All issues

The report presents a number of news and updates of the ALICE computing for RUN2 and RUN3.

This includes:

– implementation in production of a new system EOS;

– migration to the file system CVMFS to be used for storage of the software;

– the plan for solving the problem of “Long-Term Data Preservation”;

– overview of the concept of “O square”, combining offline and online data processing;

– overview of the existing models to use the virtual clouds for ALICE data processing. Innovations are shown on the example of the Russian sites.

We investigate machine learning methods with a certain kind of decision rule. In particular, inverse-distance method of interpolation, method of interpolation by radial basis functions, the method of multidimensional interpolation and approximation, based on the theory of random functions, the last method of interpolation is kriging. This paper shows a method of rapid retraining “model” when adding new data to the existing ones. The term “model” means interpolating or approximating function constructed from the training data. This approach reduces the computational complexity of constructing an updated “model” from $O(n^3)$ to $O(n^2)$. We also investigate the possibility of a rapid assessment of generalizing opportunities “model” on the training set using the method of cross-validation leave-one-out cross-validation, eliminating the major drawback of this approach — the necessity to build a new “model” for each element which is removed from the training set.

A model of forest insect population dynamics used to simulate of “forest-insect” interactions and for estimation of possible damages of forest stand by pests. This model represented a population as control system where the input variables characterized the influence of modifier (climatic) factors and the feedback loop describes the effect of regulatory factors (parasites, predators and population interactions). The technique of stress testing on the basis of population dynamics model proposed for assessment of the risks of forest stand damage and destruction after insect impact. The dangerous forest pest pine looper Bupalus piniarius L. considered as the object of analysis. Computer experiments were conducted to assess of outbreak risks with possible climate change in the territory of Central Siberia. Model experiments have shown that risk of insect impact on the forest is not increased significantly in condition of sufficiently moderate warming (not more than 4 °C in summer period). However, a stronger warming in the territory of Central Siberia, combined with a dry summer condition could cause a significant increase in the risk of pine looper outbreaks.

The technique of simplification of mathematical model of a chemical reaction by reducing the number of steps of the reaction scheme, based on an analysis of sensitivity to changes in the objective function of the model parameters, is proposed. The reduced scheme of model reaction of formaldehyde oxidation is received. Functional characterizes the measure of proximity to the calculated values for the initial kinetic reaction scheme and the scheme resulting disturbance of its parameters. The advantage of this technique is the ability to analyze complex kinetic schemes and reduction of kinetic models to a size suitable for practical use. The results of computational experiments under different reaction conditions can be included in the functional and thus to receive the reduce scheme, which is consistent the detailed scheme for the desired range of conditions. Sensitivity analysis of the functional model allows to identify those parameters, which provide the largest (or smallest) the contribution to the result of the process simulation. The mathematical model can contain parameters, which change of values do not affect the qualitative and quantitative description of the process. The contribution of these parameters in the functional value won’t be of great importance. Thus it can be eliminated from consideration, which do not serve for modeling kinetic curves substances. The kinetic scheme of formaldehyde oxidation, the detailed mechanism which includes 25 stages and 15 substances, were investigated using this method. On the basis of the local and global sensitivity analysis, the most important stage of the process that affect the overall dynamics of the target concentrations of the reaction. The reduced scheme of model reaction of formaldehyde oxidation is received. This scheme also describes the behavior of the main substances, as detailed scheme, but has a much smaller number of reaction stages. The results of the comparative analysis of modeling of formaldehyde oxidation on detailed and reduced schemes are given. Computational aspects of the problems of chemical kinetics by Sobol’ global method an example of this reaction are specified. The comparison results are local, global and total sensitivity indices are given.

