Vilnius Gediminas Technical University
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Photogrammetry-based model for the optimisation of construction-site planning
No full textDisertacijoje nagrinėjamas šių dienų aktualumas, kai reikalingas ekonomiškai naudingas ir patikimas visos statybvietės racionalus planavimas – statybos mechanizmų ir laikinosios infrastruktūros. Formuojamas šio mokslinio darbo tikslas – pagerinti statybos aikštelės planavimą, sukuriant statybvietės planavimo optimizavimo modelį, taikant fotogrametriją. Argumentuotai pasirenkamas labiausiai tinkamas statybvietės plano variantas, įvertinant esamą būklę bei projektinius sprendinius automatizuotu būdu.
Disertacijoje apibrėžiama metodika apima tik statybos inžinerijos mokslų sritį – statybos planavimą ir organizavimą – todėl informatikos inžinerijos mokslų sričiai būdingas sistemos prototipo kūrimas ir veikimo demonstravimas nėra atliekamas.
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 bei 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 matematinių modelių mokslinės literatūros, statybos planavimui skirtų programinių įrangų ir fotogrametrijos analizei. Skyriaus pabaigoje formuluojamos išvados ir tikslinami disertacijos uždaviniai.
Antrajame skyriuje sukuriamas statybvietės plano matematinis modelis, detaliai aprašant: esamos situacijos nustatymą, statybos mechanizmų ir laikinosios infrastruktūros poreikio nustatymą, statybvietės plano atvaizdavimo metodo parinkimą, statybvietės erdvinį planavimą ir optimizavimą. Poreikiui skaičiuoti reikalinga informacija gaunama iš esamos būklės fotogrametrinio modelio ir naujai statomo statinio BIM modelio. Galiausiai matematinis modelis leidžia atlikti racionalų statybos planavimą, įvertinant esa-mus ir naujai statomus statinius, užstatytus ar laisvus plotus, statybos mechanizmų ir laikinosios infrastruktūros poreikį.
Trečiajame skyriuje yra atliekama fotogrametrijos atvejo analizė. Sumodeliuojamas realybėje egzistuojančio statinio BIM modelis, sukuriamas jo fotogrametrinis modelis, nustatomas fotogrametrinio modelio tikslumas. Išbandomas matematinio modelio veikimo eiliškumas, atvaizduojant statybos mechanizmų ir laikinosios infrastruktūros parinkimą.
Disertacijos tema paskelbti šeši straipsniai. Disertacijos tema perskaityti septyni pranešimai Lietuvos bei kitų šalių konferencijose. Disertacijos rezultatai pristatyti dviejuose užsienio universitetų seminaruose.Daktaro disertacij
Rašalinio spausdinimo proceso tyrimas, įvertinant rašalo dinamiką ir specifinių spausdinimo paviršių savybes
No full textThe most well-known and commonly used printing techniques made the inkjet printing technology more popular among manufacturers for its simplicity and flexibility. Demand for printing products is increasing in such areas as textile printing, microchip production and personalised production, raising quality requirements. Thus, inkjet printing is continuously enhancing its capabilities. With the printing market expected to grow, there are many propositions to improve the productivity of inkjet process. The dissertation aims to study the dynamics of an inkjet droplet at different stages of its formation, considering its interaction with the surface to improve the quality and speed of high-class inkjet printing and improve inkjet printhead testing applications. The present dissertation reviews theoretical and numerical techniques of inkjet printing process modelling by applying the Computational Fluid Dynamics (CFD) module using the finite elements method. Inkjet printing inks are calculated as Newtonian fluid. The ink flow is modelled by the incompressible Navier–Stokes equations. The presented simulation model is solved using a level set method to determine the ink and air interface. Experimental investigation results are reported on the inkjet printing process colour reproduction on different linen fabrics, and modelling results are given for droplet ejecting, printing and interaction processes with the flat surface and the interaction with the inkjet droplet with physically treated polymer surfaces.
Based on systematic and analysed numerical simulations of research on the operation of inkjet printing heads, Article 1 describes the inkjet print-head models, which analyse how different inks impact droplet formation and movement at different time steps.
Article 2 presents an experimental realisation of colour reproduction by inkjet printing possibilities on different materials in different printing settings.
