Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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IMPACT OF FUEL CONSUMPTION ON CO2 EMISSIONS IN ROAD TRANSPORT IN EUROPEAN COUNTRIES
No full textGiven the increasing challenges posed by climate change, reducing carbon - dioxide (CO2)
emissions has become one of the key goals of the global community. Carbon – dioxide emissions are directly linked to the consumption of fossil fuels, which are used in various sectors, including
transportation, industry, and energy. This research is based on conducted detailed analysis of fuel
consumption in several European countries, in the period from 2011 to 2022. The results are
presented through diagrams that clearly illustrate CO2 emissions per capita, broken down by different types of fuel, allowing for better insight into their contribution to total emissions
PRIKAZ ADITIVNE TEHNOLOGIJE EKSTRUDIRANJEM MATERIJALA ZA IZRADU DELOVA OD KOMPOZITA
No full textradu je prikazan proces aditivne tehnologije koja se bazira na ekstrudiranju materijala uz upotrebu ojačanja sa dugim vlaknima (karbon, fiberglas ili kevlar). Primena aditivnih tehnologija, odnosno 3D štampe, postala je jedna od najrasprostranjenijih metoda za dobijanje gotovih delova i prototipova. Glavni cilj ove tehnologije je brza i efikasna proizvodnja delova, međutim, često se postavlja pitanje kvaliteta finalnih proizvoda. Brojne kompanije fokusiraju se na razvoj specijalizovanih obradnih sistema, kao i inovativnih materijala i softvera. Kako bi se unapredili atributi kvaliteta i brze proizvodnje, izdvaja se kompanija Markforged sa hardverom na bazi tehnologije ekstrudiranja materijala i podrškom specijalizovanog softvera. Njihovom tehnologijom omogućavaju korišćenje specifičnih baznih materijala i mogućnosti dodavanja ojačanja u cilju dobijanja kompozita, čime se poboljšavaju mehaničke sposobnosti i performanse gotovih proizvod
NEURAL NETWORK MODEL FOR PREDICTING THE EFFICIENCY OF A STEAM BOILER USING NATURAL GAS AS FUEL
No full textPredicting the performance of steam boilers is important to enable efficient operational monitoring and appropriate control strategies. The operation of such plants can be both steady-state and transient, with operating parameters changing according to the requirements of the technological process. The establishment of accurate mathematical models to predict boiler efficiency encounters a variety of problems related to the degradation of certain operating parameters and changes in steam production. Due to the inherent flexibility, adaptability, and robustness of neural network models, developers can take advantage of these benefits to create more accurate predictive models for boiler efficiency over time, that achieve comparable or even higher accuracy than conventional techniques. The aim of the neural network model presented in this paper is to predict the directly calculated boiler efficiency based on experimental data from existing steam boiler running on natural gas as fuel.
To overcome this challenge, two well-known machine learning techniques are compared: Feedforward 3-Layered Neural Network (2-5-2) with Levenberg-Marquardt algorithm and Adaptive Neuro-Fuzzy Inference Systems (ANFIS) with hybrid algorithm. The input datasets are the temperature of the generated steam and the steam production (mass flow rate). The data set is divided as follows: 70% of the data is used for training, 15% for validation and the last 15% is used for testing. The training set is used to train a machine learning model by exposing it to examples with known outcomes. The validation set is used to fine-tune the model parameters and to avoid overfitting, while the test set evaluates the model's performance on unseen data.
