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thc incidence direction, while the ones of the antisymmetric Lamb waves exhibit a minimum in that same direction. A simple model, based on the Huygens’ principle, and involving the polarization State of the incident wave, provides results similar to the experimental ones. First results are also presented and discussed for end sections of various angles.

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8PA4. Derivatives of the phase change on reflection from plates: A new analysis of resonance. O. Lenoir, J. L. Izbicki (Lab. d’Acoust. Ultrason. et d’Elcctron., U.R.A. C.N.R.S. 1373, Univ. du Havre, PI. R. Schuman, 76610 Le Havre, France), and J. M. Conoir (Le Centre Thomson d’Applicalions Radars, 78143 Velizy-Villacoublay, France)

Recent experimental works have yielded a renewal of interest on the study of the phase of the scattercd pressure by elastic bodies. Recent results, pointed out by Conoir about cylindrical shells, havc led the authors to be particularly interested in the derivatives of the phase of the reflection coefficient of an elastic piąte, with regard to the longitudinal, shear, and outer liquid velocities, as well as to the frequency. Three theoretical studies have been carned out: The first one consists in cal-culating the whole derivatives of the phase versus the frequency; the second one in calculating the derivatives versus the parameter chosen to derive the phase; and the third one in calculating the derivative, with respect to the frequency, versus the velocities. The goal is to exhibit the influence of these parameters on the phase when a Lamb modę is excited in an elastic piąte. Indeed, the different curves obtained give information about the prevailing character, longitudinal or shear, of the waves re-lated to Lamb modes. They also determine whether a modę is well couplcd or poorly coupled with the external medium.

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8PA5. Scattering from slender bodies at high frequency. Michel Tran Van Nhieu (Thomson Sintra ASM, 94117 Arcucil, France)

A scattercd field from rigid slender bodies at high frequency is de-termined by applying the Kirchholf and slender-body approximations; this last one is the zeroth-order term of the asymptotic cxpansion of the solution of the problem in the slenderness ratio e (M. Tran Van Nhieu, J. Acoust. Soc. Am. 85, 1834-1840 (1989)]. It is shown that the pressure scattered from complex targets can be computed from a simple integral and the geometrical knowledge of the transversal cross sections of the body along its longitudinal axis. An analytical expression for the far-field pressure is obtained explicitly. Some numerical results for the monostatic and bistatic target strengths of bodies of various shapes are presented to illustrate the theory.

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8PA7. Resonances of Scholte-Stoneley waves propagating on cylindrical shells at oblique incidence. P. Remert, O Lenoir, J. L. Izbicki, and J. Ripoche (Lab. d'Acoust. Ultrason. et d’Electron., U.R.A. C.N.R.S. 1373, Univ. du Havre, PI. R. Schuman, 76610 Le Havre, France)

This paper deals with the oblique scattering of an incident mono-chromatic piane wave by a circular cylindrical shell immersed in water. The propagation direction of the incident wave makes an angle a with a normal to the longitudinal axts of thc shell. Experiments are carried out over the broad reduced frequency rango 0<Ara>35, involving the method of isolation of resonances, for two targets: (1) an air-filled aluminum shell with b/a = 0.94 (6 = inner radius of the shell: a = outer radius of the shell) whose length is infinite with regard to the incident acoustic beam cross section; and (2) the same shell of the finite length: In this case, the incident beam insonifies the entire target. With a varying from 0* to 35°, the backscatlered spectra—obtained from the signals scattered by both targets—exhibit wide minima which are due to the reemission of Scholte-Stoneley waves. Resonance peaks are located at the same frequencies on the corresponding resonance spectra. The frequency position of these peaks slowly inereases with the inereasing values of a. Follow-up of these frequencies is easy, especially beyond the shear critical angle, which confirms that these resonances are related to extemal waves. These new experimental results are similar to theoretical ones obtained for an infinite pipę by Kaplunov et al.

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8PA8. Acoustic fields on the surface of a submerged finite cylindrical shell irradiated by piane waves. Xiaoqi Bao, Vasundara V. Varadan, Vijay K. Varadan (Depl. of Eng. Sci. and Mech. Res. Ctr. for the Eng. of Electron, and Acoust. Mater., Penn State Univ., 149 Hammond Bldg., University Park, PA 16802), and C Audoly (GERDSM, Le Brusc, Six-Fours, France)

The prediction of acoustic pressure on the surface of baffles is inter-esting for designers of transducer arrays. A Computer simulation program based on a finite/boundary element approach is developed for this purpose. In the simulation, the elastic baffle is modelcd by finite ele-ments and the infinite fluid surround the baffle by boundary elements. The two representations are coupled on the surface through eigenmode expansion. The composite program is able to predict the surface acoustic pressure of axisymmetric elastic baffles. The sensiłivity and directiv-ity of hydrophone or hydrophone arrays that are mounted on the buffer can then be obtained. A particular examplc of a baffle that is a cylindrical Steel shell with truncated ends is computed. The convergence of the computation is discussed. The results are compared with experimen-tal measurements.

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8PA6. Signatures from pulse signals scattered at oblique incidence from elongated elastic solids at carrier frequencies in the region of bending resonances. M. F. Werby and Jacob George (NOARL, Codę 221, Stennis Spacc Ctr., MS 39529)

It has been determined that time-domain signals can manifest char-acteristic signals when the midpulse frequency is in some resonance region. This will be discussed in an upcoming book on resonance scat-tering theory by Uberall. This work is a further extension of that study to illustrate unique signals characteristic of pulse scattering at frequen-cics associated with bending or flexural resonances. In thc earlier work, beat pattems and damped sinusoidal pattems (as a function of time) were associated with single or specific clusters of resonances. Here, altemating damped sinusoidal patterns are associated with intervals of interference pattems that are shown to be associated with bending modes excited at oblique incident angles.

1993 J. Acoust. Soc. Am., Vol. 89. No. 4, Pt. 2, April 1991

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8PA9. Acoustic scattering from finite elastic cylinders. Gerard Maże. Jean Ripoche (LAUE-URA, Univ. of Le Havre, 76610 Le Havre, France), Xiao-Ling Bao, and Herbert Uberall (Catholic Univ., Washington, DC 20064)

Tank experiments on acoustic bistatic and backscattering from elastic cylinders with hemispherical endcaps have been performed at the University of Le Havre and at Catholic University. The resonances apparent in these experiments have been interpreted on the basis of the phase-matching principle [H. Uberall et al.. J. Acoust. Soc. Am. 61, 771 (1977)] for surface waves that encircle these objects along closed geo-desics. Upon axial incidence, the resonances of meridionally propagating surface wavcs arc visiblc. Upon axial incidence, the resonances of meridionally propagating surface waves are visible. Upon broadside incidence, circumferential wave resonances are visible as well as the me-ridional ones. The frequencies of both types of resonances are explained very well by the phase-matching principle. (Work supported in part by the David Taylor Res. Ctr.]

121st Meefing: Acouslical Society of America 1993