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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Barari, Amin;

    The world is currently facing serious problems brought about by oil dependence. Reducing oil consumption provides an opportunity to increase competitiveness, technological development, and progress. Wind energy is currently the most costcompetitive form of renewable energy, and there are strong political and industrial forces (particularly in northern Europe) supporting the development of the offshore wind industry.Offshore structures may consist of a single shallow foundation such as gravitybased platforms or multiple shallow foundations acting in concert (e.g., jack-up rigs or tension leg platforms). General loading is particularly relevant in the design of shallow foundations for offshore structures because wind, wave, and current forces produce substantial lateral load components at magnitudes that are not commonly encountered onshore.Bucket foundations were pioneered in the offshore oil and gas industry and have recently been used in offshore wind turbines. The bucket foundation is a welded steel structure consisting of a tubular center column connected to a steel bucket through flange-reinforced stiffeners.The overall aim of the research presented in this thesis was to improve the design of offshore wind turbine foundations. The work was divided into two main research efforts: geotechnical engineering experiments to gain insight into the behavior of offshore bucket foundations, and development of methods to improve the study of infiltration into unsaturated soils, an important problem in geo-environmental engineering. The outcomes of the research have the potential to directly or indirectly reduce the risks and costs related to offshore geotechnics.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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    Other ORP type . 2012
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      Other ORP type . 2012
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Parmeggiani, Stefano;

    Denne PhD afhandling tager udgangspunkt i udviklingen af bølgeenergianlægget Wave Dragon. Bølgeenergi udgør en meget stor, ikke udnyttet energi ressource, der har potentiale til at blive en vigtig bidragyder til at løse verdens energiproblemer. Indtil i dag er den kommercielle udnyttelse af bølgeenergi blevet vanskeliggjort af udviklernes manglende evne til at demonstrere økonomisk rentable anlæg i fuld skala – først og fremmest som følge af manglende finansiering af demonstrationsanlæg. Selv om Wave Dragon teknologien har et endog meget stort potentiale for rentabel, vedvarende el-produktion, er teknologien fortsat på et prækommercielt udviklingstrin, hvor det er vanskeligt at skaffe fornøden kapital til at gennemfore et demonstrationsprojekt fuld skala. Afhandlingens formal har varet at lette dette arbejde dels ved at udbrede kendskabet til anlægget generelt som videnskabeligt, dels ved at bidrage til den seneste teknologiske udvikling af anlægget. Forskningen har først og fremmest fokuseret på at forbedre teknologiens attraktivitet set fra en investors synsvinkel på følgende to områder, der komplementere hinanden:• Pa indtægtssiden er palideligheden af forudsigelser vedrørende produktionsdata øget samtidigt med at gennemsigtigheden ved vurderingen af produktionsdata er øget. Dette er sket gennem udvikling af en forbedret, opdateret model for opskylsanlæg specielt tilpasset Wave Dragon, hvorigennem det har varet muligt at kvantificere energiproduktionen bedre sammenlignet med tidligere anvendte metoder. Parallelt hermed er beskrevet en proces, hvor den planlagte 1,5 MW prototype placeret ved DanWEC forsøgscentret ved Hanstholm, Danmark, indgår. Heri indgår muligheden af at foretage beregninger af usikkerhed for parametre relateret til eksperimentelle data fra offshore forsøg.• Pa omkostningssiden er der gennemfort en analyse dels med henblik på at bestemme design kræfter i forankringssystemet for DanWEC enheden og dels for at identificere strategier, der kan lede til reduktion i forankringssystemets samlede omkostning. Konklusionen er, at der kan opnås besparelse på op til 65 %. Den mest effektive metode til at opnå denne besparelse kraver en time-domain analyse. En numerisk model hertil er blevet kalibreret med resultater fra en fuldstændig hydrodynamisk karakterisering af Wave Dragon baseret på data fra forsøg og numeriske beregninger.Forskningen har skabt en dybere forståelse af opskylsprocessen for Wave Dragon ved at studere den bagvedliggende fysik i kombination med anlæggets udformning og det aktuelle bølgeklima. Denne analyse er mere dybdeborende end hidtil gennemfort vurderinger af anlægget, og den vil kunne anvendes generelt i forbindelse med opskylsanlæg. Herudover er gennemført en omfattende vurdering af hydraulisk respons samt kræfter i forankringssystemet, hvilket vurderes at kunne have relevans for alle udviklere af flydende offshore anlæg.Det har også været afhandlingens formål, at demonstrere ”best practice” for udvikling af bølgeenergianlæg i almindelighed ved at anvende Wave Dragons 20-arige udviklingsforløb som eksempel, -et udviklingsforløb, der har gjort Wave Dragon til et af de mest kendte bølgeenergianlæg i verden anerkendt for dets åbenhed om opnåede resultater. This doctoral thesis is framed into the development process of the Wave Dragon wave energy converter (WEC). Wave energy is a vast and untapped resource with the potential of becoming an important contributor to the World energy mix, although presently its commercial exploitation has been hindered by the difficulties of developers to demonstrate the technology feasibility at full-scale, first of all caused by lack of finance of full-scale demonstration units. Although having a large potential for the cost-effective generation of clean and renewable electricity, Wave Dragon is currently in a pre-commercial stage in which it has proven difficult to secure the necessary funding for the deployment of a full-scale demonstrator unit. The work presented aims at easing this process, by increasing public and scientific knowledge of the device, as well as by showing the latest progress in its development.Research has been mainly focused at increasing the attractiveness of the technology to potential investors, following two main complementary lines:• On the profit side, reliability of the performance figures provided and the transparency of the performance assessment process as a whole have been increased. This is mainly due to the development of an updated overtopping model specifically suited to Wave Dragon, which allows greater quality to predictions of the primary energy absorption of the device compared to previous versions. At the same time an equitable approach has been described and used in the performance assessment of the envisaged 1.5 MW unit to be deployed at the DanWEC test center in Denmark (WDDanWEC), including the possibility of providing an estimate of the uncertainty related to the given figures when these are mainly based on experimental data from sea trials. • On the cost side, an analysis has been carried out aimed at quantifying design loads in the mooring system of the WD-DanWEC unit, as well as identifying viable force-reduction strategies which would allow significant savings in design cost (estimated up to 65%). According to these results, the most cost-effective real mooring solutions will need to be identified by means of time-domain analyses. To do so, a numerical model has been calibrated for the application with the results from the complete hydrodynamic characterization of Wave Dragon, which has been carried out based on experimental data and numerical analysis.Overall, the research has also provided a deeper insight into the physics of the overtopping process by individually assessing the influence of related device configuration and wave features, which goes beyond the present application and may be used for other overtopping WECs as well. Comprehensive analysis of the motions response and mooring tension has also been carried out, which may be of relevance to other floating offshore installations.Among the objectives of the thesis is also to show best practices in the development of WECs through the Wave Dragon case, following almost 20 years of continuous development which has made it one of the best known WECs worldwide, recognized for its openness and transparency.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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    Other ORP type . 2013
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Ferri, Francesco;

