  In this paper, we give an account of the peripheral-tube model, which has
been developed to give an intuitive and dynamical description of the so-called
ridge effect in two-particle correlations in high-energy nuclear collisions.
Starting from a realistic event-by-event fluctuating hydrodynamical model
calculation, we first show the emergence of ridge + shoulders in the so-called
two-particle long-range correlations, reproducing the data. In contrast to the
commonly used geometric picture of the origin of the anisotropic flow, we can
explain such a structure dynamically in terms of the presence of high
energy-density peripheral tubes in the initial conditions. These tubes
violently explode and deflect the near radial flow coming from the interior of
the hot matter, which in turn produces a two-ridge structure in single-particle
distribution, with approximately two units opening in azimuth. When computing
the two-particle correlation, this will result in characteristic three-ridge
structure, with a high near-side ridge and two symmetric lower away-side ridges
or shoulders. Several anisotropic flows, necessary to producing ridge +
shoulder structure, appear naturally in this dynamical description. Using this
simple idea, we can understand several related phenomena, such as centrality
dependence and trigger-angle dependence.
