Vilnius Gediminas Technical University
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An Analysis of the Reliability of a Bus Safety Structure on Carrying Out the Numerical and Experimental Tests
No full textIn the paper, the reliability of a spatial tubular structure of a bus safety frame formed of different steel profiles is discussed. A methodology for the bus safety structure modeling is presented herein by applying numerical methods that enable us to simulate virtually a test for assessing bus rollover crashworthiness according to the United Nations Economic Commission for Europe (UNECE) Regulation No. 66, and also to assess and ensure the reliability and safety of the structure under operating conditions. The simulation has been performed by applying the mixed method of kinematical analysis and finite elements. In the course of the calculations, physical and geometrical non-linearity of materials was assessed. In addition, an experimental rollover test according to UNECE Regulation No. 66 was performed in this work, striving to verify the provided methodology for modeling by applying numerical methods. For the experiment, an identical safety structure and a rollover stand (identical to the one used in modeling) were used. The rollover test was shot by a Phantom v711 high-speed camera. In the paper, the results of kinematical and dynamic analysis from applying the finite element method and the ones of the experimental test, as well as their comparisons, are provided. It is assessed whether the developed safety structure model is reliable and suitable for use.This article belongs to the Special Issue Structural Health Monitoring for Smart Structure
Investigation on the characteristics of diesel engine running on microalgal oil
Get PDFMikrodumbliai išsiskiria iš visų žinomų biomasės rūšių savo galimybe atliepti ateities iššūkius, jei vertinsim jų prieinamumą, trumpą augimo periodą, greitą prieaugį, derliaus kiekį gaunamą iš ploto vieneto, konkurencijos nebuvimą su dirbama žeme. Šios savybės leidžia dumblių biomasę laikyti tinkamiausia žaliava gaminti biodegalus ir pridėtinę vertę kuriančius antrinius produktus naudojant biologinio perdirbimo technologijas. Šio darbo autorius iškėlė problemą, kad norint atsisakyti dalies iškastinių degalų naudojamų transporto sektoriuje, dalį suvartojamo dyzelino galima būtų sėkmingai pakeisti biodegalais, pagamintais iš mikrodumblių rūšies P.moriformis. Šis disertacinis darbas dedikuotas detaliam mikrodumblių aliejaus naudojamo transporte vertinimui, kuris apėmė mikrodumblių auginimo technologijos parinkimą, variklio degimo proceso skaitinį modeliavimą, pagamintų biodegalų fizikinių-cheminių charakteristikų nustatymą, išsamius dyzelinio variklio eksploatacinių ir aplinkosauginių charakteristikų tyrimus jam dirbant skirtingomis apkrovomis, paankstintais arba pavėlintais degalų įpurškimo kampais bei aktyviu /neaktyviu deginių recirkuliaciniu vožtuvu.
Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados, naudotos litera-tūros sąrašas, autoriaus publikacijų sąrašas ir priedai.
Įvadinėje dalyje suformuluota problematika, aptartas darbo aktualumas ir tyrimų tikslai. Metodika ir įvardinti uždaviniai pabrėžia ir atspindi darbo aktualumą ir jo mokslinį naujumą. Taip pat šioje dalyje supažindinama su disertacinio darbo struktūra ir autoriaus publikacijomis tyrimų tematika.
