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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: Su, Chi;

    With the growing interconnection among distant power grids, low‐frequency oscillation problem across wide area arises in some modern power systems. This oscillation problem is commonly regarded as lack of damping in inter‐area oscillation modes in the sense of small signal stability. Solutions to this problem need to be implemented in the power systems. On the other hand, wind power especially largescale wind farms are increasingly integrated into modern power systems and bring new challenges to power system operation and control. The influence of wind power integration on system oscillation performance needs to be investigated. And according to some grid code requirements, power system oscillation damping improvement supplied by wind farms might become necessary. Under this circumstance, the present dissertation aims at studying oscillation damping control strategies using different components in the power system; investigating the possible influence of large‐scale wind power integration on system oscillation performance; developing oscillation mitigation strategies for wind farms; and coordinating various damping controllers in the power system. For the power system operation aspect, an optimal power flow (OPF) strategy is introduced, with system oscillation damping considered in the constraints of the optimization process. The method is validated by simulations in two test systems. For the power system control aspect, an optimal PMU placement method is used so as to provide full topological observability of the target power system and to provide wide‐area signals for damping controllers while minimizing the total PMU installation cost. Power system stabilizer (PSS) designs with both local input signal and wide‐area input signal are studied and compared. The PSS design is based on residue method and a residue identification technique is used. Furthermore, a particle swarm optimization (PSO) based coordinating strategy to select the locations, input signals and parameters of multiple PSSs is proposed. Simulation results show that this method is able to find a group of PSSs to improve the target mode damping to a certain level, while keeping the total magnitude of the PSSs low (so that the outputs from the PSSs could be kept low).A supplementary damping controller is integrated in the control system of a static synchronous series compensator (SSSC). The design is also based on residue method and residue identification. Simulation results show the effectiveness of this damping controller under different operating conditions of the SSSC. Influence of a direct‐drive‐full‐convertor based wind farm ancillary frequency control and voltage control on power system oscillation performance is investigated by observing the oscillation damping change in relation with the change of the ancillary controller parameters. Furthermore, the forced oscillation in the power system activated by the wind power oscillation due to wind shear and tower shadow effects is analyzed. The forced oscillation amplitude is found to be dependent on the location of the wind farm, the amplitude and frequency of the wind power oscillation and the damping ratio of the system oscillation modes. To mitigate the forced oscillation, two types of controllers are designed to reduce the wind power oscillation amplitude and to increase system oscillation mode damping ratio, respectively. The former controller is implemented in individual wind turbines; the latter controller is implemented in the wind farm level as a supplementary damping controller.Finally, the coordinating selection and parameter design strategy for PSS is extended for all types of damping controllers (including PSS in synchronous generator, SSSC damping controller and wind farm damping controller). Simulation results show the effectiveness of this strategy for coordinating various damping controllers.

    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 . 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
      VBN
      Other ORP type . 2012
      Data sources: VBN
  • 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: Ramirez, Jorge Robert Rodriguez;

    Interaktionen mellem af vandbølger og en cirkulær konstruktion, det såkaldte "wave run-up" fænomen er undersøgt. Dette run-up fænomen er blevet simuleret ved brug af CFD modeller.Den numeriske model (NS3) anvendt i dette studie er blevet verificeret på flere måder. Regelmæssige og såkaldte "monsterbølger" (freak- eller rogue waves) er blevet genereret i en numerisk bølgetank med en let hældning for at undersøge "wave run-up" på en cirkulær cylinder. Fra et beregningsmæssigt synspunkt er denne form for undersøgelse "billig". I øvrigt er den numeriske model præsenteret i denne afhandling sammenlignet med de målte resultater fra forsøget og en god sammenhæng er observeret.Udover denne numeriske undersøgelse, er et omfattende skalaforsøg udført. I forsøget er "wave run-up" på en tynd cirkulær cylinder i en uregelmæssig søtilstand blevet målt med bølgemålere placeret tæt på cylinderen. Baseret på passende analysemetoder er de indsamlede data blevet analyseret med strømfunktionsteorien for at opnå de relevante parametre til brug i den af den forudsagte "wave run-up" formel. En analytisk tilgang er blevet fulgt og løst for individuelle bølger. Maksimal "run-up" og 2% "run-up" er blev undersøgt for at opnå en bedre forståelse af fænomenet. Ifølge resultaterne fra denne analyse er det blevet fastslået, at "run-up" højder i høj grad er påvirket af bølgestejlheden på dybt vand. Samlet set er resultatet af dette studie, at den forenklede model af "wave run-up" på en slank cirkulær cylinder præsenteret i denne afhandling er det mest nyttigt redskab til platformsdesignere. This study has investigated the interaction of water waves with a circular structure known as wave run-up phenomenon. This run-up phenomenon has been simulated by the use of computational fluid dynamic models.The numerical model (NS3) used in this study has been verified rigorously against a number of cases. Regular and freak waves have been generated in a numerical wave tank with a gentle slope in order to address the study of the wave run-up on a circular cylinder. From the computational side it can be said that it is inexpensive. Furthermore, the comparison of the current numerical model presented in this thesis with the measured results from the experiments has shown a good agreement.Besides this numerical study, model scale experiments have been conducted where the wave run-up on a slender circular cylinder in irregular sea state was measured with surface gauges located close to the cylinder. Based on appropriate analysis the collected data has been analysed with the stream function theory to obtain the relevant parameters for the use of the predicted wave run-up formula. An analytical approach has been pursued and solved for individual waves. Maximum run-up and 2% run-up were studied to get a better understanding of the phenomenon. According to the results from this analysis it has been established that the run-up heights are largely influenced by the deep water wave steepness. Overall, the outcome of this research is that the simplified model presented in this thesis of the wave run-up on a slender circular cylinder is the most useful tool for platform designers.

