Vilnius Gediminas Technical University
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Įtemptomis CFRP juostomis sustiprintų lenkiamųjų gelžbetoninių elementų elgsenos analizė
No full textThe use of fibre reinforced polymer (FRP) materials for the strengthening of reinforced concrete structures has many benefits in comparison to the traditional strengthening methods. Such reinforcements are lighter, easier to install, they will better meet aesthetical design and anticorrosion/durability requirements. The full potential of such high strength materials can be exploited by prestressing. This way, the deflection of the element will be reduced and the concrete cracking and steel yield loads will be increased. However, the use of FRP’s for strengthening may cause lots of issues for civil engineers regarding the appropriate evaluation of strengthened structures work, and technological issues during prestressing.
While the concrete member is uncracked, both elements deform together and it can be considered as a full composite action. However, after concrete cracking, stress concentrations appear at the cracks and it reduces the contact stiffness of concrete and FRP. Afterwards, the slip occurs in the contact surface, what leads to a sudden and brittle FRP debonding failure mode. These are the most common failure modes. Therefore, a number of studies have been conducted on debonding like failure modes. However, the failure criterion or fracture energy values in the models found in the literature were derived from experimental narrow parametric scope pull-off / pull-out shear tests, while the bond behaviour and this criterion could be different for strengthened flexural reinforced concrete members with long bond lengths. It should also be noted that the effect of concrete-FRP partial shear connection is usually ignored in the assessment of element deformations.
Considering the state of the art, a new analytical calculation model for the evaluation of concrete-FRP partial shear connection is proposed. Also, alternative new calculation techniques for the determination of the load carrying capacity, deflection, and cracking of the FRP strengthened RC members, taking into account FRP prestressing and concrete-FRP partial shear connection effects. Thus, the current thesis not only effectively evaluates the possible premature failure of the element, but also evaluates the full operation of concrete-FRP partial shear connection joint and its influence on the element deformations.
Furthermore, a novel prestressing system for externally bonded FRP laminates is proposed in response to the technological challenges of prestressing.Doctoral dissertatio
Numerical Modeling of the Motion and Interaction of a Droplet of an Inkjet Printing Process with a Flat Surface
No full textThe numerical simulation and analysis of the ejection of an ink droplet through a nozzle as well its motion through air until its contact with a surface and taking up of a stable form is performed. The fluid flow is modeled by the incompressible Navier–Stokes equations with added surface tension. The presented model can be solved using either a level set or a phase field method to track the fluid interface. Here, the level set method is used to determinate the interface between ink and air. The presented work concentrates on the demonstration how to check the suitability of ink for inkjet printhead nozzles, for instance, for the use in printers. The results such as velocity, change of size, and volume dependence on time of an ink droplet are presented. Recommendations for the use of specific inks are also given.The research was funded by the Vilnius Gediminas Technical University (VGTU)
MULTIMOORA under Interval-Valued Neutrosophic Sets as the Basis for the Quantitative Heuristic Evaluation Methodology HEBIN
Get PDFDuring the last decade, researchers put a lot of effort into the development of the multi-criteria decision methods (MCDM) capable of dealing with the uncertainty and vagueness of the initial information. MCDM approaches that work under the environment of the interval-valued neutrosophic sets (IVNS) demonstrate credibility for the analysis of different opinions as well as for the inconsistency of the criteria evaluation data. The novel multicriteria decision-making approach MULTIMOORA-IVNS (multi-objective optimisation by ratio analysis under interval-valued neutrosophic sets) is presented in this paper. A novel heuristic evaluation methodology HEBIN (heuristic evaluation based on interval numbers) that exploits MULTIMOORA-IVNS for the processing of the evaluation results is also presented in this research. HEBIN is able to increase the accuracy of the checklists-based heuristic evaluation and to diminish the impact of the inconsistencies caused by the evaluators. A comparison of six e-commerce websites is introduced to reveal the practicalities of the proposed multicriteria decision-making application.This article belongs to the Special Issue Multiple Criteria Decision Makin
Method of Singular Integral Equations for Analysis of Strip Structures and Experimental Confirmation
