Vilnius Gediminas Technical University
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Fizikinis gelžbetoninių elementų sukibimo įtempių ir slinkties ryšio modeliavimas esant eksploatacinei apkrovai
No full textThe current dissertation aims to introduce a new interaction model between concrete and reinforcement to effectively address the inner mechanism of Reinforced Concrete (RC) structures.
For investigating the concrete-reinforcement interaction, traditional methods have typically dealt with a constant bonding relationship or a perfect interaction between two materials. This can further lead to numerous models that lack consistency and compatibility with one another. However, current research advocates for implementing the stress transfer methodology, which suggests the presence of force exchange between the reinforcement bars and the surrounding concrete, in other words, the bond stress. The present study develops a new model that establishes the ascending part of a bond–slip model. It is an essential step towards a constitutive bond–slip model in future, which will be able to accurately predict the serviceability performance of RC members, such as deflection, crack spacing/width etc.
The first chapter reviews the mechanism of the reinforcement–concrete interface under the tensile load. Multiple approaches have been discussed to investigate the serviceability performance of RC structures. A major part of this chapter is dedicated to reviewing the existing bond stress and bond–slip models with their respective backgrounds. The last part of the chapter reviews various strain monitoring tools and techniques to extract strains from the core of the reinforcement bars encased within the concrete.
The second chapter represents three experimental campaigns which consist of double pull-out tests of 14 short RC ties equipped with three distinct bar diameters (16.20 and 25 mm). The results of the mentioned tests, in terms of reinforcement strain distribution along the specimen lengths, have been displayed. A mathematical algorithm programmed in MatLab has been introduced, capable of deriving bond–slip relationships from the experimental strain output. Lastly, the obtained bond–slip relationships of all 14 specimens have been portrayed at multiple load levels.
The third chapter demonstrates the formation of a novel bond–slip model based on the experimental dataset. In the latter part, the newly proposed model has been validated with the experimental results of 14 (in-sample) specimens and eight independent (out-of-sample) specimens. Furthermore, a novel validation tool has been demonstrated, which is capable of predicting reinforcement strains from a given bond–slip model. Based on the tool, another layer of validation has been performed with independent data through reinforcement strain distribution. The chapter ends with a thorough statistical analysis for assessing the existing bond–slip models in terms of their strain prediction capability.Doctoral dissertatio
Planarinių mikrobangų diodų A3B5 puslaidininkinių junginių pagrindu detekcinių savybių tyrimai milimetrinių bangų ruože
No full textSuccessful development of microwave technologies requires electromagnetic detectors capable of sensing high frequency signals at low levels of microwave power. Bulk barrier planar microwave diodes operating based on the major carrier phenomena are promising in high frequency electromagnetic radiation sensing applications.
The dissertation aimed to develop and investigate new original planar microwave diodes with a lower spread of their electrical parameters and capable of detecting an electromagnetic signal in the millimeter wavelength range.
The first chapter reviews the physical properties of microwave diode based detectors with quasi linear and non linear current voltage characteristics and microwave diodes with a two dimensional electron gas channel. Then, the application technologies for microwave detectors and methods for their investigation using appropriate probing systems are discussed. The second chapter covers the aspects of the development of planar semiconductor microwave diodes based on GaAs, AlGaAs, and AlGaAs/GaAs compounds. Next, the methodology for investigation methods of electrical parameters and detection properties of the microwave diodes is presented. The third chapter presents the results of experimental investigations of the electrical parameters and detection properties of planar dual microwave diodes based on a semi insulating or low resistivity GaAs substrate, including current voltage characteristics, detected voltage on power characteristics and dependence of voltage sensitivity on frequency in the millimeter wavelength range. The fourth chapter presents theoretical estimations and experimental investigations of the electrical and detection properties of bow tie type microwave diodes with partial gate above a two dimensional electron gas channel based on a selectively doped GaAs/AlGaAs heterostructure.
The dissertation presents new developed planar microwave diodes, advanced techniques for investigating their properties, and ways for enhancing their detection properties. Five scientific papers were published on the topic of the dissertation: three papers in scientific journals included in the list of Clarivate Analytics Web of Science database with an impact factor, and two papers in conference proceedings included in the Clarivate Analytics Web of Science and Scopus databases. A European patent based on the results of the dissertation has been granted, and twelve reports, including the results of the dissertation, were presented at national and international scientific conferences.Doctoral dissertatio
Research on multilayer semiconductor and dielectric microwave devices
No full textDisertacijoje tiriami daugiasluoksniai puslaidininkiniai ir dielektriniai mikrobangų įtaisai, sprendžiama puslaidininkinių mikrobangų įtaisų tobulinimo, juose sklindančių elektromagnetinių bangų dažninių charakteristikų tyrimo bei prognozavimo problema. Disertacijos tyrimų objektas – daugiasluoksniai puslaidininkiniai ir dielektriniai mikrobangų įtaisai ir jų charakteristikų analizės bei prognozavimo metodai.
