Technical-economic analysis, modeling and optimization of floating offshore wind farms

The offshore wind sector has grown significantly during the last decades driven by the increasing demand for clean energy and to reach defined energy targets based on renewable energies. As the wind speeds tend to be faster and steadier offshore, wind farms at sea can reach higher capacity factors compared to their onshore counterparts. Furthermore, fewer restrictions regarding land use, visual impact, and noise favors the application of this technology. However, most of today's offshore wind farms use bottom-fixed foundations that limit their feasible application to shallow water depths. Floating substructures for offshore wind turbines are a suitable solution to harness the full potential of offshore wind as they have less constraints to water depths and soil conditions and can be applied from shallow to deep waters. As several floating offshore wind turbine (FOWT) concepts have been successfully tested in wave tanks and prototypes have been proven in open seas, floating offshore wind is now moving towards the commercial phase with the first floating offshore wind farm (FOWF) commissioned in 2017 and several more are projected to be constructed in 2020. This transition increases the need for comprehensive tools that allow to model the complete system and to predict its behavior as well as to assess the performance for different locations. The aim of this thesis is to analyze from a technical and economic perspective commercial scale FOWFs. This includes the modeling of FOWTs and the study of their dynamic behavior as well as the economic assessment of different FOWT concepts. The optimization of the electrical layout is also addressed in this thesis. The first model developed is applied to analyze the performance of a Spar type FOWT. The model is tested with different load cases and compared to a reference model. The results of both models show an overall good agreement. Afterwards, the developed model is applied to study the behavior of the FOWT with respect to three different offshore sites. Even at the site with the harshest conditions and largest motions, no significant loss in energy generation is measured, which demonstrates the good performance of this concept. The second model is used to perform a technical-economic assessment of commercial scale FOWFs. It includes a comprehensive LCOE methodology based on a life cycle cost estimation as well as the computation of the energy yield. The model is applied to three FOWT concepts located at three different sites and considering a 500MW wind farm configuration. The findings indicate that FOWTs are a high competitive solution and energy can be produced at an equal or lower LCOE compared to bottom-fixed offshore wind or ocean energy technologies. Furthermore, a sensitivity analysis is performed to identify the key parameters that have a significant influence on the LCOE and which can be essential for further cost reductions. The last model is aimed to optimize the electrical layout of FOWFs based on the particle swarm optimization theory. The model is validated against a reference model at first and is then used to optimize the inter-array cable routing of a 500MW FOWF. The obtained electrical layout results in a reduction of the power cable costs and a decrease of the energy losses. Finally, the use of different power cable configurations is studied and it is shown that the use of solely dynamic power cables in comparison to combined dynamic and static cables results in decreased acquisition and installation costs due to the avoidance of cost-intensive submarine joints and additional installation activities.El sector eólico marino ha crecido significativamente durante las últimas décadas impulsado por la creciente demanda de energía limpia. Los parques eólicos en el mar pueden alcanzar factores de capacidad más altos en comparación a los parques eólicos en la tierra debido a que las velocidades del viento tienden a ser más altas y constantes en el mar. Ademas, existen menos restricciones con respecto al uso de la tierra, el impacto visual y el ruido. Sin embargo, la mayoría de los parques eólicos actuales utilizan subestructuras fijas que limitan su aplicación factible a aguas poco profundas. Las subestructuras flotantes para turbinas eólicas marinas (FOWTs en inglés) son una solución adecuada para aprovechar todo el potencial de la energía eólica, ya que tienen menos restricciones para las profundidades del agua y el fondo marino. Dado que varios prototipos de FOWTs se han probado con éxito en el mar, la industria ahora esta entrando a la fase comercial con el primer parque eólico flotante (FOWF en inglés) operativo y se proyecta que se pondrán en marcha más en los próximos anos. Esta transición aumenta la necesidad de herramientas integrales que permitan modelar el sistema completo y predecir su comportamiento, así como evaluar el rendimiento para diferentes lugares. El objetivo de esta tesis es analizar desde una perspectiva técnica y económica los FOWFs a escala comercial. Esto incluye el modelado de FOWTs, el estudio de su comportamiento dinámico, y la evaluación económica de diferentes conceptos. La optimización del diseño eléctrico también se aborda en esta tesis. El primer modelo desarrollado se aplica para analizar el rendimiento de un FOWT tipo Spar. El modelo se prueba con diferentes tipos de carga y se compara con un modelo de referencia. Los resultados de ambos modelos muestran una buena concordancia. Posteriormente, el modelo se aplica para estudiar el comportamiento con respecto a tres lugares diferentes. Los resultados muestran que incluso en el sitio con las condiciones más severas, no se mide ninguna pérdida significativa en la generación de energía, lo que demuestra el buen rendimiento de este concepto. El segundo modelo se utiliza para realizar una evaluación técnico-económica de los FOWF a escala comercial. Esto incluye una metodología integral del costo nivelado de energía (LCOE en ingles). El modelo se aplica a tres conceptos de FOWTs ubicados en tres lugares diferentes y considerando un parque eólico de 500MW. Los resultados indican que los FOWTs son una solución altamente competitiva y que la energía se puede producir con un LCOE igual o inferior en comparación con los parques eólicos con subestructuras fijas o las tecnologías de energía oceánica. Asimismo, se realiza un análisis de sensibilidad para identificar los parámetros claves que tienen una influencia significativa en el LCOE y que pueden ser esenciales para reducciones de costos. El último modelo se aplica para optimizar el diseño eléctrico en función de la teoría de optimización por enjambre de partículas. Inicialmente el modelo se valida contra un modelo de referencia y luego se utiliza para optimizar la conexión de los cables entre los FOWTs. El diseño eléctrico obtenido da como resultado una reducción de los costos de cables y una disminución de las pérdidas de energía. Finalmente, se estudia el uso de diferentes configuraciones de cables y se demuestra que el uso de cables únicamente dinámicos en comparación con los cables dinámicos y estáticos combinados da como resultado una disminución de los costos de adquisición e instalación debido a que evitan la necesidad de juntas submarinas costosas y costos adicionales de instalación.Postprint (published version

