We provide an in-deep analysis of 25 galaxies with substantial counterrotation from IllustrisTNG100 simulations in the stellar mass range 2×109−3×1010 M⊙. The counterrotation is a result of an external gas infall ≈2–8 Gyr ago. The infall leads to the removal of pre-existing gas, which is captured and mixed together with the infalling component. This mixture ends up in the counterrotating gaseous disc where ${\approx}90{{\ \rm per\ cent}}$ of counterrotating stars formed in-situ. During the early phases of the infall, gas can be found in extended structures which, in some galaxies, are similar to (nearly-) polar ring-like components. We suggest that the AGN activity does not cause the counterrotation, although it is efficiently triggered by the retrograde gas infall, and it correlates well with the misaligned component appearance. We also find the vertical-to-radial velocity dispersion ratio above unity implying the importance of misalignment in shaping the velocity ellipsoids.

The results of the numerical simulations of the dynamics of shallow waters for Volga-Akhtuba Floodplain are discussed. The mathematical model is based on the system of Saint-Venant equations. Numerical solution applies a combined Lagrangian-Eulerian (cSPH-TVD) algorithm. We have investigated the features of the spring flood in 2011 and found the inapplicability of the hydrodynamical model with the constant roughness coefficient $n_M$ . We have found a good agreement between the results of numerical simulations and the observational data at gauging stations which allows us to estimate $n_M$ in low water $n_M^{\text{min}}=0.02$ and the maximum water level in the river Volga $n_M^{\text{max}}=$ 0.06–0.07.

In this paper, we describe a numerical algorithm for the self-consistent simulations of surface water and sediment dynamics. The method is based on the original Lagrangian-Eulerian CSPH-TVD approach for solving the Saint-Venant and Exner equations, taking into account the physical factors essential for the understanding of the shallow water and surface soil layer motions, including complex terrain structure and its evolution due to sediment transport. Additional Exner equation for sediment transport has been used for the numerical CSPH-TVD scheme stability criteria definition. By using OpenMP-CUDA and GPUDirect technologies for hybrid computing systems (supercomputers) with several graphic coprocessors (GPUs) interacting with each other via the PCI-E/NVLINK interface we also develop a parallel numerical algorithm for the CSPH-TVD method. The developed parallel version of the algorithm demonstrates high efficiency for various configurations of Nvidia Tesla CPU + GPU computing systems. In particular, maximal speed up is 1800 for a system with four C2070 GPUs compare to the serial version for the CPU. The calculation time on the GPU V100 (Volta architecture) is reduced by 95 times compared to the GPU C2070 (Fermi architecture).

Using recent observational data, we construct a set of multi-component equilibrium models of the disk of a Milky Way-like galaxy. The disk dynamics are studied using collisionless-gaseous numerical simulations, based on the joined integration of the equations of motion for the collision-less particles using direct integration of gravitational interaction and the gaseous SPH-particles. We find that after approximately one Gyr, a prominent central bar is formed having a semi-axis length of about three kpc, together with a multi-armed spiral pattern represented by a superposition of $m=$ 2-, 3-, and 4-armed spirals. The spiral structure and the bar exist for at least 3 Gyr in our simulations. The existence of the Milky Way bar imposes limitations on the density distributions in the subsystems of the Milky Way galaxy. We find that a bar does not form if the radial scale length of the density distribution in the disk exceeds 2.6 kpc. As expected, the bar formation is also suppressed by a compact massive stellar bulge. We also demonstrate that the maximum value in the rotation curve of the disk of the Milky Way galaxy, as found in its central regions, is explained by non-circular motion due to the presence of a bar and its orientation relative to an observer.

Using N-body simulations (N ∼ 10⁶–10⁷), we examine how a non-axisymmetric dark halo affects the dynamical evolution of the structure in collisionless (stellar) discs. We demonstrate how the model parameters such as mass of the halo, initial conditions in the disc and the halo axis ratio affect morphology and kinematics of the stellar discs. We show that a non-axisymmetric halo can generate a large-scale spiral density pattern in the embedded stellar disc. The pattern is observed in the disc for many periods of its revolution, even if the disc is gravitationally overstable. The growth of the spiral arms is not accompanied by significant dynamical heating of the disc, irrelevant to its initial parameters. We also investigate transformation of the dark halo’s shape driven by the long-lived spiral pattern in the disc. We show that the analysis of the velocity field in the stellar disc and in the spiral pattern gives us a possibility to figure out the spatial orientation of the triaxial dark halo and to measure the triaxiality.