Darbe sprendžiami uždaviniai: daugiasluoksnių puslaidininkinių ir dielektrinių mikrobangų įtaisų struktūrų kūrimas ir patobulinimas, daugiasluoksniuose puslaidininkiniuose ir dielektriniuose mikrobangų įtaisuose sklindančių elektromagnetinių bangų fazės ir silpimo charakteristikų, mikrobangų įtaisų parametrų apskaičiavimas ir ištyrimas, valdomų daugiasluoksnių puslaidininkinių ir dielektrinių mikrobangų įtaisų dažninių charakteristikų prognozavimas, pritaikant dirbtinių neuronų tinklus.
Disertaciją sudaro įvadas, 4 skyriai, bendrosios išvados, naudotos literatūros ir šaltinių sąrašas bei autoriaus publikacijų disertacijos tema sąrašas.
Įvade nagrinėjama tyrimo problema, aptariamas darbo aktualumas, pateikiamas tyrimų objektas, darbo tikslas, iškeliami uždaviniai. Taip pat pristatoma darbo metodika, darbo mokslinis naujumas, rezultatų praktinė reikšmė, ginamieji teiginiai, pateikiama darbo rezultatų aprobavimo informacija.
Pirmajame skyriuje pateikiama šaltinių disertacijos tema analizė, nagrinėjamos daugiasluoksnių mikrobangų įtaisų struktūros, įtaisuose naudojamos medžiagos, tyrimų metodika, formuojami darbo uždaviniai.
Antrajame skyriuje aptariamas kintamųjų parametrų daugiasluoksnių mikrobangų įtaisų modeliavimas ir pateikiama įtaisų analizė. Atliekamas mikrojuostelinio juostinio filtro ant puslaidininkinių padėklų dažninių charakteristikų tyrimas ir plokštelinės antenos su įterpta medžiaga charakteristikų tyrimas.
Trečiajame skyriuje tiriama, kaip keičiasi daugiasluoksnių puslaidininkinių bangolaidžių fazės ir silpimo koeficientų dažninės charakteristikos keičiantis puslaidininkio krūvininkų tankiui, dielektriniam sluoksniui ar grafeno sluoksnio parametrams.
Ketvirtajame skyriuje tiriamos daugiasluoksnių puslaidininkinių ir dielektrinių mikrobangų įtaisų charakteristikų prognozavimo galimybės naudojant dirbtinius neuronų tinklus.
Disertacijos tema publikuoti 6 moksliniai straipsniai, iš jų 2 – mokslo žurnaluose ir 2 – konferencijų medžiagoje, įtrauktoje į CA Web of Science sąrašą, 2 – recenzuojamoje IEEE Xplore konferencijų medžiagoje. Disertacijos tema perskaityti 8 pranešimai, 7 – tarptautinėse mokslinėse konferencijose, iš jų 4 Lietuvoje ir 3 užsienyje, 1 – nacionalinėje mokslinėje konferencijoje.Daktaro disertacij
Žinių valdymo procesų vertinimas aukštojo mokslo institucijose
No full textIn the context of transformations, knowledge management appears to be an effective and efficient instrument for increasing sustainable organisational performance. Inappropriately formed knowledge strategies and selected knowledge management decisions might have destructive consequences for an organisation. Knowledge management can be analysed through a process-oriented approach that supports organisations in applying knowledge strategy for implementing a knowledge management cycle consisting of various knowledge management processes. Also, it can be viewed as a valuable instrument for evaluating a set of individual, organisational, and technological factors affecting the knowledge management cycle leading to improved organisational performance. Nevertheless, despite the potential benefits that can be realised by implementing the knowledge management cycle and the relatively significant number of studies pertaining to the knowledge management concept, there is a scarcity of research and a limited number of studies analysing how knowledge management processes can affect sustainable organisational performance in the higher education field, especially in such developing countries as Lebanon and Syria. The main purpose of this study was to develop and empirically approve a research model for evaluating knowledge management processes in higher education institutions operating in Lebanon and Syria that contribute to sustainable organisational performance. The research methods were scientific literature review, survey, expert evaluation, descriptive statistics, inferential statistics, and Partial Least Squares Structural Equation Modelling (PLS-SEM). The research model integrates individual (motivation, learning, and trust), organisational (motivation system, top management support, and organisational structure) and technological (ICT infrastructure and technologically-enabled social networks) factors influencing knowledge management processes (knowledge acquisition, storage, sharing, application, and creation), and assesses the influence of these processes on three indicators of sustainable organisational performance: innovation, quality and operational aspects. The findings revealed that the evaluation of individual, organisational and technological factors, specifically motivation, learning, trust, motivation system, top management support, organisational structure, ICT infrastructure, and technologically-enabled social networks, which are related to the knowledge management cycle involving five knowledge management processes (knowledge acquisition, storage, sharing, application, and creation), is significant to develop evaluation metrics for their consistent improvement, as well as the achievement of sustainable organisational performance in higher education institutions.Doctoral dissertatio
