Purpose
The purpose of this paper is comparison of experimental values of the drawing forces to numerical values in different contact conditions, taking into account the appearance of galling which ...occurs due to of difficult drawing process conditions.
Design/methodology/approach
The following two research approaches are used in this paper – the physical modeling, realized by the laboratory experiment, and the numerical simulation of the ironing drawing process. By analyzing the obtained results, the technique of physical modeling, with help of the laboratory equipment and numerical simulation by application of the finite element method, can be successfully used in studying the thin sheet ironing – strip drawing process.
Findings
It is significant to compare values of the deformation forces obtained by physical experiment to values obtained by the numerical simulation. In that way, it is possible to compare applied contact conditions (four lubricants in that case) and estimate matching of experimentally and numerically obtained results of the deformation forces. Presented results point out very good technological characteristics of ecologically friendly lubricant (single-bath) and grease based on MoS2. Significant decrease of the deformation force was achieved by its application, as well as maintaining of the lubricant’s layer during the forming process and almost complete elimination of galling on the contact.
Practical implications
Numerical analysis of stresses in the working piece wall, during the thin sheet strip drawing, requires precise values of the friction coefficient. It is an important indicator because one can define the contact conditions as the input data for the numerical simulation, based on its values for each type of lubricants and each value of the compressive lateral force.
Originality/value
The environmentally friendly lubricant tested exhibits a more favorable distribution of the drawing force during the process, mainly in experimental case. Grease based on MoS2 has good lubricating properties but that lubricant is conventional and environmentally unacceptable. Ecologically friendly lubricant can be successfully used in real ironing strip drawing process especially for high values of holding force achieving an increased tool life.
An experimental procedure for determination of the lateral and longitudinal deformations of the multi-layer hard faced samples made of steel for operating at elevated temperatures is presented in ...this paper. Two plates, which were hard faced in three passes, were used to determine the level of residual stresses. The cored electrodes UTOP 38 and UTOP 55 were used. Deformations were measured in two phases: before and after the hard facing. The objective of deformations measurements was to establish the correlation between deformations, namely the applied technology (the input energy/heat) and the level of residual stresses, for different plate thicknesses.
Res**ults of determination of the longitudinal, lateral and angular deformations in hard faced samples are presented in this paper, as well as the influence of the additional heat treatment on the ...level of residual deformations. Investigation assumed multi-layer hard facing of the two plates (thicknesses 7.4 and 29mm) made of steel 55CrMo8. Deformations were measured before the hard facing – after the plates’ preparation by grinding, immediately after hard facing and after tempering. The objective was to determine if and how much the additional heat treatment (tempering) influences the level of residual deformations in the hard faced joints.
Results of experimental and numerical investigations of the three types of lubricants influence on the ironing process are presented in this paper. The tribological model was based on the strip ...sliding between the two lateral contact elements. The strip was made of the low carbon steel. Variations of the friction coefficient and the contact pressure in the single-stage ironing were recorded at the constant sliding speed for each of the tested lubricants. The effective normal stress distribution within the material was simulated by the finite element method (FEM). The objective was to compare the applied lubricants from the aspect of their applicability in the ironing process.
The use of solar dish thermal collectors is a promising choice for designing
sustainable energy systems. The use of nanofluids is a new way for enhancing
the thermal performance of solar collectors ...because of their improved thermal
properties. The objective of this study is to investigate the use of mono and
hybrid nanofluids in a solar dish collector in order to determine which kind
of nanofluids leads to higher performance enhancements. The analysis is
conducted with a developed thermal model in Engineering Equation Solver and
the collector is studied thermally and exergetically. The examined hybrid
nanofluid has as base fluid syltherm 800 with 1% Cu and 1% TiO2. Moreover,
the examined mono nanofluids are the syltherm 800 with 2% Cu and syltherm 800
with 2% TiO2. The investigated solar dish collector has a spiral absorber and
it is examined for inlet temperatures from 25?C up to 300?C with a flow rate
of 200 L/h. According to the final results, the use of hybrid nanofluid leads
to higher thermal efficiency enhancement compared to the mono nanofluids
because of the higher increase in the Nusselt number in the flow. More
specifically, the use of the hybrid nanofluids leads to 0.99% mean thermal
efficiency enhancement compared to the pure oil case, while the use of Oil/Cu
and Oil/TiO2 lead to 0.42% and to 0.56% mean thermal efficiency enhancement,
respectively. Moreover, the exergy efficiency is found enhanced with the use
of all nanofluids. The mean exergy efficiency enhancement is 1.21% with the
hybrid nanofluid, while it is 0.73% with Oil/TiO2 and 0.53% with Oil/Cu.
