Vol 17, No 1 (2023)

BACKGROUND: Modern micro gas turbine units (MGTUs) with the power of dozen of kilowatts are single-shaft and recuperative. Being in the position where improvement of new MGTU cycles is being studied, it is necessary to choose optimal parameters of the MGTU cycle according to the scheme with regeneration when developing such simple units with the aim of ensuring small size and efficiency. Nevertheless, there are several practical restrictions for the development of recuperators, related to the issue of complicated designs together with pressure losses increase caused by regeneration degree increase and to the restriction of materials quality.

AIMS: Study of influence of a recuperator on efficiency of the MGTU, as it is essential for the development of MGTUs.

METHODS: As a part of the study, the overall assessment of the influence of recuperators on parameters of an ordinary Brayton cycle with recuperation is presented in the article. The influence of main parameters, including degree of pressure increase in a compressor, inlet gas temperature and regeneration degree, on MGTU efficiency is considered in depth in the article.

RESULTS: According to the study results, it is revealed that the use of the regeneration degree of over 0,9 with low coefficient of pressure losses in recuperators for the development of modern recuperative MGTUs leads to the unit effective efficiency not exceeding 38…40% because of certain restrictions of gas temperature at the MGTU turbine inlet caused by difficulties with cooling and ensuring small size and efficiency of the unit.

CONCLUSIONS: Use of new heatproof materials is to become an important part of improvement of MGTU in future, therefore it is necessary to study new technical solution when using prospective materials of recuperators for choosing optimal parameters of the MGTU cycle with regeneration. In addition, the option of using bimetallic recuperators is considered.

BACKGROUND: In the introduction to the article, a review of publications on cavitation, vibration and noise in centrifugal pumps, including the issues of cavitation erosion of impellers, is carried out.

AIMS: Comparison of cavitation properties of a centrifugal pump of a mobile pumping unit with and without a pre-engineered screw by computational fluid dynamic (CFD) modeling.

METHODS: The calculation of the flow part of a pre-injected impeller stage is described and the CFD model of its hydrodynamic simulation is described. In the CFD model, Navier-Stokes equations averaged over the Reynolds number and the working fluid continuity equation were used. A two-phase fluid model was used to simulate cavitation.

RESULTS: The final results of the calculations carried out in the above models are presented. Calculations were obtained for a pump with impeller with and without an upstream stage (screw). For the impeller without a screw, the cavitation margin of 4.7 m was obtained, which is critical for such a pump. For a pump with an impeller with an upstream auger the cavitation margin is 1,7 m, that is much better and allows to show efficiency of such solution.

CONCLUSIONS: The requirement of hydrodynamic modeling for selection of optimal flow part of centrifugal pump to improve its cavitation characteristics is formulated.

BACKGROUND: The accuracy of prediction of towing properties is related to selection of the analytical dependency for assessment of slipping in the process of development or modernization of agricultural tractor in order to define the correct configuration of a machine-tractor unit. The relevance of the study lies in justification of the dependency describing slipping of wheels of modern high-powered 4K4b tractors and needed for study of tractors’ towing properties.

AIMS: Justification of the analytical formula of slipping for better accuracy of towing properties prediction at development stages and modernization of 4K4b tractors and units conjugated to them.

METHODS: Known analytical dependencies of slipping were analyzed in the study in order to compare the theoretical assessment results with the results of field-testing at harvest field carried out at machine testing stations according to common method. The theoretical and experimental results were obtained for the Kirovets K-7 series agricultural wheeled tractors. The experimental data of the Kirovets K-7 series tractors was approximated in order to find new dependencies for analytical determination of slipping at harvest field. The approximation coefficient was taken as the criterion for assessment of accuracy of experimental data description by the dependencies.

RESULTS: Among the considered analytical dependencies for prediction of slipping coefficient value, the equations which describe the experimental data of towing testing of the Kirovets K-7 series tractors the most satisfactorily were outlined. Based on approximated experimental data, the equations of slipping depending on specific towing force were obtained. There is the equation common for all tested tractors and there are separate equations for tractors with 32-inch and 38-inch tires. These equations provide with the best approximation of description of tractors. Values of specific towing force correlating to maximal towing efficiency and acceptable slipping coefficient of 16% for the Kirovets K-7 series tractors were obtained.

CONCLUSIONS: Some existing and new proposed in the article equations can be used for prediction of values of slipping coefficient at creating of potential towing characteristic for high-powered 4K4b tractors.

BACKGROUND: The analysis of modern state of using structural and operating materials in development of road building machines is given in the article.

AIMS: To highlight the most important tendencies in obtaining modern structural and operating materials in development of road building machines.