    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
      VBN
      Other ORP type . 2012
      Data sources: VBN
  • 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: Winther, Frederik Vildbrad;

    Glasfacader er et stadigt mere dominerende valg af facadeløsning til kontorbyggeri. Glas har altid været attraktivt og spændende og har været et symbol på magt, penge og prestige. Facaden er et kommunikationsmiddel, et billede af prestige of magt. Glasfacaden lider dog voldsomt når energiforbruget af bygninger analyseres. Glasfacaden bidrager til højere energibehov til opvarmning, køling, osv. Glasfacaden har derfor behov for at overvinde væsentlige udfordringer for at forblive en attraktiv facade løsning i fremtidens nul energi byggeri.Ved brug af energiberegningsprogrammer og termisk simulerings værktøjer foretages den indledende analyse i denne afhandling af glasfacadens potentiale for en typisk kontorbygning i Danmark med glasfacade der opfylder energikravene fra 2008, for at mindske energibehovet til bygningsdrift som følge heraf. Denne simple analyse definerer de nøgleteknologier, der efterfølgende fokuseres på. Fokuseringen på hver enkelt teknologi udføres ved brugen af fuldskala forsøg af hver enkelt teknologi under varierende randbetingelser.Resultaterne fra demonstrationsforsøgene bliver efterfulgt af en udvikling af numeriske modeller tilknyttet de enkelte teknologier til brug i termiske simuleringsprogrammer samt til implementering i produktudvikling. Resultaterne fra den indledende analyse viser potentialet af en dynamisk facade, som muliggør variation af varmetabet, solenergitransmittansen, dagslys transmittans, masse transport og termisk energilagring. Potentialet fra denne analyse viser at for en typisk kontorbygning med den dynamiske glasfacade i sammenligning med den statiske glasfacade kan reducere bygningers energibehov til bygningsdrift med ca. 75 %. Fokusset flyttes derfor til de anvendte teknologier, der vedrører dynamisk U-værdi, dynamisk g-værdi, termisk energilagring og styringsstrategier for de anvendte facade teknologier. Fuldskala forsøgene anvendes til demonstration af de enkelte teknologiers ydeevne samt til validering af de udviklede numeriske modeller. De udviklede modeller viser en god beskrivelse af de anvendte teknologiers funktion og karakteristika både i termiske simuleringsprogrammer såvel som i koblingen mellem styring i termiske simuleringsprogrammer og fuldskala bygnings styringssystemer. Potentialet af facadens styringsstrategi vist numerisk, viser energibesparelsespotentialer for køling, opvarmning og belysning på mellem 50 % og 88 % som følge af facadens design og brug.De opnåede resultater fra den indledende analyse efterfulgt af udviklingen af de numeriske modeller af de anvendte facade teknologier, viser at der er væsentlige energibesparelser at hente i udformningen af den dynamiske facade. Energibesparelserne skal dog undersøges nærmere under mere kontrollerede laboratorieforhold for at kunne danne mere præcise data og numeriske modeller af de anvendte teknologier. Den videre udvikling af dynamiske facadeteknologier, som er i stand til at kontrollere energibalancen over facaden i samspil med brugere for at kunne udnytte og forstår det fulde potentiale af adaptive glasfacader. Glazed facades are becoming an increasingly dominant choice of facades for office buildings. Glass has always been attractive and intriguing and has been a symbol of power, money and prestige. The façade is a means of communicating an image of prestige and power. However the glazed suffers tremendously when analyzing the energy usage of a building. Glazed façade contribute to higher energy demand for heating. cooling, etc. The glazed façade therefore has significant challenges to overcome in order to remain as an attractive envelope solution in future zero-energy-building concepts.Through the use of energy calculation software and thermal building simulation software the initial analysis in this thesis strives towards defining the potential of controlling the energy transport across the façade. The simple analysis defines the key technologies to focus on as a result. The focus on each technology is to perform full-scale experiments on each technology showing the performance of the technology under varying boundary conditions. The results from the demonstration are then followed by a numerical model development of the technologies applied for use in thermal building simulation software as well as in practical façade control systemsThe results from the initial analysis show the performance of a dynamic façade which enables the variation of the heat transfer, transmitted irradiance, transmitted natural light, mass transport and thermal energy storage. The potential from this analysis show that the dynamic façade opposed to the static façade can decrease energy demand for building services by approximately 75 %. The focus is therefore on analyzing the used technologies which concern dynamic U-value, dynamic g-value, thermal energy storage and control strategies for dynamic facades. The full-scale experiments are used as demonstration and for validation of the performance of the developed numerical models. The developed numerical models show a good description of the applied technologies and show that the variation of the technologies function and characteristics can both be done through use of thermal building simulation software as well as full-scale experiments. The façade control system, which uses the results from the developed numerical models of the dynamic façade technologies, can lower the energy demand for heating, cooling and lighting as a results of the heat transfer across the façade by between 50 % and 88 %.The obtained results from the initial analysis through the developed numerical models to the final analysis show that there are significant energy savings in the design of the dynamic façade. The energy savings need to be further investigated under laboratory conditions generating more precise data and description of the used technologies. The further development of dynamic façade technologies which are able to control the energy balance across the façade is also necessary to analyze the behavior in practice and to gain knowledge of the human interaction with the adaptive glazed façade.

