Effective Stress-Based Seismic Analysis of Offshore Wind Turbine Support Structure Considering Wind Load Effects

Abstract Offshore wind structures are being designed for seismically active areas. Load calculations can be performed in an integrated way or using a superelement approach. This study aims to demonstrate that these two approaches can give equivalent results when earthquake excitations are included as an applied load in the superelement approach. Models of a generic 7MW wind turbine on a jacket support structure are defined in aeroelastic code Bladed and strength assessment software Sesam. Analysis is performed on the stand-alone jacket and support structure, and also including the rotor nacelle assembly. Load conditions of earthquakes, waves and wind are considered. Time domain results show that the superelement and integrated methods for modelling earthquake loading are equivalent in terms of the motions and loads at key points of the support structure. When the tower and RNA are included, an excellent match is seen for all studied variables: interface and tower top motions, loads at the interface and in the jacket, and displacements of jacket nodes. Analysis of the stand-alone jacket highlights differences in the approaches with regard to coupling of the hydrodynamic loading to the earthquake motion, which is absent in the superelement method. However, this does not appear to be significant for realistic cases including the tower and RNA.

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Reliability-based design optimization of a spar-type floating offshore wind turbine support structure

Reliability Engineering & System Safety ◽

10.1016/j.ress.2021.107666 ◽

2021 ◽

pp. 107666

Author(s):

Mareike Leimeister ◽

Athanasios Kolios

Keyword(s):

Wind Turbine ◽

Design Optimization ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Reliability Based Design Optimization ◽

Support Structure ◽

Floating Offshore Wind Turbine ◽

Reliability Based Design

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Model Test and Numerical Analysis of an Offshore Bottom Fixed Pentapod Wind Turbine Under Seismic Loads

Volume 6: Ocean Space Utilization; Ocean Renewable Energy ◽

10.1115/omae2016-54499 ◽

2016 ◽

Cited By ~ 1

Author(s):

Wenhua Wang ◽

Zhen Gao ◽

Xin Li ◽

Torgeir Moan ◽

Bin Wang

Keyword(s):

Wind Turbine ◽

Wind Wave ◽

Seismic Analysis ◽

Wind Farms ◽

Dynamic Responses ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Test Model ◽

Structural Dynamic ◽

Load Conditions

In the last decade the wind energy industry has developed rapidly in China, especially offshore. For a water depth less than 20m, monopile and multi-pile substructures (tripod, pentapod) are applied widely in offshore wind farms. Some wind farms in China are located in high seismicity regions, thus, the earthquake load may become the dominant load for offshore wind turbines. This paper deals with the seismic behavior of an offshore wind turbine (OWT) consisting of the NREL 5MW baseline wind turbine, a pentapod substructure and a pile foundation of a real offshore wind turbine in China. A test model of the OWT is designed based on the hydro-elastic similarity. Test cases of different load combinations are performed with the environmental conditions generated by the Joint Earthquake, Wave and Current Simulation System and the Simple Wind Field Generation System at Dalian University of Technology, China, in order to investigate the structural dynamic responses under different load conditions. In the tests, a circular disk is used to model the rotor-nacelle system, and a force gauge is fixed at the center of the disk to measure the wind forces during the tests. A series of accelerometers are arranged along the model tower and the pentapod piles, and strain gauges glued on the substructure members are intended to measure the structural dynamic responses. A finite element model of the complete wind turbine is also established in order to compare the theoretical results with the test data. The hydro-elastic similarity is validated based on the comparison of the measured dynamic characteristics and the results of the prototype modal analysis. The numerical results agree well with the experimental data. Based on the comparisons of the results, the effect of the wind and sea loads on the structural responses subjected to seismic is demonstrated, especially the influence on the global response of the structure. It is seen that the effect of the combined seismic, wind, wave and current load conditions can not be simply superimposed. Hence the interaction effect in the seismic analysis should be considered when the wind, wave and current loads have a non-negligible effect.

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Wind load response of offshore wind turbine towers with fixed monopile platform

Journal of Wind Engineering and Industrial Aerodynamics ◽

10.1016/j.jweia.2016.09.007 ◽

2016 ◽

Vol 158 ◽

pp. 122-138 ◽

Cited By ~ 14

Author(s):

M. Feyzollahzadeh ◽

M.J. Mahmoodi ◽

S.M. Yadavar-Nikravesh ◽

J. Jamali

Keyword(s):

Wind Turbine ◽

Wind Load ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Load Response ◽

Wind Turbine Towers

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Monitoring Changes in the Soil and Foundation Characteristics of an Offshore Wind Turbine Using Automated Operational Modal Analysis

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.569-570.652 ◽

2013 ◽

Vol 569-570 ◽

pp. 652-659 ◽

Cited By ~ 1

Author(s):

Gert de Sitter ◽

Wout Weitjens ◽

Mahmoud El-Kafafy ◽

Christof Devriendt

Keyword(s):

Wind Turbine ◽

Modal Analysis ◽

Continuous Monitoring ◽

Low Frequency ◽

Operational Modal Analysis ◽

Human Interaction ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Support Structure ◽

Lower Natural Frequency

This paper will show the first results of a long term monitoring campaign on an offshore wind turbine in the Belgian North Sea. It will focus on the vibration levels and resonant frequencies of the fundamental modes of the support structure. These parameters will be crucial to minimize O&M costs and to extend the lifetime of offshore wind turbine structures. For monopile foundations for example, scouring and reduction in foundation integrity over time are especially problematic because they reduce the fundamental structural resonance of the support structure, aligning that resonance frequency more closely to the lower frequencies. Since both the broadband wave energy and the rotating frequency of the turbine are contained in this low frequency band, the lower natural frequency can create resonant behavior increasing fatigue damage. Continuous monitoring of the effect of scour on the dynamics of the wind turbine will help to optimize the maintenance activities on the scour protection system. To allow a proper continuous monitoring during operation, reliable state-of-the-art operational modal analysis techniques should be used and these are presented in this paper. The methods are also automated, so that no human-interaction is required and the system can track the natural frequencies and damping ratios in a reliable manner.

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