190 research outputs found
Repetitive Control of Individual Pitch to Reduce Wake Effect on Wind Turbines
No full textEfterhånden som windmøller bliver større, med rotordiametre over 100 m, vil vingerne dække et større vindfelt som indeholder en række forskellige vindfænomener, såsom wakes, vindforskydning, tårnskygge, hvilket vil påføre store strukturelle laster på vindmøllen.I denne these er en løftet repetitive regulator udviklet, som reducere de strukturelle laster ved brug af individuel pitching. Til dette formål er en dynamisk model af en vindmølle udledt. Modellen indeholder en aerodynamiskmodel, mekaniskmodel, en strukturelmodel og en model af pitchingsystemet. Modellen er blevet lineariseret og valideret i forhold til simulerings koden FAST.Fra modellen er en løftet repetitive regulator blevet udviklet, ved at lave en løftet system beskrivelse, og herfra blev en reduceret output-feedback formulering fundet, hvilken lagde grunden til LQR designet af regulatoren.I en accepttest blev den løftede repetitive regulator samlignet med regulatoren fra FAST som var implementeret i Matlab. Resultatet herfra var at accepttesten ikke blev godkendt, selvom bøjningen af tårn og vinger blev reduceret. Det formodes at dette skyldes en forskel mellem implementeringen i Matlab og modellen.As wind turbines get larger, with rotor diameters above 100 m, the blades will sweep a large wind field, containing different wind phenomenas such as, wakes, wind shear and tower shadow; applying a big structural load upon the wind turbine.In this thesis, a lifted repetitive controller is developed which reduces the structural loads by the use of individual pitching. For this purpose a dynamic model of a wind turbine has been developed. The model contains an aerodynamic model, mechanical model, a structural model and a model of the pitch system. The model has been linearized and validated in accordance with simulation code FAST.From the model a lifted repetitive controller was design, by making a lifted system description where made, and from this a reduced output-feedback formulation was found, making it possible to use LQR design to calculate the controller gain.In an acceptance test, the lifted repetitive controller was compared to the controller from FAST which was implemented in Matlab. The results from this were, that the controller designed did not pass, even though the deflection of tower and blades were reduced. It is assumed that it is caused by a mismatch between the model and the implementation in Matlab
Inclusion of Dynamic Inflow in Model Predictive Control of Wind Turbines
No full textDenne afhandling analyserer behovet for inkluder- ing af dynamisk inflow i modelprediktiv regulering af vindmøller. De undersøgte hovedområder er effekt- produktion og tårntræthed. Projektet er foreslået og delvist vejledt af Vestas Wind Systems A/S i Aarhus, Danmark.I denne afhandling anvendes en 5 MW vindmølle fra NREL, som er en 3-vinget landbaseret opvinds, horisontal-akset vindmølle, der simuleres i FAST. Der er lavet en analyse af systemet og problemet, der klarlægger hvilke ting, der skal med i designet af en modelprediktiv regulator, der inkluderer dynamisk inflow. Derudover er der lavet en evaluering af de mulige forbedringer, som kan vindes ved inkludering af dynamisk inflow. I analysen er metoden rainflow counting undersøgt og anvendt til at udregne tårn- træthed, hvor en skadesækvivalent belastning bliver udregnet.Der opstilles en model, som inkluderer aerodynamik, drivtog, tårndynamik, vingeaktuator og generator. Herfra bliver modellen delt op i to modeller. En der anvender en quasistatisk inflow model og en som an- vender en simpel dynamisk inflow model. Modellerne er anvendt i to modelprediktive regulatorer, som er sammenlignet. Denne sammenligning er lavet ved hjælp af Pareto kurver, da der eksisterer en afvejn- ing imellem effektproduktion og tårntræthed. Sammenligningen viser en markant forbedring lige over rated vindhastighed, hvor dynamisk inflow er mest markant. Den modelprediktive regulator med information om dynamisk inflow er i stand til at forbedre træthedsækvivalentet med mere end 20%, samtidig med en forbedring på 5% i den gennem- snitlige absolutte effektfejl.This thesis investigates the need for including dy- namic inflow in Model Predictive Control (MPC) of wind turbines. The main design drivers are gener- ated power and tower fatigue. The project has been proposed and partly supervised by Vestas Wind Sys- tems A/S in Aarhus, Denmark.The wind turbine used in this thesis to generate re- sults is the NREL 5 MW wind turbine, which is a 3 