Wedge Waves Research Articles

A Partial Shape Matching Method for Functionalized Shape

This paper proposes a partial shape matching method for functionally approximated shapes. The proposed method consists of a feature extraction procedure and a correspondence detection procedure among convexities. In the feature extraction, we introduced a wedge-shaped tiny figure, called wedge wave, as a basis of convexities. The DP (Dynamic Programming) matching has been applied to the correspondence detection among extracted convexities using a method to reduce the amount of computation.The proposed method has been applied to several figures for evaluation. The results showed that our method could recognize partial similarity without the restriction of location, size, and orientation. It has been confirmed that, by utilizing the information of an approximating function, a large amount of computation in feature extraction can be reduced.

FINITE ELEMENT ANALYSIS OF THE PROPAGATION OF ACOUSTIC WAVES ALONG WAVEGUIDES IMMERSED IN WATER

The finite element approach has previously been used, with the help of the ATILA code, to model the propagation of acoustic waves in waveguides [A.-C. Hladky-Hennion,Journal of Sound and Vibration,194,119–136 (1996)]. In this paper an extension of the technique to the analysis of the propagation of acoustic waves in immersed waveguides is presented. In the proposed approach, the problem is reduced to a bidimensional problem, in which only the cross-section of the guide and the surrounding fluid domain are meshed by using finite elements. Then, wedges the top angles of which vary, are studied and the finite element results of the wedge wave speed are compared with experimental results. Finally, the conclusion indicates a way to extend this approach to waveguides of any cross-section.

Propagation of acoustic surface wedge waves inmagnetostrictive ferrites

Results on antisymmetric wedge acoustic wave propagation in magnetostrictive ferrite are presented. The propagation velocity can be varied by changing the applied magnetic field. The strong dependence of the fundamental mode velocity on the magnetic field demonstrates the applicability of wedge waves in magnetostrictive ferrites for variable delay lines.

Contactless characterization of antisymmetric edge wave dispersion along truncated wedge using electromagnetic acoustic transducer

Accurate laboratory measurements are compared with approximate theoretical calculations on the dispersion of antisymmetric flexural edge waves propagating along the apex of a truncated 6061 aluminum wedge with an apex angle Θ=26.7°. The wedge waves are detected with a specially designed electromagnetic acoustic transducer in the frequency range 30–500 kHz. Phase velocity dispersion plots are obtained from gated sinusoidal signals and wavelength measurements averaged over 10–20 wavelengths. The general characteristics of the experimental phase velocity dispersion data closely matched the approximate theoretical parabolic model by McKenna etal. [IEEE Trans. Sonics Ultrason. SU-21(3), 178–186 (1974)] derived for small apex angle. The measured dispersion curve was duplicated using a truncated wedge tip width 57 μm in the parabolic approximation calculations while the actual measured tip width was 62 μm Antisymmetric flexural wedge waves obtained from a sharp apex (3 μm) are practically nondispersive as expected in the same frequency range. Previously reported laser ultrasonic dispersion measurements obtained by Jia etal. [Appl. Phys. Lett. 61, 2970–2972 (1992) and IEEE Ultrason. Symp. Proc. 1993, paper B4] revealed unexplained measured dispersion behavior of antisymmetric wedge flexural waves based on a phase analysis method. Contactless electromagnetic acoustic direction of antisymmetric wedge waves provided dispersion results in agreement with theoretical calculations. [Work supported by ONR.]

Application of the theories of representations to the problems of the excitation and reflection of wedge waves

A method of solving the problem of the reflection of a wedge wave at the edge of an acute-angled elastic wedge, that is invariant under a two-parametric group of transformations, is proposed. Representations of this group are used to obtain the mean values of the intensities of the fictitious sources situated at the edge of the wedge. The mean values obtained are used to construct the unknown functions using an expansion in Hermite polynomials.

Estimation of left ventricular filling pressures using two-dimensional and Doppler echocardiography in adult patients with cardiac disease: Additional value of analyzing left atrial size, left atrial ejection fraction and the difference in duration of pulmonary venous and mitral flow velocity at atrial contraction