    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 . 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
      VBN
      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
    Authors: Grunnet, Jacob Deleuran;

    I fremtidig rumbaseret forskning stiger behovet for nøjagtige målinger i sådan en grad aten enkelt satellit på visse missioner ikke længere vil være i stand til at bære instrumenteraf den nødvendige størrelse. En af de mest lovende ideer til at overkomme dette problemer satellitformationer hvor nøjagtig positionsregulering kan bruges til at skabe meget storevirtuelle apparaturer eller meget følsomme interferometriske målinger.Satellitformationskontrol skaber en hel ny række udfordringer inden for rumfartøjskontrol,som kræver udvikling inden for aktuatorer, sensorer, kommunikation og kontrolalgoritmer.En af disse udfordringer opstår på grund af den øgede kompleksitet somduplikeringen af kontrolsystemerne til multiple satellitter medfører. Denne duplikation afkomponenter og undersystemer øger sandsynligheden for at en komponent fejler såledesat formationskontrollen påvirkes, men duplikationen øger også redundansen i formationen.Kombineret med at det er urealistisk dyrt at reparere en satellit i kredsløb, så ermotivationen for at designe fejltolerante regulatorer specifikt til satellitformationer stor.Denne afhandling bruger en hybrid systems model af en satellitformation med mulighedfor aktuator fejl som et motiverende eksempel for udviklingen af en automatiseretkontrolsyntesemetode til stykvist-affine hybride systemer (SAHS). Metoden åbner ikkekun op for fremtidig forskning i fejltolerant kontrol af satellitformationer, men kan ogsåblive brugt til at syntetisere regulatorer til en læng række af systemer hvor eksterne begivenhederkan påvirke systemets dynamik.Syntesemetoden bygger på en abstraktion af det hybride system til et diskret spil, atfinde en vindende strategi til spillet således at en “Computation Tree Logic” specifikationbliver overholdt, samt raffinering af den resulterende løsning til en tabel over stykvistaffineregulatorer.Metoden er blevet implementeret i PAHSCTRL Matlab værktøjskassen ved brug aflinere-matrix-uligheds “feasibility” beregninger til at finde den diskrete abstraktion, UppAalTiga til løsning af det diskrete spil og linear optimering for at raffinere regulatorer.Den præsenterede metode har nogle begrænsninger. Den bygger på fuld tilstandsinformationog kan derfor ikke håndtere sensorfejl, og den beregningsmæssige komplexitetaf metoden vokser eksponentielt med tilstandsrummets dimension. Den sidste af de tobegrænsninger er delvist afhjulpet af at beregninger udføres a priori og det faktum atberegningstiden skalerer næsten lineært med antallet af tilgængelige beregningsenheder.Slutteligt, må de fleste realistiske systemmodeller transformeres for at komme påSAHS form, hvilket sædvanligvis involverer partitionering af tilstandsrummet i polytoper.Erfaring har vist at den specifikke partitionering af tilstandsrummet let kan påvirke dendiskrete spilabstraktion. og yderlige forskning i partitionsmetoder er derfor nødvendigfor at den foreslåede metode bliver generelt anvendelig. To further advance space based science the need for ever more precise measurement techniquesincreases. One of the most promising new ideas are satellite formations whereaccurate spatial control of multiple spacecraft can be used to create very large virtualapertures or very sensitive interferometric measurements.Control of satellite formations presents a whole new set of challenges for spacecraftcontrol systems requiring advances in actuation, sensing, communication, and controlalgorithms. Specifically having the control system duplicated onto multiple satellites increasesthe possibility of negating faults while the added number of components increasesthe likelihood of faults occurring. Combined with the fact that once a mission is launchedit is prohibitively expensive to repair a failing component there is a good case for designingfault tolerant controllers specifically for satellite formations.This thesis uses a hybrid systems model of a satellite formation with possible actuatorfaults as a motivating example for developing an automated control synthesis method fornon-deterministic piecewise-affine hybrid systems (PAHS). The method does not onlyopen an avenue for further research in fault tolerant satellite formation control, but can beused to synthesise controllers for a wide range of systems where external events can alterthe system dynamics.The synthesis method relies on abstracting the hybrid system into a discrete game,finding a winning strategy for the game meeting a computational tree logic formula andrefining the resulting solution to a catalogue of piecewise-affine controllers.The method has been implemented as aMatlab toolbox, PAHSCTRL , using linear matrixinequality feasibility computations for finding the discrete abstraction, UppAal Tigafor solving the discrete game and linear optimisation solvers for controller refinement.To illustrate the efficacy of the method a reoccurring satellite formation example includingactuator faults has been used. The end result is the application of PAHSCTRL onthe example showing synthesis and simulation of a fault tolerant formation controller.The presented method has some limitations. It relies on full state observations andcan thus not handle sensor system faults and the computational complexity of computingdiscrete abstractions grows exponentially with the dimension of the state space. Thelatter limitation is mitigated by the fact that the computations are performed off-line andthe computation time scales almost linearly with the number of parallel execution units.Finally, most realistic system models must undergo a transformation to be brought onPAHS form and this usually involves partitioning the state space of the different failuremode into polytopes. Experience shows that the specific partitioning of the state spacecan have profound effects on the discrete game abstraction and further research is thereforeneeded into partitioning methods in order to make the proposed synthesis methodgenerally applicable.

