scholarly journals Calibration of Design Fatigue Factors for Offshore Wind Turbine Support Structure Based on Fatigue Test Database

2020 ◽  
Author(s):  
Wangwen Zhao ◽  
Wei-Ting Hsu
Keyword(s):  
Probabilistic Models ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Corrosion Condition ◽  
Structural Fatigue ◽  
Multiple Factors ◽  
Fatigue Design ◽  
Test Database ◽  
Current Standards ◽  
Offshore Wind Industry

The concept of Design Fatigue Factors (DFFs) was introduced for providing desired level of safety in structural fatigue design, often associated with damage calculated from S-N curves. Calculation of fatigue damage from S-N curves can be affected by multiple factors, e.g. types of weld class, corrosion condition, loading conditions, stress concentration on different geometries etc. Each of them can be subject to different level of uncertainties. This study intends to recalibrate the DFFs from a detailed reliability analysis by investigating the probabilistic models derived from the database of S-N curves that has been most frequently used in offshore wind industry. The results of such study indicate that the DFFs can be reduced substantially for the corrosive environmental fatigue models from current standards to the same level of target reliability.

Comparison of the Fatigue Performance of Galvanised M72 Bolts With Design Standard Recommendations

2021 ◽  
Author(s):  
Carol Johnston ◽  
Matthew Doré
Keyword(s):  
Fatigue Performance ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Design Codes ◽  
Design Standards ◽  
Threaded Fasteners ◽  
Fatigue Design ◽  
Standard Design ◽  
Wind Turbine Towers ◽  
Thickness Correction

Abstract Now that bolted flanges rather than grouted connections are used to join the transition piece to the monopile in offshore wind turbine towers, many large bolts are being used in applications which subject them to fatigue loads. The bolts in these ring flanges are typically M64 or M72 in size (ie 64mm of 72mm nominal diameter). The fatigue design codes, BS 7608, DNVGL-RP-C203 and Eurocode 3 do provide S-N curves for threaded fasteners, but the reference diameter in those documents is 25mm or 30mm. A thickness correction is provided, to account for larger diameter bolts, but this was originally derived by analysis of the performance of welded joints. It is unclear whether the S-N curves and the recommended thickness correction are appropriate for larger diameter threaded fasteners. The offshore wind industry usually specifies hot dip galvanised bolts, to provide some corrosion protection in the offshore environment. Again, there is uncertainty over whether the S-N curves in fatigue design standards apply to bolts with a galvanised coating. Since the fatigue design codes provide S-N curves for air, free corrosion or seawater with cathodic protection, it is also unclear which of these should be used to predict the fatigue performance of bolts with a galvanised coating. In order to provide data to address these uncertainties, hot-dip galvanised, grade 10.9, M72 bolts from two manufacturers were tested in both air and a seawater environment. In order to represent the conditions experienced by bolts in internal ring flanges, the artificial seawater was sprayed onto the bolts during testing. Tests were conducted with a mean stress corresponding to 70% of the specified minimum 0.2% proof strength of the bolts. Tests were also performed in air, on uncoated M72 bolts, and uncoated M64 bolts for comparison. The results suggest that the current thickness correction in DNVGL RP C203 and BS 7608 is appropriate for M72 bolts. The results in air from the galvanised bolts were below those from uncoated bolts. Although the galvanised results were above the thickness corrected in-air standard design curves (BS7608 Class X -20%, DNVGL Class G and DNVGL ST 0126 FAT 50), they were below the mean curves, suggesting that the performance of galvanised bolts is slightly lower than the existing recommendations.

Research on the Dynamic Response of Floating Foundation of a Tri-Floater Offshore Wind Turbine

2013 ◽  
Vol 275-277 ◽  
pp. 852-855 ◽  
Author(s):  
Zhuang Le Yao ◽  
Chao He Chen ◽  
Yuan Ming Chen
Keyword(s):  
Wind Turbine ◽  
Transfer Functions ◽  
Reference Value ◽  
Element Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Load ◽  
Floating Foundation ◽  
Wind Turbine System ◽  
Offshore Wind Industry

In this paper, the overall finite element model is established, to analyze the small-sized floating foundation of a tri-floater and to make a local optimization on the stress concentration area. The transfer functions and the response spectrums of wave load and motion of floating wind turbine system are calculated by AQWA. Besides the concept of the floating foundation group is put forward in this paper. It is small in structure, easy to assemble, and it can be developed for any power of wind field.This concept has a certain reference value for the development of offshore wind industry in China.

