Journal Information
EISSN : 2603-316X
Current Publisher: Technical University of Varna (10.29114)
Total articles ≅ 59
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Greg Wheatley , Darrin Gangemi, Jarod Toogood, Rendage Sachini Sandeepa Chandrasiri
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 91-99; doi:10.29114/ajtuv.vol4.iss2.179

This project was aimed at modelling the stress and deformation profile of a 6061-T6 aluminium suspension upright of a formula society of automotive engineers style vehicle with a double wishbone suspension under the loading conditions of a 1.5G corner. With these results, it would need to be determined whether the design is fit for use. Using remote displacement boundary conditions for the upper and lower wishbone connections and the control arm connection with a remote force at the centre of the wheel patch acting on the bearing surfaces the maximum stress, overall stress profile and maximum deformation of the upright was calculated. These results after, undertaking a verification and validation study, were a maximum equivalent von-Mises stress of 87.358MPa and a maximum bearing surface deflection of 0.21 mm. The maximum von-Mises stress calculated was less than the fatigue limit of 90MPa signalling infinite life and also less than the yield stress of 240MPa signalling a safe design. Verification and validation techniques were used to ensure the final result was accurate and reflected the real – life system. Structural error was used to verify the results where it was found that maximum structural error in the upright was 0.052mJ and at the location of maximum stress was between 0.0058-1.0782e-8 mJ. Validation of the model was achieved by comparing the reaction forces calculated in ANSYS to theoretical values and was found that the magnitudes were within 2.5% of the theoretical values, thus the model was considered valid.
Plamena Yankova Panayotova, Anatoli Iliev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 138-144; doi:10.29114/ajtuv.vol4.iss2.217

The present paper focuses primarily on the agrobiological and technological characteristics of the pink local vinous varieties Pamid and Muscat red. Muscat red is a late ripening vinous variety, and variety Pamid is a medium ripening vinous variety with possibility for consumption in fresh condition as well since its pellicle and seeds are not felt, and the titrated acidity is low. Variety Muscat red belongs to the most cold-resistant local varieties. Variety Pamid has increased root phylloxera resistance, on account of which it can be cultivated on its own roots without grafting in sandy soils.
Radko Petrov Mihajlow , Asparuh Atanasov, Albena Ivanova, Desislava Mihaylova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 122-129; doi:10.29114/ajtuv.vol4.iss2.203

The present study observes the development of spring crops maize and sunflower typical of the Southern Dobrudzha region. A distinct methodology for remote monitoring through the use of a small remotely piloted aircraft has been developed for the purposes of the present paper and applied accordingly. Two types of video cameras were used: for the visible range of the RGB light reflected by the plants and for the NearRed reflection close to the red light. The obtained results are presented in both tabular and graphical form and inferred, finally, in the paper are some principal conclusions about the condition of the crops under consideration.
Adebola Adebayo Adekunle, Igba Uvieoghene Tobit, Ogunrinola Oluwaseyi Gbemiga
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 100-111; doi:10.29114/ajtuv.vol4.iss2.177

: Landfill liners are underlying materials with low permeability whose main function is to mitigate the infiltration of toxic contents into ground water lying beneath. Landfill liners are primarily made of bentonite clay. Bentonite has a very low hydraulic conductivity, that might not be readily accessible, unlike kaolin which is found to have a lower hydraulic conductivity compared to that of bentonite and can be extensively obtained from numerous different sources. Explored, for the purposes of the present research paper, were various ratios of bentonite and kaolin and their hydraulic conductivity, in particular ratios of 90:10 kaolin to bentonite, 80:20 kaolin to bentonite, 70:30 kaolin to bentonite, 60:40 kaolin to bentonite and 50:50 kaolin to bentonite in an effort to achieve an acceptable barrier suitable as a liner / where tap water and ammonium solution were used as permeants. It was concluded that the ratios not lower than 20% bentonite (80:20, 70:30, 60:40 and 50:50) all had their hydraulic conductivity value reduced compared to the 100% kaolin.
Johnson Olufemi Fejoh
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 145-152; doi:10.29114/ajtuv.vol4.iss2.190