    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 . 2009
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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: Møller-Jensen, P.;

    The present thesis deals with the transport phenomena of estuarine cohesive sediment from a laboratory and a numerical point of view. The cohesive sediment used throughout the whole process was natural mud from the Danish part of the Wadden sea, Ho Bay. In the laboratory, the work was concentrated on studies of the settling velocity of particles under conditions with various salinities and suspended sediment concentrations, erosion of deposited material and compression and consolidation of deposited material due to self-weight.As part the project, equipments for settling, consolidation and erosion experiments were developed. The settling and consolidation experiments were carried out in a transparent cylinder with a diameter of 190 mm and variable height. The erosion experiments were carried out in a circular flume with a mea diameter of 1700 mm, a width of 200 mm and a depth of 260 mm.A one dimensional numerical model was developed describing the material distribution in suspension and within the bed and the transfer processes, namely, erosion and deposition. The model was calibrated using the laboratory experiments.

    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 . 1993
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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 . 1993
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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: Bønsing, Sten;
    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; Aalborg Univers...arrow_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 VBN; Aalborg Univers...arrow_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
  • 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: Pedersen, Claus;

    A numerical model simulating the sediment transport due to plunging breaking waves has been developed. The model is two-dimensional, assuming conditions in the long-shore direction invariable. A plunging breaker is simulated by superimposing a non-breaking wave with a jet.Based on the description of the sediment transport rates, a simple model describing the morphological changes has been applied to simulate the evolution of a plunge point generated vorticity included, the bottom topography from the experiments by Dette & Uliczka was not in equilibrium according to the model.

    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 . 1994
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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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    Authors: Bønsing, Sten;
    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; Aalborg Univers...arrow_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
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    Authors: Germann, Lars;

    Gennem de sidste årtier har begrebet arbejdsmiljø konstant været i fokus. Det hænger både sammen med en stigende miljøbevidsthed og voksende krav til livskvaliteter. Arbejdsmiljøet omfatter en lang række områder som f.eks. fysisk- og psykisk arbejdsmiljø, sikker hed, akustik, støj, termisk miljø, luftkvalitet etc. Alle sammen områder der har stor betydning for det almene velbefindende såvel på arbejdet som i fritiden.

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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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    Other ORP type . 1993
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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: Nielsen, Jannie Sønderkær;

