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Double layer structures consisting of stainless steel and polymer rods are designed to blur and attenuate Bragg and Bloch-Floquet scattering from a periodically ribbed plate in a given frequency bandwidth. These structures can be considered as ribbed plate-spring-mass systems, the resonance frequencies of which are obtained from random and circular permutations of five basic oscillators. Analytical and finite element methods are used to find their parameters and tank tests have been carried out to ensure the accuracy of the numerical results and validate the relevance of such a model. It has been found that the typical features associated with the periodicity of the ribs are replaced by a “Christmas tree” appearance when the far field pressure backscattered from the model is displayed in the (frequency, aspect angle) plane. An analysis of backscattering patterns is presented and comparisons with Naval Research Laboratory results are made.Double layer structures consisting of stainless steel and polymer rods are designed to blur and attenuate Bragg and Bloch-Floquet scattering from a periodically ribbed plate in a given frequency bandwidth. These structures can be considered as ribbed plate-spring-mass systems, the resonance frequencies of which are obtained from random and circular permutations of five basic oscillators. Analytical and finite element methods are used to find their parameters and tank tests have been carried out to ensure the accuracy of the numerical results and validate the relevance of such a model. It has been found that the typical features associated with the periodicity of the ribs are replaced by a “Christmas tree” appearance when the far field pressure backscattered from the model is displayed in the (frequency, aspect angle) plane. An analysis of backscattering patterns is presented and comparisons with Naval Research Laboratory results are made.

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.

The present paper examines a new procedure for estimating Young‘s modulus and Poisson‘s ratio of homogeneous materials constituting the one-layer thin tubes. The work is done from the use of the timefrequency representation. Spectrogram and its reassigned version have been chosen to analyze experimentally acoustic signals backscattered by air-filled tubes immersed in water. For reduced frequencies ranging from 0.1 to 500, time-frequency images have shown the presence of the Symmetrical and the Antisymmetrical waves. Satisfactory resolution and good localization in the time-frequency plane have been observed in the case of concentrated spectrogram. Reduced cutoff frequencies of A1 and S1 waves have also been extracted from Spectrogram and concentrated Spectrogram time-frequency images. A good agreement has, therefore, been observed. Comparisons with results obtained by experiment indicate that mechanical parameters such as Young‘s modulus and Poisson‘s ratio of aluminum and copper are evaluated accurately.

The acoustic scattering of a plane wave by an elastic cylindrical shell is studied. A new approach is developed to predict the form function of an immersed cylindrical shell of the radius ratio b/a (‘b’ is the inner radius and ‘a’ is the outer radius). The prediction of the backscattered form function is investigated by a combined approach between fuzzy clustering algorithms and bio-inspired algorithms. Four famous fuzzy clustering algorithms: the fuzzy c-means (FCM), the Gustafson-Kessel algorithm (GK), the fuzzy c-regression model (FCRM) and the Gath-Geva algorithm (GG) are combined with particle swarm optimization and genetic algorithm. The symmetric and antisymmetric circumferential waves A, S 0 , A 1 , S 1 and S 2 are investigated in a reduced frequency ( k 1 a ) range extends over 0.1 k 1 a 225 ( k 1 is the wave number). The time-frequency representation of Smoothed Pseudo Wigner-Ville (SPWV) is applied on the predicted and calculated acoustic backscattered form functions. This representation is used as a comparison criterion between the calculated form function by the analytical method and that predicted by the proposed approach on the one hand and is used to extract the predicted cut-off frequencies on the other hand. Moreover, the transverse velocity of the material constituting the cylindrical shell is extracted. The computational results show that the proposed approach is very efficient to predict the form function and consequently, for acoustic characterization purposes.

