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Macro-, micro- and nanoscale characterisation of nanocomposites reinforced with Al2O3 nanoparticles and CNTs
No full textMultifunkcionalna i rekonfigurabilna mašina alatka za brzu izradu prototipova glodanjem, laserskom obradom i dodavanjem materijala u polarno cilindričnim koordinatama
Get PDFPronalazak se odnosi na multifunkcionalnu i rekonfigurabilnu mašinu alatku za brzu izradu prototipova koja predstavlja novi koncept 3-osne CNC mašine sa horizontalnom obrtnom osom, koja radi u polarno-cilindričnim koordinatama i omogućava jedinstvenu integraciju tri proizvodne tehnologije na jednoj mašini: glodanje, lasersku obradu i dodavanje materijala (3D štampanje). Mašina svoju rekonfigurabilnost ostvaruje zamenom završnih uređaja koji mogu biti glava za glodanje, laserska glava ili glava za 3D štampu, uz razvijeni rekonfigurabilni upravljački softver koji podržava sve tri tehnologije. Mašina se sastoji od nepokretne noseće strukture (1), na kojoj se nalaze horizontalne vođice (10) po kojima je klizno pomerljiv klizač (9) ose X na kome se nalaze vođice (12) po kojima je klizno pomerljiv klizač (11) ose Z, na koji se postavlja ili glavno vreteno (13A) ili laserska glava (13B) ili glava za 3D štampu (13C) kao završni uređaj. Noseća struktura (1) sadrži se i obrtnu osu A’ koju čine pogonski motor (3) koji pomoću kaišnog para (19) prenosi obrtni moment na obrtno vreteno (2), uležišteno nosačima (20) ležaja, sa steznom glavom (21) gde se postavlja obradak. Na nosećoj strukturi (1) se nalaze i vođice (15) po kojima je klizno pomerljiv nosač (14) zadnjeg šiljka koji se koristi kao dodatni oslonac pri stezanju dužih obradaka u cilju povećanja krutosti.Spis malog patenta 1805 U1
Link
http://pub.zis.gov.rs/rs-pubserver/document?PN=RS1805%20RS%201805&iDocId=104428&iPosition=0&iFormat=
COMPOSITE MATERIALS - CURRENT STATE OF STANDARDIZATION
Get PDFIn recent decades composite materials have become widely used across various industries, either alongside traditional materials or as complete replacements for conventional materials and technologies. This shift is attributed to several advantages they offer, such as low mass, chemical resistance, significant load-bearing capacity, strength, adaptability to modern construction principles, and utilisation of new technologies as additive manufacturing. The first composite materials were developed and patented in the late 19th and early 20th century. For more than a century, composites have seen significant progress in terms of types, properties, technologies, and various applications. Consequently, the need for standardized practices has emerged that can only be achieved through the establishment of standards and standardization processes. Both the International Organisation for Standardization (ISO) and the American Society for Testing
and Materials (ASTM) have dedicated technical committees and subcommittees focused on standards for composite materials. Each of these organisations has published approximately one hundred standards related to composites, covering terminology, properties, test methods, procedures, and more. The paper provides a concise historical overview of the development of composite materials and outlines fundamental types of composites. Additionally, it presents an analysis of the quantity and content of standards related to composites published by aforementioned standardization organisations. Statistical data regarding the publication of these
standards over time and by specific area are also presented. Conclusions have been drawn based on these analyses
A RISK EVALUATION OF BULLDOZER DOWNTIMES AND ITS ECONOMIC JUSTIFICATION IN OPEN-PIT MINES
Get PDFThe mining industry has been steadily expanding annually to keep up with the increasing demands. Consequently, used machinery needs to work efficiently, which indicates that unexpected downtimes should be at the minimum possible level. Proper identification and risk evaluation of the potential breakdown is the most important element for efficient equipment maintenance and breakdown prevention. This research has focused on its reliability function determination and analyzed the consequences of downtime and the cost of repairs over a period of one year. Delays on the observed mining machine were classified according to the type of downtime: mechanical, technological, power/electricity, and downtime due to external influences. Input elements for risk assessment were severity of consequence (S), probability of occurrence (O), and failure detectability (D). The method used in this paper is based on the cost of maintenance and the impact of bulldozer breakdowns on reliability in order to maintain profitability and, by reducing the number of unwanted events caused by sudden failure of parts, increase safety during operation. Results show that the monitored bulldozer belongs to the lowest defined risk class, so its use is economically justifiable
Numerical Investigation of Impinging Heat Transfer from Acoustically Modulated Turbulent Air Jet to Flat Surface Positioned Normaly to Jet Axis
Get PDFNeizotermska stišljiva strujanja gasa u mikrokanalima
No full textОвладавање технологијом серијскe производње микро-електро-
механичких-система (МЕМС-а) крајем прошлог века, довело je до тога да
минијатурни уређаји данас буду широко распрострањени и примењиви у
свим областима људског деловања. Интензивна употреба микроуређаја у
најразличитије сврхе утицала је на снажан развој многих области науке.
