Vilnius Gediminas Technical University
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Gembinių pjezoelektrinių energijos surinkimo sistemų su netaisyklingais skerspjūviais tyrimas
Get PDFA dissertation analyses the problems of increasing an output power of piezoelectric energy harvesters based on single cantilever and cantilever arrays.
The main aim of dissertation is to propose a method to increase an output energy density and power density of piezoelectric layer of cantilever type energy harvester by introducing irregular cross section of the cantilever and rigidly composed cantilevers in cantilever arrays.
The dissertation covers a review of the most relevant scientific literature, numerical and experimental investigations of piezoelectric energy harvesters based on cantilevers with different irregular cross-sections and cantilever arrays based on rigidly composed cantilevers.
The dissertation consist of introduction, three chapters, general conclusions, references, list of scientific publications published by the author of the topic of dissertation and three appendixes. The introduction covers problem relevance, formulation of the goals and objectives, introduces novelty of the dissertation and overviews the dissertation structure.
The first chapter describes background and motivation of mechanical vibrations energy harvesting, an overviews the main mechanical vibrations energy harvesting technologies and their operation principles.
The second chapter is related to numerical and experimental investigations of piezoelectric energy harvesters based on rectangular and trapezoidal cantilevers with irregular cross-sections. The cross-sections of cantilevers were modified by rectangular, cylindrical and trapezoidal gaps. Electrical and mechanical characteristics of the piezoelectric cantilevers were analysed while different shape gaps were used.
The third chapter presents numerical and experimental investigations of polygon type piezoelectric energy harvesters. Three different designs of the cantilever arrays introduced and investigated i. e. rectangular, saw-tooth and polygon type. The investigation reveals influence of rigidly composed cantilevers and irregular cross-sections to electrical and mechanical characteristics of the energy harvesting systems.
Seven scientific articles, related to the topic of the dissertation were published: 4 papers were published in journals with citation index and included to Clarivate Analytics Web of Science database, 1 paper was published in conference material book indexed in Clarivate Analytics Web of Science “Conference Proceedings” database, 2 papers were published in the journals included in other databases. The results of the dissertation were presented at 5 international conferences
A novel approach for evaluation of projects using an interval–valued fuzzy Additive Ratio Assessment (ARAS) method: a case study of oil and gas well drilling projects
No full textThe beginning of the 21st-century resulted in a more developed multi-attribute decisionmaking
(MADM) tool and inspired new application areas that have resulted in discoveries in
sustainable construction and building life cycle analysis. Construction and civil engineering stand
for the central axis of a body consisting of a multidisciplinary (multi-dimensional) world with ties
to disciplines constituting the surface, and with the disciplines, as a consequence, tied to each other.
When dealing with multi-attribute decision-making problems generally multiple solutions exist,
especially when there is a large number of attributes, and the concept of Pareto-optimality is inefficient.
The symmetry and structural regularity are essential concepts in many natural and man-made objects
and play a crucial role in the design, engineering, and development of the world. The complexity
and risks inherent in projects along with different effective indicators for success and failure may
contribute to the difficulties in performance evaluation. In such situations, increasing the importance
of uncertainty is observed. This paper proposes a novel integrated tool to find a balance between
sustainable development, environmental impact and human well-being, i.e., to find symmetry axe
with respect to goals, risks, and constraints (attributes) to cope with the complicated problems.
The concept of “optimal solution” as the maximum degree of implemented goals (attributes) is very
important. The model is built using the most relevant variables cited in the reviewed project literature
and integrates two methods: the Step-Wise Weight Assessment Ratio Analysis (SWARA) method
and a novel interval-valued fuzzy extension of the Additive Ratio Assessment (ARAS) method. This
model was used to solve real case study of oil and gas well drilling projects evaluation. Despite the
importance of oil and gas well drilling projects, there is lack of literature that describes and evaluates
performance in this field projects. On the other hand, no structured assessment methodology has
been presented for these types of projects. Given the limited research on performance evaluation
in oil & gas well-drilling projects, the research identifies a set of performance criteria and proposes
an evaluation model using fuzzy Delphi method. An illustrative example shows that the proposed
method is a useful and alternative decision-making method
Bank profitability analysis and forecasting: Lithuania case
No full textPurpose of the article: The purpose of this paper is to analyse commercial banks operating in
Lithuania in terms of profitability, as it is one of the critical factors of economic development.
Moreover, the profitability of commercial banks is a crucial factor for banks’ financial stability
which, in turn, has an impact on the stability of the whole financial system of a country.
Variables representing banks profitability are as follows: return on equity (ROE), return on
assets (ROA), and return on risk assets (RORA). What is more, the forecast of the abovementioned variables was made in order to predict their values.