The time and frequency analyses of the acoustic scattering by an elastic cylindrical shell in bistatic method show that the arrival times of the echoes and the resonance frequencies of the elastic waves propagating in and around the cylindrical shell are a function of the bistatic angle, β, between the emitter and receiver transducers. The aim of this work is to explain the observed results in time and frequency domains using time-frequency analysis and graphical interpretations. The performance of four widely used time-frequency representations, the Smoothed Pseudo Wigner-Ville (SPWV), the Spectrogram (SP), the reassignment SPWV, and the reassignment SP, are studied. The investigation into the evolution of the time-frequency plane as a function of the bistatic angle β shows that there are the waves propagating in counter-clockwise direction (labeled wave+) and the waves which propagate in clockwise direction (labeled waves−). In this paper the A, S0, and A1 circumferential waves are investigated. The graphical interpretations are used to explain the formation mechanism of these waves and the acoustic scattering in monostatic and bistatic configurations. The delay between the echoes of the waves+ and those of the waves− is expressed in the case of the circumnavigating wave (Scholte-Stoneley wave). This study shows that the observed waves at β = 0 ° and β = 18 0 ° are the result of the constructive interferences between the waves+ and the waves−. A comparative study of the physical properties (group velocity dispersion and cut-off frequency) of the waves+, the waves− and the waves observed in monostatic configuration is conducted. Furthermore, it is shown that the ability of the time-frequency representation to highlight the waves+ and the waves− is very useful, for example, for the detection and the localization of defaults, the classification purposes, etc.

Some Lamb waves in a plate and some circumferential waves in a one-layer cylinder are characterized by the resonance frequencies where the group velocity is vanishing while the phase velocity remains finite. This paper investigates on the existence of these special waves which call zero group velocity waves (ZGV waves) in the case of the copper/polymer composite cylindrical shell immersed in water and filled with air. The acoustic scattering of a plane wave from this composite cylindrical shell is analyzed in the reduced frequency range ( 0.1 k 1 a 1 200 ; k 1 is the wave number and a 1 is the outer radius of the composite cylindrical shell). The study of the respective influence of the inner layer thickness (polymer) and the outer layer thickness (copper) shows that the existence of these waves is a function of these thicknesses. Moreover, this study depicts that the dispersion curves of the considered bilayer shell tend towards the dispersion curves of the one-layer cylindrical shell made from the material of the thicker layer of the bi-layer cylindrical shell (polymer or copper). The time-frequency representation of smoothed pseudo Wigner-Ville (SPWV) is used to extract some properties of the circumferential waves propagating in and around the bi-layer cylindrical shell. The obtained results by this representation are in good agreement with those obtained by the theoretical approach.

Acoustic scattering from a finite plate reinforced by parallel ribs with arbitrary rib spacing is investigated by applying thin plate and beam theories. The modal component of the surface pressure is calculated by an asymptotic expression that is only valid for higher-order modes at high frequencies. An approximate expression is derived for the far field scattered pressure by inverting matrices the rank of which is equal to twice the number of ribs. When the ribs are regularly spaced, approximate analytical expressions are proposed to calculate Bragg and forward Bloch-Floquet waves scattering separately from backward Bloch-Floquet waves scattering. These solutions are useful to deal with scattering problems where flexural waves are strongly attenuated after reflection on the edges of the plate. Finally the relevancy of the approximate expressions is evaluated by comparing numerical simulations to experimental data.

The fuzzy model derived from the input-output data of a given system using a fuzzy clustering algorithm is not generally optimal due to the errors introduced by the projection of the clusters onto the input variables and its approximation by the parametric functions. In the present work, the evolutionary algorithms are used to improve the initial fuzzy model obtained by fuzzy clustering algorithms. The proposed approach is applied to predict the form function of aluminum/polymer composite cylindrical shell. For this application, the performance of four fuzzy clustering algorithms: Gustafson Kessel (GK), fuzzy c-means (FCM), Gath-Geva algorithm (GG) and fuzzy c-regression model (FCRM) are optimized by genetic algorithm (GA) and hybrid particle swarm optimization with constriction factor approach (HPSO with CFA). The search space of evolutionary algorithms is restricted by the constraints in order to avoid loss of initial fuzzy model meaning. The achieved results show that the proposed approach is useful to improve the performance of an initial fuzzy model which is not optimal. The optimal model to predict the considered form function is FCM_GA with a mean square error about 0.2497 and coefficient correlation of 0.9081.

In acoustic field, the non-destructive testing and characterization purposes are carried out from the analyzing of the acoustic scattering of a progressive plane wave from the target studied. The present paper studies the signal backscattered from the copper/polymer composite cylindrical shell submerged in a fluid medium using Fourier analysis and time-frequency method. The Fourier analysis is used to find the pulse response and the resonance frequencies of the composite cylindrical shell. From large ranges of time-frequency methods, the smoothed pseudo Wigner-Ville distribution (SPWV) is applied because of its most effective properties to study the surface waves generated by the acoustic scattering of a plane wave. The time-frequency image obtained by SPWV is used to estimate the cut-off dimensionless frequencies of the surface waves. In addition, the group delay property of the SPWV distribution is applied to study the dispersion phenomenon of the waves. At each frequency, the group delay may be estimated directly from the time-frequency plane of the wave investigated. The results achieved by time-frequency method show fair agreement with those achieved by the plane of modal identification.

