Calibration of Long-Term Time-Domain Load Generation for Fatigue Life Assessment of Offshore Wind Turbine

2017 ◽  
Author(s):  
Bryan Nelson ◽  
Yann Quéméner ◽  
Tsung-Yueh Lin ◽  
Hsin-Haou Huang ◽  
Chi-Yu Chien
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Time Domain ◽  
Hot Spot ◽  
Life Assessment ◽  
Offshore Wind ◽  
Wind Loads ◽  
Offshore Wind Turbine

This study evaluated, by time-domain simulations, the fatigue life of the jacket support structure of a 3.6 MW wind turbine operating in Fuhai Offshore Wind Farm. The long-term statistical environment was based on a preliminary site survey that served as the basis for a convergence study for an accurate fatigue life evaluation. The wave loads were determined by the Morison equation, executed via the in-house HydroCRest code, and the wind loads on the wind turbine rotor were calculated by an unsteady BEM method. A Finite Element model of the wind turbine was built using Beam elements. However, to reduce the time of computation, the hot spot stress evaluation combined FE-derived Closed-Form expressions of the nominal stresses at the tubular joints and stress concentration factors. Finally, the fatigue damage was assessed using the Rainflow Counting scheme and appropriate SN curves. Based on a preliminary sensitivity study of the fatigue damage prediction, an optimal load setting of 60-min short-term environmental conditions with one-second time steps was selected. After analysis, a sufficient fatigue strength was identified, but further calculations involving more extensive long-term data measurements are required in order to confirm these results. Finally, this study highlighted the sensitivity of the fatigue life to the degree of fluctuation (standard deviation) of the wind loads, as opposed to the mean wind loads, as well as the importance of appropriately orienting the jacket foundations according to prevailing wind and wave conditions.

A Fast and Practical Method for Predicting the Fatigue Life of Offshore Wind Turbine Jacket Support Structures

2017 ◽  
Author(s):  
Chaoshuai Han ◽  
Yongliang Ma ◽  
Xianqiang Qu ◽  
Peijiang Qin ◽  
Binbin Qiu
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Time Domain ◽  
Practical Method ◽  
Computational Effort ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Support Structures

Fatigue assessment is a very important part in the design process of offshore wind turbine support structures subjected to wind and wave loads. Fully coupled time domain simulations due to wind and wave loads can potentially provide reliable fatigue predictions, however, it will take high computational effort to carry out fatigue analysis of the simultaneous wind and wave response of the support structure in time domain. For convenience and reducing computational efforts, a fast and practical method is proposed for predicting the fatigue life of offshore wind turbine jacket support structures. Wind induced fatigue is calculated in the time domain using ANSYS based on rainflow counting, and wave induced fatigue is computed in frequency domain using SACS based on a linear spectral analysis. Fatigue damage of X-joints and K-joints under combined environmental loads of wind and wave is estimated by using the proposed method. To verify the accuracy of the proposed formula, fatigue damage based on time domain rainflow cycle counting is calculated and can be considered as a reference. It is concluded that the proposed method provides reasonable fatigue damage predictions and can be adopted for evaluating the combined fatigue damage due to wind and wave loads in offshore wind turbine.

Fatigue Life Assessment of Offshore Patrol Vessel

2009 ◽  
Author(s):  
Asokendu Samanta ◽  
P. Kurinjivelan
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Design Guidelines ◽  
Life Assessment ◽  
Strength Analysis ◽  
Hot Spot Stress ◽  
Critical Locations

Fatigue is a phenomenon, which needs to be considered in the present day’s vessel design. The welded joints are particularly affected by the fatigue damage due to high stress concentrations caused by the metallurgical discontinuities present in the weld. For oil tankers and bulk carriers adequate guidelines for the fatigue strength assessment have been established by the classification societies. But for navy vessel, like offshore patrol vessel, the design guidelines for the fatigue strength analysis are not widely available. In the present paper, an attempt has been made to calculate the fatigue life of offshore patrol vessel (OPV). In general five stages of work is involved in calculating fatigue life of any ship structure. These are, load calculation, nominal and hot spot stress computation, long-term stress distribution, selection of S-N curve and the fatigue damage calculation. In the present study, the wave loads are obtained by the rule based estimation. The finite element analysis with the submodeling approach has been used to get the hot spot stress at critical locations. The two-parameter Weibull curve has been used to get the long-term distribution of stress. And at the end, the fatigue damage and the fatigue life have been computed using the Palmgren-Miner linear cumulative damage theory at the critical locations of the vessel.

