Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Experimental and numerical research of the flow inside the control valves trim
Get PDFIn this paper are presented desing, testing and numerical analysis for two manufactured control valve trims. Valve trim is consisted of cage or dick stack, plug, stem and seat. Size from app. 15.88 mm (0.625 in) up to 101.6 mm (4 in) is suitable for 3D metal and plastic print, what is presented in this paper. Selective laser melting 3D metal printing is applied on the disc presented in this paper. Even better material properties from rest of the valve parts could be obtained. This is of great importance for valve retrofitting. In this paper is presented, also, new developed channel geometry, what is followed by various fluid flow phenomena. Measurement results for second prototype manufactured by 3D printing using plastics are presented in details. Here is shown, in short, procedure for determination of KV values of the test valves according to the EN 60534-2-3, Industrial-process control valves - Part 2-3: Flow capacity - Test procedures. In addition, some aspects of CFD calculations are presented
Decompositions of optimal averaged Gauss quadrature rules
No full textOptimal averaged Gauss quadrature rules provide estimates for the quadrature error in Gauss rules, as well as estimates for the error incurred when approximating
matrix functionals of the form u
T
f (A)v with a large matrix A ∈ R
N×N by lowrank approximations that are obtained by applying a few steps of the symmetric or
nonsymmetric Lanczos processes to A; here u, v ∈ R
N
are vectors. The latter process
is used when the measure associated with the Gauss quadrature rule has support in
the complex plane. The symmetric Lanczos process yields a real tridiagonal matrix,
whose entries determine the recursion coefficients of the monic orthogonal polynomials
associated with the measure, while the nonsymmetric Lanczos process determines a
nonsymmetric tridiagonal matrix, whose entries are recursion coefficients for a pair of
sets of bi-orthogonal polynomials. Recently, it has been shown, by applying the results
of Peherstorfer, that optimal averaged Gauss quadrature rules, which are associated
with a nonnegative measure with support on the real axis, can be expressed as a
weighted sum of two quadrature rules. This decomposition allows faster evaluation of
optimal averaged Gauss quadrature rules than the previously available representation.
The present paper provides a new self-contained proof of this decomposition that
is based on linear algebra techniques. Moreover, these techniques are generalized to
determine a decomposition of the optimal averaged quadrature rules that are associated
with the tridiagonal matrices determined by the nonsymmetric Lanczos process. Also,
the splitting of complex symmetric tridiagonal matrices is discussed. The new splittings
allow faster evaluation of optimal averaged Gauss quadrature rules than the previously
available representations. Computational aspects are discussed
Dumper Operator’s Workplace Risks: Preliminary Study
No full textThe dumper vehicle is essential for carrying out material handling activities and they are the primary cause of fatal accidents at both construction and mining sites. According to earlier studies, the vast majority of these incidents are caused by the operator’s behaviour. On other side, it is evident that dumper operators are often taking awkward postures and most of them are subjected to high and medium levels of musculoskeletal disorders.Due that fact, the aim of this paper is directed towards preventing accidents and/or incidents in dumper’s operations that originate from the operator’s error and which could be mitigated by the ergonomic adjustment. Specifically, the purpose of this study is to utilize artificial neural networks in order predict the probability of incidents and accidents on the basis of dumper operators’ workplace ergonomic intervention.In this research 40 dumper’s operators participated. Survey started with the 39-item checklist, which is based on prior research and there has been noticed that questions with lowest percent of positive answers are questions related to seat and armrests, so factors such as the seat height adequacy, the seat height adjustability, the seat be horizontal adjustment, the seat back support, the seat lumbar support, armrests availability, armrests height, armrests adjustability, vibrations through the seat, vibrations from the equipment through the floor, vibrations from the equipment through the control devices, the seat attachment to the sub cabin, and possibility to recline and rotate the seat are considered as primary factors in the investigation of the ergonomic adjustment of the dumper operators’ workplace. Poor working conditions originating from organizational factors are also recognized as one of the important focuses of this research. The obtained data were statistically analysed. Surveyed dumper operators came from various age groups and with varied work experience periods in the current study. The research revealed that the average age and height of dumper operator is 36.33 years and 178.35 centimetres, respectively. Moreover, despite the fact that their average weight is 90.33 kg, these body measurements, unlike the others which followed a Gaussian distribution, regardless of the average value indicate that a substantial proportion of operators are overweight and weigh more than 110 kg. In addition, the vast majority of