bladed onshore upwind HAWT simulated in FAST. An analysis of the system and the problem is made that clarifies, which things that should be addressed in the design of an MPC including dynamic inflow. Furthermore, an initial evaluation is made of the pos- sible improvements from including dynamic inflow. In this analysis the rainflow counting method is also shown as a measurement of fatigue, where a Damage Equivalent Load is found.A model including aerodynamics, drivetrain, tower dynamics, pitch actuator and generator is estab- lished. From here the model is split into two models. One where the aerodynamics is a quasi-steady model and one where the aerodynamics contain a simple dynamic inflow model. These models of the wind turbine are used for two MPCs, which are then com- pared. The comparison are done as Pareto fronts, as there exist a trade-off between power generation performance and tower fatigue.The results show significant improvements just above rated wind speed, where dynamic inflow is most out- spoken. The MPC with dynamic inflow information is able to improve the fatigue by more than 20%, while also improving the mean absolute error from the reference of the power at about 5%
Free Time: Game Design To Promote Shared Expectations of Family Time
No full textSmart devices are a part of everyday life and screen use is quickly becoming a ubiquitous activity. Related studies have shown that families are experiencing tensions in relation to in-home screen use and that they often fail in trying to implement strategies to address these tensions. This study explore to what extent the Self-Determination Theory and gamification can be utilized to help families reflect on tensions regarding their screen use. We studied how the Self-Determination Theory can be used to map existing feelings towards the motivation to address screen use related tensions. Using Research through Design combined with digital ethnography we have investigated how implementing our board game design called "Free Time" can help sprout motivation towards establishing shared expectations to family time and thereby alleviate tensions related to screen use. In conclusion, this study is a contribution to the field of HCI research on the topic of technological tensions emanating from use of smart devices. Our main contribution with this study lies in the finding that Free Time can influence perceptions on tensions, but also actual behaviour, surrounding screen use during family time. This study suggests that the Free Time could improve upon family time by its ability to bypass the reluctance of family members to engage in screen use related discussion by fear of conflict, found in related work on the subject
Worldviews Of The Greenlanders: An Inuit Arctic Perspective. By Birgitte Sonne
No full textIn this book the author brings together all the relevant sources about the cosmology of the Greenlandic Inuit, comparing Alaskan, Eastern Inuit, and Siberian sources.This work allows access to material that is, for most people, otherwise difficult to access, and it provides valuable new insights. If anybody thought that the Greenlandic pre-colonial religion was in any way poor or simple, their view will be thoroughly shaken after reading this book.The author states that one purpose of this work was to provide a Greenland companion to the fairly recent publications about the cosmologies of Canadian and Alaskan Inuit/Yupiit, and all themes are discussed with references to the works of her counterparts in Alaska and Canada and to many other researchers.<br/
Informal Monograph on Riverine Sand Dunes
No full textThis report presents an investigation of riverine sand dunes and includes an extensive literature review on the subject. It was concluded that the principal mechanisms responsible for river bed instability, which results in the production of ripples, dunes, etc., are fairly well understood. However, several of the key constituent processes are not well formulated. Principal among these are the phase shifts that occur between the local sediment discharge, the local near-bed velocity, local bed-profile displacement, and local bed shear stress. The reasons for the current deficiencies in the theoretical models are discussed and are concluded to stem from the difficulties inherent to analysis of nonuniform, turbulent, boundary-layer-type flows. Several existing theories for prediction of dune height were verified. None of the five published predictors evaluated was found to be satisfactory. A new, "inverse" model for prediction of dune height was developed
Talking about evil...
