The nonlinear modal analysis of a barge-type offshore wind turbine

Resumo

Wind turbine use is increasing all over the world. At depth-water greater than 50 m floating support

platforms will be the most economical type of support structure to use. Among the numerous floating support-
platform configurations possible for the use with offshore wind turbines one may cites the barge, whose static

stability in pitch and roll is achieved using a large waterplane area. Such structures can exhibit large displacements
when vibrating. This scenario demands a nonlinear dynamic analysis of the problem. The main goal of this study
is to use reduced order models, based on the nonlinear normal modes, to identify and to analyze the nonlinear
dynamic behavior of a reference turbine of 5 MW supported by a barge floating structure. Free and forced
vibrations are studied. The existence of multiple solutions, unstable solutions and bifurcations are detected. The
use of the Mathieu’s chart allows the study of the stability of the solutions. The results show that the nonlinear
normal modes are an efficient tool to capture some important behavior and to perform fast parametrical studies.
The reduced order model results are compared to the numerical integration of the equations of motion and a good
agreement between both results is found.