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Abstract: A two-dimensional model of the working process—the preliminary analysis of calculations (PAC)—is developed for the preliminary planning of three-dimensional numerical calculations of the working process in spark-ignited engines. The model is based on solving the energy conservation equation in partial derivatives based on the control volume method with explicit identification of the flame front. A new approach to modeling flame propagation in a spark-ignited engine is proposed, which consists of a combination of the mesh method of control volumes and the calculation of the apparent flame velocity based on the experimental data (taking into account the stage of development of the flame source). In this case, there is no need to solve the momentum transfer equation and gas mixture components to determine the current position of the flame front. Thus, the advantages of this model are the fast execution of the calculation and good predictive ability. Additionally, the program can be used for preliminary verification of three-dimensional calculations when experimental data are not available, as well as for obtaining the heat release characteristics for zero-dimensional (thermodynamic) models of the working process. PubDate: 2022-08-01

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Abstract: On the example of the problem of modeling wave attractors in a stratified fluid, the advantages of the quasi-hydrodynamic (QHDFoam) algorithm over the classical algorithm of operator splitting (PISO) are demonstrated. Both algorithms are implemented by the finite volume method based on the OpenFOAM open source software package. It is shown that the application of the PISO algorithm does not reproduce the dynamics of multiple reflection and focusing of internal waves in a stratified fluid during the interaction with the boundaries of the computational domain. The QHDFoam algorithm based on solving the regularized Navier–Stokes equations gives results close to the data of the high-order spectral-element method, the data of which are considered as the reference in this study. PubDate: 2022-08-01

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Abstract: An entropic regularization of the conservative stable discontinuous Galerkin method (DGM) in conservative variables for two-dimensional Euler equations is constructed based on a special slope limiter. This limiter ensures the fulfillment of two-dimensional analogs of the monotonicity conditions and a discrete analog of the entropic inequality. The developed method was tested on two-dimensional model gas-dynamic problems. PubDate: 2022-08-01

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Abstract: A mathematical model for assessing the informational impact on the electorate in social media during election campaigns is developed. It is based on the well-known mathematical models of information warfare in a structured society and differs from them by taking into account the stochastic nature of the intensity of information dissemination from external sources. The final model is reduced to a system of stochastic differential equations, understood in the sense of Ito. The estimate of the number of adherents and preadherents who favor a candidate during the election campaign is given by the sample mean, which is calculated by the probability density function determined from the solution of the Fokker–Planck–Kolmogorov equation. The Fokker–Planck–Kolmogorov (FPK) equation is solved according to the proposed numerical scheme based on the projection formulation of the Galerkin method. The simulation results for the test problem are presented. PubDate: 2022-08-01

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Abstract: The direct method for determining cosmological distances uses observations at the growth stage of the luminosity of superluminous supernovae, whose light curve can be explained by the interaction of a shock wave with dense circumstellar matter. The method is based on the assumption of spherical symmetry of the dense thin layer formed in the system, which can be unstable in a multidimensional model. In this paper, we consider the simulation of the supernova SN2009ip, which has been successfully applied for the direct method, using the radiation-hydrodynamics code, FRONT. It is shown that the current implementation of the code correctly reproduces the bolometric light curve and the dynamics of the dense shell’s motion in a simplified SN2009ip model. It is also shown that in the formulation under consideration, the shell remains spherically symmetric at least during the growth period of the light curve. PubDate: 2022-08-01

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Abstract: Molecular dynamics (MD) modeling of the thermophysical properties of pure metallic gold (Au) and hysteresis is considered in order to study its behavior during melting–crystallization phase transformations, i.e., in the transition from solid to liquid. The results of computational experiments are presented, in which the temperature dependences of a number of thermophysical characteristics of the metal are obtained. The possibility of the formation of highly superheated metastable states of the solid phase upon rapid heating of Au has been confirmed. PubDate: 2022-08-01

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Abstract: A physical experiment performed to test a mathematical model for the generation of bremsstrahlung by electrons and the formation of an electromagnetic field during its scattering is considered. During the experiment, a high-current electron accelerator irradiates the converter target. The resulting bremsstrahlung generates a flux of emission electrons and an electromagnetic field in a sealed chamber. A mathematical model of the measuring circuit used for the experimental determination of the electric current in the chamber is developed. The results of physical and computational experiments simulating them coincide with satisfactory accuracy. It is established that the necessary condition for confirming the model is to take into account the measuring equipment in the computational experiment and use directly measured values for comparison. PubDate: 2022-08-01

