GENERATIVE DESIGN OF A FRAME TYPE CONSTRUCTION

Background. In recent years, there has been a rapid development of the domestic military industry. Reducing the mass and increasing the specific strength of military products used in the field – the most pressing challenges facing engineers and scientists today. The rapid development of adaptive production has significantly expanded the possibilities of methods of topological optimization in the design of new products or improvement of existing design and technological solutions in order to reduce weight. Objective. The purpose of the paper is to improve the efficiency of designing the technology of manufacturing a frame type construction based on the method of topological optimization, which will reduce the weight of the product, while maintaining all the specified functional parameters. Methods. The paper presents an analysis of topological optimization methods and offers the interaction of modern ADS, namely CAD, CAM, CAE modules at the stage of design and technological preparation of production, which once again demonstrated its effectiveness in solving problems to reduce product weight. Results. The main tasks of topological optimization were solved for the frame type constructions, such as the minimization of volume and mass under physical constraints, as well as the optimization of other parameters with given geometric constraints. As a result, the proposed method of reducing the weight of the product is improved, which due to rational design and technological measures ensured a 56 % reduction in the weight of the frame type structure from the original and reduced the complexity of the manufacturing process by 22 % due to its effective adaptation to new technological conditions. Conclusions. The application of methods of topological optimization and rational establishment of design and technological constraints on products at the design stage can be very effective in solving problems of reducing the weight of products and optimizing manufacturing processes.

CHOOSING A QUALITY CRITERION FOR EVALUATING THE FORECAST OF NONLINEAR NON-STATIONARY PROCESSES

Background. The problem of forecasting nonlinear nonstationary processes presented in the form of time series is very relevant, since such series can describe dynamics of the processes in both technical and economic systems. To establish the best model, various metrics are used to assess the quality of forecasts, such as R^2, RMSE, MAE, MAPE. However, in many tasks, when optimizing the model according to the selected criterion, the model becomes worse in relation to another criterion. Therefore it is important to understand which metric must be used to optimize and assess the quality of the forecast in the given task. Objective. The aim of the paper is to develop a criteria base for assessing forecasts of nonlinear nonstationary processes, as well as an approach to choosing a metric in accordance to the specificity of the set forecasting problem. Methods. The paper presents a comparative analysis of the basic metrics for the regression problem, their theoretical and practical meaning, advantages and disadvantages in various cases. New approaches are proposed based on the results of the analysis. Results. Based on the analysis of the selected data, it is shown that by optimizing the model according to the selected criterion, the model becomes worse in relation to another criterion. A criterion basis for assessing forecasts of nonlinear nonstationary processes has been formed, as well as an approach to the selection of a quality criterion in accordance with the specifics of the set forecasting problem. To minimize an absolute error, the RMSE (MSE, R^2) and MAE metrics are analysed and recommended, depending on the need to work with outliers. The RMSLE metric is proposed for solving the problems of minimizing the relative metric, for solving the shown problems of the MAPE metric for this class of problems. Conclusions. The paper shows the importance of choosing a metric that must be used to optimize and assess the quality of the forecasts in the given task. The obtained criterion base and approach can be used in further research to solve practical prob- lems in modelling and forecasting nonlinear nonstationary processes and to develop new methods or general method for solving such problems.

SORTING APPROACHES IN THE HEURISTIC BASED ON REMAINING AVAILABLE AND PROCESSING PERIODS TO MINIMIZE TOTAL WEIGHTED TARDINESS IN PROGRESSIVE IDLING-FREE 1-MACHINE PREEMPTIVE SCHEDULING