Pirmasis skyrius skaitytojui leidžia pažvelgti į Lietuvos transporto sektorių ir jo kelių dešimtmečių kelią darnaus mobilumo link, vertinant oro taršos pokyčius. Mikrodumblių potencialo biodegalų gamybą, procesų inžinerijos svarbą ir įvairių sinergijų paiešką siekiant efektyvumo. Apžvelgti mokslininkų tyrimai slėginio suspaudimo varikliuose naudojant grynus augalinius aliejus bei jų mišiniu su mineraliniu dyzelinu. Antrajame skyriuje aprašyta tyrimų metodologija, naudota įranga, eksperimentų eiga, degalų terminės analizės rezultatai ir paklaidų skaičiavimas. Trečiame skyriuje pateikti eksperimentinių tyrimų rezultatai, kurie apima: mikrodumblių aliejaus degimo proceso dyzelinio variklio cilindruose skaitinį modeliavimą, naudojant AVL BOOST programinį paketą; Laboratorinio variklio energetinių ir ekologinių rodiklių pokyčius, priklausomai nuo apkrovos charakteristikos; Reguliavimo charakteristikos paankstinant ir/arba pavėlinant degalų įpurškimą ir jo įtaka dyzelinio variklio energetiniams ir ekologiniams rodikliams; Išorinę greičio charakteristiką varikliui veikiant mikrodumblių aliejaus ir dyzelino mišiniu.Disertacij
Membrane computing technology for self-organization of devices in the internet of things
Get PDFDisertacijoje nagrinėjamos membraninių skaičiavimų ir daiktų interneto technologijos bei su jomis susieti metaeuristikos algoritmai, optimizavimo skruzdžių kolonijomis algoritmai, daiktų interneto informacijos valdymo ir skirstymo algoritmai. Membraniniai skaičiavimai – tai kompiuterių mokslų sritis, kurioje skaičiavimo idėjos ir modeliai abstrahuojami iš gyvų ląstelių struktūros. Daiktų internetas – nepriklausomų įrenginių rinkinys, kuris vartotojams pateikiamas kaip viena darni sistema (struktūra) skirta išmaniaisiais įrankiais jungtis prie jutiklių ir daugybės prietaisų, siekiant juos valdyti arba gauti pagrindinę jų informaciją. Daiktų interneto savitvarkos duomenų valdymo ir skirstymo problemos sprendimas yra aktualus siekiant, kad sistemos veiktų nenutrūkstamai ir darniai.
Šios disertacijos tyrimo objektas yra daiktų interneto savitvarka. Darbo tikslas – pasiūlyti originalų metaeuristika grįstą P sistemos sprendimą, sukuriant ir ištiriant membraninių skaičiavimų imitavimo ir testavimo sistemą daiktų interneto sąlygomis. Darbas skirtas prisidėti vystant darnias daiktų interneto sistemas. Atliekama analitinė membraninių skaičiavimų ir daiktų interneto literatūros apžvalga, pagrindžiant darbe iškeltos problemos aktualumą ir galimus jos sprendimo būdus tolimesniems tyrimams. Remiantis atlikta apžvalga bei pritaikant natūralioje gamtoje vykstančius procesus pasiūloma nauja daiktų interneto savitvarkos max-min skruzdžių P sistema, metodika. Pasiūlytas metodas ištiriamas MATLABTM programinėje įrangoje sukuriant virtualų tinklą imituojantį daiktų internetą.
Disertaciją sudaro įvadas, trys skyriai ir bendrosios išvados. Pirmame skyriuje pristatomos esminės teorinės žinios apie membraninius skaičiavimus ir daiktų internetą, analizuojamas saviorganizuojantis daiktų internetas, metaeuristikos algoritmai, formuluojami disertacijos uždaviniai, apibrėžiama daiktų interneto informacijos skirstymo ir valdymo problema. Antrame skyriuje pristatoma saviorganizuojančio daiktų interneto metodika grįsta gamtoje vykstančiais procesais, pateikiamos P sistemos evoliucijos taisyklės ir programos pseudokodas. Trečiame skyriuje yra suformuluojami kokybiniai vertinimo kriterijai, MATLABTM programinėje įrangoje atliekami eksperimentai ištiriant daiktų interneto informacijos skirstymo ir valdymo max-min P skruzdžių sistemą ir pateikiami eksperimentinio tyrimo rezultatai.
