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Nowadays, much attention is payed to the development of renewable energy resources. Wind energy plays a major role in this issue. That is why there is a growing interest for improving the design process of wind turbines at many aspects. This study deals with offshore wind turbines (OWT) from the reliability aspect. Estimating the uncertainties, a deeper understanding of behavior of the structure is obtained. As waves are the dominant load on OWT support structures, this paper addresses how specific wave characteristics affect the structure. Two structural types of support structures are studied, with the aim to evaluate pros and cons of both.

The project partners Duisport AG, the DLR Institute of Vehicle Concepts and the Center for Fuel Cell Technology (ZBT) have investigated the feasibility of locomotives with hydrogen fuel cell hybrid powertrains (FCH) for typical use by Duisport Rail (dpr) in the Duisburg port area and on the public rail network.

The design of support structures of offshore wind turbines contains high number of design variables that influence load characteristics and structural responses. These variables are stochastic and cause many uncertainties. Some of them are examined in this study. It is investigated how scattering of site conditions and load parameters affect the structural response. It is exemplified in terms of stresses that contribute to the accumulated fatigue damage within a monopile substructure. Random sampling of combinations of site conditions and load parameters is performed in order to classify the effects of parameter scattering on the stress variability by means of Sobol’ indices. Analysis shows that the highest influence on stress outputs have the variations in the load parameters. The reason is the sensitivity of the structural dynamical response to the wave height increase and decrease of distance between the wave peak frequency and the structural eigenfrequencies. © 2017 ISOPE

The concept of structural redundancy is implemented in the fatigue analysis of an offshore wind turbine jacket structure. The analyzed jacket is a real life example. Time domain analyses are performed for the most representative design load case. The uni-directional and multidirectional simulations of the offshore wind turbine system are carried out using a coupling of the aero-elastic code and the finite element code. Fatigue analyses are performed using hot spot stress approach and Miner's rule. Comparative studies show that considering structural redundancy leads to expanded fatigue life of the offshore wind turbine jacket structures. © 2017 ISOPE

