Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Primena i dimenzionisanje hidrociklona u papirnoj industriji
No full textKonstantni deo papir mašine je deo pripreme papirne mase između rezervoara u kome se skladišti razvlaknjena papirna masa i natočnog korita. Sastoji se od više tehnoloških celina koje obavljaju različite funkcije kao što su izdvajanje nečistoća, rafinacija, deaeracija (uklanjanje vazduha) i razvodnjavanje mase, tj. kontrola koncentracije čvrste materije, pre nego što papirna masa bude ravnomerno raspodeljena po širini papir mašine u natočnom koritu. Dobro projektovan sistem obezbeđuje kontinuirani protok suspenzije sa stalnom koncentracijom, kvalitetom i protokom, pri konstantnom pritisku, ka natočnom koritu. Poželjno je da varijacije protoka mase budu manje od 1% u odnosu na nominalnu vrednost. Hidrocikloni imaju ključnu ulogu u sistemu pripreme papirne mase jer poboljšavaju njenu čistoću pre nego što ona stigne do natočnog korita. Oni predstavljaju posebnu vrstu centrifugalnih prečistača koji uklanjaju neželjene čestice iz suspenzije, kao što su: pasak, druge čvrste čestice mineralnog porekla, metalne čestice, ostaci boje, plastika. Princip rada hidrociklona zasniva se na tangencijalnom ubrizgavanju papirne mase velikom brzinom, pri čemu se u uređaju stvara vrtložno kretanje. Zahvaljujući centrifugalnim silama, teže čestice (nečistoće) se potiskuju ka spoljnim zidovima i izlaze kroz otvor/priključak u donjem delu uređaja, dok tečna faza manej gustine, tj. prečišćena suspenzija izlazi kroz otvor/priključak u gornjem delu uređaja i nastavlja ka natočnom koritu. U ovom radu je analizirana primena hidrociklona u papirnoj industriji i prikazana je metodologija za dimenzionisanje i izbor ovih uređaja
Temporary changes in the flexural properties of 3D-printed ABS specimens
No full textThis study investigates the environmental aging effects on 3D-printed Acrylonitrile Butadiene Styrene (ABS) produced using Fused Deposition Modeling (FDM) and Digital Light Processing (DLP) techniques. The materials in filament (FDM) and resin (DLP) forms were exposed to UV light, humidity, and temperature fluctuations over two months. Mechanical testing via three-point bending and Fourier Transform Infrared Spectroscopy (FTIR) were employed to assess the impact of these environmental factors. Results showed notable mechanical strength and structural stability differences between the FDM-printed filament and DLP-printed resin ABS under aging conditions. The filament-based ABS exhibited superior mechanical properties, retaining its strength over time, while the resin-based ABS degraded significantly shortly after printing. Despite exposure to ambient environmental conditions, the chemical composition of both materials remained stable throughout the research period
Decision Support System for Ranking Risk Mitigation Measures at Mining Operator’s Workplace
No full textThe research work involved the development of a decision support system for
mitigating the risks of mining machinery operators. In this research, in contrast
to existing research, the prioritization of mitigation measures for risks in the
workplace was considered using the Risc Score analysis. Based on the ratio coefficient,
which is calculated as the quotient of the future value and the present
value of the risk, the effectiveness of the recommended mitigation measure. In
the paper, by applying the decision support system based on AHP structuring,
the prioritization of mitigation measures was carried out based on the ratio coefficient
as a weighting coefficient of the influential criterion of the effectiveness of
the proposed measure. Other influential factors in the AHP DSS model include
other criteria: the urgency of mitigation measures, pre-event/post-event, impact
on strategy, company policy, and others. The aim of the research is to emphasize
the importance of risk score analysis in the prioritization of mitigation measures
for mining mechanization operators, and it is transferable to other technical systems
as well
Stance and engagement markers in Serbian university students’ essays
No full textThe aim of the paper is to explore the frequency of use and the types
of stance and engagement markers in ESP students’ essays. Stance markers
include hedges, boosters, attitude markers and self-mentions while engagement
markers, as reader-oriented text features, comprise reader pronouns, personal
asides, appeals to shared knowledge, directives and questions. The presence of
stance and engagement markers was analysed in the essays written by the
first-year students of the Faculty of Mechanical Engineering as part of their
English course task (Ne=220; 41,156 tokens). The results indicate that students
primarily employed stance markers, such as hedges and boosters, to articulate
their perspectives. When engaging with the reader, they mostly utilised reader
pronouns, while other engagement markers had relatively low frequencies.
