The flow distribution in the primary circuit of the pressurized water reactor was studied with experiments and Computational Fluid Dynamics (CFD) simulations. The main focus was on the flow field and mixing in the downcomer of the pressure vessel: how the different factors like the orientation of operating loops, the total loop flow rate and the asymmetry of the loop flow rates affect the outcome. In addition to the flow field studies the overall applicability of CFD methods for primary circuit thermal-hydraulic analysis was evaluated based on the CFD simulations of the mixing experiments of the ROCOM (Rossendorf Coolant Mixing Model) test facility and the mixing experiments of the Paks NPP. The experimental part of the work in work package 3 included series of steady state mixing experiments with the ROCOM test facility and the publication of results of Paks VVER-440 NPP thermal mixing experiments. The ROCOM test facility models a 4-loop KONVOI type reactor. In the steady-state mixing experiments the velocity field in the downcomer was measured using laser Doppler anemometry and the concentration of the tracer solution fed from one loop was measured at the downcomer and at the core inlet plane. The varied parameters were the number and orientation of the operating loops, the total flow rate and the (asymmetric) flow rate of individual loops. The Paks NPP thermal mixing experiments took place during commissioning tests of replaced steam generator safety valves in 1987-1989. It was assumed that in the reactor vessels of Paks VVER-440 NPP equipped with six loops the mixing of the coolant is not ideal. For the realistic determination of the active core inlet temperature field for the transients and accidents associated with different level temperature asymmetry a set of mixing factors were determined. Based on data from the online core monitoring system and a separate mathematical model the mixing factors for loop flows at the core inlet were determined. In the numerical simulation part of the work package 3 the detailed measurements of ROCOM tests were used for the validation of CFD methods for primary circuit studies. The selected steady state mixing experiments were simulated with CFD codes CFX-4, CFX-5 and FLUENT. The velocity field in the downcomer and the mixing of the scalar were compared between CFD simulations and experiments. The CFD simulations of full scale PWR included the simulation of Paks VVER-440 mixing experiment and the simulation of Loviisa VVER-440 downcomer flow field. In the simulations of Paks experiments the experimental and simulated concentration field at the core inlet were compared and conclusions made concerning the results overall and the VVER-440 specific geometry modelling aspects like how to model the perforated elliptic bottom plate and what is the effect of the cold leg bends to the flow field entering to the downcomer. With Loviisa simulations the qualitative comparison was made against the original commissioning experiments but the emphasis was on the CFD method validation and testing. The overall conclusion concerning the CFD modelling of the flow field and mixing in the PWR primary circuit could be that the current computation capacity and physical models also in commercial codes is beginning to be sufficient for simulations giving reliable and useful results for many real primary circuit applications. However the misuse of CFD methods is easy, and the general as well as the nuclear power specific modelling guidelines should be followed when the CFD simulations are made.

Thesis (M. Soc. Sc.)--University of Hong Kong, 1987.

Magistriniame darbe įvertinamas Ignalinos atominės elektrinės ir gamtinių sąlygų poveikis terminiam Drūkšių ežero režimui. Tyrimo tikslas – įvertinti Ignalinos atominės elektrinės ir gamtinių sąlygų poveikį terminiam Drūkšių ežero režimui. Tyrimo objektas – atominė elektrinė ir Drūkšių ežeras. Nuo l984 m. Lietuvos didžiausias Drūkšių ežeras pradėjo tarnauti kaip Ignalinos atominės elektrinės (IAE) aušintuvas. Todėl natūralus hidrologinis režimas ir šilumos balansas ežere buvo sutrikdyti. Ypač pakito Drūkšių ežero terminis režimas. Vidutiniškai Drūkšių ežero vandens temperatūra pakilo apie 3,5 ºC. Tačiau pastaraisiais metais Lietuvoje stebimos klimato atšilimo tendencijos. Per pastaruosius dešimtmečius vidutinė oro temperatūra padidėjo apie 1 ºC. Oro temperatūros augimas taip pat turėjo įtakos visų vandens telkinių, tuo pačiu ir Drūkšių ežero vandens temperatūrai. Todėl tiek antropogeniniai veiksniai (atominė elektrinė), tiek gamtiniai veiksniai (klimato kaita) turi įtakos Drūkšių ežero terminiam režimui. Lietuvos energetikos instituto ir kitų mokslinių institucijų darbuotojai atliko daug tyrimų, susijusių su Drūkšių ežero hidrologine, hidrotermine bei ekologine būkle. Tačiau šiuose tyrimuose mažai dėmesio buvo skirta gamtinės kaitos įtakos Drūkšių ežero terminiam režimui nustatymui. Šio tyrimo tikslas buvo įvertinti atominės elektrinės ir gamtinių sąlygų poveikį terminiam Drūkšių ežero režimui. Norint įvertinti Drūkšių ežero terminio režimo pokyčius veikiant IAE... [toliau žr. visą tekstą] / The paper evaluated the Ignalina nuclear power and natural conditions, the thermal effect of the lake Drūkšiai regime. Purpose of the survey - to assess the Ignalina nuclear power and natural conditions on the thermal regime of Lake Drūkšiai. The object of research - nuclear power and natural environment impacts. Since l984, the Lithuanian Drūkšiai largest lake began to serve as the Ignalina Nuclear Power Plant (INPP) cooler. Therefore, the natural hydrological regime and heat balance in the lake has been disturbed. In particular, changes in lake thermal regime Drūkšiai. On average, Drūkšiai lake temperature has risen approximately 3.5 ° C. However, in recent years, Lithuania observed warming trends. Over the past decades, the average air temperature increased about 1 ° C. Air temperature rise is also affected by the water at the same time and lake water temperatures. Therefore, both anthropogenic factors (NPP) and natural factors (climate change) affect the thermal regime of Lake Drūkšiai. Lithuanian Energy Institute and other scientific staff, the large number of tests and touching Drūkšiai lake hydrology, hydrothermal and ecological condition. However, these studies little attention was given to natural changes affect Drūkšiai lake thermal regime. Purpose of this study was to evaluate nuclear power and natural conditions on the thermal regime of Lake Drūkšiai. To assess Drūkšiai Lake thermal regime change operation IAE... [to full text]