To achieve the 1.5 °C target of the Paris Climate Agreement that came into force in 2016 [UNI15], the conversion of the entire energy system to renewable energy sources is essential. Strong and stable wind conditions offshore as well as a high growth potential make offshore wind energy far away from shore an important energy source. The integration of such Offshore Wind Farms (OWF) has to be safe, flexible, efficient, and affordable, which makes High Voltage Direct Current (HVDC) transmission systems often the preferred choice for their grid connection. HVDC transmission systems consist of many subsystems, components, and interfaces e.g. to the OWF, which characterise them as complex systems. The complexity, many and diverse requirements and a large number of system design alternatives require grid planners, grid operators and manufacturers to employ a systematic approach to develop the most suitable design that meets all requirements and functions as expected in its environment. Systems Engineering with its procedure based on the so-called V-model, has proven itself for many years outside the energy industry as a suitable methodology for the development of complex systems. The extension to Model-Based Systems Engineering (MBSE) allows the specification of a system in a universal system modelling language (SysML) based on the activities in the V-model, which enables the collaborative system development across disciplines. Based on the MBSE methodology, a HVDC transmission system for a case study consisting of three OWFs with a total power of 3 GW is designed in this thesis. The requirements are derived from stakeholder needs and categorised before the system design process. Stakeholders are for example the OWF owner and the onshore grid operator. This thesis considers electrical engineering requirements and the objective of a low levelised cost of energy (LCOE) design. The system integration and verification of the prior defined requirements are performed, before a validated HVDC transmission system design is available following the system development process with the V-model. MBSE enables early identification of design errors through verification activities when they are still easy and cheap to correct. The SysML model forms the core element for the HVDC transmission system design as all relevant requirements, constraints, specifications, and the system objective are included in the model. The most suitable system architecture and component definition is developed with a Multi-Criteria Decision Aid assessment and selection method based on the specifications in the SysML model. In this thesis, a step-by-step guideline for the development of HVDC transmission systems based on MBSE is developed to improve the system design with an interdisciplinary and model-based approach. This approach leads to a detailed understanding of system elements and their interactions inside and outside the HVDC transmission system. The result for the case study is a HVDC configuration consisting of two symmetrical monopoles, which can be interconnected as a multi-terminal HVDC system in the event of a monopole failure. This arrangement is identified as the preferred architecture for the case study and assumptions. The converter transformer is chosen as an example to demonstrate the identification of the number and type of components as part of the Systems Engineering process. Discipline-specific models and simulations provide details to the design. At the end of the system design activities, the SysML model represents a detailed specification of the HVDC system and thereby replaces many documents with specifications. The advantage of the developed SysML model is to facilitate the design analysis and to identify the impact of requirement changes or changes in the system environment on the system design. The SysML and discipline-specific models allow the verification of system requirements, e.g. of the availability, which has a high influence on LCOE and is used as an assessment criterion on system and component level. The validation procedure is also introduced. Based on the proposed approach for HVDC transmission system development, the potential for the extension of the methodology for energy systems in general is presented to support the realisation of the energy system conversion to renewable energy sources. Um das 1,5 °C Ziel des 2016 in Kraft getretenen Pariser Klimaabkommens zu erreichen [UNI15], ist die Umstellung des gesamten Energiesystems auf erneuerbare Energiequellen unerlässlich. Starke und stabile Windverhältnisse auf dem Meer sowie ein hohes Wachstumspotenzial machen die Offshore-Windenergie fernab der Küste zu einer wichtigen Energiequelle. Die Integration solcher Offshore-Windparks (OWP) muss sicher, flexibel, effizient und bezahlbar sein, weshalb die Hochspannungs-Gleichstrom-Übertragung (HGÜ) oft für den Netzanschluss bevorzugt wird. HGÜ Systeme bestehen aus vielen Teilsystemen, Komponenten und Schnittstellen, z. B. zu den OWP, was sie zu komplexen Systemen macht. Die Komplexität, die vielen und unterschiedlichen Anforderungen und die große Anzahl von Systemalternativen erfordern für Netzplaner, Netzbetreiber und Hersteller einen systematischen Ansatz zur Entwicklung des am besten geeigneten Entwurfs, der alle Anforderungen erfüllt und in seiner Umgebung wie erwartet funktioniert. Das Systems Engineering mit seinem auf dem sogenannten V-Modell basierenden Vorgehen hat sich seit vielen Jahren außerhalb der Energiewirtschaft als geeignete Methodik für die Entwicklung komplexer Systeme bewährt. Die Erweiterung zum Model-Based Systems Engineering (MBSE) ermöglicht die Spezifikation eines Systems in einer universellen Systemmodellierungssprache (SysML) durch die Aktivitäten im V-Modell, was die kollaborative Systementwicklung über Disziplinen hinweg ermöglicht. Auf der Grundlage von MBSE wird in dieser Arbeit ein HGÜ System für eine Fallstudie entworfen, die aus drei OWPs mit einer Gesamtleistung von 3 GW besteht. Die Anforderungen werden aus der Notwendigkeit der Stakeholder abgeleitet und vor der Systementwicklung kategorisiert. Stakeholder sind beispielsweise der OWP Eigentümer und der Onshore Netzbetreiber. In dieser Arbeit werden elektrotechnische Anforderungen und das Ziel eines Designs mit niedrigen Stromgestehungskosten berücksichtigt. Die Systemintegration und Verifizierung der zuvor definierten Anforderungen wird durchgeführt, bevor ein validierter HGÜ Systementwurf nach dem Systementwicklungsprozess mit dem V-Modell zur Verfügung steht. MBSE ermöglicht die frühzeitige Identifizierung von Entwurfsfehlern durch Verifikation, wenn diese noch einfach und kostengünstig zu korrigieren sind. Das SysML Modell bildet das Kernelement für den Entwurf des HGÜ Systems, da alle relevanten Anforderungen, Randbedingungen, Spezifikationen und das Systemziel im Modell enthalten sind. Die am besten geeignete Systemarchitektur und Komponentendefinition wird auf der Grundlage der Spezifikationen im SysML-Modell mit einer multikriteriellen Methode zur Bewertung und Auswahl entwickelt.