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Rozprawy doktorskie na temat "Non linéarité matérielle"
Naceur, Hakim. "Contribution à l'optimisation de forme de structures minces en présence de non linéarités géométriques et matérielles". Compiègne, 1998. http://www.theses.fr/1999COMP1137.
Pełny tekst źródłaFlidrova, Kamila. "Contribution à la simulation numérique des crash de véhicules : prise en compte des non-linéarités matérielles et géométriques des composants de fonderie". Thesis, Ecully, Ecole centrale de Lyon, 2010. http://www.theses.fr/2010ECDL0043.
Pełny tekst źródłaNowadays, road safety is one of the main aims of car makers. To guarantee a high level of security to car drivers and passengers and also to other road users, such as for example pedestrians and two wheelers, the cars are submitted to a lot of tests before their commercialisation. Whether they are virtual or real, the experiments set out the conception and the development of a car. Nowadays, the numerical simulation plays a prime role in the development of new systems and equipments. In order to offer more and more predictivity by numerical models, the domain of the numerical simulation is inconstant evolution. The aim of this thesis is to contribute to the improvement of a car crash simulation. The subject of the study presented in this document is composed by two themes. The first one consists in inclusion of the material nonlinearities as fracture in the car crash dimensioning process. In car crash, two types of components are distinguished. Those which have to brake during the shock such as engine suspensions and those which have not to brake such as crankcase or clutch housing. The fracture is a phenomenon difficult to model, moreover, its computational time is important. Thus, the first fracture models were only functional (deactivation of fracture springs). With the arrival of numerical methods such as element deletion method, a lot of fracture models were developed. Because these models are relatively recent, the material databases are often incomplete which makes their use more difficult. Thus, one of the aims of this study is the material parameters identification of Mohr-Coulomb and Johnson-Cook fracture model with the aid of experiments on specimens. Another experiment campaign on an automotive subsystem was also realized. The numerical correlation using the material fracture parameters identified in the first step enabled to validate the "volumic"fracture modelisation and to identify the ways of progress of the current methodology. The second theme presented in this document is the modeling of linear elastic behavior of components which have not to brake in car crash and inclusion of geometrical nonlinearities as large rotations and contact. A modeling by linear elastic super elements adapted for explicit simulations with large rotations was proposed for massive cast iron components. The modeling by super elements was realized in Radioss by means of the file.fxb. A new reduction method derived from that of MacNeal was proposed. Its transformation basis is constituted by a free eigen-modes completed by residual flexibility modes. The model is reduced by means of Matlab routines which were developed in the framework of the thesis. In order to integrate the modeling by superelements in the dimensioning car crash process used at PSA, a procedure Abaqus–Matlab–Radioss was proposed. A process for the generation of the file.fxb by means of the CAD/CAMtools used at PSA was established. In order to optimize the simulation performance with superelements, three new models for contact management with a superelement were proposed. The modeling by superelement was applied in a test model and also in a frontal car crash simulation
Guelaz, Rachid. "Modélisation de systèmes ultrasonores avec VHDL-AMS : Application à la mesure du paramètre de non linéarité B/A". Nancy 1, 2006. http://www.theses.fr/2006NAN10047.
Pełny tekst źródłaThis thesis abords ultrasound modelling systems with VHDL-AMS. Goal is prediction of a measurement cell behaviour dedicated to ultrasound non linearity measurements. To preview in a near future miniaturisation and conception of a measurement system which performances could be estimated with ours models, we proceed by a decomposition of the measurement system with associating to each elements a behavioural model developed in VHDL-AMS language. Originality of ours works is the integration of the non linearity parameter B/A in the propagation medium modelling. Simulation results are rigorously compared to implantation in Matlab and PSPICE software and in vitro measurement. This work is divided in 4 parts : State of the art of the ultrasound modelling systems ; Theoretical analysis of the non linear propagation and measurement methods of the parameter B/A ; Piezoceramic transducers and non linear medium modelling with VHDL-AMS ; Modelling and conception of a non linearity measurement cell in pulse-echo and transmission mode. Results obtained show that a medium could be characterized as function to the B/A parameter estimated with different biological and liquid mediums. Perspectives open by this work has been highlighted by scientific community members at different international congress
Merit, Benoit. "Contribution à l'identification des non-linéarités des moteurs de haut-parleurs électrodynamiques : sur la réalisation de moteurs tout aimant". Le Mans, 2010. http://cyberdoc.univ-lemans.fr/theses/2010/2010LEMA1012.pdf.