Sinchroninio variklio su nuolatiniais magnetais parametrų kitimo tyrimas modeliuojant magnetinį lauką
No full textThe dissertation deals with permanent magnet synchronous motors (PMSM) classical control theory and also by applying magnetic field theory approach. The purpose of the thesis is to create the mathematical model of the PMSM based on analytical equations of magnetic field accounting torque ripple, inductance distributions and back electromotive force, to develop the measurement system for direct measurement of magnetic flux density and to propose PMSM parameter estimation method. In order to solve the stated problem and reach the goal following main tasks of the thesis are formulated: create PMSM model based on the analytical equations of magnetic flux density; develop vector control method of PMSM and investigate it experimentally; develop PMSM parameter estimation method; develop and implement a magnetic flux density measurement system; perform experimental measurement of magnetic flux density of PMSM using the developed system.
The dissertation consists of the introduction, three chapters, general conclusions, references, and the list of scientific publications of the author on the topic of the dissertation. The introduction discusses the research problem, the relevance of the dissertation, the object of the research, formulates the aim and tasks, de- scribes the research methodology, the scientific novelty of the dissertation, de- fended statements and the practical value of the research findings. At the end of the introduction, the dissertation and the structure of the dissertation are provided. The first chapter reviews the PMSM design, rotor and stator types, magnetic field analytical solutions for predicting magnetic flux in the PMSM and magnetic field measurement systems. The second chapter presents an analysis of the following topics of PMSM’s magnetic field distribution: the field created only by the rotor (open-circuit) and the field created only by the stator (armature reaction). Next, the effect of the stator slot on the magnetic field distribution is analysed. Finally, the enhanced PMSM model concept is stated based on magnetic field analysis. The third chapter presents the magnetic flux density measurement systems and compares the experimental results with the simulation results obtained using the proposed enhanced PMSM model.
The main results of the dissertation were published in seven scientific publications: four in the Clarivate Analytics Web of Science database with an impact factor and three in other databases. The results were presented at eight scientific conferences.Doctoral dissertatio
Tvarios užstatytos aplinkos atnaujinimo metodas ir intelektinė sprendimų palaikymo sistema
No full textThis dissertation examines the sustainable renovation of a built environment. The object of the dissertation research is the process of creating an analytical recommendation method with а knоwlеdgе-bаsеd dесіsіon suрроrt sуstеm іntеgrаtеd wіth а multі-lауеr аrtіfісіаl nеurаl nеtwоrk, proposing an approach that provides obtained data from the architectural environment for making decisions and analysing all life cycles of it. The dissertation includes an introduction, three chapters, a research generalisation, a literature summary and the author’s publications on the dissertation topic.
The introduction discusses the research issues, the importance of the dissertation, the object of research, scientific novelty and research methodology. The introduction ends with a presentation of the author’s publications on the dissertation topic and the description of the dissertation structure.
The First Chapter gives a review of the literature on the sustainable built environment covering the period between 2015 and 2021, analyses methods of sustainability certification systems (e.g., BREEAM, LEED) and their inclusion in research related to sustainable valuation, and widespread use in the construction industry, provides existing methods of sustainability assessment for more holistic perspective in the assessment following the recommendations for performing the sustainable renovation.
The Second Chapter introduced a knowledge-based decision support system integrated with a multilayer artificial neural network for urbanisation in city construction. The chapter presents a method of a multivariant design and multiple criteria analysis of a building’s renovation (on the example of the building reconstruction in Kyiv, Ukraine). Multiple criteria analyses in the selected location were made to determine the emotional and rational market segments by demographic criteria (males and females), psycho-graphics and consumer behaviour criteria (e.g., happy, sad, angry, surprise and heart rate variability).