The prevalence of stance over engagement markers suggests that the students
primarily took care of carefully communicating their attitudes and paid slightly
less attention to communicating with the reader.У литератури се често истиче важност развијања вештина неопходних за потребе
академског писања на страном језику код студената на универзитетском нивоу
наставе, будући да су оне једна од кључних способности да се страни језик
ефикасно користи у различитим друштвеним контекстима. У вези са тим,
важну улогу има и употреба маркера становишта и ангажовања у академском
писању. Маркери становишта односе се на језичка средства којима се исказује
став аутора према неком питању, док маркери ангажовања укључују стратегије
које имају за циљ да наведу читаоце да се укључе у разумевање аргумената
аутора. Маркери становишта обухватају ограде, појачиваче, маркере става и
самопомињања, док маркери ангажовања обухватају заменице које се односе
на читаоца, личне напомене/коментаре, упућивање на општепознате чињенице,
смернице и питања. Циљ рада је да се анализира учесталост употребе и типови
маркера становишта и ангажовања у есејима студената који уче енглески језик
струке. Истраживање је урађено на есејима које су написали студенти прве године
Машинског факултета у оквиру задатка на курсу енглеског језика, у којима је
требало да изложе своје ставове на тему „Аутономна возила у савременом свету
– предности и мане“. Резултати показују да су маркери становишта коришћени
у знатно већем броју од маркера ангажовања, што би могло да значи да су
студенти примарно водили рачуна о томе да пажљиво саопште своје ставове, а
мање пажње су посветили комуникацији са читаоцем. Унутар категорије маркера
становишта, највише су коришћене ограде и појачивачи, а у оквиру категорије
маркера ангажовања најчешће су се јављале заменице које се односе на
читаоца, док су остали маркери ангажовања коришћени са ниском учесталошћу.
Закључује се да су студенти успешно употребили различите маркере, као и
различите лексичке јединице за изражавање становишта и ангажовања, али
да је ипак важно да наставници развијају стратегије за помоћ студентима у
развијању вештина академског писања и прагматичке компетенције.br. 451-03-137/2025-03/200105;
br. 451-03-137/2025-03/20011
Electrocoagulation as a new and advanced technology for future challenges in the steel industry's water treatment plants
No full textWater is a basic necessity of life, and it may seem inconceivable to imagine living without it. The environmental impact, together with social and the economic impact of past and traditional water treatments in the steel industry plants and inevitable fact of water scarcity are leading and driving a shift to a new paradigm in water treatments. Nowadays, many communities and countries are approaching the limits of their available water supplies and because of that, many steel industry plants are facing a big problem with water availability. Although water reclamation and reuse is practiced in many countries around the world, current levels of reuse constitute a small fraction of the total volume of industrial effluent generated. In addition, to meet their growing water supply needs, communities are considering other non-traditional sources of water which could lead to water saving. Water reclamation and its reuse have become an attractive option for conserving and extending available water supply by potentially applying different solution based on biological, chemical and mechanical improved solutions. Since these trends are emerging developments in the field of water reclamation and reuse, there are a number of research needs associated with these topics. Here proposed research is needed to better understand the issues present in traditional water treatment plants in steel industry plants, to propose and explain innovative technologies, which are improving traditional solutions of the water treatment plants, and to develop tools and other assistance for the steel industry plants to implement successful water reclamation and reuse projects
Implementacija koncepta iterativnog učenja upravljanja u sistemu sa zatvorenom povratnom spregom
No full textIterativno učenje upravljanja (Iterative Learning Control - ILC) predstavlja strategiju upravljanja zasnovanu na podacima, namenjenu sistemima koji u svom funkcionisanju neprekidno ponavljaju svoje referentne trajektorie i uslove rada. Primera radi, takvu prirodu često imaju robotski sistemi u proizvodnji. Osnovna ideja je da sistem, učeći iz grešaka u prethodnim iteracijama, formira ILC signal, odnosno, kompenzacionu komponentu upravljanja koja koriguje ukupan upravljački signal i time poboljšava preciznost praćenja. U ovom radu se analiziraju različiti pristupi sinteze i implementacije ILC signala u sistemima sa zatvorenom povratnom spregom, sa posebnim osvrtom na serijsku i paralelnu implementaciju ILC signala. Rezultati pokazuju da serijska implementacija može da ponudi značajne prednosti u postizanju željenih performansi sistema