Tertiary Education Trust Fund (TETFUND) was established by Federal Government of Nigeria to tackle the problem of inadequate funding of tertiary institutions which had been a major obstacle to the achievement of sustainable developments in these institutions. This study therefore examined the impact of TETFUND interventions on sustainable development goals (research and academic growth and continuous provision of instructional materials and laboratory equipment) of Olabisi Onabanjo University, Ogun State, Nigeria. Descriptive survey research design was adopted and qualitative data were collected using a questionnaire to elicit information from a total number of 250 respondents from total population of 1,723 staff of the university. From the sample size, 128 (56%) were male while 122 (54%) were female. Data collected were analyzed using regression analysis to test all the hypotheses at 0.05 level of significance. Findings revealed that TETFUND interventions have significant impact on sustainable development goals of Olabisi Onabanjo University. It is therefore recommended that Federal Government should step up efforts to ensure that tertiary institutions (federal and state owned) are adequately funded through TETFUND and also do more in the area of human resource development for the research and academic growth of these institutions.
Greg Wheatley, Rendage Sachini Sandeepa Chandrasiri
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 112-121; doi:10.29114/ajtuv.vol4.iss2.180

High density polyethylene (HDPE) is a thermoplastic polymer which is classified as one of the highly consumed types of plastics. One major advantage of thermoplastic materials is their ability of recycling and reprocessing which will bring considerable economicand environmental benefits. The present paper, therefore, endeavours to explore the practical possibility of using recycled HDPE hollow section as a replacement of virgin HDPE made by the extrusion process. The main focus of the study was to evaluate the mechanical performance of the recycled HDPE and compare the results with virgin or non-recycled HDPE. The modulus of elasticity, tensile yield and ultimate strength, compressive yield and ultimate strength, flexural yield and ultimate strength and the coefficient of thermal expansion were the main parameters to be checked against the respective mechanical properties. Thus, pursuant to the rsults, it was found out that the modulus of elasticity and the tensile yield strength are lower in recycled HDPE compared to the non-recycled HDPE. However, there is no significant difference between the recycled and non-recycled HDPE for the tensile ultimate strength, compressive yield strength and compressive ultimate strength. The flexural yield strength and flexural ultimate strength properties of the recycled HDPE proved to be superior to those of the non-recycled HDPE. The coefficient of linear thermal expansion of the recycled HDPE sample was 130 μm/(m.°C) and that for the non-recycled HDPE was 142 μm/(m.°C).
Olori Abiola Lateef, Adedoyin Adewale Adebanjo, Omolola Aminat Ibrahim
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 23-29; doi:10.29114/ajtuv.vol4.iss1.150

The study examined influence of undergraduates’ perceived usefulness and ease of use of mobile technologies on its adoption for learning. Two research questions guided the study. Four hundred (400) students were randomly selected from the two purposively selected universities in Ogun State South West Nigeria. The study employed multiple regressions in the analysis of the data collected. From the result it was found out that undergraduate students’ perceived usefulness (=0.305, t=3.867, p
Svetlana Ivanova Todorova
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 40-54; doi:10.29114/ajtuv.vol4.iss1.165

The unemployment and the issues relating to it refer to the entire population of a given country and that's why they are always relevant. The present article examines the main factors exerting a powerful effect on the unemployment level – the active labour market policy, the labour mobility, the labour productivity and the labor force level. Developed is a theoretical model on the basis of which an empirical analysis is made of the data reflecting the unemployment level in the country over the 2013-2018 period. A special attention is paid to the mutual relation between the unemployment level and the number of the job vacancies, and it is precisely this interdependence that is examined and analysed in the paper using the Beveridge curve.
Georgi Georgiev Georgiev
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 30-39; doi:10.29114/ajtuv.vol4.iss1.162

The paper explores the shape of a fatigue crack initiation in the interval of 106-107cycles of duplex stainless steel, commercially designated as SAF 2507. Particular emphasis is placed upon the development of the crack’s growth front and its subsequent expansion in three directions x, y, z. Created, accordingly, on the basis of the experimentally obtained results, is a 3D computer model to help provide a further prediction for the physical endurance of similar materials. The growth of a fatigue crack is modeled by using The SolidWorks and AutoCAD software tools for constructing the model of fatigue crack growth.
Plamen Antonov Stanchev, Mediha Enver Mehmed-Hamza
ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA, Volume 4, pp 67-72; doi:10.29114/ajtuv.vol4.iss1.172

In the medium voltage electrical power lines, the most common fault is the phase to ground fault. The determining factors for selection of the neutral grounding mode of the medium voltage electrical power lines are the selectivity of the relay protection, the transient voltages during phase to ground fault, the magnitude of the fault currents, etc. The paper studies the influence of the transient resistance of phase to ground fault on the selectivity and sensitivity of the earth fault protection when the neutral of the power transformer is grounded through active resistance in medium voltage power grids.
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