    For havvindmøller er omkostningerne til vedligehold omfattende da der ofte er komponenter i vindmøllen, som svigter. Udover reparationsomkostningerne er der store omkostninger forbundet med leje af materiel og tabt produktion grundet begrænset tilgængelighed til vindmøllerne. For at reducere omkostningerne kan der benyttes præventive metoder, men i dag benyttes der imidlertid normalt ikke avancerede metoder, der tager højde for al tilgængelig information på en konsistent måde, når præventiv vedligehold planlægges.Beslutninger om vedligehold kan træffes ved anvendelse af risikobaserede metoder, hvor de totale forventede omkostninger i levetiden minimeres. Der er udviklet metoder til at estimere omkostningerne til korrektiv vedligehold, og ligeledes er der publiceret mange studier vedrørende præventiv vedligehold. En vigtig del er modelleringen af sammenhængen mellem vedligehold og pålidelighed, hvilket ofte ikke er modelleret på en konsistent måde. Metoderne kan derfor ikke bruges direkte til optimal planlægning af drift og vedligehold, hvor der tages højde for information fra overvågningssystemer, inspektioner, præventive reparationer samt korrektive reparationer. Dette kan gøres ved at benytte metoder, som er udviklet fra et Bayesiansk perspektiv. Den slags metoder er allerede udviklet til brug i olie- og gasindustrien under navnet Risikobaseret Inspektionsplanlægning (RBI), og er baseret på Bayesiansk preposteriori beslutningsanalyse. For at gøre løsningen beregningsteknisk muligt er det nødvendigt at indføre approksimationer. Den tilgangsvinkel, som typisk benyttes til RBI, kan ikke overføres direkte til vindmøller, da forholdene er anderledes. For vindmøllekomponenter er pålideligheden mindre sammenlignet med olie- og gaskonstruktioner. Desuden er der ofte overvågningssystemer på vindmøller, og informationerne derfra bør medtages, når der træffes beslutninger.I denne afhandling benyttes Bayesianske metoder til risikobaseret vedligeholdelsesplanlægning med det formål at træffe optimale beslutninger, der tager højde for al tilgængelig information. Først formuleres en teoretisk skadesmodel, hvorefter modellen opdateres ved hjælp af overvågningsdata, og endelig bruges den opdaterede model som basis for risikobaseret beslutningstagning. Flere fremgangsmåder til at løse beslutningsproblemerne er blevet betragtet: forskellige slags stationære beslutningsregler, influens-diagrammer med begrænset hukommelse (LIMID), og Markov beslutningsprocesser. Ved flere af fremgangsmåderne er Bayesianske netværk blevet brugt til beregningerne.Fremgangsmåderne er blevet afprøvet med teoretiske beslutningsproblemer, og de forventede omkostninger blev sammenlignet for forskellige strategier. Det var muligt at opnå store besparelser, men resultaterne afhænger naturligvis meget af forudsætningerne. For virkelige beslutningsproblemer kan det være vanskeligt at formulere modellen, hvis forudsætningerne brugt under dimensioneringen ikke er opfyldt i virkeligheden. Metoderne har store potentialer, men kræver yderligere udvikling, specielt med hensyn til at modellere virkelige eksempler. For offshore wind turbines, maintenance costs are substantial due to a large number of component failures. In addition to the repair costs, equipment costs and lost production costs are large due to limited accessibility to the turbines. In order to reduce the costs, preventive methods can be used, but presently maintenance is not planned using advanced methods taking all available information into account in a consistent manner.Maintenance decisions can be made based on risk-based methods, where the total expected life cycle costs are minimized. Methods have been developed for assessing the corrective maintenance costs, and many studies have also been published for preventive maintenance. However, an important part is the modeling of the relationship between maintenance and reliability, which is typically not modeled in a consistent way. Therefore, the methods cannot be used directly for optimal maintenance planning, taking into account monitoring, inspections, preventive repairs and corrective repairs. This can be done using methods developed from a Bayesian perspective. Such methods have been developed for use in the oil and gas industry under the name Risk-Based Inspection (RBI), and are based on the Bayesian pre-posterior decision analysis. In order to make the problem computationally feasible, approximations are necessary. The approach typically used for RBI cannot directly be transferred to wind turbines as the conditions are different. For wind turbine components, the reliability is lower compared to oil and gas structures. In addition, condition monitoring systems are often available, and the information should be taken into account when making decisions.In this thesis, methods for risk-based maintenance planning using Bayesian methods are investigated, with the aim of making optimal decisions considering all available information. First, a theoretical damage model is formulated, the model is then updated using condition monitoring data, and the updated model is used as basis for risk-based decision making. Several approaches for solving the decision problems have been considered: various types of stationary decision rules, limited memory influence diagrams, and Markov decision processes. Several of the approaches are used together with Bayesian networks.The approaches have been tested for theoretical decision problems, and the expected costs were compared for different strategies. It was possible to achieve big savings, but the results of course largely depend on the input. With real decision problems, it can be difficult to formulate the model if the design assumptions are not fulfilled in real life. The potential of the method is large, but further development is necessary, especially concerning the modeling of specific examples.

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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: Su, Chi;

    With the growing interconnection among distant power grids, low‐frequency oscillation problem across wide area arises in some modern power systems. This oscillation problem is commonly regarded as lack of damping in inter‐area oscillation modes in the sense of small signal stability. Solutions to this problem need to be implemented in the power systems. On the other hand, wind power especially largescale wind farms are increasingly integrated into modern power systems and bring new challenges to power system operation and control. The influence of wind power integration on system oscillation performance needs to be investigated. And according to some grid code requirements, power system oscillation damping improvement supplied by wind farms might become necessary. Under this circumstance, the present dissertation aims at studying oscillation damping control strategies using different components in the power system; investigating the possible influence of large‐scale wind power integration on system oscillation performance; developing oscillation mitigation strategies for wind farms; and coordinating various damping controllers in the power system. For the power system operation aspect, an optimal power flow (OPF) strategy is introduced, with system oscillation damping considered in the constraints of the optimization process. The method is validated by simulations in two test systems. For the power system control aspect, an optimal PMU placement method is used so as to provide full topological observability of the target power system and to provide wide‐area signals for damping controllers while minimizing the total PMU installation cost. Power system stabilizer (PSS) designs with both local input signal and wide‐area input signal are studied and compared. The PSS design is based on residue method and a residue identification technique is used. Furthermore, a particle swarm optimization (PSO) based coordinating strategy to select the locations, input signals and parameters of multiple PSSs is proposed. Simulation results show that this method is able to find a group of PSSs to improve the target mode damping to a certain level, while keeping the total magnitude of the PSSs low (so that the outputs from the PSSs could be kept low).A supplementary damping controller is integrated in the control system of a static synchronous series compensator (SSSC). The design is also based on residue method and residue identification. Simulation results show the effectiveness of this damping controller under different operating conditions of the SSSC. Influence of a direct‐drive‐full‐convertor based wind farm ancillary frequency control and voltage control on power system oscillation performance is investigated by observing the oscillation damping change in relation with the change of the ancillary controller parameters. Furthermore, the forced oscillation in the power system activated by the wind power oscillation due to wind shear and tower shadow effects is analyzed. The forced oscillation amplitude is found to be dependent on the location of the wind farm, the amplitude and frequency of the wind power oscillation and the damping ratio of the system oscillation modes. To mitigate the forced oscillation, two types of controllers are designed to reduce the wind power oscillation amplitude and to increase system oscillation mode damping ratio, respectively. The former controller is implemented in individual wind turbines; the latter controller is implemented in the wind farm level as a supplementary damping controller.Finally, the coordinating selection and parameter design strategy for PSS is extended for all types of damping controllers (including PSS in synchronous generator, SSSC damping controller and wind farm damping controller). Simulation results show the effectiveness of this strategy for coordinating various damping controllers.