Article 3 presents the physical and numerical experiments on the impact characteristics of inkjet printhead droplets with flat surfaces. Different surface treatment methods were investigated to increase droplet adhesion with flat surfaces.
Article 4 investigates the numerical model of the print head modelled in three-dimensional space. Various parameters of drop formation and fall were experimentally determined with a change in the time of the excitation impulse. A numerical analysis was carried out regarding the influence of the excitation time on the droplet formation and further movement.
The supplemented articles were published in four peer-reviewed scientific journals listed in the Clarivate Analytics Web of Science database with an impact factor. The study results were presented at three international conferences.Doctoral dissertatio
Fotoninių metamedžiagų elektrodinaminis tyrimas
No full textThe dissertation investigates the possibilities of applying the Maxwell–Garnett approach for homogenising different types of metamaterial structures, such as conventional nanowires, spiral nanowires, and nanostructured composite cases. The research aims to study the dispersion maps of the surface plasmon polaritons (SPPs) propagating at different interfaces, such as metallic nanowire metamaterial interface and the hollow-core metamaterial interface, nanostructured metamaterial and corrugated metal interface, spiral nanowire metamaterial and air interface, nanocomposite and hypercrystal interface.
This dissertation aims to analyse the properties of the dispersion and loss of SPPs at the investigated interfaces, aiming to achieve absorption enhancement, enabling the possible creation of the aircraft coating model, and allowing for the cancellation along with the antenna systems. The dissertation enables to analyse system engineering tools, such as the angle of the spiral, the number of grooves, etc., aiming to conclude the tunability possibilities of the structure’s properties.
Relevant dispersion relations are derived by matching the tangential components of the electrical and magnetic fields. It is demonstrated that tuning can be achieved by modifying the parameters of the metamaterial building blocks. Moreover, the tunability of the nanowire metamaterials can be enhanced further by changing either the metamaterial filling ratio or metamaterial cell geometry. Calculated dispersion relations and propagation lengths of plasmon modes in the system are presented. It has been concluded that the frequency range of the surface waves’ existence can be significantly increased by dealing with the nanowire metamaterial interface. The possible application of the proposed tunable structures is in antenna and aircraft noise reduction system design.Doctoral dissertatio
Karštųjų krūvininkų reiškinio tyrimas ir panaudojimas fotovoltikoje
No full textThe dissertation analyses the direct impact of the hot carrier phenomenon on the operation of a single-junction solar cell. Ways to suppress the influence of the hot carrier effect are determined based on the achieved results. The structure of the ratchet-based sensor operating on the hot carrier effect is modelled, and its prototype is produced.
The dissertation includes an introduction, three main chapters, general conclusions, a list of used references, and the author’s publications related to the dissertation topic.
The first chapter is an overview of the literature on the dissertation topic. This chapter observes the basic parameters of solar cells and possible losses. The structures of the first and second generation of solar cells are reviewed. Modern structures of third-generation solar cells that can minimise spectral losses are analysed. The last paragraph explains the formation of the hot carrier photocurrent under the action of infrared light in various semiconductor structures.
The second chapter represents methodologies used to achieve the obtained results. The chapter describes the manufacturing technology of the samples, the method of detecting the photo signal, the selected computer software and the arrangement of the experimental setup.
The third chapter gives an overview and explanation of the achieved results. The chapter analyses the hot carrier phenomenon’s peculiarities and describes how to suppress its influence in a single junction solar cell. The chapter presents a modelled structure and the developed prototype of an electromagnetic radiation sensor operating based on the hot carrier effect.
The results of the dissertation have been reported in fourteen scientific publications. Three of them have been published in journals with refereed Clarivate Analytics Web of Science databases refereed journals with a citation index, one in conference proceedings, and ten peer-reviewed in other scholarly journals. The author has made eight presentations at international, regional and local scientific conferences and symposiums.Doctoral dissertatio
ES bendrosios žemės ūkio politikos tiesioginių išmokų įtakos žemės ūkio ekonominiam atsparumui vertinimas
No full textAgriculture’s resilience has been identified as one of the main priorities of the 2023–2027 Common Agricultural Policy agenda (EU Commission, 2020), as it is widely accepted that resilience is a key pre-condition for the sector’s sustainable development. The goal of resilience growth necessitates an objective evaluation of resilience changes and the estimation of the impact (possibly) made by various factors on resilience. However, the concept of resilience is still very ambiguous, lacking a universally agreed methodology for its evaluation and empirical evidence on how to support policies that influence agriculture’s economic resilience. Therefore, the dissertation aimed to assess the impact of direct payments on the economic resilience of agriculture. The study resulted in an integrated index of the direct payments’ impact on agriculture’s economic resilience.