Error histograms and high correlation coefficients — which have been shown to be greater than 0.9 even for the test data sets — were used to evaluate the effectiveness of the presented machine-learning techniques. In addition, thorough analyzes and justifications of the results obtained are provided, offering important new perspectives for the practical implementation of these methods. In order to predict operating costs, one must be able to determine the actual efficiency of steam boilers with a reasonable degree of accuracy
INERTNI GASOVI I AEROSOLI KAO ALTERNATIVNA SREDSTVA HALONIMA ZA GAŠENJE POŽARA
No full textPasivni (inertni) gasovi i aerosoli igraju važnu ulogu u savremenim sistemima za zaštitu od
požara, obezbeđujući efikasno suzbijanje požara u različitim okruženjima, gde su drugi agensi za
gašenje nepraktični ili predstavljaju rizik za osetljivu opremu. Određene vrste halogenih derivata
alkana dokazani su kao veoma efikasna sredstva za gašenje požara, ali od Montrealskog sporazuma njihova proizvodnja i upotreba se zabranjuju, dok se samo u izuzetnim slučajevima tzv. kritične primene, ograničavaju. Postepeno ukidanje proizvodnje halona značajno je uticalo na sektor prevencije požara i eksplozija, i utrlo je put istraživanju i primeni alternativnih sredstava. U radu će biti prikazane ekološki prihvatljive alternative halonima za gašenje različitih klasa požara u vidu inertnih gasova i aerosola, njihova svojstva, kompatibilnost primene u različitim prostorima i proračunske procedure za izračunavanje koncentracije sredstva date različitim standardima, sa ciljem da se istakne njihov potencijal u projektovanju instalacija za gašenje požara „čistim“ sredstvima
DETERMINATION OF FRACTURE MECHANICS PARAMETERS ON PIPE RING NOTCH TENSILE (PRNT) SPECIMENS
No full textDetermining the parameters of fracture mechanics is a key segment in assessment and enhancement of the safety and longevity of materials and structures, especially when they are exposed to extreme load conditions in the presence of damage. In this work, one group of such structures is considered - thin-walled pipelines, which are used in practically all process
industry branches. Since the standard procedures prescribed by ASTM and ISO standards are not the most relevant if one of the criteria is not met, which is the testing of materials in plane strain state, it is necessary to develop a complete procedure for testing fracture mechanics parameters for thin-walled pipelines. This paper will present the results of experimental and numerical analysis of fracture mechanics parameters determined by a non-standard procedure for PRNT (Pipe Ring Notched Tensile) ring-shaped specimens, introduced in [1] through analysis of 3D printed polymer rings. The specimens are examined using a specially designed tool on a universal machine for testing the mechanical characteristics of materials with a working capacity of 100 kN and a sensitivity of 1 N. The parameters related to the displacement of points on the samples were measured and calculated based on the results obtained by the digital image correlation method (DIC). In this work, the main topic is determination of the values of previously mentioned fracture mechanics parameters; since the specimens are not standard, finite element software package Simulia Abaqus is applied for determination of these values. On the tested geometries, the ratio of the width of the sample to the initial length of the sharp stress concentrator (a sharp notch or a pre-crack) was varied (a0/W = 0.4 – 0.6). Also, a wider range of this ratio is used for one of the geometries, in order to extend the application range. Since J-integral
values are typically calculated as sum of the elastic and plastic part, the main parameters which are needed are: stress intensity factor KI, plastic geometry factor η and crack propagation correction factor γ. Generally, it can be said that the obtained parameter values showed almost linear dependence on the ratio a0/W and a slight difference in the values due to varying dimensions such as width, wall thickness and cross-section of the model. This consistency indicates a good potential of the procedure and the possibility of practical implementation on the thin-walled pipelines
Green Economy and Holistic Planning By Artificial Intelligence application
No full textArtificial intelligence (AI) is the main toolin the green economy development, as contemporary methodology
addressing environmental sustainabilitywith all opportunities, problems and challenges. This manuscript provides a
systematic overview of the advantages and drawbacks associated with AI deployment in green sectors. On the one
hand, IT such as machine learning, data analytics, and optimization algorithms offer immense potential to enhance
resource efficiency, optimize energy systems, and facilitate sustainable decision-making processes. By analyzing large
datasets and identifying patterns, AI can optimize energy consumption, streamline waste management, and accelerate
