  The presence of gas or vapour bubbles may strongly influence the forces that
occur during the impact of a liquid mass onto a solid. Here, we study this
effect numerically, in a well-controlled manner, by simulating the short-time
interaction between an impacting droplet and a solid surface, mediated by the
gas layer between droplet and solid just before collision, in the presence and
absence of bubbles. A boundary integral method is used to simulate the falling
droplet, the mediating air layer is modeled using lubrication theory, whereas
uniform gas bubbles are added to the droplet that obey a polytropic equation of
state. We show that the presence of gas bubbles inside the droplet can have a
significant influence on the force exerted on the substrate, even before
touchdown. This is due to the transmission of load from the solid, through the
gas layer and finally into the bubbly droplet, buffering the impact. We
simulate different bubble configurations, modifying their number, size, shape
and initial position. It is found that larger bubbles, as well as those close
to the impact zone, dampen the collision more as compared to small bubbles or
the ones that are far from the droplet's surface. In addition, multiple small
bubbles are shown to have a similar or even greater effect as a single large
bubble.
