Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Сто година радног века котрљајних лежаја
No full textОвај рад је посвећен стогодишњици публиковања пионирског рада Арвида Палмгрена о математичком моделу радног века котрљајног лежаја. Приказан је развој теорије радног века лежаја од Палмгренових полазних истраживања до последње актуелне верзије међународног стандарда за прорачун номиналног радног века. Разматрани су сви релевантни утицајни фактори радног века котрљајних лежаја, као и њихова међусобна повезаност. Наглашена је важност развоја математичких модела за прецизнију процену радног века котрљајних лежаја, што подразумева интеграцију различитих геометријских, кинематских и триболошких параметара самог лежаја, као и параметара радних услова. Уз напредак у истраживању радног века разматрани су утицаји индустрије, као и стандардизација формуле радног века, кроз актуелни међународни стандард за прорачун динамичке носивости и радног века котрљајних лежаја – ИСО 281. Показано је како овај стандард континуирано еволуира у складу са новим сазнањима и технолошким иновацијама. Коначно, рад закључује да је даљи развој ових модела кључан за унапређење поузданости и перформанси котрљајних лежаја у складу са савременим захтевима технологије и тржишта.
Кроз свеобухватан преглед и анализу, овај рад нуди увид у тренутно стање теорије радног века лежаја, наглашавајући заједничке напоре истраживача и представника индустрије, који доносе напредак у овој области
RESPONSE SPECTRA OF RECORDING OF VRANCEA EARTHQUAKES OF 1977 AND 1986
No full textResponse spectra are used in the design of seismically resistant structures, and evaluation of (ground motion records) accelerograms. The spectrum represents the set of maximum responses of a series of systems with one degree of freedom (SDOF) using the method of linear dynamic analysis. The aim is to use the spectrum to cover as much of the frequency range of the respective location as possible. The paper discusses the response spectra of the Vrancea earthquake records in 1977 and 1986 and one spectrum of the Imperial Valley. These diagrams-spectra indicate the possibility of significant amplifications of structures and the occurrence of resonance effects if the natural period of the structure coincides with the maximum values of the spectrum. The positions of the Vrancea 86 measuring stations are in different locations and soil-structure conditions, but they are arranged on the semicircle of the Carpathians. The theoretical foundations of response spectra including the Fourier transform (FT) and inverse transform (IFT) as well as fast FT (FFT and IFFT) are briefly commented.9th International Conference
Contemporary Achievements in Civil Engineering, Subotica, SERBIA
U štampanoj verziji je poremećen način pozivanja literature, pa se postavlja verzija koja je poslata na recenziju, a kod koje je to ispravno uradjeno. Tako se u ovom slučaju nekorigovana verzija, može smatrati korigovanom. Uzrok je verovatno novi templejt koneferencije..
Transport and mining machinery cabins’ ergonomic evaluation as a path to its redesign
No full textTransport and mining machinery cabins are still not well adapted to their users, while checklists for their evaluation are not common in the literature. This article proposes a new checklist for ergonomic evaluation and tests its universality empirically with a sample of 96 transport and mining machine operators. The objective of the article is two-fold. First, the article checks whether there are anthropometric dimension differences between different machines’ operators. Second, statistical significance testing regarding items in the proposed checklist is performed to check its universality. Significant differences have not been found between anthropometric dimensions of transport and mining machine operators. Group comparisons prove that mining machines have better ergonomics characteristics of the chair, manual controls and vision field. The recommendation for crane designers is to examine mining machines solutions and analyze the possibility of adapting these solutions, due to anthropometric fit. Wide usage of the checklist is recommended
ANALIZA ALTERNATIVNIH REŠENJA GREJANJA GRADA POŽAREVCA U SLUČAJU GAŠENJA BLOKOVA TERMOELEKTRANE ”KOSTOLAC A1 I A2”
No full textNa osnovu objavljenih ciljeva Energetske zajednice u pogledu povećanja udela obnovljivih izvora energije u finalnoj potrošnji energije, smanjenja emisija gasova sa efektom staklene baste i povećanja energetske efikasnosti, potrebno je definisati dalji obim i dinamiku rada domaćih postrojenja na fosilna goriva. Termoelektrana "Kostolac A" pored električne energije proizvodi i toplotnu energiju. Trenutno je jedini izvor toplote za daljinsko grejanje dva gradska naselja (Požarevac i Kostolac) i 25 seoskih naselja. Eventualnom odlukom o gašenju ova dva bloka, potrebno je sagledati alternativna rešenja za snabdevanje toplotnom energijom pomenutih naseljenih mesta. U ovom radu je dat prikaz sedam alternativnih rešenja grejanja u slučaju gašenja blokova A1 i A2 Termoelektrane "Kostolac". U cilju pronalaska najprihvatljivijeg varijatnog rešenja, komparativno su sagledani i predstavljeni prostorni, ekonomski, energetski i ekološki aspekti.Based on the published goals of the Energy Community in terms of increasing the share of renewable energy sources in final energy consumption, reducing greenhouse gas emissions and increasing energy efficiency, it is necessary to define the further scope and working dynamics of domestic fossil fuel plants. Thermal power plant "Kostolac A" produces simultaneously heat and electricity. Currently, it represents the only heat source for district heating of two urban areas (Pozarevac and Kostolac) and 25 rural areas. In case of decision to shut down these two units, it is necessary to consider alternative heat sources for the supply of thermal energy to the mentioned populated areas. This paper outlines seven variant heating solutions in the event of shutdown of the TEKO A1 and A2 units. Spatial, economic, energy and ecological indicators are considered in order to identify the most acceptable variant solution
Examination of the Causes for Premature Failure of Mating Surfaces in Smart Injector Actuators