This article represents numerical simulation technique for determining effective spectral electromagnetic properties (effective electrical conductivity and relative dielectric permittivity) of saturated porous media. Information about these properties is vastly applied during the interpretation of petrophysical exploration data of boreholes and studying of rock core samples. The main feature of the present paper consists in the fact, that it involves three-dimensional saturated digital rock models, which were constructed based on the combined data considering microscopic structure of the porous media and the information about capillary equilibrium of oil-water mixture in pores. Data considering microscopic structure of the model are obtained by means of X-ray microscopic tomography. Information about distributions of saturating fluids is based on hydrodynamic simulations with density functional technique. In order to determine electromagnetic properties of the numerical model time-domain Fourier transform of Maxwell equations is considered. In low frequency approximation the problem can be reduced to solving elliptic equation for the distribution of complex electric potential. Finite difference approximation is based on discretization of the model with homogeneous isotropic orthogonal grid. This discretization implies that each computational cell contains exclusively one medium: water, oil or rock. In order to obtain suitable numerical model the distributions of saturating components is segmented. Such kind of modification enables avoiding usage of heterogeneous grids and disregards influence on the results of simulations of the additional techniques, required in order to determine properties of cells, filled with mixture of media. Corresponding system of differential equations is solved by means of biconjugate gradient stabilized method with multigrid preconditioner. Based on the results of complex electric potential computations average values of electrical conductivity and relative dielectric permittivity is calculated. For the sake of simplicity, this paper considers exclusively simulations with no spectral dependence of conductivities and permittivities of model components. The results of numerical simulations of spectral dependence of effective characteristics of heterogeneously saturated porous media (electrical conductivity and relative dielectric permittivity) in broad range of frequencies and multiple water saturations are represented in figures and table. Efficiency of the presented approach for determining spectral electrical properties of saturated rocks is discussed in conclusion.

The different types of the reduced equations are known in the dynamics a heavy rigid body with a fixed point. Since the Euler−Poisson’s equations admit the three first integrals, then for the first approach the obtaining new forms of equations are usually based on these integrals. The system of six scalar equations can be transformed to a third-order system with them. However, in indicated approach the reduced system will have a feature as in the form of radical expressions a relatively the components of the angular velocity vector. This fact prevents the effective the effective application of numerical and asymptotic methods of solutions research. In the second approach the different types of variables in a problem are used: Euler’s angles, Hamilton’s variables and other variables. In this approach the Euler−Poisson’s equations are reduced to either the system of second-order differential equations, or the system for which the special methods are effective. In the article the method of finding the reduced system based on the introduction of an auxiliary variable is applied. This variable characterizes the mixed product of the angular momentum vector, the vector of vertical and the unit vector barycentric axis of the body. The system of four differential equations, two of which are linear differential equations was obtained. This system has no analog and does not contain the features that allows to apply to it the analytical and numerical methods. Received form of equations is applied for the analysis of a special class of solutions in the case when the center of mass of the body belongs to the barycentric axis. The variant in which the sum of the squares of the two components of the angular momentum vector with respect to not barycentric axes is constant. It is proved that this variant exists only in the Steklov’s solution. The obtained form of Euler−Poisson’s equations can be used to the investigation of the conditions of existence of other classes of solutions. Certain perspectives obtained equations consists a record of all solutions for which the center of mass is on barycentric axis in the variables of this article. It allows to carry out a classification solutions of Euler−Poisson’s equations depending on the order of invariant relations. Since the equations system specified in the article has no singularities, it can be considered in computer modeling using numerical methods.

The reentry vehicle of the transportation spacecraft that is being created by RSC Energia in regular mode makes soft landing on land surface using a parachute system and thruster devices. But in not standard situations the reentry vehicle also is capable of executing a splashdown. In that case, it becomes important to define the hydrodynamics impact on the reentry vehicle at the moment of the first contact with the surface of water and during submersion into water medium, and to study the dynamics of the vehicle behavior at more recent moments of time.

This article presents results of numerical studies of hydrodynamics forces on the conical vehicle during splashdown, done with the FlowVision software. The paper reviews the cases of the splashdown with inactive solid rocket motors on calm sea and the cases with interactions between rocket jets and the water surface. It presents data on the allocation of pressure on the vehicle in the process of the vehicle immersion into water medium and dynamics of the vehicle behavior after splashdown. The paper also shows flow structures in the area of the reentry vehicle at the different moments of time, and integral forces and moments acting on the vehicle.

For simulation process with moving interphases in the FlowVision software realized the model VOF (volume of fluid). Transfer of the phase boundary is described by the equation of volume fraction of this continuous phase in a computational cell. Transfer contact surface is described by the convection equation, and at the surface tension is taken into account by the Laplace pressure. Key features of the method is the splitting surface cells where data is entered the corresponding phase. Equations for both phases (like the equations of continuity, momentum, energy and others) in the surface cells are accounted jointly.

