Table of Contents

  • Human foot motion simulation during walking

    pg(s) 198-201

    The ability of a person to move quickly plays an important role in the modern, constantly accelerating world. Despite the good development of the infrastructure of large cities, a significant part of its population uses underground or ground public transport, mixing daily trips on it with walking. That is the only one fact, where the importance of the process of walking in the life of modern man can be noticed. There is a new method for evaluation of therapeutical rehabilitation complex work for human lower limbs motion recovery is introduced. Simple mathematical basis and ethalon criterias for rehabilitation complex prototype efficency control are shown.

  • Exergy analysis of low-pressure condensate heating system from cogeneration power plant

    pg(s) 202-205

    The paper presents an exergy analysis of condensate low-pressure heating system of a cogeneration power plant, which consists of one heater, one condensate pump and one pressure reduction valve. The entire system is investigated at three different plant loads. Regardless of the plant load, the highest exergy destruction is noted for the condensate heater (between 416.41 kW and 771.46 kW), after which follows pressure reduction valve with exergy destruction between 57.43 kW and 120.61 kW. Exergy destruction of condensate pump is almost negligible at any plant load and therefore condensate pump has the highest exergy efficiency (between 75.86 % and 77.08 %). Exergy efficiency of condensate heater is between 56.13 % and 59.29 %, while pressure reduction valve has the lowest exergy efficiency of all three analyzed system components and is between 36.98 % and 48.42 %.

  • Experimental and numerical analysis of wind turbine model

    pg(s) 206-209

    Global demand for electric energy is predicted to increase in the coming decades. Following this, different approaches for additional electricity production are analysed and tested worldwide. The EU supports the production and usage of electricity from renewable energy sources, particularly wind energy, because it provides electricity without giving rise to any carbon dioxide emissions. The presented work analysis the possibility for utilising of wind-generated electricity as a stand-alone system for small off grid cabin supply. The very basic turbine geometry was designed and numerically simulated with commercial CFD software. After that, the turbine model was printed using 3D printer and tested in laboratory environment. The comparison of numerically and experimentally obtained operating characteristics show reasonable agreement and strong potential for system optimisation and improvements.

  • Seismic action influence on the pressure parts of the watertube steam boiler construction

    pg(s) 210-213

    The main aim of this paper is to analyze seismic action influence on the pressure parts of the watertube steam boiler construction. Design of the structures in earthquake areas according to Eurocode 8 (EN 1998-1) has been explained and performed on pressure parts construction of one watertube steam boiler. Using the finite element method, reaction forces in the supports, which occur under the influence of boiler weight and during the earthquake in the Abaqus / CAE 2016., have been calculated. At the end, the comparison of the results is shown and analysis of the results is given. Comparison of the European standard EN 1998-1: Design of structures for earthquake resistance and Turkish TEC-07: Turkish Earthquake Code in analysis of the watertube steam boiler is also done, in order to determine whether structures analyzed by EN 1998-1 can also be built on the territory of Republic of Turkey.

  • Metrological control

    pg(s) 214-216

    In the present publication some basic principles of methodology for analysis of the IMS (Intelligent Measurement Systems) and CMS (Classic Measurement Systems) both in the field of quality control and measurement technology are discussed. It focuses on the recent problems in the regular calibration (checking) of measurement systems. The methods concerns the optimal periods between different measurements and show the economic effects. Some problems of the metrological assurance of IMS (Intelligent Measurement Systems) and CMS (Classic Measurement Systems) are considered and analyzed. Calculations of (recommended) calibration intervals based on actual data for failures of metering devices are presented.

  • Controlling wettability modes of the probes of the atomic-force microscope

    pg(s) 217-223

    It has been established that in the study of a solid surface by atomic force microscopy, the hydrophobic interaction is more advantageous due to a decrease in the interaction forces between the probe and the liquid adsorbed on the surface under study. Despite the fact that silicon is a hydrophobic material, it has been shown that the material acquires hydrophilic properties in air, as a result of which the use of carbon-modified probes has been proposed. An approach to experimental statistical modeling is proposed, based on the experiment planning method, which shows that with a scanning speed of 12 μm / s, a scanning step of up to 82 nm and a delay time before scanning of 6 ms, the interaction force between the probe and the adsorbed liquid reaches minimum values. As a result of the research, it was found that with a decrease in the scanning speed, a scanning step and an increase in the delay time of the probe before measurement, the interaction between the probe and the liquid membrane is hydrophobic. It is shown that by changing the initial parameters, it is possible to control the hydrophobic interaction between the probe and the liquid. It has been established that increased air humidity leads to hydrophilic interaction. This is due to the increase in the thickness of the adsorbed liquid layer on the surface under study.