    Med den industrielle udvikling efter 1769, tidspunktet hvor James Watt tog patent på dampmaskinen, er der opstå et økonomisk, politisk, miljømæssig og energimæssig krise – hvad enten man anser denne for antagelig eller reel. Svaret på spørgsmålet ”hvordan løser man disse problemer?” er en kompliceret og ufuldendt diskussion, men med introduktionen af vedvarende energiproduktion, er der givet et bud på, hvordan man til dels kan løse disse problemer. Bølgeenergi er en uudnyttet vedvarende energikilde, som har potentiale til at bidrage betydeligt til fremtidens blandede energiforsyning. Dog har bølgeenergisektoren endnu ikke udbudt denne mulighed på markedet grundet en række tekniske og ikke-tekniske årsager. Disse kan mest effektivt opsummeres ved at på pege produktionsudgifterne som opstår ved brug af de forskellige energitransformatorer: Sammenlignet med andre vedvarende energiteknologier, er produktionsudgifterne stadigt betydeligt højere, når man udnytter energi fra havets bølger. Hvis man bliver ved denne sammenligning, er det også vigtigt at være opmærksom på, at der ikke er en klar frontløber i bølgeenergisektoren, hvilket gør at indsats og finansering spredes over et bredt felt.For at kunne bidrage til en effektiv udvikling og analyse af bølgeenergikoncepter og dermed bidrage til en acceleration af hele sektorens fremgang mod kommercialisering, er det nødvendigt med et effektivt og på lideligt wave-to-wire værktøj, som er generelt anvendeligt. En wave-to-wire model identificerer relationen mellem en energikilde på et bestemt sted og enhedens forventede produktion. Sidstnævnte er udtrykt i form af elektricitet, der leveres til elnettet. Modellen skal kunne give et groft billede af den faktiske status af sektoren og dens potentiale, og senere bruges til at finde frem til de mest lovende koncepter.På et makroniveau kan arbejdet fordeles på to hovedindsatser.Først skal komplementaritet mellem numerisk simulation og eksperimentel erfaring fremhæves, hvilket mest effektivt kan opsummeres som: Pålidelig model. Numeriske modeller er i sig selv meningsløse men lette at manipulere, hurtige og relativt billige, hvor fysiske modeller er komplekse, langsomme og dyre, men realistiske hvis implementeret i tilstrækkelig grad. Siden der ikke er et faktisk behov for ”noget nyt” men snarere ”at få det bedste ud af hvad vi har”, er den anvendte numeriske model udelukkende baseret på veletablerede metoder. Eksperimentel data bliver anvendt som verifikation til at styre retningen af den numeriske udvikling.Dernæst, kaste lys på hvad der bør være målet for sektoren: Minimering af de samlede energiomkostninger. To forskellige teknikker til at reducere omkostningerne er sammenlignet: Den første maksimerer systemomsætning (indkomst) ved at ændre på kontrolstrategien, mens den anden udvider de første metoder ved at tilføje et straf baseret på kontrolstrategiens indflydelse på det strukturelle design. Begge modeller er igen baseret på veletablerede eller standardiserede teknikker. The wild development of the world from the 1769, years in which James Watt patented his steam engine, brought utterly to the actual, real or assumed, economical, political, environmental and energetic crisis. The answer to the question “how to solve these problems?" is a tangled unsolved discussion, but talking about renewable energy partially ravels the problem out. Wave energy is a large, mostly untapped, renewable energy resource. It has the potential to contribute significantly to the future energy mix, but the sector has not yet rolled off into the market in consequence of a number of technical and non-technical issues. These can be efficiently summarised in the cost of the energy produced by the various wave energy converters: If compared with other renewable energy technologies the cost of energy from the ocean waves is still significantly higher. Holding the comparison it also important to noticed that there is not a clear front runner in the wave energy sector, which fades effort and funding over a too broad frame.In order to assist efficient development and analysis of wave energy converters and therefore to accelerate the sector progression towards commercialisation, a generally applicable, efficient and reliable wave-to-wire model tool is needed. A wave-to-wire model identifies the relation from the source of energy of a particular location to the expected device productivity. The latter being expressed in terms of electricity fed into the grid. The model needs to output a coarse picture of the actual status of the different devices and their power productivity, which is used afterwards to sieve promising concepts out.In a macro-scale the work can be divided into two main contributionsFirst, highlight the complementarity between numerical simulation and laboratory experience, in what can be efficiently summarised as: reliable model. Numerical models are per se meaningless, but easy to manipulate, fast and relatively cheap. Physical models are complex, slow and expensive but realistic if adequately implemented. Since there is no real need of “new", but more of “how can we get the best of what we have", the numerical model used is entirely based on well established methods. The experimental data is used as a check point to verify the direction of the numerical path.Second, shed light on what should be the objective of the sector: minimisation of the cost of energy. Two different techniques to reduce the cost of energy are compared: the former maximises the system revenue (income) by acting on the control logic, while the second extends the first methods adding a penalty term due to the effect of the control logic on the structural design. Both methods are once more based on well established or standard techniques.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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    Other ORP type . 2014
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      Other ORP type . 2014
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Lashab, Abderezak;
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    VBN
    Other ORP type . 2019
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      Other ORP type . 2019
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Madsen, Søren;

    Der er i disse tider et stort politisk ønske om at udvide den grønne energisektor. En velfungerende grøn energiform er vindmøller. Et stort antal vindmøller er installeret på land i løbet af de sidste årtier. Dog resulterer den nuværende udvikling i mølledesign i stadigt større vindmøller, for at reducere energiprisen. Dette begrænser anvendelsen af vindmøller på land både pga. begrænsninger ift. transport men også pga. uvilje fra potentielle naboer til kæmpevindmøller. Derfor er der indenfor de sidste par år for alvor kommet gang i udviklingen af havvindmøller. Selv om det løser de førnævnte problemer at installere vindmøllerne til havs, forøger det energiprisen, primært på grund af øgede installations- og vedligeholdelsesomkostninger. En meget stor andel af installationsomkostningerne, op mod 30 - 50 % ved brug af den nuværende teknologi, stammer fra udgifter forbundet med installation af fundamenter. Et nyt funderingskoncept, bøttefundamentet, tegner til at kunne reducere omkostingerne til fundamenter i en havvindmøllepark. Bøttefundamentet forventes at blive billigere, da det er både hurtigere at installere i forhold til den nuværende teknologi, og det kræver ikke tungt installationsudstyr. Da et bøttefundament dybest set er en relativt tynd skalkonstruktion udsat for både aksialt og latteralt tryk under installationen, bliver foldning et vitalt designkriterium. I 2005 skulle en stor vindmølle installeres i et kystnært område ved havnen i Wilhelmshaven i Tyskland. Vindmøllen blev aldrig opført da der, under nedsugningprocessen, opstod foldning i bøttefundamentets skørt. I denne afhandling er fænomenet foldning af bøttefundamenter under installation undersøgt ved hjælp af Finite Element-analyser. Indflydelsen af randbetinglser på bøttefundamentet er undersøgt, tillige med effekten af at inkludere den omgivende jord og jord-struktur interaktion. Undersøgelser er foretaget for foldningshændelsen i Wilhelmshaven, og resultaterne er sammenlignet med gældende DNV og Eurocode standarder. Endeligt præsenteres analyser af en ny udformning af et tværsnit, betegnetmulti-shell,med en højere foldningskapacitet end et tilsvarende cirkulært tværsnit. Hovedresultaterne er listet nedenfor:• Låget på bøttefundamentet øger foldningskapaciteten i forhold til en simpelt understøttet rand,• Antallet af lågafstivninger påvirker ikke den elastiske foldningskapacitet væsentligt,• Den omgivende jord øger foldningskapaciteten væsentligt under installationen,• Kun at betragte den første svigtform fra en lineær analyse som imperfekt geometri i en ikkelineær foldningsanalyse er ikke tilstrækkelig til at opfange foldningshændelsen i Wilhelmshaven. Men det er det at betragte de første 21 svigtformer og indføre den mest kritiske som en imperfekt geometri,• Multi-shell tværsnittet er lige så følsom over for imperfektioner som en cirkulær cylinder,• Det nye multi-shell design giver en væsentligt større (75 %) foldningskapacitet i forhold til det traditionelle design. There is a great politically will to expand the green energy market in these times. A proven green technology is wind turbines. Wind turbines have been installed in great numbers on land over the last decades. However, the current development in wind turbine design leads to larger turbine sizes in order to reduce the cost of energy. This limits the on land application due to transportation limitations and unwillingness from prospect neighbours. Thus, offshore wind energy started developing over the last couple of years. Although installing the wind turbines offshore resolves the before men tioned issues, it brings up the cost of energy mainly due to increased installation and maintenance costs. A very large part—up to 30–50% using current technology—of the installation cost origins from the expenses related to the installation of foundations. A new foundation concept—the bucket foundation—has been proposed to reduce the foundation costs. The bucket foundation promises to be cheaper as it is both faster to install compared to current technology and it does not require heavy installation equipment. Since the bucket foundation is essentially a relatively thin shell structure subjected to both axial and latteral pressure during the installation process buckling becomes a crucial design consideration. In 2005, a large wind turbine was to be installed nearshore the harbour in Wilhelmshaven, Germany. The windturbine was never erected since the skirt of the bucket foundation buckled during the suction assisted installation process. In this thesis, the phenomenon of buckling of the bucket foundation during installation is investigated by means of Finite Element Analysis. The influence of boundary conditions on the bucket foundation is adressed as well as the effect of including the surrounding soil and soil–structure interaction. Investigations are made regarding the buckling incident in Wilhelmshaven and the results are compared to current DNV and Eurocode standards. Finally, analysis of a new design of the cross section with a higher buckling capacity than an equivalent circular cross seciton—denoted multi-shell—is presented. The main findings are listed below:• The bucket lid shows an increase in the buckling load compared to a pinned end,• Number of lid stiffeners does not substantially affect the elastic buckling load,• The soil restraint increases the buckling load significantly during penetration,• Considering the first mode shape from a linear buckling analysis as imperfect geometryin a nonlinear buckling analysis is not sufficient for capturing the buckling incident in Wilhelmshaven; however, considering the first 21 mode shapes and introducing themost critical one as an imperfect geometry is,• The multi-shell cross section is just as sensitive to imperfections as a circular cylinder,• The new multi-shell design provides a significantly larger (75%) buckling load compared to the traditional design.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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    Other ORP type . 2014
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      Other ORP type . 2014
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Zajas, Jan Jakub;

