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RUSSIAN FEDERAL NUCLEAR CENTER 
ALLRUSSIAN RESEARCH INSTITUTE OF EXPERIMENTAL PHYSICS 

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Issue N^{o} 4, 2022  SIMULATION OF MULTIDIMENSIONAL NONSTATIONARY MULTIMATERIALCONTINUUM FLOWS USING BLOCKSTRUCTURED MESHES OF A SPECIAL KIND IN THE "LEGAK" CODE
N. A. Volodina, S. A. Krayukhin, A. O. Naumov, S. V. Starodubov, A. P. Tikhonova, T. V. Rezvova, K. V. Tsiberev, M. O. Shirshova, E. V. Shuvalova VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 318.
The paper describes the implementation of computational algorithms in the LEGAK code for the simulation of multidimensional nonstationary multimaterialcontinuum flows using blockstructured meshes of a special kind. Meshes of a special kind mean the blockstructured meshes with the irregular blending elements at the interfaces of blocks, namely, the meshes with mating of quasispherical and cubical meshes and with a fold ratio of cells at boundaries of blocks. The main advantage of using the specialkind meshes in LEGAK is that they allow locally refining the computational mesh during the simulation of structures of different scales and also provide a higher accuracy of describing separate physical processes and the selection of the computational mesh, which is better adapted to the given flow to solve application problems. Methods of computations on blockstructured meshes, computation program modification algorithms, and algorithms of paralleling are considered. To demonstrate the code serviceability, results of computations with the use of blockstructured meshes are given for several methodological problems. Key words: the LEGAK code, blockstructured meshes, quasispherical meshes.
 NUMERICAL SOLUTION OF 1D RADIATIVE HEAT TRANSFER PROBLEMS WITH PHASE TRANSFORMATIONS IN A ONCETHROUGH RUN WITH THE "ROMB" SCHEME A. M. Mustafin, N. N. Pashentseva, S. N. Lebedev VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 1932.
The paper considers the numerical solution of 1D Stephan´s problem in a oncethrough run with the "Romb" scheme and studies the efficiency of the mesh adaptation to the problem. The algorithm of building an adaptive difference mesh for a threephase heat transfer problem is given. The difference scheme "Romb" was derived on the adaptively refined mesh, it allows approximating the heat transfer equation within one cell and operating with boundary conditions of different forms. The numerical solutions were obtained for three Stephan´s problems: for two planar threephase problems and for the application spherical twophase melting problem for a microparticle of iron. It is shown that the solutions found agree with the results obtained by the other authors. The advantages of the difference mesh adaptation against the use of conventional meshes are clearly demonstrated for the solution of Stephan´s problems. Key words: Stephan´s problem, the "Romb" difference scheme, adaptive difference mesh, hybrid data structure, binary tree, doublelinked list.
 SIMULATION OF THE OPENPORE STRUCTURE COVERING BY THIN LAYER OF LIQUID M. A. Yamshchikova VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 3340.
Studying the cylindrical openpore structure covering by a liquid layer is reduced to considering the subproblems of the droplet shape simulation in several configurations: a droplet is on the cylinder surface, or a liquid is between the horizontal and vertical cylinders. The mass and thickness of the liquid layer are the parameters of such covering. For a porous system, the description of the method of simulating the droplet shape in the uniform gravity field is given. The Laplace equation solution is presented for a cylindrical droplet. Equilibrium droplet shapes have been obtained on surfaces of various forms and inclinations. The calculated estimates of the amount of liquid covering the surface of an openpore structure are presented. Key words: droplet shape, the Laplace equation, surface tension, wetting angle.
 THE 2D NUMERICAL SIMULATION OF FULLY NONLINEAR BAROCLINIC WAVE MOTIONS ON THE NORTHEASTERN SHELF OF SAKHALIN ISLAND A. A. Kurkin, O. E. Kurkina, E. A. Ruvinskaya VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 4154.
In the framework of this work, to study the features of baroclinic currents, several vertical "sections" were selected in the northeastern part of the shelf zone of Sakhalin island, which is rich in oil and gas and represents by itself a unique ecosystem. It is shown that the baroclinic component makes a significant contribution to the flow field and has a complex multimode highly nonlinear structure. Several long wave transformation regimes have been identified and estimates of the amplitudes of both baroclinic tidal waves and shortperiod internal waves generated at their fronts have been obtained. The numerical simulation performed allows concluding that baroclinic tidal waves and intensive internal waves may contribute to the generation of underwater dunes in the coastal zone of this part of the water area, as noted in papers devoted to field observations, and also affect the functioning of the entire coastal ecosystem. Key words: stratified medium, ocean shelve, solitary waves, bottom velocities, Froude number, numerical simulation, solibore, wavelet analysis, correlation analysis.
 THE "LOGOS PLATFORM" PROGRAM MODULE ARCHITECTURE A. G. Naduev, A. D. Cherevan, A. S. Lebedeva VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 5563.
RFNCVNIIEF has been developing the LOGOS software package including the modular integration "Logos Platform", which serves to integrate different computational modules to solve a broad class of physical problems. The paper describes the "Logos Platform" program module, its purpose, tasks, key features, and main components. Such components include the integrator that controls the "Logos Platform" program module mechanisms and provides the graphics interface, the scenario handler to carry out the computation, modules for the scenario stages implementing the computation stage logics, and the transport level providing the interaction between several main computational modules during the coupled computation of multiphysics problems. Key words: "Logos Platform", mathematical modeling, multiphysics computations, parametric and optimization studies.
 ON ONE OF THE WAYS TO ARRANGE DATA STRUCTURES IN SCIENTIFIC VISUALIZATION SYSTEMS A. L. Potekhin VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 6471.
The use of visualization systems is one of the simplest and useful ways to analyze the numerical simulation results. An important issue to be resolved by the visualization system developers is the selection of data structures. It is required to maintain the balance between the memory consumption and operation speed, between the usability of the specific algorithms and generality, etc. The paper describes the data structures developed in the framework of the ScientificView parallel postprocessor and reasons for the selection of such structures. The speed and memory consumption capabilities of the selected data structures are compared with those in the system with similar capabilities. Key words: scientific visualization systems, graphical data processing, postprocessing of the numerical simulation results, parallel algorithms.
 DATA SECURITY OUT OF THE CONTROL ZONE IN FIBEROPTIC TRANSMISSION SYSTEMS V. V. Shubin VANT. Ser.: Mat. Mod. Fiz. Proc. 2022. No 4. P. 7287.
The paper considers the approaches to provide data security out of the control zone in fiberoptic transmission systems. The classification of networks is given and three ways to protect them are described: conventional and quantum cryptography and the use of technical means. The specific features of fiberoptic systems are considered: rarefied and dense wave division multiplexing, phase manipulation, forward error correction, and multitasking functionality. The conventional and quantum cryptography are described from the viewpoint of their correspondence to modern fiberoptic systems and data transmission security. The RFNCVNIIEF approach to providing the transmitted data security in fiberoptic networks with the use of technical means is presented and these technical means are compared with other versions. Key words: data security, control zone, fiberoptic transmission system, conventional and quantum cryptography, technical information protection.
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