Natural History and Management of Intraductal Papillary Mucinous Neoplasms: Current Evidence

Background: With the use of modern cross-sectional abdominal imaging modalities, an increasing number of cystic pancreatic lesions are identified incidentally. Although there is no pathological diagnosis available in most cases, it is believed that the majority of these lesions display small branch-duct intraductal papillary mucinous neoplasms (BD-IPMNs) of the pancreas. Even though a number of large clinical series have been published, many uncertainties remain with regard to this entity of mucinous cystic neoplasms. Methods: Systematic literature review. Results: Main-duct (MD) and mixed-type IPMNs harbor a high risk of malignant transformation. It is conceivable that most IPMNs with involvement of the main duct tend to progress to invasive carcinoma over time. Thus, formal oncologic resection is the treatment of choice in surgically fit patients. In contrast, the data regarding BD-IPMN remain equivocal, resulting in conflicting concepts. To date, it is not clear whether and which BD-IPMNs progress to carcinoma and how long this progression takes. Conclusion: While patients with MD-IPMNs should undergo surgical resection if comorbidities and life expectancy permit this, the management of small BD-IPMNs remains controversial. Population-based studies with long-term follow-up are needed to define which cohort of patients can be observed safely without immediate resection

Donor-Acceptor Stenhouse Adducts

Een betere beheersing van nieuwe moleculaire schakelaars opent nieuwe mogelijkheden in de ontwikkeling van materiaalkunde, geneeskunde en moleculaire machines. Materialen geven vorm aan de wereld om ons heen. Wetenschappers in deze eeuw ontwikkelen nieuwe materialen die onze toekomst mogelijkerwijs opnieuw vorm kunnen geven. In plaats van statische materialen te gebruiken teneinde functionele gereedschappen te ontwikkelen zijn het de materialen zelf die responsieve eigenschappen krijgen. Vroege voorbeelden van zulke ontwikkelingen zijn bijvoorbeeld brillen die automatisch donkerder worden wanneer de lichtintensiteit toeneemt, ‘slimme’ oppervlaktes en polymeren die reageren op elektrische signalen. Aan de basis van deze revolutie liggen moleculen die zulke materialen kunnen vormen. Om dit soort moleculen te kunnen maken moeten scheikundigen nieuwe moleculaire eigenschappen ontwikkelen en ze moeten leren hoe ze met deze nieuwe moleculen om moeten gaan. Dit proefschrift draagt bij aan een dieper begrip van de eigenschappen en mogelijke toepassingen van de zogenoemde DASA, een nieuw soort molecuul die drie jaar geleden is ontwikkeld door de onderzoeksgroep van Prof. Read de Alaniz aan de UC Santa Barbara. Deze molecuul, die verandert van structuur zodra er licht op schijnt, kan ingezet worden voor verschillende toepassingen: zo kan het bijvoorbeeld gebruikt worden in de bouw van moleculaire machines of om oppervlaktes te ontwikkelen waarvan de eigenschappen veranderen door invloed van licht. Onder begeleiding van Prof. Feringa en in samenwerking met een internationaal netwerk van wetenschappers hebben onderzoekers aan de Rijksuniversiteit Groningen de processen bestudeerd die in gang worden gezet zodra er licht op deze molecuul valt. Kennis van deze processen kan gebruikt worden voor het aanpassen van de bestaande moleculen zodat de stabiliteit en de kleurvastheid kan worden verbeterd en de algehele kwaliteit en prestatievermogen van de responsive materialen omhoog zullen gaan. Vervolgonderzoek kan de resultaten van dit onderzoek direct omzetten naar de ontwikkeling van nieuwe materialen en toepassingen.A better grip on novel molecular switches opens up new avenues in material science, medicine and molecular machines. Materials shape the world around us. In this century, scientists have started to create novel materials that have the potential to reshape our future. Instead of using static materials