Abstract
Offshore wind power research is a rapidly growing field, because of the present climate crisis and increasing focus on renewable energy. Model testing plays an important role in the risk and cost analysis associated with offshore wind turbines (OWTs). The real-time hybrid model testing concept (ReaTHM testing) solves important challenges related to model testing of OWTs, such as achieving an accurate modelling of the wind field, and the occurrence of scaling issues when modelling wind and waves simultaneously. However, ReaTHM test set-ups are generally sensitive to noise, signal loss and inaccuracies in sensor values. The present study is focused on the design and implementation of a state estimator able to accurately estimate the position and velocity of floating structures, while taking disturbances into account. By combining the information received from several different sensors with mathematical models, the estimator provides smooth and reliable position and velocity estimates for ReaTHM testing applications. The main objective of the present study is to develop a kinematic state space model that could represent the motion of any floating structure in six degrees of freedom (6-DOF). The kinematic model is implemented in MATLAB, and acceleration time series obtained with numerical simulations are used as inputs. The computed outputs agree with the corresponding simulated motions. A Kalman estimator based on the state space model is designed, implemented and tested against virtual data from the numerical model, with artificially added disturbances. Sensitivity analyses addressing the robustness towards noise, time delays, signal loss and uncertainties are performed to identify the limits of the estimator. The estimator is demonstrated to be robust to most types of disturbances. Further, the state estimator is tested against physical data from laboratory experiments. Good agreement between the physically measured and the estimated states is observed.
Highlights
The recent energy and climate crisis has led to an increasing focus towards the renewable energy, and offshore wind is one of the most important renewable energy sources
The real-time hybrid model testing concept (ReaTHM testing) solves important challenges related to model testing of offshore wind turbines (OWTs), such as achieving an accurate modelling of the wind field, and the occurrence of scaling issues when modelling wind and waves simultaneously
The main objective of the present study is to develop a kinematic state space model that could represent the motion of any floating structure in six degrees of freedom (6-DOF)
Summary
The recent energy and climate crisis has led to an increasing focus towards the renewable energy, and offshore wind is one of the most important renewable energy sources. In ReaTHM testing, the system under study is divided into a physical and a numerical substructure that interact via sensors and actuators integrated in the physical substructure (Fig. 1). This means that wind and aerodynamic loads may be replaced by actuators that are controlled by outputs from a numerical model. The inputs to the numerical model are the real-time measured motions of the structure, which are used to compute the rotor loads in full scale. These loads are scaled down to model scale, and applied to the structure in real time In this way, the Froude-scaled mass properties of the whole turbine are maintained. The focus of the present work is to design a state estimator that estimates and filters the positions and velocities of the physical substructure, to achieve better accuracy and reliability than what is possible through measurements alone
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