Abstract

The tripod foundation has been used as a popular support structure for offshore wind turbine (OWT). Typically, only deterministic computational model is considered by applying relevant standards and codes during the preliminary design of the foundations of OWT. However, uncertain parameters should also be considered in preliminary design due to complex configuration of tripod structure. In order to balance conflicting design parameters against design requirements, uncertainties from both design loads and geometric dimensions of structural components were considered to identify the dominant loads and key structural design parameters for tripod foundation. Nonlinear finite element methods were utilized to investigate the mechanical behaviors of tripod foundation and Monte Carlo simulations (MCS) were conducted to obtain sensitive design parameters of tripod foundation of OWTs. Based on the results, it is highlighted that which design parameters should be considered carefully and which design parameters can be selected relying on engineering judgment during the preliminary structural design stage of tripod foundation.

Introduction

The exploration of offshore wind energy has been expanding rapidly worldwide in the past five years, as shown in Fig. 1. According to statistical report studies from the Global Wind Energy Council (GWEC, 2015), the global cumulative offshore wind energy capacity has stood at 12,105 MW, after 3,392 MW were added in 2015. Besides, the development of increasingly larger OWT in deeper water highlights the trend of the future wind turbine technology, and design and construction of foundation structures have represented important safety and cost factors of offshore wind turbine (OWT) technology. Currently, most of OWTs are located in shallow water and 75% OWTs in Europe are supported by mono-pile foundations (LORC). But as turbine size and water depth increase, traditional mono-pile support structures encounter economic and technical limitations for larger wind turbines in water depth exceeding 30 m. Tripod foundations are potential alternative in offshore wind farms because of their good stability and overall stiffness in water depth ranging from 20 to 40 m (Herion, 2007). They have been successfully installed in Borkum West 2, Global Tech 1 (Fig.2) and Alpha Ventus wind farms, and total capacity is 830 MW with 166 installed turbines, 5 MW in average for each turbine (Madjid, 2014).

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