Pagrindiniai disertacijos rezultatai paskelbti 5 mokslinėse publikacijose – 3 iš jų atspausdintos recenzuojamuose mokslo žurnaluose, 2 – konferencijų medžiagose. Rezultatai viešinti 6 mokslinėse konferencijose.Daktaro disertacij
Foresight Based on MADM-Based Scenarios’ Approach: A Case about Comprehensive Sustainable Health Financing Models
No full textAs indicated by a worldwide common perspective about health and sustainable health systems, the health structure as a part of public health is a key theme of many societies. The future is shaped by probable future scenarios, for which dealing practically has many complications. This study is focused on the future scenarios for a comprehensive sustainable health financing model to support a superior structure for a decision and policy-making pilot for the society. This aim is followed based on multiple attribute decision making (MADM)-based scenarios using two MADM methods, step-wise weight assessment ratio analysis (SWARA) and weighted aggregated sum product assessment (WASPAS), as a hybrid model which is the first real case study of the approach. Four main probable future scenarios are identified and selected based on experts’ viewpoints about sustainable health financing models. These scenarios include membership in the World Trade Organization (WTO), dynamic basic insurance, international cooperation, and effective resources management. The process of evaluating based on the approach works as a wider picture, including all criteria and alternatives together. Sustainable medical services, empowering the private sector in both production and technology, and employing international managers took place as the top priority for considering the most applicable alternatives in the future. This structure is designed and developed in Iran’s context, and the Institute for Futures Studies in Health is the pilot of the research.This article belongs to the Special Issue Multi-Criteria Decision-Making Techniques for Improvement Sustainability Engineering Processe
0.13 μm CMOS Traveling-Wave Power Amplifier with On- and Off-Chip Gate-Line Termination
No full textBroadband amplifiers are essential building blocks used in high data rate wireless, radar, and instrumentation systems, as well as in optical communication systems. Only a traveling-wave amplifier (TWA) provides sufficient bandwidth for broadband applications without reducing modern linearization techniques. TWA requires gate-line and drain-line termination, which can be implemented on- and off-chip. This article compares the performance of identical 0.13 μm CMOS TWAs, differing only in gate-line termination placement. Measurement results revealed that the designed TWAs with on- and off-chip termination have a bandwidth of 10 GHz with a maximum gain of 15 dB and a power-added efficiency (PAE) of 5%–22% in the whole operating frequency range. Placing the gate-line termination off-chip results in an S21 flatness reduction, compared to the gain of a TWA with on-chip termination. Gain fluctuation over frequency is reduced by 4–8 dB when the termination resistor is placed as an external circuit.This article belongs to the Section Computer Science & Engineerin
Development and Use of New Polymer Adhesives for the Restoration of Marine Equipment Units
No full textA new adhesive material and a restoration technology for marine equipment units are proposed. The optimal content of hardeners of different nature is found, and the effect of temperature conditions used for crosslinking epoxy resin DER-331, on the adhesive properties of the polymeric material is determined. The polymerization of the epoxy oligomer DER-331 and polyethylene polyamine (PEPA) hardener at a temperature T = 413 ± 2 K is found to enhance the adhesive properties of the polymeric material by 3.2–3.6 times, as compared to polymer GEN-150. In addition, the separation pattern of metal surfaces was analyzed, which allowed for an in-depth evaluation of the adhesive strength at separation and its variation upon increasing the content of hardeners introduced. Based on complex studies, it is shown that the developed polymeric adhesive should be used in the restoration of marine transport units, in particular, wheel fit in the compressor section of turbocharger.This article belongs to the Section Ocean Engineerin
New β-Carotene-Chitooligosaccharides Complexes for Food Fortification: Stability Study
Get PDFThe application of β-carotene in food industry is limited due to its chemical instability. The drawback may be overcome by designing new delivery systems. The stability of β-carotene complexed with chitooligosaccharides by kneading, freeze-drying and sonication methods was investigated under various conditions. The first-order kinetics parameters of the reaction of β-carotene degradation were calculated. The complexation improved the stability of β-carotene at high temperatures and ensured its long-term stability in the dark at 4 °C and 24 °C, and in the light at 24 °C. In water solutions, the best characteristics were exhibited by the complexes prepared by freeze-drying and sonication methods. In the powder form, the complexes retained their colour for the period of the investigation of four months. The calculated total colour differences of the complexes were qualified as appreciable, detectable by ordinary people, but not large. Therefore, β-carotene-chitooligosaccharides complexes could be used as a new delivery system suitable for food fortification.This article belongs to the Special Issue Natural Carotenoids as Functional Food IngredientsThis research was funded by the European Social Fund under the No 09.3.3-LMT-K-712 “Development
of Competences of Scientists, other Researchers and Students through Practical Research Activities” measure.
