A multi-rotor system (MRS), in which multiple wind turbines are placed on one tower,\nis a promising concept for super-large wind turbines at over 10 MW due to the cost and weight\nadvantages. The coherence effects on an MRS were investigated in this study. Although a wide range\nof coherences were measured so far, a decay constant of C = 12 is recommended in the IEC61400-1\nstandard. Dynamic simulations were performed for a 14-MW MRS, which consists of seven 2-MW\nturbines and includes wind models with three different coherences. Although the results show that\na larger coherence increases the output power and the collective loads due to tower base fore-aft\nbending, it reduces the differential loads due to tower-base torque and tower-top nodding. The most\nsignificant case is the fatigue damage due to tower base fore-aft bending, which was more than\ndoubled between the decay constants of C = 6 and C = 12. The present results indicate that the\ncoherence should be defined carefully in the design of large-scale MRSs because its effect on them is\nnot straightforward.
Loading....