ABSTRACT

Floating Offshore Wind Turbines (FOWT) can be actively controlled to minimize their wave induced motions, improving wind energy harvesting efficiency and increasing structural life by reducing fatigue loads. Here, we report on the development and validation of Wave Reconstruction and Prediction (WRP) algorithms that improve the active control of floating structure motions, achieved, e.g., by moving mass or ballast. Specifically, given a sensing method, here assumed to be LiDAR-like, that acquires dense spatiotemporal surface elevation data at some distance from the FOWT in the incident wave direction, we present and validate deterministic WRP algorithms, based on fast nonlinear and dispersive Lagrangian wave models, and integrate their predictions with in-the-loop hardware and a real time control system that is informed by computations with a digital twin (DT) model of the floating structure. We implement multiple WRP wave models including a model based on linear wave theory (LWT) with a correct dispersion accounting for nonlinearity (LWT-CDR) and a 2nd-order "Choppy" wave model with improved nonlinear dispersive properties (ICWM), initialized with a linear prediction. Although we run laboratory experiments of the complete system, which are reported elsewhere, here the WRP implementation is validated against fully nonlinear potential flow simulations in a Numerical Wave Tank (NWT), which shows both LWT-CDR and ICWM models appear to provide reasonable short-term predictions at the float. Implications for the real time control system are discussed; in a companion paper, the use of short-term wave predictions with the WRP is shown to improve the real time control of float motions in waves.

INTRODUCTION

Many offshore wind farms are in development along the US East Coast, with about 3GW of total installed power, that will be equipped with turbines installed on static foundation support structures. The current goal of the US administration, however, is to install ten times as much offshore wind power in US waters by 2030, and to meet this goal, it will be necessary to develop farms also in deeper waters, beyond the continental shelf, made of floating offshore wind turbines (FOWT). In some areas of the US, such as the Gulf of Maine or the West Coast, which feature a narrow shelf, FOWTs are the only viable option.

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