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In the present paper the application of the kinetic methods to the blood flow problems in elastic vessels is studied. The Lattice Boltzmann (LB) kinetic equation is applied. This model describes the discretized in space and time dynamics of particles traveling in a one-dimensional Cartesian lattice. At the limit of the small times between collisions LB models describe hydrodynamic equations which are equivalent to the Navier – Stokes for compressible if the considered flow is slow (small Mach number). If one formally changes in the resulting hydrodynamic equations the variables corresponding to density and sound wave velocity by luminal area and pulse wave velocity then a well-known 1D equations for the blood flow motion in elastic vessels are obtained for a particular case of constant pulse wave speed.

In reality the pulse wave velocity is a function of luminal area. Here an interesting analogy is observed: the equation of state (which defines sound wave velocity) becomes pressure-area relation. Thus, a generalization of the equation of state is needed. This procedure popular in the modeling of non-ideal gas and is performed using an introduction of a virtual force. This allows to model arbitrary pressure-area dependence in the resulting hemodynamic equations.

Two test case problems are considered. In the first problem a propagation of a sole nonlinear pulse wave is studied in the case of the Laplace pressure-area response. In the second problem the pulse wave dynamics is considered for a vessel bifurcation. The results show good precision in comparison with the data from literature.

The paper proposes a new mathematical model to study the interaction dynamics of the longitudinal wall of a narrow channel with its end seal. The end seal was considered as the edge wall on a spring, i.e. spring-mass system. These walls interaction occurs via a viscous liquid filling the narrow channel; thus required the formulation and solution of the hydroelasticity problem. However, this problem has not been previously studied. The problem consists of the Navier–Stokes equations, the continuity equation, the edge wall dynamics equation, and the corresponding boundary conditions. Two cases of fluid motion in a narrow channel with parallel walls were studied. In the first case, we assumed the liquid motion as the creeping one, and in the second case as the laminar, taking into account the motion inertia. The hydroelasticty problem solution made it possible to determine the distribution laws of velocities and pressure in the liquid layer, as well as the motion law of the edge wall. It is shown that during creeping flow, the liquid physical properties and the channel geometric dimensions completely determine the damping in the considered oscillatory system. Both the end wall velocity and the longitudinal wall velocity affect the damping properties of the liquid layer. If the fluid motion inertia forces were taken into account, their influence on the edge wall vibrations was revealed, which manifested itself in the form of two added masses in the equation of its motion. The added masses and damping coefficients of the liquid layer due to the joint consideration of the liquid layer inertia and its viscosity were determined. The frequency and phase responses of the edge wall were constructed for the regime of steady-state harmonic oscillations. The simulation showed that taking into account the fluid layer inertia and its damping properties leads to a shift in the resonant frequencies to the low-frequency region and an increase in the oscillation amplitudes of the edge wall.

In this paper, we address the mathematical modeling of robots based on tensegrity structures. The pivotal property of such structures is the forming elements working only for compression or tension, which allows the use of materials and structural solutions that minimize the weight of the structure while maintaining its strength.

Tensegrity structures hold several properties important for collaborative robotics, exploration and motion tasks in non-deterministic environments: natural compliance, compactness for transportation, low weight with significant impact resistance and rigidity. The control of such structures remains an open research problem, which is associated with the complexity of describing the dynamics of such structures.

We formulate an approach for describing the dynamics of such structures, based on second-order dynamics of the Cartesian coordinates of structure elements (rods), first-order dynamics for angular velocities of rods, and first-order dynamics for quaternions that are used to describe the orientation of rods. We propose a numerical method for solving these dynamic equations. The proposed methods are implemented in the form of a freely distributed mathematical package with open source code.

Further, we show how the provided software package can be used for modeling the dynamics and determining the operating modes of tensegrity structures. We present an example of a tensegrity structure moving in zero gravity with three rigid rods and nine elastic elements working in tension (cables), showing the features of the dynamics of the structure in reaching the equilibrium position. The range of initial conditions for which the structure operates in the normal mode is determined. The results can be directly used to analyze the nature of passive dynamic movements of the robots based on a three-link tensegrity structure, considered in the paper; the proposed modeling methods and the developed software are suitable for modeling a significant variety of tensegrity robots.

