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Acoustic scattering of a plane progressive wave from the composite cylindrical shell is investigated through the solution of the wave equation and boundary conditions of stresses and displacements. The investigated range of reduced frequency extends over 0.1 k 1 a 1 200 ( k 1 is the wave number in a fluid medium surrounding the composite cylindrical shell and a 1 is the outer radius of the shell). The far field form function for two-layered stainless steel/polymer cylindrical shell is evaluated and examined. The achieved results are compared with those obtained in the case of one-layered cylindrical shells made of stainless steel or polymer. The investigation is carried out into the influence of the inner layer thickness (polymer) on the circumferential waves of the stainless steel/polymer composite cylindrical shell on the one hand and of the outer layer thickness (stainless steel) on the other hand. This influence is studied based on the evolution of the cutoff frequencies of the circumferential waves. A comparative analysis of the evolution of the cutoff frequencies of the one-layered and composite cylindrical shells is conducted. The estimation of the cutoff frequencies is done from plane of modal identification and two time-frequency planes, the spectrogram and the reassignment spectrogram. The results show that these planes are very useful to estimate the cutoff frequencies of the circumferential waves of the composite cylindrical shell. They can therefore be suggested as an alternative of the proper modes theory which is applicable in the case of homogeneous structures.

Given a lattice $L$, a basis $B$ of $L$ together with its dual $B^*$, the orthogonality measure $S(B)=\sum_i ||b_i||^2 ||b_i^*||^2$ of $B$ was introduced by M. Seysen in 1993. This measure is at the heart of the Seysen lattice reduction algorithm and is linked with different geometrical properties of the basis. In this paper, we explicit different expressions for this measure as well as new inequalities., Comment: Typos corrected

In this paper, an artificial neural network (ANN) was developed and used to predict the internal parameters inside the greenhouse during a 7-days period. The model database was collected starting from the greenhouse climatic data in real tomato culture in the Agadir area in Morocco. The External Moisture (Mext), the Total Radiation (Rt), the Wind Direction (Dw), the Wind Velocity (Vw) and the External Temperature (Text) are retained like relevant entries of the time-series model. The comparison between the obtained results and experimental ones indicates that the ANN method is suitable to predict the greenhouse climatic data.

The objective of this study is to discuss the effectiveness of two different methods, a time-frequency representation of Wigner-Ville and a frequency spectral representation, by comparing their ability to analyse experimentally received signals backscattered by two types of multilayer structures. In this paper, we will present a study of the propagation of acoustic waves backscattered by two multilayer structures with a resonant plate ‘aluminum or glass’ and a less resonant plate ‘plexiglas’ separated by a water layer. The backscattering experiments have been performed in a water immersion tank. The images obtained of time-frequency representation are compared to the frequency spectral method. The results obtained by the time-frequency analysis are interesting and robust.

The acoustic scattering from a cylindrical or spherical object immersed in water and insonified with plane wave has been theoretically and experimentally studied. The backscattering spectra show minima, which are related to the circumferential waves circumnavigating around the object. These waves are identical to the Lamb waves propagating in a plate. Two types of resonances are observed on ultrasonic spectra: the resonances related to the thickness and the resonances related to the stationary state that establish around the cylindrical shell from the circumferential waves. To eliminate the second type of resonances a focused beam is used to excite only the thickness resonances. The cylindrical shell thickness is calculated from these experimentally measured resonance frequencies.

The thickness resonances of an elastic plate normally insonified by an ultrasonic plane wave are well known. From these resonance frequencies, the plate thickness can be easily deduced. In this paper, we use a focusing ultrasonic transducer with a large bandpass to characterize an electrical melting point between two steel plane shells. This solder type is abundantly used in the manufacturing of cars. The solder is placed in the focal spot of the beam. The transducer can be parallely moved to the surface of the sheet steel. A number of time signals are recorded along a diametrical line of the melting point with a small step. For each time signal, two spectra are computed: the magnitude spectrum also called backscattered spectrum and the phase spectrum. The results are processed with graphic software. The different images allow the evaluation of the quality of an electrical melting point.