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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
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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: Ramirez, Jorge Robert Rodriguez;

    Interaktionen mellem af vandbølger og en cirkulær konstruktion, det såkaldte "wave run-up" fænomen er undersøgt. Dette run-up fænomen er blevet simuleret ved brug af CFD modeller.Den numeriske model (NS3) anvendt i dette studie er blevet verificeret på flere måder. Regelmæssige og såkaldte "monsterbølger" (freak- eller rogue waves) er blevet genereret i en numerisk bølgetank med en let hældning for at undersøge "wave run-up" på en cirkulær cylinder. Fra et beregningsmæssigt synspunkt er denne form for undersøgelse "billig". I øvrigt er den numeriske model præsenteret i denne afhandling sammenlignet med de målte resultater fra forsøget og en god sammenhæng er observeret.Udover denne numeriske undersøgelse, er et omfattende skalaforsøg udført. I forsøget er "wave run-up" på en tynd cirkulær cylinder i en uregelmæssig søtilstand blevet målt med bølgemålere placeret tæt på cylinderen. Baseret på passende analysemetoder er de indsamlede data blevet analyseret med strømfunktionsteorien for at opnå de relevante parametre til brug i den af den forudsagte "wave run-up" formel. En analytisk tilgang er blevet fulgt og løst for individuelle bølger. Maksimal "run-up" og 2% "run-up" er blev undersøgt for at opnå en bedre forståelse af fænomenet. Ifølge resultaterne fra denne analyse er det blevet fastslået, at "run-up" højder i høj grad er påvirket af bølgestejlheden på dybt vand. Samlet set er resultatet af dette studie, at den forenklede model af "wave run-up" på en slank cirkulær cylinder præsenteret i denne afhandling er det mest nyttigt redskab til platformsdesignere. This study has investigated the interaction of water waves with a circular structure known as wave run-up phenomenon. This run-up phenomenon has been simulated by the use of computational fluid dynamic models.The numerical model (NS3) used in this study has been verified rigorously against a number of cases. Regular and freak waves have been generated in a numerical wave tank with a gentle slope in order to address the study of the wave run-up on a circular cylinder. From the computational side it can be said that it is inexpensive. Furthermore, the comparison of the current numerical model presented in this thesis with the measured results from the experiments has shown a good agreement.Besides this numerical study, model scale experiments have been conducted where the wave run-up on a slender circular cylinder in irregular sea state was measured with surface gauges located close to the cylinder. Based on appropriate analysis the collected data has been analysed with the stream function theory to obtain the relevant parameters for the use of the predicted wave run-up formula. An analytical approach has been pursued and solved for individual waves. Maximum run-up and 2% run-up were studied to get a better understanding of the phenomenon. According to the results from this analysis it has been established that the run-up heights are largely influenced by the deep water wave steepness. Overall, the outcome of this research is that the simplified model presented in this thesis of the wave run-up on a slender circular cylinder is the most useful tool for platform designers.

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    Authors: Winther, Frederik Vildbrad;

