Applied Engineering Letters

47-53

Authors: V. A. Kalhapure, H.P. Khairnar

The friction pair, disc, and pad in a braking system are in a delicate balance, with the pad being a complex combination of constituents that provides predictable characteristics, including a known and consistent friction level. In this investigation, L25 orthogonal array with arranged control factors is used for the design of experiment. Taguchi design, orthogonal array, S/N ratio and variance analysis (ANOVA) are used to explore the effect of factors like applied load, sliding speed and track or interface diameter on wear rate of brake pad friction material. In dry sliding conditions, wear tests are performed on the pin‐on‐disc tribometer with different load values (25-125 N), sliding speeds (300‐1500 rpm) and track diameter values (40‐120 mm). ANOVA results stated that applied load is the most effective with 48.27 %, track diameter is 25 % and sliding speed is 19.23 % on wear rate of pad friction material. In order to obtain the minimum friction material wear rate, the optimum operating parameters have been identified as applied load is 25 N, sliding speed 1500 rpm and track diameter 60 mm. The computed and experimental values for pad material wear rate are adhere closer to 1.93 % of deviations only.

62-68

Authors: B. Novaković, E. Desnica, Lj. Radovanović, R. Ivetić, L. Đorđević, D. Labović Vukić

The research in this paper aimed to show the importance of axial alignment on the example of maintaining a technical system. In this paper, the importance of alignment is examined on industrial fans. The technical system on which the alignment was performed reached the anticipated bearing life of 23,650 operating hours prescribed by the manufacturer, while the technical system on which the alignment was not performed was exposed to excessive load by a misalignment shaft. As a result, it did not meet the expected technical expectations, and it canceled at 5,400 hours of work. Research has shown that the application of alignment can increase the service life of bearings by 4.38 times on axles on which no alignment has been performed. Implementation of modern maintenance concepts, using appropriate methods of technical diagnostics aim to optimize the operation of industrial systems for a short period of time and with as few downtimes as possible. The authors of the paper presented the method of laser alignment in order to bring the industrial fan system into optimal operation. In addition to laser alignment, the condition of the system was checked by vibro diagnostics, before and after access by laser method. The paper presents all measurements performed with vibration analysis devices as well as a visual display of the state of the system during the laser alignment check of an industrial fan. Misalignment leads to incorrect operation, which in the case of electric motors and fans is most often reflected in damage in the form of distortion of the shaft or damage to the bearings.

80-87

Authors: S. Starcevic, S. Savic, N. Filipovic, A. Milovanovic, M. Djordjevic

The main purpose of this study was to reconstruct 3D aorta models based on a series of 2D CT images of two patients suffering from an aneurysm. After the 3D models had been made, a numerical solution of the problem of the abdominal aortic aneurysm was obtained. The numerical solution incorporated mathematical models of biomechanical systems. Various parameters such as shear stress, pressure, and velocity of fluid through blood vessel could be calculated using these methods. The first part of the paper introduces the abdominal aorta and aneurysm. The second part of this paper describes the process of getting 3D model geometries of the aortic aneurysms. Finally, the results obtained from the models are discussed with the aim of predicting a rupture of an abdominal aortic aneurysm and selecting the right treatment for this disease.

1-10

Authors: B. Kumar, S. K. Verma, S. Srivastava

The present work focuses on the effect of nozzle collar exit inclination on the mixing characteristics of Mach 1.76 jet in both design and off-design conditions using commercial software package ANSYS Fluent. In order to maintain the uniform Mach number at the nozzle exit, a collar is inserted at the nozzle exit and collar exit is varied with bevel angle of 300, 450 and 600 to see the effect of bevel collar on the jet mixing. Thus, four model namely C30 (300 bevel), C45 (450 bevel), C60 (600 bevel) and collar with zero bevel angle (UJ) are constructed for investigation. From the obtained results, it is reported that the bevel collars efficiently reduce the jet core as much as 76%, indicating enhanced jet mixing and found effective in both design and off-design condition of the jet. The C60 jet shows highest jet mixing followed by C45 jet, C30 jet and UJ. Thus, increase in bevel angle led to increase in mixing enhancement of the jet. Due to asymmetry in collar, the upward and downward shift of the jet core are seen with variation in NPR for the controlled jets (C30, C45 and C60).

