scholarly journals Marine structures Low cycle fatigue assessment of offshore wind turbine monopile supporting structure subjected to wave-induced loads

2015 ◽  
pp. 307-314
Keyword(s):  
Wind Turbine ◽  
Low Cycle Fatigue ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Cycle Fatigue ◽  
Marine Structures ◽  
Fatigue Assessment ◽  
Supporting Structure ◽  
Wave Induced

Reliability of Offshore Wind Turbine Support Structures Subjected to Extreme Wave-Induced Loads and Defects

2016 ◽  
Author(s):  
Baran Yeter ◽  
Yordan Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Service Life ◽  
Wind Turbine ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Limit State ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Cycle Fatigue ◽  
Support Structures ◽  
Support Structure

The probability of existence of defects, fatigue damage and crack growth in the offshore wind turbine support structures subjected to extreme waves and wind-induced loads is very high and may occur at a faster rate in a low cycle fatigue regime and crack growth, leading to a dramatic reduction in the service life of structures. It is therefore vital to assess the safety and reliability of offshore wind turbine support structures at sea. The aim of the present study is to carry out a low cycle fatigue and crack growth reliability analysis of an offshore wind turbine support structure during the service life. The analysis includes different loading scenarios and accounts for the uncertainties related to the structural geometrical characteristics, the size of the manufacturing and during the service life defects, crack growth, material properties, and model assumed in the numerical analyses. The probability of failure is defined as a serial system of two probabilistic events described by two limit state functions. The first one is related to a crack initiation based on the local strain approach and the second one on the crack growth applying the fracture mechanic approach. The first and second order reliability methods are used to estimate the reliability index and the effect of low cycle fatigue and crack growth on the reliability estimate of the offshore wind turbine support structure. The sensitivity analysis is performed in order to determine the degree of the significance of the random variables and several conclusions are derived.

Strength Assessment of Jacket Offshore Wind Turbine Support Structure Accounting for Rupture1

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Baran Yeter ◽  
Yordan Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Wind Turbine ◽  
Low Cycle Fatigue ◽  
High Stress ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Small Scale ◽  
Support Structures ◽  
Support Structure ◽  
Strength Assessment ◽  
High Stress Concentration

The objective of the present work is to carry out the strength assessment of jacket offshore wind turbine support structures subjected to progressive rupture. A defect existing in a structure made during the fabrication may turn into a small-scale rupture and because of the high-stress concentration and low-cycle fatigue load. Therefore, the ultimate load-carrying capacity of the support structure is analyzed accounting for the progress of the rupture until the leg component experiences a full rupture along its circumference. The effect of imperfection severity is also investigated. The moment–curvature relationship of the structure concerning the studied cases is presented. Furthermore, the jacket support structures, at different water depths, are also analyzed and discussed. Finally, some of the leg components are removed one by one to study the redundancy of the jacket support structure at 80-m water depth.

Actuator Saturation Control of Floating Wind Turbines

2012 ◽  
Author(s):  
Roberto Ramos
Keyword(s):  
Wind Turbine ◽  
Actuator Saturation ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Rigid Body Model ◽  
Integral Controller ◽  
Proportional Integral Controller ◽  
Saturation Effects ◽  
Wave Induced ◽  
Blade Element

A state feedback aerodynamic controller is proposed for the stabilization and reduction of platform/tower pitch vibrations of a spar-type floating wind turbine, considering blade pitch saturation effects. The controller is synthesized from a linearized rigid body model developed for a NREL 5-MW offshore wind turbine operating at the above rated condition (region 3). Wind turbulence and wave induced loads are obtained from the blade element momentum (BEM) aerodynamic theory and Morison’s equation, respectively. The simulation results show that the proposed nonlinear control system yields significant vibration reduction in comparison to a proportional-integral controller.

Strength Assessment of Jacket Offshore Wind Turbine Support Structure Accounting for Rupture

2018 ◽  
Author(s):  
Baran Yeter ◽  
Yordan Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Wind Turbine ◽  
Low Cycle Fatigue ◽  
High Stress ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Small Scale ◽  
Support Structures ◽  
Support Structure ◽  
Strength Assessment ◽  
High Stress Concentration

The objective of the present work is to carry out the strength assessment of jacket offshore wind turbine support structures subjected to progressive rupture. A defect existing in a structure made during the fabrication may turn into a small-scale rupture and because of the high-stress concentration and low-cycle fatigue load. Therefore, the ultimate load-carrying capacity of the support structure is analysed accounting for the progress of the rupture until the leg component experiences a full rupture along its circumference. The effect of the severity of the imperfection is also investigated through 3 case studies that are created by varying the amplitude of the waves. The moment-curvature relationship of the structure with respect to the studied cases is presented. Furthermore, the jacket support structures, at different water depths, are also analysed and discussed. Finally, some of the leg components are removed one by one to study the redundancy of the jacket support structure at 80-m water depth.

