In this paper, a comparative analysis of various approaches to modeling the process of capillary imbibition in oil-saturated rocks is carried out. Today, the permeability of developed oil fields is decreasing, due to which capillary processes begin to make a significant contribution to filtration. Therefore, the issue of reservoir-scale imbibition modeling is becoming increasingly relevant. Capillary imbibition is a process of spontaneous filtration of a liquid into a porous medium under the action of capillary forces. The aim of the study is to analyze approaches to the mathematical description of this process. To do this, one-dimensional models of single-phase imbibition by Handy, Lee and Horn, Benavente and Kai are considered, the Schmid one-dimensional two-phase imbibition equation is solved, and the ability of the filtration model in the tNavigator software package to predict imbibition is checked. For verification, real experiments on core are simulated. Based on the simulation results, conclusions are drawn that single-phase models have an increased error due to the interaction of water with the second phase and non-physical values of free parameters, which is why it is not recommended to scale them to large rock volumes. The two-phase model does not consider gravity, due to which the error increases at the last stages of vertical imbibition, so this approach must be modified to consider gravitational forces in the imbibition equation. A numerical one-dimensional experiment on a hydrodynamic simulator using the proposed core modeling technique showed the best convergence with experimental data with an error of 1 to 4%, which is why it is recommended for modeling capillary processes on the scale of a well.

n this paper, we study a modified Hegselmann-Krause model of opinion dynamics based on the bounded confidence principle. This model is formulated as a discontinuous and nonlinear dynamical system. At any time moment of the process of opinion formation, the operator of forming the next opinion of an agent is two-step; first, one takes the average of opinions of agents sharing similar opinions plus his/her own; in the second step, a regularization procedure is performed. A new regularization procedure is applied. We find conditions under which every trajectory tends to a fixed point of the system and study stability properties of fixed points.

A discrete dynamic system generated by a diffeomorphism is considered. The task of constructing an invariant decomposition of the tangent space is set. This task is reduced to calculating the components of a chain recurrent set on a projective bundle. A computer-oriented tool for such a calculation is a symbolic image of a dynamic system, which is an oriented graph. The components of the chain recurrent set are determined by calculating the components of the strong connectivity of the symbolic image. A nontrivial example of calculating the desired tangent space decomposition is given.

We discuss the recent progress on studying volume contraction for linear cocycles generated by delay equations obtained by the authors. On the basis, we use adapted metrics constructed explicitly or via the Frequency Theorem. In contrast to many existing results, this approach allows to provide effective estimates in terms of the system parameters (including delays). We illustrate the exposed general results by means of the nonautonomous and classical Nicholson blowflies models, where effective dimension estimates for global attractors and robust conditions for the global stability are obtained.

In this paper, we investigate by means of second method of Lyapunov, sufficient conditions that guarantee uniform-asymptotic stability of the trivial solution and ultimate boundedness of all solutions to a certain second order differential equation. We construct a complete Lyapunov function in order to discuss the qualitative properties mentioned earlier. The boundedness result in this paper is new and also complement some boundedness results in literature obtained by using an incomplete Lyapunov function together with a signum function. Finally, we demonstrate the correctness of our results with two numerical examples and graphical representation of the trajectories of solutions to the examples using Maple software.

In this paper, the Jacobi-Poisson method of building first integrals by known integral manifolds for Hamiltonian differential systems is developed. The existence theorem of first integrals in the form of Poisson brackets from known integral manifolds for Hamiltonian systems is proved. The statement of finding additional first integrals by known first integrals and integral manifolds for Hamiltonian systems is given. In the case of polynomial Hamiltonian systems, we use the concept of partial integrals and concretize ours results. The Jacobi - Poisson method of construction first integrals in the form of Poisson brackets from known integral characteristics (integral manifolds, partial integrals, and first integrals) for general ordinary differential systems is proposed. Statements of finding first integrals for an ordinary differential system by integral characteristics of the auxiliary Hamiltonian system are obtained. The generalized Poisson theorem of construction first integrals is indicated. And, the question of the existence of partial integrals and first integrals in the form of Poisson brackets for ordinary polynomial differential systems is investigated. The results obtained in this paper can be used in the analytical theory of differential equations and in the analytical mechanics.

The paper considers the iterative learning control (ILC) design problem of a network system under changing operating mode of subsystems (agents) and configuration of information network. The network system consists of identical agents, which are discrete linear dynamic plants operating in a repetitive mode. The operating modes of agents depend on their parameters and the reference trajectory, which must be tracked with required accuracy at output of system. The configurations of information network define the group of functioning agents and the type of information exchange between them. The mode and the configuration change takes place in accordance with certain external rules. The control design is based on the divergent method of the vector Lyapunov function. For reducing the transient error caused by the mode change and the connection of new agents, a special rule for switching the ILC law is proposed. The results of modeling the obtained control law for a group of manipulators with flexible link are presented.