Струјања флуида настала услед разлике притисака или кретања зидова
канала, као и феномени транспорта одвијају се у микромоторима,
микролежајима, микропумпама, микротурбинама, микромлазницима,
микровентилима и микрофилтерима који су саставни део МЕМС-a. Таква
струјања могу да обезбеде погон микромотора, омогуће убризгавање
лекова, хлађење електронских уређаја, одговарајућу носивост
микролежаја и могу имати разне друге примене. Све то намеће потребу за
изучавањем струјања флуида у микроканалима, а добијени резултати
имају директну примену приликом планирања, конструисања и
експлоатације МЕМС-a.
У монографији се анализирају проблеми неизотермског,
дводимензијског, стационарног, стишљивог, дозвучног струјања гаса у
микроканалима променљивог попречног пресека (конвергентном,
дивергентном и каналу константне висине). Како су у питању
микрострујања ефекат разређености гаса узима се у обзир. Дају се
оригинална аналитичка решења за неизотермска струјања гаса која се
одвијају услед разлике притисaка на улазу и излазу микроканала.
Процедура решавања изложена у монографији се може применити и код
микрострујања која се остварују смицањем, тј. кретањем зидова
микроканала: код микро-Куетовог и струјања гаса у микролежајима.
Струјање гаса третира се макроскопски, решавањем система
једначина континуума: једначине континуитета, Навије-Стоксове
једначине и једначине енергије. Користе се гранични услови Максвел-
Смолуковског првог реда за брзину клизања и температурски скок гаса на
зиду, тако да добијена решења покривају области континуума и струјања
гаса са клизањем. Претпоставља се да је струјање потпуно развијено и да
се све величине споро мењају у подужном правцу. Узима се у обзир
зависност динамичке вискозности и топлотне проводљивости од
температуре према молекуларном моделу чврстих сфера. Наведене
претпоставке, уз познату везу Маховог, Кнудсеновог и Рејнолдсовог броја
омогућавају прецизну процену реда величине сваког члана система
основних једначина и граничних услова понаособ. С обзиром на величину
Рејнолдсовог броја издвајају се два карактеристична случаја која се одвојено решавају: струјање при малим и струјање при умерено великим
вредностима Рејнолдсовог броја. Аналитичка решења се претпостављају у
облику пертурбационих редова по Кнудсеновом броју и добијају
решавањем одговарајућих система основних једначина и граничних
услова. У монографији се добијају решења за прве две апроксимације
притиска, брзине и температуре за сваки од наведених услова струјања
гаса. Прва апроксимација одговара струјању гаса у условима континуума,
док друга укључује ефекат разређености и остале ефекте другог реда
зависно од случаја који се разматра.
Резултати приказани у монографији се слажу са експерименталним
резултатима из доступне литературе. Добијени аналитички резултати су
експлицитни и једноставни за употребу, па могу служити као релевантни у
истраживањима везаним за неизотермска микрострујања гасова.Mastering the production technology of micro-electro-mechanical-systems
(MEMS) and especially their serial production at the end of the last century,
has given rise to a wide adoption and ubiquitous applicability of miniature
devices in all areas of human activity. The intensive use of microdevices for
various purposes has influenced development of many scientific fields.
Pressure-driven or shear-driven fluid flows, as well as transport phenomena,
take place in micromotors, microbearings, micropumps, microturbines,
microjets, microvalves and microfilters, which are integral parts of MEMS.
Such flows can drive micromotors, inject drugs, cool electronic devices, ensure
the appropriate load capacity of microbearings and can have various other
applications. Тhis calls for a research of fluid flow in microchannels, while the
achieved results may have a direct application in design, construction and
exploitation of MEMS.
This monograph analyzes the problems of nonisothermal, twodimensional,
steady, compressible, subsonic gas flow in microchannels of
variable cross-section (convergent, divergent and channel of constant height).
The microflows are analised, so the effect of gas rarefaction has to be
considered. The original analytical solutions are given for nonisothermal,
pressure-driven gas microflows that take place due to the pressure difference at
the entrance and the exit of the microchannel. The solution procedure presented
in the monograph can also be applied to shear-driven microflows, e.g. in micro
Couette gas flow and gas flow in micro bearings.
The gas flow is treated macroscopically, using the system of continuum
equations: the continuity, Navier-Stokes and energy equation. First-order
Maxwell-Smoluchowski boundary conditions are used for the slip velocity and
gas temperature jump at the wall, so that the obtained solutions cover the
continuum and slip gas flow regions. It is assumed that the flow is fully
developed and that all quantities change slowly in the streamwise direction.
The dependence of dynamic viscosity and thermal conductivity on temperature
is considered according to the molecular model of solid spheres. The mentioned
assumptions, along with the known relation of Mach, Knudsen and Reynolds
numbers, enable a precise estimation of the order of magnitude of each term of
the system of equations and boundary conditions. Considering the value of the
Reynolds number there are two characteristic cases which are solved
separately: flow at low and flow at moderately high values of the Reynolds
number. Analytical solutions are assumed in the form of perturbation series
according to the Knudsen number and are obtained by solving the
corresponding systems of equations and boundary conditions. The monograph provides the solutions for the first two approximations of pressure, velocity and
temperature for each of the specified gas flow conditions. The first
approximation corresponds to the gas flow in continuum conditions, while the
second one includes the rarefaction effect and other second-order effects
depending on the case under consideration.