    Selv om vinduesrammer kun er en relativ lille del af den samlede bygnings klimaskærm er de ansvarlig for en stor mængde varmetab, hvilket skyldes deres dårlige isoleringsegenskaber, hvis man sammenligner med andre bygningselementer. Med fokus på den nuværende trend i forhold til at reducere bygningers energiforbrug er det tydeligt, at der er behov for at forbedre den termiske ydeevne af nutidige rammer, således at bygningerne opfylder de nye og mere skrappe krav.Denne PhD afhandling vil fokusere på forbedringerne af den termiske ydeevne af vinduesrammer lavet af glasfiberforstærket plastik (FRP). Dette materiale er for nyligt blevet introduceret på markedet for vinduesrammer, og det er blevet et interessant valg grundet dets fine termiske og mekaniske egenskaber, hvilket kan medføre en forbedring af isoleringsevnen for vinduesrammer.Der er adskillige måder at forbedre den termiske transmission af vinduesrammer. Varme overførsel via en vinduesramme er en kombination af varmeledning, konvektion og stråling og hver af disse mekanismer kan reduceres på forskellig vis. Et eksempel kunne være at inddele hulrummene for at reducere konvektionsvarme flowet eller benytte emissitvity materialer for at mindske den radiation. Disse samt adskillige andre løsninger er undersøgt i første del af Phd afhandlingen. Simuleringer af simple geometrier er udført i forhold til at kunne evaluere potentialet ved forskellige løsninger. Resultaterne viser, at anvendelse af forskellige modifikationer til en vis grad giver en betydelig reduktion af termisk transmission. For at opnå ydereligere forbedringer kræver dette mere drastiske forandringer.På den baggrund er der foretaget en omfattende undersøgelse af, hvorledes rammegeometrien kan forbedres på et overordnet niveau. Ordinære vinduesrammer kan blive udformet i mange forskellige former, hvilket giver udviklerne en stor designmæssig frihed. Selv om der kan designes et uendeligt antal versioner af vinduesrammer er det ikke alle rammer, der vil have tilfredsstillende termiske egenskaber. Det er vigtigt at klarlægge, hvorledes et korrekt design af en ramme vil biddrage til at forbedre de termiske ydeevner. Derefter kan hele rammegeometrien blive optimeret i forhold til den termiske transmission, størrelse og materialevalg.Optimeringsprocessen kan blive foretaget ved at designe et stort antal vinduesrammers geometri og derefter evaluere deres termiske egenskaber, fortrinsvis på en automatisk måde. En stor del af denne PhD afhandling er dedikeret til udviklingen af et parametrisk designværktøj, som kan benyttes til et sådant formål. Derefter er det endelig værktøj brugt til at optimere rammerne. Optimeringen har fokus på flere formål, hvilket gør opgaven endnu mere kompliceret. Undersøgelsen foreslår to fremgangsmåder: en vægtet sum fremgangsmåde og en genetisk algoritme.Et andet formål med PhD afhandlingen var at udvikle en ny kombination af materialer, der kan bruges til at forbedre vinduesrammer. Denne kombination består af på ydersiden højstyrke kompositlaminat, og isolerende skum på indersiden. Resultatet blev udviklingen af et funktionelt gradueret materiale med rummeligt varierende egenskaber. Denne usædvanlige konstruktion skaber en udfordring i forhold til eksperimentel karakterisering af produktet. Problemstillingen kan løses ved at benytte laser flash metoden, som kan tilpasses dette specifikke formål. Der er foretaget mindre modifikationer i LFA 447 laser flash apparatet, som med en fin opløsning tillader afledning af de lokale transportegenskaber af forskellige materialer. Denne metode var valideret og blev med succes benyttet til formålet. Even though the window frames cover a relatively small fraction of the entire building envelope, they are responsible for a major amount of heat loss, due to their poor insulation properties compared to the other envelope elements. With the current trends to reduce energy use in buildings, it is obvious that the thermal performance of contemporary frames needs to be improved, so that buildings can fulfill the new, more rigorous demands.This study will focus on improving the thermal performance of window frames made of fiberglass reinforced plastic (FRP). This material has been recently introduced to the window frame market and is becoming an increasingly interesting choice, due to its fine thermal and mechanical properties which can lead to a significant improvement of the insulation properties of a window frame.There are several ways to improve the thermal transmittance of a window frame. Heat transfer through a frame is a combination of conduction, convection and radiation and each of these mechanisms of heat transfer can be diminished in certain ways. An example could be subdividing the cavities to reduce convective heat flow or using low emissivity materials to limit the thermal radiation. These, and several other solutions, are investigated in the first part of the study. Simulations on simple geometries are conducted to evaluate the potential of different solutions. The results show that by applying different modifications the thermal transmittance of a frame can be significantly reduced, but only to a certain extent. To reach further improvement, more drastic changes need to be done.Therefore, an extensive study is done on how to optimize the frame geometry on a broader level. Contemporary frames can be crafted into various shapes, giving the engineers a large freedom of design. Almost an infinite number of window frame geometries can be created, but not all of them will result in a frame with satisfying thermal properties. It is important to determine how a proper design of the frame can contribute to the improvement of its thermal performance. Afterwards, the entire frame geometry can be optimized in terms of the thermal transmittance, size and material use.The optimization process can be conducted by designing very large number of window frame geometries and evaluating their thermal properties, preferably in an automated way. A large part of this study is devoted to the development of a parametric design tool that could be used for this purpose. Afterwards, the final tool is used in a process of optimizing the frames. Optimization is done with regard to several objectives, what makes the task more complicated. Two approaches to this problem are suggested in this study: a weighted sum method and a genetic algorithm.Another objective of the project was to develop a new combination of materials that could be used in improved window frames. This combination consists of a high strength composite laminate on the outside and highly insulating foam on the inside. As a result, a functionally graded material with spatially varying properties was developed. This unusual construction creates a challenge for experimental characterization of this product. This issue can be solved by using laser flash method, which can be adapted for these specific purposes. Small modifications have been done in the LFA 447 laser flash apparatus that allow for derivation of the local transport properties of various materials, with a fine resolution. The method was validated and successfully used for this purpose.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Le Dreau, Jerome;