A promising method of increasing precipitation in arid climates is the method of creating a vertical high-temperature jet seeded by hygroscopic aerosol. Such an installation makes it possible to create artificial clouds with the possibility of precipitation formation in a cloudless atmosphere, unlike traditional methods of artificial precipitation enhancement, which provide for increasing the efficiency of precipitation formation only in natural clouds by seeding them with nuclei of crystallization and condensation. To increase the power of the jet, calcium chloride, carbamide, salt in the form of a coarse aerosol, as well as NaCl/TiO₂ core/shell novel nanopowder, which is capable of condensing much more water vapor than the listed types of aerosols, are added. Dispersed inclusions in the jet are also centers of crystallization and condensation in the created cloud to increase the possibility of precipitation. To simulate convective flows in the atmosphere, a mathematical model of FlowVision large-scale atmospheric flows is used, the solution of the equations of motion, energy and mass transfer is carried out in relative variables. The statement of the problem is divided into two parts: the initial jet model and the FlowVision large-scale atmospheric model. The lower region, where the initial high-speed jet flows, is calculated using a compressible formulation with the solution of the energy equation with respect to the total enthalpy. This division of the problem into two separate subdomains is necessary in order to correctly carry out the numerical calculation of the initial turbulent jet at high velocity (M > 0.3). The main mathematical dependencies of the model are given. Numerical experiments were carried out using the presented model, experimental data from field tests of the installation for creating artificial clouds were taken for the initial data. A good agreement with the experiment is obtained: in 55% of the calculations carried out, the value of the vertical velocity at a height of 400 m (more than 2 m/s) and the height of the jet rise (more than 600 m) is within an deviation of 30% of the experimental characteristics, and in 30% of the calculations it is completely consistent with the experiment. The results of numerical simulation allow evaluating the possibility of using the high-speed jet method to stimulate artificial updrafts and to create precipitation. The calculations were carried out using FlowVision CFD software on SUSU Tornado supercomputer.

The article considers the problem of the stability of the vertical position of a Maxwell pendulum during its periodic up-down movements. Two types of transition movements are considered: “stop” — occurs when the body of the pendulum in its highest position on the string (during its “standard” upward movement) stops for a moment; “two-link pendulum” — occurs when the entire thread from the body of the pendulum is selected (the lowest position of the body on the thread during its “standard” downward movement), and the body is forced to rotate relative to the thread around the point of its attachment to the body. It is shown that for any values of the pendulum parameters, this position is unstable in the sense that oscillations of the thread around the vertical of finite amplitude occur in the system for arbitrarily small initial deviations. In addition, it has been established that no shock phenomena occur during the movement of the Maxwell pendulum, and the model of this pendulum itself, with the values of its parameters often used in the literature, is incorrect according to Hadamard. In this work, it is shown that the vertical position of the pendulum threads during the indicated oscillatory movements of the body along the threads for any non-degenerate values of the parameters of the Maxwell pendulum is always unstable in the above sense. Moreover, this instability is caused precisely by transitional movements of the 2nd type. In this work, it is further shown that no jumps in speeds or accelerations (due to which shocks or “jerks” in the tension of the threads can occur) do not occur during the indicated movements of the Maxwell pendulum model under consideration. In our opinion, the “jerks” observed in the experiments are due to other reasons, for example, the technical imperfection of the instruments on which the experiments were carried out.

In the paper the model for a one-dimensional non-equilibrium riverbed process is proposed. The model takes into account the suspended and bed-load sediment transport. The bed-load transport is determined by using the original formula. This formula was derived from the thin bottom layer motion equation. The formula doesn’t contain new phenomenological parameters and takes into account the influence of bed slope, granulometric and physical mechanical parameters on the bed-load transport. A number of the model test problems are solved for the verification of the proposed mathematical model. The comparison of the calculation results with the established experimental data and the results of other authors is made. It was shown, that the obtained results have a good agreement with the experimental data in spite of the relative simplicity of the proposed mathematical model.

