Articolele autorului Mihai Valentin Predoi
Link la profilul stiintific al lui Mihai Valentin Predoi

Effects of periodicity perturbations on the transmission by underwater phononic crystals

The effects of periodicity perturbations in underwater phononic crystal layers composed of nonin- terpenetrating rows of identical shells are investigated. The results for one row are obtained by using a multiple scattering method between shells. Then, taking into account the multiple reflections and transmissions between two adjacent rows, a Debye series method is used to calculate the reflection and transmission coefficients by a finite number

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Vibraţii Mecanice – Modele şi aplicaţii în Matlab
Influence of material viscoelasticity on the scattering of guided waves by defects

Guided waves are potential candidates for the nondestructive evaluation of viscoelastic structures due to their relatively long range of propagation. The major drawback is the difficulty in interpreting the scattered waves especially at high frequency-thickness values since many modes then exist. Moreover, in damping material waveguides, each mode of the scattered field has its own attenuation. Viscoelastic material characterization has been widely

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Guided waves in elastic plates with Gaussian section

Experimental and numerical results are presented on the behavior of guided waves in elastic plates in plane strain that include a Gaussian variation of their section, located between two areas of constant thickness. The area of varying section is wide compared to the used wavelengths, which allows wave propagation inside this area. The experimental results show that an incident Lamb wave is indeed converted into an adiabatic wave inside the varying

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Wave propagation along transversely periodic structures

The dispersion curves for guided waves have been of constant interest in the last decades, because they constitute the starting point for NDE ultrasonic applications. This paper presents an evolution of the semianalytical finite element method, and gives examples that illustrate new improvements and their importance for studying the propagation of waves along periodic structures of infinite width. Periodic boundary conditions are in fact used to

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An orthogonality relation-based technique for post-processing finite element predictions of waves scattering in solid waveguides

In this paper we propose an efficient way to post-process output data predicted by Finite Element (FE) or Boundary Element (BE) codes, when the scattering of Lamb modes by defects in plate-like structures is considered. The use of a general orthogonality relation is compared to classical post-processing made with spatial FFT. To get the amplitudes of incident or scattered modes, this orthogonality relation requires the numerical prediction of the

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Lamb Waves Propagation in Elastic Plane Layers with a Joint Strip

The Lamb waves can be used for the ultrasonic characterization of welds because of their relative long-range propagation. In this paper, a simplified model of a weld strip between two identical semi-infinite elastic layers is investigated. The reflected and transmitted ultrasonic fields are expressed by modal series whose coefficients are obtained by application of orthogonality relation. The energy balance between the incident and the scattered

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Finite element predictions for the dynamic response of thermo-viscoelastic material structures

In this paper, constitutive relations are solved in the Fourier domain using a finite-element-based commercial software. The dynamic responses of viscoelastic bars or plates to either thermal or mechanical loads are predicted by considering complex moduli (Young, Poisson, stiffness moduli) as input data. These moduli are measured in the same frequency domain as that which is chosen for modeling the wave propagation. This approach is simpler since

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Recent results about Lamb waves reflection at the free edge of an elastic layer

Most of the previous papers, which study the Lamb waves reflection on the free edge of a layer, provide partial information about the reflected amplitudes and phases of modes and about the ratios of reflected vs. incident energy for each propagating mode. Here, we use a method, based on Lamb modes series expansion. The amplitude, the phase and the energy of each reflected mode are calculated for the incident modes S0, S1, A0, A1 respectively. These

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Numerical predictions and experiments on the free-plate edge mode

In this paper, the edge mode vibration is studied with three different methods: the reciprocal work method, already used by Torvik [J. Acoust. Soc. Am. 41 (1967) 346] to model this phenomenon, the S-parameter method and a finite element model that are applied for the first time to the study of the edge resonance. Moreover, laser probe measurements of the edge mode have also been performed and compared to the numerical predictions. The good agreement

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