Stochastic reliability optimization of a controlled nonlinear energy sink under random excitation using GA-GRBFNN algorithm
No full textDesigning a control strategy to enhance the reliability of mechanical systems under random loads is crucial for maintaining system stability, resilience, performance, and safety. The primary challenge lies in optimizing the controller parameters while determining the reliability indexes. To overcome this difficulty, we have developed a novel intelligent algorithm to estimate optimal reliability of a kind of mechanical systems subjected to random loads by using a time-delay controller. This algorithm integrates a Gaussian Radial Basis Function Neural Network (GRBFNN) into a Genetic Algorithm (GA), taking the reliability function with unknown controlling parameters as the objective function, meanwhile the Backward Kolmogorov (BK) equation governing the reliability function with boundary condition and initial condition as constraints. In this algorithm, the neural network is employed to solve the BK equations at each iteration step of the GA to derive a fitness function, then the GA is utilized to obtain the optimal controlling parameters. Our algorithm enables the simultaneous optimization of implicit objectives and the solution of time-dependent BK equations. The influence of key parameters, such as population size, maximum iteration times in GA and the number of nodes in the neural network, on reliability performance is discussed in detail. The effectiveness of the proposed algorithm is testified through numerical comparisons and Monte Carlo simulations. The control strategy presented in this paper provides theoretical guidance to enhance reliability performance in mechanical engineering and shows great promise for practical applications
New Trends in Engineering Research 2024
No full textThis book is a collection of high-quality peer-reviewed research papers presented at the International Conference of Experimental and Numerical Investigations and New Technologies (CNNTech2024) held in Belgrade, Serbia, from 24 June to 27 June 2024. The book discusses various industrial, engineering and scientific applications of engineering techniques. Researchers from academia and industry present their original work and exchange ideas, experiences, information, techniques, applications and innovations in mechanical engineering, materials science, chemical and process engineering, experimental techniques, numerical methods and new technologies
Inverse Iterative Methodology for Welded Joints Characterization in Construction Designing and Comparison to Classical Approach
No full textTraditional approach in structural designing and strength assessment that
observes structure without welded joints is sufficiently accurate in terms of elastic response,
in comparison to yield strength. The main idea of this paper is to show that it is necessary to
consider welded joints and all their regions in the elastic-plastic domain. This methodology
proposes obtaining of mechanical properties of welded joint regions using inverse iterative
procedure developed by the authors of this paper. Taking into account tensile testing of
specimens containing welded joints, strain field was obtained using Digital Image
Correlation. Finite Element Method model of test specimens is formed using the same
parameters as in the experimental one (such as welded joint geometry, boundary conditions,
loads, etc.). Strain fields of all regions of welded joint (parent material, weld metal, and heat
affected zone) are imported into finite element model, setting ground for development a new,
improved, finite element model. Consequently, material properties of all three welded joint
regions were obtained. Demonstration of the proposed procedure is shown in the analysis of
two significant structures: (i) a pipeline (membrane stress), and (ii) a girder of a bucket
wheel excavator (bending of plates). Based on this analysis it was shown within the plastic
deformation domain the differences in stresses (and structural behavior in overall) between
structure with and without welded joints are considerable, while there is no difference in the
elastic domain. Stress concentration factors are formulated for each analyzed type of
structure, in order to quantify those difference