ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA

Journal Information
EISSN : 2603-316X
Published by: Technical University of Varna, Bulgaria (10.29114)
Total articles ≅ 76
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DOAJ
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Latest articles in this journal

Svetlana Ivanova Todorova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 122-131; https://doi.org/10.29114/ajtuv.vol5.iss2.251

Abstract:
The survey aims to identify the factors influencing the different levels of unemployment in Bulgaria through the use of statistical methods and official statistical information regarding the labor market for the period 2015-2019. To achieve the research goals, a regression model was developed, disclosing the relationship between a dependent variable (total unemployment rate) and a system of independent variables reflecting the influence of factors for the analyzed period. The nature of the dependencies is established, statistically significant factors are selected and ranked, the degree of influence for each of them is determined, the adequacy of the model is checked and the results obtained are fully analyzed. Based on the findings achieved, conclusions are formulated and measures are proposed aimed at a general reduction of the unemployment rate in the country, as well as to increase the opportunities for employment of various categories of unemployed persons with disabilities.
Siyana Vankova Zabunova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 100-111; https://doi.org/10.29114/ajtuv.vol5.iss2.242

Abstract:
The present paper provides a brief overview of the possibilities for nitriding the surface of Al-alloys. This treatment is still attracting scientific attention, not only as a means to increase the industrial life of materials but also as a way to comply with the current ecological requirements. On the whole, the purpose of such a process is to improve the mechanical properties like surface hardness and wear resistance of the Al-alloys, especially in automotive industry where “lightening” the whole construction is of great importance for reducing the fuel consumption. The paper, further, sets out to examine the influence of the technological parameters of this thermo - chemical treatment on the thickness of the formed nitride layer and on the mechanical properties on one hand and the naturally formed oxide on the surface of the Al-alloys on the other hand. Drawn, in the end, are some conclusions about the potential benefits of nitriding and expressed is the specific need for its thorough research in the future.
Boyka Malcheva, Pavlina Naskova, Dragomir Plamenov Dimitrov
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 146-155; https://doi.org/10.29114/ajtuv.vol5.iss2.256

Abstract:
Microbiological indexes have been studied in dynamics at lime treatment and independent planting of lavender (Lavandula angustifolia, variety “Hemus”) and sweet basil (Ocimum basilicum, variety “Genovese”) of fresh sludges from a purification plant, with concentrations of quicklime: 10%, 20% and 30% for a 40-day period of composting. The microbiological analysis includes determining of nonpathogenic (non-spore forming bacteria, bacilli, actynomycetes, micromycetes, bacteria, which assimilate mineral nitrogen) and pathogenic (Salmonella spp., Escherichia coli and coliforms, Enterococcus, Clostridium perfringens) microflora. Out of the beneficial microflora in the sludges the quantity of the non-spore forming bacteria is the biggest, and the lowest is of the actynomycetes. A basic share in the composition of the pathogenic microflora occupies Clostridium perfringens, followed by Escherichia coli and coliforms, and Enterococcus. Absence of Salmonella spp. was established in the studied sludges. The best results for the disinfection of the sludges displays the adding of 30% quicklime (followed by the variants with 20% and 30% lime), on 5-th day of the experiment setting. The pH decrease in the period of the study leads to a repeated development of pathogenic microflora. In the meantime the creation of an alkaline medium leads to decrease in the quantity of the beneficial microorganisms. The decrease of the moisture and the drying of the sludges for the study period display a weaker effect on the dynamics of the microflora in comparison with the pH increase impact. The planting of lavender and basil independently in the sludges samples from a purification plant has a beneficial effect (a little bit better with the lavender variants) for increase of the quantity of nonpathogenic microbes and pathogens frequency of occurrence decrease. The effect is intensified by increasing the plant development period.
Dimitar Todorov, Zheyno Zheynov, Hristo Valchanov, Milena Karova, Ivaylo Plamenov Penev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 140-145; https://doi.org/10.29114/ajtuv.vol5.iss2.234

Abstract:
Steganography is a modern approach to protect classified data against malicious attacks and misuse. Presented, accordingly, in this paper is a novel method for steganographic embedding of information. A template matrix is used for screening the original message embedded in an image. The efficiency of the steganographic embedding depends on the length of the message. The particular dependency is, therefore, the primary focus of the proposed work. The end results of the experiment were extremely satisfactory with the percentage of successfully retrieved messages being more than 90%, and the size of the processed images with embedded messages being fully acceptable and capable of being used in a communication environment.
Stoyan Nedelchev Stoyanov, , Zdravko Ivanov, Radostin Radev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 112-121; https://doi.org/10.29114/ajtuv.vol5.iss2.259

Abstract:
The aim of the present work is to construct a test stand for determining the characteristics of different fourth generation gas injectors working under various conditions as close as possible to the actual operating ones. For this purpose, the standard fourth generation gas system and liquefied petroleum gas (LPG) as a working fluid were used for the stand. A system has been developed to maintain the gas leakage pressure equal in value to the pressure in the intake manifold of a Spark Ignition (SI) engine. Used LPG is compressed and liquefied for reuse. Additionally, safety measures are taken. The stand provides the right conditions for determining the influence of the nozzle diameter, the length of the connecting pipe between the injector and the intake manifold, the differential pressure upstream and downstream of the injector and other factors that affect these characteristics, which may be different when installing LPG system to an internal combustion engine.
Maik Jurgen Streblau, Marin Todorov, Tatyana Dimova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 132-139; https://doi.org/10.29114/ajtuv.vol5.iss2.231

