Vol 30, No 4 (2022)

The main oil pipeline, due to its spatial extent, can be considered as a control object with distributed parameters (ODP). The dependences on time and coordinates of the flow velocity and pressure in the pipeline are considered as controlled output values of the ODP. The boundary value problem of mathematical modeling of the process of pipeline transportation of oil in the standard form is presented in the form of a linear partial differential equation of the second order. The paper presents a solution to the boundary value problem of mathematical modeling of unsteady oil flow through a trunk pipeline in the presence of internal concentrated pressure sources in the form of functions describing the dependences on time and spatial coordinates of pressures and average cross-section pipeline oil flow rates. To represent the solution of the boundary value problem in the form of convolution integrals, Green's functions and standardizing functions are obtained, which makes it possible to use non-smooth (discontinuous) dependencies to describe programs for changing the values of internal concentrated pressure sources over time. The solutions obtained make it possible to use the methods of the theory of optimal control of systems with distributed parameters to solve the problems of optimal control of the process of pipeline transportation of oil.

The presented review analyzes the approaches and methods of using simulation models in the maintenance and repair organization of the complex technical objects and systems. The development of the concept of "Industry 4.0" and the Internet of things involves the transition from periodic and preventive maintenance to predictive maintenance based on the study of processes during the object operation. It is shown that system models based on Petri nets are convenient for describing and analyzing technological processes and equipment maintenance. The effectiveness of timed stochastic colored Petri nets for virtual tests in the design of maintenance and repair procedures in complex systems is revealed. The use of hierarchical Petri nets allows building complex models that describe interrelated processes. A general model based on a hierarchical network is proposed to study the processes of deterioration and degradation of the technical object aggregates and elements and to form a predictive maintenance strategy. The model includes a Gantt chart of production tasks, a set of active and reserve units, maintenance and repair modules. The examples of simulation models on Petri nets for various technical systems are considered. Solutions for flexible production systems, railway bridges, offshore wind turbines, an aircraft fleet, a group of robotic vehicles, and a complex of computer equipment of an enterprise are given. The models of various maintenance strategies are considered and the generality of the models based on hierarchical Petri nets is shown. The article formulates methodological principles for constructing hierarchical networks to simulate the operation and maintenance of technical systems. The article analyzes known software tools for the implementation of timed stochastic colored Petri nets. The summary concludes that the use of simulation models on Petri nets is promising for organizing maintenance and repair of complex technical objects and systems.

The article deals with the problem of creating a t-protective coating for information-measuring devices and systems for various purposes exposed to external high-temperature exposure in emergency situations related to fire. As a solution to the problem, it is proposed to use thermal-protective materials containing active additives that provide a thermal-protective effect that promotes the refraction of heat flows aimed at heating the protected object. The heat-shielding effect is provided by an endothermic reaction that occurs in the material when the decomposition temperature of the selected component is reached. It should be noted that the temperature at which the reaction with heat absorption should occur should be lower than the temperature of the lesion of the protected object. In this case, the heat flows passing through the layer of heat-shielding material will be refracted, since heat will be spent on the decomposition of the endothermic filler. The heating of the material will be carried out due to the matrix of the material and decomposition products. Based on the tasks that require the use of a heat-protective material, the amount of endothermic filler is determined. Accordingly, with an increase in the time interval during which it is necessary to eliminate the fire, the content of endothermic filler also increases. The use of thermal-protective material is relevant for emergency flight data recorders, since in the event of a plane crash, a fire is likely to occur, which can lead to the loss of information necessary to determine the causes of an emergency.

In this publication, the issues of computer simulation of electromagnetic and hydrodynamic processes in an electromagnetic crystallizer mold of a silicon melt of periodic action are considered. The crystallization process proceeds under conditions of additional heating by eddy currents in the melt. The main task of the electromagnetic interaction of currents in the melt and the inductor field is to create a repulsive force to exclude mechanical contact between silicon and the lining surface. When this problem is solved, heat is released in the melt and a vector of forces is formed, which leads to mixing of liquid silicon. These processes affect the transfer of heat between the lower, upper and side surfaces of the cylinder, the shape of which is taken by the melt. To improve the quality of the crystal structure of the ingot, a temperature gradient is formed by controlling heat flows due to the thickness of the lining walls, heating the upper surface and removing heat from the lower base.

The appearance of a perturbing action under these conditions can upset the balance of heat flows and lead to the creation of thermal stresses in the ingot, accompanied by microcracks. Simultaneous modeling of all processes occurring in an electromagnetic silicon crystallizer is currently unrealizable on a personal computer.

When modeling the process of hydrodynamics in the melt, several geometry options were considered, starting from the maximum volume of the liquid phase and ending with a thin upper layer in the upper part. With a conical shape of the inductor, the distribution of the force vector in the melt depends on the axial coordinate, which leads to a significant decrease in the velocity components as the thickness of the liquid phase decreases. The results of the study showed a rapid decrease in the mixing effect as the thickness of the liquid layer of silicon decreases with a slight change in the overall parameters of the crystallization process.

The article considers the problem of determining the conditions under which the use of a frequency converter in a submersible pump control station leads to a reduction in electrical energy costs and becomes efficient from an energy point of view. Analytical expressions are given that allow calculating the specific costs of electrical energy during artificial lift oil production for the case when the operating mode and well flow rate are provided by wellhead choke throttling. At the same time, special attention is paid to determining the rotation speed of the submersible asynchronous motor, which ensures the required location of the operating point on the pump pressure characteristic. Formulas are also given that make it possible to calculate the specific costs of electrical energy during artificial lift oil production for the case when the operating mode and well flow rate are set by the frequency converter of the control station. An analytical expression has been found to determine the rotation speed and frequency of the supply voltage, which provide the required operating point of the pump with frequency regulation of the submersible motor. It is proposed, using the above analytical expressions, to use the iterative method to calculate the pump performance, at which the specific energy costs for the production of a cubic meter of liquid will be equal both in the case of using a frequency converter in the control station and without it. An example of calculating such a boundary value of pump performance for a hypothetical well is given. It is shown that a decrease in the required flow rate relative to the limiting value of the pump performance leads to a decrease in the specific consumption of electrical energy during artificial lift oil production in the case of using a frequency converter in the submersible pump control station.

The system of automatic control of the reactive power factor of the enterprise's power supply system is considered, in which one part of the transformer substations is equipped with adjustable capacitor units, and the second is not. Its advantage in comparison with the power factor control system is shown, firstly, lower requirements for its error and, secondly, the calculation of the consumer with the supplier for electricity is made taking into account the ratio of reactive energy to active energy. An estimate of the error of regulation of the reactive power factor on the higher voltage side of the transformers of the main step-down substation, where settlement meters are installed, is given, with stabilization of the reactive power factor on the low voltage side of these transformers. The synthesis of the system of automatic control of the reactive power factor, built as a function of the power of consumers and power losses in transformers, and the estimation of its error are considered. The proposed control system is intended for power supply systems with a combined load, the use of which will allow the consumer to avoid penalty coefficients to the tariff for active electricity, and ultimately reduce losses in the transmission of electricity and increase the transmission capacity of the electrical network.