Nowadays the random search became a widespread and effective tool for solving different complex optimization and adaptation problems. In this work, the problem of an average duration of a random search for one object by another is regarded, depending on various factors on a square field. The problem solution was carried out by holding total experiment with 4 factors and orthogonal plan with 54 lines. Within each line, the initial conditions and the cellular automaton transition rules were simulated and the duration of the search for one object by another was measured. As a result, the regression model of average duration of a random search for an object depending on the four factors considered, specifying the initial positions of two objects, the conditions of their movement and detection is constructed. The most significant factors among the factors considered in the work that determine the average search time are determined. An interpretation is carried out in the problem of random search for an object from the constructed model. The important result of the work is that the qualitative and quantitative influence of initial positions of objects, the size of the lattice and the transition rules on the average duration of search is revealed by means of model obtained. It is shown that the initial neighborhood of objects on the lattice does not guarantee a quick search, if each of them moves. In addition, it is quantitatively estimated how many times the average time of searching for an object can increase or decrease with increasing the speed of the searching object by 1 unit, and also with increasing the field size by 1 unit, with different initial positions of the two objects. The exponential nature of the growth in the number of steps for searching for an object with an increase in the lattice size for other fixed factors is revealed. The conditions for the greatest increase in the average search duration are found: the maximum distance of objects in combination with the immobility of one of them when the field size is changed by 1 unit. (that is, for example, with $4 \times 4$ at $5 \times 5$) can increase the average search duration in $e^{1.69} \approx 5.42$. The task presented in the work may be relevant from the point of view of application both in the landmark for ensuring the security of the state, and, for example, in the theory of mass service.

Mathematical simulation of unsteady natural convection and thermal surface radiation within a rotating square enclosure was performed. The considered domain of interest had two isothermal opposite walls subjected to constant low and high temperatures, while other walls are adiabatic. The walls were diffuse and gray. The considered cavity rotated with constant angular velocity relative to the axis that was perpendicular to the cavity and crossed the cavity in the center. Mathematical model, formulated in dimensionless transformed variables “stream function – vorticity” using the Boussinesq approximation and diathermic approach for the medium, was performed numerically using the finite difference method. The vorticity dispersion equation and energy equation were solved using locally one-dimensional Samarskii scheme. The diffusive terms were approximated by central differences, while the convective terms were approximated using monotonic Samarskii scheme. The difference equations were solved by the Thomas algorithm. The approximated Poisson equation for the stream function was solved by successive over-relaxation method. Optimal value of the relaxation parameter was found on the basis of computational experiments. Radiative heat transfer was analyzed using the net-radiation method in Poljak approach. The developed computational code was tested using the grid independence analysis and experimental and numerical results for the model problem.

Numerical analysis of unsteady natural convection and thermal surface radiation within the rotating enclosure was performed for the following parameters: Ra = 10³–10⁶, Ta = 0–10⁵, Pr = 0.7, ε = 0–0.9. All distributions were obtained for the twentieth complete revolution when one can find the periodic behavior of flow and heat transfer. As a result we revealed that at low angular velocity the convective flow can intensify but the following growth of angular velocity leads to suppression of the convective flow. The radiative Nusselt number changes weakly with the Taylor number.

The work is dedicated to the use of the software package Turbulence Problem Solver (TPS) for numerical simulation of a wide range of laser problems. The capabilities of the package are demonstrated by the example of numerical simulation of the interaction of femtosecond laser pulses with thin metal bonds. The software package TPS developed by the authors is intended for numerical solution of hyperbolic systems of differential equations on multiprocessor computing systems with distributed memory. The package is a modern and expandable software product. The architecture of the package gives the researcher the opportunity to model different physical processes in a uniform way, using different numerical methods and program blocks containing specific initial conditions, boundary conditions and source terms for each problem. The package provides the the opportunity to expand the functionality of the package by adding new classes of problems, computational methods, initial and boundary conditions, as well as equations of state of matter. The numerical methods implemented in the software package were tested on test problems in one-dimensional, two-dimensional and three-dimensional geometry, which included Riemann's problems on the decay of an arbitrary discontinuity with different configurations of the exact solution.

Thin films on substrates are an important class of targets for nanomodification of surfaces in plasmonics or sensor applications. Many articles are devoted to this subject. Most of them, however, focus on the dynamics of the film itself, paying little attention to the substrate, considering it simply as an object that absorbs the first compression wave and does not affect the surface structures that arise as a result of irradiation. The paper describes in detail a computational experiment on the numerical simulation of the interaction of a single ultrashort laser pulse with a gold film deposited on a thick glass substrate. The uniform rectangular grid and the first-order Godunov numerical method were used. The presented results of calculations allowed to confirm the theory of the shock-wave mechanism of holes formation in the metal under femtosecond laser action for the case of a thin gold film with a thickness of about 50 nm on a thick glass substrate.