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The paper presents the results of three-dimensional numerical simulation of thermal-hydraulic processes in the Intermediate Heat Exchanger of the advanced Sodium-Cooled Fast-Neutron (BN) Reactor considering a developed methodological approach.

The Intermediate Heat Exchanger (IHX) is located in the reactor vessel and intended to transfer heat from the primary sodium circulating on the shell side to the secondary sodium circulating on the tube side. In case of an integral layout of the primary equipment in the BN reactor, upstream the IHX inlet windows there is a temperature stratification of the coolant due to incomplete mixing of different temperature flows at the core outlet. Inside the IHX, in the area of the input and output windows, a complex longitudinal and transverse flow of the coolant also takes place resulting in an uneven distribution of the coolant flow rate on the tube side and, as a consequence, in an uneven temperature distribution and heat transfer efficiency along the height and radius of the tube bundle.

In order to confirm the thermal-hydraulic parameters of the IHX of the advanced BN reactor applied in the design, a methodological approach for three-dimensional numerical simulation of the heat exchanger located in the reactor vessel was developed, taking into account the three-dimensional sodium flow pattern at the IHX inlet and inside the IHX, as well as justifying the recommendations for simplifying the geometry of the computational model of the IHX.

Numerical simulation of thermal-hydraulic processes in the IHX of the advanced BN reactor was carried out using the FlowVision software package with the standard $k-\varepsilon$ turbulence model and the LMS turbulent heat transfer model.

To increase the representativeness of numerical simulation of the IHX tube bundle, verification calculations of singletube and multi-tube sodium-sodium heat exchangers were performed with the geometric characteristics corresponding to the IHX design.

To determine the input boundary conditions in the IHX model, an additional three-dimensional calculation was performed taking into account the uneven flow pattern in the upper mixing chamber of the reactor.

The IHX computational model was optimized by simplifying spacer belts and selecting a sector model.

As a result of numerical simulation of the IHX, the distributions of the primary sodium velocity and primary and secondary sodium temperature were obtained. Satisfactory agreement of the calculation results with the design data on integral parameters confirmed the adopted design thermal-hydraulic characteristics of the IHX of the advanced BN reactor.

In this paper on the basis of the riverbed model proposed earlier the one-dimensional stability problem of closed flow channel with sandy bed is solved. The feature of the investigated problem is used original equation of riverbed deformations, which takes into account the influence of mechanical and granulometric bed material characteristics and the bed slope when riverbed analyzing. Another feature of the discussed problem is the consideration together with shear stress influence normal stress influence when investigating the riverbed instability. The analytical dependence determined the wave length of fast-growing bed perturbations is obtained from the solution of the sandy bed stability problem for closed flow channel. The analysis of the obtained analytical dependence is performed. It is shown that the obtained dependence generalizes the row of well-known empirical formulas: Coleman, Shulyak and Bagnold. The structure of the obtained analytical dependence denotes the existence of two hydrodynamic regimes characterized by the Froude number, at which the bed perturbations growth can strongly or weakly depend on the Froude number. Considering a natural stochasticity of the waves movement process and the presence of a definition domain of the solution with a weak dependence on the Froude numbers it can be concluded that the experimental observation of the of the bed waves movement development should lead to the data acquisition with a significant dispersion and it occurs in reality.

Modern approach to modernization of the experimental techniques involves design of mathematical models of the wind-tunnel, which are also referred to as Electronic of Digital Wind-Tunnels. They are meant to supplement experimental data with computational analysis. Using Electronic Wind-Tunnels is supposed to provide accurate information on aerodynamic performance of an aircraft basing on a set of experimental data, to obtain agreement between data from different test facilities and perform comparison between computational results for flight conditions and data with the presence of support system and test section.

Completing this task requires some preliminary research, which involves extensive wind-tunnel testing as well as RANS-based computational research with the use of supercomputer technologies. At different stages of computational investigation one may have to model not only the aircraft itself but also the wind-tunnel test section and the model support system. Modelling such complex geometries will inevitably result in quite complex vertical and separated flows one will have to simulate. Another problem is that boundary layer transition is often present in wind-tunnel testing due to quite small model scales and therefore low Reynolds numbers.

In the current article the first stage of the Electronic Wind-Tunnel design program is covered. This stage involves computational investigation of aerodynamic characteristics of the generic flying-wing UAV model previously tested in TsAGI T-102 wind-tunnel. Since this stage is preliminary the model was simulated without taking test-section and support system geometry into account. The boundary layer was considered to be fully turbulent.

