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Call for papers
![]() | Call for Papers: Special Issue dedicated to the memory of Alexey V. Borisov |
Borisov S. V., Grishakin V. T.
Abstract
An analysis is made of the motion of a particle on a rotating disk equipped with rectilinear
blades for different types of particle collisions with a blade. The dynamics of particle motion
is considered using equations describing the dynamics of the relative motion of a particle and
is studied for the cases of inelastic and elastic interaction with the blade when the coefficient
of friction of the particle against the disk has a value that is the most probable from a practical
point of view. The impact interaction of the particle with the blade is studied using the
Routh hypothesis, which relates the normal and tangential components of the impact impulse by
a dependence similar to the Amonton – Coulomb dependence between the normal and tangential
components of the interaction force of two rough bodies. The dynamical coefficient of impact
friction is taken to be equal to half the kinematic coefficient of friction of the particle against
the disk. After an impact, depending on the values of the above-mentioned coefficients and
the angle of inclination of the blade, the particle may or may not possess a velocity component
tangential and (or) normal to the surface of the blade. In addition, depending on the overall
dimensions of the disk and the inclination angle of the blade the moving particle can repeatedly
enter into impact interaction with the blade. In this paper we consider all four patterns
of motion of the particle after its first and subsequent impacts against the blade of the rotating
disk, present graphs of time dependences of the projections of the velocity of the relative motion
of the particle, and plot trajectories of the relative motion of the particle for two practically
important cases of installation of a blade on the disk’s surface which ensure the initial collision
angles equal to 0${}^\circ$ and 30${}^\circ$. The proposed model is also used to investigate the changes in the
antitorque moment acting on the disk. For this purpose, in each of the cases we calculate the
resulting moment of impact impulse and the impulse of friction torque throughout the motion of
the particle on the disk’s surface. We present the results of numerical experiments and use them
to give recommendations on the optimization of mechanical systems of this type.
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Artemova E. M., Lagunov D. A., Vetchanin E. V.
Abstract
This paper is concerned with the motion of an elliptic foil in the field of a fixed point
singularity. A complex potential of the fluid flow is constructed, and the forces and the torque
which act on the foil from the fluid are obtained. It is shown that the equations of motion
of the elliptic foil in the field of a fixed point vortex source can be represented as Lagrange –
Euler equations. It is also shown that the system has an additional first integral due to the
conservation of the angular momentum. An effective potential of the system under consideration
is constructed. For the cases where the singularity is a vortex or a source, unstable relative
equilibrium points corresponding to the circular motion of the foil around the singularity are
found.
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Bizyaev I. A.
Abstract
This paper investigates the trajectories of light beams in a Kerr metric, which describes the
gravitational field in the neighborhood of a rotating black hole. After reduction by cyclic coordinates,
this problem reduces to analysis of a Hamiltonian system with two degrees of freedom.
A bifurcation diagram is constructed and a classification is made of the types of trajectories of
the system according to the values of first integrals. Relations describing the boundary of the
shadow of the black hole are obtained for a stationary observer who rotates with an arbitrary
angular velocity about the axis of rotation of the black hole.
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Budyansky A. V., Tsybulin V. G.
Abstract
The impact of migration effects on the formation of population distributions is studied.
We consider the model of interplay between two species (resident and invader), and apply the
theory of cosymmetry to classify different population scenarios. The system of reaction – diffusion
– advection equations is used to describe the nonlinear diffusion and taxis because of
nonuniform distribution of the resource. The logistic law of growth is taken to model local
interaction between species. We consider a one-dimensional habitat with no-flux boundary conditions.
Finite-difference discretization with a staggered grid is used for the spatial coordinate
and Runge – Kutta integrator to solve the resulting system of ordinary differential equations of
large order. A computer experiment is applied to analyze the dynamics of populations and migration
fluxes. We numerically build the maps of migration parameters for description scenarios
of invasion and competition. It is found that nonlinear diffusion has an influence on invasion
because intraspecific taxis compensates nonoptimal migration to resource. Negative coefficients
of intraspecific taxis stimulate diffusion for both species and prevent excessive concentration of
populations. This aids the coexistence of species as stationary distributions. Different coefficient
signs imply the implementation of corresponding stable semipositive solutions. Direct
numerical experiments show that the coexistence of species occurs at large positive coefficients
of intraspecific taxis. The dependence of the scenario on the initial distributions is established.
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Talamucci F.
Abstract
This paper deals with mechanical systems subject to nonlinear nonholonomic constraints.
The aspect that is mainly investigated is the formulation of an energy equation, which is deduced
from the equations of motion, via the generalization of standard procedures pertaining to simpler
cases (holonomic systems). We consider the equations of motion in two different forms (both
present in the literature): the first method introduces the Lagrange multipliers, the second one
is based on the selection of a certain number of independent velocities. The second procedure
generalizes Voronec’s equations for linear kinematic constraints to the case of nonlinear kinematic
constraints. The two kinds of equations of motion gives rise to two different ways of writing
an energy-type equation, since in the second case only the independent velocities are used and
restricted functions corresponding to the Lagrangian and to the Legendre transform consequently
appear in the energy equation. We see that the discrepancy between energy and its reduced
version disappears if and only if the explicit expressions of the constraints are homogeneous
functions of degree 1 with respect to the independent velocities. This property has an effect to
various aspects of the problem and produces certain benefits which place nonlinear nonholonomic
system near to the linear ones.
From the mathematical point of view, we prove that the homogeneity of the explicit functions
is equivalent to the homogeneity of the given constraints with respect to the full set of velocities.
This conclusion is in step with previous results, where the conservation of energy in nonlinear
nonholonomic system is strictly connected with the homogeneity of the constraint functions.