Objectives. The purpose of this study was to determine whether left atrial size and ejection fraction are related to left ventricular filling pressures in patients with coronary artery disease.Background. In patients with coronary artery disease, left ventricular filling pressures can be estimated by using Doppler mitral and pulmonary venous flow velocity variables. However, because these flow velocities are age dependent, additional variables that indicate elevated left ventricular filling pressures are needed to increase diagnostic accuracy.Methods. Echocardiographic left atrial and Doppler mitral and pulmonary venous flow velocity variables were correlated with left ventricular filling pressures in 70 patients undergoing cardiac catheterization.Results. Left atrial sin and volumes were larger and left atrial ejection fractions were lower in patients with elevated left ventricular filling pressures. Mean pulmonary wedge pressure was related to mitral E/A wave velocity ratio (r = 0.72), left atrial minimal volume (r = 0.70), left atrial ejection fraction (r = −0.66) and atrial filling fraction (r = −0.66). Left ventricular end-diastolic and A wave pressures were related to the difierence in pulmonary venous and mitral A wave duration (both r = 0.77). By stepwise multilinear regression analysis, the ratio of mitral E to A wave velocity was the most important determinant of pulmonary wedge (r = 0.63) and left ventricular pre-A wave (r = 0.75) pressures, whereas the difference in pulmonary venous and mitral A wave duration was the most important variable for both left ventricular A wave (r = 0.75) and left ventricular end-diastolic (r = 0.80) pressures. The sensitivity of a left atrial minimal volume >40 cm3for identifying a mean pulmonary wedge pressure >12 mm Hg was 82%, with a specificity of 98%.Conclusions. Left atrial size, left atrial ejection fraction and the difference between mitral and pulmonary venous flow duration at atrial contraction are independent determinants of left ventricular filling pressures in patients with coronary artery disease. The additive value of left atrial size and Doppler variables in estimating filling pressures and the possibility that left atrial size may be less age dependent than other mitral and pulmonary venous flow velocity variables merit further investigation.

Ultrasonic modeling of sea ice seismoacoustic wave phenomena

A variety of broadband Arctic seismoacoustic wave phenomena are demonstrated using laboratory ultrasonic modeling techniques introduced by the author in the mid 1970s to study the generation, propagation, detection, and scattering of low‐frequency underwater acoustic waves coupled to the heterogeneous ice cover. Data on frequency‐dependent under‐ice reflectivity, effective elastic properties, low‐frequency transmission loss, horizontal refraction, wave conversion, and low grazing angle backscattering are discussed. Different guided leaky and trapped waves from range‐dependent models are isolated and examined including flexural waves, shear horizontal waves, Rayleigh waves, Scholte waves, edge plate waves, and wedge waves. The laboratory models consisted of finite floating plates with cracks, ridges, low‐velocity layers, boreholes, trapped air pockets, solid wedges, and suspensions. The results provide physical insight into realistic 3‐D problems and lead to the development of comprehensive understanding of near‐field and long‐range seismoacoustic phenomena essential for interpreting and inverting Arctic acoustic data, planning field experiments, and predicting ice failure modes from acoustic emission. The generic findings are applicable to ocean bottom interacting acoustic waves, nondestructive testing, and ultrasonic imaging. [Work supported by DREP and ONR.]

Elastic wedge waves

Linearly elastic waves travelling along a wedge tip are nondispersive, so that, in nonlinear waves, constructive interaction between any pairs of frequencies may be substantial. The interaction coefficients depend critically on the structure of the linearized modes. This account describes some general features of the mode structure, shows how an asymptotic analysis for slender wedges incorporates the predictions of M cK enna et al. from thin plate theory, and outlines how, for obtuse wedges, the mode structure distant from the tip is a laterally attenuated, perturbed Rayleigh wave.

Harmonic generation and parametric mixing in wedge acoustic waves

The first theoretical consideration of nonlinear effects in wedge acoustic waves is given. The theory is restricted to the case of antisymmetric wedge modes propagating along the tip of a sharp-angle isotropic solid wedge. The nonlinear wave equation and corresponding tip conditions are derived and then solved using the geometrical-acoustic approach to elastic wedge propagation problems (Krylov, Akust. Zh. 35, 294 (1989)). It is shown that the lowest order of nonlinearity in this equation is cubic. Analytical expressions are derived for the amplitude of the third harmonic as well as for the amplitudes of the wedge waves with “sum” 2 ω 1 + ω 2 and “difference” 2 ω 1 − ω 2 frequencies. Numerical calculations carried out for several low-order wedge modes show a strong dependence of the growth parameter on the integrals describing the overlap of the mode-distributions with depth for different frequencies. The most interesting results have been obtained in the case of generation of waves with “difference” frequencies. Numerical calculations of the growth parameter as a function of the frequency ratio l = ω 3/ ω 1 show strong resonance behaviour around the value l = 1 corresponding to maximum growth rate. Comparison of the theoretical results with existing experiments (Adler et al., IEEE Trans. SU26, 345 (1979)) shows good qualitative agreement.