For the current research FlowVision computational code was used because of its automatic grid generation feature and stability of the solver when simulating complex flows. A two-equation k–ε turbulence model was used with special wall functions designed to properly capture flow separation. Computed lift force and drag force coefficients for different angles-of-attack were compared to the experimental data.

The study tested correctness of three interatomic potentials available in the scientific literature in reproducing a vacancy diffusion in concentrated Fe–Cr alloys by molecular dynamic simulations. It was necessary for further detailed study of vacancy diffusion mechanism in these alloys with Cr content 5–25 at.% at temperatures in the range of 600–1000 K. The analysis of the potentials was performed on alloys models with Cr content 10, 20, 50 at.%. The consideration of the model with chromium content 50 at.% was necessary for further study of diffusion processes in chromium-rich precipitates in these alloys. The formation energies and the atomic mobilities of iron and chromium atoms were calculated and analyzed in the alloys via an artificially created vacancy for all used potentials. A time dependence of mean squared displacement of atoms was chosen as а main characteristic for the analysis of atomic mobilities. The simulation of vacancy formation energies didn’t show qualitative differences between the investigated potentials. The study of atomic mobilities showed a poor reproduction of vacancy diffusion in the simulated alloys by the concentration-dependent model (CDM), which strongly underestimated the mobility of chromium atoms via vacancy in the investigated range of temperature and chromium content. Also it was established, that the two-band model (2BM) of potentials in its original and modified version doesn’t have such drawbacks. This allows one to use these potentials in simulations of vacancy diffusion mechanism in Fe–Cr alloys. Both potentials show a significant dependence of the ratio of chromium and iron atomic mobilities on temperature and Cr content in simulated alloys. The quantitative data of the diffusion coefficients of atoms obtained by these potentials also differ significantly.

The mathematical model, finite-difference schemes and algorithms for computation of transient thermoand hydrodynamic processes involved in commissioning the unified system including the oil producing well, electrical submersible pump and fractured-porous reservoir with bottom water are developed. These models are implemented in the computer package to simulate transient processes with simultaneous visualization of their results along with computations. An important feature of the package Oil-RWP is its interaction with the special external program GCS which simulates the work of the surface electric control station and data exchange between these two programs. The package Oil-RWP sends telemetry data and current parameters of the operating submersible unit to the program module GCS (direct coupling). The station controller analyzes incoming data and generates the required control parameters for the submersible pump. These parameters are sent to Oil-RWP (feedback). Such an approach allows us to consider the developed software as the “Intellectual Well System”.

Some principal results of the simulations can be briefly presented as follows. The transient time between inaction and quasi-steady operation of the producing well depends on the well stream watering, filtration and capacitive parameters of oil reservoir, physical-chemical properties of phases and technical characteristics of the submersible unit. For the large time solution of the nonstationary equations governing the nonsteady processes is practically identical to the inverse quasi-stationary problem solution with the same initial data. The developed software package is an effective tool for analysis, forecast and optimization of the exploiting parameters of the unified oil-producing complex during its commissioning into the operating regime.

The article considers a mathematical model of decomposition of a complex product into assembly units. This is an important engineering problem, which affects the organization of discrete production and its operational management. A review of modern approaches to mathematical modeling and automated computer-aided of decompositions is given. In them, graphs, networks, matrices, etc. serve as mathematical models of structures of technical systems. These models describe the mechanical structure as a binary relation on a set of system elements. The geometrical coordination and integrity of machines and mechanical devices during the manufacturing process is achieved by means of basing. In general, basing can be performed on several elements simultaneously. Therefore, it represents a variable arity relation, which can not be correctly described in terms of binary mathematical structures. A new hypergraph model of mechanical structure of technical system is described. This model allows to give an adequate formalization of assembly operations and processes. Assembly operations which are carried out by two working bodies and consist in realization of mechanical connections are considered. Such operations are called coherent and sequential. This is the prevailing type of operations in modern industrial practice. It is shown that the mathematical description of such operation is normal contraction of an edge of the hypergraph. A sequence of contractions transforming the hypergraph into a point is a mathematical model of the assembly process. Two important theorems on the properties of contractible hypergraphs and their subgraphs proved by the author are presented. The concept of $s$-hypergraphs is introduced. $S$-hypergraphs are the correct mathematical models of mechanical structures of any assembled technical systems. Decomposition of a product into assembly units is defined as cutting of an $s$-hypergraph into $s$-subgraphs. The cutting problem is described in terms of discrete mathematical programming. Mathematical models of structural, topological and technological constraints are obtained. The objective functions are proposed that formalize the optimal choice of design solutions in various situations. The developed mathematical model of product decomposition is flexible and open. It allows for extensions that take into account the characteristics of the product and its production.