Kogeneracija – techniškai pažangus šilumos ir elektros energijos gamybos būdas. Elektros energija gaunama iš generatoriaus, o šilumos energija gaunama variklio aušinimo metu. Kadangi Lietuvoje elektros ir šilumos gamyba iš atsinaujinančių energijos šaltinių yra labai aktualu, darbo tikslas: suprojektuoti kogeneracinės jėainės vidaus elektros tinklą, parinkti kogeneratorių. / Cogeneration technologically advanced of heat and electricity production. It is particularly relevant for Lithuania, because there exists a strong need for heat production, the restructuring of heat and electricity networks, is changing its legal framework, the development of market relations. Undergraduate work is designed combined heat and power plant. Cogeneration plant will be used for alternative fuel: biogas which derived from the landfill. However, in order to improve the efficiency of cogeneration landfill gas is mixed with natural gas in certain proportion. Combined heat and power plant is designed according to the Republic of Lithuania laws and regulations. Heat comes from cogeneration emissions into the atmosphere in summer. It was found that in order to increase the heat recovery efficiency, not only in winter but in summer, for example to be equipped with heated vegetable production complexes.

Teorinėje dalyje nagrinėjama žmogų supanti aplinka, kaip vienas iš ugdymo veiksnių. Labiau akcentuojama gamtinė ir kultūrinė aplinka, bei detaliau analizuojama Ignalinos AE regiono pažintinį turizmą sudaranti gamtinė ir kultūrinė aplinka ir jų vieta moksleivių ugdyme. Praktinę dalį sudaro anketinė apklausa, vykdyta 2006m. rugsėjo mėn. Ignalinos, Zarasų rajonuose bei Visagino mieste. Tyrime dalyvavo gimnazijų bei vidurinių mokyklų moksleiviai, tuo metu besilankantys Ignalinos ir Zarasų rajonuose. Tyrimu siekiama atskleisti kelionių su klase dažnumą, tikslus, moksleivų tarpusavio santykius, Ignalinos AE regiono išskirtinumą, šio regiono pažintinio turizmo (gamtinės ir kultūrinės aplinkos) veiksnių svarbą moksleivių ugdyme. / The study consists of theoretical and practical parts. At the theoretical part there are the researches about the environment surrounding a human-being like one of the education factors. The nature and culture environments are more emphasized. The nature and culture environments forming the cognitive tourism in Ignalina Nuclear Power Plant (further – Ignalina NPP) region and their influence in pupils’ education are analyzed more elaborately. The practical part consists of a questionnaire, data of which were gathered in September 2006 in Ignalina district, Zarasai district and Visaginas town. The students of the Ignalina and Zarasai districts’ secondary and grammar schools took a part at the research. Research target is to discover how often the class trips are organized, what are their targets and tasks, what are the rapports within the pupils, what are the advantages of Ignalina NPP region and what is the importance of this region’s cognitive tourism to pupils’ education.

