Search

Objective. The purpose of the study is to develop a new method of analyzing seismic vibrations of seismically isolated structures.Method. The structure is modeled by a system with one degree of freedom with a nonlinear stiffness characteristic. In the absence of damping an analytical solution of oscillation equations on the phase plane is obtained. In this case the connection between speeds and displacements is accurate, and the law of uniformly variable motion is used to calculate displacements.Result. To take into account the attenuation, the law of change in mechanical energy at each integration interval is used.Conclusion. An example of calculating a seismically isolated system with a sliding belt and a spring with a linearly varying characteristic of stiffness is considered. The influence of dry friction and viscous damping on the displacement and acceleration of the system is analyzed.

The article considers dynamical systems on the plane, defined by continuous piecewise smooth vector fields. Such systems are used as mathematical models of real processes with switching. An important task is to find the conditions for the generation of periodic trajectories when the parameters change. The paper describes the bifurcation of the birth of a periodic trajectory from the loop of the separatrix of a sewn saddle-node — an analogue of the classical bifurcation of the separatrix loop of a saddle-node of a smooth dynamical system. Consider a one-parameter family $\{ X_\varepsilon \} $ of continuous piecewise-smooth vector fields on the plane. Let $z^0 $ be a point on the switching line. Let's choose the local coordinates $x,y$ in which $z^0 $ has zero coordinates, and the switching line is given by the equation $y = 0$. Let the vector field $X_0 $ in a semi-neighborhood $y \ge 0$ ($y \le 0$) coincide with a smooth vector field $X_0^ + $ ($X_0^ - $), for which the point $z^0 $ is a stable rough node (rough saddle), and the proper subspaces of the matrix of the linear part of the field in $z^0 $ do not coincide with the straight line $y = 0$. The singular point $z^0 $ is called a sewn saddle-node. There is a single trajectory $L_0 $ that is $\alpha $-limit to $z^0 $ — the outgoing separatrix of the point $z^0 $. It is assumed that $L_0 $ is also $\omega $-limit to $z^0$, and enters $z^0 $ in the leading direction of the node of the field $X_0^ + $. For generic family, when the parameter $\varepsilon $ changes, the sewn saddle-node either splits into a rough node and a rough saddle, or disappears. In the paper it is proved that in the latter case the only periodic trajectory of the field $X_\varepsilon $ is generated from the contour $L_0 \cup \{ z^0 \} $ — a stable limit cycle.

There are presented the results of analysis of some irregularities in the series of displacement coordinates on the Earth’s surface for the geographic North Pole in order to relate them temporally to some global jerks in the geomagnetic field. The calculations were made using the International Earth Rotation and Reference Systems Service (IERS) data on the average daily motions of the North Pole from 1962 to 2021 and the information on global jerks in the geomagnetic field measured by the magnetic observatories throughout the world. The identification and analysis of the irregularities in the pole displacement along the Earth’s surface were performed by the Fourier Method and wavelet methods for time series analysis, methods of fixed threshold determination and minimax analysis of the non-Gaussian noise, phase and pseudo-phase space methods, and stroboscopic methods of construction of Poincare maps.The analysis of local Fourier spectra and wavelet-spectra reveals irregularities in the displacement of the North Pole in the time intervals from 1967.04.09 to 1967.11.30, from 1974.03.29 to 1974.09.12, and from 2005.11.03 to 2006.03.07. It is supposed that energy reconstructions which caused short-term pole deviations from the trajectory and starting to follow its previous trajectory at the return points are related to the specific features of oscillatory interactions in the process of the translational-rotational motion of the Earth’s in the Solar System. The time of marking specific points on graphs of the displacement of the pole along the surface of the Earth in 1967 and 1974 is ahead of global geomagnetic jerk occurrence times.

A method of construction and calculation of the structural scheme of the facility management system is proposed, which is constructively formed by the serial connection of the first-order aperiodic link and the integrator, and is formally described by a mathematical model in the form of a product of the corresponding transfer functions. An electric motor with an input voltage source can serve as a common typical implementation of the specified control object. The proposed method makes it possible to build a control system that is close to optimal in terms of speed. Moreover, optimality, in this case, is determined by the fact that the object in the process of functioning is turned on in relay mode. The transient process for a defined control object, under the conditions of the optimal mode, is two stages: acceleration and braking, which are carried out at the maximum values of the input influence - that is, the input voltage. To determine the switching moments of the input influence (signal), the phase plane method is used, and the phase coordinates are: on the abscissa axis, the output value (for the given example, the frequency of rotation of the motor shaft), and on the ordinate axis, the rate of change of the output value (or derivative from the rotation frequency of the motor shaft, i.e. the corresponding acceleration). A structural diagram of the control system was developed, which ensures acceleration and braking of the object at the maximum values of the input signal. The optimality of the transition process is ensured by the fact that the control error is compared with the signal coming from the link of the configured switching line. Formulas for calculating the switching line on the phase plane are presented, as well as the program for calculating the switching line, written in the MATLAB environment in m-file format. The system was modeled in the MATLAB-Simulink package, which confirms the optimality of the control process. [ABSTRACT FROM AUTHOR]

The article aims to document PhaPl that’s a teaching software to plot and research phase portraits of autonomous systems of 2 differential equations on a plane. Interactive computer teaching materials allow to demonstrate tasks describing large number of states of investigated systems clearly and involving students into solving. Plotting and research of phase portraits of autonomous system of 2 differential equations is an important task in “Differential equations” course and other courses that use dynamic systems. The software allows to visualize phase portraits and to perform analysis easily. Plotting of phase portraits needs a lot of routine computations. The software allows teacher to focus on analytical research of autonomous systems of 2 differential equations. The software supports linear and nonlinear autonomous systems of 2 differential equations. The software differs is very different compared with previously known programs: it has very easy graphical user interface and it gives clarity because it demonstrates all steps of solution. To get the full solution, it is enough to just enter a system to research. Initial conditions to plot phase trajectories are chosen automatically. Graphical representation of the phase plane is interactive and allows user to draw additional trajectories with specified initial conditions by mouse hovering over the phase plane. The software is based on popular Free Software (Maxima, Qt4, LaTeX) and it is Free Software itself, thus it is accessible to wider audience, including online students. The software is portable and works on Windows and Linux operating systems. The article describes advantages, disadvantages and peculiar properties of the software, and some aspects of teaching experience. The software is deployed in Moscow State University of Economics, Statistics, and Informatics (MESI), Lomonosov Moscow State University (MSU) since 2013, and in Plekhanov Russian University of Economics since 2016. Further development will be focused on reduction of binary size of the software, portability improvements, and number of analytical results showed.