The following main tasks were resolved during the study: the analysis of the scientific literature was performed to study the nature, development, measurement, and use of the resilience concept and, subsequently, to apply it to the assessment of agriculture’s resilience; the existing research on the assessment of direct payments’ impact on individual agricultural indicators was systematized; a set of indicators reflecting agriculture’s economic resilience was formed; a theoretical model for the assessment of the direct payments’ impact on agriculture’s economic resilience was created; and its practical adaptability was verified at the level of the EU-27, the OMS-15 and the NMS-12 in 2005–2019.
The dissertation consists of an introduction, three chapters, general conclusions, references, and a list of the author’s publications on the topic of the dissertation. The first chapter presents the analysis of the resilience concept, its operationalization and measurement, and the rationale for integrating the resilience construct in the agricultural context. Also, it provides a developed theoretical model of the direct payments’ impact on agriculture’s economic resilience. The second chapter presents the theoretical model for assessing the direct payments’ impact on agriculture’s economic resilience and the description of its elements. The third chapter presents the empirical results of the model application in the EU-27, the OMS-15, and the NMS-12. The obtained results were used to formulate conclusions and proposals on how to improve the system of direct payments support.
Six scientific articles were published on the topic of the dissertation; presentations were made at two international scientific conferences; and an internship took place at the University of Łódź (Poland), where the results of the dissertation were presented.Doctoral dissertatio
Žinių valdymo procesų vertinimas audito ir konsultavimo įmonėse
No full textThe doctoral dissertation examines knowledge management processes and their effect on sustainable organisational performance, also the impact of human (trust, interaction and self-efficacy), organisational (rewards, organisational culture, teamwork and organisational structure) and technological factors (information technology and social networks) on the knowledge management cycle including five processes (acquisition, creation, storage, sharing and application), focusing on the knowledge-intensive field of auditing and consultancy, which lacks research of knowledge management processes in the developing economies of the Mid-East region (Lebanon, Syria, and Jordan). The dissertation aims to measure knowledge management processes in auditing and consultancy firms by creating a model allowing for a complex assessment of different human, organisational, and technological factors affecting the processes and forming decisions to enhance the process implementation in auditing and consultancy firms to improve sustainable organisational performance. Scientific literature analysis, expert evaluation, and structural equation modelling (SEM) techniques were used to test the hypothesised research model and analyse the relationship between the variables. The empirical study results proved the significant and positive effects of knowledge management processes on sustainable organisational performance. It determined significant positive effects of trust, interaction, self-efficacy, rewards, organisational culture, teamwork, organisational structure, information technology, and social networks on the knowledge management processes cycle. Some exceptions were related to the effects of interaction on knowledge sharing, rewards on knowledge application, organisational culture on knowledge acquisition, information technology on knowledge acquisition, and social networks on knowledge application. Based on the results, the model for measuring knowledge management processes was created for auditing and consultancy firms. Similar organisations operating in the knowledge-intensive sector would also benefit from considering the positive association between knowledge management processes and sustainable organisational performance and the demonstrated positive effects of specific factors on the knowledge management cycle. These practical implications are relevant to a wider culture that guides sustainable organisational performance to the members and stakeholders of organisations, which, in turn, benefits society and contributes to the improvement of developing economies.Doctoral dissertatio
