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Publisher Technical University of Varna, Bulgaria

32 articles
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Anastas Todorov Yangyozov, Damjanka Stojanova Dimitrova, Lazar Georgiev Panayotov
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 70-79; doi:10.29114/ajtuv.vol2.iss2.95

Abstract:A small turbine, working with air and water to generate electricity, was designed and its performance was reported in this paper. The rotor diameter is 150mm. The numerical calculations of the power coefficient, torque, and tip speed ratio of turbine were carried out for a wide range of inlet velocities. The flow passing through the turbine was investigated with commercial CFD code ANSYS CFX 18
Maciej Sulowski, Ewa Lichańska, Paweł Kulecki, Monika Tenerowicz-Żaba, Anna Staniek
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 1-13; doi:10.29114/ajtuv.vol2.iss2.79

Abstract:Sintering behavior in high purity nitrogen and mixture of 5% H2-95% N2 of Fe-(Cr)-(Mo)-C system was investigated. The mixtures, differ from chromium, molybdenum and carbon content were prepared in Turbula mixer. Then, using single-action pressing in a rigid die at pressing pressure 400 MPa, green compacts with density level 5.9±0.17 g/cm3 were pressed. Sintering was carried out in a horizontal push rod dilatometer Netzsch 402E at 1120 and 1250°C for 60 min. Heating and cooling rates were 10 and 20°C/min., respectively. After heating, compacts were isothermal sintered at 1120 or 1250°C for 60 minutes an cooled up to 200°C, then isothermally hold for 60 minutes and definitely cooled to the room temperature. Pure nitrogen and mixture of 5% H2-95% N2 were employed as sintering atmospheres. During investigations the influence of isothermal sintering temperature, chemical composition of sintering atmosphere, chromium, molybdenum and carbon content was followed by dilatometry. The aim of investigations was to determine transformation temperatures. It was shown that the dimensional changes occurring during heating and isothermal sintering and the final density of sintered compacts are influenced by sintering parameters and the alloying elements concentration in powder mixture.
Nadezhda Ognjanova Doseva, Daniela Chakyrova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 62-69; doi:10.29114/ajtuv.vol2.iss2.94

Abstract:This paper considers the questions of techno-economic optimization in order to determine the thermal transmittance coefficient of the external walls of an existing residential building.The optimization procedure is conducted for the climatic and economic conditions in Bulgaria and taking into account the existing legal framework. The minimum of the building life cycle costs is determined by using genetic algorithm
Momchil Todorov Tachev, Tihomir Atanassov Dovramadjiev, Ginka Velikova Jecheva, Kremena Cankova Markova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 54-61; doi:10.29114/ajtuv.vol2.iss2.93

Abstract:Bulgarian female folk costume is rich in multiple characters, elements and details. One of the most characteristic is the belt buckles. As well as specially designed symbolism, the belt buckle - with their unique identity belong to the national - historical heritage of Bulgaria. In the present study a model of a belt buckle is digitized and reconstructed, and possessing grace and beauty. The realization of the completed three-dimensional computer model goes through stages of photogrammetry and computer design with special sculpting tools.
Hristina Vasileva Tacheva, Tsena Radkova Murzova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 80-86; doi:10.29114/ajtuv.vol2.iss2.100

Abstract:The digital image is an integral part of the contemporary design process. Regardless of the method used to create the image of a conceptual idea /sketch, esquisse/. The result is a digital image, which permits manufacturing, modification and printing. In the design for academic purposes such cases are the majority. This research examines the possibilities for the specific application of 3D scanning in the design of specific complex forms with volume with an artistic character in the field of the award and memorabilia academic system. The application of these technologies noticeably decreases the time needed for design, which is key in such tasks. There is an increase in the precision of the manufacturing of the specific form, as well as a possibility for its printing and modification should the need of other projects, demanding the presence of the same object arise.
Ginka Velikova Jecheva, Tihomir Atanassov Dovramadjiev, Momchil Todorov Tachev, Kremena Cankova Markova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 46-53; doi:10.29114/ajtuv.vol2.iss2.91

Abstract:Bulgaria has been known for its rich history since ancient times. Within its current territory, the country encompasses a variety of cultures that bear their specific specificity and identity. The present study aims at the digitization of models of national and historical value, applying modern technological means. To achieve the goal, a methodical process is used to optimize the interaction of the different working steps.
Emil Ivanov Panov
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 20-39; doi:10.29114/ajtuv.vol2.iss2.88

Abstract:The paper presents some new chapters of the relativistic circuit theory, which are part of the special theory of relativity. It explores the alternating current regimes in the linear electric circuits, which are moving with very high speeds less than the speed of light. In the paper a large group of basic problems, connected with the relativistic fundamental laws in the time domain and in phasor form for the linear electric circuits are observed. The relativistic forms of the phasors of the basic quantities of the electric circuits (currents, voltages), the complex powers and the relativistic relations of the basic parameters of the circuits (angular frequencies, phases, phase shifts, reactances, susceptances, impedances, admittances) are presented, too. Additionally, some phenomena as resonances and transient processes in fast moving linear electric circuits are observed, as well. All the formulas in the paper are extracted consecutively and they are followed by explanations in full details. The final results are supported by many simple examples about fast moving linear electric circuits.
Radko Petrov Mihajlow, Vladimir Georgiev Demirev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 14-19; doi:10.29114/ajtuv.vol2.iss2.84

Abstract:A brief analysis has been made about the emergence of the concept of "navigation". The benefits of optimal guidance of agricultural aggregates through GPS navigation are outlined. Some of the positioning accuracy methods that are practiced in agricultural aggregates are analyzed. A poll has been conducted among users of agricultural equipment using GPS navigation. Issue and conclusions are drawn on the benefits and problems for more efficient use of GPS navigation in agriculture.
Marinela Yordanova Yordanova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 40-45; doi:10.29114/ajtuv.vol2.iss2.90

Abstract:The hazards of electric arcs in Bulgarian norms, as the Regulations on Health and Safety at work in electrical installations of electrical and thermal power stations and electric power lines and Ordinance №9 on the technical operation of power stations and electric power lines mainly govern the safety at work with high-voltage equipment, are not subject to a special section. NFPA 70E Standards for electrical safety in the Workplace requires to assess whether there are arc-dangers; to calculate the energy released by the arc; to define the permissible arc protection boundaries; to provide adequate personal protective equipment and to label the equipment. The aim of the paper is to summarize the Bulgarian requirements connected somehow with the flash hazard, to compares similarities can be found in approaches to ensuring electrical safety with those of international standards.
Hristiyan Toshkov Petrov
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 2, pp 61-70; doi:10.29114/ajtuv.vol2.iss1.74

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