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We analyze variants of considering the inhomogeneity of the environment in computer modeling of the dynamics of a predator and prey based on a system of reaction-diffusion–advection equations. The local interaction of species (reaction terms) is described by the logistic law for the prey and the Beddington –DeAngelis functional response, special cases of which are the Holling type II functional response and the Arditi – Ginzburg model. We consider a one-dimensional problem in space for a heterogeneous resource (carrying capacity) and three types of taxis (the prey to resource and from the predator, the predator to the prey). An analytical approach is used to study the stability of stationary solutions in the case of local interaction (diffusionless approach). We employ the method of lines to study diffusion and advective processes. A comparison of the critical values of the mortality parameter of predators is given. Analysis showed that at constant coefficients in the Beddington –DeAngelis model, critical values are variable along the spatial coordinate, while we do not observe this effect for the Arditi –Ginzburg model. We propose a modification of the reaction terms, which makes it possible to take into account the heterogeneity of the resource. Numerical results on the dynamics of species for large and small migration coefficients are presented, demonstrating a decrease in the influence of the species of local members on the emerging spatio-temporal distributions of populations. Bifurcation transitions are analyzed when changing the parameters of diffusion–advection and reaction terms.

A mathematical model of two-phase capillary-nonequilibrium isothermal flows of incompressible phases in a double porosity medium is constructed. A double porosity medium is considered, which is a composition of two porous media with contrasting capillary properties (absolute permeability, capillary pressure). One of the constituent media has high permeability and is conductive, the second is characterized by low permeability and forms an disconnected system of matrix blocks. A feature of the model is to take into account the influence of capillary nonequilibrium on mass transfer between subsystems of double porosity, while the nonequilibrium properties of two-phase flow in the constituent media are described in a linear approximation within the Hassanizadeh model. Homogenization by the method of formal asymptotic expansions leads to a system of partial differential equations, the coefficients of which depend on internal variables determined from the solution of cell problems. Numerical solution of cell problems for a system of partial differential equations is computationally expensive. Therefore, a thermodynamically consistent kinetic equation is formulated for the internal parameter characterizing the phase distribution between the subsystems of double porosity. Dynamic relative phase permeability and capillary pressure in the processes of drainage and impregnation are constructed. It is shown that the capillary nonequilibrium of flows in the constituent subsystems has a strong influence on them. Thus, the analysis and modeling of this factor is important in transfer problems in systems with double porosity.

Buckling problems of thin elastic shells have become relevant again because of the discrepancies between the standards in many countries on how to estimate loads causing buckling of shallow shells and the results of the experiments on thinwalled aviation structures made of high-strength alloys. The main contradiction is as follows: the ultimate internal stresses at shell buckling (collapsing) turn out to be lower than the ones predicted by the adopted design theory used in the USA and European standards. The current regulations are based on the static theory of shallow shells that was put forward in the 1930s: within the nonlinear theory of elasticity for thin-walled structures there are stable solutions that significantly differ from the forms of equilibrium typical to small initial loads. The minimum load (the lowest critical load) when there is an alternative form of equilibrium was used as a maximum permissible one. In the 1970s it was recognized that this approach is unacceptable for complex loadings. Such cases were not practically relevant in the past while now they occur with thinner structures used under complex conditions. Therefore, the initial theory on bearing capacity assessments needs to be revised. The recent mathematical results that proved asymptotic proximity of the estimates based on two analyses (the three-dimensional dynamic theory of elasticity and the dynamic theory of shallow convex shells) could be used as a theory basis. This paper starts with the setting of the dynamic theory of shallow shells that comes down to one resolving integrodifferential equation (once the special Green function is constructed). It is shown that the obtained nonlinear equation allows for separation of variables and has numerous time-period solutions that meet the Duffing equation with “a soft spring”. This equation has been thoroughly studied; its numerical analysis enables finding an amplitude and an oscillation period depending on the properties of the Green function. If the shell is oscillated with the trial time-harmonic load, the movement of the surface points could be measured at the maximum amplitude. The study proposes an experimental set-up where resonance oscillations are generated with the trial load normal to the surface. The experimental measurements of the shell movements, the amplitude and the oscillation period make it possible to estimate the safety factor of the structure bearing capacity with non-destructive methods under operating conditions.

An algorithm is proposed to identify parameters of a 2D vortex structure used on information about the flow velocity at a finite (small) set of reference points. The approach is based on using a set of point vortices as a model system and minimizing a functional that compares the model and known sets of velocity vectors in the space of model parameters. For numerical implementation, the method of gradient descent with step size control, approximation of derivatives by finite differences, and the analytical expression of the velocity field induced by the point vortex model are used. An experimental analysis of the operation of the algorithm on test flows is carried out: one and a system of several point vortices, a Rankine vortex, and a Lamb dipole. According to the velocity fields of test flows, the velocity vectors utilized for identification were arranged in a randomly distributed set of reference points (from 3 to 200 pieces). Using the computations, it was determined that: the algorithm converges to the minimum from a wide range of initial approximations; the algorithm converges in all cases when the reference points are located in areas where the streamlines of the test and model systems are topologically equivalent; if the streamlines of the systems are not topologically equivalent, then the percentage of successful calculations decreases, but convergence can also take place; when the method converges, the coordinates of the vortices of the model system are close to the centers of the vortices of the test configurations, and in many cases, the values of their circulations also; con-vergence depends more on location than on the number of vectors used for identification. The results of the study allow us to recommend the proposed algorithm for identifying 2D vortex structures whose streamlines are topologically close to systems of point vortices.

