The Poincaré – Zhukovsky – Hough model describing the motion of a rigid body with an ellipsoidal cavity filled with an ideal vortex liquid is used. The possibility of regular precession in a uniform force field of a system not possessing axial symmetry is shown. For the case where the axis of proper rotation is one of the system principal inertia axes and the center of gravity lies on this axis, two conditions of precession are obtained. One of the conditions coincides with the condition of regular precession in the absence of external forces for the system without axial symmetry found earlier by the author. This condition imposes one constraint on the system configuration. The other condition relates the proper rotation and precession velocities to the mechanical parameters of the system. A record is given of the conditions in the form of relations between the inertia moments of the rigid shell and the semiaxes of the ellipsoidal cavity, as well as between the distance to the center of gravity and the nutation angle, the precession velocity and the proper rotation velocity. It is shown that in the case where the cavity differs little from the sphere, the conditions obtained differ from the Lagrange conditions for an axisymmetric rigid body with a fixed point in a uniform gravity field by small values of the second order.

The interaction of various climatic zones (northern, temperate and southern) as circulation cells of large-scale atmospheric currents is represented in the form of a superposition of six-dimensional systems that describe the motion of stratified fluids in the space of linear velocity and temperature fields. The effect of each of the zones on neighboring zones occurs only through temperature gradients along the meridional direction which are due to sources and sinks of heat (short-wave radiation, downcoming long-wave radiation, outgoing long-wave radiation). The resulting nonlinear system, in which each of the blocks contains vortex and temperature components of the fields, is discretized by an implicit scheme. Long-period nonlinear oscillations are modeled, showing the natural “breath” of the climate of the atmosphere, in which the amplitudes of vortex intensity and temperature differences of various zones change with characteristic times of decades. In this case, the transition between quasi-stationary states of the system can occur over several years. A comparison is made between various numerical methods that show long-term oscillations in convective systems.

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.

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.

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.

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.

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.

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.

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.

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.

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.