No full textThis paper presents a rigorous solution of the Helmholtz equation for regular waveguide structures with the finite sizes of all cross-section elements that may have an arbitrary shape. The solution is based on the theory of Singular Integral Equations (SIE). The SIE method proposed here is used to find a solution to differential equations with a point source. This fundamental solution of the equations is then applied in an integral representation of the general solution for our boundary problem. The integral representation always satisfies the differential equations derived from the Maxwell’s ones and has unknown functions μe and μh that are determined by the implementation of appropriate boundary conditions. The waveguide structures under consideration may contain homogeneous isotropic materials such as dielectrics, semiconductors, metals, and so forth. The proposed algorithm based on the SIE method also allows us to compute waveguide structures containing materials with high losses. The proposed solution allows us to satisfy all boundary conditions on the contour separating materials with different constitutive parameters and the condition at infinity for open structures as well as the wave equation. In our solution, the longitudinal components of the electric and magnetic fields are expressed in the integral form with the kernel consisting of an unknown function μe or μh and the Hankel function of the second kind. It is important to note that the above-mentioned integral representation is transformed into the Cauchy type integrals with the density function μe or μh at certain singular points of the contour of integration. The properties and values of these integrals are known under certain conditions. Contours that limit different materials of waveguide elements are divided into small segments. The number of segments can determine the accuracy of the solution of a problem. We assume for simplicity that the unknown functions μe and μh, which we are looking for, are located in the middle of each segment. After writing down the boundary conditions for the central point of every segment of all contours, we receive a well-conditioned algebraic system of linear equations, by solving which we will define functions μe and μh that correspond to these central points. Knowing the densities μe, μh, it is easy to calculate the dispersion characteristics of the structure as well as the electromagnetic (EM) field distributions inside and outside the structure. The comparison of our calculations by the SIE method with experimental data is also presented in this paper.This article belongs to the Section Mathematical Physic
The interaction of artistic forms and rein-forced concrete technologies in Lithuanian architecture
No full textDisertacijoje nagrinėjama meninių formų ir gelžbetonio technologijų sąveika Lietuvos architektūroje, koncentruojantis į XX a. antros pusės kūrinius. Tyrimo objektas yra tokios meninės formos, kurių pagrindines idėjas išreiškia struktūrinės ir / ar dekoratyvios inovacijos, susijusios su betonu. Disertacijos tikslas yra nustatyti meninių formų ir gelžbetonio technologijų sąveikos ištakas, išraiškas ir aktualią betono architektūros kultūrinę vertę, pasitelkus dviejų lygių teorinį modelį.
Norint pasiekti užsibrėžtą tikslą, darbe sprendžiami šie uždaviniai: suformuluojamas aktualus meninės formos ir gelžbetonio technologijų sąveikos apibrėžimas; nustatomos estetinės-technologinės inovacijos, lėmusios betono architektūros ištakas ir raidą; sąveikos specifikai tirti sudaromas teorinis modelis, kuris padeda identifikuoti estetinius-technologinius formos sudarymo principus ir ištirti specifinius ir kultūrinę vertę nurodančius sąveikos bruožus XX a. antros pusės Lietuvos architektūros objektuose; apibendrinamas sąveikos specifiškumas ir vertingųjų objektų / elementų saugojimo galimybės bei apžvelgiamos naujausios sąveikos reiškinio formos.
Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados, naudotos literatūros ir šaltinių bei autorės publikacijų disertacijos tema sąrašai ir keturi priedai.
Pirmasis skyrius yra teorinis, skirtas atskleisti meninių formų ir technologijos ryšį, identifikuoti betono architektūros ištakas ir estetines-technologines inovacijas, skatinusias tokios architektūros raidą. Taip pat nagrinėjami aktualūs tyrimai ir metodikos susijusios su betono architektūra, kurie padeda suformuluoti teorinį sąveikos specifiškumą nustatantį aspektų ir jų indikatorių tinklą. Antrajame skyriuje, pagal pasiūlytą metodiką, tiriamos naujos sąveikos formos Lietuvos architektūroje. Tiriamos keturios pastatų grupės pagal estetinį-technologinį formos sudarymo principą: vientisi erdviniai kevalai ir klostės; modulinė tektonika ir architektūrinis betonas; mišrios formos; vertikalūs apgyvendinimo modeliai. Trečiajame skyriuje aptariami saviti ir specifiniai sąveikos požymiai, būdingi XX a. antros pusės Lietuvos betono architektūrai; išryškinami betono architektūros, kaip modernaus paveldo objekto iššūkiai, įvertinamos teorinio modelio galimybės sprendžiant modernaus paveldo problemas bei aptariamos naujausios meninių formų ir gelžbetonio technologijų sąveikos tendencijos.