This article is dedicated to numerical algorithms for solving problems of ignition and unsteady combustion of gunpowder on a uniform computational grid, and a grid with concentration near the surface of the combustion at a constant and adapts the depth under the heated layer of computational domain. The analysis of efficiency of a numerical grid.

Molecular dynamics simulation using the embedded-atom method is applied to study the structural evolution of the particle diameter of 40 Å during the quenching process. Was carried comparative analysis of the structural reconstruction for the particle and the bulk models. Was a reduction in temperature of the beginning and end of the transformation of the particle. In formation of a percolation cluster from interpenetrating and contacting icosahedrons, for model of the particle, it is involved for 10 percent of atoms more, than for model of a bulk.

Molecular dynamics (MD) simulations of rigid water model TIP4P-EW at ambient conditions were carried out. Delaunay’s simplexes were considered as structural elements of liquid water. Topological criterion which allows to identify the water microstructure in snapshot of MD cell was used to allocate its dense part. Geometrical analysis of water Delaunay’s simplexes indicates their strong flatness in comparison with a regular tetrahedron that is fundamentally different from the results for dense part of simple liquids. The statistics of TIP4P-EW water clusters was investigated depending on their cardinality and connectivity. It is similar to the statistics for simple liquids and the structure of this dense part is also a fractal surface consisting of the free edges of the Delaunay’s simplexes.

Dynamic game theoretic models of the corporative innovative development are investigated. The proposed models are based on concordance of private and public interests of agents. It is supposed that the structure of interests of each agent includes both private (personal interests) and public (interests of the whole company connected with its innovative development first) components. The agents allocate their personal resources between these two directions. The system dynamics is described by a difference (not differential) equation. The proposed model of innovative development is studied by simulation and the method of enumeration of the domains of feasible controls with a constant step. The main contribution of the paper consists in comparative analysis of efficiency of the methods of hierarchical control (compulsion or impulsion) for information structures of Stackelberg or Germeier (four structures) by means of the indices of system compatibility. The proposed model is a universal one and can be used for a scientifically grounded support of the programs of innovative development of any economic firm. The features of a specific company are considered in the process of model identification (a determination of the specific classes of model functions and numerical values of its parameters) which forms a separate complex problem and requires an analysis of the statistical data and expert estimations. The following assumptions about information rules of the hierarchical game are accepted: all players use open-loop strategies; the leader chooses and reports to the followers some values of administrative (compulsion) or economic (impulsion) control variables which can be only functions of time (Stackelberg games) or depend also on the followers’ controls (Germeier games); given the leader’s strategies all followers simultaneously and independently choose their strategies that gives a Nash equilibrium in the followers’ game. For a finite number of iterations the proposed algorithm of simulation modeling allows to build an approximate solution of the model or to conclude that it doesn’t exist. A reliability and efficiency of the proposed algorithm follow from the properties of the scenario method and the method of a direct ordered enumeration with a constant step. Some comprehensive conclusions about the comparative efficiency of methods of hierarchical control of innovations are received.

Functional modeling of blood clotting and fibrin-polymer mesh formation is of a significant value for medical and biophysics applications. Despite the fact of some discrepancies present in simplified functional models their results are of the great interest for the experimental science as a handy tool of the analysis for research planning, data processing and verification. Under conditions of the good correspondence to the experiment functional models can be used as an element of the medical treatment methods and biophysical technologies. The aim of the paper in hand is a modeling of a point system of the fibrin-polymer formation as a multistage polymerization process with a sol-gel transition at the final stage. Complex-value Rosenbroke method of second order (CROS) used for computational experiments. The results of computational experiments are presented and discussed. It was shown that in the physiological range of the model coefficients there is a lag period of approximately 20 seconds between initiation of the reaction and fibrin gel appearance which fits well experimental observations of fibrin polymerization dynamics. The possibility of a number of the consequent $(n = 1–3)$ sol-gel transitions demonstrated as well. Such a specific behavior is a consequence of multistage nature of fibrin polymerization process. At the final stage the solution of fibrin oligomers of length 10 can reach a semidilute state, leading to an extremely fast gel formation controlled by oligomers’ rotational diffusion. Otherwise, if the semidilute state is not reached the gel formation is controlled by significantly slower process of translational diffusion. Such a duality in the sol-gel transition led authors to necessity of introduction of a switch-function in an equation for fibrin-polymer formation kinetics. Consequent polymerization events can correspond to experimental systems where fibrin mesh formed gets withdrawn from the volume by some physical process like precipitation. The sensitivity analysis of presented system shows that dependence on the first stage polymerization reaction constant is non-trivial.

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.