Including load sequence effects in the fatigue damage estimation of an offshore wind turbine substructure

Retardation is a load sequence effect, which causes a reduced fatigue crack growth rate after an overload is encountered. Retardation can be cancelled when the overload is followed by an underload. The net effect is beneficial to the fatigue lifetime of Offshore Wind Turbines (OWTs). To be able to take this into account, computationally demanding cycle-by-cycle approaches are required. This paper presents a methodology which aims at reducing a very long variable amplitude stress signal, such that it can be used to estimate the cycle-by-cycle fatigue damage, without jeopardizing accuracy. Filtering and reduction techniques are combined, based on typical events seen in the loading pattern of an OWT, e.g. during a storm. The effectiveness of the method is shown by comparing the numbe

Innovative fatigue prediction model for improved fatigue performance of welded steel connections in offshore wind turbine jackets

Offshore Wind power is considered one of the fastest growing maritime sectors and the most promising sources of ‘clean’ energy towards meeting the European targets for 2020 and 2050. The growth of the sector has also been mirrored in other continents like China and US. The technology keeps rapidly growing and the top offshore turbine makers in the industry, Siemens and MHI Vestas, are already developing wind turbines with power ratings up to 7.0 MW and 8.0 MW, respectively. The combination of increasing wind tower heights, rotor blade diameters and water depths, needed for the multi-megawatt wind turbines, makes the need for complex jacket support structures inevitable. As the design of jacket support structures is fatigue driven, the challenge is to balance fatigue performance, structural weight and the operating and maintenance (O&M) strategies in order to reduce the Capital Expenditure (CAPEX) and the Operating Expenditure (OPEX). The current industry-wide accepted methods of fatigue life prediction, according to offshore wind design standards and guidelines, have certain known conservatism. This is due to the uncertainty in load and resistance variables, required safety and assumptions and simplifications in the calculation procedures

Approach to include load sequence effects in the design of an offshore wind turbine substructure

Fatigue is one of the main design drivers for offshore wind substructures. Using Fracture Mechanics methods, load sequence effects such as crack growth retardation due to large load peaks can be included in the fatigue damage estimation. Due to the sequence dependency, a method is required that represents the sequences of loads in the design or maintenance procedures. This paper presents a methodology to deal with this challenge. First, a framework is presented for coupling between the design load cases and the Fracture Mechanics methods, resulting into the requirements for loads and load sequences. Second, a 2-stage Markov Chain Monte Carlo model is presented which is able to create realistic loading sequences based on measurement data. The method is elaborated for fluctuating wind loads

Approach to include load sequence effects in the design of an offshore wind turbine substructure

Fatigue is one of the main design drivers for offshore wind substructures. Using Fracture Mechanics methods, load sequence effects such as crack growth retardation due to large load peaks can be included in the fatigue damage estimation. Due to the sequence dependency, a method is required that represents the sequences of loads in the design or maintenance procedures. This paper presents a methodology to deal with this challenge. First, a framework is presented for coupling between the design load cases and the Fracture Mechanics methods, resulting into the requirements for loads and load sequences. Second, a 2-stage Markov Chain Monte Carlo model is presented which is able to create realistic loading sequences based on measurement data. The method is elaborated for fluctuating wind loads.</p