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Analyse modale expérimentale d'une structure vibrant dans l'eau en écoulement turbulent

Abassi, Khaled (2005). Analyse modale expérimentale d'une structure vibrant dans l'eau en écoulement turbulent. Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

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Résumé

Les systèmes mécaniques sont soumis à des excitations diverses lors de leur fonctionnement. Selon le type d'excitation, la réponse vibratoire diffère aussi. Les excitations telles que les chocs et excitations aléatoires excitent les fréquences de résonances. Dans le cas particulier des turbines hydrauliques, les ailettes opérant dans l'eau sont soumises à des écoulements turbulents et à des contraintes mécaniques générant des vibrations pouvant être amplifiées à la résonance. Ces excitations peuvent nuire à l'état des ailettes, sujettes à la rupture à cause de l'apparition de fissures, ce qui provoque des relâchements des points de soudures. Ceci se répercute sur la bonne marche de la turbine et peut affecter notablement son rendement énergétique.

Titre traduit

Experimental modal analysis for a structure subjected to turbulent water flows

Résumé anglais

The mechanical systems are subjected to various excitations during their operation. According to the type of the excitation, the vibratory response differs too. The excitations such as the shocks and random excitations excite the resonance frequencies of the system. In the special case of the hydraulic turbines, the blades operating under water are subjected to turbulent flows and mechanical constraints generating vibrations which are may be amplified when the resonance occurs. This fact may harm the state of the turbine blades subjected to the rupture because of the appearance of cracks and that produces the slackening of the welding. This is reflected on the safety functioning of the turbine, and affects notably its energetic efficiency. Thus, the production process is disturbed and colossal costs of repairs and unavailability are generated. One can easily understand the importance of the knowledge of the structural resonance frequencies of the machine in order to specify a safety range of operating conditions during the engineering conception. It is well known that the resonance frequencies of underwater structures are not the same when these structures vibrate in vacuum because of the effects of the added mass and added damping. The first effect is the result of the presence of water itself or fluid in general, the second is caused by the fluid flows. However, if the identification of the parameters of the structures in vacuum is well controlled nowadays, the identification of the parameters of the turbine blades in operating conditions is not obvious, so it becomes complicated as the perceived vibratory signals are disturbed and there is no information about the excitation. Hydro-Quebec which has a several hydroelectric plants is interested by these phenomena. The Research tasks carried out in this field, gave rise to the theoretical prediction software of the underwater resonance frequencies computation which is called WETFREQ. Hence, this present work aims to perform an experimental modal analysis for underwater structure subjected to turbulent flows. Nine chapters are presented, and where one can distinguish two experimental modal analysis techniques. The first is the traditional spectral identification method using the impact hammer, and which is applied in the air and stagnated water conditions, and the second is known as the temporal identification method, which offers the advan tage of determining of the structural modal parameters from only the temporal response measurement with no need the knowledge of the excitation nature, which is applied in the air, in stagnated water and in flow conditions and which is correlated with the spectral identification method. Another correlation is made in air condition with respect to ANSYS software computation. Finally, an underwater model of a prediction of the resonance frequencies Water-Air-Equivalent Model (W.A.E.M) is proposed.

Type de document: Mémoire ou thèse (Mémoire de maîtrise électronique)
Renseignements supplémentaires: "Mémoire présenté à l'École de technologie supérieure comme exigence partielle à l'obtention de la maîtrise en génie mécanique". Bibliogr.: f. 197-199. Chap. 1. Revue de la littérature -- Chap. 2. Vibration d'une structure dans l'eau -- Chap. 3. Identification dans le domaine fréquentiel -- Chap. 4. Application de la méthode d'identification dans le domaine spectral -- Chap. 5. Méthodes d'identification des systèmes -- Chap. 6. Identification dans le domaine temporel -- Chap. 7. Étude théorique et mise au point numérique -- Chap. 8. Application de la méthode d'identification dans le domaine temporelle i.e. [temporel] sur la structure oiseau de l'IREQ -- Chap. 9. Modèle eau-air équivalent (M.E.A.E).
Mots-clés libres: Ailette Analyse Domaine Eau Ecoulement Experimental Frequentiel Hydro-Quebec Identification Immerge Ireq Methode Modal Modele Oiseau Parametre Spectral Structure Temporel Turbulent Vibration
Directeur de mémoire/thèse:
Directeur de mémoire/thèse
Thomas, Marc
Programme: Maîtrise en ingénierie > Génie mécanique
Date de dépôt: 26 janv. 2011 15:12
Dernière modification: 31 oct. 2016 23:23
URI: http://espace.etsmtl.ca/id/eprint/362

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