No full textProjektet undersøger forskellige ondskabsopfattelser i Vesten og viser, gennem analyser af modtagelsen af Hannah Arendts rapport 'Eichmann in Jerusalem' og diskussioner om Anders Breiviks terrorangreb, hvordan de forskelle opfattelser af ondskab mulig og umuliggør visse forhold til ondskab.This paper investigates the conception of evil in the west and how the public debate reacts in two specific debates about evil. In order to do that, we delve into the philosophy of evil, and explain different view- points and theories of evil. The paper discusses the moral agent and its relation to evil, and the system in which the actor acts and its relation to evil - and the relation between those two. Through this theoretical light the paper analyses two cases of public debates concerning evil: the de- bate around Hannah Arendt and her view of the Eichmann trial, and the debate around Anders Breivik and the Utøya massacre. We examine how evil are understood, and how people react to evil behavior - in the debate. Then the paper discusses the pitfalls and potentials of the different types of explanations and views of evil, which were expressed in the debate. The paper concludes that there is a complexity to evil, which makes it difficult talk about for two reasons. 1) When you debate evil you are in a vulnerable position where your worldview can change. 2) The language and understanding of what the term evil means differ. The paper also concludes that based on the two debates the choice of doing evil has a profound place in western understanding of evil
Incidence of joint replacement surgery among biologics and non-biologics treated patients with rheumatoid arthritis:a propensity score matched cohort study from denmark
No full textBackground Biologics have improved several clinical, patient-reported and radiological outcomes in patients with rheumatoid arthritis (RA), but little is known about the potential impact on the need for joint replacement surgery.Objectives To investigate the incidence of joint replacement surgery among biologics treated compared with biologics naïve patients with RA.Methods A nationwide, register-based propensity score matched cohort study. RA patients registered between 2006 and 2016 in the DANBIO register with a disease duration ≤ 2 years were identified. Patients initiating their first treatment series with biologics were followed up to 10 years for a first joint replacement of the hip, knee, shoulder, elbow and finger/wrist. Biologics naïve patients were followed up for the same outcome from their first clinical visit registered in DANBIO. Following a 1:n propensity score matching, Cox-models were undertaken to calculate the hazard ratio (HR) for a first joint replacement surgery among biologics compared with non-biologics treated RA patients. Further, subgroup analyses based on within-strata propensity score matched patients were carried out. All information on surgical outcomes was obtained in the Danish National Patient Registry.Results In total, 1187 biologics treated were matched with 3666 non-biologics treated patients (See Table). View this table:Abstract THU0059 – Table1 Baseline characteristics of biologics treated and biologics naïve patients with rheumatoid arthritis and a disease duration &lt; 2 years registered in DANBIO between 2006 and 2016.During follow-up, 43 biologics-treated and 124 naive patients had a first joint replacement surgery corresponding to an overall HR of 0.95 (0.65 to 1.40) for biologics treated compared with naïve patients (Figure 1). Patients with a DAS28-CRP &lt; 4.6 at start of follow-up (low and moderate disease activity)1, biologics treated had a lower risk of joint replacements compared with biologics naïve patients.Conclusion In this nationwide Danish cohort study, there was no difference in the incidence of joint replacement surgery among newly diagnosed RA patients selected for treatment with biologics compared with patients naïve to biologics.Abstract THU0059 – Figure 1 References [1] Fleischmann, et al. DAS28-CRP and DAS28-ESR cut-offs for high disease activity in rheumatoid arthritis are not interchangeable. RMD Open 2017;3:2–6.Disclosure of Interests René Cordtz: None declared, Samuel Hawley: None declared, Daniel Prieto-Alhambra Grant/research support from: Grants from Amgen, UCB Biopharma and Servier outside the submitted work, Consultant for: UCB Biopharma, Speakers bureau: Amgen, Lars Erik Kristensen Grant/research support from: UCB, Biogen, Janssen Pharmaceuticals, and Novartis, Consultant for: Consultant for AbbVie, Amgen, Biogen, BMS, Celgene, Eli Lilly, Janssen Pharmaceuticals, MSD, Novartis, Pfizer, Roche, Sanofi, and UCB Pharma., Speakers bureau: Pfizer, AbbVie, Amgen, UCB, BMS, Biogen, MSD, Novartis, Eli Lilly and Company, and Janssen Pharmaceuticals, Søren Overgaard: None declared, Anders Odgaard: None declared, Lene Dreyer Consultant for: MSD, UCB and Janssen Pharmaceuticals, Speakers bureau: MSD, UCB and Janssen Pharmaceuticals, Speakers bureau: UCB, MSD, Eli Lilly and Janssen Pharmaceuticals