Background. In preemptive job scheduling, total weighted tardiness minimization is commonly reduced to solving a combinatorial problem, which becomes practically intractable as the number of jobs and the numbers of their processing periods increase. To cope with this challenge, heuristics are used. A heuristic, in which the decisive ratio is the weighted reciprocal of the maximum of a pair of the remaining processing period and remaining available period, is closely the best one. However, the heuristic may produce schedules of a few jobs whose total weighted tardiness is enormously huge compared to the real minimum. Therefore, this heuristic needs further improvements, one of which already exists for jobs without priority weights with a sorting approach where remaining processing periods are minimized. Three other sorting approaches still can outperform it, but such exceptions are quite rare. Objective. The goal is to determine the influence of the four sorting approaches and try to select the best one in the case where jobs have their priority weights. The heuristic will be applied to tight-tardy progressive idling-free 1-machine preemptive scheduling, where the release dates are given in ascending order starting from 1 to the number of jobs, and the due dates are tightly set after the release dates. Methods. To achieve the said goal, a computational study is carried out with applying each of the four heuristic approaches to minimize total weighted tardiness. For this, two series of 4151500 scheduling problems are generated. In the solution of a scheduling problem, a sorting approach can “win” solely or “win” in a group of approaches, producing the heuristically minimal total weighted tardiness. In each series, the distributions of sole-and-group “wins” are ascertained. Results. The sole “wins” and non-whole-group “wins” are rare: the four sorting approaches produce schedules with the same total weighted tardiness in over 98.39 % of scheduling problems. Although the influence of these approaches is different, it is therefore not really significant. Each of the sorting approaches has heavy disadvantages leading sometimes to gigantic inaccuracies, although they occur rarely. When the inaccuracy occurs to be more than 30 %, this implies that 3 to 9 jobs are scheduled. Conclusions. Unlike the case when jobs do not have their priority weights, it is impossible to select the best sorting approach for the case with job priority weights. Instead, a hyper-heuristic comprising the sorting approaches (i. e., the whole group, where each sorting is applied) may be constructed. If a parallelization can be used to process two or even four sorting routines simultaneously, the computation time will not be significantly affected.

MODELLING APPROACH IN THE DEVELOPMENT OF ELECTROCHEMICAL 3D-PRINTING SYSTEMS

Background. New 3D-printing technologies are becoming more and more advanced and widespread in the twenty-first century. One of the types of 3D-printing is electrochemical 3D-printing, in which electrochemical deposition of metals is used to form metal products. Potentially, this method of 3D-printing is the most energy efficient, the least material-intensive, and also the easiest to implement. There- fore, research aimed at creating and improving systems for electrochemical 3D-printing is promising. Objective. The aim of the paper is to study the influence of geometric parameters of the system and the composition of the elec trolyte on the current distribution on the surface of the working electrode (cathode) in the process of electrochemical 3D-printing, and therefore print accuracy. Methods. Volt-amperometric measurements and multi-physical computer modelling of the secondary distribution of current density using COMSOL MULTYPHYSICS for different geometric parameters of the working part of the 3D-printer and different composition of electrolytes. Results. Based on the simulation of the secondary distribution of current density in copper sulphate electrolyte, it was found that the content of sulfuric acid in the solution should be minimal in order to purposefully deposit metal in the area directly under the working electrode. Based on the condition of maximum energy efficiency and accuracy of electrochemical 3D-printing, the optimal ratio between the deposition surface (cathode) and the edge of the non-conductive body of working electrode was found. Conclusions. It was established that in order to narrow the zone of current scattering (increase the accuracy of electrochemical 3D-printing) it is necessary to ensure the optimal ratio between the diameter of the capillary and the edge of the non-conductive body of the counter electrode. It was shown that this ratio should not be less than 5 [mm / mm]. Further applied research will be aimed at adaptation and practical implementation of the obtained model data, optimization of the electrolyte composition and design of the 3D-printer.

DETERMINATION OF “WEAK” BY POWER TRANSFORMERS RELIABILITY OF POWER SYSTEMS ACCORDING TO THE RESULTS OF FAILURE RISK ASSESSMENT UNDER EXTERNAL SHORT CIRCUITS

Background. The increase of technological violation intensity and its consequences severity is caused mainly by objectively existing aging and service life depletion of electrical equipment. The power industry liberalization exacerbates the reliable operation problem of the power system and requires identification of power system operation accompanied by the maximum emergency risk with possible cascade accidents development. Therefore, the model development task for assessment of the equipment failure risk based on the diagnostic results of technical condition in particular under short circuit in the external network is relevant today. Objective. The aim of the work is to develop a fuzzy mathematical model for probability assessment of power transformer failure in the presence of a windings defect, short circuit in external network and emergency risk assessment under power transformers out of service. Methods. The fuzzy set theory and fuzzy logic were used for developing a mathematical model of risk assessment of power trans- former failure. The problems of determining the “weak” in terms of power transformers reliability of power systems based on the results of failure risk assessment due to external short circuits were solved by methods of fuzzy logic and probabilistic-statistical simulation of electric power system modes. Results. The necessity of complex simulation of electric power system modes is substantiated for probability assessment of power transformer failure under electrical network disturbances. The simulation of technical condition of power transformer windings was carried out. The short circuit influence on operability level of power transformers of electric power system was investigated. The quantitative indicators of operational risk of electric power system were determined under power transformers out of service. Conclusions. The linguistic mathematical model for estimating the failure probability of power transformer windings in the presence of defect and short circuit in electrical network has been developed to determine the quantitative indicators of emergency risk in power system.