    Glasfacader er et stadigt mere dominerende valg af facadeløsning til kontorbyggeri. Glas har altid været attraktivt og spændende og har været et symbol på magt, penge og prestige. Facaden er et kommunikationsmiddel, et billede af prestige of magt. Glasfacaden lider dog voldsomt når energiforbruget af bygninger analyseres. Glasfacaden bidrager til højere energibehov til opvarmning, køling, osv. Glasfacaden har derfor behov for at overvinde væsentlige udfordringer for at forblive en attraktiv facade løsning i fremtidens nul energi byggeri.Ved brug af energiberegningsprogrammer og termisk simulerings værktøjer foretages den indledende analyse i denne afhandling af glasfacadens potentiale for en typisk kontorbygning i Danmark med glasfacade der opfylder energikravene fra 2008, for at mindske energibehovet til bygningsdrift som følge heraf. Denne simple analyse definerer de nøgleteknologier, der efterfølgende fokuseres på. Fokuseringen på hver enkelt teknologi udføres ved brugen af fuldskala forsøg af hver enkelt teknologi under varierende randbetingelser.Resultaterne fra demonstrationsforsøgene bliver efterfulgt af en udvikling af numeriske modeller tilknyttet de enkelte teknologier til brug i termiske simuleringsprogrammer samt til implementering i produktudvikling. Resultaterne fra den indledende analyse viser potentialet af en dynamisk facade, som muliggør variation af varmetabet, solenergitransmittansen, dagslys transmittans, masse transport og termisk energilagring. Potentialet fra denne analyse viser at for en typisk kontorbygning med den dynamiske glasfacade i sammenligning med den statiske glasfacade kan reducere bygningers energibehov til bygningsdrift med ca. 75 %. Fokusset flyttes derfor til de anvendte teknologier, der vedrører dynamisk U-værdi, dynamisk g-værdi, termisk energilagring og styringsstrategier for de anvendte facade teknologier. Fuldskala forsøgene anvendes til demonstration af de enkelte teknologiers ydeevne samt til validering af de udviklede numeriske modeller. De udviklede modeller viser en god beskrivelse af de anvendte teknologiers funktion og karakteristika både i termiske simuleringsprogrammer såvel som i koblingen mellem styring i termiske simuleringsprogrammer og fuldskala bygnings styringssystemer. Potentialet af facadens styringsstrategi vist numerisk, viser energibesparelsespotentialer for køling, opvarmning og belysning på mellem 50 % og 88 % som følge af facadens design og brug.De opnåede resultater fra den indledende analyse efterfulgt af udviklingen af de numeriske modeller af de anvendte facade teknologier, viser at der er væsentlige energibesparelser at hente i udformningen af den dynamiske facade. Energibesparelserne skal dog undersøges nærmere under mere kontrollerede laboratorieforhold for at kunne danne mere præcise data og numeriske modeller af de anvendte teknologier. Den videre udvikling af dynamiske facadeteknologier, som er i stand til at kontrollere energibalancen over facaden i samspil med brugere for at kunne udnytte og forstår det fulde potentiale af adaptive glasfacader. Glazed facades are becoming an increasingly dominant choice of facades for office buildings. Glass has always been attractive and intriguing and has been a symbol of power, money and prestige. The façade is a means of communicating an image of prestige and power. However the glazed suffers tremendously when analyzing the energy usage of a building. Glazed façade contribute to higher energy demand for heating. cooling, etc. The glazed façade therefore has significant challenges to overcome in order to remain as an attractive envelope solution in future zero-energy-building concepts.Through the use of energy calculation software and thermal building simulation software the initial analysis in this thesis strives towards defining the potential of controlling the energy transport across the façade. The simple analysis defines the key technologies to focus on as a result. The focus on each technology is to perform full-scale experiments on each technology showing the performance of the technology under varying boundary conditions. The results from the demonstration are then followed by a numerical model development of the technologies applied for use in thermal building simulation software as well as in practical façade control systemsThe results from the initial analysis show the performance of a dynamic façade which enables the variation of the heat transfer, transmitted irradiance, transmitted natural light, mass transport and thermal energy storage. The potential from this analysis show that the dynamic façade opposed to the static façade can decrease energy demand for building services by approximately 75 %. The focus is therefore on analyzing the used technologies which concern dynamic U-value, dynamic g-value, thermal energy storage and control strategies for dynamic facades. The full-scale experiments are used as demonstration and for validation of the performance of the developed numerical models. The developed numerical models show a good description of the applied technologies and show that the variation of the technologies function and characteristics can both be done through use of thermal building simulation software as well as full-scale experiments. The façade control system, which uses the results from the developed numerical models of the dynamic façade technologies, can lower the energy demand for heating, cooling and lighting as a results of the heat transfer across the façade by between 50 % and 88 %.The obtained results from the initial analysis through the developed numerical models to the final analysis show that there are significant energy savings in the design of the dynamic façade. The energy savings need to be further investigated under laboratory conditions generating more precise data and description of the used technologies. The further development of dynamic façade technologies which are able to control the energy balance across the façade is also necessary to analyze the behavior in practice and to gain knowledge of the human interaction with the adaptive glazed façade.

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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
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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: Grunnet, Jacob Deleuran;