Pełny tekst źródłaThis PhD thesis (CIFRE, Orkidia Audio SARL, Bidart) deals with identification and characterization of the nonlinearities of traditional electrodynamic loudspeaker motors and with the achievement of a loudspeaker motor totally made of magnets. The first part of the dissertation is dedicated to the analysis of the nonlinearities specific to the loudspeaker motors. More particularly, it is shown that most of the motors characteristics depend on the current flowing through the voice-coil, on the frequency of this current and on the position of the voice-coil in the magnetic circuit. The dependence of the loudspeaker blocked impedance with frequency due to eddy currents is modelled, showing that each dependence is coupled to the other and therefore becomes a source of distortion in loudspeakers. These three dependences find their origin in the use of ferromagnetic materials in the magnetic circuit of traditional loudspeakers. Thus, the second part of the dissertation deals with the use of a magnetic circuit indicated as "magnet-only structure" because it is totally made of permanent magnets. It is shown that electrical and magnetic linear properties of the magnets improve the linearity of loudspeaker motors at high frequencies. The last source of distortion comes from the fact that the force factor of the loudspeaker can still be a function of the voice-coil displacement. Thus, two structures that have been conceived and patented solve this problem and extend the linearity of the transducer to the low frequencies
Koutoati, Kouami. "Modélisation numérique du comportement statique et vibratoire des poutres sandwich viscoélastiques à gradient de propriétés". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0290.
Pełny tekst źródłaThis thesis proposes a numerical tool for the static and dynamic study of viscoelastic structures made of Functionally Graded Materials (FGM) for vibration control by passive damping. The objective is to make available to engineers a generic code based on the finite element approach for sizing calculations on FGM sandwich beam with viscoelastic core for applications requiring lightness and good thermal and mechanical resistance such as aerospace, automotive and nuclear. To reach this objective we first proposed a numerical model for the static and free vibration study of FGM sandwich beams with elastic behavior. This finite element model is implemented in the Matlab code environment. Using this code, we compare different beam theories for different geometric properties and boundary conditions. Thus, the limit of the classical beam theory in the study of short structures is highlighted. Also with this numerical model, the study of axial-bending and axial-rotation coupling is possible. From this, it is shown that FGM structures are very sensitive to spatial coupling and warping effects because of the non-symmetrical distribution of the material in their cross sections. In the proposed code, the resolution of the vibration problem is possible using classical eigenvalue and eigenvector problem solving methods. Then to introduce passive damping in the FGM sandwich structure, we proposed a sandwich beam model with FGM materials faces and viscoelastic materials core. This model is also implemented in the Matlab language and proposed as a generic tool. The interest of this numerical tool lies in its ability to compute the modal properties as well as the behavior of the viscoelastic FGM sandwich beam while taking into account the frequency dependence of the viscoelastic behavior, the boundary conditions and the axial-bending and axial-rotation coupling specific to FGM materials. The free vibration problem is non-linear in this case due to the material non-linearity induced by the soft layer. In the proposed code, the resolution of this problem is possible thanks to the coupling of the homotopy technical, the asymptotic numerical method and the automatic differentiation. Through this work, the contribution of FGM materials in the improvement of the damping power of structures is highlighted. In the continuation of the work, we propose a finite element formulation to compute the amplitude of forced vibrations of viscoelastic FGM sandwich structures. The resolution of the forced vibration problem is possible by using the bandwidths method. A study on the contribution of FGM materials in the reduction of vibration amplitudes is carried out for different viscoelastic laws. It is proved in this study that by a direct control of the composition gradient of FGM materials it is possible to optimize the damping power of structures even for low frequency modes for which classical composite materials have a damping power requiring improvement
Kongo, Konde Ange. "Modélisation du roulement d'un pneumatique d'avion". Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10009.
Pełny tekst źródłaThis PhD Thesis presents the approach adopted for the setting of numerical model based on Finite Element Method for jumbo-jet tire. The model takes into account the real geometry, the complex material structure, the various materials and their properties as well as the interactions between the tire and the ground (contact, friction and thermal-mechanical coupling due to friction). Tests are performed in order to identify geometrical and material parameters.Static and dynamic simulations using a Lagragian approach and an Eulerian/ Lagrangian mixed approach were performed on this proposed model. This second approach which significantly reduces the computational cost time was validated for cornering tire simulation. The model allows thereby to estimate the forces in the tire/ ground contact patch. We show the influency of loading parameters (vertical load, inflating pressure and rolling velocity) and of the slip angle on the self aligning torque (MZ) and on the lateral friction coefficient (µY) corresponding on the ratio between lateral force and vertical load due to the aircraft weight. We also present a sensitivity study on geometrical and material parameters.Coulomb's and thermal diffusion tests were performed in order to identify the friction coefficient law as function of temperature (on concrete and asphalte surfaces) and the temperature evolution in the aircraft tire thickness. These tests allowed to take into account thermal effects in the model and to propose a thermal-mechanical coupling model which emphasized the decreasing of µY and the rapid vanishing of MZ towards zero beyond a critical slip angle βmax varying with the tire loading conditions. These variations were observed experimentally