Radiation conductance of apodized ID transducers in wedges

The radiation conductance of an apodized ID transducer for acoustic waves in wedges is derived from normal-mode theory. Using the analytical expressions for the field distribution developed in an earlier paper, the radiation conductance is calculated for an ID transducer on a 40° LiNbO3 wedge. The calculated values are in good agreement with published experimental results.

Numerical solution of the problem of wave diffraction by a wedge

The systematic development of the theory of shock reflection from a solid wall started in [1]. Regular reflection and a three-shock configuration originating in Mach reflection were considered there under the assumption of homogeneity of the domains between the discontinuities and, therefore, of rectilinearity of these latter. The difficulties of the theoretical study include the essential nonlinearity of the process as well as the instability of the tangential discontinuity originating during Mach reflection. Analytic solutions of the problem in a linear formulation are known for a small wedge angle or a weak wave (see [2–4], for example). The solution in a nonlinear formulation has been carried out numerically in [5, 6] for arbitrary wedge angles and wave intensities. Since the wave was nonstationary, the internal flow configuration is difficult to clarify by means of the constant pressure and density curves presented. A formulation of the problem for the complete system of gasdynamics equations in self-similar variables is given in [7] and a method of solution is proposed but no results are presented. Difficulties with the instability of the contact discontinuity are noted. The problem formulation in this paper is analogous to that proposed in [7]. However, a method of straight-through computation without extraction of the compression shocks in the flow field is selected to compute the discontinuous flows. The shocks and contact discontinuities in such a case are domains with abrupt changes in the gasdynamics parameters. The computations were carried out for a broad range of interaction angles and shock intensities. The results obtained are in good agreement with the analytical solutions and experimental results. Information about the additional rise in reflection pressure after the Mach foot has been obtained during the solution.

Wedge-wave transduction by means of interdigital electrodes

Experimental results on wedge-wave transduction by means of interdigital electrodes are presented. It is shown that tightly confined low-velocity wedge waves can be launched with high efficiency. Experiments on both PZT and LiNbO3 wedges are reported.

Parametric interaction of acoustic-surface wedge waves

A slow nondispersive antisymmetric flexural wave is tightly bound to the apex of a wedge. An acoustic convolver, which takes advantage of its characteristics to enhance efficiency, is described. It is demonstrated that wedge waves can be generated and tapped using photolithographically defined transducers.

Synthetic seismograms ofP-waves propagating in solid wedges with free boundaries

A numerical method for the synthesis of seismograms for body wave propagation in solid wedges is presented. The method is based on the superposition of multiple reflections arising from the entrance of a plane primary wave. Therefore the method is restricted to those domains in time-space where no diffracted waves from the wedge axis occur. In spite of this restriction, the dispersion of body waves in wedges can well be studied by this method.

SYNTHETIC SEISMOGRAMS OF P WAVES PROPAGATING IN SOLID WEDGES WITH FREE BOUNDARIES

A numerical method for the synthesis of seismograms for body wave propagation in solid wedges is presented. The method is based on the superposition of multiple reflections arising from the entrance of a plane primary wave. Therefore the method is restricted to that part of the time domain where no diffracted waves from the wedge axis occur. In spite of this restriction, dispersion of body waves in wedges can well be studied by this method. Seismograms have been synthesized which show the dispersion of a primary p‐signal propagating in a solid 10‐degree and a 5‐degree wedge with free boundaries. For wedge angles less than 10 degrees the signal front (to be distinguished from the wavefront) suddenly decreases its velocity from that in the infinite medium to about that of the plate wave as the signal approaches the wedge axis. Simultaneously in this transition zone a decrease of the dominant period of the interference signal occurs. These observations are concordant with previous model studies. Particle motion diagrams disclose elliptical polarization of the interference signal in the neighborhood of the wedge axis; the polarization changes its sense from prograde to retrograde on passing through the transition zone.

TRANSMISSION AND REFLECTION OF RAYLEIGH WAVES BY WEDGES

Experimental observations have been made of the transmission and reflection of Rayleigh waves by wedges. Results are reported for Rayleigh waves in aluminum wedges. It is observed that the wave shapes of the transmitted and reflected waves differ from that of the incident wave and depend on the angle of the wedge. The change of shape is attributed to an interference between part of the incident wave‐form and the radiation from a line source placed at the vertex. A procedure is given for the calculation of the partition between the two terms.