ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA

Journal Information
EISSN : 2603-316X
Published by: Technical University of Varna, Bulgaria (10.29114)
Total articles ≅ 70
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DOAJ
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, , , 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.
, Petar Georgiev Georgiev
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.
Evgeni Nikolaev Malev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 56-64; https://doi.org/10.29114/ajtuv.vol5.iss1.210

Abstract:
The paper focuses exclusively on the analysis of the simulation software and the main parameters of the driver circuits for power electronic converters. A mathematical model of the driver circuit in the Matlab Simunink software environment has been created. This model enables the analysis of the process of frequency formation through the boostrap capacitor and examines the interaction between the protection of the scheme at , and the other digital blocks in the circuit. Considered, additionally, are the basic physical processes behavior of a driver with a similar structure in Infineon designer.
Antim Hristov Yordanov
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 94-99; https://doi.org/10.29114/ajtuv.vol5.iss1.205

Abstract:
The reaction of different materials to external magnetic fields depends on the frequency of propagation of radio waves in substances and is determined by the dielectric constant, magnetic permeability , by the vectors of the electric and magnetic field. When irradiated with a flat wave on a flat surface, the phenomenon occurs at the boundary between two media, which will be described by an algorithm through reflection and transmission coefficients used in the processing of transmitted and reflected signals from radars, and adopted in radiology as well.
Desislava Mladenova Argirova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 42-55; https://doi.org/10.29114/ajtuv.vol5.iss1.233

Abstract:
The countries of the European Union, which are final destinations or transit for refugees and migrants, face many social, humanitarian and financial challenges. They are expected to invest efforts and resources to enable migrant communities and the host society to activate their abilities, qualities and skills to build social cohesion and well-being between them. Local administrations provide many services that directly affect the integration of migrants and there-fore have a greater capacity to support the process of social cohesion, as opposed to governance at national level, which in many cases hinders local government initiatives to address social and economic problems arising from immigration. Integration is an extremely individual process and individual needs must be taken into account by the various institutions involved in this activity. Refugee integration is one of the indicators of democratic society, an indicator of the development and promotion of human rights and freedoms. It is a continuous and dynamic process that requires efforts and readiness on the part of refugees to adapt to their host society without having to give up their cultural identity, and therefore - readiness and understanding on the part of the host community and public institutions to perceive refugees as equal persons of themselves. Integration is a long-term two-way process of mutual adjustment of incoming immigrants and citizens of the host country.
, 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).
Svetlozar Kirilov Zahariev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 1-12; https://doi.org/10.29114/ajtuv.vol5.iss1.224

Abstract:
One of the most significant error contributors to preliminary design tools for Photovoltaic power systems is related to the simple parametric Clear Sky models. Therefore, this paper focuses on providing a methodology and a more sophisticated open-source tool for 3 commonly used Clear Sky models. This includes all relevant steps involved in the process - from filtering the raw meteorological data, identification of Clear Sky regions, data redistribution to genetic optimization of selected model parameter, etc.use case is built upon a multiyear dataset obtained from TU Varna meteorological station between 2012-2016. A significantly higher density distribution of Clear sky segments was identified during the summer through the Clear Sky Identification algorithm. To avoid the risk of overfitting the models to purely summer months and poor model fits in winter months, which was found to be the case with the legacy model, the underrepresented clear sky regions (based on θ) were replicated until uniform distribution is attained. Subsequently, a genetic optimization was applied to selected parameters in the Clear Sky algorithms and the updated models showed a significant improvement in low winter months (θ) and even overall performance boost RMSE / MAE /R2. Furthermore, such validations and optimizations are recommended prior to any design or real-time PV-system analysis for the specific location.
Sibel Ilhanova Ahmedova, , Eredzep Musov, Soner Aziz
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 13-18; https://doi.org/10.29114/ajtuv.vol5.iss1.222

Abstract:
With the development of technology, there is a growing need to improve communication between young entrepreneurs and businesses. The ability of these two groups to communicate effectively with each other would rebuild the poor communication between them and help establish a more efficient and sustainable relationship. The paper based on a research into the opportunities to increase the level of communication between young entrepreneurs and businesses, endeavors to propose a set of guidelines for their improved communication and cooperation.
Ventsislav Georgiev Nikolov, Aleksandar Krastev, Snezhina Yanakieva
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 5, pp 19-24; https://doi.org/10.29114/ajtuv.vol5.iss1.226

Abstract:
The present paper provides a full description of a software implementation of a system for statistical distributions. Such a system is almost indispensable in many simulation applications where the factors incorporated adhere to a specific non-normal distribution. The realization is developed as a software library that can be integrated in different other applications. There is also the possibility for additional theoretical distribution types to be added.
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