the transition to renewable energy sources with the goal of green economy. However, the widespread adoption of AI in
the green economy also raises concerns regarding data privacy, algorithmic bias, and job displacement. Additionally,
the energy-intensive nature of AI training and computing poses environmental challenges, potentially offsetting the
environmental benefits gained from its implementation. Therefore, while AI holds promise as a tool for advancing
environmental sustainability in the green economy, careful consideration of its implications is necessary to maximize
its positive impacts and mitigate potential risks
Parametric programming of CNC lathes
No full textParametarsko programiranje CNC mašina spada u napredne tehnike programiranja koje pruža niz
prednosti u odnosu na do sada opšte prihvaćene načine izrade G-kod programa. Proizvođači CNC
mašina i njihovih upravljačkih jedinica su u najvećoj meri koristili ovaj način programiranja za izradu fiksnih ciklusa obrade. I pored niza mogućnosti koje pruža, parametarsko programiranje nije dovoljno zastupljno kod krajnjih korisnika CNC mašina. Programeri CNC mašina ne koriste ovaj način programiranja zbog nedovoljne obučenosti kao i zbog nedostatka literature za edukaciju. U okviru ovoga rada prikazane su osnove parametarskog programiranja CNC mašina. Prema datim
objašnjenjima, može se napisati parametarski program za bilo koju CNC mašinu. U radu su prikazani primeri parametarskih programa napisani za tipske zahvate koji se realizuju na CNC strugu.Parametric programming of CNC machines belongs to advanced programming techniques that provide several advantages compared to the generally accepted ways of creating G-code programs. Until now, manufacturers of CNC machines and their control units have mostly used this way of programming to create fixed processing cycles. Despite the range of possibilities it provides, parametric programming is not sufficiently representative of the end users of CNC machines. CNC machine programmers do not use this way of programming due to insufficient training and a lack of literature for education. This paper presents the basics and principles of parametric programming of CNC machines. According to the explanations, a parametric program can be written for any CNC machine. The paper presents examples of parametric programs written for typical operations realized on a CNC lathe.UDC: 004.42:621.
METHOD OF DETERMINING NON-LINEAR TEMPERATURE DISTRIBUTION ACROSS THE THICK PLATE THICKNESS THAT SIMPLIFIES NUMERICAL CALCULATIONS
No full textIn this paper thermal loading of plate elements under several different heat sources (sinks), while sources are defined by the power and time of action, is considered. The heat sources are placed on the plate element sides parallel to the middle plane, while lateral sides are thermally insulated. Firstly, the dynamic problem was solved in closed analytic form using the technique of integral transformations. While discussing numerical examples that represent establishment of a non-linear distribution of temperature across the thickness of the element, laws on the basis of which this distribution can be calculated relatively simply without solving differential equations are established. Based on that idea, for steel elements, two basic diagrams were formed, which represent the procedure for calculating the temperature distribution. The procedure defined in this paper is suitable for simplifying the procedure of deformation and stress calculations of some real thermal loaded structures, using the finite element method
A conservative approach to 2SS modeling of KJc size effect in the transition region
No full textEnormous scatter of fracture toughness (KJc) experimental data in the ductile-to-brittle transition (DBT) region requires statistical methods for engineering design when using ferritic steels at sub-zero temperatures. The data-driven 2SS (two-step-scaling) method has been proposed recently to tackle the closely-related scatter and size effects in the DBT region. The present study introduces a further upgrade of the 2SS technique developed to include a predetermined level of conservatism tailored to specific applications. This controlled level of conservatism is incorporated in the 3-parameter Weibull (K0, Kmin, β) 2SS procedure by prescribing a single multiplier χ ≤ 1 as expressed by Eq. (1) and and illustrated in Figure 1. In Eq. (1), B stands for the C(T) specimen thickness (i.e., the length of the crack front), κ and ξ for the scaling exponents, while B0 and K0 refer to the reference specimen. The practical application of this conservative version of 2SS technique is demonstrated using the EURO fracture toughness dataset for 22NiMoCr37 reactor steel. The KJc experimental data shown in Figure 1, which corresponds to temperature of -91 ºC within the core of the DBT region for the specified steel, is utilized to assess the accuracy of predictions of the KJc cumulative distribution function (CDF) achieved through extrapolation for the specified χ values