21-28

Authors: S. Mulahasan, A. Y. Mohammed

Flow-through a bridge opening may run either partially or fully. In this research, backwater rise, hydraulic loss coefficient, and drag coefficient for two bridge models and three flow conditions are investigated. Based on the dimensional analysis theory, an equation was developed to calculate the water level difference Δh between the upstream and the downstream for the bridge models. Results showed that the derived equation of the backwater rise is valuable to the experimental data which showed a percentage error not exceed 5%. The hydraulic loss coefficient CL and the drag coefficient CD were calculated. The drag coefficient values for the lateral constriction models are ranged from 0.5 to 2.0, and for the submerged bridge, the model was in the range of (0.5-3.5) with an average of 2.1. The impact of the blockage ratio on the hydraulic loss coefficient showed an increase of 1-2 times when the blockage was changed from 0.70 to 0.483.

39-45

Authors: M. Embiale, A. Bekele, C. Venkatachalam, M. Parthiban

In this paper, the velocity and pressure drop distribution in flowing water through circular, square, rectangular with aspect ratio of 2:1 and 4:1 as well as an equilateral triangle cross-sectional ducts with the same duct length and hydraulic diameter have been numerically studied using ANSYS FLUENT tools. The boundary conditions used for the simulation are: at the entrance a velocity inlet of 0.2 m/s at 25 oC constant temperature, at exit a pressure outlet with zero gage pressure and a non-slip is used for the duct walls condition. A steady state and kepsilon turbulence flow model is used. The results have shown that velocity in the ducts gradually increases from zero at the walls to the maximum at the center. In the circular duct 20.327%, 15.273%, 13.5% and 6.834% more pressure is lost than in triangular, square, rectangular aspect ratio of 2:1 and rectangular aspect ratio of 4:1 ducts respectively. In turn, circular duct requires the highest pumping power while triangular one needs the lowest.

111-119

Authors: V. Lazić, D. Arsić, M. Mutavdžić, R. R. Nikolić, B. Hadzima

This paper presents an analysis and the test results of certain physical properties of the rock materials excavated from quarries in Serbia. The four rock aggregates, considered in this analysis, are used for building the driveway constructions' layers on roads, streets, airports and base layers on railways. To that purpose, both the general and specific technical properties (petrographic, physical, mechanical and technological) of those rocks must be known to users. The four rocks, whose physical properties are analyzed, are the most important types of the building stones: limestone, dolomite marble, calcite-dolomite marble and andesite. Their physical properties tested included volumetric mass, specific mass (density), porosity and water absorption. The service life, reparation jobs and maintenance procedures of the construction machinery parts, which come into direct contact with building materials like rocks and stones, strongly depend on those stones' properties. The four tested rock materials belong into a group of the massive rocks with various porosities and tendency to absorb water.

126-134

Authors: H. U. Zaman, R. A. Khan

Unidirectional composites of polypropylene (PP), reinforced with abaca fiber was fabricated by compression molding with and without the presence of stearic acid (SA) as a coupling agent. Raw abaca fiber was utilized and four levels of filler loading (10, 20, 30 and 40 wt%) were used during composite manufacturing. Mechanical tests (tensile, bending and impact properties) of the resultant composites were conducted. Based on fiber loading, 30% fiber-reinforced composites had the optimum set of mechanical properties. Optimized abaca fiber was chemically treated with SA to increase its compatibility with the polymer matrix. SA treated abaca fiber-reinforced composites yielded better mechanical properties compared to the raw composites. In order to know more about the fibermatrix adhesion, scanning electron micrographs (SEM) of the tensile fractured samples showed improved adhesion between abaca and PP matrix upon treatment with SA. Water uptake and simulating weathering test of the composites were also investigated.

142-151

Authors: F. Synák, J. Synák

The article focuses on determining the impact of using different types of gasoline on selected vehicle properties. To perform the measurements, there were six types of gasoline chosen from different gas stations and they differed in price, octane rating, and in an amount of additives and biocomponents. The immediate effect of petrol on engine performance and torque, exhaust gas composition and fuel purchase costs was examined. The results have shown a relatively low impact of gasoline on a vehicle’s dynamic properties. The most visible change was measured when comparing the most expensive fuel to the cheapest one. There was an increase in the engine torque from 156 Nm to 160 Nm measured. Such a difference is lower than the deviation of measuring. The differences measured in the composition of the exhaust gases are low. However, there is a significant impact in choice of gasoline on the costs of fuel purchase.

75-79

Authors: D. Varecha, O. Bokůvka, L. Trško, M. Vicen, R. Nikolić

Research results of influence of the UIT (Ultrasonic Impact Treatment) on welded joints, executed on the Strenx 700MC steel, are presented in this paper. The fatigue tests of those joints were performed by rotating bending in the region of the high number of loading cycles (105 to 107) with parameters: frequency 35 Hz, cycles asymmetry factor – 1, at the ambient temperature 20 ± 2 °C. The fatigue safety coefficient was calculated before the UIT (in the original state) and after the UIT, according to four methods. An increase was recorded for the latter state: for the Goodman method of 10.45 %, for the Gerber method of 10.21 %, for the ASME method of 5.96 % and for the Soderberg method of 7.40%.

