  Simulations of the collapse and fragmentation of turbulent molecular clouds
and dense young clusters show that encounters between disc-surrounded stars are
relatively common events which should significantly influence the resulting
disc structure. In turn this should alter the accretion rate of disc matter
onto the star and the conditions under which planet formation occurs. Although
the effects of star-disc encounters have been previously investigated, very
little is known about encounters where both stars are surrounded by discs. In
this paper encounters of such disc-disc systems are studied quantitatively. It
is found that for low-mass discs ($M_D$= 0.01 $M_\sun$) the results from
star-disc encounters can be straightforwardly generalized to disc-disc
encounters as long as there is no mass transport between the discs. Differences
to star-disc encounters occur naturally where significant amounts of matter are
transported between the discs. In this case it is found that although the mass
distribution does not change significantly, matter caught onto highly eccentric
orbits is transported surprisingly far inside the disc. The captured mass
partly replenishes the disc, but has a much lower angular momentum. This can
lead to a reduction of the angular momentum in the entire disc and thus
considerably increased accretion shortly after the encounter as well as in the
long term.
