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Influence of Yaw Misalignment on Wind Turbine Wakes and Power Production Under Different Atmospheric Conditions: An LES and Analytical Modeling Study
Get PDFAs global reliance on renewable energy grows, optimizing wind farm performance has become essential for meeting sustainable energy demands. The interaction between wind turbines and the atmospheric boundary layer presents significant challenges, particularly in understanding wake dynamics and power production under varying atmospheric conditions and yaw misalignment. This thesis investigates the use of WRF-SADLES and an analytical wake model developed by Bastankhah and Porté-Agel (2016) to evaluate yaw misalignment as a wake mitigation strategy.
Simulations are conducted for two distinct atmospheric conditions with varying yaw angles to identify best practices for optimizing power production relative to non-yawed configurations. A two-turbine system, where the upwind turbine is yawed, is analyzed to capture the complex interactions between upwind and downwind turbines. Power production is evaluated across different turbine spacings, yaw angles, and atmospheric conditions, capturing a broad spectrum of scenarios. Key wake phenomena, such as wake deflection, wake recovery, and wake curling, are analyzed for their contributions to total power production.
The LES data generated with WRF-SADLES is used to calibrate and validate an analytical wake model. The analytical model demonstrated reasonable agreement with LES results for non-yawed and moderate yaw angles, successfully capturing the primary mechanisms driving power production under yaw misalignment. However, at larger yaw angles, it struggled to represent the asymmetric wake shapes associated with wake curling. These findings highlight the highly interdependent nature of yaw misalignments effectiveness, which is primarily governed by the extent to which wake deflection and recovery improve inflow conditions for the downwind turbine. While not universally beneficial, yaw misalignment can be a viable strategy when these improvements sufficiently compensate for the yaw-induced power loss of the upwind turbine.
Results further emphasize that the nuanced effectiveness of yaw misalignment depends on a delicate balance of atmospheric stability, turbine spacing, yaw angles, and site-specific conditions. Moderate yaw angles (10 −20 degrees) offer reliable performance, while more aggressive yawing benefits configurations with limited turbine spacing ( 10 x/D). The convective atmosphere enhanced power gains, reinforcing yaw misalignment as a promising wake mitigation strategy when tailored to favorable wind farm configurations. This research contributes to the growing body of evidence supporting yaw misalignment’s potential while underscoring the need for further advancements in LES and analytical modeling to refine its application across diverse operating environments.Masteroppgave i energiENERGI399MAMN-ENER
A hypercubic Mk model framework for capturing reversibility in disease, cancer, and evolutionary accumulation modelling
Get PDFMotivation
Accumulation models, where a system progressively acquires binary features over time, are common in the study of cancer progression, evolutionary biology, and other fields. Many approaches have been developed to infer the accumulation pathways by which features (e.g. mutations) are acquired over time. However, most of these approaches do not support reversibility: the loss of a feature once it has been acquired (e.g. the clearing of a mutation from a tumor or population).
Results
Here, we demonstrate how the well-established Mk model from evolutionary biology, embedded on a hypercubic transition graph, can be used to infer the dynamics of accumulation processes, including the possibility of reversible transitions, from data which may be uncertain and cross-sectional, longitudinal, or phylogenetically/phylogenomically embedded. Positive and negative interactions between arbitrary sets of features (not limited to pairwise interactions) are supported. We demonstrate this approach with synthetic datasets and real data on bacterial drug resistance and cancer progression. While this implementation is limited in the number of features that can be considered, we discuss how this limitation may be relaxed to deal with larger systems.publishedVersio
Weak solvability of elliptic variational inequalities coupled with a nonlinear differential equation
No full textIn this paper we establish existence, uniqueness, and boundedness results for an elliptic variational inequality coupled with a nonlinear ordinary differential equation. Under the general framework, we present a new application modeling the antiplane shear deformation of a static frictional adhesive contact problem. The adhesion process has been extensively studied, but it is usual to assume a priori that the intensity of adhesion is bounded by introducing truncation operators. The aim of this article is to remove this restriction.
The proof is based on an iterative approximation scheme showing that the problem has a unique solution. A key ingredient is finding uniform a priori bounds for each iterate. These are obtained by adapting versions of the Moser iteration to our system of equations.publishedVersio
Value based radiology - quality improvement in refferal of radiological examinations within musculoskeletal disorders.
No full textBruken av bildediagnostikk øker, samtidig sees en høy andel lav-verdi undersøkelser. Gjennom kvalitetsforbedringsprosjektet «VeRaVest» ønsker man å forbedre fastlegers henvisningspraksis ved muskel – og skjelettlidelser.
Hensikten med studien var å kartlegge hvordan fastleger som deltar på kurset «Verdibasert radiologi» oppfatter egen henvisningspraksis, og om det finnes potensiale for økt kvalitet på henvisninger ved bruk av kvalitetsforbedringsverktøy. Samtidig ble det sett på sammenheng mellom dette og fastlegens alder og erfaring.