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Abstract: The impact ionization of a rarefied gas by high-energy electrons is considered. An approximate hydrodynamic model of the current density of low-energy secondary electrons formed during impact ionization is constructed. The concentration, drift velocity, and specific energy are calculated by an approximate solution of the kinetic equation for secondary electrons. Spatial homogeneity, isotropy of the initial distribution of secondary electrons, coincidence of the direction of their drift and the electric field are assumed. Additional approximations are related to the structure of the distribution function of secondary electrons and cross section averaging. The results of model validation by comparison with direct collision simulation are presented. PubDate: 2022-08-01

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Abstract: Mass transfer in a carbonate reservoir of a fractured-porous type is considered. Such reservoirs have a natural system of destruction in the form of fractures and cavities. In this paper, a mathematical model of the fluid redistribution between a porous-type matrix and a network of natural fractures is proposed and studied. The resulting system of differential equations is quasi-linear and quite complex. A number of difficulties arise in its numerical solution. First, the system contains a large number of unknown functions. Second, the nature of the nonlinearity of the equations is such that the corresponding linearized system no longer has the property of the self-adjointness of the spatial differential operators. To solve this problem, the method of splitting by physical processes and the approximation of differential operators by the finite difference method are used. The resulting split mesh model is equivalent to the discrete original balance equations of the system (conservation of mass components of fluids and total energy of the system) written in the divergent form. This approach is based on a nonlinear approximation of mesh functions in time, which depends on the fraction of the volume occupied by fluids in the pores, and is simple to implement. This paper presents the results of numerical calculations and analyzes the space-time dynamics of pressure change processes. PubDate: 2022-08-01

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Abstract: The technique and results of three-dimensional modeling of a radiative shock wave that occurs when a supernova remnant expands into the surrounding interstellar medium are presented. The aim of the calculations is to analyze the hydrodynamic instability in a dense layer of matter formed during the deceleration of the remnant in the interstellar gas. The layer structure, which largely determines the efficiency of cosmic ray generation, depends on a number of factors and, in particular, on the rate of radiative cooling of the interstellar plasma, the magnitude of the magnetic field, and the presence of a neutral component in the ionized medium. The creation of a methodology and software for assessing these factors is the defining motivation for this work. For modeling, the MARPLE3D software package (Keldysh Institute of Applied Mathematics, Russian Academy of Sciences) is used, which was developed to solve problems of magnetic radiative gas dynamics on high-performance computing systems of the cluster type. PubDate: 2022-08-01

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Abstract: This study is devoted to the development of a method for calculating the process of a nonstationary flow of compressible fluid in a pipeline network based on a system of quasi-one-dimensional (averaged over the cross section of a pipe) equations of mass and energy and momentum conservation equations. A finite-difference scheme and the corresponding calculation algorithm implemented in a program computer code are constructed. The difference scheme has the property of conservatism with the fulfillment of grid analogs of the main conservation laws and satisfies the stability and monotonicity criteria of the solution. The proposed solution method consists of reducing the calculation of the flow in a multicircuit network of pipes with a large number of junctions and branches to a set of three-point sweeps performed independently on each pipe. The advantage of the method is the possibility of natural parallelization of the computational process. In relation to this, the method is promising for use in multiprocessor systems. Examples of numerical calculations by the developed method are given. PubDate: 2022-08-01

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Abstract: A complex computer model of thermomechanical phenomena and a technique for end-to-end modeling of processes occurring in a solid material under the action of an intense energy flux are developed. Using the example of calculating the impact on a polymer material, the dynamics of nonlinear wave processes leading to internal damage in a sample of the material and spalling phenomena are discussed. The created software can be used in the analysis of the results of intense energy impacts in engineering practice, verification of models of volumetric fractures, and spallation in brittle materials, as well as validation of wide-range equations of state. PubDate: 2022-08-01

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Abstract: This paper discusses supercomputer modeling of the dynamics of plankton populations, including phyto- and zooplankton, in coastal systems. The mathematical model of the dynamics of plankton populations includes a system of convection-diffusion-reaction equations with nonlinear terms, which makes it possible to study the mechanism of external hormonal regulation based on the scenario approach. The proposed mathematical 3D model is linearized, discretized, and based on coordinate splitting, a chain consisting of two-dimensional and one-dimensional problems is obtained. For the numerical implementation of the proposed mathematical model of hydrobiology of the coastal system in the form of a software module (SM), a multiprocessor computer system (MCS) designed for massively parallel computing is used; its use makes it possible to significantly reduce the running time of the SM. To improve the accuracy of calculations, a procedure is used to refine the solution on a sequence of condensing uniform rectangular grids. The effect of the mechanism of ectocrine regulation and the mode of intake of biogenic substances on the production and destruction processes of plankton is studied. The mathematical model includes a nonlinear dependence used to describe the growth rate of algae cells on the concentration of the metabolite, which made it possible to describe the ability of algae excretion products to control their growth even under conditions of the massive intake of pollutants. The approach used corresponds to modern ideas about the functioning of hydrobiocenosis. Based on the developed software toolkit, focused on the supercomputer, not only direct trophic interactions but also the actions of the products of the vital activity of individuals, which are mediated–chemical interactions, are studied. PubDate: 2022-08-01