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Several theoretical and experimental studies show that the characterization of a tube can be done through the cut-off frequencies of the anti-symmetric circumferential waves A1 propagating around the tube of various radius ratio b/a (a: outer radius and b: inner radius). This work investigates the abilities of Artificial Neural Networks ANN to predict the thickness of a tube immersed in water for various cut-frequency of anti-symmetric circumferential wave A1. The useful data determinated from calculated trajectories of natural modes of resonances, were used to develop and to test the performances of these models. The ANN model was trained using Levenberg-Marquardt(LM) algorithm. Several configurations are evaluated during the development of these networks. The Mean Absolute Error (MAE), Mean Relative Error (MRE), Standard Error (SE), Root Mean Square Error (RMSE) and Correlation Coefficient (R) were the statistical performance indices, that were used to evaluate the accuracy of the various models. Based on the comparison between ANN and theoretical method, it was found that the ANN model can be applied successfully in the in the modeling of the thickness of a Submerged Tube.

In this note, we derive non trivial sharp bounds related to the weighted harmonic-geometric-arithmetic means inequalities, when two out of the three terms are known. As application, we give an explicit bound for the trace of the inverse of a symmetric positive definite matrix and an inequality related to the coefficients of polynomials with positive roots., Comment: Reviewed article, to appear in Math. Ineq. App

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

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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.

Population viability analyses (PVA) are increasingly used in metapopulation conservation plans. Two major types of models are commonly used to assess vulnerability and to rank management options: population-based stochastic simulation models (PSM such as RAMAS or VORTEX) and stochastic patch occupancy models (SPOM). While the first set of models relies on explicit intrapatch dynamics and interpatch dispersal to predict population levels in space and time, the latter is based on spatially explicit metapopulation theory where the probability of patch occupation is predicted given the patch area and isolation (patch topology). We applied both approaches to a European tree frog (Hyla arborea) metapopulation in western Switzerland in order to evaluate the concordances of both models and their applications to conservation. Although some quantitative discrepancies appeared in terms of network occupancy and equilibrium population size, the two approaches were largely concordant regarding the ranking of patch values and sensitivities to parameters, which is encouraging given the differences in the underlying paradigms and input 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.

A non-invasive ultrasonic method was used to control the change in physical properties of milk gel and the syneresis, which is an essential step in the manufacture of cheese. The velocity and the attenuation were recorded for ten hours. They provide a good indicator of syneresis occurring. The firmness of the milk gel increases with the variation in velocity (ΔV). The effects of the temperature, calcium chloride and rennet concentration on the syneresis were studied.

The problem of a plane acoustic wave scattered by a layered cylinder submerged in water is considered. This cylinder consists of a tube made of aluminum with a solid Lucite cylinder concentrically fitt inside it. These two components are coupled by a thin layer of water. A particular investigation is made on the influence of the thickness of the water layer on the presence of the bending wave A on the tube and the Scholte–Stoneley wave on the cylinder. The presence of these waves is examined in the function of the varying water layer thickness: two special cases are discussed. First, for a layer thickness greater than the tube thickness, it is shown that both the A wave on the aluminum tube and the Scholte–Stoneley wave on the Lucite cylinder are generated. Second, for a thickness much smaller than the tube thickness, a different wave is generated, which is a combination of both waves. These two cases are experimentally verified in a setup that employs a short pulse method.

The influence of evenly spaced ribs (internal rings) on the acoustic scattering from a finite cylindrical shell is examined over the dimensionless frequency range 1

We propose to study the behavior of diluated suspensions of clay and non colloidal particles by a combination of experiments. We plan to study these diluate particulate systems by changing the masse fraction of clay. We have developed a technique based on the ultrasound, by measuring ultrasonic attenuation waves in clay slurries. This technique makes it possible to control in real time the presence of the clay grains whose dimension is about 10 micron, using an interface conceived under Labview program. The slurries with different weight of clay were controlled. The detection of weak amount of clay’s grains and colloid were provided by the transducer 30Mhz. High sensitivity is obtained by analyzing the attenuation measurements founded from multiple paths through the slurry. The experimental results obtained show that the attenuation of waves due to particles varies linearly with mass fraction and the frequency of transducers. Therefore, such measures of the attenuation at a given frequency give the concentration of clay in the suspension. These frequency charts will be used for the quality control of the dam’s water. General Terms 0.N.E.P: Office National de l’eau Potable, (National office of drinking water). FFT: Fast Fourier Transform.