According to the present work, the known result is put into perspective together with other
aspects of nonlinear nonholonomic systems, mainly investigating the unifying role exerted by the
homogeneity property of the explicit constraint functions. A selection of cases and examples is
discussed.
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Butusova O. A., Sitnikov S. A., Bulychev N. A.
Abstract
In this paper, the possibility of using gas plasma treatment for testing the samples of discharge
chambers of electrojet engines is investigated. These discharge chambers were used for
a prototype of the high-frequency ion engine. The model of a hemispherical discharge chamber
was fabricated of Al$_2^{}$O$_3^{}$-Si$_3^{}$N$_4^{}$ composite ceramics by the heat shrink molding method in such
a way that a uniform wall thickness with an error of $0.2$ mm and a high accuracy of the forming
surfaces and coupling sizes were achieved. A high-frequency ion engine, a modification of
the electrojet engine, was employed to test the new composition and the new ceramics molding
technology. When testing the boundary layer of the samples of the discharge chambers of
electrojet engines by gas plasma treatment, the composition of the gas phase (consumption of
components), power consumption, gas flow rate and the exposure time were varied. The tests
revealed that the wear of ceramics in the engine’s exit section is nonlinear depending on the
depth of the boundary layer and is an average of $0.1$ mm, which is less compared to quartz
and corundum based materials used previously. The results of weighing the rings showed that
the decrease in the weight of the inner ring was $1.25$%, and that of the outer ring, $2$%, which
is in good agreement with the surface profile measurements. It is shown that the developed
silicon nitride based ceramics obtained by three-dimensional modeling is a high-quality structural
material resistant to ion-plasma erosion, and that the developed technological processes of
heat shrink molding allow a fast manufacture of the functional prototypes of ceramic parts of
electrojet engines. The application of new ceramics has the potential to increase the destruction
time of the discharge chamber by a factor of no less than $1.2$, and hence the time of trouble-free
operation of this model of the electrojet engine and the possibility of manufacturing relatively
narrow rings widens the range of potential materials while relaxing the requirements concerning
their structural strength. The gas plasma treatment that was used by us is suitable not only for
testing of the structural elements of electrojet or plasma engines, but also for various technical
machines operating under high-temperature, thermostressed or other loaded conditions.
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Maslov D. A.
Abstract
This paper develops the holomorphic regularization method of the Cauchy problem for
a special type of Tikhonov system that arises in the mathematical modeling of wave solidstate
gyroscope dynamics. The Tikhonov system is a system of differential equations a part of
which is singularly perturbed. Unlike other asymptotic methods giving approximations in the
form of asymptotically converging series, the holomorphic regularization method allows one to
obtain solutions of nonlinear singularly perturbed problems in the form of series in powers of
a small parameter converging in the usual sense. Also, as a result of applying the holomorphic
regularization method, merged formulas for an approximate solution are deduced both in the
boundary layer and outside it. These formulas allow a qualitative analysis of the approximate
solution on the entire time interval including the boundary layer.
This paper consists of two sections. In Section 1, the holomorphic regularization method
of the Cauchy problem for a special type of Tikhonov system is developed. The special type of
Tikhonov system means the following: singularly perturbed equations are linear in the variables
included in them with derivatives, the matrix of the singularly perturbed part of the system is
diagonal, the remaining equations have separate linear and nonlinear parts. An algorithm for
deriving an approximate solution to the Cauchy problem for the Tikhonov system of special type
by using the holomorphic regularization method is presented. In Section 2, the mathematical
model describing in interconnected form the mechanical oscillations of the gyroscope resonator
and the electrical processes in the oscillation control circuit is considered. The algorithm for
deriving an approximate solution proposed in Section 1 is used. Formulas for an approximate
solution taking into account the structure of the Tikhonov system are deduced.
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Gasanov M. V.
Abstract
This paper considers a nonlinear fourth-order ordinary differential equation. The study of
this class of equations is conducted using an analytical approximation method based on dividing
the solution domain into two parts: the region of analyticity and the vicinity of a movable singular
point. This work focuses on investigating the equation in the region of analyticity and solving
two problems. The first problem is a classical problem in the theory of differential equations:
proving the theorem of existence and uniqueness of a solution in the region of analyticity. The
structure of the solution in this region takes the form of a power series. To transition from
formal series to series converging in a neighborhood of the initial conditions, a modification of
the majorant method is used, which is applied in the Cauchy – Kovalevskaya theorem. This
method allows determining the domain of validity of the theorem. Within this domain, error
estimates for the analytical approximate solution are obtained, enabling the solution to be found
with any predefined accuracy. When leaving the domain of the theorem’s validity, analytical
continuation is required. To do this, it is necessary to solve the second task of the study: to
study the effect of perturbation of the initial data on the structure of the analytical approximate
solution.
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Misyurin S. Y., Nosova N. Y., Kreinin G. V., Rybak L. A.
Abstract
This article discusses the mechanism of parallel structure, which includes hinged parallelograms.
These mechanisms have a certain peculiarity when composing kinematics equations,
consisting in the fact that some of the equations have a linear form. This simplifies the system
of coupling equations as a whole. By solving direct and inverse kinematics, we will determine
the size and shape of the working area. A method was chosen by solving the inverse kinematics
to determine the workspace. The size and shape of the working area of the mechanism under
consideration with three degrees of freedom are experimentally determined under given initial
conditions. The presence of a large working area allows us to recommend this mechanism for use
in various branches of robotics, medicine, simulators, etc. The Jacobian matrix of the coupling
equations of the mechanism is written out to determine the singularities.
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