No full textFuel injector actuators in diesel engines are vital and widely used parts, particularly in hydraulics and fuel injection systems. They largely influence the technical, economic, and environmental quality of an engine. Therefore, it is of utmost importance for actuators to be highly reliable during their service life. Actuator reliability is a distinct feature of their mating surface performance. Due to complex operational conditions, increased surface stress, friction, and environmental impact, mating surfaces are exposed to various types of surface damage, wear, erosion, cavitations, and fatigue. Depending on the quality of production and the conditions they are used in, these damages are often generated much earlier than predicted, which is reflected in the reduction of the actuators' expected life span and reliability. In addition to the above, generated damage triggers the occurrence of other problems with fuel injection systems in diesel engines, resulting in increased fuel consumption and incomplete combustion, together with increased exhaust gas emission. The research conducted here analyzes the working performance of fuel injector actuators in diesel engines in heavy duty vehicles. The research is focused on inspecting the causes that lead to premature damage of mating surfaces
Kinematic Modeling of a Compliant and Extensible Robotic Manipulator
No full textCompliance properties in robotic manipulators are becoming increasingly important for industry applications. Compliance is now considered one of the desirable properties of the emerging flexible assembly systems. Contrary to the traditional designs, compliance properties increase safety in today's human-robot collaborative systems. This paper methodologically studies the existing compliance robotic system solutions and presents one approach and solution for designing future compliant manipulators. It presents the usefulness of compliance and ways it can be inherently integrated into modern robotic systems. A novel approach to building a robotic manipulator that incorporates compliant joints, capable of easy extension and retraction is proposed. Further, it is shown how compliant kinematics and springs interaction with moving platforms solve spatial mobility
RAREFIED GAS FLOW IN CONVERGENT AND DIVERGENT MICROTUBE
No full textAn axisymmetric stationary isothermal flow of a rarefied gas through convergent and
divergent microtubes of circular cross-section was considered. The gas flow is
compressible, subsonic and occurs at moderately high values of the Reynolds number.
The flow is caused by the pressure difference between the inlet and outlet of the
microtube. As flow through micropipes is considered, rarefaction is included. Low
rarefied gas flows are examined, which implies low values of the Knudsen number - slip
gas flows. In this flow regime boundary conditions of gas slip on the wall for the velocity
field are applied. To reduce the dimensional system of equations (continuity, NavierStokes, equation of state of an ideal gas) to a form suitable for solving, it is necessary to
introduce appropriate reference quantities, reference dimensionless numbers and
assumptions based on the flow model. Also using a perturbation approach, velocity
components and pressure are expressed in the form of a perturbation series. The first
term in the perturbation series represents the continuum, while the second term
represents the influence of slip and inertia. It is shown that rarefaction decreases the
pressure along the microtubes, regardless of their geometry. The highest ratio of inlet
and outlet pressure is required for divergent microtubes, and the smallest ratio is
required for convergent microtubes. It is revealed that the presence of inertia increases
the pressure along the microtubes, for all considered geometries
COMPARATIVE ANALYSIS OF STATISTICAL FEATURES OF SIGNALS IN THE TIME DOMAIN IN INTERNAL TURNING OPERATIONS
No full textThis paper presents the results of research on the use of statistical features of the processed signal, recorded
during the machining process, on the occurrence of chatter. The change in the value of the selected features is also
their ability to indicate the occurrence of chatter during machining. The signals recorded during the internal turning
of a stepped surface at certain processing modes were compared. The idea is that by changing the depth of cutting
during internal turning, the values of the measured signals change. On that occasion, the stepped inner surface was
machined, in such a way that the tool keeps the same diameter during processing. During machining, two signals
were measured, force and acceleration along the Y direction. The obtained results show that the analyzed statistical
features in stable and unstable processing modes show significantly different values and that they can be useful as
indicators for the detection of chatter during the machining process
Decision Support System for Mining Machinery Risk Mitigation Driven by Ergonomics and Contextual Theory
No full textDespite being very old, the mining industry continues to be one of the major sources
of pollution, with more people killed or injured than in all other industries. Prevention of incidents/
accidents on machinery in mining pits and the issues of operator safety on mining machinery
largely depend on the ergonomic adaptation of the workplace, compliance with safety procedures
and policies, and organizational and other influential factors. Evidently, scarce consideration of those
factors in the available literature has not given satisfactory results till now. The aim of this paper
is to first set up a comprehensive model based on ergonomic factors and contextual theory, which
takes into account all the influencing factors on the occurrence of incidents/accidents and represents
a complex system of interdependence of influential variables of diverse, mostly stochastic nature,
and then design a software solution on the given basis. In this research, based on the extensive data
collected, a model was generated using the structural equations modelling methodology, which was
then used to design the reasoning logic in the expert system for mitigating the risks of the operation
of mining machines. An innovative solution incorporating a mathematical model of the interdependence
of influential variables into the stored knowledge base offers a decision support system that
provides recommendations for the maintenance of a particular mining machine, depending on the
assessment of model factors in a specific decision-making situation at the higher organizational level
and ergonomic suitability for the operator at the lower organizational level, and, in that manner,
enables the mitigating of risky/unwanted events
Control and physical intelligence
No full textChapter 5 focuses on biological and synthetic control/intelligence. This chapter of the 2nd edition includes discussion of deep learning, do-it-yourself (DIY) robotic projects, popular microcontrollers, contributed by Marko Popovic as well as material contributed by new co-author Mihailo Lazarevic on fractional PID control approach. All these are quite relevant in the context of biomechatronics research