Patellofemoral arthroplasty is cheaper and more effective in the short term than total knee arthroplasty for isolated patellofemoral osteoarthritis:cost-effectiveness analysis based on a randomized trial
No full textAIMS: The aim is to assess the cost-effectiveness of patellofemoral arthroplasty (PFA) in comparison with total knee arthroplasty (TKA) for the treatment of isolated patellofemoral osteoarthritis (OA) based on prospectively collected data on health outcomes and resource use from a blinded, randomized, clinical trial.METHODS: A total of 100 patients with isolated patellofemoral osteoarthritis were randomized to receive either PFA or TKA by experienced knee surgeons trained in using both implants. Patients completed patient-reported outcomes including EuroQol five-dimension questionnaire (EQ-5D) and 6-Item Short-Form Health Survey questionnaire (SF-6D) before the procedure. The scores were completed again after six weeks, three, six, and nine months, and again after one- and two-year post-surgery and yearly henceforth. Time-weighted outcome measures were constructed. Cost data were obtained from clinical registrations and patient-reported questionnaires. Incremental gain in health outcomes (quality-adjusted life-years (QALYs)) and incremental costs were compared for the two groups of patients. Net monetary benefit was calculated assuming a threshold value of €10,000, €35,000, and €50,000 per QALY and used to test the statistical uncertainty and central assumptions about outcomes and costs.RESULTS: The PFA group had an incremental 12 month EQ-5D gain of 0.056 (95% confidence interval (CI) 0.01 to 0.10) and an incremental 12 month cost of minus €328 (95% CI 836 to 180). PFA therefore dominates TKA by providing better and cheaper outcomes than TKA. The net monetary benefit of PFA was €887 (95% CI 324 to 1450) with the €10,000 threshold, and it was consistently positive when different measures of outcomes and different cost assumptions were used.CONCLUSION: This study provides robust evidence that PFA from a one-year hospital management perspective is cheaper and provides better outcomes than TKA when applied to patients with isolated patellofemoral osteoarthritis and performed by experienced knee surgeons. Cite this article: Bone Joint J 2020;102-B(4):449-457.</p
Optimal Wind Farm Lifetime Power Production
No full textThis project is a collaboration between Goldwind, Technical University of Denmark (DTU) and Delft University of Technology (TUDelft), of which focusing in developing an optimization model that could determinate the optimal operation schedule for wind turbine under the uncertainty of the electricity price and limitation in life-time equivalent fatigue loads, for the purpose of improving and maximizing the revenue or cash flow for wind farm project.The project comprises of two main parts, including the design and validation of up- and de-rated operation modes, and the model development and optimization of the revenue. The design of the different operation modes provide varies rated power without sacrificing the life-time structural integrity, as such offer extra flexibility in wind turbine operation schedule according to the fluctuation in electricity price. Life-time equivalent loads would be calculated for the different operation modes design and a weighting factor, that indicate the rate of fatigue consumption relatively to the normal operation, would be computed and used in the optimization process. An optimization model is developed based on the turbine structural constraints as well as the financial profile. The optimization model processes the electricity price data and other wind turbine data, for example the fatigue consumption, to reproduce the optimal operation schedule and operation price thresholds that would yield utmost financial benefits.The optimizer has a proven performance improvement in revenue generation of 1.5% and 5% reduction in the project related interest payment under one of the case study under electricity price uncertainty. The model is effective in scheduling the turbine operation upon the varying electricity price. This optimization model is providing game changing insights and operation strategies that could be used throughout the turbine life-time under the ever changing electricity price of the energy market. And further drive down the cost of energy in the highly competitive market. By improvising continuous input to the optimizer including bending moment sensors inputs, the optimization process could reproduce a more accurate revenue improvement.European Wind Energy Masters (EWEM
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