METHOD OF SYSTEM ENGINEERING OF NEURAL MACHINE TRANSLATION SYSTEMS

Background. There are not many machine translation companies on the market whose products are in demand. These are, for example, free and commercial products such as “GoogleTranslate”, “DeepLTranslator”, “ModernMT”, “Apertium”, “Trident”, to name a few. To implement a more efficient and productive process for developing high-quality neural machine translation systems (NMTS), appropriate scientifically based methods of NMTS engineering are needed in order to get a high-quality and competitive product as quickly as possible. Objective. The purpose of this article is to apply the Eriksson-Penker business profile to the development and formalization of a method for system engineering of NMTS. Methods. The idea behind the neural machine translation system engineering method is to apply the Eriksson-Penker system engineering methodology and business profile to formalize an ordered way to develop NMT systems. Results. The method of developing NMT systems based on the use of system engineering techniques consists of three main stages. At the first stage, the structure of the NMT system is modelled in the form of an Eriksson-Penker business profile. At the second stage, a set of processes is determined that is specific to the class of Data Science systems, and the international CRISP-DM standard. At the third stage, verification and validation of the developed NMTS is carried out. Conclusions. The article proposes a method of system engineering of NMTS based on the modified Erickson-Penker business profile representation of the system at the meta-level, as well as international process standards of Data Science and Data Mining. The effectiveness of using this method was studied on the example of developing a bidirectional English-Ukrainian NMTS EUMT (English-Ukrainian Machine Translator) and it was found that the EUMT system is at least as good as the quality of English-Ukrainian translation of the popular Google Translate translator. The full version code of the EUMT system is published on the GitHub platform and is available at: https://github.com/EugeneSel/EUMT.

FLEXIBLE AND BIODEGRADABLE SENSORS: MATERIALS, MANUFACTURING TECHNOLOGY AND DEVICES ON ITS BASIS

Background. Currently, there is a significant number of technologies and materials in the world that are used to manufacture flexible electronics devices. Therefore, a review of various technologies and materials for the manufacture of flexible sensors, which would not be inferior in terms of sensitivity to their solid-state counterparts, is in demand. In addition, most modern flexible electronics technologies are based on the use of artificial polymers, the production of which pollutes the environment and which need to be disposed of at the end of its service life. Therefore, there is an urgent need to find an alternative to artificial polymers, environmentally friendly material. Objective. The purpose of the paper is to determine design and technological features of manufacturing and application of flexible and biodegradable electronic sensors. Methods. The article analyses, classifies and compares different technologies and materials for the manufacture of flexible sensors, which would not be inferior to their solid-state counterparts in terms of sensitivity. The technological features of synthesis and the main characteristics of flexible sensors made on the basis of artificial and biodegradable materials were also compared in the paper. Results. The design and technological features of manufacturing as well as application of flexible electronic sensors in comparison with their solid-state analogues were determined in the paper. Three groups of substrate materials that can be used for the synthesis of flexible sensors have been identified and their performance characteristics analysed. A comparison of different production techniques for flexible electronic sensors in terms of environmental friendliness, cost and manufacturability is carried out. Conclusions. The most promising biodegradable material, on the surface of which one can create a flexible sensor, is nanocellulose. Different types of printing are the most promising production technique for the manufacture of such devices, because they are cheap and can provide high productivity. Based on the obtained results, it is possible to improve the existing and develop new methods of creating flexible electronics devices that do not require recycling.

