Aerospace Research in Bulgaria

Journal Information
ISSN / EISSN : 1313-0927 / 2367-9522
Published by: Pensoft Publishers (10.3897)
Total articles ≅ 66
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Maretta Kazaryan
Aerospace Research in Bulgaria, Volume 33, pp 140-156; https://doi.org/10.3897/arb.v33.e10

Abstract:
Currently, geographic information systems have taken strong positions in economics, politics and in almost all spheres of human activity. The result of human activity in urbanized areas is the emergence and further spread of unauthorized landfills and industrial waste. In order to timely intervene and stop the spread of foci of infection and changes in the soil composition, it is necessary to have an automated system for monitoring the disposal facilities and industrial waste. The purpose of the work is to design a model of an automated system for monitoring waste disposal sites, including industrial sites, using remote sensing technologies. General research methodology: The paper uses modern methods of information systems design, using the theory of databases, data warehouses, and geographic bases data. Scientific novelty: The paper suggests a model of an automated space system monitoring for the presence of waste disposal facilities. A general methodology for constructing a geo-information model that monitors territories for the presence of waste disposal sites and also a methodology for the development of geodatabase are given. Landfill geo-databases are a structure of attribute and geographic data obtained in an automated mode. An analysis of current perspectives in the creation and operation of such automated geo-information systems is given using specific knowledge in the field of very large, distributed and open data archives. As a realization of theoretical reasoning, the practical part of the formation of software, technical and mathematical support of the remote monitoring system of the waste disposal area (WDA) and industrial waste (IW) landfill is given. In general, the work is survey-research in nature.
Mohamed Roudane, Merouane Salhi, Ahmed Boucherit
Aerospace Research in Bulgaria, Volume 33, pp 134-151; https://doi.org/10.3897/arb.v33.e12

Abstract:
This present work focused on new nozzles design method, based on the characteristics method, which is a technique method to reduce a partial differential equation to linear differential equations along which the solution can be integrated from initial conditions. The latter is developed under the real gas theory, because when the both pressure and temperature of a gas increases, the specific heat and their ratio do not remain constant anymore and start to vary with the gas parameters. The gas doesn’t stay perfect, and it becomes a real gas. The presented equations of the characteristics remain valid whatever area or field of study. With the assumptions that Berthelot’s state equation accounts for molecular size and intermolecular force effects, expressions are developed for analyzing the supersonic flow for thermally and calorically imperfect gas. The resolution has been made by the finite differences method using the corrector predictor algorithm. As result, the developed mathematical model used to design 2D minimum length nozzles under effect of the stagnation parameters of fluid flow. A comparison for air with the perfect gas PG and high temperature HT models on the one hand and our results by the real gas theory on the other of nozzles are made. An important gain of length and weight can rise up to 40% and 20% respectively. It is in this context that Minimum Length Nozzle (MLN) nozzles for aerospace engines based on real gas theory were developed to achieve maximum thrust with the smallest possible nozzle weight (minimum length).
Maria Dimitrova
Aerospace Research in Bulgaria, Volume 33, pp 76-86; https://doi.org/10.3897/arb.v33.e06

Abstract:
This article presents an investigation of seasonal behavior of Sahara desert dust transport over the Balkans. The data used is satellite measurements of monthly averaged Absorption Aerosol Index (AAI) value. The researched period is from June 1995 till the end of 2019. The data used is from four different space instruments onboard five satellites. The area of interest is a rectangle with corners 23 E 43 N and 24 E 35 N. The data from different sources is compared and discussed.
Zoya Hubenova, Konstantin Metodiev, Svetla Dimitrova, Liubomir Alexiev
Aerospace Research in Bulgaria, Volume 33, pp 221-236; https://doi.org/10.3897/arb.v33.e16

Abstract:
This article proposes yet another approach towards looking into causes for attention distribution of an operator of unmanned aerial vehicle. During examination, the operator is being tested at dedicated flight simulator while data are gathered and visualized through a mobile eye tracker. Two work stages are considered sequentially, i.e. building a geometric 2D transformation of region of interest (homography) within an image, and overlaying a dynamic heatmap as well. In the former stage, spontaneous movements of the operator’s head, recorded by the video, are eliminated thus enabling the operator to use the mobile eye tracker instead of a desktop-based one. During the latter stage, the distribution of operator’s attention over time is displayed. In order to implement the current research, a source code has been developed in C++ for some features readily available in OpenCV library to be used. In addition, data gathered after carrying out flight session are processed and discussed thoroughly.
Maretta Kazaryan
Aerospace Research in Bulgaria, Volume 33, pp 124-139; https://doi.org/10.3897/arb.v33.e09

Abstract:
The article analyzes the factors that stimulate research and development of an automated system for processing and analyzing satellite imagery data. In particular, the study of satellite imagery for the presence of waste disposal objects is considered as an application. This problem is of particular interest when conducting scientific research. The development of automated control systems (ACS) in the field of space image (SI) recognition is characterized primarily by the approach of interest, i.e. for what purpose and for solving of which particular problem of the subject area the system is created. Obviously, the system is a set of certain information technologies and the main factor in the development of an automated system is and remains the study of peculiarities of creating an appropriate information system (IS). The article proposes a methodological approach to the processing and analysis of data by the IS. The approach is based on the conceptual idea of fractal sets. This enhances the detection of abnormal signals in difficult phono-target environments. Testing is conducted on the detection of WDS under conditions of a low signal-to-noise ratio.
Konstantin Metodiev
Aerospace Research in Bulgaria, Volume 33, pp 157-166; https://doi.org/10.3897/arb.v33.e11

