Session: 09-01-02 Wind Energy: Aero-hydrodynamics 2

Paper Number: 123986

123986 - Comparison of Motion Characteristics of Floaters for Offshore Wind Turbines by Using Controllability Gramian of Linear Systems 

Offshore wind is one of key renewable energies for achieving a near-future carbon neutral society. Available offshore wind is huge, but most of it is present over the deep-sea area where fixed-bottom offshore wind turbines are not economically viable. A floating offshore wind turbine (FOWT) is a promising technology for harvesting wind energy in such sea areas. FOWTs use a floater (platform) that supports a tower and a rotor nacelle assembly (RNA). A careful design of floaters is required because i) the floaters have to mitigate the wind turbine's motions under wind, waves, and current disturbances, and ii) they should be cost-effective. Various floater concepts have been proposed so far, and they have different pros and cons. To compare the performance of different floater types, a typical way is to carry out coupled simulation under various wind/waves conditions. This simulation is possibly time-consuming, and thus a less computationally demanding method is desirable.

In this paper, we focus on FOWTs' motions subject to wind disturbances and propose a computationally less demanding method to compute their motion susceptibility to the disturbances. To be more specific, the method computes the maximum deviation value from an operating point under normalized wind disturbances with respect to each degree of freedom chosen in the mathematical model of FOWTs. Comparing the obtained maximum values for different floater types, the susceptibility can be quantitatively evaluated. The proposed method is based on the idea of the controllability gramian for linear systems in the field of control engineering. To demonstrate the proposed method, we consider NREL 5MW wind turbines installed on the three different floaters: TLP, barge, and spar buoy. The comparison results are consistent with the characteristics of these floaters that have been reported in the offshore wind turbine community. Note that the proposed method does not perform time-domain coupled simulation, and thus it provides a less computationally demanding way for comparing the motion characteristics of the wind turbines with different floaters.

Presenting Author: Naoyuki Hara Osaka Metropolitan Univ.

Presenting Author Biography: Dr. Hara is working at Osaka Metropolitan Univ. as an associate professor. He is working on control of floating offshore wind turbines and other control applications.

Authors:

Naoyuki Hara Osaka Metropolitan Univ.
Yuhei Yamade Osaka Metropolitan Univ.
Keiji Konishi Osaka Metropolitan Univ.