    Varme- og køleanlæg kan inddeles i to hovedkategorier: konvektive systemer (fx. aircondition, aktiv kølebaffel, fan-coils) og stråle køling/varme systemer. De to systemer har forskellige former for varmeoverførsel; den første er hovedsageligt baseret på konvektion, mens den anden er baseret på både stråling og konvektion. Strålevarmesystemer har den fordel at kunne gøre brug af lav kilder (dvs. opvarmning ved lave temperature og køling ved høje temperaturer) og dermed reducere bygningers primære energiforbrug. Der er imidlertid en mangel på viden om varmeoverførsel fra terminalen mod rummet og på de parametre, der påvirker anlæggenes ydelse. Derfor er der foretaget en sammenligning af komfortbetingelserne og energiforbruget for fire typer anlæg (aktiv kølebaflen, strålende gulv, væg og loft) for et typisk kontorlokale, både numerisk og eksperimentelt.Fra den stationære numerisk analyse og fuldskalaforsøgene er det observeret, at forskellen mellem de to typer anlæg primært skyldes ændringer ventilationstab. Ved lave ventilationstilskud (under 0,5 ACH), har stråle- og luftbaserede systemer samme energibehov. Ved højere ventilationstilskud er strålevarmesystemers energiforbrug lavere end de luftbaserede systemers på grund af den højere lufttemperatur. Ved 2 ACH kan en strålevægs energibesparelser vurderes til ca. 10 % sammenlignet med den aktive kølebaflen (med hensyn til leveret energi). Asymmetrien mellem luft og strålingstemperatur, lufttemperaturgradienten og den mulige kortslutning mellem indløb og udløb spiller en lige så vigtig rolle ved reduceringen af strålevæggens kølebehov sammenlignet med den aktive kølebaflen. Jo højere et luftskifte og jo højere, jo større er de opnåede besparelser med en strålekølesystem. Derfor har strålekølesystemet et stort potentiale for energibesparelser i bygninger med et højt ventilationskifte (fx butikker, togstation, industriel opbevaring ). Blandt strålesystemer er der kun observeret små forskelle i den påtænkte geometri. Kun hvis beboerne antages at sidde ned, kan den store vinkelforhold med gulvet føre til en reduktion af energibehovet for gulvkølesystemer.Disse konklusioner gælder for fler-etagers eller højisolerede bygninger (R > 5 m2.K/W). Når det drejer sig om en enetagers bygning med et lavt isoleringsniveau, er strålesystemers effektivitet lavere på grund af de større klimaskærmstab, og et luftbaseret system kan være mere energieffektivt end et stråleanlæg (med hensyn til leveret energi).Et tilsvarende globalt komfort niveau er blevet observeret for stråle- og luftbaserede systemer i både numeriske og eksperimentelle undersøgelser, men de forskellige anlæg opnåede ikke den samme ensartethed i rummet. Den aktive kølebaflen opnår teoretisk de mest ensartede komfortbetingelser (når der ses bort fra risikoen for træk) efterfulgt af kølelofter. De mindst ensartede betingelser blev opnået med det afkølede gulv, på grund af store forskelle mellem siddende og stående stilling. Lokale komfortbetingelser (strålingstemperaturasymetrien, lufttemperaturgradient, risiko for træk) er også blevet evalueret både teoretisk og numerisk, og der er ikke observeret ubehag ved normal kølekapacitet.Udover denne sammenlignende undersøgelse af forskellige anlæg, er sammenhængen mellem kølesystemer og interne konvektionsstrømme også blevet undersøgt eksperimentelt. Sammenligningen med eksisterende modeller påpegede specificiteten af eksisterende sammenhænge og begrænsningen i deres anvendelsesområder. På grund af forskelle i indblæsning stråle, har eksisterende korrelationer en tendens til at overvurdere konvektionsstrømningen, især ved loftet. To fremgangsmåder er således blevet testet for bedre at kunne forklare strømingsformer i definitionen af konvektion koefficienter. Ved den første fremgangsmåde blev lokale værdier af lufthastigheden anvendt til at evaluere konvektion ved loftet. En alternativ fremgangsmåde består i at inkludere et modificeret Archimedes tal i definitionen af konvektion koefficienter. Begge fremgangsmåder forbedrede modelleringen af konvektion koefficienter med en afvigelse på ± 15-17% . Før implementeringen af disse sammenhænge i BES-værktøjer er der er behov for yderligere valideringer for andre typer og placeringer af indløb og andre rum geometrier. Heating and cooling terminals can be classified in two main categories: convective terminals (e.g air conditioning, active chilled beam, fan coil) and radiant terminals. The two terminals have different modes of heat transfer: the first one is mainly based on convection, whereas the second one is based on both radiation and convection. Radiant terminals have the advantage of making use of low grade sources (i.e. low temperature heating and high temperature cooling), thus decreasing the primary energy consumption of buildings. But there is a lack of knowledge on the heat transfer from the terminal towards the space and on the parameters influencing the effectiveness of terminals. Therefore the comfort conditions and energy consumption of four types of terminals (active chilled beam, radiant floor, wall and ceiling) have been compared for a typical office room, both numerically and experimentally. This thesis addressed mainly the cooling case. From the steady-state numerical analysis and the full-scale experiments, it has been observed that the difference between the two types of terminals is mainly due to changes in the ventilation losses (or gains). At low air-change rates (below 0.5 ACH), radiant and air-based terminals have similar energy needs. For higher air change rate, the energy consumption of radiant terminals is lower than that of air-based terminals due to the higher air temperature. At 2 ACH, the energy savings of a radiant wall can be estimated to around 10 % compared to the active chilled beam (in terms of delivered energy). The asymmetry between air and radiant temperature, the air temperature gradient and the possible short-circuit between inlet and outlet all play a role equally important in decreasing the cooling need of the radiant wall compared to the active chilled beam. The higher the air change rate and the warmer the outdoor air, the larger the savings achieved with a radiant cooling terminals. Therefore radiant terminals have a large potential of energy savings for buildings with high ventilation rates (e.g. shop, train station, industrial storage). Among radiant terminals, only small differences have been observed for the geometry considered. Only if the occupants are assumed to be sitting, the large view factor with the floor can lead to a reduction of the energy need for floor cooling systems.These conclusions are valid for multi-storey and/or highly insulated buildings (R > 5 m2.K/W). In case of single-storey building with a low level of insulation, the effectiveness of radiant terminals is lower due to the larger back losses, and an air-based terminal might be more energy-efficient than a radiant terminal (in terms of delivered energy). Regarding comfort, a similar global level has been observed for the radiant and air-based terminals in both numerical and experimental investigations. But the different terminals did not achieve the same uniformity in space. The active chilled beam theoretically achieves the most uniform comfort conditions (when disregarding the risk of draught), followed by the radiant ceiling. The least uniform conditions were obtained with the cooled floor due to large differences between the sitting and standing positions. Local comfort conditions (radiant asymmetry, vertical air temperature gradient, risk of draught) have also been evaluated both theoretically and numerically, and no discomfort has been observed for normal cooling needs.Besides this comparative study of different terminals, the relation between cooling system and internal convective flow has also been investigated experimentally. The comparison with existing models pointed out the specificity of existing correlations and the limitation of their range of application. Because of differences in the air jet trajectory, existing correlations tend to overestimate the convective flow, especially at the ceiling. Two approaches have thus been tested to better account for the air flow pattern in the definition of convective heat transfer coefficients (CHTC). In a first method, local values of air velocity have been used to evaluate convection at the ceiling. An alternative approach consists of including a modified Archimedes number in the definition of CHTC. Both methods improved the modelling of CHTC with an error around ± 15-17 %. Before implementing these correlations in BES tools, further validations are needed for other types and positions of inlet and other room geometries.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Barari, Amin;