Abstract:
The present paper considers the impact of the degree of damage to a squirrel-cage rotor of an induction motor on the spectrum of the stator current. The study is based on the motor current signature analysis. Performed, for this purpose, were scientific experiments on eight samples of squirrel-cage rotors, seven of which with pre-inflicted faults using Dynamic Motor Analyser. The obtained results are herein presented in graphical and tabular form and are further compared with the ones acquired from an induction motor with an intact rotor winding. It can be clearly ascertained that the larger the number of damaged rotor bars, the more significant the increase in the current amplitude as correspondent to the side band amplitude.
, Tanya Panayotova, Neli Dobrinova Veleva
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 65-75; https://doi.org/10.29114/ajtuv.vol5.iss1.237

Abstract:
In today's dynamic business environment, the success and competitiveness of any production organization is ensured by continuous improvement, sustainable development, effective planning and management. There is a growing scientific interest in the importance and relevance of production management in view of the strong need to redefine the policies and priorities within the respective strategic plan for business development - with increased focus on capacity planning in order for the industrial enterprises to adapt successfully to the dynamically changing conditions of the global environment and intense competition. Accordingly, full advantage is taken from the ample opportunities to study the impact of a number of factors on capacity planning and management. Based on an in-depth literature analysis, interviews and surveys, selected were 18 key factors that have a profound influence on the effective planning and capacity management of the production organization. Using the relationship between each of these factors and the capacity management is closely examined by applying the method of Interpretive Structural Modeling (ISM). Additionally, the interrelationships between the key factors under study are further analyzed by means of a Structural self-interaction matrix (SSIM).
, , , Todorka Stankova, Diyana Dimova, Krasimir Lesidrenski
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 86-93; https://doi.org/10.29114/ajtuv.vol5.iss1.240

Abstract:
Pollen productivity еstimate (PPE) and relevant source area of pollen (RSAP) are critical parameters for quantitative interpretations of pollen data in palaeolandscape and palaeoecological reconstructions, and for analyses of the landscapes evolution and anthropogenisation as well. In light of this, the present paper endeavours to calculate PPE of key plant taxa and to define the RSAP in the Kamchia River Downstream Region (Eastern Bulgaria) in order to use them in landscape simulations and estimations. For the purposes of this research, a dataset of pollen counts from 10 modern pollen samples together with corresponding vegetation data, measured around each sample point in concentric rings, were collected in 2020. Three submodels of the Extended R-Value (ERV) model were used to relate pollen percentages to vegetation composition. Therewith, in order to create a calibrated model, the plant abundance of each pollen type was weighed by distance in GIS environment. The findings led to the conclusion that most of the tree taxa have PPE higher than 1 (ERV3 submodel). Cichoriceae, Fabaceae and Asteraceae have lower PPE.
Nikolay Hristov, Maik Jurgen Streblau, Tatyana Dimova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 76-85; https://doi.org/10.29114/ajtuv.vol5.iss1.228

Abstract:
This article proposes an integrated system for monitoring and analysis of the operation of a small photovoltaic plant with the possibility of remote access via the Internet. The system has been built on the territory of Varna Technical University and is based on a mini computer Raspberry Pi 3B + using a Linux operating system. The monitoring is performed by keeping track of the environmental parameters and the input-output parameters of the photovoltaic inverter. Data are presented for a period of three months: October 1, 2020 to December 31, 2020. The results are visualized by appropriate graphs, demonstrating the change in the observed indicators, both for the entire specified period and for a randomly selected day.
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 25-41; https://doi.org/10.29114/ajtuv.vol5.iss1.227

Abstract:
The present paper provides a thorough analysis of the prerequisites in adopting a new paradigm in the conceptual ship design accounting for the environmental pollution driven by maritime transportations. A survey of presently issued IMO environmental requirements outlines the framework within ship design solutions. Identified and carefully examined are several competing optimal design solutions, based on the energy efficiency design index introduced for shipbuilding, operation cost, and the resale costs at the end of the service life, which are used as input variables in a risk-based analysis. Reviewed are the immediate steps taken in the risk-based conceptual ship design to minimise the risk of environmental pollution while considering the life cycle assessment and energy efficiency of the ship propulsion system. Brought forth in the current paper are the results of a study into the concept design of series of containerships operating in the Black Sea for transporting 20, 40 and 45-foot containers aimed at identifying the main dimensions, capacity, visibility, freeboard, stability, bow, and stern design, propulsion complex and propeller design, control and manoeuvrability, seakeeping, energy efficiency design index, capital, and operational expenditures, that leads to the required fright rate for the ships in the range of 4,000 to 14,000 DWT. Accordingly, a bulk carrier’s risk-based concept ship design methodology is employed for the ship life cycle assessment and energy efficiency in pursuance of the optimal design solution in reference to the energy efficiency design index as most applicable to shipbuilding, operation, and resale costs at the end of the service life, and used as input variables in the risk estimate.
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