operators in this survey had less than ten years of experience. Regarding the machines, the age of examined dumpers was less than ten years.In order to reduce the likelihood of accidents/incidents and injuries at work resulting from poor seat design, this study uses questions that covers the most significant factors affecting the quality of the working conditions related to the seat and armrests in dumper’s cabin. Furthermore, neural network was trained to predict the likelihood of injuries based on 14 different responses related to the seat and armrest, as indicated by the research's finding that the questions to which respondents provided the worst responses concerned the cabin's seat and armrest. The training dataset consisted of 80% of the obtained data, while 10% was allocated for validation and the remaining 10% was reserved for testing purposes. Used network has one hidden layer with 12 neurons. The neural network underwent training for a total of 16 epochs. The correct classification of 92.5 percent of the data demonstrates a high degree of accuracy in predicting potential accidents/incidents on sites where dumpers operate.Conclusions from the study indicate the need for additional research into an ergonomically optimized workspace for dumper operators in terms of the possibility of resolving identified issues through the further anthropometric surveys and possible application of modern information technologies, such as the installation of sensors, monitoring, and similar solutions.The sample size is a limitation of this study, and additional data collection is ongoing. The proposal for additional research is to collect additional data to increase the reliability of the analysis, and possibly investigate other types of mining machines to determine if similar problems occur with them
Risk Assessment of Pressure Vessels by Using Fracture Mechanics and Advanced Ultrasonic Testing
No full textRisk assessment of cracked cylindrical pressure vessels for compressed air by using basic fracture mechanics and advanced methods of non-destructive testing (NDT), such as Phased Array Ultrasound (PAUT) and Time-of-Flight Diffraction (TOFD), is presented. Basic fracture mechanics equations are used to calculate the stress intensity factor, KI, in the case of unacceptable defects found in the pressure vessel 970 in the Reversible Hydro Power Plant "Bajina Basta", and get the ratio KI/KIc, according to the minimum measured values for fracture toughness for welded joints, as the typical zones where crack-like defects are found. The ratio Snet/Sc, where Snet is the net stress in cross-section with a crack, and Sc is the critical stress, is then evaluated to define the operating point in the Failure Assessment Diagramme (FAD), and thus, to estimate the likelihood of failure of the pressure vessel 970. In combination with estimated high consequence for the pressure vessel 970, the risk matrix was used, as a simple tool to assess the risk. In this paper the focus is on one aspect of this procedure, being the NDT role, since it is of utmost importance to use as precise as possible method for detected defects in welded joints. In this paper advanced ultrasound methods, PAUT and TOFD, are used to get precise image of defects in pressure vessel 970 welded joints, which were previously detected by conventional NDT methods. It is shown that the use of PAUT and TOFD is of utmost importance for decision making process in this case. © 2024, Strojarski Facultet. All rights reserved
The Taxonomy of Agricultural Residues for Sustainable Eco Building Materials, Biomass Plant and a Hybrid Heat Pump
No full textThere are practical endorsements that agricultural residues have been utilized as additives for soil stabilization, advancement of geotechnical properties, concrete and cement supplements, road construction, etc. Sustainability is multifaceted and has to be retained. One kilogram of cement induces 800 kg of CO2 gas. Over 50 % of all biomasses in the world are made of crop residues. The solid biomass constitutes around 50 % of overall production, liquid and gaseous 25 % each individually. According to certain EU documentation, in 2050th, it is going to be feasible to produce 1000 TWh of biomethane. This manuscript serves as a technical paper - a reminder of how building materials can be sustainably composed and as a technical map of binding the biomass plant and a hybrid heat pump. The novelty of the manuscript is summing up all research on the utilization rate of agricultural residues for sustainable eco-building materials upon now
Mass optimization of PLA cantilever beams
No full textNumerical and experimental approaches are combined in order to examine the possibility of material
reduction in modeling cantilever beams of circular cross-sections. Partial differential equations are used for
the Euler-Bernoulli beam theory and the rigid body is placed eccentrically with respect to the top of the
beam. For the required first natural frequency of the coupled axial and transvers vibrations, the beam
diameter is computed using the Symbolic-Numeric Method of Initial Parameters in Differential Form. Mass
optimization for the same frequency is conducted using Pontryagin’s maximum principle. Compared results
of the beam diameters across its length are presented in Fig. 1. Two cantilever beams are printed of PLA material using FFF/FDM technology. Models and test
specimens with detailed experimental setup are given in Figs. 2 and 3. The Accelerometer mounted at the
