The offshore wind turbines (OWTs) are getting larger in scale in order to efficiently generate the electricity. Therefore the natural period of OWT becomes longer due to heavier weight of a nacelle and higher supporting towers for OWTs, resulting in possible fatigue damage. As we estimate that the diameter of the conventional tower to be more than seven meters, the tower having large rigidity such as a truss may be alternatively required. Therefore we made a comparison of required weights and rigidities through structural analyses of the cylindrical and truss towers for 5000kW OWTs. We also conducted a 1/100 scale model test on the both towers to obtain the wind loads acting on a rotor and the tower and to examine the differences in their downstream flow. The paper describes the ascendancy of the truss over the cylindrical tower.
