Long-term fatigue analysis of multi-planar tubular joints for jacket-type offshore wind turbine in time domain

• Published in: Engineering structures Vol. 33; no. 6; pp. 2002 - 2014
• Main Authors: Dong, Wenbin, Moan, Torgeir, Gao, Zhen
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2011; Elsevier
• Subjects: Applied sciences; Building failures (cracks, physical changes, etc.); Buildings; Buildings. Public works; Durability. Pathology. Repairing. Maintenance; Exact sciences and technology; External envelopes; Fatigue; Fatigue failure; Gamma; Hot-spot; Hydraulic constructions; Joints; Mathematical models; Multi-planar tubular joints; North Sea; Offshore; Offshore engineering; Offshore structure (platforms, tanks, etc.); Offshore structures; Stresses; Stresses. Safety; Structural analysis. Stresses; Time domain simulation; Weibull; Wind turbines; ANE, North Sea; Hot-spot; Gamma; Fatigue; Multi-planar tubular joints; Weibull; Time domain simulation; Dynamic response; Wave effect; Aerodynamics; Hydrodynamics; Wind effect; Wind generator; Jacket platform; Long term; Time domain method; Tubular joint; Failure analysis; Building dynamics; Numerical simulation; Probabilistic model; Weibull distribution; Offshore structure
• ISSN: 0141-0296; 1873-7323
• DOI: 10.1016/j.engstruct.2011.02.037

Long-term fatigue analysis of welded multi-planar tubular joints for a fixed jacket offshore wind turbine designed for a North Sea site in a water depth of 70 m is performed. The dynamic response of the jacket support structure due to wind and wave loads is calculated by using a decoupled procedure with good accuracy (Gao et al., 2010). Hot-spot stresses at failure-critical locations of each reference brace for 4 different tubular joints (DK, DKT, X-type) are derived by summation of the single stress components from axial, in-plane and out of plane action, the effects of planar and non-planar braces are also considered. Both a 2-parameter Weibull function and generalized gamma function are used to fit the long-term statistical distribution of hot-spot stress ranges by a combination of time domain simulation for representative environmental conditions in operational conditions of the wind turbine. A joint probabilistic model of mean wind speed U w , significant wave height H s and spectral peak period T p in the northern North Sea is used to obtain the occurrence frequencies of representative environmental conditions (Johannessen, 2002). In order to identify the contributions to fatigue damage from wind loads, wave loads and the interaction effect of wind and wave loads, 3 different load cases are analyzed: wind loads only; wave loads only; a combination of wind and wave loads. The representative environmental condition corresponding to the maximum contribution to fatigue damage is identified. Characteristic fatigue damage of the selected joints for different models is predicted and compared. The effect of brace thickness on the characteristic fatigue damage of the selected joints is also analyzed by a sensitivity study. The conclusions obtained in this paper can be used as the reference for the design of future fixed jacket offshore wind turbines in North Sea.