**5. Conclusions**

In this work, an aeroelastic tool has been developed to provide a two-way FSI model for wind turbine blades and a tower. The tool is validated for a single-rotor configuration and gave very reasonable results. It has been extended to model the aeroelastic behavior of a twin-rotor configuration. Dynamic response of the support tower was investigated for two load cases. The outcomes of this work can be summarized as follows:


The next step to improve the present tool is to implement pitch control, so that high power regions can be modeled. Also, eliminate the assumption of no aerodynamic interaction between the rotors, to study its effect on the dynamics and the optimum distance between the rotors to improve performance.

**Author Contributions:** A.I. did most of the work for modelling, programming, analyses, discussion, and writing of the manuscript. S.Y. contributed by supervising the work, mentoring, technical advising, and revising the work.

**Funding:** This work was conducted with the support of Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT).

**Acknowledgments:** Special thanks to Professor Martin O. L. Hansen, and Professor Taeseong Kim who helped a lot in understanding the fundamental information for wind turbine aeroelasticity.

**Conflicts of Interest:** The authors declare no conflict of interest.
