Host: The Japan Society of Mechanical Engineers
Name : Dynamics and Design Conference 2016
Date : August 23, 2016 - August 26, 2016
This paper theoretically investigated the unstable vibrations of the blades of floating offshore wind turbines. The blade is modeled as a rigid flat plate and pinned to the rotating shaft by a rotational spring. The blade is subjected to the vertical, harmonic excitation due to waves and the wind with vertically uniform speed. The equation of motion for the inclination of the blade includes the parametric excitation terms which have the excitation frequency of the wave and the rotational speed of the blade. In the theoretical analysis for the linearized model, the periodic solution of the blade at the boundaries of the unstable regions is assumed to determine the expression for the unstable regions, and the influence of the wave excitation and the stiffness of the rotational spring on the unstable regions are examined. These theoretical results are compared with the simulation results. As a result, it is found that the amplitude of the wave excitation affects the number and the width of the unstable regions. In the theoretical analysis for the nonlinear model, the swept sine test is conducted to calculate the frequency response curves. It is found that the frequency response curves bent to the left due to the soft-type nonlinearity of the system, but the rotational speeds at the unstable regions calculated in the linearized model are almost in agreement with the results of the swept sine tests.