Methodology/methods: In order to analyse and assess the dynamics of the profitability
indicators (ROA, ROE, RORA), the financial reports of six banks operating in Lithuania were
analysed. After analysing the profitability indicators, the forecasts for three years were made
using a moving average method.
Scientific aim: To analyse commercial banks profitability indicators and make a forecast. The
forecast of the indicators makes it possible to conclude that the banking system of Lithuania
will continue to carry out profitable activities
Findings: The findings of the research showed that the estimated values of ROA, ROE and
RORA are stable. The results of indicators forecasting makes showed that the banking system
of Lithuania would continue to carry out profitable activities.
Conclusions: Summarising the indicators of profitability group: return on equity, return on
assets, and assets and equity ratio, it can be argued that the Lithuanian banking system is
able to manage resources efficiently, in order to ensure the profitability of operations, despite
market disturbances, such as the financial crisis of 2008
Experimental study on spine segment fixation technique
No full textThe paper presents a study on instrumented evalu-ation of the single spinal segment fixation techniques. In vitro tests have been completed with 6 porcine spinal sam-ples. Two different methods of rigidly fixed segment of the lumbar spine were tested and compared with control group/unfixed spinal units (CO). One fixation technique was obtained using screws and straight rods (FSR), another - screws and bent rods simulating the anatomy of the spine (FBR). Experimental data contains deformation data under experimental test loading limitations. Obtained results showed no significant difference between fixation tech-niques FSR and FBR in any case of loading parameters. However, results indicated significant differences under flexion tests after rigid fixation of the spine. Due to these results, we can presume that flexion movement is the most hazardous for developing adjacent segment disease
Energy security issues in contemporary Europe
No full textThroughout the history of mankind, energy security has been always seen as a means of protection from
disruptions of essential energy systems. The idea of protection from disorders emerged from the process of securing political
and military control over energy resources to set up policies and measures on managing risks that affect all elements of
energy systems. The various systems placed in a place to achieve energy security are the driving force towards the energy
innovations or emerging trends in the energy sector.
Our paper discusses energy security status and innovations in the energy sector in European Union (EU). We analyze the
recent up-to-date developments of the energy policy and exploitation of energy sources, as well as scrutinize the channels of
energy streaming to the EU countries and the risks associated with this energy import. Moreover, we argue that the shift to
the low-carbon production of energy and the massive deployment of renewable energy sources (RES) might become the key
issue in ensuring the energy security and independency of the EU from its external energy supplies. Both RES, distributed
energy resources (DER) and “green energy” that will be based on the energy efficiency and the shift to the alternative energy
supply might change the energy security status quo for the EU
Piezoelectric cantilevers for energy harvesting with irregular design of the cross sections
Get PDFResults of the numerical and experimental investi-gations of the piezoelectric rectangular cantilevers with ir-regular design of the cross section area are presented in this paper. The aim of the investigation was to analyse how mod-ification of the cross section area by periodical gaps acts on power density of the piezoelectric energy harvesting sys-tems based on a rectangular cantilever. It was found out, that modifications of the cross section area ensure higher strain values and allows to improve strain distribution in piezo ce-ramic layer and by this way to improve power density of the energy harvesting systems. Numerical investigations of the piezoelectric cantilevers with irregular design of the cross section area were performed in order to analyse strain dis-tribution and predict electrical characteristics of the im-proved energy harvesting systems. Experimental investiga-tions of the prototypes were performed and results of the numerical modelling were validated. Results of the numeri-cal and experimental investigation are discussed as well
The usage and perception of pedestrian zones in Lithuanian cities: multiple criteria and comparative analysis
No full textAs pedestrian zones are public spaces in urban areas, they are important in terms of
meeting people’s needs. However, it is worth noting that attention should be paid not only to
the development of the physical infrastructure, but also to a sustainable balance between the
socio-economic and environmental aspects. To guide urban planning and management initiatives
towards more sustainable patterns, it is essential to re-examine the already existing characteristics of
cities, establishing how they are used and perceived by inhabitants. The present research suggests
environmental, economic and social criteria that determine a greater vitality of pedestrian zones
in cities and better life quality for the inhabitants. A questionnaire survey was used to assess