    The world is currently facing serious problems brought about by oil dependence. Reducing oil consumption provides an opportunity to increase competitiveness, technological development, and progress. Wind energy is currently the most costcompetitive form of renewable energy, and there are strong political and industrial forces (particularly in northern Europe) supporting the development of the offshore wind industry.Offshore structures may consist of a single shallow foundation such as gravitybased platforms or multiple shallow foundations acting in concert (e.g., jack-up rigs or tension leg platforms). General loading is particularly relevant in the design of shallow foundations for offshore structures because wind, wave, and current forces produce substantial lateral load components at magnitudes that are not commonly encountered onshore.Bucket foundations were pioneered in the offshore oil and gas industry and have recently been used in offshore wind turbines. The bucket foundation is a welded steel structure consisting of a tubular center column connected to a steel bucket through flange-reinforced stiffeners.The overall aim of the research presented in this thesis was to improve the design of offshore wind turbine foundations. The work was divided into two main research efforts: geotechnical engineering experiments to gain insight into the behavior of offshore bucket foundations, and development of methods to improve the study of infiltration into unsaturated soils, an important problem in geo-environmental engineering. The outcomes of the research have the potential to directly or indirectly reduce the risks and costs related to offshore geotechnics.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Parmeggiani, Stefano;

    Denne PhD afhandling tager udgangspunkt i udviklingen af bølgeenergianlægget Wave Dragon. Bølgeenergi udgør en meget stor, ikke udnyttet energi ressource, der har potentiale til at blive en vigtig bidragyder til at løse verdens energiproblemer. Indtil i dag er den kommercielle udnyttelse af bølgeenergi blevet vanskeliggjort af udviklernes manglende evne til at demonstrere økonomisk rentable anlæg i fuld skala – først og fremmest som følge af manglende finansiering af demonstrationsanlæg. Selv om Wave Dragon teknologien har et endog meget stort potentiale for rentabel, vedvarende el-produktion, er teknologien fortsat på et prækommercielt udviklingstrin, hvor det er vanskeligt at skaffe fornøden kapital til at gennemfore et demonstrationsprojekt fuld skala. Afhandlingens formal har varet at lette dette arbejde dels ved at udbrede kendskabet til anlægget generelt som videnskabeligt, dels ved at bidrage til den seneste teknologiske udvikling af anlægget. Forskningen har først og fremmest fokuseret på at forbedre teknologiens attraktivitet set fra en investors synsvinkel på følgende to områder, der komplementere hinanden:• Pa indtægtssiden er palideligheden af forudsigelser vedrørende produktionsdata øget samtidigt med at gennemsigtigheden ved vurderingen af produktionsdata er øget. Dette er sket gennem udvikling af en forbedret, opdateret model for opskylsanlæg specielt tilpasset Wave Dragon, hvorigennem det har varet muligt at kvantificere energiproduktionen bedre sammenlignet med tidligere anvendte metoder. Parallelt hermed er beskrevet en proces, hvor den planlagte 1,5 MW prototype placeret ved DanWEC forsøgscentret ved Hanstholm, Danmark, indgår. Heri indgår muligheden af at foretage beregninger af usikkerhed for parametre relateret til eksperimentelle data fra offshore forsøg.• Pa omkostningssiden er der gennemfort en analyse dels med henblik på at bestemme design kræfter i forankringssystemet for DanWEC enheden og dels for at identificere strategier, der kan lede til reduktion i forankringssystemets samlede omkostning. Konklusionen er, at der kan opnås besparelse på op til 65 %. Den mest effektive metode til at opnå denne besparelse kraver en time-domain analyse. En numerisk model hertil er blevet kalibreret med resultater fra en fuldstændig hydrodynamisk karakterisering af Wave Dragon baseret på data fra forsøg og numeriske beregninger.Forskningen har skabt en dybere forståelse af opskylsprocessen for Wave Dragon ved at studere den bagvedliggende fysik i kombination med anlæggets udformning og det aktuelle bølgeklima. Denne analyse er mere dybdeborende end hidtil gennemfort vurderinger af anlægget, og den vil kunne anvendes generelt i forbindelse med opskylsanlæg. Herudover er gennemført en omfattende vurdering af hydraulisk respons samt kræfter i forankringssystemet, hvilket vurderes at kunne have relevans for alle udviklere af flydende offshore anlæg.Det har også været afhandlingens formål, at demonstrere ”best practice” for udvikling af bølgeenergianlæg i almindelighed ved at anvende Wave Dragons 20-arige udviklingsforløb som eksempel, -et udviklingsforløb, der har gjort Wave Dragon til et af de mest kendte bølgeenergianlæg i verden anerkendt for dets åbenhed om opnåede resultater. This doctoral thesis is framed into the development process of the Wave Dragon wave energy converter (WEC). Wave energy is a vast and untapped resource with the potential of becoming an important contributor to the World energy mix, although presently its commercial exploitation has been hindered by the difficulties of developers to demonstrate the technology feasibility at full-scale, first of all caused by lack of finance of full-scale demonstration units. Although having a large potential for the cost-effective generation of clean and renewable electricity, Wave Dragon is currently in a pre-commercial stage in which it has proven difficult to secure the necessary funding for the deployment of a full-scale demonstrator unit. The work presented aims at easing this process, by increasing public and scientific knowledge of the device, as well as by showing the latest progress in its development.Research has been mainly focused at increasing the attractiveness of the technology to potential investors, following two main complementary lines:• On the profit side, reliability of the performance figures provided and the transparency of the performance assessment process as a whole have been increased. This is mainly due to the development of an updated overtopping model specifically suited to Wave Dragon, which allows greater quality to predictions of the primary energy absorption of the device compared to previous versions. At the same time an equitable approach has been described and used in the performance assessment of the envisaged 1.5 MW unit to be deployed at the DanWEC test center in Denmark (WDDanWEC), including the possibility of providing an estimate of the uncertainty related to the given figures when these are mainly based on experimental data from sea trials. • On the cost side, an analysis has been carried out aimed at quantifying design loads in the mooring system of the WD-DanWEC unit, as well as identifying viable force-reduction strategies which would allow significant savings in design cost (estimated up to 65%). According to these results, the most cost-effective real mooring solutions will need to be identified by means of time-domain analyses. To do so, a numerical model has been calibrated for the application with the results from the complete hydrodynamic characterization of Wave Dragon, which has been carried out based on experimental data and numerical analysis.Overall, the research has also provided a deeper insight into the physics of the overtopping process by individually assessing the influence of related device configuration and wave features, which goes beyond the present application and may be used for other overtopping WECs as well. Comprehensive analysis of the motions response and mooring tension has also been carried out, which may be of relevance to other floating offshore installations.Among the objectives of the thesis is also to show best practices in the development of WECs through the Wave Dragon case, following almost 20 years of continuous development which has made it one of the best known WECs worldwide, recognized for its openness and transparency.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Ferri, Francesco;