Decommissioning of Offshore Monopiles, Occuring Problems and Alternative Solutions

2018 ◽  
Author(s):  
Nils Hinzmann ◽  
Philipp Stein ◽  
Jörg Gattermann
Keyword(s):  
Wind Farm ◽  
Complex Structure ◽  
Complete Removal ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Farm ◽  
Narrow View ◽  
Alternative Solutions ◽  
German Offshore Wind Industry ◽  
Offshore Wind Industry

The German offshore wind industry has historically grown since the first offshore wind farm (OWF) “alpha ventus” was completed in 2010. Since the end of 2017 a total number of 18 OWF with a capacity of about 5 GW have been operating in the German Exclusive Economic Zone (EEZ) [1]. While the majority of the population and the industry focus on new projects, it appears the life cycle observation and especially the decommissioning phase remain largely unattended. This narrow view can lead to unexpected and expensive consequences in the future. The decommissioning of a complex structure as an offshore wind turbine (OWT) needs to be planned well in advance. There are numerous aspects that make the decommissioning a challenge, such as the federal regulations, the marine environment and the technical limitations of offshore operations. This article gives an overview of the problematic matter of dealing with monopiles after the predicted lifetime, the geotechnical condition, analyses of the current decommissioning options and identification of issues in regards to the decommissioning method. Furthermore, other promising decommissioning methods for a complete removal of offshore monopiles, such as vibratory extraction, internal dredging, external jet drilling and the use of buoyancy force, are presented and compared concerning a possible combination. Some of the presented methods are highly experimental, others are commonly used in other industries.

scholarly journals Validation of Improved Sampling Concepts for Offshore Wind Turbine Fatigue Design

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 603 ◽  
Author(s):  
Clemens Hübler ◽  
Wout Weijtjens ◽  
Cristian Gebhardt ◽  
Raimund Rolfes ◽  
Christof Devriendt
Keyword(s):  
Environmental Conditions ◽  
Wind Farm ◽  
Measurement Data ◽  
Monte Carlo Sampling ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Sampling Effort ◽  
Data Set ◽  
Ongoing Research ◽  
Fatigue Design

Fatigue damage is a design-driving phenomenon for substructures of offshore wind turbines. However, fatigue design based on numerical simulations is quite uncertain. One main reason for this uncertainty is scattering offshore conditions combined with a limited number of simulations (samples). According to current standards, environmental conditions are sampled using a deterministic grid of the most important environmental conditions (e.g., wind speed and direction, significant wave height, and wave period). Recently, there has been some effort to reduce the inherent uncertainty of damage calculations due to limited data by applying other sampling concepts. Still, the investigation of this uncertainty and of methods to reduce it is a subject of ongoing research. In this work, two improved sampling concepts—previously proposed by the authors and reducing the uncertainty due to limited sampling—are validated. The use of strain measurement data enables a realistic estimate of the inherent uncertainty due to limited samples, as numerical effects, etc., are excluded. Furthermore, an extensive data set of three years of data of two turbines of the Belgian wind farm Northwind is available. It is demonstrated that two previously developed sampling methods are generally valid. For a broad range of model types (i.e., input dimensions as well as degrees of non-linearity), they outperform standard sampling concepts such as deterministic grid sampling or Monte Carlo sampling. Hence, they can reduce the uncertainty while keeping the sampling effort constant, or vice versa.

scholarly journals Revaluation of Fatigue Thickness Effect Based on Fatigue Test Database

2020 ◽  
Author(s):  
Wangwen Zhao ◽  
Wei-Ting Hsu
Keyword(s):  
Fatigue Strength ◽  
Offshore Wind ◽  
Thickness Effect ◽  
Exposure Level ◽  
Corrosive Environment ◽  
Current Standard ◽  
Tubular Joint ◽  
Offshore Oil ◽  
Test Database ◽  
Offshore Wind Industry

This paper reassesses the detrimental effect on fatigue performance due to thicker sections based on extensive fatigue strength test database, taken from research program worldwide over the past half of a century in offshore oil & gas and renewable industry. The data entries in the database have been evaluated to ensure its data integrity. Statistical analyses on these S-N data are performed with or without the thickness correction at different exposure level to corrosive environment, in order to re-evaluate the suitability of current standards in regard to the thickness effect. The study has concentrated on T-joint, transverse butt welded joint and tubular joint as these are the most commonly used joint types in the offshore wind industry. The analysis indicates general agreement of fatigue strength with the thickness effects in current standard for in air conditions but great conservatism for corrosive environment.

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