In this article, time–frequency representation of Wigner–Ville is used to analyse the acoustic signal backscattered by a thin elastic tube of radii ratio b / a . This analysis allows to determine the reduced cutoff frequency of the circumferential antisymmetric wave A1 propagating around the tube. The evolution of this reduced cutoff frequency in function of b / a is reported. The values obtained of reduced cutoff frequency are compared to the values computed from the proper modes method.

Resume Le calcul numerique du champ de pression emis par un transducteur focalisant est relativement long. C'est la raison pour laquelle nous avons developpe une methode simple pour prevoir la pression emise par ce genre de transducteur. Cette methode, presentee par une seule integrale, est nommee modele a 1-dimension. Ce modele permet d'avoir un calcul rapide des pressions axiale et radiale qui seront comparees aux resultats a 2-dimensions et validees par l'experience.

The characterization of an elastic tube can be done on the basis of its reduced cut-off frequencies of circumferential waves scattered around the tube and of its transversal sound velocity. The Wigner-Ville time-frequency representation, that takes into account both the time parameter and the frequency parameter of a signal, is used in this work to access to the sought parameters. In this article, the Wigner-Ville method is applied to acoustic signals scattered by a thin aluminium tube. The transversal velocity, estimated by the Wigner-Ville image, is in good agreement with thetransversal sound in velocity aluminium given in the scientific litterature.

The experimental measurement of the group and phase velocities of some circumferential waves propagating around a thin elastic tube is a still complex operation. In this study, we show that the dispersion velocity can be determined from a time–frequency representation. We use the Wigner–Ville method by virtue of its interesting properties. On some time–frequency images, the symmetric (S0) and antisymmetric (A1) circumferential waves are identified. The group velocity dispersion estimated from these images is compared with that computed by the proper mode theory method. A good agreement is obtained. The phase velocity is also determined from the group velocity.

In this work the pressure field radiated by a PVDF focusing transducer has been determined experimentally and compared to the theory. The transducer has the form of spherical bowl, excited by sinusoidal wave trains. The influence of the excitation frequency on the distribution of the ultrasonic pressure is studied on and out of the axis of the transducer. A good agreement between theory and experiment is obtained.

Resume Nous presentons des mesures de transmission d'une onde ultrasonore dans des toles collees immergees dans l'eau. Les experiences ont ete realisees en faisant varier l'angle d'incidence. L'etude a ete effectuee sur des structures constituees de deux plaques identiques soit en aluminium soit en acier collees par une resine epoxy. Les resultats obtenus mettent en evidence l'existence d'un mode vertical qui permet de controler la qualite de ces assemblages.

Resume Dans de ce travail, nous presentons une methode ultrasonore permettant de controler la qualite d'un collage de deux toles d'aluminium de meme epaisseur. Cette methode est basee sur le comportement du dedoublement des modes des deux toles. Pour expliquer le comportement du coefficient de reflexion en fonction de la qualite du collage un nouveau modele est introduit. Une etude theorique et experimentale montre que ce dedoublement de mode depend tres fortement de la qualite du collage. Les resultats obtenus mettent en evidence l'existence d'un critere qui permet de controler la qualite d'un collage de type Aluminium / resine epoxy/Aluminium.

The acoustic resonances of cylindrical finite length targets are investigated experimentally. The targets have different length-to-diameter ratios η:η=1.33 for a solid aluminium cylinder, η=1.66 for an aluminium cylindrical shell (with a ratio between the inner radius b and the outer radius a of 0.89), η=1.85 for a stainless steel cylindrical shell ( b a =0.94 ). The insonification is performed at normal or slightly oblique incidence. Resonances related to Whispering Gallery, guided waves and Scholte-Stoneley waves are identified. For a given vibration mode n it is possible to identify two resonances at frequencies close to each other. A comparison is made with theoretical values at normal incidence. The experimental resonances related to Whispering Gallery and guided waves are shifted towards the high frequencies; resonances related to Scholte-Stoneley waves are shifted towards the low frequencies.

