Abdelaziz Soufyane

Stabilisation de la poutre de Timoshenko

Resume Dans cette Note on etudie la stabilisation de la poutre de Timoshenko. Pour ce faire on utilise une seule force de controle.

Simulations of surface acoustic wave devices built on stratified media using a mixed finite element/boundary integral formulation

The demand for high frequency surface acoustic wave devices for modern telecommunication applications imposes the development of devices able to answer the manufacturer requirements. The use of high velocity substrates for which a piezoelectric layer is required to excite and detect surface waves has been widely investigated and requires the implementation of accurate theoretical tools to identify the best combinations of material. The present paper proposes a mixed formulation combining finite element analysis with a boundary integral method to accurately simulate the capability of massive periodic interdigital transducers to excite and detect guided acoustic waves in layered media. The proposed model is exploited for different typical configurations.

Finite-element analysis of periodic piezoelectric transducers

The need for optimized acoustic transducers for the development of high-quality imaging probes requires efficient simulation tools providing reliable descriptions of the behavior of real devices. The purpose of this work is the implementation of a finite-element model for the simulation of periodic transducer arrays. By using the assumption of harmonic excitation, the harmonic admittance of the studied structure can be derived. It is then shown how the mutual admittance is deduced from this feature, allowing one to estimate the amount of cross-talk effects for a given periodic transducer. Computation results are reported for standard linear acoustic probes, 2-2 (one-dimensional periodic) and 1-3 (two-dimensional periodic) piezocomposite materials. In the case of 2-2 connectivity composites, a comparison between nonperiodic and periodic computations of the mutual admittance is conducted, from which the minimum number of periods for which periodic computations can be trustfully considered can be estimated.

Energy decay for Porous-thermo-elasticity systems of memory type

Linear systems of porous-thermo-elasticity including a memory term in one dimension are studied. We establish an exponential and polynomial decay results.

Measured throughput and SNR of IEEE 802.11g in a small enterprise environment

Wireless local-area networks (WLANs) based on IEEE 802.11 a/b/g standards are growing rapidly. WLANs can provide the benefits of network connectivity without the restrictions of being tied to a location or restricted by wires. Despite the convenience of mobility, the performance of the WLAN must be addressed carefully before the WLAN can be adopted as part of an enterprise network. In this paper, the impact of various key parameters on the actual performance of IEEE 802.11g is verified by a serious of controlled experiments. Overall, three sets of independent experiments were conducted to measure IEEE 802.11g effective application level throughput and signal-to-noise ratio in three typical indoor scenarios. The analysis results and measurement campaign provide insights into the required provisioning for 802.11g WLAN to ensure that it provides the needed coverage and capacity for the intended users.

Stability result of the Timoshenko system with delay and boundary feedback

Our interest in this paper is to analyse the asymptotic behaviour of a Timoshenko beam system together with two boundary controls, with delay terms in the first and second equation. Assuming the weights of the delay are small enough, we show that the system is well-posed using the semigroup theory. Furthermore, we introduce a Lyapunov functional that gives the exponential decay of the total energy.

Solution of linear and nonlinear parabolic equations by the decomposition method

Adomian decomposition method (ADM) has been applied to solve many differential equations. In this paper, we have used the ADM to solve linear and nonlinear parabolic equation with variable parameters depends on time and space. The ADM does not need linearization or weak nonlinearity assumptions. The results obtained indicate that the ADM is efficient and accurate.

Boundary stabilization of memory type in thermoelasticity of type III

In this article, we establish a boundary stabilization of memory type result for solutions of a multidimensional system of thermoelasticity of type III.

Polynomial and exponential stability for one-dimensional problem in thermoelastic diffusion theory

We consider one-dimensional problem for the thermoelastic diffusion theory and we obtain polynomial decay estimates. Then we show that the solution decays exponentially to zero as time goes to infinity; that is, denoting by E(t) the first-order energy of the system, we show that positive constants C 0 and c 0 exist which satisfy E(t) ≤ C 0 E(0)e −c 0 t .

Stabilization of the simulation of saw devices on stratified structures: application to transverse plate mode resonators

Two approaches are investigated to model accurately the physical characteristics of plate mode devices, and more particularly of resonators. They are respectively based on finite element analysis (FEA) and on mixing FEA with a boundary integral method (FEA/BIM). In the later case, using a transfer matrix approach for the computation of the spectral Greens function results in numerical instabilities for large layer thickness or large slowness. A new stable algorithm is described for the computation of the spectral Greens function of a multilayer structure, that is inherently numerically stable. The main parameters of wave propagation (velocity, coupling factor, reflection coefficient) can then be estimated considering an infinite periodic structure and computing the harmonic admittance. For comparison with measurements of quartz transverse plate mode resonators, the estimated parameters can be inserted in a P-matrix model. Theory and experiments are found to comply well for both the pure FEA and the FEA/BIM approaches.