METHODS: The study subject is modern structural and operating materials in development of road building machines. The novelty of the study lies in highlighting main modern tendencies of modification and technological features of modern structural and operating materials for road building machines with enhanced mechanical strength characteristics. The materials of the study include main scientific and practical information on ways of using structural and operating materials in development of road building machines. The study methods include classification and integration of the information on the topic of modern structural and operating materials in development of road building machines.

RESULTS: It is found that the key difference between steel types for structural and operating materials as a part of development of units, mechanisms and parts of road building machines is parameters of corrosion resistance, which is defined by qualitative and quantitative chemical composition directly. Among the main issues of modern industry development, improvement of cost-performance ratio of road building machines, their mechanisms and engineering parts by means of reducing specific metal content and increasing operational reliability and durability is outlined.

CONCLUSIONS: It is shown that, opposed to majority of low-alloyed structural steel types, change of austenite in steel types, micro-alloyed with vanadium and niobium and with strength class in the range from S350 to S490, with constant cooing according to the thermal cycle of welding performs mainly in bainitic range. As a result of structural changes, taking place in steel and influenced by thermal cycles of welding, the static strength indicators of the metal in zones of thermal impact of welding joints increase, whereas the indicators of plastic properties reduce. Sufficient reduce of impact viscosity of the metal in zones of thermal impact of welding joints of micro-alloyed structural steel types is observed at w6/5 5°C/s. With increasing of cooling speed, the impact viscosity of the metal in zones of thermal impact rapidly increases and it may achieve the level of the main metal in some steel types.

BACKGROUND: An essential condition of existence for enterprises of all forms in the face of rapid external and internal transformations is digital reformation of their business processes. The Saint Petersburg subway is no exception, which has an aging fleet of escalators, for which the introduction of digital technologies, accompanied by the optimization of the control system for the main technological processes, can provide a balance between ever-increasing costs and limited, not always rhythmically flowing supplies.

AIMS: To establish one of the possible options for the software architecture for planning and monitoring maintenance and repair of the subway escalator fleet. At the same time, the object of research in the study is the subway escalator fleet, and the subject is automation of the maintenance and repair system.

METHODS: Analysis of modern architectural solutions used in the design of software (materials), and the synthesis on their basis of a microservice architecture implemented by tools taken from the field of machine learning and artificial intelligence are the methods used in this study.

RESULTS: A significant result of the work for practical application is the proposed scheme of the two-circuit IT landscape of the information system and the block diagram of the software implementing the internal processing circuit. The proposed version of the software is intended for regular use as a tool for monitoring and controlling the register of management objects (works) that create and do not create value for the company (providing/not providing transportation of passenger traffic). At the same time, the implementation of the proposed circuit design solution can be carried out using ready-to-use and free software components, significantly reducing the design time and the cost of its creation and operation.

CONCLUSIONS: The results obtained may be one of the options for implementing the concept of digital transformation of the maintenance and repair system of the subway escalator fleet.

BACKGROUND: When a vehicle is in motion, self-oscillations which properties are dependent on slip rate in a contact patch may occur in the area of tire interaction with ground surface. Oscillations frequency will vary in dependence with value of wheel slip relative to ground surface. Soft self-oscillations are excited by variable set of initial conditions at full slip in traction and driven wheel rolling modes as well as in mixed braking mode with partial slip. Hard mode of self-oscillations occurs at full wheel slip in braking mode. These processes have a negative impact on the processes in electric drive and mechanical drivetrain reducing their efficiency and may cause damage of components. Oscillations in the system are excited by interaction forces of an elastic tire with ground surface featuring vertical oscillations due to elastic behavior of its interaction with road unevenness.

AIMS: Research of features of oscillating process’ behavior in the nonlinear system of individual traction drive of an electrobus.

METHODS: Simulation of self-oscillation excitation processes in the area of contact interaction of a wheel and road was carried out in the MATLAB/Simulink software package.

RESULTS: The article features the results of simulation and experimental studies of self-oscillation excitation processes of the KAMAZ 6282 electrobus moving on asphalt-concrete surface. It was found that vertical wheel displacement when moving through unevenness lead to oscillating behavior of vertical reaction forces in contact patches and, as a consequence, to oscillating behavior of longitudinal reaction forces, torque and rotation velocity of the shaft of the traction electric motor of the individual drive. It was defined that tire oscillation frequency is 6–7 Hz that coincides with electric motor shaft rotation oscillation frequency and this value is the same for both experiment and simulation.

CONCLUSIONS: Practical value of the study lies in ability of using the study results at development of self-oscillation processes exclusion algorithms as a part of vehicle control system.