    I fremtidig rumbaseret forskning stiger behovet for nøjagtige målinger i sådan en grad aten enkelt satellit på visse missioner ikke længere vil være i stand til at bære instrumenteraf den nødvendige størrelse. En af de mest lovende ideer til at overkomme dette problemer satellitformationer hvor nøjagtig positionsregulering kan bruges til at skabe meget storevirtuelle apparaturer eller meget følsomme interferometriske målinger.Satellitformationskontrol skaber en hel ny række udfordringer inden for rumfartøjskontrol,som kræver udvikling inden for aktuatorer, sensorer, kommunikation og kontrolalgoritmer.En af disse udfordringer opstår på grund af den øgede kompleksitet somduplikeringen af kontrolsystemerne til multiple satellitter medfører. Denne duplikation afkomponenter og undersystemer øger sandsynligheden for at en komponent fejler såledesat formationskontrollen påvirkes, men duplikationen øger også redundansen i formationen.Kombineret med at det er urealistisk dyrt at reparere en satellit i kredsløb, så ermotivationen for at designe fejltolerante regulatorer specifikt til satellitformationer stor.Denne afhandling bruger en hybrid systems model af en satellitformation med mulighedfor aktuator fejl som et motiverende eksempel for udviklingen af en automatiseretkontrolsyntesemetode til stykvist-affine hybride systemer (SAHS). Metoden åbner ikkekun op for fremtidig forskning i fejltolerant kontrol af satellitformationer, men kan ogsåblive brugt til at syntetisere regulatorer til en læng række af systemer hvor eksterne begivenhederkan påvirke systemets dynamik.Syntesemetoden bygger på en abstraktion af det hybride system til et diskret spil, atfinde en vindende strategi til spillet således at en “Computation Tree Logic” specifikationbliver overholdt, samt raffinering af den resulterende løsning til en tabel over stykvistaffineregulatorer.Metoden er blevet implementeret i PAHSCTRL Matlab værktøjskassen ved brug aflinere-matrix-uligheds “feasibility” beregninger til at finde den diskrete abstraktion, UppAalTiga til løsning af det diskrete spil og linear optimering for at raffinere regulatorer.Den præsenterede metode har nogle begrænsninger. Den bygger på fuld tilstandsinformationog kan derfor ikke håndtere sensorfejl, og den beregningsmæssige komplexitetaf metoden vokser eksponentielt med tilstandsrummets dimension. Den sidste af de tobegrænsninger er delvist afhjulpet af at beregninger udføres a priori og det faktum atberegningstiden skalerer næsten lineært med antallet af tilgængelige beregningsenheder.Slutteligt, må de fleste realistiske systemmodeller transformeres for at komme påSAHS form, hvilket sædvanligvis involverer partitionering af tilstandsrummet i polytoper.Erfaring har vist at den specifikke partitionering af tilstandsrummet let kan påvirke dendiskrete spilabstraktion. og yderlige forskning i partitionsmetoder er derfor nødvendigfor at den foreslåede metode bliver generelt anvendelig. To further advance space based science the need for ever more precise measurement techniquesincreases. One of the most promising new ideas are satellite formations whereaccurate spatial control of multiple spacecraft can be used to create very large virtualapertures or very sensitive interferometric measurements.Control of satellite formations presents a whole new set of challenges for spacecraftcontrol systems requiring advances in actuation, sensing, communication, and controlalgorithms. Specifically having the control system duplicated onto multiple satellites increasesthe possibility of negating faults while the added number of components increasesthe likelihood of faults occurring. Combined with the fact that once a mission is launchedit is prohibitively expensive to repair a failing component there is a good case for designingfault tolerant controllers specifically for satellite formations.This thesis uses a hybrid systems model of a satellite formation with possible actuatorfaults as a motivating example for developing an automated control synthesis method fornon-deterministic piecewise-affine hybrid systems (PAHS). The method does not onlyopen an avenue for further research in fault tolerant satellite formation control, but can beused to synthesise controllers for a wide range of systems where external events can alterthe system dynamics.The synthesis method relies on abstracting the hybrid system into a discrete game,finding a winning strategy for the game meeting a computational tree logic formula andrefining the resulting solution to a catalogue of piecewise-affine controllers.The method has been implemented as aMatlab toolbox, PAHSCTRL , using linear matrixinequality feasibility computations for finding the discrete abstraction, UppAal Tigafor solving the discrete game and linear optimisation solvers for controller refinement.To illustrate the efficacy of the method a reoccurring satellite formation example includingactuator faults has been used. The end result is the application of PAHSCTRL onthe example showing synthesis and simulation of a fault tolerant formation controller.The presented method has some limitations. It relies on full state observations andcan thus not handle sensor system faults and the computational complexity of computingdiscrete abstractions grows exponentially with the dimension of the state space. Thelatter limitation is mitigated by the fact that the computations are performed off-line andthe computation time scales almost linearly with the number of parallel execution units.Finally, most realistic system models must undergo a transformation to be brought onPAHS form and this usually involves partitioning the state space of the different failuremode into polytopes. Experience shows that the specific partitioning of the state spacecan have profound effects on the discrete game abstraction and further research is thereforeneeded into partitioning methods in order to make the proposed synthesis methodgenerally applicable.

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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: Møller-Jensen, P.;

    The present thesis deals with the transport phenomena of estuarine cohesive sediment from a laboratory and a numerical point of view. The cohesive sediment used throughout the whole process was natural mud from the Danish part of the Wadden sea, Ho Bay. In the laboratory, the work was concentrated on studies of the settling velocity of particles under conditions with various salinities and suspended sediment concentrations, erosion of deposited material and compression and consolidation of deposited material due to self-weight.As part the project, equipments for settling, consolidation and erosion experiments were developed. The settling and consolidation experiments were carried out in a transparent cylinder with a diameter of 190 mm and variable height. The erosion experiments were carried out in a circular flume with a mea diameter of 1700 mm, a width of 200 mm and a depth of 260 mm.A one dimensional numerical model was developed describing the material distribution in suspension and within the bed and the transfer processes, namely, erosion and deposition. The model was calibrated using the laboratory experiments.

    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
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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: Bønsing, Sten;
    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; Aalborg Univers...arrow_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
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    Authors: Pedersen, Claus;

    A numerical model simulating the sediment transport due to plunging breaking waves has been developed. The model is two-dimensional, assuming conditions in the long-shore direction invariable. A plunging breaker is simulated by superimposing a non-breaking wave with a jet.Based on the description of the sediment transport rates, a simple model describing the morphological changes has been applied to simulate the evolution of a plunge point generated vorticity included, the bottom topography from the experiments by Dette & Uliczka was not in equilibrium according to the model.

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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
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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: Bønsing, Sten;
    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; Aalborg Univers...arrow_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 VBN; Aalborg Univers...arrow_drop_down
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    Authors: Germann, Lars;

    Gennem de sidste årtier har begrebet arbejdsmiljø konstant været i fokus. Det hænger både sammen med en stigende miljøbevidsthed og voksende krav til livskvaliteter. Arbejdsmiljøet omfatter en lang række områder som f.eks. fysisk- og psykisk arbejdsmiljø, sikker hed, akustik, støj, termisk miljø, luftkvalitet etc. Alle sammen områder der har stor betydning for det almene velbefindende såvel på arbejdet som i fritiden.

    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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