to create functional tools, the materials themselves are becoming responsive. Early signs of such approaches are glasses that automatically darken with higher intensity of light, smart surfaces and polymers that can respond to electric signals. At the heart of this revolution are molecules that can form such materials. In order to be successful, chemists need to create new molecules with properties that have never been seen before, and they need to know how to properly handle them. This thesis helps us to better understand and make use of a novel class of molecules that was discovered only three years ago by the group of Prof. Read de Alaniz at UC Santa Barbara: the so-called DASAs. This molecule changes its structure upon illumination, which has enabled the creation of surfaces that can change their properties with light or it helps building molecular machines. Researchers from the University of Groningen, under the guidance of Prof. Feringa and in cooperation with an international network of scientists, have uncovered the processes that happen when light hits the molecule. This knowledge helps modifying the existing molecules in order to reduce decomposition, improve color fastness, and overall quality and performance of these responsive materials. Subsequent research will take the lessons learned from this work and directly translate them to the development of new tools and materials for the future

Collection grid optimization of a floating offshore wind farm using particle swarm theory

Floating substructures for offshore wind turbines is a promising solution in order to harness the vast wind potential of deep water sites where bottom-fixed turbines are not feasible. The electrical system of large scale floating offshore wind farms will experience the application of new technologies and installation procedures that likely affect the cost-competitiveness. Thus, in this work, an optimization model based on the particle swarm theory is presented that allows optimizing the collection grid of a floating offshore wind farm. The developed model is applied to a study case consisting of a 500MW floating offshore wind farm located at the Golfe de Fos in the Mediterranean Sea. The resulting layout allows to reduce the total cost of the collection grid by more than 6% and to decrease the energy losses by 8% compared to the actual layout. Besides this, a further study analyzes the effect of a quantity discount with a reduced number of power cable cross sections.Postprint (published version

The influence of different wind and wave conditions on the energy yield and downtime of a Spar-buoy floating wind turbine

Floating offshore wind turbines (FOWT) have been extensively proven in model tests and are reaching currently a pre-commercial phase where large scale demonstrators are being built offshore. This transition increases the need for models able to assess the performance at suitable offshore locations. A simplified model is proposed that computes the dynamic response of FOWT to different met-ocean conditions and calculates the energy production considering the behavior of the structure as well as the downtime of the turbine due to exceeding operating limits. The model is validated against FAST and applied to three offshore sites. The motions response and hub acceleration are largest for West of Barra followed by Gulf of Maine and Costa Brava. The energy generation is also the highest at West of Barra, where a capacity factor of 75% is reached. A comparison between the energy generation of a bottom-fixed and FOWT indicates a difference of less than 1% for all sites. Finally, a sensitivity analysis of hub acceleration and platform pitch limits studies the impact on the capacity factor and downtime. The model can be useful for feasibility or pre-engineering studies and can be of interest for both investigators and developers of offshore wind projects.Peer ReviewedPostprint (author's final draft