Disertacijos tema yra paskelbti septyni moksliniai straipsniai recenzuojamuose mokslo žurnaluose: vienas iš jų referuojamas „Web of Science”, du – „Scopus“ duomenų bazėse, trys iš jų – užsienio žurnaluose ir leidiniuose, anglų kalba. Disertacijos tyrimo eiga ir rezultatai pristatyti šešiuose pranešimuose nacionalinėse ir tarptautinėse mokslinėse konferencijose.Daktaro disertacij
Effective Management of Energy Consumption during the COVID-19 Pandemic: The Role of ICT Solutions
No full textThis research tackles effective and functional management practices in energy consumption using advanced technological solutions to mitigate unexpected events. This study specifically focuses on the recent COVID-19 pandemic that led to a reduction in energy consumption and therefore meddled with the project management’s status quo for the energy sources. Moreover, this research analyzes the role of information and communication technology (ICT) solutions in energy management before and after the recent coronavirus pandemic turmoil. This study also examined the role and place of sustainable energy resources in the effective management of energy consumption during the COVID-19 pandemic. The main purpose of this research is to demonstrate how the recent coronavirus pandemic affected energy consumption and energy prices in many countries and how it paved the way for the new ICT in managing energy consumption. This study elaborated a model to show how these changes evolved in selected European Union (EU) Member States. It turns out that adjusted electricity consumption, as well as the average daily spot electricity prices for the baseload power in the EU countries, declined, and this trend is likely to continue in the next years to come. Due to the COVID-19 pandemic, substantial changes in the economy led to reduced office space usage, cutting commuting and business trips, and bringing commercial travel almost to a halt, further shifting the energy balance towards renewable energy sources (RES). Besides, it becomes apparent that ICT solutions used in maintaining and superintending the energy balance are gaining popularity and wide recognition worldwide and will help pave the way towards modern and smart high-renewables grids.This article belongs to the Special Issue Knowledge and Project Management Peculiarities in Energy Sources and Energy Consumptio
Study of Indicators of CI Engine Running on Conventional Diesel and Chicken Fat Mixtures Changing EGR
No full textThis article presents a change in the indicators of a compression ignition (CI) engine by replacing conventional diesel fuel (D100) with pure chicken fat (F100) and mixtures of these fuels. Mixtures of diesel and fat with volume ratios of 70/30, 50/50 and 30/70 were used. Research of the fuel properties was conducted. In order to reduce the fuel viscosity, blends of fat and diesel were heated. The experimental research was conducted at different engine loads with exhaust gas recirculation (EGR) both off and on. The conducted analysis of the combustion process revealed a significant change in the rate of heat release (ROHR) when replacing diesel with chicken fat. Chicken fat was found to increase the CO2 and CO emissions, leaving hydrocarbon (HC) emissions nearly unchanged. Having replaced the D100 with diesel and chicken fat mixtures or F100, a significant reduction in smoke and nitrogen oxide (NOx) emissions was observed when EGR was off. When EGR was on, the smoke level increased, but the blends with chicken fat reduced it significantly, and the increased fat content in the fuel mixture reduced the NOx emissions. The engine’s brake specific fuel consumption (BSFC) increased while the brake thermal efficiency (BTE) decreased, having replaced conventional diesel with chicken fat due to differences in the fuel energy properties and the combustion process.This article belongs to the Special Issue Applications of Alternative Fuel
Project Portfolio Construction Using Extreme Value Theory
No full textChoosing proper projects has a great impact on organizational success. Firms have various factors for choosing projects based on their different objectives and strategies. The problem of optimization of projects’ risks and returns is among the most prevalent issues in project portfolio selection. In order to optimize and select proper projects, the amount of projects’ expected risks and returns must be evaluated correctly. Determining the relevant distribution is very important in achieving these expectations. In this research, various types of practical distributions were examined, and considering expected and realized risks, the effects of choosing the different distribution on estimation of risks on construction projects were studied.This article belongs to the Special Issue Sustainable Decision Making in Civil and Construction Engineerin