end of the beam, as well as force hammer are used for experimental determination of first natural frequency,
that is derived using FFT analysis. The difference between the values of the first natural oscillation frequency
was less than 2%, i.e. 10.6Hz for the non-optimized and 10.4Hz for the optimized. This is a significant
indicator that optimizing the shape can significantly affect the mass of parts intended for 3D printing, as well
as the production time
PROJEKTOVANJE I IZRADA OKVIRA BESPILOTNE LETELICE PRIMENOM GENERATIVNOG DIZAJNA I ADITIVNIH TEHNOLOGIJA
No full textU ovom radu je prikazan proces projektovanja prototipa okvira za bespilotnu letelicu primenom generativnog dizajna u okruženju Autodesk Fusion i njegova izrada primenom aditivnih proizvodnih tehnologija, konkretno postupkom fotopolimerizacije u kadi. Jedan od značajnijih napredaka u proizvodnoj industriji predstavlja razvoj aditivnih proizvodnih tehnologija, koje omogućavaju izradu kompleksnih struktura. Ove tehnologije u kombinaciji sa generativnim dizajnom, koji koristi algoritme i veštačku inteligenciju za stvaranje optimizovanih oblika, transformišu tradicionalne pristupe u dizajnu i proizvodnji. Bespilotne letelice, kao jedan on najbrže rastućih segmenata u vazduhoplovnoj industriji, predstavljaju idealnu platformu za primenu ovih agilnih tehnologija, sa ciljem izrade lakših i funkcionalno prilagođenijih letelic
INTEGRATION OF LOOP HEAT PIPE ANTI-ICING SYSTEM IN THE AIRFOIL LEADING EDGE
No full textIntegration of heat pipes into the leading edge of airfoils presents a viable option for anti-icing applications, owing to their lightweight, compact design, passive operation, and heat transfer characteristics. Aircraft operation is greatly influenced by ice formation, which can cause aerodynamic performance deterioration and generally present a threat to flight safety. Complex heat transfer processes due to evaporation and freezing of water droplets, sensible heat loss, but also heating due to kinetic energy of water droplets hitting the airfoil and pneumatic heating, variable weather conditions, etc, all make the analytic solution unattainable for prediction
of ice formation. Simulation methods today are affirmed for aircraft’s icing/de-icing system prediction, from small ones – UAVs, over helicopter rotors, to large passenger planes' airfoils. Insights gained from the numerical simulation study can provide valuable guidance for optimising the design and operation of heat pipe based anti-icing and deicing systems in the aerospace industry. One of the primary ways to evaluate the anti-icing effect is to predict the temperature of the wing skin on the outside. Here presented numerical simulation deals with the loop heat pipe integrated into the wing’s leading edge. The volume of fluid method (VOF) was employed for simulating the condensation process inside the loop heat pipe, leading to further investigation of
temperature distribution over the leading edge outer surface. In perspective, results can be the basis for further customised solutions of anti-icing operations for particular aircraft
Uporedna analiza algoritama za detekciju pozicije i orijentacije objekata u okviru sistema veštačkog gledanja
No full textAutomatski sistemi za montažu imaju ključnu ulogu u današnjoj proizvodnji, omogućavajući visoku preciznost, povećanu efikasnost i smanjene troškove proizvodnje. Zadaci manipulacije i montaže često zahtevaju informacije o poziciji i orijentaciji delova u okviru radnih stanica. U automatskim sistemima ove informacije dobijaju se korišćenjem sistema veštačkog gledanja koji imaju implementirane različite tehnike za obradu i analizu slike. Iako su tradicionalne tehnike u praksi pokazale dobru funkcionalnost, robusnost i brzinu rada, njihova primenljivost u kompleksnim okruženjima često je okarakterisana lošijim performansama. Sa druge strane, tehnike veštačke inteligencije, pre svega veštačke neuronske mreže, kroz koncept dubokog učenja donose značajna unapređenja u vidu performansi, posebno u složenim aplikacijama, ali često prouzrokujući kašnjenja koja mogu biti neprihvatljiva za primenu u realnom vremenu. U ovom radu kreirani su sistemi veštačkog gledanja za prepoznavanje pozicije i orijentacije izabranog dela korišćenjem tradicionalnih tehnika i tehnika zasnovanih na veštačkoj inteligenciji. Poređenje performansi primenjenih tehnika izvršeno je na osnovu više usvojenih kriterijuma.Automated assembly holds a key role in today’s manufacturing by offering high precision, improved
efficiency, and reduced production costs. Applications that include manipulation and mating often require information
about object position and orientation. In automated systems, such information is provided by computer vision-based
systems that employ different techniques for image processing and analysis. Although traditional techniques have
proven to be well-performing, robust, and time-efficient in practice, their performance in more complex environments is
often limited. On the other hand, artificial intelligence (AI) techniques, particularly neural networks through deep
learning (DL), offer significant performance improvements in complex applications, but often at the cost of delays that
are not suitable for real-time applications. In this paper, computer vision-based systems were developed to detect the
position and orientation of a selected part using both traditional and AI-based techniques. The performance
comparison of these techniques was conducted using several different criteri
