Motion control studies of a barge mounted offshore dynamic wind turbine using gyrostabilizer

Abstract

This paper is a sequel to our recently published article “Motion control of a barge for offshore wind turbine (OWT) using gyrostabilizer’, Ocean Eng. 209 (2020). https://doi.org/10.1016/j.oceaneng.2020.107500.The present investigation focuses on the performance of a gyrostabilizer on a barge mounted dynamic Offshore Wind Turbine (OWT) on reducing the angular motions with rotor operating at different speeds through experimental studies. The adjective ‘dynamic’ refers to model wind turbine with rotor that is in motion. To represent the operational scenario, different wind turbine rotor rotating conditions such as below rated power (60 rpm), rated power (85 rpm) and above rated power (114 rpm) were selected. Experiments were conducted in the wave basin with a 1:50 Froude-scaled model of ITI barge supported 5-MW NREL OWT. Forced vibration tests were conducted to evaluate the platform rotations and nacelle response under regular and irregular waves in parked and operating conditions. The platform rotations and nacelle accelerations during roll and pitch DOF for gyrostabilizer ‘off’ and ‘on’ condition with gyro flywheel spin velocity of 5700 rpm were measured and compared to evaluate the motion reduction rates. Using gyrostabilizer, under regular waves, roll/pitch motion reduction by 64/54% for parked, 57/39% for below rated, 67/45% for rated and 64/39% for above rated conditions were obtained. For irregular waves a better reduction of these motions was obtained. By reducing the roll and pitch motions, the nacelle responses are also reduced significantly.