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.

Forward acoustic scattering of an immersed solid LINE (cylinder bounded by hemispherical endcaps) in water is investigated in our study. The object is made of stainless steel and its L/2a ratio is equal to 2 (L: Length of the cylinder part and a: the radius is equal to 60 mm). An impulse measurement method is used in the experimentation. Most of results are obtained experimentally, in bistatic configuration. Mobile receiver transducer is located in a distinct position from the emitter. The polar diagram patterns of the scattered pressure shows an important amplitude of pressure in the shadow side of this object. Analysis of this phenomenon is based on theoretical and experimental results obtained for a sphere with the help of elasticity theory. Moreover, this study relies on the grey-level representation of the angular position of the receiver in function of recorded time signals. Thus on forward acoustic time signals, it is possible to identify echoes due to propagation paths of waves on this object.

This paper studies the acoustic backscattering of short ultrasonic pulses by air-filled stainless steel-solid polymer two-layer cylindrical tubes immersed in water. The stainless steel one-layer tube is taken as a reference. The focus of this paper is on revealing the effects of physical characteristics of the solid polymer on the scattering phenomenon. The work is done from the calculation of the backscattered pressure, an inverse Fourier Transform, which provides a temporal signal. Wigner-Ville representation has been chosen in order to analyze the acoustic signal backscattered by each tube. For reduced frequencies ranging from 0.1 to 200, the resonance spectrum and resonance trajectories have shown the manifestations of the guided waves. In this respect, the bifurcation of the A0 wave to the A0 - and the A0 + waves has been observed. The authors investigate the reduced cutoff frequencies of the symmetrical and the antisymmetrical guided waves, specially the curves changes. The findings are then compared with those obtained for the stainless steel onelayer cylindrical tube. Reduced cutoff frequency values have also been extracted from Wigner-Ville time-frequency images. A good agreement has, therefore, been obtained. The study of acoustic scattering by stainless steel-solid polymer two-layer tubes has revealed the sliding of the reduced cutoff frequencies of A1 and S1 guided waves towards low values, due the repulsion phenomena. The relationship between reduced cutoff frequency and velocity of wave in the solid polymer is linear; which is a very interesting result.

Using a pulse reflection technique an ultrasonic system has been developed to monitor in situ the coagulation process of rennetted milk. The velocity and attenuation of ultrasonic waves through coagulating milk were continuously monitored. The observed changes in ultrasonic velocity during coagulation were used to predict the coagulation time. The coagulation time is indicative of the transition from the enzymatic phase to the physicochemical phase. The determination of coagulation time has a decisive role in determining the qualities of the end product in cheesemaking.

Recent results [J. D. N. Cheeke et al., J. Acoust. Soc. Am. 104, 3678 (1998)] reported a 20% decrease in group velocity for flexural mode circumferential waves propagating around water-filled thin-walled stainless-steel tubes. In the present work, the full theory of such modes is developed to explain the structure modes which originates from the coupling between the water filler and stainless tube. Calculated values of the group velocity for the first two coupled modes are in excellent agreement with experiment. The results are of interest for the physics of acoustic waves in fluid-loaded structures and have potential application for liquid level detection.

Acoustic backscattering from elastic cylindrical shells of finite lengths, immersed in water, is investigated. These objects, characterized by the ratio of length over diameter (L/2a = 9.76, 4.88, 2.44, a: outer radius), are excited by an obliquely incident plane acoustic wave. In the three cases studied here, the radii ratio b/a (b: inner radius) is fixed at 0.97. The investigated dimensionless frequency range extends over 10 k1aor = 50 (k1 : wave number in water). The first guided wave, T0, is of particular interest here. The influence of the shell's length on the backscattered pressure is experimentally observed in the time-angle and frequency-angle representations. In support of this experimental study, a time-domain representation is used by extending a theoretical model that provides a geometrical description of the helical propagation of the surface waves around the shell [Bao, J. Acoust. Soc. Am. 94, 1461-1466 (1993)]. Theoretical results on cylindrical shells considered as infinitely long, with identical characteristics, are compared with both experimental representations.

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.