Det er samlet inn data fra spørreskjema ved to ulike tidspunkt. Utvalget besto av 50 fastleger. Fastlegene har benyttet kvalitetsforbedringsverktøyene «clinical outreach activities», «clinical decision support system», «reminders» og «audit and feedback».
Over halvparten (62%) tror de vil klare å innføre – og følge anbefalinger om riktig bruk av radiologi. Andelen fastleger som har gjort endring i praksis, har økt fra 42% til 50% (p = 0,04). Fastlegene tar opp grundig sykehistorie og gjør en grundig klinisk vurdering (98%), her sees ingen endring fra baseline til oppfølgingstidspunkt. Studien finner endring i andelen fastleger som informerer pasientene fra 56% til 82% (p = 0,006). Studien finner ikke sammenheng mellom fastlegens alder, erfaring, og vurderinger hen gjør før henvisning eller hvilke kliniske opplysninger som inkluderes i henvisningen.
Fastlegene i studien opplever at riktig bruk av radiologiske undersøkelser er så viktig at det er verdt innsatsen. De tror de vil klare å innføre- og følge anbefalinger, halvparten oppgir å ha endret praksis i henhold til dette ved oppfølgingstidspunkt. Sammenheng mellom alder, erfaring og henvisningspraksis blir ikke påvist.Masteroppgave i helse og samfunnHELSAM395MAMD-HESA
Explorations of Physical Attacks Against Embedded Systems and Their Defences
Get PDFTil dagleg omgir me oss med hundrevis av elektroniske system. Desse systema, som gjerne blir kalla innvevde system, finst i bilane me køyrer, i kritisk infrastruktur, og i heimane våre. Som brukarar tek me ofte for gitt at desse systema er sikre, men realiteten er at mange slike system inneheld sårbarheiter, og at nokon med rett motivasjon og kunnskap kan utnytte desse sårbarheitane.
Det finst mange typar sikkerheitsproblem som kan oppstå i innvevde system, og dei er ikkje alltid like godt forstått. Dette gjer at det er ei framifrå vanskeleg oppgåve å utvikle innvevde system som er sikre mot angrep.
For å betre dette, er det viktig å prøve å forstå dei forskjellige typane angrep slike system kan bli utsett for.
Sidekanalsanalyse og feilinjisering er eksempel på angrep som kan
bli brukt til å hente ut hemmeleg informasjon frå eit system, eller gjere at systemet oppfører seg på feil måte.
Sjølv om desse angrepa har vore kjende i fleire tiår, kjem det stadig nye variantar og det vert oppdaga nye svakheiter. Ved å finne desse svakheitene og undersøke dei underliggande årsakene, kan me forstå dei betre. Denne forståinga er naudsynt for å kunne utvikle beskyttelsesmetodar og meir robuste system.
Hovudfokuset til denne avhandlinga er fysiske angrep, det vil seie sidekanals- og feilinjiseringsangrep, mot innvevde system og metodar for å beskytte mot desse. Artiklane i denne avhandlinga ser på ulike tema innan dette. Ein artikkel demonstrerer eit sidekanalsangrep mot ein implementasjon av ein kvantesikker krypteringsalgoritme, og ein anna beskrive ein metode for å beskytte verdas mest brukte krypteringsalgoritme mot sidekanalsangrep. To andre artiklar fokuserer på feilinjisering. Den eine av dei analyserer ein eksisterande metode for å beskytte mot slike angrep og peikar på moglege problem med denne metoden. Den andre beskriv ein lite kjend metode for å injisere feil i elektroniske system og diskuterer betydninga av dette og korleis ein kan beskytte system mot metoden. Den siste artikkelen forlet temaet fysiske angrep, og beskriv ein metode for å finne ulineært tilbakekopla skiftregister med maksimal periode, noko som kan vere ein nyttig byggekloss i sikre system.Every day, we rely on hundreds of electronic systems embedded in the cars we drive, the appliances in our homes, and important infrastructure that supports our communities.
End users often assume these embedded systems are secure. However, the reality is that many of them can be compromised by individuals with the right skills and determination, especially when physical access to the system is possible.
Designing secure embedded systems presents a significant challenge due to the many and sometimes poorly understood vulnerabilities. To enhance the security of these systems, it is important to understand the various attack methods they may face. For instance, side-channel and fault-injection attacks can be used to extract sensitive information or manipulate system behaviour. Although these attacks have been recognized for decades, new variants and vulnerabilities continue to emerge. By identifying these vulnerabilities and investigating their root causes, we can increase our understanding of the security challenges in embedded systems - an understanding that is essential for developing effective countermeasures and more robust systems.