common attitudes regarding the research topic in major cities in Lithuania. The multiple criteria
decision-making COPRAS (COmplex PRoportional ASsessment) method was used for the formation
of a priority queue. The research results showed the attitudes of inhabitants towards pedestrian
zones in Vilnius, Kaunas and Klaip˙eda. The inhabitants of these three cities regarded social and
environmental criteria groups as the most significant. Contrary to what was expected and anticipated,
respondents do not consider economic criteria as playing a key role in the sustainable preservation
and development of pedestrian zones
Manifestations of postmodern ideas in Lithuanian architecture at the end of 20th – the beginning of the 21st century
Get PDFDisertacijoje nagrinėjama Lietuvos postmodernizmo architektūra. Tyrimo tikslas yra atskleisti, kaip šis reiškinys, XX a. pab. jį perkėlus į sovietinį kontekstą, buvo lokaliai suvokiamas ir vertinamas; kaip ir kokiais būdais šio laikotarpio objektai Lietuvoje atliepia esmines postmodernizmo idėjas, kiek šios idėjos yra ypatingos ir specifinės; kokios buvo jų raiškos ypatybės; kaip jos nulėmė architektūros objektų koncepcijas, formas, estetinę raišką. Darbe sprendžiami šie uždaviniai: apžvelgiant postmodernizmo sampratą Vakarų filosofijoje bei kultūros teorijoje, atskleisti jos perkėlimo į architektūrą ypatybes; išnagrinėti, kaip postmodernizmas Lietuvoje buvo suvokiamas kultūros lauke, kaip jis buvo vertinamas architektų, architektūros kritikų ir visuomenės; nustatyti postmodernizmo architektūros diskurso Lietuvos architektūroje formavimosi aplinkybes, santykį su XX a. pabaigos sociokultūriniais procesais, jo dėsningumus ir ypatybes; įvardinti reikšmingiausius postmodernizmo architektūros objektus Lietuvoje, ištirti svarbiausius jų raiškos bruožus; atskleisti, kaip postmodernizmo idėjos įtakojo Lietuvos architektūros raidą, kokie postmodernizmo bruožai integravosi į architektų kūrybą, išnagrinėti jų vertę vadovaujantis chronologiniais, estetiniais, sociokultūriniais kriterijais. Mokslinio darbo naujumas – kompleksiškai ištirta postmodernizmo architektūros Lietuvoje raiška, nustatyti jos raidos pokyčiai, įvertintos meninės raiškos savybės. Kitas naujumo aspektas yra ne tik estetinė, bet ir socialinė šio reiškinio analizė, gilinantis į tai, kokiomis visuomenės gyvenimo aplinkybėmis buvo aktuali postmodernizmo architektūra. Nagrinėjamo laikotarpio pastatų bruožų ir savybių analizė naudinga XX a. pab. – XXI a. pr. Lietuvos architektūros menotyrinio ištirtumo plėtrai ir turi edukacinę reikšmę. Ištirti postmodernizmo architektūros pavyzdžiai ir jų vertingųjų savybių nustatymas padeda šio laikotarpio architektūros dokumentavimo, saugojimo ir vertinimo procesams, tyrimo metu gauti rezultatai gali būti pritaikyti naujausiojo paveldo vertingųjų savybių metodikai pagerinti
Analyses of archival cartographic materials for geomorphological changes of river channel
No full textIn Lithuania, the old archival topographic maps of locations of small and medium scale and 1 :10,000 scale contour photo plans
were created on the basis of aerial images. -e material of these scales provides documented records on the condition of the objects
in the location and the landscape at the moment of aerial photography. -ose maps can be used to restore the accurate topographic
image of the terrain and buildings in 1945–1951 and in later years and perform the necessary topographic, photogrammetric, and
geodetic measurements of the parameters of objects, to identify the location of objects and changes. -is information is necessary
for a variety of disputed property issues and for building farmhouses in reserves, in areas of forestry land parcels, and for
assessment of changes in the landscape. Studies of landscape changes are needed for the assessment of renaturalization processes.
-is paper presents the geodetic method used for geomorphological changes at the channel of River Zalesa during the period ˇ
1942–2017, based on the collected archival cartographic materials: historical topographic maps from archive of the Lithuanian
State Company Land Fund, Land Information System, and land management projects and orthophoto maps from Lithuanian
spatial information portal and free open-access Sentinel-1 satellite data from the Copernicus Open Access Hub
The impact of primary sludge from paper industry on the properties of hardened cement paste and mortar
No full textIn the paper, the impact of paper production waste (primary sludge, or PS) on the properties of cement
pastes and mortars is discussed upon. Some specimens were formed with fine PS fraction that replaced a
part of cement content in them (5%, 10%, 15%, or 20%); in other specimens, coarse fraction of sludge (2/4)
was used and a part of content of fine filler (sand) was replaced by PS. The properties of mixtures, such as
water content required for cement paste of normal consistence, the setting time, exothermic temperature, flow diameter and plunger penetration, were established. In addition, the properties of hardened
mortar, such as its density, flexural strength and compressive strength, were established. The microstructure of hardened specimens was examined as well. It was found that PS retarded hydration processes and
reduced exothermic temperature; in addition, it reduced the flow diameter and the plunger penetration.
While assessing the properties of hardened mortar, it may be stated that 5% PS waste might be used for
replacement of a part of cement content