NANOCELLULOSE FROM REED STALKS TO IMPROVE THE PROPERTIES OF PAPER FOR PACKAGING FOOD PRODUCTS

Background. The development of technologies for obtaining materials from plant raw materials, the use of which improves the consumer properties of cardboard and paper products and does not pollute the environment with harmful substances from synthetic polymers, is an urgent problem of our time. Objective. The purpose of the paper is to obtain pulp and nanocellulose from reed stalks by environmentally friendly methods and apply nanocellulose to improve the quality parameters of paper for packaging food products on automatic machines. Methods. To obtain pulp from reed stalks with a minimum residual content of lignin and minerals, two processing stages were used: alkaline extraction and organosolv cooking at a temperature of 97 ± 2 °C. Nanocellulose was obtained by the oxidation of organosolv reed pulp with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in the TEMPO / NaBr / NaClO system, which is more environmentally friendly than acid hydrolysis. The resulting nanocellulose was applied to paper samples from waste paper and sulphate unbleached pulp at a consumption from 1 to 3 g/m2. Results. Organosolv pulp was obtained from reed stalks with a residual lignin content of 0.53 % and an ash content of 0.045 %, which was used to obtain nanocellulose. The resulting nanocellulose particles have a transverse size in the range of 5–20 nm, a length of up to several micrometers, and the tensile strength of nanocellulose films is up to 60 MPa. It is shown that the application of nanocellulose to the surface of the samples increases the breaking strength and breaking length, and reduces the surface absorbency of paper. It was determined that with a nanocellulose consumption of up to 3 g/m2, paper samples have indicators that meet the requirements of the standard for paper for packaging food products on automatic machines. Conclusions. The use of nanocellulose from reed stalks as a hardening substance for paper production will allow replacing environmentally harmful polymer additives and up to 50 % of more expensive softwood pulp with waste paper, while maintaining paper quality indicators at the level of standard requirements.

DEPOSITION OF Al/SnAl OHMIC CONTACT ON SILICON FROM A LIQUID PHASE

Background. Single- and multi-layer metal films are widely utilized in modern electronics and optoelectronics as ohmic contacts. As a rule, the films are deposited by thermal evaporation, ion sputtering and chemical vapour deposition. However the methods of deposition from a liquid phase are the most simple and cost-effective. Thus the ohmic contact deposition by these methods is still an actual problem. Objective. The purpose of the paper is to study the possibility of deposition of multi-layer ohmic metal films over a semiconductor wafer surface from a liquid phase, particularly by scanning liquid phase epitaxy technique. Methods. In this work we considered the influence of a long-term temperature gradient at the interface metallic solution-melt – semiconductor wafer on the possibility of deposition of multi-layer ohmic metal films on the semiconductor wafer surface during segmental contact between the solution-melt and the wafer. For this purpose we carried out the simulation of heat transport process, wafer wetting process as well as the process of wafer cleansing off the solution-melt taking into account capillary phenomena in the mask openings using the method of scanning liquid phase epitaxy. For experimental confirmation of adequacy of the model proposed we carried out the deposition of Al/SnAl layer on silicon wafer in the above mentioned conditions. Results. We have deposited the contact layer Al/SnAl on the surface of silicon wafer from Al-Sn solution-melt by scanning liquid phase epitaxy technique using supplementary heater for the wafer and mask installed in the apparatus. The contact layer is made as three identical pads located at different distance one from each other. By the analysis of current-voltage characteristic we determined that the metallic film contact with the semiconductor is a non-rectifying, i.e. ohmic contact. The specific contact resistance was determined by the Transmission Line Method using linear configuration of the contact pads (LTLM). Its value was 7.2∙10-4 Ohm·cm2. Conclusions. The principal possibility of obtaining of multi-layer ohmic contacts to the semiconductor by scanning liquid phase epitaxy technique in conditions of segmental contact between the solution-melt and the wafer as well as long-term gradient at the contact interface was shown. The conditions were realized by using extra heating of the wafer back side and the high-temperature mask through which the solution-melt contacted the wafer.

TUNABLE POLARIZERS FOR X-BAND RADAR AND TELECOMMUNICATION SYSTEMS

Background. Nowadays processing of signal polarizations is widely applied in modern information and telecommunication radio engineering systems for different purposes. Commonly polarization processing is carried out in polarization adaptive antenna systems. The essential elements of such systems are transformation devices for polarization processing. They perform the transformation of the types of polarization and separate the different types to isolated channels. The most simple, effective, technological and actual for analysis are polarizers based on square waveguides with irises and posts. Objective. The purpose of this work is to improve the electromagnetic characteristics of an adjustable polarizer by creating a mathematical model of such device. The device must provide optimized polarization and matching characteristics. Methods. The article presents a mathematical model of a waveguide polarizer with irises and posts by the decomposition method using wave transmission and scattering matrices. The developed model takes into account the influence of the polarizer design parameters on its characteristics. Results. The article contains the results of calculations based on the developed mathematical model of the polarizer. In addition, the results of modelling of the device using the finite element method are presented for comparison. For the developed waveguide polarizer we have compared the polarization characteristics and the matching. Conclusions. The created mathematical model allows us to effectively analyse the characteristics when the design parameters change. These parameters include the size of the wall of the square waveguide, the heights of the irises and posts, the distance between them, the thickness of the irises and posts. The developed polarizer is recommended for the application in modern telecommunication and radar systems.