    Med den industrielle udvikling efter 1769, tidspunktet hvor James Watt tog patent på dampmaskinen, er der opstå et økonomisk, politisk, miljømæssig og energimæssig krise – hvad enten man anser denne for antagelig eller reel. Svaret på spørgsmålet ”hvordan løser man disse problemer?” er en kompliceret og ufuldendt diskussion, men med introduktionen af vedvarende energiproduktion, er der givet et bud på, hvordan man til dels kan løse disse problemer. Bølgeenergi er en uudnyttet vedvarende energikilde, som har potentiale til at bidrage betydeligt til fremtidens blandede energiforsyning. Dog har bølgeenergisektoren endnu ikke udbudt denne mulighed på markedet grundet en række tekniske og ikke-tekniske årsager. Disse kan mest effektivt opsummeres ved at på pege produktionsudgifterne som opstår ved brug af de forskellige energitransformatorer: Sammenlignet med andre vedvarende energiteknologier, er produktionsudgifterne stadigt betydeligt højere, når man udnytter energi fra havets bølger. Hvis man bliver ved denne sammenligning, er det også vigtigt at være opmærksom på, at der ikke er en klar frontløber i bølgeenergisektoren, hvilket gør at indsats og finansering spredes over et bredt felt.For at kunne bidrage til en effektiv udvikling og analyse af bølgeenergikoncepter og dermed bidrage til en acceleration af hele sektorens fremgang mod kommercialisering, er det nødvendigt med et effektivt og på lideligt wave-to-wire værktøj, som er generelt anvendeligt. En wave-to-wire model identificerer relationen mellem en energikilde på et bestemt sted og enhedens forventede produktion. Sidstnævnte er udtrykt i form af elektricitet, der leveres til elnettet. Modellen skal kunne give et groft billede af den faktiske status af sektoren og dens potentiale, og senere bruges til at finde frem til de mest lovende koncepter.På et makroniveau kan arbejdet fordeles på to hovedindsatser.Først skal komplementaritet mellem numerisk simulation og eksperimentel erfaring fremhæves, hvilket mest effektivt kan opsummeres som: Pålidelig model. Numeriske modeller er i sig selv meningsløse men lette at manipulere, hurtige og relativt billige, hvor fysiske modeller er komplekse, langsomme og dyre, men realistiske hvis implementeret i tilstrækkelig grad. Siden der ikke er et faktisk behov for ”noget nyt” men snarere ”at få det bedste ud af hvad vi har”, er den anvendte numeriske model udelukkende baseret på veletablerede metoder. Eksperimentel data bliver anvendt som verifikation til at styre retningen af den numeriske udvikling.Dernæst, kaste lys på hvad der bør være målet for sektoren: Minimering af de samlede energiomkostninger. To forskellige teknikker til at reducere omkostningerne er sammenlignet: Den første maksimerer systemomsætning (indkomst) ved at ændre på kontrolstrategien, mens den anden udvider de første metoder ved at tilføje et straf baseret på kontrolstrategiens indflydelse på det strukturelle design. Begge modeller er igen baseret på veletablerede eller standardiserede teknikker. The wild development of the world from the 1769, years in which James Watt patented his steam engine, brought utterly to the actual, real or assumed, economical, political, environmental and energetic crisis. The answer to the question “how to solve these problems?" is a tangled unsolved discussion, but talking about renewable energy partially ravels the problem out. Wave energy is a large, mostly untapped, renewable energy resource. It has the potential to contribute significantly to the future energy mix, but the sector has not yet rolled off into the market in consequence of a number of technical and non-technical issues. These can be efficiently summarised in the cost of the energy produced by the various wave energy converters: If compared with other renewable energy technologies the cost of energy from the ocean waves is still significantly higher. Holding the comparison it also important to noticed that there is not a clear front runner in the wave energy sector, which fades effort and funding over a too broad frame.In order to assist efficient development and analysis of wave energy converters and therefore to accelerate the sector progression towards commercialisation, a generally applicable, efficient and reliable wave-to-wire model tool is needed. A wave-to-wire model identifies the relation from the source of energy of a particular location to the expected device productivity. The latter being expressed in terms of electricity fed into the grid. The model needs to output a coarse picture of the actual status of the different devices and their power productivity, which is used afterwards to sieve promising concepts out.In a macro-scale the work can be divided into two main contributionsFirst, highlight the complementarity between numerical simulation and laboratory experience, in what can be efficiently summarised as: reliable model. Numerical models are per se meaningless, but easy to manipulate, fast and relatively cheap. Physical models are complex, slow and expensive but realistic if adequately implemented. Since there is no real need of “new", but more of “how can we get the best of what we have", the numerical model used is entirely based on well established methods. The experimental data is used as a check point to verify the direction of the numerical path.Second, shed light on what should be the objective of the sector: minimisation of the cost of energy. Two different techniques to reduce the cost of energy are compared: the former maximises the system revenue (income) by acting on the control logic, while the second extends the first methods adding a penalty term due to the effect of the control logic on the structural design. Both methods are once more based on well established or standard techniques.

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    Authors: Lashab, Abderezak;
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Madsen, Søren;

    Der er i disse tider et stort politisk ønske om at udvide den grønne energisektor. En velfungerende grøn energiform er vindmøller. Et stort antal vindmøller er installeret på land i løbet af de sidste årtier. Dog resulterer den nuværende udvikling i mølledesign i stadigt større vindmøller, for at reducere energiprisen. Dette begrænser anvendelsen af vindmøller på land både pga. begrænsninger ift. transport men også pga. uvilje fra potentielle naboer til kæmpevindmøller. Derfor er der indenfor de sidste par år for alvor kommet gang i udviklingen af havvindmøller. Selv om det løser de førnævnte problemer at installere vindmøllerne til havs, forøger det energiprisen, primært på grund af øgede installations- og vedligeholdelsesomkostninger. En meget stor andel af installationsomkostningerne, op mod 30 - 50 % ved brug af den nuværende teknologi, stammer fra udgifter forbundet med installation af fundamenter. Et nyt funderingskoncept, bøttefundamentet, tegner til at kunne reducere omkostingerne til fundamenter i en havvindmøllepark. Bøttefundamentet forventes at blive billigere, da det er både hurtigere at installere i forhold til den nuværende teknologi, og det kræver ikke tungt installationsudstyr. Da et bøttefundament dybest set er en relativt tynd skalkonstruktion udsat for både aksialt og latteralt tryk under installationen, bliver foldning et vitalt designkriterium. I 2005 skulle en stor vindmølle installeres i et kystnært område ved havnen i Wilhelmshaven i Tyskland. Vindmøllen blev aldrig opført da der, under nedsugningprocessen, opstod foldning i bøttefundamentets skørt. I denne afhandling er fænomenet foldning af bøttefundamenter under installation undersøgt ved hjælp af Finite Element-analyser. Indflydelsen af randbetinglser på bøttefundamentet er undersøgt, tillige med effekten af at inkludere den omgivende jord og jord-struktur interaktion. Undersøgelser er foretaget for foldningshændelsen i Wilhelmshaven, og resultaterne er sammenlignet med gældende DNV og Eurocode standarder. Endeligt præsenteres analyser af en ny udformning af et tværsnit, betegnetmulti-shell,med en højere foldningskapacitet end et tilsvarende cirkulært tværsnit. Hovedresultaterne er listet nedenfor:• Låget på bøttefundamentet øger foldningskapaciteten i forhold til en simpelt understøttet rand,• Antallet af lågafstivninger påvirker ikke den elastiske foldningskapacitet væsentligt,• Den omgivende jord øger foldningskapaciteten væsentligt under installationen,• Kun at betragte den første svigtform fra en lineær analyse som imperfekt geometri i en ikkelineær foldningsanalyse er ikke tilstrækkelig til at opfange foldningshændelsen i Wilhelmshaven. Men det er det at betragte de første 21 svigtformer og indføre den mest kritiske som en imperfekt geometri,• Multi-shell tværsnittet er lige så følsom over for imperfektioner som en cirkulær cylinder,• Det nye multi-shell design giver en væsentligt større (75 %) foldningskapacitet i forhold til det traditionelle design. There is a great politically will to expand the green energy market in these times. A proven green technology is wind turbines. Wind turbines have been installed in great numbers on land over the last decades. However, the current development in wind turbine design leads to larger turbine sizes in order to reduce the cost of energy. This limits the on land application due to transportation limitations and unwillingness from prospect neighbours. Thus, offshore wind energy started developing over the last couple of years. Although installing the wind turbines offshore resolves the before men tioned issues, it brings up the cost of energy mainly due to increased installation and maintenance costs. A very large part—up to 30–50% using current technology—of the installation cost origins from the expenses related to the installation of foundations. A new foundation concept—the bucket foundation—has been proposed to reduce the foundation costs. The bucket foundation promises to be cheaper as it is both faster to install compared to current technology and it does not require heavy installation equipment. Since the bucket foundation is essentially a relatively thin shell structure subjected to both axial and latteral pressure during the installation process buckling becomes a crucial design consideration. In 2005, a large wind turbine was to be installed nearshore the harbour in Wilhelmshaven, Germany. The windturbine was never erected since the skirt of the bucket foundation buckled during the suction assisted installation process. In this thesis, the phenomenon of buckling of the bucket foundation during installation is investigated by means of Finite Element Analysis. The influence of boundary conditions on the bucket foundation is adressed as well as the effect of including the surrounding soil and soil–structure interaction. Investigations are made regarding the buckling incident in Wilhelmshaven and the results are compared to current DNV and Eurocode standards. Finally, analysis of a new design of the cross section with a higher buckling capacity than an equivalent circular cross seciton—denoted multi-shell—is presented. The main findings are listed below:• The bucket lid shows an increase in the buckling load compared to a pinned end,• Number of lid stiffeners does not substantially affect the elastic buckling load,• The soil restraint increases the buckling load significantly during penetration,• Considering the first mode shape from a linear buckling analysis as imperfect geometryin a nonlinear buckling analysis is not sufficient for capturing the buckling incident in Wilhelmshaven; however, considering the first 21 mode shapes and introducing themost critical one as an imperfect geometry is,• The multi-shell cross section is just as sensitive to imperfections as a circular cylinder,• The new multi-shell design provides a significantly larger (75%) buckling load compared to the traditional design.