The Third Chapter covers how to measure the segmentation of crowd composition effects (by age and gender) and emotional and physiological indicators of potential buyers. This allows offering stakeholders rational, environmentally friendly and energy-efficient building alternatives. To achieve this goal, the developed multi-criteria analysis of neuromarketing and video advertising was used to create the required conditions. More than 200 million multisensory pieces of data were analysed. This experiment was performed on the example of energy-efficient buildings to demonstrate the developed method. The results presented in this chapter are confirmed by the results of worldwide research.
The research highlights were discussed at 5 scientific conferences; the key research study was presented in 3 research papers.Doctoral dissertatio
Virtualios komandos sprendimų priėmimą lemiančių veiksnių modeliavimas
No full textVirtual teams (VTs) are becoming increasingly popular in organizations due to their significant benefits, such as improving performance and efficiently achieving objectives. While VTs have many advantages, they also face many challenges that, if not addressed, may prevent them from delivering the desired results. Decision-making is an important issue hindering the effectiveness of VTs. Organizations may fail in implementing successful strategies when there are improper decisions among team members. Research is lacking in understanding decision-making in VTs in the Middle East, especially in such situations as the Covid-19 pandemic. The Middle East has been overlooked despite such studies being conducted in the United States and Europe. In the Middle East, VTs have some behavioral characteristics which make specific scientific solutions necessary. To gain scientific knowledge of Middle East specificities, this study is carried out in the region, taking UAE as a representative case. The objective of this research is to create a model for enhancing VT decision-making by evaluating the factors affecting decision-making in VTs in the Middle East. The methodology used is a literature review, survey methods, expert evaluation, and structural equation modeling.
The results showed that (1) decision-making is positively correlated with information sharing, trust, Transformational Leadership, Culture Intelligence, and task conflict, (2) decision-making is negatively correlated with Relationship Conflict (3) Language showed no correlation with VT decision-making. The findings of this study serve as a step toward future research into factors useful for improving VT-associated decision-making.Doctoral dissertatio
Informacinių ryšio technologijų sprendimų modeliavimas energetikos sektoriui valdyti
No full textThe modern world is facing challenges in the area of energy management. Information and Communication Technologies (ICTs) are among the most important tools for managing, monitoring, and improving energy consumption efficiency, provided they are implemented and used for this purpose. Not all countries are dealing with these issues successfully and effectively. Therefore, scientific and practical solutions based on region specifics are necessary. It is crucial to understand that energy management in modern theories does not only mean reducing energy consumption but also includes controlling and preventing energy loss. It also focuses on energy efficiency, the use of natural renewable and sustainable energy, energy recovery, and solar energy, which is the most abundant source next to wind energy, hydropower, ocean energy and bioenergy. Modern global energy consumption is drastically increasing since many factors determine the need. Important factors vary from socioeconomic to population increase, making the need for energy security and efficiency assurance essential to secure energy resources in the world in general and in developing countries specifically.
ICTs are spreading worldwide and affecting the global systems in many livelihood sectors. ICTs have a wide positive impact on huge economic and developmental factors, from increasing productivity to controlling and monitoring the systems. The importance of energy supply in developing countries and the possibilities brought by ICTs for their management are deniable. The role of innovation in the world is very important, as well as the possibilities that were brought by ICTs for their management to create solutions that positively affect sustainability. The dissertation aims to identify the factors determining the improvement of energy sector management with the help of ICTs in developing countries.Doctoral dissertatio
Research and creation of a semi-active damper-energy harvester system
No full textDisertacijoje nagrinėjama virpesių valdymo problema esant stochastiniams virpesiams. Pagrindinis tyrimo objektas – virpesių slopintuvas, kurio slopinimo valdymas grindžiamas magnetinio slopinimo ir energijos generavimo iš virpesių į elektros energiją. Disertacijos tikslas – sukurti virpesių slopintuvą su magnetinio slopinimo galimybe ir ištirti virpesių energijos generavimo bei virpesių valdymo galimybes.
Darbe sprendžiami keli uždaviniai: pasiūloma virpesių energijos generavimo į elektros energiją metodika tiesiniam slopintuvui ir nustatoma galimybė naudoti šį procesą virpesių slopinimui valdyti. Pirmasis uždavinys suformuluotas, nes, atlikus literatūros apžvalgą, nustatyta, jog virpesių energija nepanaudojama, nors jos kiekis yra svarbus šiuolaikinių sistemų maitinimui ir lengvai integruojamas į bendras prietaisų maitinimo sistemas. Antrasis siejasi su pirmuoju, nes virpesių slopinimo valdymas sunkiai įgyvendinamas ir reikalauja papildomos išorinės
energijos, tad šie du procesai galėtų būti sujungti.
