  The development of perturbations in the circumstellar disks of
pre-main-sequence stars caused by clumpy accretion was investigated. Here we
perform 3D hydrodynamical smoothed particle hydrodynamics simulations of disks
perturbed by a recent clump accretion event. These simulations are further
explored by radiative transfer calculations to quantify the observational
appearance of such disks. It was shown that the density waves in the disks were
formed at the fall of the clump. After several revolutions they can transform
into spirals and ring structures. Their images in millimeter wavelengths are
very similar to those observed with Atacama Large Millimeter/submillimeter
Array in some protoplanetary disks. We assume that clumpy accretion may be the
source of such structures.