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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Zajas, Jan Jakub;

    Selv om vinduesrammer kun er en relativ lille del af den samlede bygnings klimaskærm er de ansvarlig for en stor mængde varmetab, hvilket skyldes deres dårlige isoleringsegenskaber, hvis man sammenligner med andre bygningselementer. Med fokus på den nuværende trend i forhold til at reducere bygningers energiforbrug er det tydeligt, at der er behov for at forbedre den termiske ydeevne af nutidige rammer, således at bygningerne opfylder de nye og mere skrappe krav.Denne PhD afhandling vil fokusere på forbedringerne af den termiske ydeevne af vinduesrammer lavet af glasfiberforstærket plastik (FRP). Dette materiale er for nyligt blevet introduceret på markedet for vinduesrammer, og det er blevet et interessant valg grundet dets fine termiske og mekaniske egenskaber, hvilket kan medføre en forbedring af isoleringsevnen for vinduesrammer.Der er adskillige måder at forbedre den termiske transmission af vinduesrammer. Varme overførsel via en vinduesramme er en kombination af varmeledning, konvektion og stråling og hver af disse mekanismer kan reduceres på forskellig vis. Et eksempel kunne være at inddele hulrummene for at reducere konvektionsvarme flowet eller benytte emissitvity materialer for at mindske den radiation. Disse samt adskillige andre løsninger er undersøgt i første del af Phd afhandlingen. Simuleringer af simple geometrier er udført i forhold til at kunne evaluere potentialet ved forskellige løsninger. Resultaterne viser, at anvendelse af forskellige modifikationer til en vis grad giver en betydelig reduktion af termisk transmission. For at opnå ydereligere forbedringer kræver dette mere drastiske forandringer.På den baggrund er der foretaget en omfattende undersøgelse af, hvorledes rammegeometrien kan forbedres på et overordnet niveau. Ordinære vinduesrammer kan blive udformet i mange forskellige former, hvilket giver udviklerne en stor designmæssig frihed. Selv om der kan designes et uendeligt antal versioner af vinduesrammer er det ikke alle rammer, der vil have tilfredsstillende termiske egenskaber. Det er vigtigt at klarlægge, hvorledes et korrekt design af en ramme vil biddrage til at forbedre de termiske ydeevner. Derefter kan hele rammegeometrien blive optimeret i forhold til den termiske transmission, størrelse og materialevalg.Optimeringsprocessen kan blive foretaget ved at designe et stort antal vinduesrammers geometri og derefter evaluere deres termiske egenskaber, fortrinsvis på en automatisk måde. En stor del af denne PhD afhandling er dedikeret til udviklingen af et parametrisk designværktøj, som kan benyttes til et sådant formål. Derefter er det endelig værktøj brugt til at optimere rammerne. Optimeringen har fokus på flere formål, hvilket gør opgaven endnu mere kompliceret. Undersøgelsen foreslår to fremgangsmåder: en vægtet sum fremgangsmåde og en genetisk algoritme.Et andet formål med PhD afhandlingen var at udvikle en ny kombination af materialer, der kan bruges til at forbedre vinduesrammer. Denne kombination består af på ydersiden højstyrke kompositlaminat, og isolerende skum på indersiden. Resultatet blev udviklingen af et funktionelt gradueret materiale med rummeligt varierende egenskaber. Denne usædvanlige konstruktion skaber en udfordring i forhold til eksperimentel karakterisering af produktet. Problemstillingen kan løses ved at benytte laser flash metoden, som kan tilpasses dette specifikke formål. Der er foretaget mindre modifikationer i LFA 447 laser flash apparatet, som med en fin opløsning tillader afledning af de lokale transportegenskaber af forskellige materialer. Denne metode var valideret og blev med succes benyttet til formålet. Even though the window frames cover a relatively small fraction of the entire building envelope, they are responsible for a major amount of heat loss, due to their poor insulation properties compared to the other envelope elements. With the current trends to reduce energy use in buildings, it is obvious that the thermal performance of contemporary frames needs to be improved, so that buildings can fulfill the new, more rigorous demands.This study will focus on improving the thermal performance of window frames made of fiberglass reinforced plastic (FRP). This material has been recently introduced to the window frame market and is becoming an increasingly interesting choice, due to its fine thermal and mechanical properties which can lead to a significant improvement of the insulation properties of a window frame.There are several ways to improve the thermal transmittance of a window frame. Heat transfer through a frame is a combination of conduction, convection and radiation and each of these mechanisms of heat transfer can be diminished in certain ways. An example could be subdividing the cavities to reduce convective heat flow or using low emissivity materials to limit the thermal radiation. These, and several other solutions, are investigated in the first part of the study. Simulations on simple geometries are conducted to evaluate the potential of different solutions. The results show that by applying different modifications the thermal transmittance of a frame can be significantly reduced, but only to a certain extent. To reach further improvement, more drastic changes need to be done.Therefore, an extensive study is done on how to optimize the frame geometry on a broader level. Contemporary frames can be crafted into various shapes, giving the engineers a large freedom of design. Almost an infinite number of window frame geometries can be created, but not all of them will result in a frame with satisfying thermal properties. It is important to determine how a proper design of the frame can contribute to the improvement of its thermal performance. Afterwards, the entire frame geometry can be optimized in terms of the thermal transmittance, size and material use.The optimization process can be conducted by designing very large number of window frame geometries and evaluating their thermal properties, preferably in an automated way. A large part of this study is devoted to the development of a parametric design tool that could be used for this purpose. Afterwards, the final tool is used in a process of optimizing the frames. Optimization is done with regard to several objectives, what makes the task more complicated. Two approaches to this problem are suggested in this study: a weighted sum method and a genetic algorithm.Another objective of the project was to develop a new combination of materials that could be used in improved window frames. This combination consists of a high strength composite laminate on the outside and highly insulating foam on the inside. As a result, a functionally graded material with spatially varying properties was developed. This unusual construction creates a challenge for experimental characterization of this product. This issue can be solved by using laser flash method, which can be adapted for these specific purposes. Small modifications have been done in the LFA 447 laser flash apparatus that allow for derivation of the local transport properties of various materials, with a fine resolution. The method was validated and successfully used for this purpose.

