Journal of Mechanical Engineering

Computational and Experimental Studies on the Efficiency of Combined Electromagnetic Shielding of the Magnetic Field of Overhead Power Lines

2025-03-07T13:40:12+02:00

To improve the efficiency of reducing the power frequency of the magnetic field generated by overhead power lines in residential buildings, experimental studies based on the results of 3D modeling when using a combined electromagnetic shield consisting of active and passive parts were conducted. The problem of designing a combined electromagnetic shield consisting of a robust active shielding system and an electromagnetic passive shield is solved on the basis of a multi-criteria antagonistic game between two players. The vector of game wins is calculated using the finite element calculation system COMSOL Multiphysics, and the game solution is calculated using particle multiswarm optimization algorithms. When designing combined electromagnetic shields, the coordinates of the spatial location of the shielding winding, currents and phases in the shielding windings of the robust active shielding system, as well as the geometric dimensions and thickness of the electromagnetic passive shield, were calculated. The results of experimental studies of the effectiveness of magnetic field shielding using 3D modeling for a residential building and a power line, when using combined electromagnetic shielding with active and passive parts, are given. For the first time, in order to increase the effectiveness of a combined electromagnetic shield, which consists of active and passive parts, and is designed to reduce the industrial frequency of the magnetic field created by overhead power lines in residential buildings, experimental studies using 3D modeling were conducted. According to the results of experimental studies, the effectiveness of shielding the output magnetic field was determined. It was found that the shielding coefficient of the electromagnetic passive shield is more than two units, and the effectiveness of the system with an active shield is more than four units, and for a system with a combined electromagnetic passive and active shield it is more than 10 units. The possibility of reducing the level of magnetic field induction in a residential building from power lines when using combined electromagnetic passive and active shielding to a level safe for the population is proven.

Optimization of Electricity Consumption by a Group of Monopolar Electrolysis Plants of the Same Type

2025-10-16T13:14:27+03:00

Recently, more and more attention has been paid to environmental problems associated with excessive extraction of traditional energy resources. The transition to sustainable and renewable energy sources is becoming a key solution to overcome the depletion of natural resources and reduce the negative impact on the environment. One of the promising areas is the use of technology for obtaining hydrogen and oxygen through electrolysis. However, these days the mentioned technologies require large energy costs. Yet, in some of group operating modes, several electrolysis plants that operate simultaneously (in this paper, we are talking about monopolar electrolyzers with an active electrode) were used. At the same time, they might have a very negative impact on the elements of the electrical network that supplies this group of electrolysis plants. The optimization of the operation of a group of monopolar electrolysis plants of the same type in order to minimize their negative impact on the electrical network is considered in this paper. The results of the approximation of the function that describes the change in voltage for electrolysis with an active electrode, obtained from experimental data, using Fourier series were given. The optimization objective function was determined and the problem of finding the optimal sequence of starting a group of electrolysis plants was solved using stochastic methods. As a result of the calculations, it was established that the use of stochastic methods is appropriate, and based on the proposed solution, it is possible to create a prototype of a real control system for a group of similar electrolysis plants.

Elasticity Problem for a Layer with a Cylindrical Cavity Under Periodic Loading

2025-10-16T12:47:23+03:00

In aerospace and mechanical engineering, elements that are loaded by periodic loads (periodic function) are used. In problems for a layer with cylindrical inhomogeneities, it is difficult to take such loads into account. Therefore, there is a need to develop a methodology for calculating the stress state for a layer with a cylindrical cavity and taking into account the boundary conditions in the form of a periodic function. In this paper, we propose a solution to the problem of elasticity theory for a layer with a cylindrical cavity within the framework of the generalized Fourier method. Stresses are given at the upper boundary of the layer and on the surface of the cylindrical cavity, and displacements are given at the lower boundary of the layer. The layer and cylindrical cavity are considered in different coordinate systems (Cartesian and cylindrical). The redistribution functions of the generalized Fourier method are applied to the Lamé equations. The problem is reduced to the sum of two solutions – an auxiliary problem and the main problem. Both problems are reduced to infinite systems of linear algebraic equations, which allow the application of the reduction method to them. After finding the unknowns in the auxiliary problem, the stresses at the geometric location of the cavity are found. The main problem is solved for the layer with the cavity, on which stresses obtained from the auxiliary problem are set with the reverse sign. The complete solution consists of the auxiliary and main problems. Having calculated all the unknowns, it is possible to obtain the stress-strain state at any point of the body with a given accuracy. Numerical analysis of the stress state showed high accuracy of the boundary conditions and dependence on periodic loading. Thus, the stresses s_x and s_z at the upper boundary of the layer have extremes in the places of maximum values s_y and their negative values increase at the location of the cavity. At the same time, the stresses s_x exceed the specified s_y.