Hexapod Robot Gait Switching for Energy Consumption and Cost of Transport Management Using Heuristic Algorithms
No full textDue to the prospect of using walking robots in an impassable environment for tracked or wheeled vehicles, walking locomotion is one of the most remarkable accomplishments in robotic history. Walking robots, however, are still being deeply researched and created. Locomotion over irregular terrain and energy consumption are among the major problems. Walking robots require many actuators to cross different terrains, leading to substantial consumption of energy. A robot must be carefully designed to solve this problem, and movement parameters must be correctly chosen. We present a minimization of the hexapod robot’s energy consumption in this paper. Secondly, we investigate the reliance on power consumption in robot movement speed and gaits along with the Cost of Transport (CoT). To perform optimization of the hexapod robot energy consumption, we propose two algorithms. The heuristic algorithm performs gait switching based on the current speed of the robot to ensure minimum energy consumption. The Red Fox Optimization (RFO) algorithm performs a nature-inspired search of robot gait variable space to minimize CoT as a target function. The algorithms are tested to assess the efficiency of the hexapod robot walking through real-life experiments. We show that it is possible to save approximately 7.7–21% by choosing proper gaits at certain speeds. Finally, we demonstrate that our hexapod robot is one of the most energy-efficient hexapods by comparing the CoT values of various walking robots.This article belongs to the Special Issue Modelling and Control of Mechatronic and Robotic System
Development and research of an adaptive control system for an autonomous road vehicle
No full textDisertacijoje nagrinėjami autonominių sausumos kelių transporto priemonių judėjimo dėsningumai, kai judėjimo valdymui yra naudojamos skirtingos valdymo sistemos. Autonominės kelių transporto priemonės valdymo sistemos kūrimas susideda iš tokių uždavinių sprendimo, kaip duomenų apdorojimo sistemos, judėjimo maršruto planavimo ir valdymo algoritmų kūrimas. Nors vienam iš valdymo sistemą sudarančių algoritmų veikiant nepakankamai patikimai, daugeliu atvejų nebus galima užtikrinti saugaus, tikslaus ir stabilaus autonominės kelių transporto priemonės judėjimo. Dėl šios priežasties patikimas valdymo sistemos veikimas yra vienas iš svarbiausių veiksnių, nuo kurio priklausys sklandus autonominių kelių transporto priemonių integravimas į transporto priemonių eismą.
Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados, naudotos literatūros sąrašas, autoriaus publikacijų disertacijos tema sąrašas ir trylika priedų.
Įvadiniame skyriuje įvardijama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, suformuluojamas darbo tikslas ir uždaviniai. Taip pat aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo re-zultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pateikiamos disertacijos tema autoriaus paskelbtos publikacijos, pranešimai mokslinėse konferencijose ir seminaruose bei disertacijos struktūra.
Pirmajame skyriuje yra pateikiama su disertacijos tema susijusių mokslinių darbų apžvalga. Aprašoma autonominių kelių transporto priemonių klasifikavimo sistema, analizuojami matematiniai modeliai, judėjimo maršrutų planavimo ir valdymo algoritmai, kurie yra taikomi kuriant autonominių kelių transporto priemonių valdymo sistemas.
Antrajame skyriuje aprašomas judėjimo maršrutų planavimo ir valdymo algoritmų, taip pat neadaptyvios ir adaptyvios valdymo sistemų kūrimas.
Trečiajame skyriuje pateikiama eksperimentinių tyrimų metodika, aprašomas sukurtas pirmojo lygio autonominės kelių transporto priemonės prototipas ir jame panaudota nuoseklioji duomenų perdavimo sąsaja. Atliekama eksperimentinių važiavimų metu gautų duomenų analizė.
Disertacijos tema yra paskelbti aštuoni moksliniai straipsniai: du – mokslo žurnaluose įtrauktuose į Clarivate Analytics Web of Science duomenų bazę, du – kitų duomenų bazių mokslo žurnaluose, keturi – recenzuojamose tarptautinių konferencijų medžiagose.Daktaro disertacij