  Wave slamming onto a structure is often accompanied by the entrapment of an
air pocket. A large scale impact typically has a rapidly evolving and disturbed
liquid-gas interface, such that several bubbles are entrapped upon impact.
While it is largely understood how the peak pressure is created by liquid
coming into contact with the solid structure, it is more challenging to
ascertain how an isolated air pocket is pressurised by an impulsive impact, and
how the maximum impact pressure inside this bubble evolves. We study such a
Bagnold-type impulsive compression of an air bubble by performing
well-controlled experiments, where we use an inverted, hollow cone as an
impactor. The cone is kept immersed throughout in a water bath, such that it
encloses an air bubble of known and controlled volume. A high-sensitivity
sensor measures pressures at the vertex of the cone. Using high-speed imaging
we show how incoming liquid deforms the air bubble enclosed in such a geometry,
and how an impact peak is registered inside the bubble, which can be traced
back to the impact of a liquid jet onto the pressure sensor. We compare the
measured pressures to a Bagnold model, and discuss the dominant resonances in
the bubble. From visualisations of the deforming bubble, we also discuss the
air-pocket's deformations, resulting from the presence of surrounding rigid
geometry (such as corrugations in an LNG containment membrane).
