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Rozprawy doktorskie na temat "Couplage acoustique-élastique"
Nassor, Alice. "Domain decomposition method for acoustic-elastic coupled problems in time-domain. Application to underwater explosions". Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAE015.
Pełny tekst źródłaThis work addresses global-in-time domain decomposition approaches for the numerical solution of transient fluid-structure interaction problems. To determine an optimal algorithm, we first study the solvability for the transient acoustic and elastodynamic problems with Robin and Neumann boundary conditions. We state solvability results along with the different space-time regularities of the solutions. We also study the solvability for the transient coupled elastodynamic-acoustic problem. Using on these mathematical results we then propose a global-in-time iterative algorithm based on Robin boundary conditions for the coupled elastodynamicacoustic problem and we prove its convergence.These results are leveraged to design a computational methodology by coupling two efficient numerical methods. The fluid response is formulated in the discrete-time domain, using a Z-BEM approach that combines (i) a boundary element method (BEM) accelerated with hierarchical matrix implemented in the Laplace domain and (ii) a convolution quadrature method. The structure response is modelled using the finite elements method. We thus propose a global-in-time iterative coupling with guaranteed convergence, which enables the use of two distinct numerical methods in a non-intrusive manner.Several improvements are then explored: an acceleration method is implemented and a high-frequency approximation is proposed to improved the Z-BEM efficiency. A second iterative global-in-time coupling based on an acoustic-acoustic interface is then proposed and its convergence is also proved. This coupling enables the addition of non linear effects due to the cavitation phenomenon to derive a more realistic fluid model. The Z-BEM is lastly adapted using the method of images to take a free surface into account.This method is applied on fast-time problems of acoustic shock wave scattering by submerged elastic structures and enables to simulate realistic configurations from naval industry
Hamidouche, Louiza. "Spectroscopie micro-onde pour la mesure des charges d'espace à haute résolution spatiale dans les isolants en couche mince". Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS275.
Pełny tekst źródłaThe objective of this thesis is to come up with and test a new method for the measurement of space charge in very thin insulating films with a high spatial resolution. The proposed method is called Electro-Acoustic Reflectometry (EAR) method. The EAR method relies on the electro-elastic coupling of the sample under test. Both excitation and measurement are of electrical nature and are performed in frequency domain. A microwave setup is used for high frequency measurements. The measurement principle is the generation of ultasonic waves when space charge undergoes an applied electrical field. The energy that is used up in the generation of these waves leaves a feature in the reflection of the electrical excitation. It is this feature that is used to find the space charge distribution by a simple inverse Fourier transform. A measurement setup comprising a vector network analyser, a dedicated sample holder and an acquistion interface allows to test the EAR method. The obtained results are promising. A bulk spatial resolution of 1.2µm has been demonstrated. It exceeds the current best spatial resolution achieved by existing conventionnal ultrasonic methods by a factor of about 10. To further enhance the spatiale resolution of the EAR method, it is necessary to broaden the measurement frequency range. An approach to deal with the problems occuring at high frequnecy is proposed
Parpiiev, Tymur. "Ultrafast magneto-acoustics in magnetostrictive materials". Thesis, Le Mans, 2017. http://www.theses.fr/2017LEMA1044/document.
Pełny tekst źródłaWith the advent of femtosecond lasers it became possible to measure how femtosecond optical demagnetization can probe the exchange interaction in ferromagnetic metals. Laser-induced demagnetization of materials with strong magneto-elastic coupling should lead to the release of its build-in strains, thus to the generation of both longitudinal (L) and shear (S) acoustic waves. In this thesis, generation of shear picosecond acoustic pulses in strongly magnetostrictive materials such as Terfenol is processed analytically and shown experimentally. In case of Terfenol with strong magneto-crystalline anisotropy, laser induced demagnetostriction is responsible for S excitation. First, the phenomenological model of direct magnetostriction in a Terfenol monocrystalline film is developed. The shear strain generation efficiency strongly depends on the orientation of the film magnetization. Time-resolved linear MOKE pump-probe experiments show that transient laser-induced release of the magnetoelastic strains lead to the excitation of GHz L and S acoustic waves. These results are the first experimental observation of picosecond shear acoustic wave excitation by laser-induced demagnetostriction mechanism. Second, the interaction of an optically generated L acoustic pulse with the magnetization of a Terfenol thin film is reported. Arrival of the picosecond strain wave alters a change of its magnetization and leads to acoustic mode conversion, which is another pathway of shear acoustic wave generation. The frequency bandwidth of the generated acoustic pulses matches the demagnetization timescale and lies in the range of several hundreds of GHz, close to 1 THz
Lahyaoui, Otmane. "Contribution to the study of magnetostrictive energy conversion : from material to device". Thesis, Compiègne, 2019. http://www.theses.fr/2019COMP2472.
Pełny tekst źródłaIn this era of all-electric, the demand for electrical technology is clearly increasing in several sectors (automotive, rail and aeronautics). Unfortunately, magnetic noise and vibrations originating from these technologies remain a worrying issue in these means of transport, thus disrupting passenger comfort. Knowing that the operation of these electrical devices such as motors, generators and transformers relies largely on ferromagnetic materials, the main noise sources are magnetostriction and magnetic forces. The thesis works discussed in this manuscript aim to improve the current knowledge on the magnetic and magnetostrictive properties of ferromagnetic materials (NO Fe-3% Si) in a perspective of understanding and control of their behavior under different solicitations (mechanical stress, frequencies ...). The presented study offers a complete investigation approach from the material to the electrical device. A first experimental part presents the magnetic and magneto-elastic characterizations carried out on magnetic sheets and on a laminated structure. A study on the magnetic resonance induced by the magnetostriction including on an experimental modal analysis is presented as well. A second part deals with the modeling of the magneto-elastic behavior of magnetostriction and its integration into a finite element tool to predict the impact of the magnetostriction on a more complex structure than simple electrical sheet. Finally, a study of a possible interaction of magnetostriction with magnetic forcesis described with a comparison of simulation results with an analytical method and experimental measurements
Dagher, Gulnar. "Mesure directe et non destructive de la distribution de charges d'espace à l'échelle nanométrique dans les isolants et les semi-conducteurs : application à la microélectronique". Paris 6, 2008. http://www.theses.fr/2008PA066573.
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