Host: The Japan Society of Mechanical Engineers
Name : Dynamics and Design Conference 2019
Date : August 27, 2019 - August 30, 2019
This paper investigates the unstable vibrations in an offshore floating wind turbine blade subjected to vertical wave excitation. The blade is modeled as a rigid bar connected to a horizontal, rotational shaft with a rotational spring, and inclines to only edgewise direction. The vertical motion of the rotational shaft is synchronized to a floater motion subjected to vertical wave excitation. The equation of motion of the blade includes parametric excitation terms which have the excitation frequency of the wave, Ω, and the rotational speed of the blade, ω. In the theoretical analysis for the linearized model, the regions where unstable vibrations occur, referred to as unstable regions, are theoretically determined and compared with the results of numerical simulations. The influence of the wave excitation and the rotational speed of the blade on the unstable regions are examined. The swept sine tests for the nonlinear model are conducted to calculate the frequency response curves with respect to the rotational speed of the blade and the excitation frequency of the wave. They confirm that the unstable vibrations occur within the regions where p=(Ω+nω)/2 (n=±1, ±2, ±3…, p is the natural frequency), is satisfied. They also demonstrate that resonances occur near Ω and ω where p=Ω+nω (n=0, ±1, ±2, ±3, ...) is satisfied.