Research of the combustion process in a compression ignition engine fuelled with liquid and gaseous biofuels
No full textDisertacijoje nagrinėjamas dviejų rūšių biodegalų (skystųjų ir dujinių) naudojimo slėginio uždegimo vidaus degimo variklyje efektyvumas, lyginant su iškastiniais degalais, dujas tiekiant kartu su įsiurbiamu oru ir jas uždegant, į cilindrą tiesiogiai įpurškus skystuosius degalus. Pagrindinis tyrimų objektas – dviejų rūšių biodegalų (biodujų ir antros kartos biodyzelino) degimo procesas tiesioginio įpurškimo slėginio uždegimo variklyje, biodujas tiekiant į įsiurbimo kolektorių. Disertacijos tikslas – eksperimentiškai ir teoriškai ištyrus skirtingais dviejų rūšių biodegalais veikiantį slėginio uždegimo variklį, nustatyti dujinių degalų energinės dalies,
įpurškimo pradžios momento ir deginių recirkuliacijos (DR) poveikį degimo procesui bei energiniams ir ekologiniams rodikliams. Darbe sprendžiami keli pagrindiniai uždaviniai: eksperimentiškai ištirti degiajame mišinyje esančios dujinių degalų energinės dalies įtaką slėginio uždegimo (SU) variklio energiniams ir ekologiniams rodikliams. Remiantis SU variklio rodiklių pokyčio teorine analize ištirti skirtingos dujinių degalų energinės dalies įtaką degimo procesui
esant įvairioms variklio apkrovoms. Remiantis teorinių ir eksperimentinių tyrimų rezultatais pasiūlyti rekomendacijas dviejų rūšių biodegalų sudėčiai, skystųjų degalų įpurškimo pradžios momentui ir DR naudojimo efektyvumui nustatyti.
Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai.
Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, pateikiama tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertaci-jos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra.
Pirmajame skyriuje apžvelgti moksliniai straipsniai disertacijos tema ir dviejų rūšių degalų naudojimą skatinantys veiksniai. Formuluojamos skyriaus išvados ir tikslinami disertacijos uždaviniai.
Antrajame skyriuje pateikiama dviejų rūšių degalų naudojimo SU variklyje tyrimo metodika, naudota įranga bei ekologinių ir energinių rodiklių skaičiavimo metodika.
Trečiajame skyriuje pateikti dviejų rūšių degalų naudojimo slėginio uždegimo variklyje eksperimentinių tyrimų ir skaitinio modeliavimo rezultatai.
Disertacijos tema paskelbti 7 moksliniai straipsniai: 2 – mokslo žurnaluose, įtrauktuose į Clarivate Analytics Web of Science duomenų bazę su citavimo rodikliu, 1 – Clarivate Analytics Web of Science duomenų bazės „Conference Proceedings“ leidinyje, 1 – kitų tarptautinių duomenų bazių leidinyje, 3 – kituose recenzuojamuose mokslo leidiniuose. Disertacijoje atliktų tyrimų rezultatai buvo paskelbti trijose mokslinėse konferencijose Lietuvoje ir Lenkijoje.Daktaro disertacij
Gamybos produktyvumas tvariosios žemės ūkio plėtros kontekste
No full textSustainable agricultural development is one of the most important policy goals in the European Union. Agricultural production and its intensification cause a negative impact on the environment, including climate change. The main goal of sustainable agricultural development is to increase agricultural productivity, reducing the negative impact of this production on the environment. As climate change is one of the most important environmental challenges for sustainable agricultural development, productivity growth should be assessed by introducing greenhouse gas (GHG) emission restrictions. Thus, when evaluating agricultural productivity, it is imperative to simultaneously assess and restrict undesirable production outputs, such as GHG emissions, thus ensuring sustainable agricultural productivity growth.
Extensive scientific research has been done on agricultural productivity and sustainable agricultural development; however, scientists lack consensus regarding undesirable outputs, such as GHG emissions assessments, when studying the efficiency and productivity of agricultural production. Assessing agricultural productivity in sustainable agricultural development requires identifying and assessing environmental constraints, especially related to integrating climate change mitigation into the production function, which is a complex task.
This work aimed to develop methods for evaluating agricultural productivity in the context of sustainable agricultural development. The goal of the dissertation is to develop a model for assessing productivity with undesirable outputs and to apply it for sustainable productivity assessment in agriculture in the EU. The dissertation reviews productivity evaluation methods and discusses various models, emphasising evaluations of undesirable production outputs in the production function.
