Vol 26, No 2 (2022)

   The influence of the main parameters of a dual-mass oscillation system on its dynamic characteristics is examined.   The object of the study comprises the oscillation system of a vibration machine, containing two masses, connected by elastic and dissipative elements. A reduction in the instability of the operating mode when changing the load or frequency of the driving force can be achieved by expanding the resonance zone. Mathematical modelling and simulation experiment approaches were used for the research. Based on the results obtained using the mathematical model for dual-mass oscillation system by Matlab-Simulink, an algorithm is proposed that includes a procedure for forming an amplitude-frequency response with an extended resonance zone and describing the influence of the main parameters of the oscillation system on the location and width of the specified resonance zone. It is shown that with an increase in the second mass of the oscillation system, the horizontal section of the amplitude-frequency response declines and shifts to the region of lower frequencies. This is explained by the increasing inertness of the system to the driving force. With a larger initial mass, the gain of amplitude-frequency response was shown to increase, while the width of the horizontal section decreases. Further, with increased stiffness of the first elastic element, the resonance section descends even lower and shifts towards higher frequency values of the driving force; however, the width of the section increases. Therefore, the method of correcting the amplitude-frequency response by introducing additional mass into the structure of an oscillation machine in order to expand its resonance zone with no additional automated devices seems promising. The obtained results may form the basis for a calculation method for energy-efficient resonance oscillation machines.

   In this work, a module of an automated design system for machining using a multi-contact vibrating impact tool, namely a ball-rod hardener, was developed.   The technological process of machining using such a hardener was studied. The performance and production cost of machining expressed as the duration and cost of achieving the specified hardening parameters were used to assess the efficiency. The specified geometric, physical and mechanical parameters of the surface layer of processed parts were used as restrictive functions. Residual stresses in samples were determined by Davydenko’s method. The Microsoft Visual Studio software and the C# programming language were used to automate process design. The studies established that the quality of the surface layer of parts is influenced by the main technological parameters (the impact energy of the indenter, the number of rods and grinding radius and tension in processing). The adequate theoretical models of developing various quality parameters of the surface layer of machined parts and processing time were obtained from the theoretical studies of the machining process using a ball-rod hardener. The obtained dependence was subjected to a comprehensive verification under the operating conditions at PJSC “Rostvertol” (Rostov-on-Don). Residual stresses in the surface layer of the BRH machined parts were measured using the ASCON-3-KI automated test stand produced by the Kazan Aviation Institute. The discrepancy between the theoretical and experimental results of the machining process was less than 15 %. The adequacy of the theoretical formulas was assessed by Fisher’s criterion. Based on the research findings, an algorithm and method of designing rational parameters for machining parts of complex geometry using a ball-rod hardener were developed. Using this software for the automated design of technological processes allowed the time of manufacturing preparation to be reduced and the stable quality of machined parts to be ensured. This offers manufacturing preparation in a digital production environment and ensures a significant increase in the useful life of manufactured products.

   A method for the online determination of the resilience of an electric power system using artificial neural networks having various structures is presented. A developed algorithm comprised of an artificial neural network with multiple learning paradigms is used for the rapid calculation of the adaptability index of the electric power system. A satisfactory time for obtaining results is ensured by dividing the adaptability calculation into offline and online processes. To train the neural networks, various methods were used. The multilayer perceptron was trained using the method of back-ward propagation of error, while training of the Kohonen neural network was performed based on the winner-take-all rule. Euclidean distance was used as a proximity measure between the studied vectors. An algorithm for analysing the results obtained by two types of artificial neural networks having dissimilar structures was developed in order to select their optimal structure and recommend a neural network for the real-time determination of the resilience of an electric power system. The proposed algorithm was validated on a 6-node scheme following the command script: computing the resilience of a given system, functioning in multiple modes. The criterion analysis showed that the structures of multilayer perceptron having 16 neurons in a hidden layer and Kohonen neural network having 9 output neurons represent the optimal solution for determining the steady-state mode at the minimum resilience in real-time. According to the results, the value of the resilience of the system varies over the course of a day. The possibility of using artificial neural networks for determining the resilience of electric power systems in real-time is demonstrated.

   In this work, we determine the control efficiency of grids with distributed generation and the possibility of eliminating flicker therein using group predictive voltage and frequency regulators. A small-size thermal power plant with the transformer connection to a power grid and consisting of three turbogenerators with a capacity of 2.5 MV·A each and a voltage of 6 kV was considered as a distributed generation plant. An isolated power supply system with three 2.5 MV·A gas turbine units each operating on static and motor loads was also considered. Automation control methods were used. Studies were conducted in the MatLab environment using the Simulink and SimPowerSystems simulation packages. The obtained results demonstrate that, upon temporarily activating the power load in the point of connecting a distributed generation unit and using inconsistent regulators, fluctuations occurring in the rotor speed and turbogenerator voltage indicate the presence of flicker effects. A similar situation can be caused by a sudden change in the forecast time for individual predictive speed controllers. Following the disconnection of a 0.4 s short circuit, a voltage flicker was found to occur in the vicinity of the gas turbine plant. However, local or group predictive regulators allow the problem of flicker emergence to be solved. The use of group predictive regulators allows flicker to be eliminated more effectively: the transient time is reduced by 1.7 and 2.7 times for the generator rotor speed and voltage, respectively. Moreover, for voltage, over-regulation is practically eliminated. The conducted computer simulation confirmed that flicker can be eliminated by applying group control of turbine generators using predictive speed controllers. Similarly, for a grid with gas turbine units, the use of predictive control algorithms made it possible to eliminate flicker without solving the problem of adjusting regulators. At the same time, group predictive regulators eliminate flicker more effectively, thereby improving the quality indicators of the control process.