Naujausi tyrimai rodo, o ir kiekvienas informacijos gavėjas pastebi, kad informacijos teikėjas labai dažnai nesugeba atsiriboti nuo subjektyvumo. Taip atsitinka todėl, kad kiekvienas informacijos koduotojas turi skirtingus patyrimus, interesus, įvairias nuomones apie įvykius, jį supantį pasaulį, požiūrį į vieną ar kitą situaciją, dalyką ir pan. Tyrimo tikslas – atpažinti žiniasklaidos tekste vartojamus vertinamuosius elementus, suklasifikuoti juos ir aprašyti, kaip, pasitelkus vertinamuosius elementus, atspindima autoriaus pozicija, požiūris, nuomonė apie žinomą įvykį, realų faktą ar įvykusią situaciją. Šio mokslinio darbo objektas – vertinamieji elementai, vartojami Lietuvos interneto žiniasklaidos tekstuose. Siekiant užsibrėžto tikslo buvo numatyti 6 uždaviniai, apibendrintai jie yra tokie: apžvelgti atliktus mokslinius tyrimus ir jų rezultatus bei metodus pritaikyti lietuvių kalbos interneto žiniasklaidos tekstuose vartojamiems vertinamiesiems elementams tyrinėti; pagal sudarytą pagrindinių ir šalutinių vertinamųjų parametrų schemą atpažinti, suklasifikuoti vertinamuosius elementus, juos išanalizuoti ir aprašyti; pristatyti darbo metu kilusias problemas ir sunkumus, ypač susijusius su vertinamųjų elementų atpažinimu; atlikti apklausą-eksperimentą ir aptarti rezultatus. Atlikus vertinamųjų elementų, vartojamų interneto žiniasklaidos tekstuose, tyrimą, patvirtinta kelta hipotezė, kad pasitelkęs vertinamuosius elementus teksto autorius gali perteikti asmeninę poziciją... [toliau žr. visą tekstą] / Both the latest studies and the opinion of information receivers show that information providers are often unable to distance themselves from subjectivity. This happens because every information addresser has particular experiences and interests, various opinions about the events and environment, different view to one or another situation, and etc. The aim of the thesis is to identify the evaluative elements used in media discourse, to classify them and, with the help of evaluative elements, to describe how author’s position on the event, actual fact or situation is reflected. The object of this work is the evaluative elements, used in the texts of Lithuanian media websites. In order to achieve the object, six tasks were set: to overview the carried out scientific researches and their results and to adapt the methods to the exploration of evaluative elements used in the texts of Lithuanian media websites; to identify, classify, then analyze and describe evaluative parameters, according to the main and secondary evaluative parameters scheme; to present problems and challenges arisen, particularly those related to evaluative elements recognition; to carry out an experiment-survey and to discuss the results. After a study of evaluative elements used the discourses of media websites, the following the hypothesis was confirmed: with the help of evaluative elements, the author of the text can convey a personal attitude and shape reader’s opinion. There are various categories to... [to full text]

Ištirti mažos galios horizontaliosios ašies vėjo jėgainės energetines charakteristikas ir nustatyti efektyvumo didinimo galimybes. / Survey energy characteristics of little capacity horizontal axis wind power plant and identify efficiency increase potential.

This research work focuses on the reactive power compensation of the permanent magnet synchronous generator (PSG) in wind power plants. PSG feeds a fixed voltage dc grid through a rectifier bridge. In variable speed operation, the PSG will be able to build torque only in small speed range. This is due to the fixed magnet of the PSG. External reactive power compensation provides an attractive solution to overcome this problem. Different reactive power compensation configurations were examined. Statics synchronous series compensation and a shunt passive filter were chosen as a compensation method. Simulation and implementation of small wind power plant were performed. The wind power plant consists of the synchronous generator, inverter, rectifier, coupling transformers and shunt passive filter. The experimental results agree to the proposed theory and simulation results. / Der Schwerpunkt meiner Promotion ist die Blindleistungskompensation bei einem permanenterregten Synchrongenerator. Der Synchrongenerator speist das Gleichsspannungsnetz über ein Gleichrichter. In der Drehzahlvariablen Betriebsverhalten können Nachteile auftreten. Die Folge ist, dass bei konstanter Gleichspannung und fester Erregung durch die Permanenterregung nur ein sehr kleiner Drehzahlbereich mit vernünftiger Drehmomentausbeute bedienbar ist. Ein möglicher Ausweg wäre eine variable Kompensationsspannung. Verschiedene Kompensationsverfahren wurden untersucht. Ein Series Active Filter und ein Shunt Passive-Filter wurden als Blindleistungskompensation gewählt. Im Rahmen meiner Dissertation beschäftige ich mich mit dem Aufbau und der Simulation einer Windkraftanlage. Diese besteht aus einem permanenterregten Synchrongenerator, einem Wechselrichrter, einem Gleichrichter, drei Transformatoren und einem passiven Filter. Das Versuchsergebnis zeigt, dass die Theorie mit der Simulation übereinstimmt.

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 164-168).

Thesis (M.Soc.Sc.)--University of Hong Kong, 1987. / Also available in print.