Grant No 09.3.3-LMT-K-712-02-0039
A Bibliometric Analysis of Symmetry (2009–2019)
No full textSymmetry is an international journal in the research fields of physics, chemistry, biology, mathematics, computer science, theory and methods, and other scientific disciplines and engineering. The first paper was published in 2009. Here, we make a bibliometric analysis of publications in Symmetry from 2009 to 2019. According to Web of Science (WoS), we obtained 3215 publications in this journal. First, we explore the publications, citation number, and citation structure based on bibliometric indicators. Second, we analyze the most influential objects, including countries/regions, institutions, authors, and papers. Cooperation networks are also presented. Next, the co-citation and burst detection analyses are conducted according to the techniques of visualization tools, i.e., VOSviewer and CiteSpace. Furthermore, the co-occurrence analyses and timeline view analyses of keywords are investigated, aiming to explore the research hotspots. Finally, this paper provides relatively thorough perspectives and reviews and discloses the future development trend of this journal and challenges for scholars, which will promote the development of the journal and in-depth research of scholars.This article belongs to the Special Issue Symmetric and Asymmetric Data in Solution ModelsThis work was funded by the National Natural Science Foundation of China under Grant 71771155
3DOF Ultrasonic Motor with Two Piezoelectric Rings
Get PDFA novel design of a multiple degrees of freedom (multi-DOF) piezoelectric ultrasonic motor (USM) is presented in the paper. The main idea of the motor design is to combine the magnetic sphere type rotor and two oppositely placed ring-shaped piezoelectric actuators into one mechanism. Such a structure increases impact force and allows rotation of the sphere with higher torque. The main purpose of USM development was to design a motor for attitude control systems used in small satellites. A permanent magnetic sphere with a magnetic dipole is used for orientation and positioning when the sphere is rotated to the desired position and the magnetic field synchronizes with the Earth’s magnetic dipole. Also, the proposed motor can be installed and used for robotic systems, laser beam manipulation, etc. The system has a minimal number of components, small weight, and high reliability. Numerical simulation and experimental studies were used to verify the operating principles of the USM. Numerical simulation of a piezoelectric actuator was used to perform modal frequency and harmonic response analysis. Experimental studies were performed to measure both mechanical and electrical characteristics of the piezoelectric motor.This article belongs to the Special Issue Development of Piezoelectric Sensors and ActuatorsThis research was funded by the European Regional Development Fund under a grant agreement with the Research Council of Lithuania, grant number 01.2.2-LMT-K-718-01-0010
Flat Cross-Shaped Piezoelectric Rotary Motor
Get PDFA numerical and experimental investigation of a flat, cross-shaped piezoelectric rotary motor is presented. The design and configuration of the motor allow it to be mounted directly to the printed circuit board or integrated into the other system where mounting space is limited. The design of the motor is based on the cross-shaped stator with 16 piezo ceramic plates, which are glued on it. The rotor is placed at the center of the stator and consists of two hemispheres, a shaft, and a preloading spring. Special clamping of the stator was developed as well. It consists of four V-shaped beam structures that allow it to rigidly clamp the stator with reduced damping effect to vibrations. The operation principle of the motor is based on the first in-plane bending mode of the cross-shaped stator. The motor excitation is performed through four harmonic signals, which have a phase difference of π/2. A numerical investigation of the motor was conducted to optimize the geometrical parameters of the stator and to analyze the displacement characteristics of the contacting point. The prototype of the motor was made, and the electrical, as well as rotation speed characteristics of the motor, were measured. The results of the experimental investigation showed that the motor is able to provide a maximum rotation speed of 972.62 RPM at 200 Vp-p when the preload force of 22.65 mN was applied.This article belongs to the Special Issue IWPMA (International Workshop on Piezoelectric Materials and Applications in Actuators) 2019. This paper is an extended version of the paper published in the International Workshop on Piezoelectric Materials and Applications in Actuators in 2019 & Enhance Workshop, IWPMA 2019, held in Lyon, 1–4 October 2019