87-93

Authors: A. Mishra

Data analysis is divided into two categories i.e. classification and prediction. These two categories can be used for extraction of models from the dataset and further determine future data trends or important set of classes available in the dataset. The aim of the present work is to determine location of the fracture failure in dissimilar friction stir welded joint by using various machine learning classification models such as Decision Tree, Support Vector Machine (SVM), Random Forest, Naïve Bayes and Artificial Neural Network (ANN). It is observed that out of these classification algorithms, Artificial Neural Network results have the best accuracy score of 0.95.

104-109

Authors: A. Radojević, D. Nikolić, J. Skerlić

Annual energy consumption in Kragujevac elementary schools is 1.909 MWh of electric energy and 12.510 MWh of heat energy, while the total CO2 emission is 6.406 t. This paper provides an overview of energy consumption and CO2 emissions in 61 elementary school buildings, divided in 12 groups. The goal of this paper is to determine which group of school facilities, depending on the year of construction and area, consumes the most energy and produces the most CO2 emissions. It has been shown that most electrical (36,33%) and heat (41,42%) energy are consumed in the school buildings constructed in the period 1971-1990. Most CO2 emissions (40,39%) come from energy consumed in the school buildings constructed in the same period. It is this group of buildings that represents a significant potential for energy savings and reduction of CO2 emissions, through the implementation of various energy efficiency measures.

39-45

Authors: N. Petrović, N. Kostić, N. Marjanović, J. Živković, I. I. Cofaru

In truss structural optimization the most frequently optimized factor of a structure is its weight. The minimization of weight contributes not only to savings in material, but also in other aspects of the structure such as number of elements used, number of welds needed, outer surface area, etc. This research aims to show the difference in optimal solutions for four different topological cases of a typical trapezoidal roof truss looking at their effects on overall outer surface area. The truss layouts are optimized for sizing, and a combination of sizing and shape with a minimal weight objective function. In order to ensure the most practically applicable solutions the example optimized in this paper uses dynamic constraints for buckling, stress constraints, and nodal displacement constraints. The overall outer surface area for all cases is compared, as surface protection accounts for a substantial part of the total cost of roof truss construction. Optimal solutions show a lack of correlation between weight and surface area, which is discussed in the conclusion.

50-61

Authors: M. P. Vasić, B. Stojanović, M. Blagojević

The paper presents the results of testing gearboxes in coal open pit mine which have been damaged by various mechanisms. Gearboxes, as constituents of belt conveyors, bucket-wheel excavators and bucket chain excavators and spreaders, are the most loaded segments of drive units the functionality of which affects the operation of complete coal and overburden systems. Therefore, special attention has to be paid to their condition so that the analysis of relevant condition indicators could lead to correct conclusions as to their functionality, as well as point to the factors causing their fault. Tests were carried out on 95 gearboxes throughout 2017, during general repairs at Drmno mine workshop. After examination, all identified failures were illustrated with an appropriate photo, classified according to the appropriate standard, and described in the form of manifestation and cause. The research has shown that the most dominant were faults of bearings and lubrication, whether seals and cuffs or a thin hermetic layer between the housing and covers. In addition, some of the faults happened on gears and toothed and stepped shafts. Major irregularities in operation, resulting from damage to gearbox elements, are show by fault tree analysis (FTA).

68-74

Authors: B. Vujic, J. Pekez, V. Mihajlovic, Lj. Radovanovic, U. Marceta, I. Palinkas

Serbia, as a developing country and EU accession country, faces many challenges. One of the key areas identified as the most complicated problem in the negotiation process is the issues of environmental protection and improvement, including the energy sector. Since population in Serbia is concerned because of poor living standards, high unemployment rate, and other social issues it could be questioned what is their concern and awareness about climate change since it is a realistic and visible phenomenon that is hard for someone to ignore and neglect. This paper presents some of the results of a survey conducted among adults in rural and urban parts of the Autonomous Province of Vojvodina on their perception, awareness, and knowledge about climate change issues. The research/survey also examined the specific actions that respondents would take as a personal contribution to mitigating the effects of climate problems. The results indicate that respondents have a high awareness of climate change, but the knowledge on climate change is relatively low even though the respondents graduated from faculty (about 52%).