Offshore wind turbine nonlinear wave loads and their statistics

Due to the large influence of lateral flexible vibrations on offshore wind turbine foundations and the higher natural frequencies of the offshore wind turbine foundation relative to the dominant frequencies of the linear wave load model, the modeling of the dynamic behavior of the foundation under nonlinear wave loads and analysis of their statistical characteristics have become an important issue for offshore wind turbine design. This thesis derives an approximate model of the nonlinear wave loads in the time domain by Fluid Impulse Theory, verifies it with a boundary element method software WAMIT and validates it with experimental measurements. The load level crossing rates and the load power spectral density is obtained in multiple sea states. The simulated nonlinear wave loads are applied as the forcing mechanism on the offshore wind turbine and its foundation, and the mudline bending moments are computed and compared with experimental measurements. The system identification is conducted by fitting the model with the experimental data using linear regression method. The analytical extreme and fatigue prediction of the offshore wind turbine system are derived and evaluated in waters of finite depth and in multiple seastates. Key words: Nonlinear wave loads, nonlinear wave loads statistics, system identification, extremes and fatigue

Name thesis:degree_name

Doctoral

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Mechanical Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2019

Author dc:creator

• Zhang, Yu,Ph.D.Massachusetts Institute of Technology. Department of Mechanical Engineering.

Advisor dc:contributor.advisor

• Paul D. Sclavounos.

• Mechanical Engineering.

Statement dc:rights

• MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1721.1/122220

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/122220