This thesis primarily focuses on physical attacks against embedded systems and their corresponding countermeasures, with a particular emphasis on side-channel and fault-injection attacks. Among the included research papers, one demonstrates a side-channel attack against an implementation of a post-quantum cryptographic algorithm, while another proposes a countermeasure against side-channel attacks for our most widely used cryptographic algorithm. Additionally, two papers concentrate on fault injection, with one evaluating an existing countermeasure and highlighting a potential weakness, and another introducing a potentially novel fault-injection method and discussing related countermeasures. Lastly, a final paper diverges from physical attacks and presents a search method for finding nonlinear-feedback shift registers with maximal periods, which can be a useful building block for secure systems.Doktorgradsavhandlin
Assessing Slope Stability under the Influence of Climate Change: A Case Study from Ål, Norway
Get PDFMasteroppgave i geovitenskapGEOV399MAMN-GEO
Lung function outcomes in adults born extremely preterm across three decades of advancing perinatal medicine
Get PDFAim: Advances in perinatal medicine from 1980 to 2000 improved survival in extremely preterm (EP) neonates. Long-term effects of these developments remain unclear, and we aimed to investigate potential cohort effects on adult lung function.
Methods: Three 18-year-old population-based cohorts born at ≤28 weeks gestation or with birthweight ≤1000 g during 1982–85, 1991–92 and 1999–2000 and term-controls underwent spirometry, body plethysmography, and tests of lung diffusing capacity, bronchodilator reversibility, and airway hyperresponsiveness. We used Welch's t-tests to compare term- with EP-born as a group and split by bronchopulmonary dysplasia (BPD), and regression models to test group/cohort interactions.
Results: In all EP-born cohorts, z-scores for FEV1, FEV1/FVC, FEF25%–75%, DLCO and KCO were reduced compared with term-born. For the 82–85, 91–92 and 99–00 cohorts, deficits for z-FEV1 and z-DLCO were 1.23 and 0.53; 0.68 and 0.92; and 0.51 and 0.57, respectively (p ≤0.01 for all). Cohort analyses showed stable lung function across the three cohorts overall, but improvements across cohorts for the BPD subgroups in z-FEV1, z-FEV1/FVC, and z-FEF25%–75%.
Conclusion: Adults born EP across three formative decades of neonatal care had stable lung function overall, with notable improvements in BPD subgroups across cohorts.publishedVersio
Conceptualizing the implementation of post-discharge malaria chemoprevention in Malawi using a co-design approach
Get PDFBackground
Severe malaria poses a significant challenge to under-five children in Malawi, leading to high rates of hospitalization and mortality. The World Health Organization has recently recommended post-discharge malaria chemoprevention (PDMC) as a preventive strategy for under-five children with severe anaemia in malaria-endemic regions. In response to this recommendation, Malawi's Ministry of Health (MoH) plans to implement PDMC nationwide. To facilitate effective implementation, the MoH has partnered with the Training and Research Unit of Excellence (TRUE) to conduct PDMC delivery trials to gather evidence for practical implementation in Malawi and similar settings. A key component of this initiative involved the MoH leading the co-design workshops with key stakeholders to foster collaboration, spur innovation, and develop user-centred strategies. This collaborative effort aimed to investigate optimal PDMC implementation strategies to guide the scale-up in Malawi and contribute to policy-making processes that enhance transparency, accountability, and ownership.
Methods
This participatory action research occurred in the Salima district, Malawi, from 11 to 12 May 2023. Two co-design workshops were utilized, involving policymakers (n = 15), healthcare providers (n = 8), and prospective users (n = 2). The approach consisted of two stages. First, separate information-gathering sessions were held with policymakers, healthcare providers, and prospective users. Second, a structured discussion was facilitated, allowing collaboration between policymakers, healthcare providers, and prospective users to develop strategies for delivering and integrating the intervention. Discussions were audio recorded, transcribed verbatim, and manually analyzed using a thematic approach.
Results
The inductive analysis yielded four overarching themes from the data. These key themes are PDMC adaptability, trialability, implementability, and sustainability. Stakeholders recommended adopting PDMC in Malawi, with health facilities as the optimal delivery option, ensuring that discharged children receive dihydroartemisinin-piperaquine doses for three months. PDMC aligns with existing systems, offering integration opportunities for managing childhood illnesses. However, gaps in policy development, approval, and health system strengthening—including supply chain, monitoring, evaluation, and follow-up—must be addressed to ensure PDMC's sustainability.
Conclusions
The co-design results indicate stakeholders' willingness to adopt and implement PDMC in Malawi. However, there is an awareness of the challenges that must be addressed to facilitate PDMC's successful implementation and sustainability.publishedVersio
Sustainable Films for Rain Energy Harvesting on top of Solar Panels
No full textMasteroppgave i energiENERGI399I5MAMN-ENE