Abstract:
In the paper hereby, a numerical (panel) method is applied to analyze steady two-dimensional flow of ideal gas around an airfoil. Initially, the airfoil is divided into a finite number of panels. Then the panels are replaced by doublets with constant strength. In addition, a wake panel is added to fulfill Kutta condition at the airfoil trailing edge. In order to implement this, a numerical realization is developed and built by means of Tiny C Compiler. To work out a solution to the linear non-homogeneous algebraic system, direct schemes for lower-upper factorization/decomposition of matrix of coefficients were applied, namely Crout, Doolittle, and Cholesky. The obtained results are validated against exact solution and shown for various values of angle of attack and Reynolds number.
Georgi Jelev, Dilyana Stefanova, Petar Stefanov
Aerospace Research in Bulgaria, Volume 33, pp 51-78; https://doi.org/10.3897/arb.v33.e05

Abstract:
The Corine Land Cover (CLC) is a digital data about land cover which is distributed into 44 classes whereas for the territory of Bulgaria the CLC classes are 36. The minimal mapping unit is 25 hectares (for 2D objects and 100 m for linear objects). Data sets for the years 1990, 2000, 2006, 2012, and 2018 are available, as well as for the changes which have occurred between each couple of years (1990–2000, 2000–2006, 2006–2012, and 2012–2018). The great data sets provide to track over a nearly 30-year period of land cover changes in model karst regions which are strongly vulnerable to anthropogenic and natural influences. This paper considers the changes in the land cover types on the Devetashko plateau – a typical karst plateau in North Bulgaria. Land cover and land use changes affect directly the processes of modern karst-genesis, the soil-vegetation cover, the quantity and quality of underground karst waters.
Konstantin Metodiev
Aerospace Research in Bulgaria, Volume 33, pp 101-123; https://doi.org/10.3897/arb.v33.e08

Abstract:
This article represents a showcase of two different coding approaches with GAMMA, used to calculate topographic and differential phases from high resolution TanDEM-X bistatic data, provided by DLR. The first implementation approach comprises “BASH” scripting in Linux environment, having direct control of the GAMMA executables. The second approach is utilization of the PyroSAR framework, via GAMMA-API, in Python environment. Two spatial resolution scales are used – of 4 and 12 meters, to test feasibility of TanDEM-X InSAR output products in mountainous forest in rugged region. The first approach allowed thorough processing with abundant GAMMA output, whereas the high scale PyroSAR framework via GAMMA-API showed fast implementation. Comparison over 4 and 12m spatial resolution products showed good feasibility with strong influence from topography. Intense multi-looking resolved better connection of coherence amplitude to the volume decorrelation in canopy, despite preserving high resolution reveals plenty of details in land cover. Differential height calculation, without phase unwrapping, showed its significance in data processing over mountainous regions. Intensities normalization and terrain flattening showed good performance in both resolution scales. Finally, utilization of GAMMA in InSAR processing of high resolution TanDEM-X bistatic SAR data showed good feasibility and flexibility to derive interferometric products.
Adelina Miteva, Anna Bouzekova-Penkova
Aerospace Research in Bulgaria, Volume 33, pp 195-209; https://doi.org/10.3897/arb.v33.e14

Abstract:
Functionally graded materials (FGMs) are currently the subject of great and ever-growing interest from industry and science, and are widely used due to their advantages. These advantages are due to their unique properties and, therefore, their many real and potential applications in various fields of industry, science and everyday life. In this literature review paper, we will briefly focus on some of the properties of FGMs and on some of the existing and expanding future applications of FGM in aerospace and related industries. A critical discussion is presented. Possible future expansion of work in this area is being considered.
Petar Dimitrov, , Eugenia Roumenina,
Aerospace Research in Bulgaria, Volume 33, pp 40-50; https://doi.org/10.3897/arb.v33.e04

Abstract:
Advanced possibilities have emerged in the recent years for semi-automatic crop type mapping at national level due to the availability of Sentinel-1 and -2 satellite data. In this study, 14 crop type classes were mapped over Bulgaria using three bi-monthly composite image mosaics for 2019 generated in the Google Earth Engine (GEE) cloud computing platform. The overall accuracy, when both Sentinel-1 and -2 mosaics were used, was 78%, while the accuracy was slightly less when only Sentinel-2 data was used (75%). The accuracy was highest for "Cereals", "Maize", "Sunflower", "Winter rapeseed", and "Rice" - over 80% for both user's and producer's. However, the accuracy for classes such as "Vegetables", "Technical crops", "Forage crops", "Fallow", etc. was low. These classes represent categories suitable for the agricultural practice and statistics but are too general and difficult to distinguish using satellite data. It was found also that accuracy tend to be higher for larger parcels. Using composites with higher frequency and adapting the legend classes to include only crops which are similar in phenology and morphology are suggested as possible ways forward.
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