scholarly journals Reducing the number of load cases for fatigue damage assessment of offshore wind turbine support structures using a simple severity-based sampling method

2018 ◽  
Vol 3 (2) ◽  
pp. 805-818 ◽  
Author(s):  
Lars Einar S. Stieng ◽  
Michael Muskulus
Keyword(s):  
Wind Turbine ◽  
Design Optimization ◽  
Fatigue Damage ◽  
Simple Procedure ◽  
Computational Effort ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Support Structures ◽  
Fatigue Assessment ◽  
Operational Conditions

Abstract. The large amount of computational effort required for a full fatigue assessment of offshore wind turbine support structures under operational conditions can make these analyses prohibitive, especially for applications like design optimization, for which the analysis would have to be repeated for each iteration of the process. To combat this issue, we present a simple procedure for reducing the number of load cases required for an accurate fatigue assessment. After training on one full fatigue analysis of a base design, the method can be applied to establish a deterministic, reduced sampling set to be used for a family of related designs. The method is based on sorting the load cases by their severity, measured as the product of fatigue damage and probability of occurrence, and then calculating the relative error resulting from using only the most severe load cases to estimate the total fatigue damage. By assuming this error to be approximately constant, one can then estimate the fatigue damage of other designs using just these load cases. The method yields a maximum error of about 6 % when using around 30 load cases (out of 3647) and, for most cases, errors of less than 1 %–2 % can be expected for sample sizes in the range 15–60. One of the main points in favor of the method is its simplicity when compared to more advanced sampling-based approaches. Though there are possibilities for further improvements, the presented version of the method can be used without further modifications and is especially useful for design optimization and preliminary design. We end the paper by noting some possibilities for future work that extend or improve upon the method.

Low Cycle Fatigue Analysis of Offshore Wind Turbines Subjected to Hurricane

2017 ◽  
Author(s):  
Gholamreza Amirinia ◽  
Sungmoon Jung
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Low Cycle Fatigue ◽  
Turbulence Models ◽  
Offshore Wind ◽  
Cycle Fatigue ◽  
Offshore Wind Turbines ◽  
Hurricane Wind ◽  
New Formulation ◽  
Spectrum Model

The main objective of this paper is to investigate the effects of hurricanes on low cycle fatigue of tower and blades in offshore wind turbines. For this purpose, first, recent observations on hurricane turbulence models were discussed. Second, the buffeting wind loads on the wind turbine structure were introduced. A new formulation was used to address unsteady wind forces on the tower. This new formulation was later used to modify NREL-FAST (Fatigue, Aerodynamics, Structures, and Turbulence) for the analysis. In the next step, according to importance of recent findings about hurricanes, hurricane wind and wave fields were simulated based on the Saffir-Simpson hurricane wind scale. Then, to investigate the effects of various turbulence models on the wind turbine structures, the modified NREL-FAST was used to analyze structure-wind-wave-soil interaction of the NREL-5 MW monopile wind turbine. Finally, the low cycle fatigue analysis was presented and discussed. Results for various hurricane turbulence models showed that by using quasi-steady analysis of the tower, the spectrum Model A and Model B resulted in average 53% lower and 12% higher damage index compared to the conventional Kaimal spectrum model respectively; however, by considering unsteady formulation on the tower, spectrum Model A and Model B resulted in average 96% and 24% lower blade root damage indices compared to the conventional Kaimal spectrum model respectively.

The Marine Environment Impacts on the Supporting Structure of the Offshore Wind Turbines and Discussions on the Protective Measures

2014 ◽  
Vol 1065-1069 ◽  
pp. 1381-1389
Author(s):  
Yong Xiang Wu ◽  
Hong You Li ◽  
Hong Ming Chi ◽  
Li Yuan Liu ◽  
An Min Cai ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Marine Environment ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Protective Measures ◽  
Offshore Wind Turbines ◽  
Supporting Structure ◽  
Seawater Corrosion ◽  
Negative Factors

Offshore wind turbine supporting structure long term works in the harsh marine environment, suffering from a variety of negative factors such as the seawater corrosion, marine growths, water scour, collision of sea ice and ship, etc.. Through numerical analysis software SACS and ANSYS, the marine environment impacts on the supporting structure and protective measures were put forward. The study found that such adverse environmental factors might easily result in a whole or partial component damage of the foundation support structure, and eventually lead to the reduction of security and durability. Reasonable preventive measures to ensure the security of the offshore wind turbine supporting structure were proposed and theoretical guidance for the design of future offshore foundation was provided.

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