Chafik Karra

An integral equation formulation for boundary element analysis of propagation in viscothermal fluids

A new variational formulation using integral equations for the resolution of a propagation problem in a viscous and thermally conducting fluid is investigated. Numerical techniques are applied to a geometry of revolution. Results are compared to an analytic solution for a cylindrical cavity filled with air. These results illustrate the effects of viscosity and thermal conductivity of air in the case of micro cavities.

Boundary Element Analysis of Vibro-Acoustic Interaction between Vibrating Membrane and Thin Fluid Layer

This paper presents a variational formulation for the study of the acoustic propagation and radiation of a vibrating membrane coupled to a cavity filled with a visco-thermal fluid. This formulation is obtained by combining a variational formulation by integral equations of both internal and external fluids, which takes account of acoustic and entropic waves coupling, with a classical variational formulation of the membrane. Numerical results obtained by this new formulation are compared to those obtained when the viscous and thermal effects are not considered.

Topological approach to solve 2D truss structure using MGS language

In this paper we are interested in introducing the notion of topological collections and transformations for the modeling of mechatronic systems by applying the MGS language (General Modeling System). This approach provides a generic local model that optimizes the global behavior by separating the topology and the physics of the studied system. For this purpose, the MGS language is implied in the case of 2D truss structure. Since a good argument is observed, this approach can be generalized for modeling more complex systems (mechatronic systems).

Vibration Behavior of Composite Material with Two Overlapping Delaminations

The paper presents an analysis of the vibration behavior of glass fiber reinforced composites with two overlapping delaminations. The effect of delamination length on the vibration parameters is studied. Throughout a series of vibration tests, the change of natural frequencies and modal damping due to delaminations is evaluated. A numerical simulation considering finite element analysis allows to predict the change of natural frequencies for a known damage size. Modal damping was established which evaluates the different energies dissipated in the material layers direction of the fiber reinforced composites. A comparison of the different results was performed. Next, strain energy of layers directions were established by a numerical analysis and discussed.

Topological modeling of a one stage spur gear transmission

Finding a basis of unification for the modeling of mechatronic systems is the search subject of several works. This paper is a part of a general research designed to the application of topology as a new approach for the modeling of mechatronic systems. Particularly, the modeling of a one stage spur gear transmission using a topological approach is tackled. This approach is based on the concepts of topological collections and transformations and implemented using the MGS(modeling of general systems) language. The topological collections are used to specify the interconnection laws of the one stage spur gear transmission and the transformations are used to specify the local behavior laws of its different components. In order to validate this approach, simulation results are presented and compared with those obtained with MODELICA language using Dymola solver. Since good results are achieved, this approach might be used as a basis of unification for the modeling of mechatronic systems.

New topological approach for the modelling of mecatronic systems: application for piezoelectric structures

In this study, a new topological approach for the modelling of mecatronic systems is presented. This approach offers the opportunity to separate the behaviour laws (physics) and the interconnection laws (topology) at local level. Then, it can be used as a unification basis for the modelling of the different fields of Mecatronics. This approach is based on the notion of topological collections and transformations and applied using the MGS language (Modelling of General Systems). The emphasis is placed on the application of this approach to the piezoelectric structures (Multi layer piezoelectric stack and piezoelectric truss structure). To validate this approach, simulation results are presented and compared with those obtained by the finite element analysis ANSYS software.

Mechanical behaviour and damage evaluation by acoustic emission of composite materials

Purpose – The aim of the present study is to investigate the mechanical behaviour of cross‐ply laminates under static tensile and buckling loading. Different cross‐ply laminates constituting of carbon fibers (CFRP), hybrid fibers (HFRP) and glass fibers (GFRP) in an epoxy matrix were considered. This work is also interested in identifying and characterizing the local damage in the composites with the use of acoustic emission method (AE).Design/methodology/approach – The cross‐ply laminates are differentiated by the stacking sequences, thickness of 90° oriented layers and reinforcement. They are subjected to the static tensile and buckling load. The damage investigation is reached by the analysis of acoustic emission signals collected from static buckling tests.Findings – The results show the effects of reinforcement type, stacking sequences and thicknesses ratio of 90° and 0° layers on the stiffness, failure load and displacement. A cluster analysis of acoustic emission data is achieved and the results are...

Topological Modeling of 2D Piezoelectric Truss Structure Using the MGS Language

In this paper, we are interested in the change sustained by the topology transformation and in introducing the notion of variable topology of dynamics systems. We are also interested in using substitution to model complex patterns by applying the MGS language (General Modeling System). This later is applied to a 2D piezoelectric truss structure. In fact, the process has been validated since the modeling by using the KBR topological graph, and then by using MGS language, it shows the same result. The major interest in presenting this model of piezoelectric structure is that it contains both electrical and mechanical parameters, and this allows us to treat it as a mini-mechatronic system (actuator and sensor). Considering that any system which is complex is legible to be represented by a topological graph, and knowing that each component of the mechatronic system has its local behavior’s law, so the process that applies to any mini-mechatronic system can be extended later to complex systems. This work highlights the importance of the MGS language, and it also makes the topological graph modeling more flexible. Moreover, we can do the modeling smoothly by changing the topological structure without modifying the behavior’s law, but simply by modifying the topological structure.

Characterization of sandwich beams with shear damages by linear and nonlinear vibration methods

The aim of the present work is to study the vibration behavior of sandwich composites with shear damages on the foams. The effect of the densities of damage on the linear and nonlinear vibration parameters is studied. The sandwich materials used in this study is constructed with glass fiber laminates as skins and with PVC closed-cell foams with density 60 and 100 kg m−3 as core. After a serie of vibration tests, the change of natural frequencies and modal damping due to the damage and the foam densities. For an intact specimen, the resonance frequency was constant when we increase the excitation amplitude. For damaged specimens, the resonance frequencies decrease and the loss factors increase proportionally with the increasing excitation amplitude. The nonlinear parameters corresponding to the elastic modulus and damping were determined for each frequency modes and each damage and foam densities. The results showed that nonlinear dissipative parameters were more sensitive to damage than linear elastic and dissipative parameters.

Fatigue behavior and damage analysis by the acoustic emission technique of cross-ply laminates under tensile loading

Purpose The purpose of this paper is to study the mechanical behavior in fatigue tensile mode of different cross-ply laminates constituted of unidirectional carbon fibers, hybrid fibers and glass fibers in an epoxy matrix; and to identify and characterize the local damage in the laminated materials with the use of the acoustic emission (AE) technique. Design/methodology/approach The tests in the fatigue mode permitted the determination of the effect of the stacking sequences, thickness of 90° oriented layers and reinforcement types on the fatigue mechanical behavior of the laminated materials. The damage investigation in those materials is reached with the analysis of AE signals collected from fatigue tensile tests. Findings The results show the effects of reinforcement type, stacking sequences and thicknesses ratio of 90° and 0° layers on the mechanical behavior. A cluster analysis of AE data is achieved and the resulting clusters are correlated with the damage mechanism of specimens under loading tests. Originality/value The analysis of AE signals collected from tensile tests of the fatigue failure load allows the damage investigation in different types of cross-ply laminates which are differentiated by the reinforcement type, stacking sequences and thicknesses ratio of 90° and 0° layers.