First Basic Problem of Elasticity Theory for a Layer with Cylindrical Cavities Smoothly Contacting Two Cylindrical Bushings

2025-10-16T13:01:42+03:00

A spatial problem of elasticity is solved for a layer with n longitudinal cylindrical cavities, two of which contain thick-walled pipes in smooth contact with the layer. Stresses are given on the surfaces of the layer, the inner surfaces of the pipes, and the cavities. All canonical surfaces do not intersect each other. The material of the layer and cylindrical pipes is homogeneous and isotropic. An analytical and numerical calculation method, which assumes the fulfillment of statics conditions (for the first basic problem of elasticity theory) and is based on the Lamé equation, is proposed. The basic solutions of the Lamé equation are taken in a form that makes it possible to obtain an exact solution for a separate boundary surface in each separate coordinate system. The basic solutions in these coordinate systems (Cartesian for the layer and local cylindrical for the cylindrical inhomogeneities) are interconnected through the mathematical framework of the generalized Fourier method. The fulfillment of boundary conditions on the upper and lower surfaces of the layer, on the inner surfaces of pipes, on cylindrical cavities, as well as the consideration of interface conditions, create an infinite system of integro-algebraic equations, which is reduced to an infinite linear one. In the numerical study, the reduction method is applied to the resulting infinite linear algebraic system of equations. The solution of the system of equations gives the values of the unknown functions. Numerical calculations have shown the rapid convergence of approximate solutions to the exact one. The numerical analysis of the stressed state of the layer and thick-walled pipes showed that the use of polyamide bushings has almost no effect on the stress-strain state of the structure (compared to their absence), the use of steel bushings reduces the stress in the body of the layer in the areas of their location, redistributing the stress to the bushings themselves. The proposed solution method makes it possible to obtain the stress-strain state of structures containing cylindrical cavities and bushings, and the numerical analysis allows to assess the influence of the material on the values of stress distribution in the structures of machines and mechanisms at the design stage.

Kinetics of the Drying Process of Composite Biopellets on a Convective Drying Bench

2025-10-16T12:25:19+03:00

In Ukraine, there is a problem of overflowing sediment maps, to which activated sludge, which eventually turns into sludge deposits, is constantly added. The accumulated sludge deposits are outdated, have lost most of their nutrients, became too mineralized and are practically unsuitable for direct biofuel production. The elimination of accumulated sediments is necessary for the efficient and uninterrupted operation of treatment plants, as well as for land reclamation. However, due to the energy crisis around the world, it is possible to use them with the creation of fuels based on obsolete sludge, peat and biomass to solve this problem. Therefore, it is important to develop a technology for processing obsolete sludge into fuel pellets that can be used as fuel for, as an example, mini-CHPPs that simultaneously produce heat and electricity. Since obsolete sludge deposits have a low content of organic matter, it is proposed to create composite pellets for their better utilization, followed by their drying and combustion, in which the resulting ash will be used to make building materials. Therefore, the aim of the study was to investigate the drying processes of composite pellets on a convective plant and generalize them with a theoretical calculation. The drying processes of composite pellets based on obsolete sludge deposits, peat and biomass and identifies effective drying modes are studied in the paper. As a result, the influence of the coolant temperature on the drying time of the sludge-peat composition was determined, which shows that an increase in temperature reduces the drying time of the pellets by 1.4 times. Comparison of the drying kinetics of two- and three-component pellets at 80 °C and 120 °C indicates that the drying time of three-component pellets is by 1.1 to 1.4 times shorter than that of two-component pellets. Increasing the temperature of the coolant reduces the drying time of three-component pellets by about 1.5 times. Theoretical studies with the construction of generalized drying curves for composite pellets calculated by the method of V. V. Krasnikov showed a coincidence with experimental data. The relative and kinetic drying coefficients were calculated from the generalized drying curves and the drying speed, and the formulas for the drying time of two- and three-component pellets were obtained.

Enhancing the Efficiency of the Turbogenerator Cooling System Through the Use of Finned Tubes in the Gas Cooler

2025-10-16T12:35:44+03:00

The reliability of a high-power turbogenerator largely depends on its cooling system. The trouble-free and efficient operation of this system, in particular the gas cooler, is a problem that has not been fully resolved as of now. A modernized design of a gas cooler for a 325 MW turbogenerator, featuring high-finned bimetallic tubes, is proposed in the paper. To substantiate the efficiency of such a design and determine the heat transfer reserve of the gas cooler, its thermal state was calculated. The obtained results showed that the water overheating in the gas cooler is 5 °C. At the same time, one section of the gas cooler provides heat loss removal of 1266 kW at a hydrogen flow rate of 6.66 m³/s and a cooling water flow rate of 200 m³/s, which meets the requirements for this gas cooler.

Power Engineering in Innovative Changes in the Nature of Economic Activity

2025-10-16T12:06:38+03:00

Numerous studies of the processes of transformation of economic activities in Ukraine during the implementation of the policy of transition from a planned-distributive to a market-organized system have shown that the most significant changes took place due to the package of innovative changes, which involved both economic and social components. As a result, over a period of almost 15 years, the economy of Ukraine emerged and was recognized internationally, in particular, by the USA in 2006, as a market-oriented one. In the process of transition, a certain deindustrialization took place, primarily due to the decline in manufacturing, products of which had both low competitiveness and limited possibilities of sale in the domestic and foreign markets. At the same time, economic activities were gradually adjusted in the sectors, main features of which were, on the one hand, the expansion of traditional activities with a relatively low degree of technological complexity, and on the other, the need to ensure the functioning of the economy in market conditions. A special feature of the period was the limited role of the factors of economic growth based on innovative achievements, capable of contributing to the development of industries with a relatively high level of added value. Such activities include, in particular, nuclear energy, functioning and development of which, in the conditions of the "new reality", depends on timely replacement of capacities service life of which is ending and on the expansion of energy generation. In Ukraine’s nuclear sector, there is a possibility of localization of certain activities at the expense of the capacities of the Ukrainian energy machine building in order to significantly reduce the cost of relevant projects, which is extremely important in conditions of limited financial resources and the growing cost of building new capacities. The paper, based on the identification of the features of "new reality" of exogenous economic activities, shows the possibilities and substantiates the feasibility of developing and using energy machine building for innovative changes in the nature of economic activities.