Coupled Dynamic Analysis for Multi-Unit Floating Offshore Wind Turbine in Maximum Operational and Survival Conditions

2015 ◽  
Author(s):  
H. K. Jang ◽  
H. C. Kim ◽  
M. H. Kim ◽  
K. H. Kim
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Time Domain ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Random Waves ◽  
Mooring Lines ◽  
Floating Offshore Wind Turbine ◽  
Coupled Dynamic Analysis ◽  
Floating Offshore Wind Turbines

Numerical tools for a single floating offshore wind turbine (FOWT) have been developed by a number of researchers, while the investigation of multi-unit floating offshore wind turbines (MUFOWT) has rarely been performed. Recently, a numerical simulator was developed by TAMU to analyze the coupled dynamics of MUFOWT including multi-rotor-floater-mooring coupled effects. In the present study, the behavior of MUFOWT in time domain is described through the comparison of two load cases in maximum operational and survival conditions. A semi-submersible floater with four 2MW wind turbines, moored by eight mooring lines is selected as an example. The combination of irregular random waves, steady currents and dynamic turbulent winds are applied as environmental loads. As a result, the global motion and kinetic responses of the system are assessed in time domain. Kane’s dynamic theory is employed to formulate the global coupled dynamic equation of the whole system. The coupling terms are carefully considered to address the interactions among multiple turbines. This newly developed tool will be helpful in the future to evaluate the performance of MUFOWT under diverse environmental scenarios. In the present study, the aerodynamic interactions among multiple turbines including wake/array effect are not considered due to the complexity and uncertainty.

Evaluating the Coupledness of the Aerodynamics and Hydrodynamics on the Estimation of Fatigue Damage Equivalent Load for a Floating Offshore Wind Platform

2018 ◽  
Author(s):  
Samuel Kanner ◽  
Bingbin Yu
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Environmental Conditions ◽  
Offshore Wind ◽  
Coupled Analysis ◽  
Offshore Wind Turbine ◽  
Wave Conditions ◽  
Equivalent Load ◽  
The Waves

In this research, the estimation of the fatigue life of a semi-submersible floating offshore wind platform is considered. In order to accurately estimate the fatigue life of a platform, coupled aerodynamic-hydrodynamic simulations are performed to obtain dynamic stress values. The simulations are performed at a multitude of representative environmental states, or “bins,” which can mimic the conditions the structure may endure at a given site, per ABS Floating Offshore Wind Turbine Installation guidelines. To accurately represent the variety of wind and wave conditions, the number of environmental states can be of the order of 103. Unlike other offshore structures, both the wind and wave conditions must be accounted for, which are generally considered independent parameters, drastically increasing the number of states. The stress timeseries from these simulations can be used to estimate the damage at a particular location on the structure by using commonly accepted methods, such as the rainflow counting algorithm. The damage due to either the winds or the waves can be estimated by using a frequency decomposition of the stress timeseries. In this paper, a similar decoupled approach is used to attempt to recover the damages induced from these coupled simulations. Although it is well-known that a coupled, aero-hydro analysis is necessary in order to accurately simulate the nonlinear rigid-body motions of the platform, it is less clear if the same statement could be made about the fatigue properties of the platform. In one approach, the fatigue damage equivalent load is calculated independently from both scatter diagrams of the waves and a rose diagram of the wind. De-coupled simulations are performed to estimate the response at an all-encompassing range of environmental conditions. A database of responses based on these environmental conditions is constructed. The likelihood of occurrence at a case-study site is used to compare the damage equivalent from the coupled simulations. The OC5 platform in the Borssele wind farm zone is used as a case-study and the damage equivalent load from the de-coupled methods are compared to those from the coupled analysis in order to assess these methodologies.

Long-Term Dynamic Monitoring of an Offshore Wind Turbine

2013 ◽  
pp. 253-267 ◽  
Author(s):  
Christof Devriendt ◽  
Filipe Magalhães ◽  
Mahmoud El Kafafy ◽  
Gert De Sitter ◽  
Álvaro Cunha ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Dynamic Monitoring ◽  
Offshore Wind Turbine
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