of multimode Lamb waves.     

Investigation of acoustic waves propagation and flow in nanodispersed medium

Propagation of acoustic waves in nanodisperse powders and powder flow under the influence of acoustic vibrations have been investigated in the horizontal tube with the use of visualization and hot-wire anemometer methods.     

Investigation of surface acoustic waves in laser shock peened metals

Laser shock peening is a well-known method for extending the fatigue life of metal components by introducing near-surface compressive residual stress. The surface acoustic waves (SAWs) are dispersive when the near-surface properties of materials are changed. So the near-surface properties (such as the thickness of hardened layers, elastic properties, residual stresses, etc.) can be analyzed by the phase velocity dispersion. To study the propagation of SAWs in metal samples after peening, a more reasonable experimental method of broadband excitation and reception is introduced. The ultrasonic signals are excited by laser and received by polyvinylindene fluoride (PVDF) transducer. The SAW signals in aluminum alloy materials with different impact times by laser shock peening are detected. Signal spectrum and phase velocity dispersion curves of SAWs are analyzed. Moreover, reasons for dispersion are discussed.