A new model for evaluating agricultural production with undesirable results was developed based on an expanded production function that includes the main factors of agricultural production (energy consumption in agriculture, capital, labour and land costs in agriculture) and GHG emissions related to energy consumption in agriculture. The new model allows for a new expansion and use of DEA capabilities in the production function, supplementing it with the global slacks-based method (SBM) for efficiency measurement, the Luenberger productivity index, the index of contribution to structural efficiency with the help of which all production factors and GHG emissions can be analysed and studied in detail and the contribution of GHG emissions to overall changes in efficiency and productivity can be evaluated.Doctoral dissertatio
Žemės ūkio ekonominio rezultatyvumo vertinimas struktūrinių pokyčių kontekste
No full textStrategic management decisions in regulating any economic sector require an integrated methodology for assessing its performance. The main sources of total factor productivity growth in agriculture include improving agricultural practices and ensuring optimal input intensities. A total factor productivity analysis is closely related to the problem of productivity measures and data sources. Multiple factors often characterise a particular activity, and aggregation is needed to capture the available information.
Lithuania’s agriculture has seen transformations related to the EU accession, especially implementing the common agricultural policy (CAP). Public support is often given to maintain the quality of environmental protection by increasing the provision of services, ensuring food affordability and promoting technological progress. Agricultural total factor productivity studies can help determine whether the performance of the agricultural sector is improving due to public support measures or other factors.
Following scientific research examining the productivity analysis of farmers’ farms, the dissertation aims to create a methodology for assessing agricultural performance and to apply it to assess selected EU countries at various aggregation levels.
A total factor productivity assessment method was developed to assess the main trends determining agricultural productivity growth and apply the obtained results to international comparisons. An analysis of a total factor productivity growth was performed using different calculation methods.
Differences in the agricultural labour productivity were decomposed in terms of land and labour endowments and intermediate consumption. This allows shedding more light on the development of the agricultural sectors of the Baltic States from the viewpoint of labour productivity.
The analysis showed structural changes and production growth in the agricultural sectors of selected countries. New technologies and production practices are being applied in the agricultural sector, and the average farm size and farming specialization are changing. As a result of these changes, relative input and output prices and farm incomes have changed.Doctoral dissertatio
Termomechaninė skaitinė mikrodalelės smūgio vertinant sparčiąsias deformacijas analizė
No full textThe design of materials with desired properties is a challenge for most industries. It has become even more critical with the innovations in additive manufacturing (AM) and 3D printing technologies allowing for higher resolution of the metal parts’ topology.
The impact between particles and the material surface is a micro-scaled physical phenomenon found in various technological processes and while studying the mechanical properties of materials. High-velocity interaction between particles and non-flat surfaces is relevant to processes occurring in AM, such as cold spray CS.
The dissertation aimed to study strain-rate-dependent plasticity at a wide range of strain rates. Particular cases of the axisymmetric particle-substrate contact were simulated using an elastic material model and different plasticity models (PM). The problem is approached by numerical simulation applying finite element analysis (FEA) using strain, strain-rate, and temperature-dependent plasticity models.
The investigated problem was high-rate elastic-plastic deformation of the micro-sized copper particle impacting against a copper substrate. The thermomechanical FEA was performed using selected PM. The performance of the strain-rate-dependent Johnson–Cook (J–C), Cowper–Symonds (C–S) and strain-rate-independent Ludwig models was studied by comparing displacements, velocities, strains, strain rates, stresses, contact forces, temperatures, and their contribution to material yield stress. The study has shown the importance of the high-strain-rate PM and its adequacy to experimental data. Both rate-dependent models complement each other and may be regarded as soft and hard bounds of the solution.
The new two-function combined model containing two independent functions for each of the two regimes was suggested. The proposed model describes a low strain-rate sensitivity regime using the modified J–C expression while allowing to fit the model for experimental results in a high strain-rate sensitivity regime using the modified C–S expression. This combination can describe both low- and high-strain-rate regimes giving the minimum deviation from experimental results. The performance of the new plasticity model was investigated in elastoplastic particle impact and dynamic indentation simulations. The new model shows an equal contribution of strain and strain rate hardening during impact.
Additionally, the dissertation addresses normal contact interaction between particles and spherical surfaces. Here, the focus is on showing the contribution of colliding particle radii to interaction parameters. The results include contact duration, contact surface area, displacement, heat energy, stress, and strain rate.Doctoral dissertatio