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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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  • image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
    Authors: Le Dreau, Jerome;

    Varme- og køleanlæg kan inddeles i to hovedkategorier: konvektive systemer (fx. aircondition, aktiv kølebaffel, fan-coils) og stråle køling/varme systemer. De to systemer har forskellige former for varmeoverførsel; den første er hovedsageligt baseret på konvektion, mens den anden er baseret på både stråling og konvektion. Strålevarmesystemer har den fordel at kunne gøre brug af lav kilder (dvs. opvarmning ved lave temperature og køling ved høje temperaturer) og dermed reducere bygningers primære energiforbrug. Der er imidlertid en mangel på viden om varmeoverførsel fra terminalen mod rummet og på de parametre, der påvirker anlæggenes ydelse. Derfor er der foretaget en sammenligning af komfortbetingelserne og energiforbruget for fire typer anlæg (aktiv kølebaflen, strålende gulv, væg og loft) for et typisk kontorlokale, både numerisk og eksperimentelt.Fra den stationære numerisk analyse og fuldskalaforsøgene er det observeret, at forskellen mellem de to typer anlæg primært skyldes ændringer ventilationstab. Ved lave ventilationstilskud (under 0,5 ACH), har stråle- og luftbaserede systemer samme energibehov. Ved højere ventilationstilskud er strålevarmesystemers energiforbrug lavere end de luftbaserede systemers på grund af den højere lufttemperatur. Ved 2 ACH kan en strålevægs energibesparelser vurderes til ca. 10 % sammenlignet med den aktive kølebaflen (med hensyn til leveret energi). Asymmetrien mellem luft og strålingstemperatur, lufttemperaturgradienten og den mulige kortslutning mellem indløb og udløb spiller en lige så vigtig rolle ved reduceringen af strålevæggens kølebehov sammenlignet med den aktive kølebaflen. Jo højere et luftskifte og jo højere, jo større er de opnåede besparelser med en strålekølesystem. Derfor har strålekølesystemet et stort potentiale for energibesparelser i bygninger med et højt ventilationskifte (fx butikker, togstation, industriel opbevaring ). Blandt strålesystemer er der kun observeret små forskelle i den påtænkte geometri. Kun hvis beboerne antages at sidde ned, kan den store vinkelforhold med gulvet føre til en reduktion af energibehovet for gulvkølesystemer.Disse konklusioner gælder for fler-etagers eller højisolerede bygninger (R > 5 m2.K/W). Når det drejer sig om en enetagers bygning med et lavt isoleringsniveau, er strålesystemers effektivitet lavere på grund af de større klimaskærmstab, og et luftbaseret system kan være mere energieffektivt end et stråleanlæg (med hensyn til leveret energi).Et tilsvarende globalt komfort niveau er blevet observeret for stråle- og luftbaserede systemer i både numeriske og eksperimentelle undersøgelser, men de forskellige anlæg opnåede ikke den samme ensartethed i rummet. Den aktive kølebaflen opnår teoretisk de mest ensartede komfortbetingelser (når der ses bort fra risikoen for træk) efterfulgt af kølelofter. De mindst ensartede betingelser blev opnået med det afkølede gulv, på grund af store forskelle mellem siddende og stående stilling. Lokale komfortbetingelser (strålingstemperaturasymetrien, lufttemperaturgradient, risiko for træk) er også blevet evalueret både teoretisk og numerisk, og der er ikke observeret ubehag ved normal kølekapacitet.Udover denne sammenlignende undersøgelse af forskellige anlæg, er sammenhængen mellem kølesystemer og interne konvektionsstrømme også blevet undersøgt eksperimentelt. Sammenligningen med eksisterende modeller påpegede specificiteten af eksisterende sammenhænge og begrænsningen i deres anvendelsesområder. På grund af forskelle i indblæsning stråle, har eksisterende korrelationer en tendens til at overvurdere konvektionsstrømningen, især ved loftet. To fremgangsmåder er således blevet testet for bedre at kunne forklare strømingsformer i definitionen af konvektion koefficienter. Ved den første fremgangsmåde blev lokale værdier af lufthastigheden anvendt til at evaluere konvektion ved loftet. En alternativ fremgangsmåde består i at inkludere et modificeret Archimedes tal i definitionen af konvektion koefficienter. Begge fremgangsmåder forbedrede modelleringen af konvektion koefficienter med en afvigelse på ± 15-17% . Før implementeringen af disse sammenhænge i BES-værktøjer er der er behov for yderligere valideringer for andre typer og placeringer af indløb og andre rum geometrier. Heating and cooling terminals can be classified in two main categories: convective terminals (e.g air conditioning, active chilled beam, fan coil) and radiant terminals. The two terminals have different modes of heat transfer: the first one is mainly based on convection, whereas the second one is based on both radiation and convection. Radiant terminals have the advantage of making use of low grade sources (i.e. low temperature heating and high temperature cooling), thus decreasing the primary energy consumption of buildings. But there is a lack of knowledge on the heat transfer from the terminal towards the space and on the parameters influencing the effectiveness of terminals. Therefore the comfort conditions and energy consumption of four types of terminals (active chilled beam, radiant floor, wall and ceiling) have been compared for a typical office room, both numerically and experimentally. This thesis addressed mainly the cooling case. From the steady-state numerical analysis and the full-scale experiments, it has been observed that the difference between the two types of terminals is mainly due to changes in the ventilation losses (or gains). At low air-change rates (below 0.5 ACH), radiant and air-based terminals have similar energy needs. For higher air change rate, the energy consumption of radiant terminals is lower than that of air-based terminals due to the higher air temperature. At 2 ACH, the energy savings of a radiant wall can be estimated to around 10 % compared to the active chilled beam (in terms of delivered energy). The asymmetry between air and radiant temperature, the air temperature gradient and the possible short-circuit between inlet and outlet all play a role equally important in decreasing the cooling need of the radiant wall compared to the active chilled beam. The higher the air change rate and the warmer the outdoor air, the larger the savings achieved with a radiant cooling terminals. Therefore radiant terminals have a large potential of energy savings for buildings with high ventilation rates (e.g. shop, train station, industrial storage). Among radiant terminals, only small differences have been observed for the geometry considered. Only if the occupants are assumed to be sitting, the large view factor with the floor can lead to a reduction of the energy need for floor cooling systems.These conclusions are valid for multi-storey and/or highly insulated buildings (R > 5 m2.K/W). In case of single-storey building with a low level of insulation, the effectiveness of radiant terminals is lower due to the larger back losses, and an air-based terminal might be more energy-efficient than a radiant terminal (in terms of delivered energy). Regarding comfort, a similar global level has been observed for the radiant and air-based terminals in both numerical and experimental investigations. But the different terminals did not achieve the same uniformity in space. The active chilled beam theoretically achieves the most uniform comfort conditions (when disregarding the risk of draught), followed by the radiant ceiling. The least uniform conditions were obtained with the cooled floor due to large differences between the sitting and standing positions. Local comfort conditions (radiant asymmetry, vertical air temperature gradient, risk of draught) have also been evaluated both theoretically and numerically, and no discomfort has been observed for normal cooling needs.Besides this comparative study of different terminals, the relation between cooling system and internal convective flow has also been investigated experimentally. The comparison with existing models pointed out the specificity of existing correlations and the limitation of their range of application. Because of differences in the air jet trajectory, existing correlations tend to overestimate the convective flow, especially at the ceiling. Two approaches have thus been tested to better account for the air flow pattern in the definition of convective heat transfer coefficients (CHTC). In a first method, local values of air velocity have been used to evaluate convection at the ceiling. An alternative approach consists of including a modified Archimedes number in the definition of CHTC. Both methods improved the modelling of CHTC with an error around ± 15-17 %. Before implementing these correlations in BES tools, further validations are needed for other types and positions of inlet and other room geometries.

    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
    image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao VBNarrow_drop_down
      image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
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      Other ORP type . 2014
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