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Abstract: The results of numerical simulation of a vertical-axis wind turbine (VAWT) based on the solution of three-dimensional Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model are presented. The results of parametric calculations of a viscous compressible flow under conditions simulating urban infrastructure for a helicoid-type wind turbine with three spirally twisted blades are presented. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030048

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Abstract: Atomic and ion properties calculated in the Hartree–Fock–Slater quantum-statistical model are used in the direct calculation of the differential and total cross sections of electron impact ionization of singly ionized oxygen and nitrogen atoms by the distorted wave approximation. The convergence of the cross sections justifies applicability of the approximation for calculating the cross sections for impact ionization of ions by electrons in gas-plasma formations. The calculated cross sections are compared with analytical approximations and available experimental data. The calculation results show that the proposed method gives reliable results, which, combined with the applicability of the Hartree–Fock–Slater model in a wide range of temperatures and densities, allow it to be used in a wide range of energies and ion charges. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030164

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Abstract: This contribution is concerned with mixed convection flow across a vertical cone in the presence of heat source/sink and chemical reaction effects; the two-dimensional, steady, laminar, viscous incompressible fluid flow case has been discussed with favorable applications in the science, engineering, and industries. The flow model is designed in the form of mathematical equations and, for the sake of numerical solution simplicity, non-dimensionalization has been performed and the gained non-similarity equations are solved numerically via an efficient numerical technique called the bivariate Chebyshev spectral collocation quasi-linearization method. A schematic illustration of the obtained results at various stream-wise locations of the velocity, temperature, and concentration profiles for variations of the governing parameters are exhibited in the results and discussions section; and we have noted that higher rate of heat generation made heat transfer to the surface from the flow, and it enhances temperature profile as well. Moreover, skin friction, heat, and mass transfer rate are also illustrated in tabular form. To authenticate the accuracy of the present computations, we organize a favorable comparison with prior published computation; the residual analysis study also depicted which determines the convergence of the framed numerical simulation. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030127

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Abstract: A computer system for modeling sea currents, which is based on a hydrodynamic model with regularized shallow water equations, is presented. A system of regularized equations is presented and a technique for solving it is briefly described, including an algorithm for calculating dry-bed areas. The efficiency of the program code’s parallelization is tested on a high-performance computing system. The acceleration curve is obtained. The structure of the program and its interaction with external modules are presented. Test calculations of tidal fluctuations in the northern seas are carried out. The computational domain covers the White Sea, the Pechora Sea, parts of the Barents and Kara seas, and the Kara Strait. The results describe well the tidal phenomena in the study area. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030097

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Abstract: In this study, we consider a two-component medium with subdiffusive transport and nonlinear chemical kinetics. Formally, such a system can be represented as coupled equations with Caputo derivatives of various orders. It is shown by means of linear analysis that the ratio of the indices of fractional derivatives significantly affects the selection of patterns that may occur in the system. A new type of bifurcations is also demonstrated, which cannot be observed in a similar system with ordinary derivatives. The analysis carried out is supplemented by the results of direct numerical simulation. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030176

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Abstract: The motion of a spacecraft (SC) in an ultralow orbit at a height of 175 km is simulated. The SC is equipped with a ramjet electric propulsion engine (REPE), which makes it possible to compensate the drag force. The controllable angular motion of the SC is simulated taking into account the main disturbing factors, including errors in the layout of the SC and engine installation, as well as the effect of wind in the atmosphere. The energy consumption of the control system in different attitude modes is estimated. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030139

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Abstract: The results of modeling sound pressure in the calibration system of measurement microphones of the LS type based on the reciprocity method and using the quasi-gas dynamic (QGD) approach in the frequency range from 1 Hz to 10 kHz are presented. A numerical method based on QGD equations for a compressible viscous heat-conducting gas is constructed using an explicit scheme, the finite difference method for a uniform grid with the approximation of spatial derivatives through central differences, and the fictitious node method to approximate the boundary conditions. The Mach numbers ranging from 7.3 × 10–10 to 7.3 × 10–6 are a feature of the computational problem in the studied frequency range. The close agreement of the modeling results with the known analytical solution points to the applicability of the QGD approach for modeling gas flows with extremely small Mach numbers and acoustic problems in particular. PubDate: 2022-06-01 DOI: 10.1134/S2070048222030061