ABSTRACT

The concept of a "hybrid offshore wind turbine" originated from articulated loading platforms (ALPS). In this study, we have developed a concept design for the major structural components. Orcaflex was used to create a numerical model. A yaw controller was included in the numerical model by calling external functions through Python script. We have simulated the turbine's behavior with constant wind loads under different sea states and yaw rates. The primary objective was to investigate the torque exerted on the universal joint located at the seabed, a crucial design parameter for this wind turbine concept, as well as the turbine's efficiency in various sea states and yaw misalignments. A total of 57 cases were simulated with various combinations of wind and waves. The results show that the structure's stability is sufficient, with a maximum inclination of approximately 2.7 degrees in the roughest wave conditions. The torque is more sensitive to the yaw rate (ϕ) than to the significant wave height, and the deceleration of the turbine's yawing generates the highest torque values. Wave loads reduced the turbine's efficiency. However, an increase in wave height did not significantly impact the generator's efficiency since the structure's inclination did not change significantly.

INTRODUCTION

Offshore wind is a rapidly growing industry for generating energy from wind turbines installed offshore. Over the years, several designs for offshore wind turbines (OWT) have been developed, and the design is typically dependent on environmental conditions. Fig. 1 shows some typical designs available today. The monopile structure is the most common substructure for OWT in Europe, representing up to 81.2% of the market in 2020 (see Fig. 1 a and b). The monopile structure is relatively cheap to manufacture and less complex. However, one drawback of this concept is its limited applicable water depth. The articulated tower design for offshore wind structures is not yet widespread. However, similar concepts were introduced to the oil and gas industry in the 1970s (as seen in Habardsholm L., 1994). The concept of articulated loading platforms (ALPS) was first installed on the Statfjord in 1994, and Fig. 2 illustrates the components and configuration of the articulated loading platform concept.

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