In 2007 Kasman conducted a series of original computer experiments with sine-Gordon kinks moving along artificial DNA sequences. Two sequences were considered. Each consisted of two parts separated by a boundary. The left part of the first sequence contained repeating TTA triplets that encode leucines, and the right part contained repeating CGC triplets that encode arginines. In the second sequence, the left part contained repeating CTG triplets encoding leucines, and the right part contained repeating AGA triplets encoding arginines. When modeling the kink movement, an interesting effect was discovered. It turned out that the kink, moving in one of the sequences, stopped without reaching the end of the sequence, and then “bounced off” as if he had hit a wall. At the same time, the kink movement in the other sequence did not stop during the entire time of the experiment. In these computer experiments, however, a simple DNA model proposed by Salerno was used. It takes into account differences in the interactions of complementary bases within pairs, but does not take into account differences in the moments of inertia of nitrogenous bases and in the distances between the centers of mass of the bases and the sugar-phosphate chain. The question of whether the Kasman effect will continue with the use of more accurate DNA models is still open. In this paper, we investigate the Kasman effect on the basis of a more accurate DNA model that takes both of these differences into account. We obtained the energy profiles of Kasman's sequences and constructed the trajectories of the motion of kinks launched in these sequences with different initial values of the energy. The results of our investigations confirmed the existence of the Kasman effect, but only in a limited interval of initial values of the kink energy and with a certain direction of the kinks movement. In other cases, this effect did not observe. We discussed which of the studied sequences were energetically preferable for the excitation and propagation of kinks.

This article is devoted to the development of an algorithm for trajectory control of a highly maneuverable four-wheeled robotic transport platform equipped with mecanum wheels, in order to organize its movement behind some moving object. The calculation of the kinematic ratios of this platform in a fixed coordinate system is presented, which is necessary to determine the angular velocities of the robot wheels depending on a given velocity vector. An algorithm has been developed for the robot to follow a mobile object on a plane without obstacles based on the use of a modified chase method using different types of control functions. The chase method consists in the fact that the velocity vector of the geometric center of the platform is co-directed with the vector connecting the geometric center of the platform and the moving object. Two types of control functions are implemented: piecewise and constant. The piecewise function means control with switching modes depending on the distance from the robot to the target. The main feature of the piecewise function is a smooth change in the robot’s speed. Also, the control functions are divided according to the nature of behavior when the robot approaches the target. When using one of the piecewise functions, the robot’s movement slows down when a certain distance between the robot and the target is reached and stops completely at a critical distance. Another type of behavior when approaching the target is to change the direction of the velocity vector to the opposite, if the distance between the platform and the object is the minimum allowable, which avoids collisions when the target moves in the direction of the robot. This type of behavior when approaching the goal is implemented for a piecewise and constant function. Numerical simulation of the robot control algorithm for various control functions in the task of chasing a target, where the target moves in a circle, is performed. The pseudocode of the control algorithm and control functions is presented. Graphs of the robot’s trajectory when moving behind the target, speed changes, changes in the angular velocities of the wheels from time to time for various control functions are shown.

It proposes a new alternative approach to explain the flat spectrum of the velocity for stars orbital motion on the periphery of spiral galaxies. In particular, that velocity significant excess of speed calculated according to the virial theorem. The concept is the assumption of the existence for gravitational field of the Central body of the galaxy cylindrical, and not spherical, symmetry. The configuration of this field can be explained by the presence on galaxy axis the cosmic string, the length of which covers the diameter of the disk of the galaxy. This model will be subjected to comparison with the more traditional concept of the availability of the spiral galaxy ball halo of dark matter. For this approach it will also be offered a kinematic model, and the hypothesis about the nature of dark matter. It examines the data of astronomical observations about the presence of cosmic strings in the zones adjacent to galaxies.

The work aims to study the admissibility of the quasi-steady approach application in fluid flow modeling inside of evaporating drops placed on a solid horizontal substrate. Non-steady model has been developed to compare results with a quasi-steady model. For the first time one-dimensional motion equation of fluid in a drop is proposed from a momentum conservation law. We have shown that inward flow is possible on the edge of drop in one-dimensional models. It may be explained by existence of stagnation points.