Up to now, resonance isolation by means of a pulse method has been performed by the calculation of the FFT of the free elastic response of the insonified target immersed in water. We propose a new method which allows the resonance detection from the FFT of the whole backscattered signal, involving the imaginary and real part spectra and in some cases, the phase spectrum. Experiments are carried out on several targets at normal incidence. This method seems to be the appropriate one to detect the resonances in the case of a “very absorptive material/elastic material” double layered plane structure.

The method of isolation and identification of resonances (MIIR) allows a direct verification of “resonance scattering theory” (RST). Indeed it provides the resonance spectra of aluminum elastic cylindrical shells, insonified by plane acoustic waves and it also allows the experimental determination of the mode number of each resonance of the target. At this day, when the shells are insonified by a short pulse it is only possible to obtain the resonance spectrum with a fast Fourier transform of the backscattered response. This paper presents an impulse method which allows the isolation of resonances and besides the identification of each eigenmode of the target.

Recent studies of acoustic scattering have allowed the explanation of the existence of additional lines in the resonance spectrum of an elastic solid cylinder immersed in water by the examination of natural modes. A first group of natural modes, related to the propagation of the circumferential waves (Rayleigh, Whispering Gallery waves), is detected when the cylinder is insonified perpendicularly to its axis. A second group of natural modes related to the guided waves which propagate in the direction parallel to the axis of the cylinder is detected when it is insonified obliquely. In this Paper, the authors examine the acoustic scattering from cylindrical shells filled with a fluid (air or liquid) by the method of isolation and identification of resonances (MIIR). It allows resonance spectra to be obtained; in addition, the mode number, n , given by the identification, makes it possible to separate the resonances into different series. It is possible to explain the experimental resonance spectra of a liquid-filled tube insonified perpendicularly to its axis with a non-perfect directive transducer, by the calculation of the eigenfrequencies of the different parts of the target. The authors show the great importance of the guided waves along the axis and of the resonances of the liquid column when the shell is filled with a liquid. The resonance spectra of liquid-filled targets and the reradiation patterns giving by MIIR, i.e. after the end of excitation, are shown for the first time.

Using an optical method a surface wave is detected ‘in situ’, which is the reflection from an immersed plane metallic surface, of an ultrasonic beam propagating in water. The amplitude and attenuation of the beam are measured on a stainless steel sample and it is shown that the attenuation fits the f 4 law, where f is the frequency.

The experimental method described for the first time by Maze, Taconet and Ripoche and now called “method of isolation and identification of resonances” (MIIR) has been applied to the study of cylindrical targets immersed in water. It allows the isolation of resonances in quasilinear spectra and their identification. An analysis of the “resonance spectra” shows that some lines do not belong to series supplied by the theory when the calculation is made with a plane acoustic wave which has its wave vector perpendicular to the axis of the target. The origin of a series of lines is determined by studying the guided propagation along the axis of the cylindrical shells.

An experimental method which allows measurement of the frequency ( ka ) of circumferential wave resonances which propagate in aluminium cylinders is described. It is also possible to deduce the number of wavelenghts on the circumference or the vibration mode of circumferential waves. This study allows a better understanding of the complex structures of the form function in the far field. It specifies the theoretical results which show the effect of each circumferential wave in the angular diagram.

A “Franz-type” wave was generated on the outside of solid cylinders immersed in water with “ka” values ranging from 25 to 800. In this investigation, the velocity and the attenuation of this wave have been obtained for different materials. Good agreement is obtained with the theory and other experiments.

Resume The result of the mixing of two noncollinear surface waves is detected with an optical device. We obtain the frequencies ω 1 - ω 2 (and ω 1 + ω 2 ) in the predicted directions. The surface waves are generated in water at Rayleigh angle on a stainless steel sample, in the range 4–7 MHz.

An optical method detects the surface waves on a metal cylinder hit by an ultrasonic beam in water and reveals their multiple revolutions. We obtain their velocity by beat measurement according to the circumference to wavelength ratios between 100 and 200.