Disertaciją sudaro įvadas, trys skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai.
Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas ir uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra.
Pirmasis skyrius skirtas literatūros apžvalgai. Jame pateikiama virpesių slopintuvų konstrukcijų, virpesių valdymo principai ir techninis realizavimas bei virpesių energijos generatorių apžvalga. Skyriaus pabaigoje formuluojamos išvados ir tikslinami disertacijos uždaviniai.
Antrajame skyriuje pateiktas viso automobilio dinaminis modelis, kuriame yra virpesių slopintuvas. Skyriuje taip pat pateikti magnetinio lauko simuliacijos modelis, kurio rezultatai leido suformuoti mechatroninio įrenginio modelio struktūrą ir pagaminti įrenginį.
Trečiajame skyriuje aprašyti virpesių slopintuvo eksperimentiniai tyrimai. Nurodoma naudojama įranga, eksperimentų metodika ir pateikti rezultatai, kurie leidžia įvertinti tiriamosios problemos sprendimo galimybes.
Disertacijos tema yra atspausdinti šeši moksliniai straipsniai, trys – mokslo žurnaluose, įtrauktuose į Clarivate Analysis Web of Science duomenų bazę su citavimo rodikliu sąrašą; trys – mokslo žurnaluose, įtrauktuose į kitas tarptautines duomenų bazes. Disertacijoje atliktų tyrimų rezultatai buvo paskelbti dviejose konferencijose užsienyje.Daktaro disertacij
Simulation of conflict situations between two-aircraft in flight considering deterministic and stochastic parameters
No full textDisertacijoje nagrinėjamos orlaivių konfliktinės situacijos. Pagrindinis tyrimo objektas yra dviejų skrendančių orlaivių konflikto situacijų modeliavimas, vertinant determinuotus ir stochastinius parametrus.
Darbe sprendžiami keli pagrindiniai uždaviniai: išanalizuoti naudojami orlaivių konfliktinių situacijų sprendimo metodai ir palyginti jų efektyvumai, ištirti dviejų orlaivių konfliktą aprašantys veiksniai, turintys įtakos skrydžių efektyvumui ir saugai, pasiūlytos naujos Dubinso ir 3HC algoritmų taikymo ribos, įvertinant saugos ir racionalaus maršruto parinkimo kriterijus, ir pritaikyta stochastinio uždavinio metodika orlaivių konflikto analizei. Po to, sukurtas programinis orlaivių konfliktų modeliavimo kodas įvertinant saugą ir racionaliai parenkant maršrutą.
Disertaciją sudaro įvadas, keturi skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašas.
Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas ir uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra.
Pirmasis skyrius skirtas literatūros apžvalgai. Jame pateikti orlaivių konfliktų sprendimo būdai / metodai, jų taikymo ribos, privalumai ir trūkumai. Aptarti orlaivių konfliktą aprašantys veiksniai, turintys įtakos skrydžių saugai ir efektyvumui. Skyriaus pabaigoje pateiktos išvados.
Antrajame skyriuje pateikta pasiūlyta Dubinso ir 3HC algoritmų metodika bei jos taikymo ribos, įvertinant saugos ir racionalaus maršruto parinkimo kriterijus, taip pat išvesta netiesinė lygtis apskritimo taškams apskaičiuoti bei judėjimui neapskritomis kreivėmis aprašyti.
Trečiajame skyriuje pasiūlyta nauja patikslinta orlaivių konflikto stochastinio uždavinio metodika.
Ketvirtajame skyriuje pasiūlytas stochastinis dviejų orlaivių konfliktinės situacijos modeliavimas taikant Dubinso skaitinį modelį neapibrėžtumo sąlygomis.
Disertacijos tema paskelbti 5 straipsniai: du – recenzuojamuose mokslo žurnaluose, įtrauktuose į Clarivate Analytics Web of Science duomenų bazės sąrašą, du – kitų tarptautinių duomenų bazių leidiniuose, vienas – recenzuojamoje tarptautinių konferencijų medžiagoje. Disertacijos tema perskaityti 6 pranešimai Lietuvos ir kitų šalių konferencijose.Daktaro disertacij