We study the collapse of a transient cavity of air in water created by the impact of a solid body. Experimentally, we characterize the dynamics of the cavity from its creation (t = 0) until it collapses (t = τ) in the limit where inertia dominates viscous and capillary effects. Theoretically, we find in this regime an approximate analytical solution which describes the time evolution of the shape of the cavity. This theoretical solution predicts the existence of two different types of cavities that we also observe experimentally.

We study the capillary instability of a liquid film (thickness $h_0$) coating a horizontal cylindrical tube (radius $R_0$). We show experimentally that the instability only occurs if $h_0/R_0>0.3(R_0/a)^2$, where $a$ is the capillary length. If this criterion is not fulfilled, the liquid film does not destabilize into an array of drops, owing to the gravitational drainage

Abdominal aortic aneurysms are a dilatation of the aorta, localized preferentially above the bifurcation of the iliac arteries, which increases in time. Understanding their localization and growth rate remain two open questions that can have either a biological or a physical origin. In order to identify the respective role of biological and physical processes, we address in this article these questions of the localization and growth using a simplified physical experiment in which water (blood) is pumped periodically (amplitude a, pulsation ω) in an elastic membrane (aorta) (length L, crosssection A 0 and elastic wave speed c 0 ) and study the deformation of this membrane while decharging in a rigid tube (iliac artery; hydraulic loss K). We first show that this pulsed flow either leads to a homogenous deformation or inhomogenous deformation depending on the value of the non-dimensional parameter c 2 0 /(aLω 2 K). These different regimes can be related to the aneurysm locations. In the second part, we study the growth of aneurysms and show that they only develop above a critical flow rate which scales as A 0 c 0 / √ K.