Optimized design of the offshore monopile foundation under extreme condition

Loh, Kein Yuin (2025) Optimized design of the offshore monopile foundation under extreme condition. Final Year Project, UTAR.

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Abstract

This thesis investigates advanced analysis and design methodologies for monopile foundations supporting offshore wind turbines, leveraging the PISA (Pile Soil Analysis) framework based on Timoshenko beam theory. The study emphasizes the role of monopile foundations in ensuring structural integrity and long-term operational performance in challenging offshore environments. The initial chapters establish the core design principles, including structural components, theoretical underpinnings, load transfer mechanisms, and methodological approaches. Critical factors influencing design such as site-specific geotechnical properties, hydrodynamic forces from wave action, and wind-induced loading are examined in detail. To identify the governing design condition, a comprehensive load combination analysis was conducted. The most severe case was found to be an extreme operating gust at rated wind speed combined with a 50-year return period wave height. Under these conditions, and for a water depth of 60 meters, a lateral eccentric load of 5,777 kN applied at 90 meters height results in an overturning moment of 709 MNm at the mudline. The study integrates both one-dimensional and three-dimensional finite element modelling techniques to capture the structural behaviour under extreme loads more accurately. A key component of the analysis involved the use of PLAXIS Monopile Designer software, which enabled a rigorous simulation of soil-structure interaction based on site-specific parameters. Through the integration of PISA-based soil response curves and finite element modelling, the tool was used to optimize the foundation design, ensuring reliability and material efficiency. The resulting optimized monopile foundation for a 6.0 MW offshore wind turbine features an outer viii diameter of 8 meters, a wall thickness of 0.06 meters, an embedment depth of 43 meters, and a total length of 103 meters. The proposed design demonstrates improved performance and cost-effectiveness while complying with modern offshore design standards. Keywords: Offshore, Wind Turbine, Monopile, Structural Modelling, Plaxis Monopile Designer Subject Area: TC1501-1800 Ocean engineering

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