Igor Kulikov

HYDRODYNAMICAL CODE FOR NUMERICAL SIMULATION OF THE GAS COMPONENTS OF COLLIDING GALAXIES

In this paper, a new hydrodynamical code for the numerical simulation of the collision of the gas components of galaxies is described. The code is based on the Fluids-in-Cells method with the Godunov-type scheme at the Eulerian stage. Also, the velocity correction is employed at the Lagrangian stage and energy imbalance is minimized. The performance of the code is shown by the simulation of the collision of gas components of two similar disk galaxies in the course of the central collision of the galaxies in the polar direction. As a result of the numerical simulations within the model, we succeeded in determining the main scenarios of the collision of galaxies. At low velocities, both galaxies and their gas components coalesce. At high velocities, the massive stellar components of galaxies dissipate almost freely, leaving their gaseous components slowed down and heated by the collision. If the common gas component of the colliding galaxies cools down to the virial temperature, a new galaxy is formed from the two. With the high collision velocity, the gas component has no time to cool and therefore the gas dissipates in the intergalactic medium.

Computational methods for ill-posed problems of gravitational gasodynamics

Abstract A new numerical model of a galaxy interaction in gasodynamical approach is considered. In this model the equations of a gas dynamics with a cold function and the Poisson equation for a gravity potential are solved. A total system of equations is illposed. It allows us to describe a gravitational instability of astrophysical processes. As an example, the results of the collapse simulation are presented. The gas dynamic system of equations is solved by the Fluids-in-Cell method with the energy balance correction. Using the 3D Cartesian simulation a rotation, a self-consistent gravitational field, a complex central body geometry and a gas temperature were taken into account. A parallel implementation of the method for the simulation of various galaxy interaction scenarios was used in the model. Also, a research of the numerical model application range for various collision velocities and a mass relation of gas and star components was made here.

Supercomputer Simulation of an Astrophysical Object Collapse by the Fluids-in-Cell Method

Parallel implementation of the Fluids-in-Cell Method (FlIC) method is created for 3D cartesian simulation of an astrophysical object collapse. The main parameters of the parallel implementation are given of the FlIC method. The equations under solution are the gas dynamics equations and Poisson equation. Simulation of collapse with FlIC method is compared to SPH simulation. As a result, we can state that FlIC method provided fine enough grid gives better spatial resolution than SPH.

Astrophysics Simulation on RSC Massively Parallel Architecture

AstroPhi code is designed for simulation of astrophysical objects dynamics on hybrid supercomputers equipped with Intel Xenon Phi computation accelerators. New RSC PetaStream massively parallel architecture used for simulation. The results of AstroPhi acceleration for Intel Xeon Phi native and offload execution modes are presented in this paper. RSC PetaStream architecture gives possibility of astrophysical problems simulation in high resolution. AGNES simulation tool was used for scalability simulation of AstroPhi code. The are some gravitational collapse problems presented as demonstration of AstroPhi code.

The Co-design of Astrophysical Code for Massively Parallel Supercomputers

The rapid growth of supercomputer technologies became a driver for the development of natural sciences. Most of the discoveries in astronomy, in physics of elementary particles, in the design of new materials in the DNA research are connected with numerical simulation and with supercomputers. Supercomputer simulation became an important tool for the processing of the great volume of the observation and experimental data accumulated by the mankind. Modern scientific challenges put the actuality of the works in computer systems and in the scientific software design to the highest level. The architecture of the future exascale systems is still being discussed. Nevertheless, it is necessary to develop the algorithms and software for such systems right now. It is necessary to develop software that is capable of using tens and hundreds of thousands of processors and of transmitting and storing of large volumes of data. In the present work the technology for the development of such algorithms and software is proposed. As an example of the use of the technology, the process of the software development is considered for some problems of astrophysics.

High-Performance Computing in Astrophysical Simulations

The authors approach for simulating of multiscale astrophysical objects with using of supercomputers is described in the paper. Astrophysical objects consists of several components with different nature, and as a result are described with different mathematical models. This fact leads us to need of formulation of mathematical model and numerical method for each component. The two-phase model (gas + particles) was used in case of simulation of protoplanetary disks. The numerical method and details of parallel implementation for that model were disclosed. The mathematical model for galactic objects, describing stellar component and dark matter, based on the first momenta of Boltzmann equation was built. Such approach allows us to use unified numerical method to describe collisionless and gas component of galaxies.

A new Intel Xeon Phi accelerated hydrodynamic code for numerical simulations of interacting galaxies

In this paper, a new hydrodynamics code to simulate of interacting galaxies on Intel Xeon Phi processors with KNL architecture is presented. A new vector numerical method implemented in the form of a program code for massively parallel architectures is proposed in details. A detailed description is given and a parallel implementation of the code is made. A 92 per cent scalability is reached with 64 processors. The scenarios of interacting galaxies S+E is presented.

The Integrated Approach to Solving Large-Size Physical Problems on Supercomputers

This paper presents the results obtained by the authors on applying an integrated approach to solving geoseismics, astrophysics, and plasma physics problems on high-performance computers. The concept of the integrated approach in the context of mathematical modeling of physical processes is understood as constructing a physico-mathematical model of a phenomenon, a numerical method, a parallel algorithm and its software implementation with the efficient use of a supercomputer architecture. With this approach, it becomes relevant to compare not only the methods of solving a problem but, also, physical and mathematical statements of a problem aimed at creating the most effective implementation of a chosen computing architecture. The scalability of algorithms is investigated using the multi-agent system AGNES simulating the behavior of computing nodes based on the current state of computer equipment characteristics. In addition, special attention in this paper is given to the energy efficiency of algorithms.

Improving the Performance of an AstroPhi Code for Massively Parallel Supercomputers Using Roofline Analysis

Astrophysics is the branch of astronomy that employs the principles of physics and chemistry “to ascertain the nature of the heavenly bodies, rather than their positions or motions in space”. Numerical modeling plays a key role in modern astrophysics. It is the main tool for the research of nonlinear processes and provides communication between the theory and observational data. New massive parallel supercomputers provide an opportunity to simulate these kinds of problems in high details. Our astrophysics code AstroPhi was written for new massive parallel supercomputers based Intel Xeon Phi architecture. The original numerical method based on the combination of the Godunov method, operator splitting approach and piecewise-parabolic method on local stencil was used for numerical solution of the hyperbolic equations. The piecewise-parabolic method on local stencil provides the high-precision order. After the transition of AstroPhi to KNL architecture, we obtained abnormally low performance of solver on KNL cores. In this paper, we will show the roofline analysis using Intel Advisor application and the results of the AstroPhi optimizations.

Numerical simulations of astrophysical problems on massively parallel supercomputer

Astrophysics is the branch of astronomy that employs the principles of physics and chemistry “to ascertain the nature of the heavenly bodies, rather than their positions or motions in space”. We describe new version of our AstroPhi code for simulation of astrophysical objects dynamics and other physical processes on hybrid supercomputers equipped with Intel Xeon Phi accelerators. New version of AstroPhi code was rewritten in accordance to co-design technique. It means that we use latest knowledge about last Intel Xeon Phi generation during code development. The results of simulation by means AstroPhi code for Intel Xeon Phi based massive parallel supercomputer are presented in this paper. The RSC PetaStream architecture is used for astrophysical problems simulation in high resolution. The are some galaxies collision with chemodynamics problems and spiral galaxy formation tests are presented as a demonstration of AstroPhi code.