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In this thesis we study the 2D incompressible Euler equations in the case where the vorticity is sharply concentrated around N points. We are interested into the singular system obtained in the limit, called the point-vortex system. This dynamics can lead to collapses, namely the distance of point-vortices can go to 0 in finite time. It is also possible that in presence of a boundary, point-vortices hit the boundary. In both cases, the dynamics makes no sense from the time of collision. We prove that in bounded domains, the initial data leading to a collapse are exceptional. When a collision happens, we prove under a non degeneracy hypothesis that the trajectory of the point-vortices staying far from the boundary is Hölder regular, with an optimal exponent. For the points that go to the boundary it is their distance to the boundary that is Hölder regular. We prove that the Hölder regularity of the trajectories also stands true for the generalized point-vortex system coming from the SQG equations, that we call alpha-model. Finally, we study the vorticity confinement problem, which goal is to quantify the desingularization : if the vorticity is sharply concentrated, how long does it stay concentrated around the singular system ? We prove that when the confinement happens around a well chosen point in some bounded domains, the lower bound of the time of confinement is much better that in the general case. ; Dans cette thèse nous étudions les équations d'Euler 2D incompressibles dans le cas particulier d'un tourbillon très concentré autour de N points. Nous nous intéressons au système singulier limite, appelé système point-vortex. La dynamique de ce système peut produire des collisions, c'est-à-dire que la distance séparant les points-vortex peut tendre vers 0 en temps fini. Il est également possible qu'en présence d'un bord, les points-vortex collisionnent avec le bord. Dans ces deux cas, la dynamique cesse d'avoir du sens au temps de la collision. Nous prouvons que dans les domaines bornés du plan, l'ensemble des ...
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