  • CAD/CAE/CAM end-to-end design and optimization of the principal wheel of a centrifugal submersible pump

    pg(s) 224-228

    The article presents the methodology for the CAD/CAE/CAM end-to-end design of the impeller of a submersible centrifugal pump for leaching of uranium. The design efforts at the CAD stage are presented, the principle of the functioning of the automated module for designing the profile of the meridian section and the wheel blades created in the MATLAB environment is described. The algorithm for drawing the profile of the blade is proposed. A method for constructing an optimized profile of a centrifugal pump (CP) wheel blade with double curvature is delineated. The computational mechanical scheme for determining the stresses and strength of a designed wheel with double curvature blades is shown. The results of the CAE strength calculation of the designed wheel in the NASTRAN program are provided. The experience of using CAM systems and 3D printing technology to create a centrifugal impeller prototype is given in the article.

  • Experimental determination of some tribological characteristics of radial plain bearing

    pg(s) 229-233

    In the current paper is presented experimental determination of the hydrodynamic pressure in a radial journal bearing using a specially designed stand. The latter is used also for determining the friction moment of the bearing. The results obtained show that the influence of the shaft angular speed and the static load on the pressure values present tendencies identical to those published by other authors. The same can be claim also for the studied effect of the shaft speed on the values of friction moment.

  • Determining the surface quality obtained after thermal cutting

    pg(s) 234-237

    The measurement of deviations from planeness, rectilinearity and parallelism of plane surfaces is a set of measuring tools (instruments, devices, high performance measuring means, etc.) and the conditions under which the measurements are made (temperature mode, way of basing during the measurment, stability or non-stability of the measured quantity in the measurement process, etc.), which implies that the method of measurement is a complex concept, i.e. a set of signs and conditions that accompany the measurement process. The present work determines the surface quality obtained after air plasma cutting of 41Cr4 steel by standard methodologies for measuring its parameters. For this purpose, a methodology is used to measure the shape and configuration as well as a methodology for measuring the profile of the surface.

  • Permeability of porous graphene composite membrane

    pg(s) 238-240

    The present paper focuses on analysing selective properties of a membrane made of graphene sheets in terms of separation of methane-helium mixtures. The regular allocation of pores allows considering a representative fragment of space near the investigated membrane. Sampling of molecules with respect to velocity values is performed on the basis of the Maxwell distribution which is valid at a distance from the membrane. The frequency of molecular strikes against the surface of the membrane is determined by the gas state parameters and the size of the representative fragment. The particles are started from the input face of the representative fragment with a frequency which is characteristic for methane molecules and their accumulation inside and near the membrane is investigated. The mobile particles which are present in the carbon structure increase the potential barrier of graphene sheets. This new barrier is used in the wave model of helium atoms passing through porous graphene sheets.

  • Multiscale modeling of short fibre reinforced composites and it’s relationship to modal analysis of machinery parts

    pg(s) 241-244

    Although molding of thermoplastics is very productive method of machinery manufacturing, pure plastics are almost not used in so much quantity. Particle reinforced composites are more popular, because presence of solid inclusions reduces volume of organic matrix and usually improve strength and stiffness. Final properties are strongly influenced by manufacturing process which affects inner material structure. In composites where fibers are continuous in one direction or placed in layers, i.e. the fibers do not end inside the composite and it`s length is close to the dimension of machinery parts, elastic [1] [2] and thermal properties [7] can be predicted quite easily by Halpin-Tsai equations or derived simplified methods [2] with high accuracy. This paper is focused on prediction of density and material stiffness of composites, which are reinforced with very short glass fibers in thermoplastic matrix. In the first part we define the field of problem. Then we present simplified analytical calculus in compare to finite element method. We focus on ABAQUS 2018 and its features, which can be used for solving those problems. Estimation approaches such as representative volume element method and mean field homogenization are also studied. After this presented methods are confronted with selected material datasheet of Ultramid® A3WG6 [9] and Zytel® 70G35HSLRA4 [12] composite material. The effect of fiber randomization on material stiffness is introduced [4]. At the end of thesis we use previously calculated material data for modal analysis of real parts which are made from molded thermoplastic with short glass as well.