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RUSSIAN FEDERAL NUCLEAR CENTER 
ALLRUSSIAN RESEARCH INSTITUTE OF EXPERIMENTAL PHYSICS 

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Issue N^{o} 3, 2019  NUMERICAL STUDY OF THE INTERRELATION OF TURBULENT MIXING AREA AND LOCAL DISTURBANCES OF INTERFACE IN THE GRAVITATIONAL TURBULENT MIXING PROBLEM
Yu. V. Yanilkin VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 317.
The paper discusses the numerical simulation of a separate local disturbance in the turbulent mixing area generated due to the RayleighTaylor instability with a permanently accelerating interface between two gases of different densities. The direct 3D numerical simulation using the EGAK code (without models of turbulence and viscosity) was performed to study the behavior of a semispherical disturbance on an interface of two media, with one of them being significantly heavier than the other. The turbulent mixing area in this problem is generated due to the background disturbances of the interface specified at initial time. Regularities in separate disturbances of the interface growing against the background of developing turbulent mixing have been found. The calculated results are in a good agreement with results of experiments by Nevmerzhitskiy et al. Key words: RayleighTaylor instability, turbulent mixing area, local disturbance, direct numerical simulation, the EGAK code.
 DIFFERENCE SCHEME "URAL" FOR SOLVING A HYPERBOLIC SYSTEM OF P_{1}–EQUATIONS I. S. Chubareshko, A. A. Shestakov VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 1834.
Issues of constructing monotone difference schemes to solve the heat transport equation in the P_{1}–approximation are discussed in many papers. This paper offers a new difference scheme that improves the solution monotonicity while approximating the hyperbolic equation. For this purpose, the technique of constructing dissipative schemes for a system of P_{1}–equations written in Riemann invariants is used. The specific feature of the new scheme is in accounting the Planck function in expressions describing the relationship between the integral mean values of quantities and the values of quantities at nodes of difference intervals. Key words: a transport equation in the P_{1}approximation, difference scheme.
 AN ALGORITHM OF ITERATIVELY CORRECTING DETONATION TIMES BY MEANS OF ACCOUNTING THE MOVING DETONATION WAVE DIRECTION IN "LEGAK" CODE N. A. Volodina, S. A. Krayukhin VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 3547.
The paper describes several methods to improve the accuracy of the basic stepbystep algorithm of computing the perfect HE detonation used in the LEGAK code. The paper is focused on the algorithm of iteratively correcting the HE initiation time owing to the account for the direction of a moving detonation wave. The calculated results for several methodological problems of detonation waves propagating in HE are given to demonstrate the algorithm applicability. Key words: highexplosive, perfect detonation, detonation initiation time, a detonation wave propagation velocity, detonation wave front.
 THE "GROUND2" SOFTWARE SYSTEM FOR EVALUATED NUCLEAR DATA PROCESSING AND GROUP CONSTANT SYSTEMS CALCULATION A. V. Alekseev, A. V. Bnyatov, N. A. Krutko, S. S. Ratkevich VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 4860.
The paper describes the GROUND2 software system for the processing of evaluated nuclear data and calculation of unified selfconsistent systems of group constants for interactions of neutrons, gammas, and fast charged particles with nuclei of isotopes. The software system structure and capabilities of the GDF program shell, as well as the procedure of setting input data and calculating spectral and group characteristics of the interaction of particles with nuclei are presented. The software system capabilities of storing and visually representing the group data are demonstrated. Key words: provision of group constants, processing code, database, evaluated nuclear data, group constants system.
 COMPUTATIONAL LOAD BALANCING METHODS IN "TIM" CODE S. S. Sokolov, I. G. Novikov, A. A. Voropinov, T. N. Polovnikova VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 6172.
The paper describes the computational load balancing methods implemented in the TIM code. The set of criteria used for the dynamic and quasidynamic balancing is described. The dynamic balancing consists in transferring the calculation of cells from one process to another, the quasidynamic balancing consists in completely reinitializing the problem data with no interrupts of the computing process and constructing a new decomposition. Fields of application are considered for the dynamic and quasidynamic balancing algorithms. The use of the computational load balancing methods allows efficiently loading the field of processors allocated to solve the problem and speeding up the computational process. Key words: the TIM code, decomposition, dynamic balancing, quasidynamic balancing, criteria for the decomposition quality estimation.
 MODELS OF SATURATEDUNSATURATED AND CONFINEDUNCONFINED FLOWS IN "NIMFA" SOFTWARE A. N. Bakhaev, P. A. Mashenkin, M. L. Sidorov VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 7383.
The paper describes models of saturatedunsaturated and confinedunconfined isothermic flows in porous media. Both qualitative and quantitative agreement between the results obtained for problems having analytical solutions and problems solved using the commercial code FEFLOW has been demonstrated. Key words: NIMFA software, saturatedunsaturated flow, verification, crossverification.
 A MODEL OF THE RAILWAY GROUND BED DEFORMATION BY PASSING LONG TRAINS V. P. Solovev, A. V. Anisin, I. M. Anisina, S. S. Nadezhin, M. M. Zheleznov, V. O. Pevzner, I. V. Tretyakov VANT. Ser.: Mat. Mod. Fiz. Proc. 2019. No 3. P. 8489.
The paper describes the extension of the earlier suggested computation technique to soils having viscoelastic properties. The experimental data obtained by the VNIIZhT employees for the railway track section KovdorPinozero has been analyzed. It has been demonstrated that the best rheological model describing the railway deformation under the load of a passing train is the model of a standard linear solid body with parameters G_{1} = 17 MPa, G_{2} = 41 MPa, η_{2} = 6⋅10^{3} MPa⋅s. The semianalytical solution to the equation of ground bed deformation under a cyclic load from a passing long train with subsequent relaxation has been found. Key words: railway, subballast foundation, settlement of track, model of a standard linear solid body, viscosity.
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