Influence of the contact pressure in the deep drawing processes is a very actual research topic in the metal forming technology. Within this research the tribological model of the strip sliding in ...the flat die was developed. The original experimental computerized apparatus for testing of the strip sliding in the variable contact pressure conditions was developed, as well. The complex, multi-factor experiment was performed by application of the Al thin sheet, with the contact elements of various roughnesses, with different lubricants application and with the variable contact pressure. Besides the description of the developed apparatus, the theoretical way for determination of the pressure dependences was also presented. Based on the theoretical changes of pressure, set in advance, the real influence of the contact pressure was obtained, for each of the given conditions. That makes possible to determine the influence of the tribological factors on the actual pressure. The obtained real contact pressure has verified the reliability of the experimental apparatus, namely the degree of the theoretical pressure dependences deviation from the real ones.
Background: The Travelling Salesman Problem is an NP-hard problem in combinatorial optimization with a number of practical implications. There are many heuristic algorithms and exact methods for ...solving the problem. Objectives: In this paper we study the influence of hybridization of a genetic algorithm with a local optimizer on solving instances of the Travelling Salesman Problem. Methods/Approach: Our algorithm uses hybridization that occurs at various percentages of generations of a genetic algorithm. Moreover, we have also studied at which generations to apply the hybridization and hence applied it at random generations, at the initial generations, and at the last ones. Results: We tested our algorithm on instances with sizes ranging from 76 to 439 cities. On the one hand, the less frequent application of hybridization decreased the average running time of the algorithm from 14.62 sec to 2.78 sec at 100% and 10% hybridization respectively, while on the other hand, the quality of the solution on average deteriorated only from 0.21% till 1.40% worse than the optimal solution. Conclusions: In the paper we have shown that even a small hybridization substantially improves the quality of the result. Moreover, the hybridization in fact does not deteriorate the running time too much. Finally, our experiments show that the best results are obtained when hybridization occurs in the last generations of the genetic algorithm.
Oranges and snow Simic, Charles; Simic, Charles
2010., 20101101, 2010, 2011-01-01, Letnik:
3
eBook
Pulitzer Prize-winning poet Charles Simic has done more than anyone since Czeslaw Milosz to introduce English-language readers to the greatest modern Slavic poets. InOranges and Snow, Simic continues ...this work with his translations of one of today's finest Serbian poets, Milan Djordjevic. An encounter between two poets and two languages, this bilingual edition--the first selection of Djordjevic's work to appear in English--features Simic's translations and the Serbian originals on facing pages. Simic, a native Serbian speaker, has selected some forty-five of Djordjevic's best poems and provides an introduction in which he discusses the poet's work, as well as the challenges of translation.
Djordjevic, who was born in Belgrade in 1954, is a poet who gives equal weight to imagination and reality. This book ranges across his entire career to date. His earliest poems can deal with something as commonplace as a bulb of garlic, a potato, or an overcoat fallen on the floor. Later poems, often dreamlike and surreal, recount his travels in Germany, France, and England. His recent poems are more autobiographical and realistic and reflect a personal tragedy. Confined to his house after being hit and nearly killed by a car while crossing a Belgrade street in 2007, the poet writes of his humble surroundings, the cats that come to his door, the birds he sees through his window, and the copies of one of his own books that he once burnt to keep warm.
Whatever their subject, Djordjevic's poems are beautiful, original, and always lyrical.
This paper gives insight on the WebSocket communication method in Internet of Things system, where the hardware part of the system is based on ESP32 microcontroller. Method of implementation is ...discussed and the reliability of the real-time data transfer in Wi-Fi networks is tested and compared with the long-polling method. Special circuit is designed with the goal to stress the hardware part of the system and the client-server communication link in order to enable proper comparison of data transfer methods. For the comprehensive testing of the real-time data ow, a web server application is designed and used to visualize received data. Impact of RSSI on transfer methods is discussed as well. Eciency of the WebSocket method is discussed and then compared to the long-polling method.
Background: Diabetic ketoacidosis (DKA) is an acute complication of diabetes, a severe metabolic disorder that requires urgent treatment. The aim of this article is to present a case of ...steroid-induced diabetes with complications.
Case presentation: A young 25-year-old man without any co-morbid, presented to the emergency department with fever, vomiting, coughing, and buttock pain which started 3 days before. On the right gluteus, there was a hematoma approx. 10 × 5 cm with fluctuation. The patient had hyperglycemia (9.1 mmol/l), associated with high anion-gap metabolic acidosis, acute kidney injury (AKI), grossly elevated muscle enzymes, hyperkalemia, hyperphosphatemia, hypoalbuminemia, hypocalcemia and hypomagnesemia, and deranged liver function tests. The urine dipstick was grossly cola-colored and biochemically was positive for glucose, ketones, and proteins. Abscess drainage was performed, and Streptococcus pyogenes was isolated on culture and sensitivity. The patient was treated for DKA, complicated by an AKI and infection. Diabetes is confirmed based on glycosylated hemoglobin.
Conclusion: The risk of ketoacidosis and hyperglycemia should be considered in the course of steroid therapy, even without a diagnosis of diabetes, in patients who abuse steroids or have risk factors for diabetes and obesity.
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