   In this work, heat transfer coefficients from the working surfaces of a multi-vortex heat-and-mass exchange apparatus developed by the authors are determined along with dimensionless equations for calculating the heat transfer coefficients from the inner wall of a housing and bottom when generating. Numerical modelling is carried out using the ANSYS Fluent software package. When determining the velocity profile of a fluid in order to calculate the coefficient of heat transfer, the SST k-ω turbulence model is used. This allows for an adequate convergence in near-wall fluid and gas flow areas when simulating flows in similar constructions used, for example, to classify finely dispersed bulk solids. Dimensionless equations are obtained that relate the Nusselt number to the Reynolds and Prandtl numbers. Relationships are obtained for the increase in the heat transfer intensity as a function of the Reynolds number. It is established that the intensity of heat transfer from the inner wall in the multi-vortex apparatus exceeds the heat transfer from the bottom by 12.7–15.8 % depending on the Reynolds number. The values of heat transfer coefficients at the inner wall of the proposed apparatus can reach 14747 W/(m2 ∙ K) at an average fluid flow rate of 1 m/s. The proposed multi-vortex heat-exchange apparatus ensures swirling gas or fluid flow in the annular gap between the branch pipe and unit housing to provide high heat transfer coefficients and, hence, high intensity of heat transfer, especially through the wall of the contact stage. The numerical studies demonstrate the possibility of achieving high values of specific heat flux through the wall of the contact stage, which enables the most efficient use of the apparatus in the processes associated with the additional heat supply or removal from the contact stage through its external.

   A developed mathematical model of an asynchronous motor – turbomachinery pipeline technological complex is presented. An analysis of starting conditions is carried out by a nonlinear differential calculus and graphic analytical method. The calculations for the model were performed using the MATLAB software package. The flow, head, efficiency of the pump mechanism and entire pump unit, stator current, angular frequency and torque of the asynchronous motor were calculated at pump start-up and with an increase of pipeline resistance coefficient by 2, 5, 10, and 1000 times. At an increase in the pipeline resistance coefficient by 10 times, the pump efficiency is shown to be reduced by 2.8 times, while the head is increased by 1.28 times; meanwhile, the torque, stator current, and rotational speed of the asynchronous motor change insignificantly. The torque and current decrease by 1.167 and 1.034 times, respectively, while the speed increases by 1.0046 times; the efficiency of the pump mechanism and pump assembly (including motor) decreases by 1.78 and 1.89 times, respectively. The start-up time of the pump motor equals 0.5 s; the maximum stator current at start-up exceeds the nominal value by 4.39 times; the steady-state stator current comprises no more than 59.3 % of the nominal value. The developed mathematical model of the asynchronous motor – turbomachinery – pipeline technological complex is established to allow the operational and energy parameters of the unit to be quantitatively estimated at start-up, while the pump capacity is capable of being controlled by throttling.

  This article investigates the energy efficiency of thyristor converters with an active load. The conversion of electric energy in a “thyristor converter – electric heating element” installation is considered from the standpoint of electromagnetic theory. The energy characteristics of the considered installation was calculated in the MATLAB environment. When thyristor voltage converters are operated under the mode of controlling the power of active load, passive power was found to be generated at the input during the non-conductive state of the converter (thyristor is locked). The use of passive power allows additional thermal energy to be obtained by means of an extensive use of voltage, without increasing the current consumption. An increase in the depth of power control of electric heating elements by thyristor voltage converters leads to a significant increase in passive power. In the active power control range (50–100% of the nominal value), the factor accounting for variations in the total power in the converter due to an incomplete use of the voltage at the input of the considered installation decreases from 1.0 to 0.93. This reduces the power factor of the load converter from 0.97 to 0.925. Despite the high value of the load power factor (in the control interval 0–50% of the rated power value), the factor accounting for variations in the total power was found to be reduced to 0.66. As a result, the power factor of the converter with the load is reduced by ~ 33%. In order to increase the efficiency of converting electrical energy to control the active load power, it is proposed to use thyristor resistance converters that vary the electrical resistance of the load over time. It is shown that unsatisfactory operation of a thyristor voltage converter can be caused by inefficient use of voltage at the input of the “thyristor converter – electric heating element” installation. When using thyristor resistance converters, the current non-sinusoidality factor does not exceed 1.5 % and the voltage non-sinusoidality factor in a 0.38 kV network does not exceed 0.2 %.

   This article analyses available methods for processing low-grade copper concentrates, including existing hydrometallurgical schemes of their conditioning. To this end, we review Russian and foreign publications investigating existing technologies for processing substandard copper raw materials, which are used to deepen the extraction of valuable components from raw materials. Particular attention is paid to the technologies of hydrometallurgical processing of raw materials in terms of their feasibility for conditioning low-grade copper-containing materials as a substitution for conventional processing methods. The most promising technologies in terms of their further development and industrial application were identified among autoclave (MT Gordon, Platsol, CESL, hydrothermal treatment, etc.) and atmospheric leaching (HydroCopper, Intec Copper Process, Albion, etc.) methods. A number of research gaps in the field of copper raw and copper alloy processing were revealed, including problems related to conditioning of low-grade raw materials. Copper ores contain a significant amount of zinc and copper sulphides, whose complete extraction can be achieved using modern hydrometallurgical methods thus contributing to the efficiency of raw materials processing. In this respect, the Albion process seems to be a highly promising solution, thus requiring further studies.