Détermination de l'épaisseur et la résistivité au passage de l'air d'un matériau poreux à structure rigide en utilisant les ondes transmises.

National audienceUne méthode acoustique est proposée pour mesurer la résistivité au passage de l’air et l’épaisseur d’un échantillon poreux à structure rigide. Les méthodes classiques 3,4 permettant la mesure de la résistivité (où la perméabilité visqueuse) nécessitent la connaissance préalable de la porosité. La méthode présentée dans ce travail est basée sur un modèle temporel du problème direct dans lequel une expression simplifiée (indépendante de la fréquence et de la porosité) du coefficient de transmission dans le régime de Darcy (très basses fréquences) est établie. Cette expression ne dépend que de la perméabilité visqueuse (où la résistivité au passage de l’air) et de l’épaisseur d’un échantillon poreux. Le problème inverse est résolu en minimisant, l’écart entre le signal transmis théorique et expérimentale, permettant ainsi la détermination de l’épaisseur et de la perméabilité visqueuse (où la résistivité) d’une mousse en plastique. Cette méthode présente l’avantage d’être simple, rapide et efficace

Ultrasonic waves Reflected at Oblique Incidence by Porous Rigid Medium.

International audienceAn ultrasonic reflected wave at oblique incidence by porous medium with rigid frames is considered using equivalent fluid model. The viscous and thermal losses of the medium are described by two susceptibility kernels which depend on the viscous and thermal characteristic lengths. Analytical derivation of reflection coefficient is given in frequency domain. The simulated reflected wave is obtained at time domain by convolution between the reflected operator and the incident field. Experimental results for plastic foam samples of air-saturated porous media are given and compared with theoretical prediction

Transient Acoustic Wave Propagation in Porous Media

International audienceTransient Acoustic Wave Propagation in Porous Medi

Characterization of rigid porous medium via ultrasonic reflected waves at oblique incidence

International audienceIn this paper, an enhanced method is proposed for measuring porosity, tortuosity, viscous and thermal characteristic length of porous materials having a rigid frame via reflected ultrasonic waves at oblique incidence using the equivalent fluid model. The advantage of the proposed method is that the four parameters are determined simultaneously just using reflected experimental waves for a porous material saturated by air. The inverse problem is solved based on the least-square numerical method using experimental reflected waves in time domain. Tests are performed using industrial plastic foams. Experimental and numerical validation results of this method are presented

Generalized equation for transient-wave propagation in continuous inhomogeneous rigid-frame porous materials at low frequencies

International audienceThis paper provides a temporal model for the propagation of transient acoustic waves in continuous inhomogeneous isotropic porous material having a rigid frame at low frequency range. A temporal equivalent fluid model in which the acoustic wave propagates only in the fluid saturating the material, is considered. In this model, the inertial effects are described by the inhomogeneous inertial factor [A.N. Norris., J. Wave Mat. Interact. 1 365 (1986)]. The viscous and thermal losses of the medium are described by two inhomogeneous susceptibility kernels which depend on the viscous and thermal permeabilities . The medium is one dimensional and its physical parameters (porosity, inertial factor, viscous and thermal permeabilities) are depth dependent. A generalized wave propagation equation in continuous inhomogeneous material is established and discussed

Ultrasound Measuring of Porosity in Porous Materials

This chapter provides a temporal method for measuring the porosity and the tortuosity of air-saturated porous materials using experimental reflected waves. The direct problem of reflection and transmission of acoustic waves by a slab of porous material is studied. The equivalent fluid model has considered in which the acoustic wave propagates only in the pore-space. Since the acoustic damping in air-saturated porous materials is important, only the reflected waves by the first interface are taken into account, and the multiple reflections are neglected. The study of the sensitivity analysis shows that porosity is much more sensitive than tortuosity to reflection, especially when the incident angle is less than its critical value, at which the reflection coefficient vanishes. The inverse problem is solved using experimental data at a different incidence angle in reflection. Some advantages and perspectives of this method are discussed

Inverse estimation of the permeability of porous materials using experimental data via reflected waves at low frequencies

International audienceAn acoustic reflectivity method is proposed for measuring the permeability or flow resistivity of air-saturated porous materials. In this method, a simplified expression of the reflection coefficient is derived in the Darcy's regime (low frequency range), which does not depend on frequency and porosity. Numerical simulations show that the reflection coefficient of a porous material can be approximated by its simplified expression obtained from its Taylor development to the first order. This approximation is good especially for resistive materials (of low permeability) and for the lower frequencies. The permeability is reconstructed by solving the inverse problem using waves reflected by plastic foam samples, at different frequency bandwidths in the Darcy regime. The proposed method has the advantage of being simple compared to the conventional methods that use experimental reflected data, and is complementary to the transmissivity method which is more adapted to low resistive materials (high permeability)

GWO-super-twisting integral sliding mode control of 60 KW PV system based on interleaved boost converter

The energy provided by the PV system is strongly influenced by climatic conditions such as solar radiation and cell temperature. A suitable DC /DC converter and a robust control strategy combined with the maximum power point tracking (MPPT) algorithm are required to harness the maximum power of the panel. This paper proposes a super-twisting integral sliding mode control (ST-ISMC) for four legs interleaved boost converter (FLIBC) as an interface to the MPPT algorithm for a 60 KW PV system. The FLIBC has been used to overcome the drawbacks of the conventional boost converter (CBC). The ST-ISMC is proposed to maintain the PV voltage track the reference provided by the MPPT algorithm and ensure the equal sharing of input current between legs. The controller gains of the proposed ST-ISMC have been calculated using the grey wolf optimization algorithm for better performance. The simulation results prove the excellent performance of the proposed controller over the conventional controller