The results presented in the monograph are in a good agreement with the
experimental results from the available literature. The obtained analytical
results are explicit and easy to reproduce, so they can serve as benchmarks in
research related to non-isothermal gas microflows
Modeling of Shaped Charge Jet Penetration Depth: Analytical and Numerical Approach
No full textShaped charge is the most effective armor-piercing mechanism, harnessing explosive charge detonation energy to form and accelerate a hypervelocity metal penetrator known as a jet. The process entails intricate dynamics including detonation wave propagation, its interaction with the metal liner, and subsequent liner collapse leading to jet formation. While both analytical and numerical models offer insight into this complex process, each approach presents distinct challenges. Analytical models, while conceptually straightforward, often rely on simplifications that compromise accuracy. Conversely, uncertainty or even unavailability of relevant material properties and high computational cost are the most important drawbacks of numerical
models. Notably, the jet penetration phase imposes significantly greater computational demands compared to preceding processes of jet formation. This research aims at providing a deeper understanding of the jet interaction with target, as well as on determining its influence on penetration depth. We revisit an analytical model based on the virtual origin concept and
complement it with numerical simulations using Abaqus/Explicit in a pure Eulerian domain. Through comprehensive analysis, we explore various jet parameters – such as kinetic energy, diameter, length, velocity gradient, and effective standoff distance – and their impact on penetration depth. The insights derived from this study hold practical significance for the
preliminary evaluation of the shaped charge’s effectiveness and consequent refinement of the design of shaped charge projectiles or warheads.NITRA, ugovor 451-03-65/2024- 03/200105 od 05.02.202
Contemporary Management, Circular Economy and Sustainable Development as Paradigm of the Future
No full textIn today's business world, contemporary management, circular
economy and sustainable development are gaining more and more importance
and becoming the paradigm of the future. This research will show how these
concepts interact and how they can contribute together to the creation of a
more sustainable global economic system. Contemporary management focuses
on efficiency, innovation and responsibility to interest groups, which achieves
long-term competitiveness and profitability of organizations. In the context of
the circular economy, the emphasis is on minimizing waste and efficient use of
resources, which directly supports the goals of sustainable development.
Sustainable development, on the other hand, strives for a balance between
economic, social and environmental aspects in order to meet the needs of
today's generations, without jeopardizing the opportunities of future
generations. The combination of these paradigms can create positive synergistic
results. For example, implementing a circular economy requires innovative
approaches in supply chain management, which reduces costs and negative
environmental effects. At the same time, contemporary management can
support sustainability by integrating social responsibility into business
strategies and practices. In the future, these paradigms will open more and
more new business opportunities. Companies that successfully integrate the
circular economy into their operations can create a competitive advantage in a
market that increasingly values sustainability. At the same time, management
that relies on the principles of sustainable development can attract investors
and customers who are increasingly responsible and aware of social and
environmental problems. It is concluded that contemporary management,
circular economy and sustainable development represent integrative approaches that can transform the way of business and live. Their implementation requires changes in organizational culture, technology and regulatory framework. Promising results in the form of better environmental
protection, social justice and economic stability make them indispensable for
the future of global business
Design and Analysis of a Variable Pitch UAV Propeller
No full textThe interest in UAV technology and applications has skyrocketed in recent years establishing a growing trend in research and development in the field. One of the main areas of interest in UAVs is the energy efficiency of the aircraft with better energy efficiency meaning longer flight durations or larger payload capacity. Hence, a lot of effort is invested in the aerodynamic and structural optimization of UAVs, however, the principal contributor to energy savings would be the increase in efficiency of the propulsion system. Most of UAVs today employ constant pitch propellers driven by an electric or an internal combustion engine for thrust generation.
Constant pitch propellers have become a standard due to their simplicity and reliability, however, they have limitations that can be exceeded by the use of variable pitch propellers. This is especially emphasized for fixed wing UAVs, VTOL (Vertical Take-Off Land) and UAVs requiring higher maneuverability where different operational ranges and high agility are expected. Two different methods were considered for the design of the variable pitch propeller: active and passive variable pitch. In the active method, the pitch is controlled via a servo actuator, providing the possibility of optimal matching with the propeller driver and advanced control in different operating regimes but with the introduction of higher weight and additional complexity in the system.
In the passive variable pitch propeller, there is no need for an actuation system since the propeller is designed in such a way as to use the aerodynamic moments as a mean to change the pitch. This reduces the operational complexity of the system, however, it increases the design complexity since more complex aero-structural optimization methods need to be utilized. By considering the design and analysis of both variable pitch methods, a better understanding of the design approach and the advantages and disadvantages of each is established. The analysis of obtained results provides an insight into the applicability of each system as well