An isolated system, which possesses a discrete set of microscopic states, is considered. The system performs spontaneous random transitions between the microstates. Kinetic equations for the probabilities of the system staying in various microstates are formulated. A general dimensionless expression for entropy of such a system, which depends on the probability distribution, is considered. Two problems are stated: 1) to study the effect of possible unequal probabilities of different microstates, in particular, when the system is in its internal equilibrium, on the system entropy value, and 2) to study the kinetics of microstate probability distribution and entropy evolution of the system in nonequilibrium states. The kinetics for the rates of transitions between the microstates is assumed to be first-order. Two variants of the effects of possible nonequiprobability of the microstates are considered: i) the microstates form two subgroups the probabilities of which are similar within each subgroup but differ between the subgroups, and ii) the microstate probabilities vary arbitrarily around the point at which they are all equal. It is found that, under a fixed total number of microstates, the deviations of entropy from the value corresponding to the equiprobable microstate distribution are extremely small. The latter is a rigorous substantiation of the known hypothesis about the equiprobability of microstates under the thermodynamic equilibrium. On the other hand, based on several characteristic examples, it is shown that the structure of random transitions between the microstates exerts a considerable effect on the rate and mode of the establishment of the system internal equilibrium, on entropy time dependence and expression of the entropy production rate. Under definite schemes of these transitions, there are possibilities of fast and slow components in the transients and of the existence of transients in the form of damped oscillations. The condition of universality and stability of equilibrium microstate distribution is that for any pair of microstates, a sequence of transitions should exist, which provides the passage from one microstate to next, and, consequently, any microstate traps should be absent.

The paper is devoted to the study of wave and relaxation effects during the pulsed outflow of a gas mixture with a high content of solid particles from a cylindrical channel during its initial partial filling. The problem is formulated in a two-speed two-temperature formulation and was solved numerically by the hybrid large-particle method of the second order of approximation. The numerical algorithm is implemented in the form of parallel computing using basic Free Pascal language tools. The applicability and accuracy of the method for wave flows of concentrated gas-particles mixtures is confirmed by comparison with test asymptotically accurate solutions. The calculation error on a grid of low detail in the characteristic flow zones of a two-phase medium was 10^-6 . . . 10^-5.

Based on the wave diagram, the analysis of the physical pattern of the outflow of a gas suspension partially filling a cylindrical channel is performed. It is established that, depending on the degree of initial filling of the channel, various outflow modes are formed. The first mode is implemented with a small degree of loading of the high-pressure chamber, at which the left boundary of the gas-particles mixture crosses the outlet section before the arrival of the rarefaction wave reflected from the bottom of the channel. At the same time, the maximum value of the mass flow rate of the mixture is achieved. Other modes are formed in cases of a larger initial filling of the channel, when the rarefaction waves reflected from the bottom of the channel interact with the gas suspension layer and reduce the intensity of its outflow.

The influence of relaxation properties with changing particle size on the dynamics of a limited layer of a gas-dispersed medium is studied. Comparison of the outflow of a limited gas suspension layer with different particle sizes shows that for small particles (the Stokes number is less than 0.001), an anomalous phenomenon of the simultaneous existence of shock wave structures in the supersonic and subsonic flow of gas and suspension is observed. With an increase in the size of dispersed inclusions, the compaction jumps in the region of the two-phase mixture are smoothed out, and for particles (the Stokes number is greater than 0.1), they practically disappear. At the same time, the shock-wave configuration of the supersonic gas flow at the outlet of the channel is preserved, and the positions and boundaries of the energy-carrying volumes of the gas suspension are close when the particle sizes change.

This work gives results of numerical simulation of a superconducting magnetic focusing system. While modeling this system, special care was taken to achieve approximation accuracy over the condition u(∞)=0 by using Richardson method. The work presents the results of comparison of the magnetic field calculated distribution with measurements of the field performed on a modified magnet SP-40 of “MARUSYA” physical installation. This work also presents some results of numeric analysis of magnetic systems of “MARUSYA” physical installation with the purpose to study an opportunity of designing magnetic systems with predetermined characteristics of the magnetic field.

An algorithm of applied problem solving was described to calculate electrical characteristics of electrical field effects in ferroelectrics electron-beam charged. The algorithm was based on implementation of the deterministic model using finite element method as well as taking into account Monte-Carlo simulation results of electron transport. The program application was developed to perform computing experiments.